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Les diagrammes suivants illustrent la mdthode. 1 2 3 " "^;t r ^ r:9'" 4 5 6 I I TEXT - BOOK OF CHEMISTRY FOE STUDENTS OF MEDICINE, BY W. L. GOODWIN, D.Sc. (Edin.), queen's UNIVBRSITV, KINGSTON. TORONTO: THE COPP, CLARK CO., LIMITED, PRINTEKS, COLBORNE STREET. 1887. sm (x6 Entered according to Act of the Parliament of Canada, in the year one thousand eifrht hundred and elgrhty-seven. by Thk Copp, C.AaK Co LiMiTRD, in the Office of the Minister of .^griculture. PREFACE. This book was written to meet a want in my own teaching, and is inten«le(l to give an outline of C/hemistry, from the medical point of view, as far as possible. While no attempt has been male to treat the theory of chemistry exhaustively, I have tried to explain and apply the fundamental laws and princiides of the subject in such a way as to render the mastering of the facts an easier task. The writers of text-books of chemistry have perhaps, in many cases, erred in arranging their matter too logically, e.g., adopting an invariable order in describing the compounds of the metals ; while, in other cases, the ei lor has ])eeu in the opposite direction. It has oeen my aim to steer a course between these two. The principle adopted has been to })roceed from the known to the unknown, as far as is consistent with the limits of time and space imposed upon the teacher. Thus, water is studied before oxyrien and hydrogen are introduced, the study of air precedes that of nitrogen, &c., &c. I have found it advantageous in teaching chemistry to medical students to let them make for themselves such experiments as those de- scribed in the text of this book. Nearly all the experiments de- 1 scribed are such as can be made by students easily and with [very simple apparatus. Class experiments have a rather limited lvalue, and can be advantageously replaced in most cases by jimpler experiments made by the students themselves. The jompounds 'f carbon have been described alo:ag with that ele- lent, as there seems to be no longer any necessity for relegating them to the end of the book, as is generally done. In the Ap- jpendix is a Table of solubilities, which I have found very useful for reference. Tests are given at the end of the description of leach acid, metal, &c., and are collected into analytical tables in [the concluding chapter. I wish to express my gratitude to my colleagues, Professors [Dupuis and Shortt, and to my friend Dr. John Waddell, for I valuable assistance in revising proofs. W. L. GOODWIN. Queen's University, Kingston, Ontario. March Ist, 1887 TABLE OF CONTENTS. CHAPTER I. Chemical Action. — States of Matter— Pure Substances — Elu- triatioii — Filtration — Solution— Crystallisation — Distillation — Sublimation — Fusion — Chemical Decomposition and Com- bination — Elements and Compounds. — pp. 1-6. CHAPTER II. Weights and Measures.— Specilic Weight— Hydrometer or Areometer. — pp. 6-12. CHAPTER III. Water. — Heat— Conduction — Radiation — Relation of Light and Heat — Convection — Expansion by Heat — Temperature — Thermometers — Maximum Density Point of Water — Freez- ing and Melting — Change of Freezing Point by Pressure — Change of Volume on Freezing — J^atent Heat of Water — Specilic Heat — Evaporation and Ebullition — Ijatent Heat of > Steam — Solution —Freezing Mixtures — Crystallisation — In- fusion, &c. — Decomposition of Water — Composition of ; Water.— pp. 12-31. •I CHAPTER IV. Oxygen. — Preparation, &c. — Combustion in Oxygen — Tempera- ture of Ignition — Slow Combustion — Chemism — Metals and Non- Metals —Table of the Elements.— pp. 32-40. CHAPTER V. Conservation of Matter — Definite Proportions — Combining VVeights —Equivalents — Multiple Proportiois — The Atomic Theory — Avogadro's Law— Combination by Volumes — Mole- cules and Atoms — Molecular Weight of Gases — Chemical Notation — Atomic Weights — Chemical Equations — Chemical Calculations — Ozone. — pp. 41-54. CHAPTER VI. Hydrogen, — Hydroxides — Valence — Diffusion — Hydrogen Di- oxide — pp. 55 66. TABLE OF CONTENTS. CHAPTER VII. j^ir. — Boyle's Law — Charles' Law — Measurement of Volumes of v'jases — Composition of Air — Combusticm in Air— Respira- tion.— pp. 67-78. CHAPTER VIII. Nitrogen. — Ammonia -Nitric Acid— Nitrates — Basicity— Salts ~Oxide.-i of Nitrogen — Monoxide — Dioxide — Trioxide — Nitrous Acid — Tetroxide — Pentoxide — pp. 79-97. CHAPIER IX. The Halogens. — Sea Water — Chlorine — Hydrochloric Acid — Chlorides — Oxides of Chlorine — Monoxide — Trioxide — Te- troxide — Oxygen Acids of Chlorine — Hypochlorous Acid — Chlorous Acid — Chloric Acid — Chlorates — Perchloric Acid — Bromine — Hydrobromic Acid —Bromine and Oxygen — Iodine — Hydriodic Acid — Iodides — lodiile and Chlorine — Iodine and Oxygen — Iodic Acid — Fluorine* — Hydrofluoric Acid — Fluorides. — pp. 98-119. CHAPTER X. The Sulphur Group. — Sulphur — S-iilphur Dioxide — Sulphur Trir./iide— Oxygen Acids of Sulphur — Hyposulphurous Acid — Sulphurous Acid — Sulphites— Sulphuric Acid — Sulphstiea — Normal and Acid Salts —Fuming Sulphuric Acid — Thio- sulphuric Acid — Thiosulphates — Hydrogen Sulphide — Chlor- ides, &c., of Sulphur — Selenium — Tellurium. — pp. 120-141. CHAPTER XI. Phosphorus- — Oxides of Phosphorus — Pentoxide — Trioxide — Phosphoric Acid — Phosphates — P^hosphorous Acid — Hypo- phosphorous Acid — Hypophosphites — Phosphoretted Hydro- gen — Phosphorus and the Halogens. — pp. 142-154. CHAPTER XII. Arsenic. — Trioxide — Pentoxide — Arsenious Acid — Arsenites — Arsenic Acid — Arsenates — Sulphides of Arsenic — Arseniu- retted Hydrogen — Marsh's Test — Arsenic Chloride, &c. — ■ Tests for Arsenic. — pp. 155- 163. * This element has been lately prepared by the (jlectrolysis of dry hydro- fluoric acid. It is a gas having powerful cheniisuj. VI TABLE OF CONTENTS. CHAPTER XIIT. Carbon. — Carbon Compounds— Sources of Carbon Compounds — Dioxide — Carbonic Acid — ( ' irbonates — Monoxide — Bisul- phide — Hydrocarbons — Marsli (ias — Chloroform— Ethylene — Isomerism — Acetylene — Cyanogen Compounds — Potassic Ferrocyanide — Hydrocyanic Acid-C'yanides — Cyanic Acid — Sulphocyanates — Urea — Uric Acid — Urates — Alcohols — Methyl Alcohol — I'^thyl Alcohol— Fermentation — Amyl Al- cohol — Isomeric Alcohols — Amines — Etheis — Aldehydes — Ketones — Chloral- - Fatty Acids — Formic Acid — Acetic Acid — Acetates — Butyric Acid— Valerianic Acid — Acids of Fats and Oils — Glycol — Oxalic Acid — Oxalates — Succinic Acid — Glycerine — Hydroxy-acids — Lactic Acid — Tartaric Acid — Tartrates — Citric Acid — Citrates — Carbohydrates — Sac- charoses — Cane Sugar — Milk Sugar — Malt Sugar — Glucoses — Dextrose — Levulose — Amyloses — Starch — Dextrin — Gly- cogen — Gums — Cellulose. — pp. 164-!2v{l, '^ CHAPTER XIV. Aromatic Compounds. — Coal Tar — Benzene Series — Benzene — Nitrobenzene — Aniline — Carbolic Acid — Creosote — Picric Acid — Benzylic Alcohol — Benzoic Aldehyde — Benzoic Acid --Saccharine — Salicylic Acid — Gallic Acid — Tannic Acid — Terpenes — Camphor — Ciunamic Acid — Esfiential Oils — Indigo — Naphthalene — Anthracene — Glucosides — Alkaloids — Conine — Nicotine — Morphine — Quinine — Cinchonine — Strychnine — C-ocaine — Atropine — Kairine, Antipyrine, Thai- line — Albuminoids. — pp. *23'2-255. CHAPTER XV. : Silicon. — Silica — Silicic Acid and Silicates — Fluosilicic Acid- Boron — Boric Acid — Borax, —pp. 250 -202. CHAPTER XVi. The Metals* — General Characters — Ores — Alloys — Compounds — (Jxides — Sulphides — Chlorides, ^;c. — Oxygen Salts — Clas- sification — Analysis. — pp. 203-271 . CHAPTER XVII. Metals of Group I. — Lead — Oxides — Salts — Acetate — Nitrate — White Lead — Chloride — Iodide — Lead Plaster — Sulphate — Commercial Preparations — Lead Poisoning. — Silver — Ox- ides — Salts — N itrate — Mercuni — Amalgams — Mercurous Compounds — Nitrate — Chloride — Iodide — Mercuric Com- pounds — Nitrate — Sulphate — Chloride — Oxide — Iodide — White Precipitate — Sulphide — Mercurial Poisoning. — pp. 271-292. TABLE OF CONTNETS. Vll CHAPTER XVIIT. Metals of Group II.— Co;>;jfr— Compomifls— Cupric Sulphate — Oxide — Commercial Preparations — Cmfmium — N itrate — Sulphate— Iodide— 7?J«mHM — Nitrate — Snbiiitrate — Trioxide — Bismuthyl — Carbonate — A ututumi/ — Trisulphide — Tri- chloride — Trioxide — Tartar Emetic — Thi— Stannic Oxide — Stannous Chloride — Stannic Chloride— Oohl — Compounds — Phitinum — Compounds — Palladium, &c. — pp. 293-315. CHAPTER XIX. Metals of Group III. — Iron —Ferrous Salts — Sulphate — Car- bonate — Arsenate — Phosphate — Ferric Salts — Chloride — Sulphate — Nitrate — Hydroxide — ' ' Scale " Compounds — Chronihuii — Potassic Bichromate — ChroniicAcid- -Cnromates — Chrome Alum — Chromic Hydroxide — Almninium — Alu- mina — Alums — Aluminic Sulphate — Porcelain, &c. — Zitic — Oxide — Chloride — Sulphate — Carbonate — Acetate — MaiKja- nese — Dioxide — Manganous Salts — Manganic Salts — Man- ganates — Permanganates — Cobalt — Oxides — Nitrate — Chlo- ride — Nickel — Oxides — Sulphate — Cerium. — pp. 316-350. CHAPTER XX. Metals of Groups IV. and V.—<^'«^c''<"i— Oxide— Hydroxide — Carbonate — (Jhloride — Sulphate — Bleaching Powder — Phosphates — Mortars and Cements — Strontium— Barium — Oxides — Chlorides — Nitrate — Majnesiiim — Sulphate — Car- bonate — Magnesia — pp. 350-307. CHAPTER XX r. Metals of Group VI. — Sodium — Chloride — Sulphate— Carbon- ate — Bicarbonate — Hydroxide — Nitrate — Sulphite — Phos- phate — Bromide — Sulphide — Class — Potamium — Carbonate — Bicarbonate — Hydroxide — Chlorate — N itrate — Bromide — Iodide — Ammonium — Sulphate — Chhmde — Carbonate — Phosphate- -Microcosmic Salt — Sulphiile — Lithium — Carbon- ate — Euhidimn — Ccesium — Spectrum Analysis. — pp. 368-390. CHAPTER XXII. Electricity. — Electrolysis — Electro-chemical Series. 3^0-392. CHAPTER XXIII. Analysis. — Chemical Toxicol<»gy — Analytical Tables. 393-404. ^' ^ Appendix.— Table of Solubilities— pp. 405-408. Index.— pp. 409-416. — pp. — pp. ADDENDA ET CORRIGENDA. Page 7, table, for 0.064 read 0.0648. " 7, table, for 28.3549 read 28.3495. " 1 1, 1. 8, for 96 read 88, ** 26, 1. 18, for no read not much. " 35, 1. 3, from bottom, for is read was called. " 48, 1. 15, for always read generally. " 48, 1. 15, for 6.6 read 6.3. " 48, Is. 19 and 20, for specific read atomic. " 53, last line, for BgO read ^HgO, ** 66, for Experiment 28 read Experiment 28 A. " 57, 1. 3, for atomic read atom. " 83, 1. 16, for red read blue. " 122, 1. 4 from bottom, for that read tJie atom. " 141, 1. 8, for KOH read NaOff. " 145, 1. 7, for amphorcus read amorphous. " 154, last line, for Ga^{PO^)^ read 3{Ca^{P0^)^). " 163, first equation, for N&^CO read Na^GO^. " 179, 1. 3 from bottom, for 151 read 159.' " 193, 1. 6, after absent, insert, Fermentations are also caused by certain nitrogenous organic compounds called un- organised f€rm.ents, e.g. diastase, synaptase, &c. ** 201, 1. 4 from bottom, after chlorine read by a series of reactions. " 203, 1. 17, for C.H^Os read C^H^O^. *' 209, 1. 2, for a solution of read sparingly soluble. " 219, 1. 15, omit sparingly. CHEMISTRY FOB STUDENTS OF MEDICINE. CH APTE R I INTRODUCTORY. 1. Chemical Action.— /ron rusts in air, and the mat differs in pioperties from the iron. Iron heated in -iftir becomes changed to a black substance (as in a black- pmith's shop) unlike the iron in many respects. When Placed in vinegar iron gradually disappears into the vinegar, ^. e. dissolves, and a red liquid is formed, having the properties of neither vinegar nor iron. Wood burns, Heaving only a small portion of ash, unlike the wood in Icolour, and other properties. The greater part of the I wood has been changed into substances like air. A plant Itakes food from the soil and from the air in the form of [water, carbonic acid, ammonia, and various mineral sub- stances. From these it elaborates sugars, starch, gums, wood, &c., substances totally different from the original [articles of food, and not to be found in the sources from t which the plant gets its ^.od. An mivrnal brings about [similar changes, forming out of its food substances quite 2 PURE SUBSTANCES. unlike that food, converting starch into sugar, albumin into fat, &c. In all these cases, substances undergo such changes that they become converted into other and differ- ent substances. Such processes are called chemical actions, and Chemistry is, for the most part, the study of chemical actions. 2. Three States of Matter. — All substances can be grouped into three classes, viz. : solids, liquids, and gases. Solids have a definite form and volume. Liquids have no definite form, but their volume does not tend to change. Gases are indefinite both in form and volume. They tr.,ke the shape of the vessel in which they aj-e con- fined, and readily undergo compression and expansion, 3. Pure Substances. — Simple inspection of granite shows it to contain more than one substance. It is a mixture or mixed substance. Soil, pudding stone, milk, and, air, are other examples of mixtures. There are many methods of separating mixtures into their ingredients, ard thus obtaining pure substances, or chemical indivi' duals. The commoner methods are given in the following sections. 4. Elutriation, or " washing out," is a process used by the gold miner who washes away the light earth, sand, u/C, from the heavier gold. Winnowing is a similar process. 5. Filtration is separating a liquid from a solid by allowing the former to flow through some porous sub- stance which retains the latter. Thus, muddy water can be separated into mud and vater. Unsized paper, called Jikcr paper, is very commonly used. SEPARATION OF MIXTURES. G. Solution. — In this process, a liquid called a solvent is used to separate a soluhle substance, sugar for instance, from an insoluble substance such as sand, > : 7. Crystallisation. — When all tho ingredients of ■ mixture are soluble in some one solvent, e. g. in water, se[)aration can often be brought about by evaporating the solvent. When there is not enough of the solvent left to dissolve all the substances, that one whicli is most difficult to dissolve (or the least soluble), separates from the liquid, generally in regularly formed crystals. At another stage of the evaporation, the substance next in solubility cri/stallises, and thus a separation more or less complete is effected. It is by this process that common salt is separated from the other substances dissolved in ijea water. -,. '^...v .^.^s /.v- ■.,. .,, - •^--, - ...• - ■' 8. Distillation. — If a dish of alcohol and one of water be set side by side on a hot stove the alcohol begins to boil much before the water. Alcohol boils at a lower tejnpe7'ature than water, and a mixture of these two liquids can be separated by distilling them. For, when ^eat is applied to the vessel (the boiler, or retort,) contain- ing the mixture, the alcohol is first changed to vapour, passes as vapour into the cold tube (or condenser), and is there cooled and condensed (or made liquid). Thence it runs into the receiver. Iiater, water begins to distil over and may be collected in a different vessel. In a similar way fresh water can be prepared from sea water, the pure water distilling, and the salt remaining in the boiler. 9. Sublimation. —This is distillation applied to solids which can be changed to gases by heat. Sulphur 4 CHEMICAL DECOMPOSITION. is purified by heating it until it i& changed to a gas which is then condensed in a clean vessel. The impuri- ties rc^main, since they are non-volatile. 10. Fusion. — Some substances melt or fuse at lower temperatures than others. Thus, butter fuses at the temperature of the hand ; while salt can be fused only by a strong, red heat. If a mixture of butter and salt be gently heated, the butter melts, the salt sinks to the bottom, and the liquid butter can be poured off. This is the pharmaceutical process >! clarification. In some cases the impurities are ligi.ter than the melted sub- stance to be clarified. They, then, rise as a scum and are removed by skimming. 11. Chemical Decomposition and Combina- tion. — In the processes described above, no permanent change is brought about in the pure substances which are separated out of the mixtures. They preserve their identity. In chemical actions substances lose their identity. lExperiment 1. — Heat a little red oxide of merctiry in a tube of glass. The oxide disappears gradiially, and a silvery liquid, quicksilver, gathers on the inside of the tube. Thrust a splinter of wood with its end still glowing into the tube. Tho splinter begins to burn very brightly. Two substances have been formed from the oxide of mercury, viz., the liquid metal quicksilver or mercury, and the gas oxygen^ which causes a live coal to burst into bright flame and therefore differs from ordinary air. This is an example of chemical decomposition. Red oxide of mercury has been decomposed by heat, and the pro- ELEMENTS AND COMPOUNDS. ducts of itft decomposition are mercury and oxygen. This process differs from the separation of a mixture into its ingredients, because the products of decomposition have not the properties of the substance decomposed. The chief agents which bring about chemical decomposition ar(! heat, light, electricity, mechanical force (as in the explosion of dynamite), and contact with certain sub- stances. Chemical decompositions are also brought about in some unknown way by living beings, as in fermentation. Experiment 2- — Mix well four parts, of flowers of sulphur witli seven parts of very fine iron filings. A powder is obtained in which the presence of both iron and sulphur can be easily recognized. Shake up a little of the mixture with water in a test-tube. The iron sinks to the bottom more quickly than the sulphur and the two are separated. Move a magnet over another small portion of the mixture. The iron sticks to the magnet and the sulphur remains. The two substr.nces were merely mixed. Now, heat the remainder of the mixture in a a small, porcelain dish. It gets red hot, blackens, aud becomes quite uniform in appearance. The closest examination does not «how the precence of either sulphur or iron. Powder a little of the black substance and shake it up with water as before, No separation takes place. Move a magnet over another part. No iron sticks to it. The iron and sulphur have disappeared and this single black substance has taken their place. This is an example of chemical combination. Iron and sulphur have combined to form sulphide of iron (ferrous sulphide), a substance differing altogether in properties ftom iron or sulphur. Chemical combination must be -distinguished from mixture. 12. Elements and Compounds. —The majority of substances can be decomposed, but there are certain b WEIGHTS AND MEASURES. which cannot, so far as known. Thus, it has been found impossible to obtain from a portion of pure mercury any- thing else ; and the same is true of iron and sulphur. These substances will combine with others to form new substances, but from themsel ves, taken alone, nothing dif- ferent has been obtained by any process yet tried. Such substances are called Elements, or Simple Substances. They unite to form compounds. Definitions. — A chemical action or reaction is a change in which from one or more substances there are formed other sub- stances differing from the original in essential properties, e.g. in colour, taste, smell, &c. In chemical combination simpler sub- stances unite to form more^^ complicated. In chemical decomposition complex substances are broken up into simpler. An element is a pure substance which has never been decompoB of sea, river, lake, spring or rain water. A solid residue is left in each case. But if this distilled water {aqua distillata) be redistilled again and again no residue is left in the retort. Distilled water is a pure substance, a chemical individual. It is generally a liquid, but if sufficient heat be removed from it, it becomes solid (ice); and when heat is added liquid water is changed to a gas (water vapour, steam). 20. Heat - Conduction. — Heat and light were once thought to be substances. They are now known to be motion of some sort. When a body becomes hotter its particles move {vibrate) faster, and the motion is com- municated to any other body in contact with it. Simi- larly, heat passes from a hot to a cooler part of a body without any movement of the body as a whole. This process is called conduction of heat. Experiment 3. — Choose a piece of copper wire and anocher of iron wire of about the same size and length. Hold the end of each in the flame of a burner, and observe the time required for the heat to become unpleasant at the other end held between the fingers. The time is much longer for the iron than for the copper. Copper is a belter conductor of heat than iron. RADIATION. 13 A "Ihhs rod may be heated at one end until it melts before the other end becomes warm. Glass is a poor conductor of heat. The metals generally are the heat luctora of heat. Wool, feathers, asbestos, fur, air kd gases generally, and most liquids are bad conductors. \e use bad conductora, as clothing, to keep the heat )m leaving our bodies ; but we also use them as pack- Ig for ice, &c., to keep the heat out. Experiment 4 -Wrap a piece of copper wire round a iall lump of ice and allow the ice to fall to the bottom of a st-tube full of cold water. Holding the test-tube aslant, heat water near the top until it begins to boil. The icf at the bottom remains unmelted. Water is a bad conductor of heat. .21. Radiation. — Heat reaches us from the sun by ft j)roce8s different from conduction. It may warm the •arth to 90° or 100° F., and still leave the air through which it passes cool. In this way, too, heat and light pass through space empty of everything as far as known, Tliis movement of heat and light is called radiation. It is extremely rapid — about 180,000 miles per second. 22. Relation of Light and Heat.— Light and h(>at are related to each other just as the high notes of music are related to the low. Light consists of short waves, or I'apid vibrations, which produce in the eyes the sensation ordinarily called light. Heat consists of the longer, slower waves which are not capable of exciting tliis sensation, — in our eyes at least. When light falls upon a body which is not a good reflector, it is absorbed and may be thus transformed into heat. It is in this kway, principallj% that the earth is heated b/ the sun. 14 CONVECTION — EXPANSION. 23. Convection. Experiment 5. —Fill a tall glass vessel (beaker) with wattr containing tine sawdust, ami heat at the bottom. The movtv ments of the sawdust show that the water as it is heated rises to the top, while the couler water sinks. Thus, heiut is conveyed from place to place by motion en masse of the substance which is being heated, i. e., by convection currents. Winds are convection currents on a grand scale ; drafts are the same on a smaller scale. From experiments 4 and 5 it is easily seen that a mass of water can be much more quickly heated by applying; the heat at the bottom, than by applying it at the top. 24. Expansion by Heat. — In Experiment 5 the water rises as it becomes warm, because it is lighter than the cold water. Its volume harj been increased. Meat expands water. Experiment 6. — Fill a glass tlask full with cold water, and heat the water to boiling. A small quantity runs over as the water becomes hot. Allow the water to cool. It sinks down the neck of the ilask. Water expands when heated and con- tracts when cooled. Other liquids expand when heated and contract on cooling, hut different liquids expand differently. For example, mercury expands less than water for the same increase in degree of heat. Solids also expand when heated, but not so rapidly as liquids. It will be shown later on that gases expand when heated much moie than either liquids or solids, and that all gases expand almost exactly at the same rate. TRMPERATURE. 15 Ixperiment 7. — Fit a cork to a glass flask, boro a hole through the cork, arnl through the hole put a glass tube fitting tigh tly. Fill the flask with water, push in the cork tightly so U^o cause the water to rise an inch or two in the tube. Pour ^■H water on the flask. The water in the tube at first sinks, but '^mnediately afterwanls begins to rise steadily. When it has ■tQp])e(l rising it begins to fali, and finally remains at about the le level as before the hot water was poured on the flask. he flask expandt first when the hot water is poured and the cont;unbU '.ater sinks down the tube. Then the heat penetrates to the water which expands /aster than the glass, and therefore rises in the tube. — Builders of bridges allow for the expansion and contraction of iron witli change of season, &c. In laying rails in cold weather the ends are not put close together, but space is allowed for the increased length in warm weather. *o' '25. Temperature — If an instrument such as that desci-ibed in Experiment 7 were put into a body of water which caused the water in the tube to rise, the conclu- sion drawn from such an experiment would be that the boi!\ of water was hotter than that in the flask. If, on tihe other hand, the liquid should fall in the tube, it would be concluded that the water under examination was cooler ^^an that in the flask ; if no change were produced, the ^[^nclusion would certainly be that it was neither hotter abr colder. The sense of touch would confirm these con- clusions in each case, if the hand were immersed succes- "■'vely in the two quantities of water. - Experiment 8.- -Lay a piece of iron and a block of wood side by side on a table and after half an hour touch each of them ^th the hand. The iron feeU colder than the wood ; and yet, ".'S 16 TISRMOMETERS. if an instrurnent such as that used in Experiment 7 be touched! first to one and then to the other it shows them to be exactly inl the same state. The sense of touch does not always give the same ver-! diet regarding heat as the effect on volume does. The^ iron feels colder because it conducts heat away from the hand more rapidly, being a better conductor than wood. For the same reason blankets feel warmer than sheets. The words " hot " and " cold " do nob convey a correct idea of tlie state of a body with regard to its sensible heat. Generally, bodies which have been in contact for some time are in the same state with regard to sensible heat, for, if they are at first in different states, heat flows from the hotter to the colder until they are, as it were, at the same heat-level, or at the same temperature. Definition. — Temperature is the state of a body with regard] to sensible heat ; or temperature is heat-level. 26. Thermometers. — Teiuperatures are measured] by thermometers, or heat-measures. In most thermo- meters the temperature is indicated by the amount of! ex[)ansion of a liquid enclosed in a graduated glass tube with '\ bulb or resorvoir at the lower end. The most convenient liquid for ordinary ranges of temperature is mercury. It expands regv.larly, freezes only at a low, and boils only at a high temperature. Alcohol is used for very low temperatures as it does not freeze until the temperature sinks much below any that oocui*s naturally. The thermometer is graduated by placing it first in a mixture of ice and water, then in steam at ordinary pressure, and marking on the stem or scale the level at which the mercury stands in each case. These are the THERMOMETERS. 17 fa-ed lioints, and always whon the thermometer is placed in melting ice the mercury stands at the lower fixed point, and when it is placed in water boiling under ordinary circumstances, the mercury remains stationary at the higher fi^xed point. Under the same circumstances water freezes always at the same temperttcure, and also boils always at the same temperature. It only remains to divide the interval between the fixed points into equal parts called degrees, and to number these in re^^ular ord(ir. The numbers chosen are diffi^rent in tliermo- meters devised by different men. Any numbers may be chosen, according to taste or convenience. On the Cen- tigrade or Celsius thermometer, the one always used for scientific purposes, the lower fixed point is marked 0°, the upper 100°, and the space between is divided into 100 degrees. On the Fahrenlielt thermometer, generally used in this country, the two points are marked 32° and 21 'J" respectively, so that the zero Fahrenheit is o2 de- gi-c(is below the freezing point of water. On the Reau- mur thermometer the space between the fixed points is divided into 80 degrees numbered from 0^ to 80°. Thur:, the degrees on the Reaumur scale are longer than on the Qeutigrade, which in their turn are longer than those on the Fahrenheit. The relations betw ien the degrees are eicpressed as follows : — 1 degr^^e F. = \%% — % degree Wm ^ tVo = ^ degree R. To change any temperature Tfahrenheit to Centigrade (or Reaumur) subtract 32 and multiply by f (or |). The 32 degrees between the faluenheit zero and the freezing point must be sub- '^:-A(^ted first, because the other thermometers reckon from j|ie freezing point. To change any temperature Centi- grade (or R^iumur) to Fahrenheit, multiply by | (or f ) ^d add 32. Or, if t represent any temperature Fahren- I 3 I 18 MAXIMUM DENSITY POINT. | I heit (t — 32) f represents the same temperature Centi | grade, and {t — 32) f the same temperature Reaumur. | Also let t be any temperature Centigrade, then § ^ + 32 1 represents that temperature Fahrenheit. Similarly for | Reaumur. Ten^ peratures be^ow zero are indicated Ly | the minus sign ( — ). 3 '■4 27. Maximum Density Point of Water. '^ 'a Experiment 9- — Bore a second hole in the cork in the appa | ratus of Experiment 8, fit a centigrade thermometer in it, and | arrange the apparatus as in Experiment 8. Surround the flask | with snow or ice. The water in the tube falls until the ther | mometer marks 4" 0. It then begins to rise, and continues to | do so until the temperature sinks to 0°. , | i Water has the smallest volume at 4° C, and has,f| therefore, the greatest specific weight at that tempera i ture, which is for this reason called the maximum densUM point of water. Most liquids are densest at their freezinjl points. Water is exceptional in this respect. When if body of water cools at the surface, as a lake in autumn the cooled water sinks until the whole lake is at the teni perature 4° C. When the water at the surface is cooled! below thif? it remains at the surface, because it expands and thus becomes specifically lighter than the warmer water below. As water is a very poor conductor of henti (see Experiment 4), the water below cools very slowlyj even if the surface becomes changed into ice. Were it not for this exceptional feature in the effect of cooling 011 water, our lakes would become masses of ice every winter. 28. Freezing and Melting. Experiment 10- — Heat slowly a vessel containing snow or ice, stirring constantly with a thermometer. The temperature FREEZING AND MELTING. 19 of tlie whole mass remains at 0° C. until the last portion "f snow or ice is melted. It then begins to rise. Ice melts at 0° C. always, under ordinary circum- stances. Other solids have different melting points, e. g. Lead melts at 300° C. The word fuse is used instead of melt, especially of solids which become liquid only at high temperatures. If a portion ot water be cooled it begins to freeze at 0° C, and the temperature does not sink below that until the whole of the water is changed to ice. The freezing point of water is the same as the melting point of ice. This is true of most liquids, but not of all. 21). Oiiange of Freezing Point by Pressure. Experiment 11- — Support a slab of clear ice at either end and lay over it a thin clean wire having a weight attached to eacli end so as to cause the wire to press upon the ice. The wire gradually passes through the ice, but does not cut it in two. The ice is melted by the pressure of the wire upon it, It solidities again as sooii as the pressure is removed by onward movement of the wire. Ice at 0° C, can be 3lted by pressure, and cannot be frozen as long as the jssure continues, without reducing the temperature )?/? 0° C. In other words the freezing point of water lowered by pressure. Water is exceptional in this iipect also ; most liquids have their freezing points liaised by pressure. ''"*(). Change of Volume on Freezing.— Since I(^ floats on water it m ..o be specifically lighter than j^tcr. Water expands on freezing. Most liquids con- 20 LATENT HEAT OF WA I'ER. tract on solidifjing, e.g., solid lead sinks in liquid lead Water expands about one-eleventh of its volume oi freezing. Enormous force is exerted during this expan sion ; hence the bursting of water-pipes, the splittin| of rocks, the "heaving" of the foundations of build ings, &c. 31. Latent Heat of Water. — From Experimen 10 we learn that when ice is melting heat goes into i without I'aising its temperature. This heat become latent or hidden. In order to freeze latent heat must be removed from it. latent or hidden. In order to freeze the water again tl Experiment 12. — Mix 1,000 grams ice-cold water with l,()i grams boiling water. The temperature of the mixture is 50° ( Now, mix 1,000 grams ice with 1,000 grams boiling water, st well until the ice is melted. The temperature of the mixture only 10.5° C. From these experiments it is plain that the ho; rendered latent by melting 1,000 grams ice would wan 2,000 grams water from 10.5° C to 50° C. If we tal ^ as the iinit of heat (or thermal unit) the quantity of lie; required to raise the temperature of 1 gram of water degree Centigrade, then 2,000 x 39.5 = 79,000 uni tj of heat are rendered latent in melting 1 ,000 grams ic ii or 79 for 1 gram. The Latent Heat of Water is 7 a thermal units ; or, to change ice at 0° into water at n as much heat is rendered latent as would warm the saii p weight of water from 0° to 79°. The latent heat tU water is much greater than that of most substance p That of mercury is only 2.28; that of molten lead T).-^ Ice is thus an excellent cooling agent. ■ ^ -ftfe SPECIFIC HEAT. 21 32. Specific Heat. Experiment 13- — Take equal weights of iron and lead, about 1,00() grams ; cool them to 0° and immerse them in equal quan- tities of water (500 c. c. ) at 50° C. After stirring for a moment note the temperatures. That of the water in which the iron is will be about 40° C. ; of that in which the lead is, about 47° C The iron has taken more heat from the water than the lead has, and yet its temperature has not been raised «o high. Iron is harder to heat than an equal weight of lead, i.e., requires more heat to raise its temperature, say, one degree. Diflferent substances require different quan- tities of heat to raise the temperature of equal weights of til em one degree. Definition. — The Specific Heat of a substance is the quantity of h((it required to raise the temperatxire of unit weight (1 gram or 1 Ih.J of the substance one degree (from 0° C. to 1° C.) The specific heat of water is of course the thermal unit. That of most other substances is much less. That of l(;ad is only 0.031, of iron, 0.1137, and of copper, 0.095. 33. Evaporation and Ebullition.— Water in the state of gas (water vapour) is constantly escaping into the air from every exposed surface of water or ice ; and, other things being equal, the hotter the water the mor(! rapidly does it become changed to vapour. This pro((5ss is called evaporation. Thus the air always con- tains water-vapour. At any particular temj)erature a pclHion of air is capable of containing only a certain qt^iitity of water-vapour. When air contains as much witer- vapor as it is capable of holding, it is saturated ; 22 EVAPORATION AND EBULLITION. and if it be then cooled, some of the vapour is condensed ; if it be heated, it becomes capable of containing more vapour. The air coming from our lungs is warm and saturated with water- vapour. When it comes in contact with cold air in winter some of the vapour is condensed and forms a " cloud." Dew, fogs, clouds, mists, (fee, are explained similarly. Air is moist or dry according as it is near to, or far away from, its point of saturation. Thus, if moist air be heated it becomes dry, i.e., capable of receiving more water- vapour. Evaporation is hastened by heat, or by a current of dry air. Experiment 14. — Heat some water in a glass flask until it begins to boil, observing the temperature by a thermometer in the water. The water begins to boil when the temperature rises to 100° C. Observe the temperature of the steam. It is also 100°. Use a larger flame so as to make the water boil more vigorously. The temperature does not rise. Now, close the flask with a cork through which the thermometer passes. Heat very carefully, and observe that the temperature rises above 100° and yet the water scarcely boils. Remove the lamp when the mercury has risen one or two degrees, otherwise the cork will be driven out by the pressure of the steam. Take out the cork, boil the water vigorously for a minute or two and while steam is still coming out put in a cork firmly at the same time taking the flask away from the lamp. Allow the water to cool a little, and then pour cold water on the flask. The water in the flask begins to boil. Water in an open vessel boils at 100° C, and the tem- perature cannot be raised above that, unless the vessel be closed so as to increase the pressure on the surface of the water. When the pressure on the surface is lowered, as by condensing the steam — filling the closed flask in Ex- periment 14, water boils at temperatures below 100° C. The boiling 'point of water depends on the pressure on its LATENT HEAT OF STEAM. 23 lurface, being higher the greater the pressure. On the )p of a high mountain where the weight of air pressing (n surfaces is less than it is lower down, water boils at low a temperature that it can not cook. Experiment 15- — Boil some alcohol in a flask, observing the smperature of the boiUng liquid and of the vapour. If the Icohol is pure, the temperature in each case is 78.4" C. Try bie boiling point of ether, heating it by means of hot water. Bther boils at 34,2°. Every liquid boils at a particular temperature, just as bvery solid fuses at a particular temperature. BOILING litrous oxide — 87.9 Carbon dioxide — 78.2 inimonia — 33.7 Sulphur dioxide — 10.5 Idehyde +19.8 ether 34.2 Jarbon Bisulphide .... 47.9 lethylic alcohol 55.1 Jhloroform 61 .0 Jromine 63.0 POINTS. Ethyhc Alcohol 78.4 Benzene 80.4 Water 100.0 Acetic Acid 116.9 Naphthalene 216.8 Phosphorus 290.0 Mercury 350.0 Sulphur 440.0 Cadmium 860.0 Zinc 1040.0 34. Latent Heat of Steam. — From Experiment [4 we learn that the heat which goes into boiling water id changes it to steam does not cause any rise of tem- )erature. This heat becomes latent, just as in the case )f melting ice. The latent heat of steam is 536 thermal mits ; i.e., to change any weight of water at 100° C. to Jteam at the same temperature heat is required sufficient raise the temperature of 536 times the weight of ijrater one degree. The latent heat of steam is very freat compared with that of other vapours. Water in jvaporating from the earth's surface carries away a great 24 SOLUTION. deal of heat. Wet clothes feel cold because of the heat consumed by the evaporating water. Much heat is lost to the body by thg evaporation of water through the skin and lungs. The cooling effect of ether and other rapidly evaporating liquids is explained in the same way. Water can be frozen by rapidly evaporating ether. That such an enormous amount of heat is required to evapo- rate a liquid is accounted for by the great change of volume. For example, I cubic inch of water forms 1,700 cubic inches of steam. 35. Solution. Experiment 16. — Mix 100 grams finely-powdered saltpetre with 100 grams distilled water in a beaker, stirring for some time with a glass rod. Part of the saltpetre disappears ; the water has now the taste of saltpetre, and is colder. Apply heat, carefully stirring all the time. More of the saltpetre, and at length all of it, disappears. Allow the liquid to cool ; some of the saltpetre reappears in long crystals which grow as the liquid cools. When quite cool, pour off some of the liquid into a small porcelain basin, boil away some of the water, and allow the re- maining liquid to cool again. More saltpetre crystallises out. This process is called concentration. Hepeat this experiment, using washing soda instead of saltpetre. Experiment 17. — Carefully heat 300 grams saltpetre with 100 grams water. (Do not apply the flame to the beaker.) Only part of the saltpetre disappears even when the water begins to boil. Mix 10 grams of gypsum with 100 of water, and heat to boiling. The gypsum does not disappear. Filter some of the liquid into a porcelain basin and evaporate to dryness. A small quantity of white substance, gypsum, is left. Repeat this experiment, using clean white sand, and again with chalk. In each case little or nothing remains when the water is evapo- rated. SOLUTION. 25 tltpetre and wasliing soda dissolve readily in water, irting their taste and other jjroperties to the water. They are soluble in water, and form solutions from wli?oh they can be got again by evaporating the water. Bxperiment 18- — Mix lO c c. hydrochloric acid with about tour times as much water, pour it over three or four iron tacks in ft porcelain basin, and warm gently. Bubbles rise from the tacks, which gradually disappear, giving a greenish color to the water. Evaporate the water. A solid remains, but it is not iron ; it is ferrous chloride. Repeat the experiment, using inarV)le instead of iron. In Experiment 18 the process of solution is accom- panied by chemical action. This kind may be called ch§rnical solution. — Substances are generally more soluble in hot than in cold water. — Gypsum is much less soluble thiin saltpetre or washing soda. Sand and chalk are vi^folable. A given quantity of water can dissolve only a (Pertain maximum weight of each soluble substance at a given temperature, forming in. each case a saturated scmtion. For example, 100 grams of water will always iiasolve 13^ grams of saltpetre at 0° C, and always 250 git-ms at 100° J. These weights may be taken to repre- sent the solubility of saltpetre at the two temperatures. (I^pr Table of Solabilitieii, see Appendix.) To make a saturated solution of a substance at any temperature, either stir it up with water at that temperature until no m^e will dissolve (this requires much time and stirring), of heat the water to a higher temperature, dissolve in it as much as possible of the substance, cool, and decant or filler. Water saturated with one substance will still dissolve others. Solutions of solids in water are heavier n pure water and boil at higher temperatures. Heat 26 SUPERSATURATED SOLUTIONS — FREEZING MIXTURES. is rendered latent when solids dissolve in liquids, andl reappeai*s when they become solids again (comparej Art. 31). Experiment 19. — Heat some sodic acetate in a flask withj very little water until the salt is dissolved and steam issuesl from the flask. Put a plug of cotton wool, or a cork, in thej mouth of the flask, and let cool. The solution remains liquidl Oi^en the flask and drop in a small grain of aodic acetate. CrysH tals shoot out from the point where it falls, and soon the wholej mass becomes solid. At the same time the flask becomes warm.! (Why?) A solution of this sort is supersaturated. It containgl more of the salt than can be dissolved at the lower temperature,! Water dissolves a great many substances, solids, liquids,! and gases. It is a good menstruum^ or solvent. Many substances insoluble in water will dissolve in other! liquids. Thus, mercury dissolves most of the metals alcohol dissolves resins ; and ether dissolves fats ; all in! soluble in water. No heat becomes latent when one liquid dissolves another ; there is no change of state.* When a liquid dissolves a gas the latent heat of the gas becomes sensible, but becomes latent again when the gas resumes its former state. This accounts for the coolness of effel'- 1 vescing drinks. 36. Freezing Mixtures. Experiment 20. — Mix quickly and .loroughly 5 parts by weight of snow with 2 parts of salt. Observe the intense cold. Freeze some water in a test-tube. Note the melting of both snow and salt. The temperature can be reduced in this way to | —20° C. What becomes of the heat ? (See Art. 31 and Art. 35). Salt water will not freeze until the temperature sinks much below or 0. ' In some cases heat becomes sensible, as when alcohol and water ai'e mixed. <<: CRYSTALLISATION. 27 Another freezing mixture is IG parts water, 5 parts si^tpetre, and 5 of sal-ammoniac. h '37. Crystallisation. — Crystals are beautiful geo- metiic forms, e.g., cubes, pyramids, in which solids can bo obtained. They may be produced in several ways, par- ticularly by cooling or evaporating solutions, as in the experiments with saltpetre (Art. 35). A substance is known to be at least nearly pure, if it consists of distinct and well-formed crystals. Tlus is the reason for the care taken by manufacturers to prepare well-crystallised chemi- cals in particular cases where adulterations are common. Crystals are generally obtained by gradually cooling hot saturated solutions, or by slowly evai)orating cold solu- tions. The impurities remain dissolved in the mother- Uquor. Substances are often purified by crystallisation. Many substances combine with water as they crystallise. Washing-soda crystals contain 63% of water of ci'ystallisa- tion. The water is necessary to the form of the crystals. It is chemically combined, and is solid. If it be driven off by heat the crystals fall to powder. Many crystalline Wibstances containing water of crystallisation lose this on exposure to air, and become powdery. This phenomenon ia called efflorescence. Other solid substances attract moisture from the air and at last become liquid. This is called deliquescence. 38. Infusion, &C. — Water and other solvents are ^ed to separate the soluble from the insoluble parts of Medicinal plants, &c. Maceration, or cold infusion, is CTirried on at the ordinary temperature of the atmos- phere. The substance to be macerated is ground up, or "in some other way intimately mixed with the solvent, is 28 INFUSION, ETC. allowed to stand for some timo, and tlio liquid is then I strained or filtered off. An in/usimi (hot infusion) is made by pouring the boiling solvent on the substance, and allowing it to cool gradually. Digestion (or simmer- iny) is the process of making a solution with the solvent I kept just below its boiling point. The differences in these methods are mainly differences of temperature. When it is required to extract a substance which is de- composed at or below the boiling point of the solvent, or a substance which is very volatile (easily evaporated), the raetiiod of cold infusion or digestion is used. Tea should be infused, or at most digested, and never boiled, since boiling extracts a bitter and unwholesome principle, which is not dissolved in so great quantity by infusion or digestion. Tinctures are mostly macerations with alcohol as the solvent. Percolation has now largely superseded maceration in the preparation of tinctures. The sub- stance is placed in a filter [percolator), and the solvent is poured upon it and allowed to percolate (run through) slowly. This method has the advantage of allowing a fresh portion of the solvent to be poured on the partially exhausted material ; so that the extraction can be com- pleted more quickly and thoroughly. (Why 1) The same principle is employed in filtrt\tion when it is wished to wach away a soluble from an insoluble substance with as little as possible of the solvent. Very little is poured on at a time, and one portion is allowed to run through before another is added. 39. Decomposition of Water.— In Experiment 1 heat was the kind of energy used to decompose a com- pound. Very many chemical substances can be decom- posed by heat, and under certain conditions water under DECOMPOSITION OF WATER. 29 le action of her.t breaks u}) into two differbnt substances ; hjit another kind of energy, electricity^ is more convenient Ibr sliowing the compound nature of water. It must be f^iiieuibered that electricity is no more a substance than IjK'Ht is. It is classed along with light, heat, 6. A Fahrenheit and a centigrade thermometer are placed side Igr side in a vessel of water. The centigrade thermometer reads 80°. What does the Fahrenheit read ? 7. What is the latent heat of water if the Fahrenheit ther- niometer is the standard ? j: 8. Twenty grams of ice at 0° C. is melted with 1,000 grams of water at 50°. What is the temperature afterwards ? .• 9. W^hat weight of water at 100° C. is required to melt 10 lbs. a| ice at 0° C. ? ?, 10. Why does snow fall powdery in very cold weather, and in lirgt' Hakes in mild weather ? I li. If 100 grains of steam at 100° be condensed in 1 lb. of water at 0° C, what is then the temperature of the water ? 12. A piece of silver weighing 120 grams is heated in boiling •flfater and then put into a vessel containing 500 grams of water # 10° C. After stirring, the temperature of the water is found %) be 11.2°. Calculate the specific heat of silver. - IH. Why does stirring facilitate the solution of a substance ? 14. How much steam must be condensed to heat 10 kilograms invented. The pneumatic trough is a vessel provide with a perforated shelf. The vessel is filled with wati or other liquid until the shelf is covered ; jars or bottli are filled with the liquid in the trough, inverted, and s* upon the shelf. These jars or bottles can be filled with an gas by allowing it to rise in bubbles through the liquid which it displaces downward. In 1744 (August 1st) Pri 3stly heated a compound of mercury known as rr precipitate, or precipitate per se, and collected a colourles gas which was driven off. (He called it an air, the nanv gas not being used until later). He found that this ga had the remarkable propert}'^ of causing a glowing coa to burst into flame. For reasons to be presently explainei it was afterwards called oxygen. 42. Preparation of Oxygen. — The most convon lent way of preparing oxygen is by heating potam chlorate mixed with a little black oxide of manganese. Experimeni 22- — Grind about 10 grams of potassic chlorat to powder in a mortar. Dry it by heating in a porcelain basin taking care not to fuse it. It is best to stir constiintly with ; PREPARATION AND PROPEKTIES OF OXYGEN. 33 glass rod while heating it. Dry in the same way about 1 gram manganese dioxide. TTeat a small part of the potassic chlorate in a small glass tube closed at one end, until the salt-like sub- stance fuses (melts), and bubbles of gas rise through it. Insert »Bmall glowing splinter, and observe its briglit flame. Mix the remainder of the chlorate thoroughly with the manganese dioxide, and put it in a larger hard-glass tube (test-tube size) provided with a gas delivery tube leading from the test-tube and dipping under the surface of water in the pneumatic trough. The tube passes tightly through a cork in the mouth of the test-tube. Arrange the test-tube, &c., conveniently, and heat at the bottom, applying the heat gradually, but not removing the lamp when once applied, unless the open end of the delivery tube is first lifted out of the water. Otherwise, as the heated gas in the retort (test-tube) cools, it will contract, and the cold water will run back into the retort, breaking it. Collect the gas which bul)bles off, until about as much as would fill the retort and ^eliv^ry tube is collected, then change the receiver (collecting ssel), and fill 5 small bottles with the gas. (Why reject the Jrst portion ?) Oxygen can also be prepared by heating black oxide of inganese or potassic bichromate, either alone or with ^11 of vitriol. The black oxide of manganese used in Experiment 22 undergoes no change. It enables tlie Oxygen to escape at a lower temperature. This is a case if so-called contact-action. When oxygen is prepared poni potassic chlorate it is generally contaminated by le poisonous gas, chlorine, from which it should be freed by bubbling it through water, in which chlorine \b very soluble. It is very necessary to do this when the oxygen is to be inhaled. 43. Properties of Oxygen.— Oxygen is an in- risible gas, odourless, tasteless, and a little heavier than ^ir. Below — 130° C. it can be condensed to a liquid. ?here is a certain temperature for each gas, above which it 4 34 COMBUSTION IN OXYGEN. cannot be condensed to a liquid by pressure, below wliicli it can. This is the critical temperature, about — 130'^ (J, for oxygen. Oxygen is a "supporter of combustion"— many substances burn in it. It is necessary to anini;i] and, generally, to vegetable life. It is obtained from tlic air by animals when breathing, diffusing through tlic thin walls of the lungs into the blood. In the air, oxygen is diluted with four times its volume of anoi r gas, nitrogen, so that its action is moderated. An at- mosphere of pure oxygen would throw us into a state of excitement and fever, and would cause a vast conflagra tion over the surface of the earth. It was once oft(!ii given as a stimulant. In cases of asphyxia and dyspnaa it is valuable. The patient obtains tho necessary supply of oxygen in a much smaller space, therefore with less breathing. Oxygen is somewhat soluble in water, about 4 c. c. in 100 c. c. of pure water. When a glass vessel filled with water is heated slowly, bubbles of gas collect on the sides, and at length rise to the surface. These have been collected and proved to be largely oxygen. Fish ol>fcain their oxygen by diffusion from the water. Hence, the necessity for a current of water, through the mouth and out over the gills. When fish are drowned they are in reality smothered. Water dissolves gases according to a certain law. The quantity of any gas which is dissolved by a given quantity of wafer is pro- port: onal to the pressure and inversely as the temperature. This law does not hold fo'* gases which unite chemically with water, e.g., ammonia, carbon dioxide. 4t. Combustion in Oxygen. — When chemical action is accompanied by light and much heat it is called combustion. Flame also usually accompanies combus- 1 v*i, ACIDS. " 35 tion. Ordinary combustion takes [)lace in an atmos- phere which unites partially at least with tlie substance burned. It is a supporter of the combustion. Oxygen is tl'r The substances formed by burning these metals in : oxygen in the presence of water have a character opposite \ to that of the acids. They are called bases. That formed | from sodium is called caustic soda. Some other mc ;als I form soluble bases, but most bases are insoluble and jan I only be prepared indirectly from the metals. I Experiment 27. — Pour a few drops of litmus into a solution of hydrochloric acid so as to produce a distinct red colour. ; Then, add some solution of caustic soda, dropping it from a ; pipette gradually, and stirring, until the red just begins to turn ! blue, i.e., becomes purplish. Observe that the solution now ' tastes neither sour nor soapy, but salt. Both acid and base have disappeared ; the colour is neither blue nor red ; the solution is ; neutral in its action on litmus. Evaporate it in a porcelain dish. ; Crystals of common salt are obtained. A similar result c\i\ be produced with sulphuric or T nitric acid, and caustic potash. In eac'i case, by mixing i I hj TKMrEUATURK OF IGNITION. "S? solutions of tlie acid and base in the right proportions a point is reached whera the sohition turns litmus neitlier blue nor red, both sour and soapy taste disappear, and a |ttlt-like substance can be separated from the solution by evaporation. Substances formed by the action of acids on bases are called salts. Experiment 28. — Make a bundle of thin strips of zinc foil, idip the ends iu a little melted sulphur (Why?), set on fire and plunge into a jar of oxygen. The zinc burns with a white light, forming zinc oxide, or " philosopher's wool." Pour a little water into the jar, and observe that the oxide does not dissolve. Add A few drops of sulphuric acid ; the oxide dissolves ; evaporate in a porcelain dish ; a salt, zinc sidphate, or white vitriol, remains. Burn some fine iron wire in the same way. The oxide of zinc is a base-foryiiing oxide, because it acts on an acid to form a salt ; but it does not dissolve in water forming a base, as the oxides of sodium and of potassium do. But the corresponding base, known as zinc hydroodde, can be prepared in another way. It is insoluble in water, and does not turn red litmus blue, nor feel soapy when rubbed between the fingers, as tlie char- acteristic bases do. It is nevertheless called a base, b(!cause it forms salts with acids. Iron and other metals c;in be burned in oxygen. They all produce base-forming oxides ; but it is to be noted that most bases have not the 8t rongly marked characteristics of ct.ustic soda. They are mostly insoluble in water, and do not turn red litmus blue, [but thei/ are all acted on by acids, and thereby form salts. 45. Temperature of Ignition.— It is necessary [to heat combustible substances to a certain temperature before they will catch fire. This is called the tempera- Iture of ignition. It is very different for different sub- 3tl SLOW COMBUSTION — CHEMISM. stances. Thus, pliosphorus catches fire v\ air below 100° C, carbon bisulphide at 150^, sulphur at 400°, while coal and wood begin to burn only at a red heat. 46. Slow Combustion. — Combustible substances often combine slowly with oxygen at temperatures below that of ignition. In such cases the more striking ap- pearances of combustion are absent. Rusting of metals, respiration, decay of animai and vegetable substances, are processes of this kind, modified more or less by the action of water. Heat is i)roduced in slow combustion.s (as in the heating of grain, of damp hay, urn 23 grams of sodium to form 31 grams of sodic fxide ; 8 grams of oxygen burn 32.5 grams of zinc to vm 40.5 grams of zinc oxide. From this statement it h f 42 DEFINITK PROPORTIONS — KQUIVALENTS. is seen that in chomical combinations, also, the sum o?" the weights of tlie substances combining is always equa The to the weight of the substance formed. It may thus 1. in stated generally that in chemical actions no matter i app lost — put out of existence ; nor is there any gain <■ poii matter. The weights of the elements entering into of \ chemical action remain the same at the end of tli wei) action ; but the elements become differently arrang(;(i oxic This law, founded on experiments, is the Law of the Cor B p< servatlon of Matter. It is the fundamental law of tli den> Science of Chemistry. pou^ 50. Definite Proportions— Another law can l ^jj^ deduced from the facts stated in Art. 49. It is fouiic^^i., that water is always composed of hydrogen and oxyj gen in the proportion of 1 to 8, that mercuric oxiilJ is always composed of oxygen and mercury in the pro portion of 8 to 100, and so with the others. Stated iri general terms this is the Law of Dejinlte Proportions\ Each chemical compound is always composed of the sam^ elements and these are always in the same proportion in this compound. In this respect chemical compounds diffei Bf ^ from mixtures, which may be made in any proportions^^" 51. Combining Weights -Equivalents. -ThfHy weight ' '"vgen which combines with 1 part by weigha of h''' - to form water is called the combining weiyhi o ^L).. 17ie weight of any element which comhim? Wvv.^ I 2)art of hydrogen is its combining weight; but, ;U|^e many of the elements do not form compounds wittHrD hydrogen, their combining weights must be ascertained] as it were, at second hand. Thus, the weight of zina which combines with 8 parts by weight of oxygen (itJ MULTIPLE PROPORTIONS. 43 coni'iniiijL,' woij^ht) is the combining wciglit of zinc. The expression eq^uvalent, or equivalent weight, is used in Icxactly the same sense as comhining weight when applied to the elements ; but it is also applied to com- poui^'l^- Thus, the equivalent of water is the quantity of water which will produce, when decomposed, 1 part by weight of hydrogen, i e., 9. Again the equivalent of zinc oxide is 40.5, since this weight of zinc oxide contains 8 parts (an equivalent) of oxygen. The equivalent of an elem*'nt or a compound is the weight oj the element or cotn- pound equal in value in chemical action to 1 part bi/ wieigJit of hydrogen. (Calculate the equivalents of all the substances mentioned in Art. 40.) Hydrogen is here, as in most cases, taken as the standard element. 2. Multiple Pre portions. — When charcoal (car- boll) burns in a free supply of oxygon, 8 parts of oxygen unite with 3 of carbon to form carbon dioxide ; but if supply be scant, as in the centre of a fire, only 4 of oxygen unite with 3 of carbon, and carbon mon- 'e is formed. Thus, carbon combines with oxygen in ))roportions, and these are as 8 to 4, or as 2 to 1. en phosphorus burns in oxygen it also forms two coHpoiinds, the pentoxide when the oxygen is plentiiul, anp the trioxide when it is scant. In the pentoxide 6.2 of phosphorus (Why use this particular number'?) combined with 8 of oxygen; in the trioxide this lit of phosphorus is combined with 4.8 of oxygen, quantities of oxygen are as 5 to 3. Sulphur also s two compounds with oxygen, the relative quanti- of which are as 2 to 3. Many other exanq^les could iven of an element combining with another in two ore proportions ; and it is noticed that in every such 1 44 THE ATOMIC THKORY. ■ case these proportions have a siriiplc Mrithtuetical relati" to each otlier, as in the above cases. This is stated ^ • t the Lavb of Multiple Proportions : If tioo elements fur several compounds with each other, then the divert quantities oj the, first which combine with a fixed quanli! of the second bear a sirnph ratio to each other, as 1 k 2 to 3, 3 to 5, (See. (Apply this law to the exani|ii given.) I 53. The Atomic Theory.— To explain these r i markable facts Dalton ( 1804 modified the atomic tlieo' iw , ancient Greeks. According to this theory^ its modern form the elements are made up of indivisillfKi extremely minute })articles — atoms. (What is a theory The atoms of the same element are exactly alike, those of different elements differ in weight, &c. atoms of different elements unite to form molecu/cs compounds, and this union always takes place 1 it with 1 atom, 1 atom with 2, 2 wiJi 3, &c. For ample, when zinc burns in oxygen, 1 atom of zinc coi bines with 1 atom of oxygen, 1,000 atoms of zinc wi; 1.000 of oxygen and so on, until the whole of the ziiics burned, when, of course, the oxide which is formed co2 tains equal numbers of atoms of zinc and of oxygen, follows from this that if the ratio of the weights of tl atoms of zinc and oxygen are as 65 to 16, the ratio! the whole quantities combining must be in this prdiK tion. As a matter of fact, zinc oxide is always coij posed of the two elements isi this ratio. In this \vi the atomic theoiy explains tl o lav) of definite propi tions. The explanation o^ the law of multiple prop^ tions is equally simple. For example, sul}>hur uiiit|; ' with oxygen in two proportions. According to tf i AVOGADROS LAW. 45 lie theory the auvlition of oxygen to sulphur takes place always by atoms, never parts of an atom ; in the two 'ompounds different numbers of atoms of oxygen unite with an atom of sulphur, in one case 2, and in the othr). Combination by Volumes. — When water decomposed by electricity (Art. 39) two volumes of Idrogen are set free for one of oxygen. If the gases be c(m1 and caused to unite again, water is formed, and le of either gas is left over. It has been found that |all cases where gases combine with each other, the lines combining have a simple ratio to each other, as 2,2to3,<&c. . .-- : _ .--_ - >(). Molecules and Atoms. — Two litres of hydro- unite with one litre of oxygen to form water. If union takes place at, say 200'' C, the water is in V 46 MOLECULES AND ATOMS. the gaseous state. It is then found that the vohinieiC di steam formed is the same as the vohime of hydrogci used, and according to Avogadro's law contains tl same number of particles (Dalton's atoms). Let suppose that the two litres of hydrogen contain t\fl v< millions of particles ; then one litre of oxygen contaii* it one million particles, and two millions particles of steawii] are farmed. Each particle of steam contains oxygen, sf if that the oxygen must be divided into two millions ilBa parts when combination takes place. Therefore, tig of particles of oxygen must be divisible. They are nttre atoms, but 2)airs of atoms, which cannot be separat*^ excei)t by chemical action. They are called moleculm^ (little masses). The molecules of elements consist (wiiBB't few exceptions) of two like atoms ; and those of cow'h pounds, of two or more unlike atoms. The molecules ^^ substances are imagined as in constant motion of souftw'^ sort, the motion being different in solids, liquids, anP'J^ gases. In solids the motion is mostly vibration, tlfc?* molecules moving about particular points ; in liquldME there is a comparatively slow motion from place to place! and in gases this motion from place to place goes Mpi with great velocity, the molecules moving faster as m gases become hotter. It is the battering of the moll cules of an enclosed gas against the walls of the enck ing vessel which produces pressure. Deflnitions. — A molecule is the smallest portion of any m stance which can exist by itself. Imagine a drop of water divida and subdivided. A point is at last reached when no furtlwji division is possible by mechanical means ; and if the division J|ie forced by electricity or heat, it is no longer portions of wat« which are obtained, but two different substances — oxygen aiij hydrogen. At this point we have reached the molecule MOLECULAR WEIGHTS OF GASES. 47 vn^^r. All atom is the smallest portion of an element tvhich can exMt ill a molecule. The atom cannot be divided even by cliemi- cal action ; it must enter into combination aa a whole. 7. Molecular Weights of Gases. — Since equal niies of gases contain the same number of molecules, it ft)llows that the weights of equal volumes of gases are in proportion to the weights of single molecules. TJ us, if a certain volume of hydrogen weighs 2 grams, if the same volume of oxygen weighs 32, of nitrogen 28, and o^arbon dioxide 44, these numbers may be taken to esent the weif^l '^'^ of the molecules, or the molecular his of the gases. In the case of the elementary IS half the molecular weight gives the weight of the , or the atomic weight (why halj ?). In estimating specific weights of gases, the weights of equal volumes compared, one gas being taken as standard, and its ght taken as 1. Hydrogen is now usually taken as standard gas, and it can readily be shown that the ijic weight of a (/as is half its molecular weight. (Miplain this. ) 8. Chemical Notation— Atomic Weights. — leal symbols are letters used to denote the atomic hts of the elements. They are the initial letters of tS| Latin names. Where two or more names begin with til same letter, a second is added to distinguish. For e:^nple H denotes 1 part by weight of hydrogen ; O, 1 6 by weight of oxygen ; C, 1 2 parts by weight of n ; CI, 35.37 parts by weight of chlorine, &c. These bers are obtained by experiments, by weighing and uring. For example, it has been found that a litre ygen weighs 16 times as much as a litre of hydrogen, which it is concluded that a molecule of oxygen 48 CHKMICAL NOTATION. weighs U> times as mucli as a molecule of liydrogen (An| 54), and that the atom of oxygen must also weigh IG tiiiid as much as the atom of hydrogen i why 1). If, then, the! atom of hydrogen be assumed to weigh I (1 what?), tJiJ atom of oxygen will weigh 16. Again, 16 parts ofl oxygen combine with 65 of zinc, and there is evidenal that in this combination one atom of oxygen unites witlj one of zinc. Hence it is concluded that the atomic weigli| of zinc is 65. By similar methods the atomic weights o| all the elements have been determined. There is a metlio of determining the atomic weights which depends oi| measuring the specific heats of the elements. It was dm covered V>y Dulong and Petit that, if the atomic wel'jht J each element is multijdied hy its sjiecijic heat, the iwodm is always the same number {inearly), that is, 6.6. Froi which it follows that 6.6 divided by the specific he of any element gives its atomic weight. This number called the specific heat of the elements, and Dulong an Petit's law may be stated thus : The specific heat of l/| elements is a constant quantity. The symbols of the atoms are combined into formim representing molecules. Thus (Art. 56), since the moll cule of water contains 2 atoms of hydrogen and 1 oxygen, its formula is HjO. This formula is used express the following : — 1. Water is a compound of the two elements, hydrogen a oxygen, in the proportion by weight of 2 to 16. This is e^t lished by experiment. 2. The molecule of water is made up of 3 atoms, viz. : 2 of 1 drogen and 1 of oxygen. This is deduced from the atoii theory, which is now strongly supported by experimental t dence. CHEMICAL EQUATIONS. 49 Similarly, the molecule of oxide of sodium is repre- sented by NajO ; of oxide of zinc, by ZnO ; of sulphuric acid, by H0SO4, and so on. In these formulas the small figure below the line multiplies the symbol immediately before it. Thus, the molecule of sulphuric acid contains 2 atoms of hydrogen, 1 atom of sulphur, and 4 atoms of oxygen. Very often the formulas are used loosely for the names of compounds, but it must be always remem- bered that they mean more than this. For example, 11.2^ means J.8 parts by weight of water, and not simply ij^ter, or any quantity of water. The formulas of sub- stances are used to express their molecular weights, and, ^ven the formula of a compound, its molecular weight is found by adding together the weights of all the atoms in the molecule. For example, the molecular weight of sulphuric acid is (2 x 1) + 32 + (4 x 16) = 98. To represent 2, 3, &c., molecules the number is prefixed to tie formulas thus, 2ZnO, 3H2O, 4H2SO4, &c. Or, a formula may be multiplied thus, (H20)3, (]S'aC])5. rO. Chemical Equations. — These are short-hand repi (!sentations of the quantities of the substances taking Hprt in chemical actions. Before they can be written, ^eiiiical actions must be studied by weighing and moiisuring. For example, the decomposition of water electricity is represented as follows : — 2H2O = 2H2 Og,* a short-hand method of stating that 36 parts by fit might be written tiiore aimply H^ O = H^ -\- 0, but since, accordiniar to >ry, tiie molecule is the smallest portion capable of existing free, it is by Sy considered advisable not to represent single atoms in equations. How- \r, where weights alone are bein^ considered, this adherence to theory is necessary and often cumbrous ; and, except when considering the volumes iscs, 1 shall always write the equations in the simplest form. 5 50 CHEMICAL CALCULATIONS. weight (or 2 molecules) of water decompose into 4 pait> by weight (2 molecules) of hydrogen, and 32 parts by weight (1 molecule) of oxygen. (1) The equation should represent all the substances taking part in the action, in the proportions in which thev act on each other or are produced in the action. (2) Tin sum of the weights on the left side of the sign (=) shoulii be equal to the sum of those on the right. (3) The nuin ber of atoms of each element represented on the left should be the same as that on the right. The decomposition of potassic chlorate into oxygen and potassic chloride is represented by the folio wiiifff|| equation :—2KC103 = 3O2 + 2KC1. That is 2 x 12 gv3i.ms o^ potassic chlorate decomposes into 3 x 22 gramsl of oxygen and 2 x 74.6 grams of potassic chloride. (Isj it necessary then to use 245.2 grams of potassic chlorate! in preparing oxygen V) 60. Ohemical Calculations— From a chemical! equation we can calculate readily the proportions of tlie! substances represented in the equation ; and equationsl are useful as permanent records of chemical actions, tol which we can refer when we wish to know in what prol portions to use chemical substances in any reactionl Thus, suppose it is desired to prepare 100 grams o| phosphorus pentoxide by burning phosphorus in air] The equation representing this action has been niada out as follows : ~2P + 50 = P2O5. Referring to tli( table, p. 40, we see that P represents 31 parts bj weight of phosphorus. Also, P2O5 represents 62 + m = 142 parts by weight of phosphorus pentoxide; aTil 62 grams of phosphorus burn to form 142 grams VOLUMES OF GASES. 51 phosplionis peutoxide ; and 142 : 100 : : 02 : 43.62, or 43.62 grams of phosphorus burn to form 100 grams of j)entoxide. Gases are usually measured instead of weighed. But, since equal volumes of all gases (at the same temperature and pressure) contain the same number of molecules, weights of gases in the ratio of the molecular weights are the weights of equal volumes of the gases. The molecular weights of hydrogen and of oxygen are 2 and %'l respectively; therefore, 2 grams of hydrogen will Oieasure the same as 32 grams of oxygen ; and so for other gases. The measurement has been made with the greatest care many times, and it is found that 2 grams of hydro- gen gJis measure (at 0° C. and 760 millimetres of mercury pd'essure) 22.33 litres. The molecular weight in grama, QSr gram-molecule, of any gas measures, at 0° G. and 760 mm., 22.33 litres. Oab. Hydrogen t^ygen itrogen 4tniinonia tkrl)()n Dioxide arsh Gas ' &c. Formula. NHg CO 2 Molecular Weight. 2 32 28 17 44 16 &c. Volume of Gratii- Moleoule. I 22.33 litres. HpCalculate the volume of oxygen formed by heating 50 ^a HI s potassic chlorate. The equation is : 2KCIO3 = 2KC1 + 30, 246.2 grams. 149.2 grams. .3 X 22.33 litres. 52 OZONE. That is, 245.2 grams potassic chlorate givo 66.99 litres of oxygen. Therefore, 50 grams give iff?.^ x 66.99 = 13.66 litres. In making such a calculation we simply assume that what is true for the molecules as represented in the equation, is true for weights which are taken propor- tionately to the weights of the molecules. How much sulphur can be burned by 10 litres of oxygen measured at 0° C. and 760 mm. pressure? The equation is : 8 + 0^ = 32 grams— 22.33 litres. SO, That is, 32 grams of sulphur use up 22.33 litres of oxy- gen. Then, 22.33 : 10 : : 32 : 14.33 ; i. e., 14.33 grams of sulphur use up 10 litres of oxygen. What volume of] sulphur dioxide is formed in this action ? On looking at the equation we see that a molecule of sulphur dioxide is formed from a molecule of oxygen ; therefore, the volume of sulphur dioxide is the same as that of oxygen, viz., 10 litres. 61. Ozone. — This is a peculiar modification of oxy- gen produced chiefly by the action of electricity. It is a gas of a penetrating odour. It is one and a half times as heavy as oxygen,,and its molecule must therefore con- tain three atoms (O3), if that of oxygen contains two (0,). Ozone has very powerful oxidizing properties, destroy- ing paper, india-rubber, tfec, by rapid oxidation. It is I slightly soluble in water, more so in turpentine. It is I iioid to be a valuable means of disinfecting and deodoriz- ing the atmosphere, and is supposed to exercise a bene-j OZONE. 53 licial influence on the animal body. Of late, however, some investigators associate the prevalence of certain diseases of the respiratory passages with an excessive (juiintity of ozone in the air. Ozone is produced by the passage of electricity through air (or oxygen) — for example, by flashes of lightning. It is more abundant in pure than in impure air ; in the air of the country than in that of the towns ; and in the higher than in the lower strata of the atmosphere. Its quantity is said to be smaller where cholera and other epidemics are prevalent. Ozone is also produced in small quantity during the electrolysis of water, and during the slow oxidation of phosphorus in moist air. It is also formed about an electrical machine when in motion. — If a strip of filter paper soaked in starch and solution of potassic iodide be brought into an atmosphere containing ozone, the paper turns blue. Iodine is set free by the ozone, and ■unites with the starch forming the blue iodide of starch. — When an element occurs in different modifications, these Lare called allotropic modifications. Ozone is an allotropic \form of oxygen. QUESTIONS AND EXERCISES. 1. What percentages of sulphur and oxygen are there in sul- Iphur dioxide (SO2), and in sulphur trioxide (SO3) ? 2. What are the molecular weights of the following : Chlorine, I carbon monoxide (CO), ethylene C2H4), nitric acid (HNO3), and cane sugar (CigHaaOu)? 3. What weight of mercuric oxide is required to give 20 litres i of oxygen measured at 0° C. and 760 millimetres pressure ? [K(iuation : HgO = 2Hg + O2. 54 QUESTIONS AND EXERCISES. 4. Calculate the weights of 1 litre of the following gasts measiiretl at 0° C. and 760 millinietres of pressure : Oxygen, nitrogen, carbon dioxide (COo), ammonia (NHg), acetylene (CjHa), and sulphur dioxide (SO .^). 5. What volume (at standard temperature and pressure) will 60 grams of oxygen occupy ? 6. What weight of carbon dioxide will fill a vessel of 15 litres capacity? 7. Point out the errors in the following eq^uation : — 2FeS04 = Fe,0, +SO3. 8. The products of the combustion of a candle are collected, and are found to weigh more than the weight of candle burned. Is this contrary to the law of conservation of matter ? Explain. 9. In what respects does a chemical compound of iron and sulphur differ from i , mixture of these two substances ? 10. 100 grams of oxygen combine with 39.*^. 75 grams of cop- per. What is the equivalent of copper V 11. Iron forms two basic oxides. The percentage composition of one is, — iron, 77.78% ; oxygen, 2'2.22y^ ; and of the other,— iron, 70% ; oxygen, 30%. Apply the law of multiple proportions. 12. A litre of nitrogen unites with 3 litres of hydrogen. The molecule of the compound formed contains 1 atom of nitrogen and 3 of hydrogen. What is the change of volume when com- bination takes place ? 13. What is the composition of the substances represented by the following formulas :— NH3, H3PO4, S0^(0H)2, Fe^Ol,,, CO(NH.2)2, and K4Fe(CN)6 ? How many atoms in the mole- cules represented as follows :—Cili^(Oil)^, (NH.i)^f',0^, FeSO^.- 7H2O, and Fe.^(OH)e? 14. What weights of the following gases measure, at Stand^ftrd temperature and pressure, 22.33 litres, viz. : — carbon monoxiib (CO) ; ethylene (G^W^) ; hyilric sulphide {H ^S) ; phosphine (PH3), and methylamine (CH^.N!!.^) ? HYDROGEN. to CHAPTER VI. HYDROGEN. ' ' ' ' ■ ■ ^ ' 62. Hydrogen. — It was noticed by very early inves- itif^ators that when metals dissolve in acids, an inflammable gas is given off", but the properties of this gas (injlammable \air) were not fully investigated till the advance of pneumatic chemistry in the hands of Priestly and Caven- dish towards the end of last century (1766 to 1781). Cavendish showed that when it burns in air it forms water; hence its name, which means, water-generator. Hydrogen is found uncombined only in small quan- tities, in volcanic gases, in the gas which occurs with petroleum, and in meteoric iron. In combination, how- ever, it occurs in vast quantities, forming ^th by weight of water, |th of marsh gas, and a considerable part of Bugar, wood, starch, and animal and vegetable substances generally. 63. Preparation of Hydrogen.— Hydrogen can [be prepared : 1. By the electrolysis of water : H2O = H2 + O. 2. By the action of various acids on certain of the [metals, particularly sulphuric acid (diluted) on zinc : Zinc. Sulphuric Acid. Zinc Sulphate. Hydrogen. Zn + K,80, = ZnSOi + H2 r: 65 98 IGl 2 m- 56 HYDROGEN. Hydrochloric acid may also be used : Zinc. Hydrochloric Acid. Zinc Chloride. Zn + 2HC1 = ZnCl, + 66 73 1 36 and iron may be used as the metal : Iron. Hydrochloric Acid. Ferrous Chloride. Fe + 2HC1 = Fed, + H2 66 73 127 ' 2 (If the weights of metals represented in these equations be taken in grams, what volumes of hydrogen will be i)ro- 1 duced ?) . 3. By decomposing water by metals. Sodium and potassium decompose water at ordinary, and even at very I low, temperatures ; magnesium begins to decompose it only at 100°C.; und iron, copper, and silver, only at a red] heat. > - , iSxperiment 28.— Put some small pieces of zinc in a tiiisk provided with a gas delivery tube, and pour over the zinc some sulphuric acid previously diluted with about five times its volume of water and cooled. Collect the gas which comes off, at first in an inverted test-tubo filled with water, and test it from time to time with a match until it no longer explodes, but burns quietly (Why does it explode ?) Then collect the gas in jars for further experiments. When the gas ceases to come off pour the liquid in the flask into a porcelain basin and set it to evaporate. Crystallised zinc sulphate, or white vitrloll (ZnSO^.THaO), is obtained. Repeat this experiment using iron (in the form of tacks) instead of zinc. Hydrogen is obtained as before, and on evaporating the liquid crystallised ferrous sul- phate, or lve scraps of zinc, iron, and tin, in Iniill ((uautities of hydrochloric acid (dihited with four times its Wlk of water), in test tubes ; and observe that an inflammable jas l>u])bles oflF. Evaporate the remaining liquids and examine It' salts obtained (zinc chhride, ZnCla, ferrous chloride, B>Clj, Iknd stannous chloride, SnClj). (Write the equations). If the same weights of zinc and iron were used in this jxperiment, as in Experiment 28, the same volume of lydrcgen would be formed. The volume of hydrogen lolved by dissolving any weight of a m,etal is not influ- enced by the acid, if there are no secondary actions. Experiment 30. — Stick a small piece of metallic sodium to he end of an iron wire and push the sodium quickly under an nverted test-tube tilled with water (a small jar may be used). [ho sodium rises to the bottom of the tube disengaging a gas hioh pushes the water down. Closing the tube with the thumb, jmove it, and touch its mouth with a flame. The gas burns ; it hydrogen. Pour a few drops of red litmus solution into the Dst-tube and shake it up. The litmus turns blue, showing the )resence of caustic soda An atom of sodium displaces an atom of hydrogen from Iwater : H.,0 + Na = NaOH + H. 18 23 40 1 (( 'ompare with zinc and iron. What is the equivalent, )r ( ombining weight, of sodium). The remaining atom 6^ :- - avDRoxrDEs. of hydrogen can be driven out of the caustic soda by heating it with a second equivalent of sodium, when aodic oxide (NajO) is formed. (Write the equation for this action). Similar actions may be brought about with potassium (K) and water ; and it is found that 39.1 grains of potassium decompose 18 grams of water, forming ?-2^^i litres of hydrogen (1 gram), and 56.1 grams of caustic potash. (Write the equation). 04. Hydroxides. — Caustic soda and caustic potash are, in composition, midway between water and the oxides of sodium and potassium. They are called hydrox- ides. Other examples of hydroxides are quick lime, or calcic hydroxide (CafOH).^), magnesic hydroxide (Mg(OH)y), and hiitmuthic hydroxide (Bi(0H)3). (How many atoms of bismuth, oxygen, and hydrogen in a mole- cule of the last of these?) The two atoms OH constitute a group, which, united with atoms of the metals, forms hydroxides of the metals. Such a group of atoms, acting together as a single atom, and being present in a series of similar compounds, is called a compound radical The name given to the compound radical OH is hydroxyl (= hydrogen oxygen radical). 65. Properties of Hydrogen. -- (Symbol, H; atomic weight, 1 ; molecule contains 2 atoms (H.>) ; 1 litre vreighs 0.089G gram.) Hydrogen is an invisible gas, the lightest substance known. Air is 14.43 times as heavy as *.t. Experiment 31. — Take a jar of hydrogen from the pneu- matic trough, holding it upside and pour it carefully upward into another jar filled with air. To show that the hydrogen has PROPERTIES OF HYDROOKN. 09 risen into the second jar apply a flame to its mouth. (What properties of hydrogen does this experiment illustrate ?) Hydrogen is buoyant in air just as a cork is buoyant in water. It was formerly used for inflating balloons, but the cheaper coal gas has now largely taken its place. If soap bubbles be blown with hydrogen they rise rupiiUy, and can be set on fire while in the air. Experiment 32. — Thrust up a burning pine splinter, or small taper, into a jar of hydrogen held upside down. The hydrogen catches tire and burns, but puts out the taper. Hydrogen is not a supporter of ordinary combustion, but is itself combustible. Still, a jet of oxygen will burn in an atmosphere of hydrogen, just as a jet of hy- drogen will burn in an atmosphere of oxygen. This shows that the terms combustible and supporter of com- bustion are only relative and would need to be reversed in their application if we happened to be living in an atmosphere of hydrogen. — When hydrogen burns in air it unites vith the oxygen of the air to form water. It is a constituent of most kinds of fuel, as wood, coal, oils, &c., so that water is a constant product of fires and lights. (Account for the gathering of water on the bot- tom of a kettle of cold water set on the fire. ) Experiment 33. — Fill an inverted test-tube one-third with oxygen (by pouring it upwards in the pneumatic trough) from a jar of the gas, and the remaining two-thirds with hydrogen. Close the tube with the thumb, remove it from the trough, turn it several times to mix the gases, and apply a flame to its mouth. The mixed gases explode with violence. Repeat the experiment using air and hydrogen in the proportions of 5 to 2 liy vokuiie. The explosion is less violent. 60 PROPERTIES OF HYDROGEN. The mixture of 2 volumes of liydr«^^en and 1 of I oxygen is known as knall gas. The gases may remain mixed for any length of time at the ordinary tempera- ture without combining, but as soon as the temperature is made high enough at any point, combination begins at that point, water is formed, and enough heat is set free to raise the temperature of the surrounding uncom- bined gases to the point at which union takes place, that the combination goes on spreading throughout the] whole mass. This takes place with great rapidity, and] an explosio7i results. (Why mix the gases in the pro- portions given, rather than in any other 1) One gram I of hydrogen in combining with oxygen liberates 34,462 heat units. (What is a heat unit ?) Thus, in Experi- ment 33, the water formed by the combination of the] gases is heated to a very high temperature; it expands suddenly, and, losing heat, contracts suddenly, making a disturbance in the air which reaches our ears as the| sound of the explosion. — The flame of hyarogen is a very j hot one. In the oxyhydrogen blowpipe a mixture of I oxygen and hydrogen is used to give a flume of intense heat. When directed upon a piece of lime, this flame, although giving very little light it-elf, heats the lime to a { bright white heat, producing the lime-light. Coal gas is often used instead of hydrogen. — Hydrogen can be con- densed to a liquid by pressure at a very low tempera- ture. — Although hydrogen and oxygen do not usually combine at the ordinary temperature of the air, yet in contact with certain substances which have the power of condensing gases on their surface, the two gases unite at the ordinary temperature. Platinum has this power very strongly, especially when in the finely divided con- VALENCE. 61 litions of spongy platinum and platinum black. If a boil of platinum wire is held in a flame of hydrogen mtil it is red hot so as to drive the condenvsed gases oflf its surface, it acquires the power of setting tire to a mix- bure of hydrogen and air, even after it has cooled. This )roperty of platinum is utilised in heating a kind of Isurgical knife, which burns instead of cutting. — Hydro- Igen is very slightly soluble in water. It can be [breathed, and then gives a high squeaking tone to the voice. It is not poisonous, but will not support animal respiration. — Hydrogen is evolved during the growth of fungi, and as it is being set free it has the power of con- verting arsenic, antimony, and sulphur into poisonous gaseous compounds. This accounts to some extent for the poisonous effects of arsenical dyes in wall papei-s and carpets. 66. Valence. — Two volumes of hydrogen unite with one of oxygen. This indicates a difference between hydrogen and oxygen atoms. "Wc shall hereafter study ciises in which gases unite with hydrogen in equal volumes, or, as is deducible, one atom with one atom. One atom of nitrogen is united with three of hydrogen to form ammonia ; and one atom of carbon is united with four of hydrogen in the molecule of marsh gas. On refer- ring to Art. 63 we find that while an atom of sodium dis- places an atom of hydrogen, an atom of zinc displaces two. The following formulas express some of these facts : — Hydrochloric acid. Water. Ammonia. Marsh gas. HCl, H,0, H3N, H,C. The atoms of chlorine, oxygen, nitrogen, and carbon tliffer in the number of atoms of hydrogen which they I 62 DIFFUSION. can take to form a molecule. The power, varying in tliis way, is called atomicity, valence, or quantivalence. It is measured for any element by the number of atoms oj hydrogen with which an atom of the element will combine • or by the n mber of atoms of hydrogen which an atom oj the element will replace in a compound *Art. 63). The woids bivalent, trivalent, quadrivalent, quinquevalent, &c., are used to denote the valence of atoms which combine with or replace one, two, three, (fee, atoms of hydrogen. The words monad, dyad, triad, tetrad, hexad, &c., are also used. It will be seen later that the valence of an element varies in different compounds, but it nearly always in creases by twos. Thus, the valence of phosphorus is sometimes 3 and sometimes 5, e. g., PClg and PCI-, (Form a table of the elements mentioned in this article, writing the valence of each opposite its symbol). The valence of atoms is often indicated by Roman numerals attached to the symbols, as H', Na', CI', O", Ca", Zn" ; N"S Bi'", F" ; C'^ Si'^ ; N^, P^, Sb^, &c. In writing the fonuulas of compounds the valence of the atoms is often shown by lines joining the symbols. Formulas thus written are used to picture the knowledge we have of the way in which the atoms are groujyed in the molecide, and are called Graphic, or Constitutional Form.ulas. For II example, H — O — H, water : ZnZzO, zinc oxide ; N^ "' ammonia ; OazzS-il. calcic hydroxide. 67. Diffusion. — If a lump of sugar be placed at the bottom of a glass of water, it dissolves ; but the water is not at once sweetened, if it is kept still. After some time the taste of the sugar can be detected at the top. «,nd the sugar will at length become evenly mixed with DIFFUSION. 63 jtlie v/hole quantity of water, without the sliglitest ap- parent motion of the liquid. There must be some motion of the particles of sugar; in fact, the motion of mole- cules mentioned in Art. 56. It is supposed that the molecules of sugar, after dissolving, move about continu- ally until they are evenly (Hffused. This change of place of substances by molecular movements is called \di fusion. In one form or another it goes on in the I most im})ortant processes of animal and vegetable life ; e.g., digestion, assimilation, respiration, secretion, and excretion. Various words, osmose, endosmone, dialysis, kc, are used to describe diffusion under certain condi- tions, but the process is essentially the same in each case. Experiment 34. — Fill a tall glass cylinder nearly full of water, and pour through a funnel with long capillary tube lead- ing to the bottom a layer of saturated solution of potassic bi- chromate. If the cylinder be kept undisturbed, the red liquid will not be evenly diffused until several months have elapsed. Diffusion of liquids is very slow. (Will solids diffuse?) Experiment 35. — Fit with a bored cork a clean, dry, porous earthenware vessel (inner cell of a galvanic battery); push a long glass tube through the cork (it must fit tightly); and fix this apparatus so that the free end of the tube may stand in a vessel of some coloured liquid. Place over the cell a glass beaker or other convenient vessel bottom up, and fill the space between with Iiydrogen. The coloured liquid is at once forced down the tube, and bubbles of gas are driven out. Remove the outer ves- sel, and the liquid rises in the tube . (Coal gas answers in place of hydrogen, ) In (he first part of the process, there is air inside and hydrogen outside the porous cell. Both find their way through the pores, but hydrogen diffuses faster than air, I 64 HYDROGEN DIOXIDE. the volumo of gases inside the tube is increased, and the liquid is forced down to make room. (Explain tlie second part of the experiment. ) Diffusion of gases is a much more rapid process than that of liquids. (Why 1) Law of Diffusion of Gases (Graham): — Gases diffuse at rates {measured by volume) inversely proportional to the square roots of their relative weights. For example, the relative weights of hydrogen and oxygen are 1 and IG. Their rates of diffusion are as \/\Q to yT, or as 4 to 1, i.e., hydrogen diffuses four times as fast as oxygen. 68. Hydrogen Dioxide. — (H.^Oa). This substance IS also called peroxide of hydrogen, and oxygenated water. It is present in the air, and comes down with rain and snow, but only in minute quantities. It is a compound of hydrogen and oxygen in the proportion of 1 to 16 by weight. The simplest formula representing this compo- sition is HO, but if we try to write this graphicallij, showing the atomicities, thus H — O, an anomaly ap- pears ; the oxygen atom must be represented as monad, and there is every reason to believe that it is dyad. From this and other considerations the formula is doubled,— HA , or H-0— 0-H. Preparation. — Mix barium dioxide with dilute sulphuric acid, allow to settle, and pour off the clear liquid. The sub- stances formed in this reaction are hydrogen dioxide and baric sulphate : H3SO4 + BaO, ^ H2O2 4- BaSO^. 4 ' (Put this equation into words, giving weights and names.) — In this action the hydrogen dioxide is obtained diluted with water, while the heavy, white, insohible baric .sulphate falls to the HYDROGEN I'EROXIDE. 05 bottom. As the dioxide is decomposed ])y heat it cannot be separated from water by boiling away the latter ; but the water can he removed by placing the solution under the receiver of an air pump along with a vessel of oil of vitriol, which is very hygruscojnc (attracts moisture strongly). When the air is pumped out the water evaporates rapidly, and is absorbed by the oil of vitriol. Properties. — A colourless, oily liquid, heavier than water (specific weight 1.452), soluble in water ; very unstable, decom- posing slowly at low temperatures, rapidly when heated, into water and oxygen. (Write the equation.) It easily parts with half its oxygen to oxidisable substances ; i.e., it is an oxidismj cKjeiU. For this reason it bleaches many colouring matters ; e. g., that of the hair; and is commonly used for bleaching dark hair, old paintings, &c. It forms a froth when taken into the mouth, and excites the flow if saliva. It blisters when undilute 1. Its principal use in medicine depends on its oxidis- ing power. Test. — Add a few drops of sulphuric acid to a solution of hydrogen peroxide, then a little ether, and a few drops of pot- assic bichromate solution. After being shaken the mixture turns deep blue. The ether takes up the colouring matter, and formb a layer at the top. QUESTIONS AND EXERCISES. [ 1. Would you expect to find hydrogen uncombined in the air? 2. Calculate the percentage composition of water, i. e., the quantities of hydrogen and oxygen in 100 parts. . - . 3. What volume of mixed gases, measured at 1000 mm. pres- sure and 10° C, is produced by the electrolysis of 100 grams of water ? ft 66 QUESTIONS AND EXKHCISES. 4. 50 grams of zinc are put into a closed vessel of 10 litres capacity along with 1 litre of dilute sulphuric acid. What is the pressure of gas when the action is completed ? 5. What weight of zinc must be dissolved in order to give SO litres of hydrogen measured at 3 atmospheres pressure and 1G° C? G. 20 grams of iron are dissolved in hydrochloric acid, and tbo evolved gas is measured at 750 mm. pressure and 20° C. What is its volume ? . m- , v :. 7. " One atom of zinc sets free a molecule of hydrogen." What evidence can you bring in support of this statement ? 8. What is a hydroxide ? Are there hydroxides of the non- metals ? 9. Define compound radical. What is the meaning of the word radical as used here ? Should it not be spelled radicle ? 10. Calculate the weight of 20 litres of hydrogen measured at 25° 0. and 1000 mm. pressure. What volume of oxygen has the same weight under the same conditions ? 11. How does it happen that the atomic weight of hydrogen is 1? 12. Why does hydrogen explode less violently with air than with oxygen ? 13. From the following formulas deduce the atomicity of bis- muth (Bi), phosphorus (P), tin (Sn), and Sulphur (S) : HCl, BiClg. PCI5, HaO, SnOa, SO3. 14. The specific weights of water vapour and oxygen are 9 and 16 (Hydrogen =1). If 100 c.c. of water vapour difi'use into a vacuum in a certain time, what volume of oxygen will diflfuse under the same conditions in the same time ? 15. Hydrogen dioxide is sometimes called %t/roa:y^. Explain. TUB ATMOSIMIEUE. 07 CHAPTER VII. AIR. 69. The Atmosphere. — This is the gas(50iis ocean, supposed to be from 50 to 100 miles deep, at the bottom of which we are living. Spaces said to bo empty are generally full of air. Experiment 36. — Pass the tube of a small glass funnel through a bored cork having a short glass tube passing through a seoontl hole (as in a xoash-hottle). Fit the cork into a flask, close the glass tube with a finger and fill the funnel with water. A little runs into the flask ; remove the finger from the tube, and the whole of the water runs in freely. If the tube have only a small opening, the water runs in slowly, and a flame held near the opening will be blown by a stream of air coming out. (What conclusions do you dra w from this experiment 1 Why is it necessary in filling a cask with water through a funnel, to bore a second hole in the cask V) Air has weight, as can be shown by weighing a glass globe emptied by the air pump, then allowing the air to flow in, and weighing it again ; a delicate balance shows an increase in weight. One cubic foot of dry air at standard temperature and pressure weighs 565^ grains (calculate the weight, in grams, of 1 litre). Since air has weight, the atmosphere presses upon the surface of the earth, and upon every object on that sur- face. This pressure can be shown by the barometer. Fill a glass tube, closed at one end, and about 35 inches long, I 68 ATMOSI'IIEUIC PRESSURE. with mercury ; close it with the thumb, invert it, and place the end beneath the surface in a dish of mercury. Remove the thumb, and the mercury after a few oscilla- tions comes to rest at about 30 inches above the level of the surface in the dish (Torricelli, 1G43). Some pressure on this surface balances the weight of the mercury in the tube, otherwise the mercury would fall. This pressure is the weight of the atmosphere. It is exerted in every direction on the surface of any body placed in it. (What is there inside the tube above the mercury 1) Experiment 37. — Make an experiment such as that described above, using water instead of mercury. Tlie water does not fall at all when the inverted tube is opened under water. But if the tube were, say, 40 feet long the water would fall and remain at the height of about 34 feet. An ocean of water 34 feet deep, or one of mercury 30 inches deep, would exert the same pressure upon the earth as the atmosphere does. (Calculate the specific weight of mercury). A column of mercury 30 inches high and 1 inch square in section weighs 14.7 lbs.; and the pressure of the atmosphere is generally taken as 15 lbs. on the square inch. When a barometer is carried up a tower (Blaise Pascal, 1648), or mountain, the mercury falls ; if it is carried down a deep mine the mercury rises. (Explain). At the top of Mont Blanc, it stands at 1 (5 inches only. When any great portion of the atmosphere is heated, it expands and part of the air flows away over to colder regions. This diminishes the weight of the air in the heated region, and the barometer falls, until air rushes in from surrounding regions to equalise the pres- sure. (What natural phenomena does this explain ?) Similarly, cooling causes rise of the barometer. These royle's law. 09 iind other causes protluce variations in the hei<^ht of the niorciiry in the bai'onieter, so tliat, in studying weatlier, careful attention must be given to the readings of the barometer. The average height at the see-level is 30 inches, or 7 GO millimetres. This is taken as the standard pressure in calculating volumes of gases. 70. Boyle's Law (1662>. — If a quantity of air be confined and the pressure upon it increased, its volume is lessened ; if the pressure be decreased the volume be- comes greater. This can be shown by a cylinder closed at one end and provided with an air-tight piston. If one presses the piston down, one feels a resistance^ but the volume is diminished ; on the other hand, if the piston is raised above a certain distance, one feels that a weight is being lifted (\yhat is the weight"?) as the volume increases. The law of change of pressure with change of volume is as follows : — The volume of any portion of air is inversely proportional to the pressure, the temperature being constant. (Consult a work on Physics for the experimental demonstration.) When any j)ortion of air is closed ofi' from the rest of the at- mosphere, the pressure upon it is that shown by the barometer at that moment, say 30 inches of mercury. If the pressure be doubled, the volume is reduced to | the original ; if the pressure be tripled, to ^, &c. On the other hand, if the pressure is reduced to ^, the volume is increased to twice the original and so on. Stated in general terms, V : V^ : : PM P, where V and V^ repre- sent volumes at pressures P and P^ This law applies to all gases far removed from their ])oini of condensation* It does not, for example, apply to water at 105° C. * At hif,'h pressures Boyle's Law is only approximately true. 70 Charles' law. 71. Expansion of Air by Heat — Oharles' Law. Experiment 38. — Place a narrow-necked flask with its .lock downwards and dipping under water. Pour hot water on the bottom of the llask ; the air inside expands and part of it is driven out of the flask. Allov/ the ttaak to cool j the air con- tracts, and the water rises in the neck of the flask. The amount of tliis expansion and contraction has been accurately measured for air and other gases. It u almost exactly the same for all gases. If we begin with a i)ortion of gas at 0° C and heat it to 1°, its volume increases by ^fjrd ; at 2° its volume is greater than at 0°, by ufjrds, and so on. If the gas be cooled to — 1° its volume is less by ^^I'd, at — 10° less by ^jVVtls, and at — 273° (if we could reach such a temperature) the volume would be 0. Hence — 273" C. is called the absolute zero of temperature, and temperatures reckoned from this point are called absolute temperatures. Evidently the absolute temperature corresponding to 0° C. is 273°, and gener- ally any temperature t of the centigrade scale is 273 + t of the absolute scale. The Law of Expansion of Gases ia as follows : — 17ie volume of any portion oj ecomes necessary in coni[)arin. } r C. and 74C mm. example 2. — What weighb of potassic chlorate, when de- composer, will give 10 litres of oxygen measured at 20° C. and 1000 mm. pressure ? Equation : 2 KCIO, = 2 KCl + 3 O^ 2 X 122.6 3 X 22.33 fjrams. litres. i. e., 245.2 grams of the salt give 66.99 Ltres of oxygen measured at 0" C. and 76t mm. In order tc coU'^are this volume with the voliTme required, they must be reckoned at the same tomperature and pressure. It is well, to avoid confusion, to compare volun^ea of gases alicays at 0° and 760. In this case, then, we first reduce the 10 litres to the vf»lume at 0° and 760 : 27 + C 1000 1<^ >< 2~93inio ^ ^3 = ^''^^- »* 0° and 760. 273 100 Then, 66.99 : 10 x ^ x yT — 245.2 : x _ 10 X 273 X 100 X 2'i5.2 ^ = 293 x"76~ X 66.99 73. Composition of Air. Usperiment 39. — Put a bit of pbosphonis, dried on filter paper, into a amall porcelain cup floated on a flat cork in a basin of water. Touch the phosphorus with a hot wire and immediately cover it with a beaker. It burns for some time, but at length goes out. As the enclosed gas cools, water rises in the beaker, showing a lessening of volume. Decant some of the gas ii\to ?. tcbt-tube (Art. 41), close the test-tube with the thumb, remove it, and thrust a burning match or splinter into the gas. The flame is put out. Fui-ther examina!,j.O'- of tliis gas has «hown it to be an element, 7dtrogen, The combu.3r'o:. of phosphorus is driD VOLUMETRIC ANALYSIS OF AIR. 1 3 to the oxi/i/en of the air. (What has become of thef«« in the experiment 1} — Air is a mixture of tha two elementary yoses, nitrogen and oxygen. That it is a mixture, and not a chemical compound, is ^^een from the following facts : — 1. If air be shaken up with water, oxygen dissolves in greater relative quantity than does nitrogen. 2. Tiie two gases can l^e partially separated by dif- fusion. (Which gas diffuses faster]) Ij. If nitrogen and oxygen be mixed in the ratio in which they are present in air, no heat is given out, and there is no other evidence of chemical action ; but the mixture has the properties of pure dry air. 4. The volumes of the gases are not in any simple ratio. (What law is here referred to?) Volumetric Analysis of Air. — This analysis is made in a graduated glass tube called a eudiometer. The tube is closed at one end, at which two jdatinuin wires are melted through the glass so as nearly to meet within the tube. The endiometer is filled partly with mercury, inverted in a trough of the same liquid, and the volume of air thus closed off is noted, as well as the temperature and pressure. To this air is added about half its volume of pure hydrogen, find volume, temperature, and pressure are once more noted. The eudioi! ^ter is now tightly pressed d' wn on a sheet of India-rubber, and an electric spark is passed between the platinum wires. An ex- plosion takes [)lace within the tube, and the volume of gas is seen to be much reduced. Volume, temperatui'e, 74 ANALYSIS OF AHl RY WEIGHT. and pressure are once more read olf. The remaining gas is a mixture of nitrogen and hydrogen. One-third of tlie loss of volume after the explosion is due to the disap- pearance of oxygen (What h:'s become of it?) ; and the volume of oxygen being known, the remainder of tho original volume of air is reckoned as nitrogen. Sxample. — Volume of air enclosed, 20 c.c. ; temperature, 15° C. ; pressure, 750 mm. — Volume after addition of hydrogen, 32 c.c; t, 16* 0. ; j5, 718. Volume after explosion, 20 c.c; t, 18° 0. ; p, 710 mm. Reduce these volumes to 0° C. and 760 mm., and find the decrease of volume after explosion to l)e 11.03 cc Calculate from this that 100 c.c. of air consist of 20.96 of oxygen and 79.04 of nitrogen, COMPOSITION BY VOLUME, Oxygen 20.90 Nitrogen 79.04 100.00 Analysis of air by Weight. — Air is dried and purified, and then allowed to flow slowly tlirough a weighed tube containing red hot copper filings. It loses oxygen, cupric oxide (CuO) being formed ; and the nitro- gen passes on into a weighed vacuous globe of glass, he increase in weight of the tube gives the weight of cxygen, and the increase in the globe the weight oi Tiitrogen. The average of many careful experiments gives as the percentage com[)Osition of air by weight : Oxygen 22.77 Nitrogen 77.23 100.00 CARBON DIOXIDE, ETC". 75 Tlie composition of air is almost constant in all parts of the world, and in all situations. In towns and in fof^gy weather the percentaj];e of oxygen, by volume, may sink to 20.8 ; and in crowded rooms it sometimes sinks much lower. — The oxygen of the air is necessary to sup- port life, fires, decaying processes, &c. (What is tho use of nitrogen ]) 74. Other Substances in the Atmosphere.— The atmosphere contains several substances besides oxygen and nitrogen, but in small and variable quantities. Carbon Dioxide (CO^). — Constantly present in air, from 4 to 6 volumes in 10,000. Its presence is of great imi)ortance, as it forms an essenthil constituent of the food of plants. The supply is kept up by the processes of combustion, respiration, and the decay of organic matter. Water (H^O). — This is present in the air, in the form of vapour, in very variable quantities, depending on tem- perature and degree of saturation. A cubic metre of air at 25° C. contains when saturated 22.5 grams of water vapour ; at 0° C, only 5.4 grams. Dew is formed by the condensation of aqueous vapour from the air by con- vCt with cooled surfaces. Leaves radiate heat much fister ohan other objects, and therefore condense water va[)oar much more rapidly. (Why does not dew form on a cloudy or a windy night I) Aqueous vapour in the air tempers the heat of the sun, thu rays of which would be unbearably hot, if a large fraction of the heat were not stopped on its passage through the atmosphere. Water vapour has in a very high degree the power of absorbing radiant heat. 76 co?.:bustion in air. Compounds op Nitrogen. — Minute quantities of oxides of nitroijen are formed in the atmosphere by tlie action of electricity. (On what?) Ammonia (NH3) is present in small proportions, generally as amnionic nitrite or nitrate. These substances are brought down to earth in rain and snow, and serve for plant food. Dust, &c. — Under this head are included solid par- ticles of all sorts, organic and inorganic. Com,mon salt is always present in the air. If a little clean rain-wator is evaporated on a microscope slide and the residue ex- amined with the microscope, crystals of common salt (NaCl) can always be seen. Spores, or eggs of minute plants and animals, are constantly present. Many of them are the eggs of ferments ; others are the cause, or at least the concomitants, of diseases. The object of the antiseptic spray in surgery is to kill such living dust ; and it is important to note that disinfectants and anti- septics which are to purify air must (unless the air is drawn over them) be volatile. A\v can be purified from dust by drawing it through ootton-wool, and other filters. Ozone and hydrogen dioxide have been already men- tioned. 75. Oombustion in Air. — Substances which burn in oxygen usually burn in air, but not so rapidly. (Why 1) The substances burned in la.mps, candles, and fires are composed mostly of carbon and hydrogen, which unite with oxygen to form carbon dioxide and water. Thus, the oxygen of the air is used up, and in lamps and stoves, (fee, provision must be made for a renewal of the supply of air, — in other words, there must be a draught. v.v : ,•/?•/!' f-fitr^i"^ RESPIRATION. 77 The consumption of oxygen must be taken into account in considering questions of ventilation. An orcliiiary lamp consumes as much oxygen in 1 hour as a man does in 5. (How does a lamp or gas flame differ from a fire in a stove or grate in their effect on the air 1) 76. Respiration. — In the air cells of the lungs the air is separated from the blood by a very thin membrane through which diffusion goes on readily and rapidly. The blood comes into the lungs charged with carbon di- oxide, a waste product which it has gathered from the fur- naces of the body, — the muscles, glands, &c. These need a continual supply of oxygen to feed the slow fires going on in them. Carbon dioxide passes outwards by diffu- sion, and is exhaled ; oxygen diffuses inward and is car- ried away to the tissues. Thus, the air which returns out of the lungs contains less oxygen and more carbon dioxide than when it was inspired. In one hour an adult man consumes about 29 grams (how many litres?) of oxygen, and breathes out about 33 grams carbon di- oxide. Besides carbon dioxide, water vapour and small quantities of complex organic compounds are exhaled. Botli the organic compounds and the carbon dioxide are injurious to health ; and therefore the necessity for re- newing the air which is breathed. It is estimated that an average adult man requires 1500 cubic feet of fresh air per hour. QUESTIONS AND EXERCISES. I. A flask billed with water and closec^ with a cork through which passes a narrow tube open at both ends is held upside ilowii. The water does not run out. Why ? 78 QUESTIONS AND EXERCISES. 2. Air is found to become less and less dense as we ascend. Account for this. 3. Why do men need to breathe faster at great elevations than lower down ? 4. Why does blood burst through any place where the skin is thin, when a very great elevation is reached, as in balloons ? 5. What is the pressure of the atmosphere in grams on every square centimetre ? 6. The specific weight of alcohol is 0. 784. What would be the average height of an alcohol barometer ? 7. A quantity of air measures 2G4 c.c. at a pressure of 700 mm. What will it measure when the pressure is increased to 1000 mm.? 8. Calculate the weight of hydrogen in a vessel of 10 litres capacity, filled when the barometer reads 756 and the ther- mometer 18° C 9. A quantity of air under a pressure of 32 inches of mercury undergoes a change of pressure and increases from 10 cubic feet to 12.4 cubic feet. Wliat is the new pressure? (Temperature constant. ) 10. What pressure must be used to compress 18 litres of oxygen into a vessel of 6 litres capacity, the oxygen being origi- nally under a pressure of 785 mm. ? 11. 150 c.c. of air at 50° 0. is cooled to 10° C. Calculate the volume (pressure being constant). 12. A quantity of air measures 24 litres at 15°. ; the tempera- ture is reduced to — 16° C. What is now the volume ? (Pres- sure constant.) 13. What volume of gas at 200° C. will measure 320 c.c. at 0° C? (Pressure constant.) 14. What volume of oxygen measured at 2000 mm. and 12° C. is formed by the decomposition of 600 grams potassic chlorate ? NITROGEN. 79 CHAPTER VIII. NITROGEN AND ITS COMPOUNDS. Nitrogen— (N'" = 1^). 11. Occurrence. — Forms about fo'U'-fifths by volume of the atmosphere ; in combination, it forms part of all living matter, and is tlioreforo an essential consti- tuent of plant and animal food. Other compounds oc- curring in nature are nitre (KNOa^, Chili nitre (NaNOg), and ammonia (NHg). 78. Preparation. — Nitrogen is most readily pre- j)ared from air (Exp't 39) ; see Art 73, " Analysis of Air by Weight." It can also be prepared from nitre (salt- petre). Experiment 40- — Heat 10 grams iron filings in a hard-glass test-tube with ^ gram saltpetre. Collect the evolved gas in the usual way. It is nitrogen, the ^^nitre-generator," 79. Properties. — An invisible gas, without smell or taste. It is 14 times as heavy as hydrogen and a little lighter than air. (Calculate its specific weight, air being standard.) It is incombustible and not a supporter of combustion (Make experiments to show this). It is re- markable for chemical inactivity, not entering readily into combination with other elements. Under the in- fluence of electric sparks or flashes it unites with oxygen, and, in very small quantities, wit)i hydrogen. It is ^T 80 AMMONIA. slightly soluhlo in vvjiter, about 1^ vols, in 100 of water. It })as boeii liquefied at — 146° C. by a pressure of 33 atmospheres. Coinpouruls of Nitrogen. 80. Ammonia.— (NH3 = 17.) Experiment 41. — Heat apiece of dried meat in a glass tube closed at one entl. It chars, and moisture collects. Wet a small strip of filter paper with red litmus and bring it in contact with this moisture. The litums is turned blue. Same result, if a hit of coal, bread, or horn be heated. The alkaline reaction of the moisture is due to the presence of a volatile alkali, ammonia. (What alkalis have already been noticed 1) It is always formed when animal or vegetable bodies are destructively distilled. Coal, wood, bones, and other animal and vegetable sub- stances are distilled on a large scale in the manufacture of gas, charcoal, bone-black, &c.; and the watery liquid (a by-product) contains much ammonia. From gas liquor ammonia is prepared by heating with lime and condensing the ammonia in cooled water. Formerly, it was prepared by distilling scraps of the horns of the hiirt ; hence the popular name, " spirits of hart's horn." — Ammonia is always one product of the decay of ani- mals and vegetables, excrement, guano, &c. Preparation. — Ammonia is most conveniently pre- pared from one of its salts, sal ammoniac (NH^Cl). Experiment 42. — Mix thoroughly about 2 parts of dry powdered sal ammoniac with 1 of powdered quick-lime. Note the smell of ammonia. Put the mixture into a hard glass test- ^ AMMONIA. 81 tube or flask, ar.d arrange a gas delivery tube so as to collect the evolved gas in inverted bottles, to the tops of v hich the delivery tube mu8t reach. ( Why not over water ?) Equation : Ammonic Calcic I-ime. Cliloriile. Cliloriiic. CaO + 2Nir,01 = CuCJ, + 2Nlf., + lf,(). 56 1()G.8 110.8 44.()6 grams. grams. grams. litres. Aininonia is generally used in water. To pioprue the solution slaked lime is employed instead of quick lime, and the gas is passed into water, which must be kept well cooled. (Why I) Properties. — Ammonia is an invisible gas, with a pungent smell, and a sharp alkaline taste. It is lighter than air. (How does Exp't 42 show this "?) (Calculate its specific weight, air being standard ; also when hydrogen is standard.) It is liquid at 15.5° C. under a pressure of 7 atmospheres (What is an atmosphere of pressure ?), and at — 70° C. is solid. It is ,very soluble in water, 1148 vols, dissolving in 1 of water at 0° C. Much heat is given out during the process. (Account for this.) When a solution of ammonia is warmed the gas is driven off ra})idly. Experiment 43. — Fill a test-tube with ammonia gas (Experi- ment 42), close with the thnmb, place the mouth under water, and remove the thumb. The water rises to the top, if there is no air in the tube. Close again with the thumb, remove the tube and examine the water in it, as to its smell, taste, feel, and action on red litmus. The solution of ammonia in water {liquor ammoniae) has a strong alkaline reaction and probably contains cuiimonic hydroxide (NH4OH). It neutralises acids, and 7 -- 82 LIQUOll AMMONIiE. thereby forms salts. The dry gas, also, combines with acids, and it is to be observed that no WHter is pro- duced when ammonia unites with acids to form salts, e.g., NH3 + HCl = NH4CI. These salts are called ammonium salts, since they contain the compound radical ammonium (NH4) acting as a monad metal. Ammonia is not a supporter of combustion, and is incombustible in air ; but a mixture of the gas and oxygen burns with a pale bluish flame, and forms water, nitrogen, and a little nitric acid. Experiment 44. — Try the combustibility of anunoiiia gas l)y thrusting a burning match into a jar of it. Composition of Ammonia. — Tiie gas is decomposed by electric s{)arks. Two volumes of ammonia give one of nitrogen and three of hydrogen. That is, two mole- cules of ammonia decompose into one molecule of nitrogen and three of hydrogen. From this it is concluded that the molecule of ammonia contains an atom of nitrogen and three of hydrogen. Liquor ammonlce fortior is a nearly saturated solution of am- monia in water, prepared by distilling in an iron retort 3 lbs. ammonic chloride (NH^Cl), with 4 lbs. slaked lime (Ca(OHj._,), and receiving the gas in water. It is lighter than water (sp. wt. 0.892), and contains 32.5 per cent, of ammonia. It must be kept well stoppered, otherwise the ammonia escapes. As ammonia is less soluble at high than at low temperatures this solution should not be allowed to get very warm, (What would happen ?) Liquor ammonioi or aqua ammonioe is a weaker solution, made by mixing 1 pint of the stronger solution with 2 pints distilled water. It contains 10 per cent, of ammonia. Ammonia has a stiong inflammatory action on the respi- ratory and other mucous membranes. When breathed NITRIC ACID. 83 diluted with air, it stinuilatos ; but its constant uso may at length produce serious indumination. Since it unites with acids to form mild salts, it is an antidote to acid gases. (What are antidotes for ammonia ?). Hydroxylamine (NH3O) ia a substance nearly related to am- monia. Its molecule contains hydro xyl (OH) instead of one of the atoms of hydrogen. If the molecule of ammonia is repre- eeuted by N-^h> that of hydroxylamine is N^u • It is pre- pared by the action of nascent (just being set free) hydrogen on nitrogen dioxide (NO) :— NO + 3H = NH;,0. 81. Nitric Acid (HNO3 = 63). Experiment 45. — Put a little saltpetre in a test-tube, and drop on it from a pipette a small (quantity of oil of vitriol. Heat very gently, and observe the drops of fuming liquid wliich gather on the sides of the tube. Gather them on a glass rod and try their action on red litmus. The acid liquid is nitric add, or aquafortis. Saltpetre is a salt of the base, potassic hydroxide, and nitric acid. When it is acted upon by the stronger acid, the weaker is displaced, and a new salt, potassic sulphate, is formed. 2KNO3 + H2SO, = 2HNO3 + K2SO4. Nitric acid occurs naturally only in small quantities ; but its salts are found in large quantities. Chili salt- petre, or sodic nitrate (NaNOg), is most plentiful, and is • now used in preparing the acid. Preparation. — Distil at a gentle heat, from a glass retort, equal weights of Chili* saltpetre and oil of vitriol, keeping the receiver well cooled. Nitric acid distils, and a white salt remains in the retort. This salt has t> 9MAGE EVALUATION TEST TARGET (MT-3) /. V :A f/. 1.0 Sri I.I 2.8 u 1^ 2.5 1^ 11 i.8 L25 III U i 1.6 V] <^ /i « A ^ % > y .»' '*^^*»' V-^* y /;^^ <9 / /A Photographic Sciences Corporation ^^ 4^ o A % V 'o 23 WEST MAIN STREET WEBSTER, NY. 14580 (716) 872-4503 o^ V 84 NITRIC ACID. acid properties. In fact it is still half acid, and is called acid sulphate of sodium, or sodic hydrio sulphate : NaNOa + H^SO^ = HISTOa + NaHSO,. Why not use double the quantity of sodic nitrate, as represented in the preceding equation? Because, in this case, the action would go on only at such a high temperature that the nitric acid would be partially decomposed. Properties. — Pure nitric acid is a colourless fuming liquid of sp. wt 1.52. It has a strong attraction for water, and it is hard to prepare it free from water. The strong acid of commejce a,] ways contains about 10% of water, and is generally reddish or yellowish from im- purities. Red fuming nitric acid is strong nitric acid coloured by nitrogen trioxide and tetroxide. When strong nitric acid is boiled it loses acid faster than it does water, until a liquid containing 70% of acid distils at 121° C. unchanged. If a weaker acid be boiled it loses water faster than acid until it contains 70°/^ of acid. Experiment 46. — Put a few cubic centimetres of strong nitric acid in a test-tube, and add an equal volume of water. Note the rise of temperature. ( Account for it. ) Pour the contents of the tube into about one litre of water, stir well, and taste. Nitric acid is a powerful oxidising agent. (Calculate the percentage of oxygen which it contains). Experiment 47. — Drop a little strong nitric acid on some powdered charcoal heated to redness in a deflagrating spoon. N. B. — The acid must contain very little water. KITRIC ACID. 85 Experiment 48— Very carefully drop a small piece of phos- phorus into a little nitric acid in a small porcelain dish. It dis- solves with the evolution of reddinh fumes. If the acid is very strong, the phosphorus catches fire. K the solution from Experiment 48 be evaporated, phosphoric acid is left. (How has this acid been before obtained 1) Similarly, sulphur can be oxidised to sul- phuric acid by boHing with nitric acid. Turpentine can be set on fire by . lixture of nitric and sulphuric acids. Experiment 49- — Dilute a few cubic centimetres of nitric acid with about 4 times its volume of water, and pour it over a small bit of lead in an evaporating dish. The lead begins to dissolve, and red, strongly-smelling fumes come off. Apply heat to hasten the action, and when the lead is completely dissolved evaporate the solution on the water bath. Crystals of colourless plumbic vitrate (i'b(N03).^) ^-re left. Eepeat the experiment, using cop- per instead of lead. Fine blue crystals of cupric nitrate are formed : 3Pb + 8HNO3 = 3Pb(N03)2 + 2N0 + 4H2O. 30u + 8HNO3 = 3Cu(N03)2 -f 2N0 + 4U^0. (Write down the names and weights.) Nitric acid dissolves most metals, forming nitrates of the metals, oxides of nitrogen, and water. It dissolves silver, but not gold, and can thus be used to separate silver from gold. If the strong acid be used in dissolv- ing metpis, the gaseous product is nitrogen trioxide (N2O3); dioxide (NO), monoxide (NoO), nitrogen, and even ammonia, are obtained at successive stages of dilu- tion. As a rule, the more violent (rapid) the action of tlie acid, the less oxygen does it lose. Thus, the higher oxides of nitrogen are formed when the acid is strong^ 86 NITRATES. the temperature high, or the metal ea^sily oxidised. — Nitric aciJ is a strong corrosive poison. It 'eats up' or- ganic tissues when it is strong, and partially destroys them even when it is weak. The antidotes are mild alkaline substances, as magnesia. A drop of the weak acid left on the skin for a few moments colors it bright yellow {Picric acid is formed). Nitro-glycerine and gun-cotton are chemical compounds of glycerine and cotton with nitric acid, in which the oxygen of the acid is ready to combine with the carbon and hydrogen of the glycerii>e and cotton. (Explain their explosiveness.) Dynamite is a commercial prepara- tion of nitro-glycerine. Tests. — 1 . Heat with some bits of copper. Red fumes are given oflF. 2. Colour light blue with a drop of sulphate of indigo, and heat. The colour disappears, because the indigo is oxidised. 3. Mix in a teat-tuba about equal volumes of strong sulphuric acid and solution of ^errous sulphate (FeS04), cool, and., holding the test-tube aslant, carefully pour down the side so as to form a layer on the top a dilute solution of nitric acid. Either at once or after a few moments a brown ring appears between the two layers. This is due to the formation of a brown compound of ferrous sulphate and nitrogen dioxide : SHjSO^ -f- 2HN0g + 10 FeSO^ = 3Fea(SOj3 + 2(FcSOj2NO -f 4H2O. 82. Nitrates.— Basicity. Experiment 50. — Put a pipette ful of caustic potash solution in a porcelain basin, colour with litmus, and add dilute nitric acid (1 of strong acid to 4 of watei) slowly with a pipette, stir- ring constantly, until the blue litmus turns purple. Taste the solution. Evaporate on the water bath. Long prismatic crys- tals of saltpetre are obtained. BASICITY. 87 If this experiment be made quantitatively it will be found that to get the neutral point, pure potash and pure acid must be mixed in the ratio by weight of 56.1 to 63. If any other ratio be used, some of the acid or of the base is left over : KOH 4- HNO3 = KNO3 + H2O. 66.1 63 Base and add give salt and water. If a similar experiment be made with caustic soda, sodic nitrate, in cubical crystals, is formed ; and it is found that in this case also the base and acid unite in only one proportion^ viz., 40 to 63. NaOH + HNO3 = NaNO., + H.O. 40 63 40 g. of caustic soda are equivalent to 63 g. nitric acid (and to what weight of caustic potash 1) Since nitric acid acts on these two bases in only one proportion for each, and forms only one salt for each, it is called a monobasic acid. The bases are monacid bases. Experiment 51.— Put some dilute nitric acid in a porcelain dish, colour with litmus, and add dilute solution of ammonis. until the litmus just turns blue. Then evaporate to dryness on the water bath, and preserve the crystals of ammonic nitrate for a later experiment : — NH3 + HNO3 = NH4NO3. Experiment 52. — Warm a little plumbic oxide (litharge) in a porcelain basin with dilute nitric acid. The oxide dissolves to a colourless solution. Evaporate on the water-bath. Colourless crystals of plumbic idtrate (PbfJsOg),) are left : — PbO 4- 2HNO3 = PMNOs)^ 4- H^O. Keep this salt for a later experiment. 88 SALTS. The molecule of plumbic oxide is equivalent to two molecules of nitric acid. There is a corresponding base, plumbic hydroxide, Pb(0H)2 , the molecule of which is also equivalent to two of nitric acid. It is therefore called a di-acif base. We shall see later that there are also di-basic acids. (We have observed three ways in which nitric acid forms salt. What are they ?) The nitrates are, almost without exception, soluble in water. They can all be decomposed by heat. The nitrates of the heavy metals ^copper, iron, lead, ° under a pressure of six atmospheres ; causes suffoca- tion when breathed ; has violent irritating action on mucous membranes, and may cause catarrh or ulceration; soluble in water, 3 v^ols. in I at 10° C; the aqueous solu- tion acts as a powerful irritant both externally and inter- nally ; antidotes are white of egg, milk, ammonia, lime water, soap, and other alkaline substances. Chlorine, both as gas and solution, is a powerful antiseptic and deodoriser; it is an antidote to poisoning by prussic acid (HON), sulphuretted hydrogen (HgS), and ammor,i< sulphide ((NH4)2S). The action on prussic acid has not been ex- plained ; that on sulphuretted hy'rogen and ammonic sulphide is explained by the follow; ^ equations : HjS + CI2 = 2HC1 -t S (NHJ^S -h 4CI2 = 8HC1 + N, 4- S. The substances formed are not poisonous. Experiment 65. — Prepare a little chlorine as in Experiment 63, and hang a narrow strip of moist turkey-red cloth in the t.t. It is bleached whit'^. Try other vegetable colours, e.g., a small flower. Try a mineral colour, e.g., red lead. Chlorine and water bleach organic colouring matters, but not mineral. The presence of water is necessary. If dry chlorine be used, it does not bleach. A solution of chlorine in water griidnally decomposes : H2O -f CL, = 2HC1 -f- O. HYDROCHLORIC ACID. 101 This shows the nature of the bleaching action of chlo- rine. It is really an oxidation by means of the oxygen of water, the hydrogen combining with chlorine to form hydrochloric acid. The colouring matter is destroyed, — geiit^rally oxidised to carbon dioxide and water. Experiment 66. — Prepare some chlorine water, by leading the gas prepared as in Experiment 63 into a bottle of water, using a gas-iJelivery tube bent twice at right angles and reaching to the bottom of the bottle. (This should be done under a hood or in ,1 draught crpboard. ) Note the colour of the solution. Try its effect on litmus. Explain. Chlorine combines directly with most elements and thereby forms chlorides. Experiment 67- -Prepare a little chli>rine (Experiment 63) and drop some powdered antimony into the tube. It catches tire as soon as it falls into the gas : 8b -|- 5C1 = SbClg. Try a bit of ph 'sphorus in the deflagrating spoon ; and a lighted taper. Chlorine supports the combustion of tallow, wax, tur- pentine, and other organic substances containing a large percentage of hj'^drogen. It combines with the hydrogen to form hydrochloric acid, setting the carbon free. Test. — Add some starch paste to a dilute solution of potas- sic iodide (Kl), and then a few^ drops of chlorine water. The deep blue iodide of starch is formed : KI -|- CI = KC) -f- I. Compounds of Chlorine. 93. Hydrochloric Acid (HCl = 36.37.)-Alao called muriatic acid, and spirit of salt. If equal volumes of hydrogen and chlorine 1 • mixed in the dark and then exposed to diffused daylight they combine without any 102 HYDROCHLORIC ACID. change of volume, forming a colourless gas, hydrochloric acid. If exposed to direct sunlight they combine with a violent explosion. ' Preparation. — Experiment 68. — Put some dry sodic chlo- ride in a t.t., pour strong sulphuric acid over it, fit the gas-delivery tube used in Experiment 66, warm gently, and collect a t. t. of the gas by displacting the air. (You can see when the t. fc. is full by the fuming of the gas at the top ; and by its overflowing on Ihe fingers and making them feel warm.) Close with the thumb and open under water. Test, by taste and litmus, the water which rises in the tube. Solution of hydrochloric acid is prepared in this way on the large scale as a by-product of the alkali manufac- ture : 2NaCl + H2SO4 = 2HC1 -f- Na^SO,. (Write the names and weights. What remains in the t. t. in Experiment 68]) Properties. — A colourless gas, soluble in water, 500 vols, in 1 at O'* C; the solution is heavier than water. The saturated solution becomes weaker on boiling until it contains 20;^ p. c. of the acid, then distils unchanged at 110° C. The specii^c weight of this solution is 1.11. (What similar case has been studied already 'i) The specific weight of the gas is 1.269 (air = 1 ). At — 4° C. and with a pressure of 25 atmospheres it condenses to a colourless liquid. iExperiment 69. — Colour some solution of hydrochloric acid with litmus, and add to it a solution of caustic soda until the litmus begins to turn blue. Taste the solution. (What does it taste of?) Evaporate to dryness on the water bath. Crystals of common salt remain: NaOH + HCl = NaCl -f H2O. Try the same with potassic hydroxide. CHLORIDES. 103 Hydrochloric acid is a monobasic acid, as can be seen from xi/8 formula. Its molecule contains only one atom of liydrogen, which cannot be partially replaced by atoms of metals. It is called a haloid acid Its aquecub solu- tion dissolves tin, iron, zinc, alumii.ium, and other metals. Chlorides. — These are formed by replacing the hydrogen of the acid by metals, a monad replacing H, a dyad 211. a triad 3H, >* substance already stu 'ed is similar ?) : 01,0, -f ?KOH = KCIO, 4- KCIO3 4- H,0. 98. Oxygen Acids of Chlorine. — Like nitrogen chlorine combines with hydrogen and oxygen in several proportions, forming a series of oxygen acids : Hypochlorous acid HCIO Chlorous acid HCIO.^ Chloric acid HCIO3 Perchloric acid HCIO^ The names of these acids illustrate very well the use of the terminations -ic and -ous ; and of the prefixes hi/po- und per-. Hypoc\i\oronH acid is below chlorous acid in proportion of oxygen, /^erchloric contains more oxygen than chloric- -These acids are all monobasic, and mostly unstable. 99. Hypochlorous Acid.— HCIO. Prepakation. — By the action of chlorine watei on freshly precipitated mercuric oxide : HgO -f H,0 4- 2CI2 = HgCl, + 2HC10. Properties. — It has never been obtained except as a dilute aqueous solution. It has a pleasant, somewhat chlorous, smell (that of bleaching powder), and bleaches powerfully. Hypochlorites. — The salts of hypochlorous acid are important, particularly bleaching powder : (CaCl, . Ca(OCl),). 106 CHLOROUS ACID. Erperiment 72. — (Generate some chlorine as in Experiment 62, and pass it for a short time into a beaker containing a very dilute solution of sodic hydroxide : 2NaOH -h CI, = NaCl -|- NaClO + H,0. Sodic chloride, sodic hypochlorite, and water are lorraed. Keep tlie solution for furtlier experiments. Experiment 73. — Moisten a small piece of turkey-red cloth with acetic acid, and put it into a portion of the solution from Experiment 72. The colour is bleached. Experiment 74. — Heat another portion of the solution nearly to boiling, and then try Experiment 73 with it. The colour is not bleached. Hy})oclilorites are readily decomposed by heat into chlorides and chlorates, one portion giving up its oxygen to the other : 3KCI0 = KCIO3 + 2KC1. Experiment 75. — Warm a third portion gently with a little hydrochloric acid and note the smell of chlorine : KCIO + HCl = HCIO + KCl HCIO 4- HCl = CI, + H,0. Hypochlorous acid is a very weak acid, its salts being decomposed even by carbonic acid. Hence the chlorous smell of bleaching powder. (Explain). 100. Chlorous Acid. — HCIO2. Cannot be obtained except as a solution in water (Art. 96). Its salts, the chlorites, are unstable and unimportant. 101. Chloric Acid. — HCIO3. There is no corres- ponding oxide known. (What would its formula be 1 Compare with nitric acid.) CHLORIC ACID. 107 Preparatiox, — By action ofjluosilicicacid on solution of potassic cljlorate. An insoluble salt of potassium is formed {jyrecipitated)^ and chloric acid remains in solu- tion : 2KCIO3 -\- HjSiF^ = K,SiF8 + 2HCIO3. Properties, — It forms a colourless, acid solution, of strong oxidising properties. It readily decomposes into chlorine, oxygen, and perchloric acid, and cannot be ob- tained free from water. Uhlorates. — Chloric acid is monobasic, and its salts are all soluble in water. They can be prepared by dis- solving the corresponding bases in chloric acid ; but those of the stronger bases can be formed directly by the action of chlorine. Thus, when chlorine gas is passed into a Jiot solution of pocassic hydroxide, chloride and chlorate are formed (Exp't 74) : 6K0H -f 3CI2 = KCIO3 -f- 5KC1 -f 3H2O. Similarly with sodic, calcic, baric, and other hydrox- ides. The weaker bases, however, do not react in this way. Potassic chlorate is only sparingly soluble, and can thus be separated from the more soluble chloride. (How 1) Experiment 76. — Pass chlorine gas through a strong solution of caustic potash until it begins to smeil of chlorine. Evaporate on the watei- bath until crystals begin to form, then set aside to cool. Pour off the liquor, dry the crystals on filter paper and keep them. Tests. — 1. Dry chlorates are known by the formation of chlorine tetroxide when acted on by strong sulphuric acid. 2. Colour with indigo sulphate, add a few drops of sulphuric acid, and boil. The colour disappears. (What other acid an- swers to this test ? How would you distinguish ?) 108 PERCIILOKH' A('II>. 102. Perchloric Acid— H CI 04. This is the most stable of all the oxygen acids of rllorine. PuEPARATioN. — By 'Hstilliiig chloric acid : 3HCIO3 -= HCIO, -h 01, + 20, -f- H,0. AIho, by the action of fiuosilicic acid on solution of potas- sic perchloratfi : 2KC10, -I- H,SiF8 = KaSiFfl + 2HC10,. (How are tlie two substances separated?) pHOPEUTiKs. — It is a strong acid, of very great oxid- ising power, exploding violently when dropped on char- coal. It sets fire to wood, paper, tfec. Tlie acid and its salts are uniniportaut practically. Perchlorates. — Potassic perchlorate is prepared by heating potassic chlorate until it fuses and at length be- comes nearly solid again : 2KCIO3 = KCIO4 + Oo + KCl. (How can the two salts formed be separated i) BROMINE AND ITS COMPOUNDS. i03. Bromine. — (Br' = 79.75.) Found as bromides in sea water, salt springs, and crude Chili saltpetre ; also as silver bromide (AgBr) in some silver mines. Certain sea-weeds extract bromine and iodine from sea water and store it up in their tissues. These two elements are pre- pared generally in one operation from the " mother liquor " of common salt, kelp (ashes of sea-weed), or Chili saltpetre. Prepa RATON. — A jmall sample of the liquor is first analysed and the quantities of iodine and bromine de- BROMINE. 109 tenuiiied. Then enough niangaueso dioxide and sul- phuric acid to set free the whole of the iodine is added to a large quantity of liquor : 2K[ -\- 3H.^S04 -f MnO.^ = 2KHSO4 + MnSO^ + J, + 2H2O. The iodine is distilled off, more manganese dioxide and sulphuric acid are added to set free the bromine, which is then distilled and condensed in separate receivers : 2KBr -j- 3H2SO4 -f MnOj = 2KHSO4 + MnSO^ + Bra + 2H,0. Experiment 77. — Mix about equal (juantities of well pow- dered manganese dioxide and potassic bromide, put in a t.t., add a little sulphuric acid, and heat gently. Bromine is evolved, condensing on the sides of the t.t. as a dark reddish -brown liquid. Take care not to breathe the vapour. Pour some of the heavy vapour into a second t.t. containing a little water, and shake it up. The water dissolves the bromine. Properties. — A heavy liquid (specific weight = 3. 18), almost black when in ma.ss ; dark red, in thin layers. It is the only liquid element at ordinary temperature, excepting mercury. It freezes at — 22° C, and boils at 63° C, forming a reddish-brown vapour, which has a very unpleasant smell and an irritating action on the mucous membranes. On account of its low boiling point and corrosive action bromine should be handled very care- fully. Its vapour should never be inhaled unless diluted with much air. Experiment 78. — Try to bleach with bromine water made in Experiment 77. Bromine is soluble in water to about 3%. It bleaches in the same manner as chlorine, but not so powerfully. Experiment 79- — Dissolve a small crystal of potassic bro- mide (KBr) in a test-tube one-third full of water, and add a few 110 HYDROBROMIC ACID. drops of chlorine water. Bromine is set free. Add a few drops of carbon bisulphide, close with the thumb and shake the t.t. violently. Allow to stand a moment and observe. (What property of bromine is illustrated ?) Chlorine displaces bromine from combination with metals ; in other words chlorine has greater chemical affinity (chemism) for the metals. COMPOUNDS OF BROMINE. 104. Hydrobromic Acid.— HBr. Preparation.— Experiment 80.— Add a few drops of strong sulphuric acid to a crystal of potassic bromide and warm. (What action would you expect ? What do you observe ?) Hydrobromic acid cannot be prepared in this way because of its decomposition by strong sulphuric acid ; H^SO^ 4- 2HBr = Br^ + SO, -f 2H,,0. Compare hydrochloric acid. Hydrobromic acid is prepared by the action of phos- phorus and bromine on water. A bromide of phos- phorus is first formed and this is then decomposed by the water : P. tribroniide. Phosphorous acid. . PBrg -f 3H2O = 3HBr + P(OH) 3- To prepare it on the small scale, put a little bromine in the bottom of a t.t , then a layer of pieces of glass on which a few small bits of phosphorus are laid, cover this with an inch or two of small bits of glass, moisten with a drop or two of water, and distil with a gentle heat, receiving in a t.t. of water. A solution of hydrobromic acid is obtained. Properties. — A heavy^ fuming gas, very soluble in water, forming a solution similar to that of hydrochloric BROMINE AND OXYGEN. Ill a.iu. It is a monobasic acid, and acts on bases to form salts called bromides. Bromides. — These are very like the chlorides in ap- pearance and properties. Bromine unites directly with nearly all metals. The bromides can all be decomposed by chlorine. The potassium salt (KBr) is the most im- portant. It is much used in medicine. Argentic bromide (AgBr) is used in photography. Ammonic bromide (NH^Br) is used as a medicine. Most of the bromides are soluble in water. A few are insoluble. Experiment 81. — To a few drops of solution of potassic bromide add a drop of argentic nitrate. Argentic bromide is precipitated : AgNOj 4- KBr = KNO , + AgBr. Note its colour and try the action of ammonia solution and of nitric acid on it (dividing it into two portions). Make the same experiment with solutions of mercurous nitrate (Hga(N03)a), and plumbic acetate (Pb(C2H302)5), instead of argentic nitrate. Write the equations. Tests for Bromides. — Experiments 79 and 81. In the test with chlorine care must be taken not to use too much, as there is a colourless chloride of bromine. Except in weak solu- tions the bromine can be liberated by strong sulphuric acid. (Try it. ) Free bromine colours starch-paste orange-yellow. 105. Bromine and Oxygen. — No compounds of bromine and oxygen are known, but two oxygen acids, hypobromous (HBrO), and bromic (HBrOg), have been prepared. They and their salts (the hypobromites and bromates) are prepared by methods similar to those for the hypochlorites and chlorates. Potassic hypobromite (KBrO) is used in estimating urea. (Write equations 112 IODINE. for the action of bromine on moist mercuric oxide, and on dilute and strong solutions of potassic hydroxide). IODINE AND ITS COMPOUNDS. 106. Iodine.— (I' = 126.5). Never f und free in nature, but always as iodides, in small relative quanti- ties, but widely ditfused. Minute traces of iodides are present in sea-»7ater. Certain plants (kelp and sponges) extract these and store them in their tissues. Some sea animals do the same, e.g., the cod. The ashes of kelp contain from 0.1 per cent, to 0.3 per cent, of iodine, and are the principal source of this element. The weed is washed up on the coasts of Ireland and Scotland in great quantities. It is gathered, dried, burned in shallow pits at a temperature not hisfh enough to volatilise the iodides and bromides, and then lixivi- ated. The solution contains sodic carbonate (NajCOg), chloride (NaCl), sulphate (Na2S04), bromide (NaBr), iodide (Nal), &c. It is evaporated to crystallise the carbonate, chloride, and sulphate ; and the iodine and bromine are prepared as described in Art. 103. Preparation. — Experiment 82. — Mix well about equal quantities of potassic iodide (KI) and manganese dioxide, put in a t.t., add a little strong sulphuric acid, and heat very slightly for a few minutes. Violet vapour of iodine appears and con- denses on the cooler parts of the tube, as a steely looking solid. 2KI + 3H2SO4 -f MnOa = MnSO.^ + 2KHSO4 + Ig + 2HaO. Properties. — Blackish grey solid, somewhat metallic in appearance (compare sulphur, selenium, and tel- lurium), opaque and crystalline. Its odour suggests that of rotting sea-weed. The specific weight of the solid is 4.948 (calculate that of the gas). It melts at 11 4** C, IODINE. 113 and boils at 200° C, forming a splendid deep-blue vapour, which is purple when mixed with air. It volatilises slowly at ordinary temperatures and must therefore be kept in well stoppered bottles. Both iodine and bromine (as well as chlorine) corrode cork. Experiment 83. — Put a few crystals of iodine in a t.t., fill half-full of water, shake for some time, and note that a little of the iodine dissolves. Add a small quantity of potassic iodide, and shake up. The whole of the iodine dissolves. A tri-iodide (KI3) is formed. Iodine is sparingly soluble in water, but freely so in solutions of certain salts, particularly potassic iodide. Experiment 84- -To f ion of potas&ic iodid, in two test- tubes add respectively chlorine water and bromine water, then a few drops of carbon bisulphide (CSg) ; shake well and allow to stand a moment. tWhat conclusions do you draw with regard to the relative chemism of the three halogens ?) Experiment 85- — Try the solubility of iodine in a mixture of equal volumes of alcohol and water, and in chloroform, using small quantities of each of the substances mentioned. Iodine has an irritating action on the skin and mucous membranes, but not so violent as chlorine and bromine. It stains the skin yellow, but the stain disappears very soon, unless the iodine is applied often. It promotes absorption and thus reduces swellings, and is much used as an external application. Tincture of Iodine is a solu+ion of iodine and potassic iodide in rectified spirit (alcohol a'ld water) — I pint of spirit to ^ oz. iodine and ^ oz. potassic iodide. Solution of Iodine. — Twenty grains of iodine, thirty grains of potassic iodide, dissc' ed in 1 oz. of distilled water. 9 114 HYDKIOlJlO ACID. Tests. — 1. With chloriEe water and carbon bisulphide as in Experiment 84. 2. Free iodine colours starch paste deep blue. (Try with iodine water). COMPOUNDS OF IODINE. 107. Hydriodic Acid, HI.— Preparation. — In the same way as hydrobromic acid (Art. 104). (Write the equation.) Hydrogen and iodine do not unite directly under ordinary circumstances. It can also be prepared in solution by the action of iodine on sulphuretted hydrogen iHoS) in presence of water. Ezperimeilt 86. — Put a few small pieces of ferrous sulphide in a t.t. fitted with the gas-delivery tube of Experiment 66, add some sulphuric acid diluted with about five times its volume of water, and pass the evolved gas into a test-tube of water in which is some finely divided iodine. The iodine disappears and sulphur is precipitated : HaS + la = 2HI -f- S. Test a portion of the solution with litmus, add a little iodine water, shake up, and set aside for further experiments. Properties. — A heavy gas (specific weiglit 4.41G), colourless, fuming in moist air owing to its strong attrac- tion for water, with which it forms minute droi)s of solu- tion. It dissolves readily in water, forming a strongly acid solution similar to those of hydrochloric and hydro- bromic acids. The gas is easily decomposed by heat, and the solution in water is decomposed by the oxygen of the air : 2HI 4- O .= H,0 + I,. IODIDES. 115 (Compare with the stability of hydrochloric acid.) It is a monobasic acid and unites with bases to form iodides, e &f< • KOH + HI = KI + HjO. Iodides. — Of these the most impoT-tnant is potassic iodide (KI), of which very large quantities are used in medicine. The following iodides are insoluble in water and are bright in colour : Argentic (Agl), merairous (Hg2l2), mercuric (Hgl2), cuprous (Cu^IaS and plumbic (Pblj), the latter very sparingly soluble. Experiment 87. — Put a little of the solution of hydriodic acid in four test tubes, and add a drop or two of argentic nitrate to one, of mercurous nitrate to a second, of mercuric chlo'ide (HgClj) to a third, and of plumbic acetate to a fourth, xsote the color, &c., of the precipitates formed : AgNO, + HI =- Agl + HNO,. Write equations for the other three. Try the same experiments with a dilute solution of potassic iodide (KI). Tests. — These apply to both free acid and iodides. 1 . Add to the solution a few drops of argentic nitrate solution. A yellow precipitate of argentic iodide is formed. Divide this into two portions. Test one part with ammonia solution ; it is whitened, but not dissolved. Test the other with nitric acid ; it is not dissolved. 2. Add some starch paste and a few drops of chlorine water to any solution containing an iodide. A blue colour appears. (Explain). To test for chlorides, bromides, and iodides in a mixture — Distil a small portion of the carefully dried mixture with dry powered potassic bichromate (K^CrjOy), and strong sulphuric acid. (The apparatus must be dry.) Receive the distillate in a t. t. contain- ing a little water, add caustic soda to it, until the colour of the 116 IODINE AND OXYGEN. bromine and iodine disappears. A yellow colour remains, that of sodic chromate. This proves the presence of a chloride in the mixture. — Explanation : A volatile compound, chromic oxychloride (CrOjCl.^), is formed, distils, and forms chromic acid with the water : CrOaCl, + 2H2O = H^CrO^ + 2HC1. Dissolve a small quantity of the mixture in water in at. t., add a few drops of carbon bisulphide, and then chlorine water drop by drop, shaking up after each addition and observing the colour of the carbon bisulphide. The violet of iodine appears first, but disappears on the addition of more chlorine owing to the formation of an almost colourless compound (ICl); after- wards, on the addition of more chlorine, the orange colour of bromine appears. 108. Iodine and Chlorine. — Two compounds are known, the monochloride (ICl), and the trichloride (ICI3), formed by direct union of the elements. (What, then, is the valence of iodine 1) 109. Iodine and Oxygen. — ^Only one compound of these two elements is known, viz., iodine pentoxide (I.2O5), prepared by carefully heating the corresponding acid, iodic acid (HIO3) • 2HIO3 = H.,0 + I.A- When heated more strongly it decomposes into its ele- ments. It is a deliquescent white solid, and unites with water to form iodic acid. Iodic Acid, HIO3. — Can be prepared by oxidising iodine with strong nitric acid, and evaporating the solu- tion to dryness. It is a white crystalline solid, freely soluble in water, forming a strongly acid solution. It FLUORINE. 117 is a powerful oxidising cagent. When mixed with hydri- odic acid, it oxidises the latter, setting free iodine : HIO3 + 5HI = 31, + 3H,0. loDATES. — Besides the normal iodates (KIO3, ifec), there are peculiar acid iodates, e.g., KIO3.HIO3, and KIO3.2HIO3. Tests — Add chlorine water and starch paste to a solution of an iodate. No blue colour appears. (What conclusion do you draw with regani to chemisra of iodine and chlorine in oxygen salts?) Now add a little sodic sulphite or sulphurous acid. Blue colour appears : KIO3 + SNa^SO, = KI + SNa^SO^. KI + CI = KCl + I. FLUORINE AND ITS COMPOUNDS. 110. Fluorine (F' = 19.1).— Is not known free, but only through its compounds, the fluorides. Many attempts have been made to prepare it, but with no suc- cess. It invariably attacks the vessels in which its preparation is attempted. It seems to have even stronger chemical affinities than chlorine. — The chief compounds of fluorine occurring in nature are fluor spar or calcic fluoride (CaF,), and cryolite (3NaF.AlF3). — Fluorine forms no compound with oxygen, and is the only element of which this is true. 111. Hydrofluoric Acid.— HF. Preparation. — By distilling fluor spar with sulphuric acid in lead or platinum vessels and receiving in water : CaF2 + H2SO, = 2HF 4- CaSO^, Glass or porcelain vessels cannot be used, as they are corroded by hydrofluoric acid. The pure acid is very IIH HYDROFLUORIC ACID. dangerous, and is not often prepared. The aqueous solution is kept in leaden or gutta percha bottles. Properties. — A colourleay, fuming, acid liquid, boiling at 19.4'^ C. It is soluble in water, forming a strongly acid solution. Experiment 88- — Put a little calcic fluoride in a small leaden dish, add some sulphuric acid and cover the dish with a piece of glass which has been coated with paraffin wax through which some word has been scratched with a knife or a pin . Set aside for a while, then warm the wax, and rub it oflF. The word has been etched into the glass. Glass contains silica (SiO.^). This is acted on by the hydrofluoric acid with the formation of volatile com- pounds : SiO, + 4HF = SiF^ -I- 2H2O. Hydrofluoric acid is monobasic. It forms salts called fluorides, analogous to chlorides, bromides, and iodides. Fluorides. — These are mostly colourless salts, soluble in water ; but calcic Jluoride (CaFj), baric Jluoride (BaFj), and strontic jluoride (SrFj) are insoluble. The fluorides have a tendency to unite with each other and with hydro- fluoric acid forming double Jluorides, e.g., SNaF.AlFaand HF.KF. Test.— See Expt. 88. QUESTIONS AND EXERCISES. 1. Compare the halogens (1) as to their chemism for metals, and (2) as to their chemism for oxygen. QUKSTIONS AND EXERCISES. 119 2. What wtiight of manganese dioxide (MnOa) must be used to prepare chlorine for tlie conversion of 10 lbs. of potassic hydrox- ide (KOH) into chlorate and chloride ? 3. Calculate the specific weight of chlorine (air = 1). Calcit- late the weight of I litre at 0° and 760 mm. 4. Why cannot chlorine be collected over mercury or water ? 5. What weight of pure hydrochloric acid is there in 1 litre of the solution of sp, wt. 1.11? 6. Compare the bleaching power of chlorine (and water), and hypochlorous acid . CI2 + HjO = 2HC1 + 0. HCIO - HCl -j- 0. What weight of chlorine is equivalent to 100 grams of hypochlor- ous acid ? 7. Compare the oxygen compounds of chlorine and of nitrogen. 8. What weight of sodium chloride must be used to prepare chlorine enough to set free the bromine from 100 oz. of potassic bromide (KBr) ? 9. What weight of potassic chlorate (KCIO3) contains one equiv-^lent (in grams) of oxygen ? 10. Write the formulas of magnesic, amnionic, ferric, cobaltie, and wercMrojis chlorides ; of mercuric, argentic, and ftaric iodides ; and of ferric bromide. 11. Fluorine has never been prepared. How then has its atomic weight been determined ? 12. Write the formulas of the chlorine acids and calculate the percentage of oxygen in each. Apply the Law of Multiple Pro- portions. 13. What weight of hydrochloric acid is equivalent to 100 grams sodic hydroxide (NaOH) ? To 100 grams potassic hydrox- ide (KOH) ? To 100 grams calcic hydroxide (Ca(OH) J ? 120 THE SULPHUR (JROUP. CHAPTER X. SULPHUR, SELENIUM, AND TELLURIUM. 112. The Sulphur Group.— The three elements mentioned hero form a group closely related in their chemical and physical properties. Each unites witJi hydrogen to form a gas analagons to water in formula (HjS, H.^Se, HjTe). They unite with oxygen in two proportions (SOj, SO3 ; SeOj, — ; TeOj, TeOg) ; and eacli has tw ) acids corresponding to the oxides. As in the case of the halogens, there are gradations in the proper- ties in passing from one element to the next of this group of elements. Thus, while sulphur is a distinct non-metal, selenium is slightly metallic, and tellurium more so, in its appearance. The attraction for oxygeii is stronger in sulphur, weaker in selenium and tellu- rium. SULPHUR AND ITS COMPOUNDS. 113. Sulphur (S"'*^'^^ = 31.98). Occurrence. — Found uncombined, in grea^ isses in volcanic districts, particularly in Italy, Iceiand, and Sicily. The compounds of sulphur found in nature are very numerous and abundant. There are two principal classes : (1) sulphides, including a great many ores of metals, e.g., galena (PbS), zinc blende (ZnS), cinnabar (HgS), and iron and copper pyrites; and (2) sulphates, e.g., gypsum (CaS04.2H20), heavy spar (BaSO^), Epsom SULPHUR. 121 salts (MgS0,.7H,0), and green vitriol (FeSO^.TH.O). Sulphur also forms an essential constituent of animal and vegetable bodies. Preparation. — (1) Crude sulphur is heated in shallow pits, and the melted sulphur is run ofl' from the earthy impurities. It is further purified by distillation, the vapour being led into cool chambers where it solidi- fies and falls down as " flowers r>f sulphur." When the walls of the chamber become hot the sulphur remains li(piid and is run off into moulds roll brimstone). (2) Iron pyrites (FeSo) when distilled gives off one- third of the sulphur : 3FeS, = Fe^S^ + Sj. This can be condensed, « P- -n„factu.d a„„,.a„, inteat BHttir'"'" '""' "^ Manufacture Tn f it « necessary only to ^,1^''^:'' "' "•'P''""« -W yh>-a and a molecule of water : SO, + O + H,0 = H,SO,. J>ut this union does n^^f + i "■e influence of pTa inl": l^:? tf ^"^ --P' -der '"bstance. In practice r^ . " "°"*^'^' ='««<»> " o'.en.ical action. ' ^:Z^^'f"-: "^ --"- femes with the oxygen of tL Jr A^^ '""""^ '="^'"''i"e« "; (NO,). Thisifrers;" s .; tTrr^ ''" *«"-- Phur dioxide and water and T, Z^ ^^ '*^^«<'" *° «"1- •"sygen from the air Th,„ !•. '° "'''''' "S^*'" "-itt "carrier of oxygen "froLtheT" '''""''^ "^'^ «» a j^ yg from the air to sulphur dioxide and 130 SULPHURIC ACID. water. (Of course, this carrying goes on between mole- cules, and not between vessels or rooms ! ) Thus : NO + O = NOj. NO2 + H2O + SO2 = H2SO, + NO., re8ence of plumbic sulphate. Arsenic, derived from the pyrites, is often present; and, as it forms many volatile compounds, it is a danger- ous impurity. For example, when arsenical sulphuric acid is used in the preparation of hydrochloric acid, the arsenic distils over as trichloride (AsClg), and thus renders the hydrochloric acid highly poisonous. It can be tested for by diluting the sulphuric acid with water and adding hydric sulphide (HjS), when the yellow arsenic trisulphide (AsjSg) is thrown down. — The colour of B. O. V. is due to organic matter. — Sulphur dioxide, and oxides of nitrogen occasionally occur as impurities. Sulphates. — Sulphuric acid is a dibasic acid. Its molecule contains 2 atoms of hydrogen, and both of these, or one of them only, can be replaced by metal. Thus, there are two series of sulphates, nor^nal and acid', e. g., K2SO4, normal potassic sulphate, and KHSO4, acid potassic sulphate. The acid sulphates are often called bisulphates {Art. 121). — The following normal sulphates are insoluble or very sparingly soluble in water : Plum- bic (PbSOi), baric (BaSO^), and strontic (SrS04). Calcic (CaS04), argentic (Ag2S04), and mercurous (Hg2S04) are "OKMA,, .K„ ^^,^ .^^^^ si«n»g/;, soluble. TI,e.-esfnfM , "'0«ly easily or^stallisable 1°L "''*"""" "^ «"•""«. ''-Trot J'^"' ^"*-^"'' * '- --pa of ,„,„f . " 0' "'"IP'esic sulphate (MgSO,) '""" *'"' »»'"- I2h Normal and Acid Salts -txpenment 105 ~Pnf ^ ;» -^ poreaiain ba.! o„r"jr rf" "' "■''"*-"'P"-Tic acid "^th- Repeat this operation I . . «*'»Po™te o„ the water l-*»d<'a.econdpip'ett:;X;,:;":;;^7 '^^""'"^ '"^ -"-' ."■f ; -'I ti.at obtain dt,:*r ^ ^^-'" l-perties - taste, Ac. In fe^j^ ;, is "t IJ h!,r ■ ?'''''"'' '^ -" ^3' referring to the equatills '"'' "' "^^ '- --en 2NaOH + H,SO. = Na ^n , „ NaOH+HSO ,, ^*'^' + 2H,0. f no:« : :«. ~ 7;;;- ^wo p™,ortion, ' '« '>ase a neutral salt is fol , T"' P^Po^ion of ""aiier proportion an Jrf 1 *^ f "^"^- With the term "„eut„,l salt" applies a" f ' "''"''• ^«-. *he ba^e are well n^arked but f A, ^^ "^ '""'' ^^id and 134 FUMING SULPHUHK? ACID. litmus to red, or red to blue. It has been agreed to restrict the use of the term ** neutral " to the action of substances on litmus ; and to use the word normal instead. Deflnitions. — A normal nail is one in which all the replace- able hydrogen is replaced by metal. An acid salt is one containing replaceable hydrogen (i.e., re- placeable by metal). (Can monobasic acids form acid salts?) 122. Fuming Sulphuric Acid, or Nor dhausen sul- phuric acid. — This is of somewhat variable composition. It is sulphuric acid combined with the trioxide ; gener- ally H.2SO4 -f SO3. It is prepared from green vitriol (FeSO4.7H.2O) by roasting in air to drive off the water of crystallisation and oxidise the salt : 2(FeS04.7H20) + O = Yq,0,.{^0,\ + UHA and then distilling. Enough moisture is obtained from the air and the apparatus to form a certain proportion of sulphuric acid : FeA.(S03), + H^O = FeA -f H,S04.S03. It is used to dissolve indigo, and in the manufacture of alizarine. 123. Thiosulphuric Acid, HaSjOa.—Formerly called hyposulphurous acid. The name now in use means suU pho-sulphuric acid, and refers to the composition, the acid containing an atom of sulphur in place of one of the four atoms of oxygen. The acid itself cannot be isolated, as it decomposes quickly on being set free from its salts : HoS-Pa = H.,0 H" S -h SO,. THIOSULPHATES. Experiment lOfi a.h ( Wnte the equation.) '^^^- ^^"^ note the odour. Thiosulphates TJi* .™l»'t-t -It is soclic S ; :^ "^ ■"■"«'• Tl.e .noat "'« «0''io sulphite with sulphur ' ^''''""'''' ''^ '■""''i°- Experiment m? p i ^'™e -^ » i'"-,ai,fi;.7,r::tr;::r;i:t """"-•'^ ""• «- '"," ''"'•'"<' to small bulk »„.|! "'P''"''' «"". evaporate ^'ourfes, crystals (xVaAO 4 1, """' *" "'•^'*»"-- Ftae ''■■ythemonfiit paper^^ =•'''""' "^ 'ormed. Collect and --'""'g«- It is an al nt T^ '""^'' '° ^''^'^n *« ^.2 ; insouble in carbon bi,, T /'"' "' 'P<«"^« --ght 250«, catches fire onl/a? o''''l'%*'^-^ "^ -' f"- at i« prepared on the large scaieln V' ''"''°"""'- ^* --es, to repiace the p^oison^ ^7:;::: " aJhf<:3,aSt;™rretrT:vr"^-- eg-, m ca,e3 of pois„„i„g, the sub.t»„ ";' ™''" l-^tities, " ^ ^-^ --. When t J' u;c:r :;;'-« -"^ -« PHOSPHORUS AND OXYGEN wHh' IS?' °' ^^-PJ^O-a-Two are W„ Phosphorus pentoride. . p n Phosphorus trioxide .' p '"" »d the existence of a third is probable." ' ' Phosphorus monoxide p^q i>e-ved from these are three acids : Phosphoric acid. ... „ Phosphorous acid H p * ^^ Hypophosphorous acid .' ." ." .' ." .' ;h3Po' 146 OXIDES OF PHOSPHORUS. 130. Phosphorus Pentoxide.— PA— Already noticed. Prepared by burning phosphorus in air. It is a snow-like solid, very hygroscopic, and hence used to dry gases, and in separating water from acids. In moist air it quickly deliquesces forming metaphosphoric acid : H2O + PA = 2HPO3. If put into water it hisses and dissolves, forming at first metaphosphoric acid ; but, gradually at ordinary tempera- tures, and quickly if heated, it combines with more water to form orthophosphoric q,cid : HPO3 + H.,0 = H3PO4. 131. Phosphorus Trioxide. — PA— Prepared by burning phosphorus skwly with a scant supply of air. If heated in air it combines with oxygen and forms the pentoxide : P.A + 0, = P2O5. It combines with water to form phosphorous acid : P2O3 + 3HoO = 2H3PO3. 132. Phosphoric Acid. — Phosphorus pentoxide unites with water in three proportions, forming three different acids, each of which is called phosphoric acid, but prefixes are used to distinguish them. The ordinary acid is that formed with the greatest proportion of water, and is called or^/iophosphoric acid : 3H,0 + P.Og = 2H3PO4. (1) Orthophosphoric Acid, H3PO4. — This is gener- ally called simply phosphoric acid. PHOSPHORIC ACi;,. Pkeparation.— Bone n^h • solved in nitric acid : "'"'^'''"^ P^^^«I^^^-*e is dis- Plumbic acetate /PbA \ I'o ^ 1 . - J^Osli'OJj 4. CaA^ -f 4Ha. Tlie object of the first ,■»..„*• • -J impurities i„ soluti^ Z ''rf^' '''' ''''"^'^''''^ '■«"ove tlie phosphoric aci,I V " '^''»"'' "« to "-" »m« tinfe obtain a p 1^. ? '""""•'"-' -" -' «• be easily obtained in 2 f T "'""'' *'"' «''» Pi-^phate is washed, suspenid ' "^ '''"' P'-""""" h ^.Iphuretted hyd;oger ""^''' """ ^''^''"'Posed Phosphoric acid dissolves and r.1 u- ""dissolved. (How is he 0.0 ^ """ ' '"^^^^^^^ ^'^"^-i-« V IS tlie process completed ?) Experiment lie — Pnf ^ J'- phoaph„r„3 melts aid „'r' """° ''°"'- ^-^ g^nu; »">es. (What are the"?, ^"7 . '"," '™"'«™ «' -d d'"P» concentrated nitric acid I?, *" '''■*'""'»• ''dd a few -^P-'^o acid regain.; ^I^^rir^nTC ""^^' ^e'sre7t°:r:r::^7''t-p-me„t,asitea„ «P'osivel,on,eliow;ro!;tl"''™ ^''"'' "'''"" -»' Properties A thi V ' »'ou.-less orystais ; solubieTn" water '"'' """'P"-"'. water, giving a strongly 148 PHOSPHATES. acid solution, (Try it by taste and litmus.) It is a tribasie acid, and forms three series of salts, e. g. : (1) NagPO^, trisodic phosphate. (2) Na2HP04, disodic hydric phosphate. (3) NaHjPOi, sodic dihydric phosphate. (To which of these classes do the phos[)hates mentioned in Preparation belong 1) Phosphoric acid is used in medicine in dilute solution as a tonic, &c. Phosphates (orthophosphates). — Of the normal and the mon-acid phosphates, only those of the alkali metals (Na, K, NH.4, tfec), are soluble in water. The di-acid phosphates are all soluble. Tests. — 1. Add a drop or two of argentic nitrate to a solu- tion of sodic phosphate (Na.^HPOJ. A yellow precipitate is formed. Divide into 3 parts, and add to one part ammonia ; to the second, dilute nitric acid ; and to the third, acetic acid. The precipitate is soluble in each. (Could this test be used in a solu- tion containing hydrochloric aoid?). 2. Add ammonic chloride, magnesic sulphate, and ammonia to a solution of sodic phosphate, and stir with a glass rod. A granular white precipitate of magnesic ammonic phosphate (Mg.NH^.POJ is formed : Na.HPO^ + NH3 + MgSO^ = MgNH^PO, + Na,SO,. 3. Baric chloride (BaCl2) gives a white precipitate, soluble in nitric acid. Phosphates are present dissolved in urine, and when the urine becomes alkaline by decomposition (Explain.) crystals of microcosmic salt, or sodic amnionic hydric phosphate (Na.NH^.H.PO^) are formed. META PHOSPHORIC ACID. 149 (2) Metaphosphoric Acid. — HPO3. — Formed when phosphorus pentoxivlc is dissolved in cold water ; but is generally prepared by heating orthophosphoric acid to a red heat : H3PO4 = HPO3 -i- H2O. Properties. — It is a hard glassy colourless solid {glacial phosphoric acid) — the common phosphoric acid of commerce. It dissolves in water, but gradually com- bines with the water to form ortho-phosphoric acid. — It is a monobasic acid (To what acid is it similar in compo- sition "J), and forms salts called metaphosphates, e.g., NaPOa, Mg{P03)2, kc. Tests.— 1. Add argentic nitrate to a solution of the acid or a salt. A gelatinous white precijntate is formed . It is soluble in nitric acid. 2. Add some white of egg to a solution of metaphosphoric acid, or to a metaphosphate acidified with acetic acid. The white of egg is coagulated. Try with orthophosphate. (3) Pyrophosphoric Acid. — K^Pfi^ ( = PoOg -|- 2H,0). Preparation. — Heat orthophosphoric acid till the temperature rises to 215° C. : 2H3PO, = H,P.,0; + H.,0. Properties. — A sott glassy liquid ; when heated with water, forms orthophosphoric acid. It is a tetrabasic acid. Its salts can be formed by heating acid orthophos- phates of the class M2HPO4. (Write the equation.) The pyrophosphates are changed to acid ortho-salts when they are boiled with water. 150 PHOSPHOROUS acid. Tests. — I. White precipitato with argentic nitrate, soluble in nitric acid. 2. Pyrophosphoric acid does not coagulate white of egg. 133. Phosphorous Acid — H3PO,. Preparation. — This acid is formed when phosphorus oxidises slowly in moist air j but it is best prepared by the action of phosphorus trichloride (POI3) on water : PCI3 + 3H2O =-- P(0H)3 + 3HC1. This action of water on a chloride is a very frequent one. Observe that hydroxyl ( — OH) replaces chlorine ( — CI). Properties. — A white solid with garlic odour. Oxi- dises readily to phosphoric acid. When heated it de- composes into phosphoric acid and gaseous phosphorettcd hydrogen (PHg) : 4H3PO3 = 3H3PO, + PH3. There are many decompositions of compounds containing oxygen, such that one part gains oxygen at the expense of another part. (Mention ono already described.) — The phosphites are unimportant. Only two of the three atoms of hydrogen seem to be readily replaceable by metal. Tests. — 1. Add argentic nitrate to a solution of a phosphite. Metallic silver is precipitated. 2. Add solution of 6anc chloride. It gives a white precipitate soluble in nitric acid. * 3. Heat a little of the substance on mica and smell. The odour of phosphorettcd hydrogen is observed. 4. Add lime water to solution of phosphorous acid or a phos- phite. A white precipitate is thrown down (CaHPOs). J HYPOPHOSPHOROUa ACID. 151 134. Hypophosphorous Acid. — HgPOj. — The acid itself is of little importance. It can be prepared from its barium salt by treating with sulphuric acid, (Why use the barium salt in particular 1) It is a monobasic acid, of very strong redu(;ing power, and quickly absorbs oxygen from the air. HYPOPHOSPHITES.--Experiment 117.— Heat a small piece of phosphorus in a t. t. with milk of lime. Connect the t. t. with a gas-delivery tube dipping under water. A gas having the smell of decaying fish is evolved, and catches fire as soon as it comes in contact with the air. Continue the heating until the phosphorus is dissolved, and no more gas appears. The solution contains calcic hypopho$phiie (Ca(H2PO,)2). Filter, pass into the clear solution a current of carbon dioxide to preci- pitate the uncombined calcic hydroxide as calcic carbonate (CaCOg), then filter again. The actions which take place are represented thus ; 3Ca(OH)2 + 8P -f GHoO = 3Ca(H,PO.,)2 + SPH,. Ca(OH)., -;- CO., = CaCOg + H.,0. The hypophosphites of sodium, potassium, barium, and strontium, may be prc:>ared in the same way. The hypophosphites are powerful reducing agents. They must be kept out of oontact with air, otherwise they become oxidised to phosphites and finally to phosphates. They are used in medicine, and are supposed to produce the same specific effects as free phosphorus ; but this is very doubtful. Tests. — 1. Argentic nitrate gives a white precipitate which quickly turns brown and then black : iAgNOg + H3PO2 + 2H2O = 4HNO3 -f H3PO4 + 4Ag. 2. Baric chloride gives no precipitate, 152 PHOSPHINE. 3. Zinc and hydrochloric acid (nascent hydrogen) give the amell of piiosphoretted hydrogen. 4. Evaporate to dryness, heat residue on mica ; odour of phoa- phoretted hydrogen : 2H3POa = PH3 + H3PO4. Note. — Try these tests with the solution of calcic hypophos- pliite (Experiment 117); also with a sample of " hypophosphites " from the druggist's. The " hypophosphites " of medicine is a preparation of calcic hypophosphite. 135. Phosphorus and Hydrogen. — There are three compounds known : Gaseous phosphoretted hydrogen, or phosphine . .PH3 Liquid '* " ..P2H4 Solid " " ..P4H2 Only the first will be described. 136. Phosphine (gaseous phosphoretted hydrogen). PHg. — Prepared as in Experiment 117, but better with a strong solution of potassic or sodic hydroxide : 3K0H + 4P + 3H2O = 3KH.,P02 + PH3. It is formed by the decay of fish and other animal and vegetable bodies. It is supposed to be the cause of that dancing phosphorescent light which, under the name of ignis fatuus, or will 0' the wisp, wanders over marsh} and swampy places. Properties. — An invisible gas, of strong smell (that of rotting fish), very poisonous, even when largely diluted with air. It readily burns in air (spontaneously inflam- mable when containing vapour of the liquid compound, as in Experiment 117) : PH3 + 2O2 = H3PO4. CHLORIDES OP PHOSPHOKUS. jgj In Chemical characters it resemhlp, w.th acids to form salts e. . """''''' """"onia, uniting pxT ,^^ Phosphonium iodide. ^^3 + HI == pjjj. PHOSPHORUS XNO THK HALOOBNS. pounds a^\Ti°™' """^ OWorine.-Two corn- Phosphorus trichloride pp. pentachloride . p!^,' Phosphorus Tk.chlor.de rPCl , ;' ' "'gdry chlorine gas over hJ,A P'"^P*™d bypa^s- It is a colourless Tiquid fumi! '""<"i^''°"« Phosphorus. ^>y water ,A... .^ 'VS!;™-' ^i^- "composed Phosphohus P™tac„lor,„. /PC, ,' ; reatmg amorphous phosphorus with d T'""'"' ''^ low temperature until n„ '*'■•'' "^loi-ine at a -"d. of pungent r:;''"r'-''--''ed. Iti^awhite posed b, warer in Z^'J:;^. "" """"' "''•' '"'"^ ''-- n ^ Pni . TT oxychloride. /S-cl^X^^-Ao^n'sHOl Pi>on.s oxyohlorfde; and hv7 tf '''''^•'* (» P'-- TMs is the action with a ,2 "" •"'" '"'^ ^<'™«<'- 'i.e second stage the three rl" '^™^°''' "" °^ *«'-- I" ^placed by three hydroxv 7 ^"^ ''°"^ "' ^'"»"— e '^ formed, alor.g with a forth '"'' '"' "'"^"''""^ -"<» «««• Prom thfs it 1 se^r',:rt""T "' ''^'^™«'"<'- VdroxideofatrivalentTri '/'r'T" '"'"'^ '^ '"« «- acids generally can be Xl:^^^^ ^^^ -^^2 -OH, SO,(OH),. ^" 154 QUESTIONS AND EXERCISES. 138. Phosphorus and Bromine, &c. — With the other halogens phosphorus combines forming compounds the formulas of which are : PBr^ PBrs ; P2I4, PI3 ; and PF,. These compounds, excepting the last, are prepared by direct union of the elements ; and all are of great value in preparing halogen derivatives of carbon compounds. By means of these (as well as the chlorides), the oxygen and hydroxyl of carbon compounds can be replaced by the halogens. (Compare the action of phosphorus penta- chloride on water. ^ QUESTIONS AND EXERCISES. 1. Compare nitrogen and phosphorus, as to their compounds. 2. In what dehydrating processes is phosphorus pentoxide used ? 3. When an orthophosphate of the class MH2PO4 is heated, water is driven off. What is left ? Write the equation. 4. Mix a solution of sodic phosphate (NaaHPO^) with one of plumbic acetate. What result ? Try with phosphite and hypo- phosphite. 5. When an orthophosphate of the class M2HPO4 is heated, water is driven off. What is left ? Write the equation. 6. What is the basicity of phosphorous acid ? 7. By what tests can the acids hypophosphorous, phosphorous, and phosphoric be distinguished from each other ? 8. "The atomicity of phosphorus is 3 in some compounds and 6 in others." Apply this statement. 9. Calculate the wt. of 1 litre of phosphorus vapour at 400° C, and 760 mm. pressure. 10. Calculate the wt. of 1 litre of phosphorus vapour at 1040° C, and 760 mm. pressure. 11. What is the percentage of phosphorus in pure apatite (Ca3(P0jo.0aCl,,)V ARSENIC. 155 CHAPTER XII. ARSENIC AND ITS COMPOUNDS. 139. Arsenic (As'"''= 75). — Arsenic is found free in nature in crystalline masses. The ores from which the elementary substance is principally derived are mis- pickel (FcgAsoS.,), arsenical iron (FeAso), and arsenical ores of cobalt, nickel, and copper. Iron pyrites often contain arsenic. Preparation. — Chiefly by sublimation from mispickel. The ore is 'leated in earthenware retorts, and the metal condensed m sheet iron and earthen cylinders : FesAs^Sa = 2FeS + 2 As. It can be prepared on the small scale by heating* the tri- oxide (As.^O,) with charcoal. Experiment 118- — Mix a small quantity of white arsenic (AsgOg) with powdered charcoal, put in a narrow hard-glass +.ube closed at one end (matrass), drop in a small splinter of charcoal, and heat the tube slowly in the Bunsen flame, applying the flame first to the part of the tube in which the charcoal splinter is. A mirror of arsenic forms as a ring around the inside of the tube. The charcoal has reduced the oxide of arsenic : A82O3 + 3C = 2As + SCO. Properties. — A steel grey solid, of somewhat metallic appearance. Sp. wt. = 5.727. It sublimes at 356^ C. It can be melted by heating under pressure. Sp. wt. 156 ARSENIC TRIOXIDE. of vapour =10,2 (air =1). (Calculate the number of atoms in the molecule.) It oxidiseb in moist air ; and burns brightly when heated in air or oxygen, forming the trioxide (AS2O3). Can also be oxidised by heating with nitric or sulphuric acid. It is not soluble in hydrochloric acid. ^rsenic and all its volatile compounds are very poisonoas. Lead is hardened in the manufacture of shot and bullets by alloying it with a small proportion of arsenic. UO. Arsenic and Oxygen. — Two oxides are known, viz. : Arsenic trioxide A82O3 Arsenic pentoxide AsgO^ They are both acid-forming oxides, and this marks arsenic a3 a non-metal, although it has some metallic characters. 141. Arsenic Trioxide (AsoOg). — Also called (in- correctly) arsenious acid. This is the *' white arsenic " of the shops. Preparation. — By roasting arsenical pyrites and other ores of arsenic in a good current of air and receiving the fumes in cool chambers to condense them. These crude ^' flowers of arsenic " are purified by resublimation. Properties. — A white solid, either a crystalline po"/- der, or a porcelain-like cake ; of sweetish, metallic taste ; sparingly soluble in water. (Carefully study the appear- ance of specimens.) It is volatile, and sublimes readily. (Try a little in a 1. 1.) Experiment 119, — Boil a little arsenic trioxide with distilletl water in a t, t. It dissolves only to a small extent. Prove this by evaporating a little of the clear lic^uid in a watch glass. Add ARSENIC PENTOXIDE. 157 about I of its volume of hydrochloric acid to the water, and heat again. The arsenic trioxide dissolves readily. Keep the solution. Experiment 120- — Try the solubility of arsenic trioxide in solutions of Bodic hydroxide, ammonia, nitric acid, and sulphuric acid. Arsenic trioxide has very weak basic j)roperties. It forms with acids no salts which are not decomposed by water. Its acid forming properties are distinct. (What proof of this have you had 1) It is used in the manufac- ture of pigments, glass, &c., and in calico printing. — One grain (0.06 gram) of arsenic trioxide is a dangerous dose. Doses of 2 to 4 grains are nearly always fatal ; but by use the system becomes able to withstand its action. In one case more than five grains were eaten without ill effect. 142. Arsenic PentOXide—AsaOg.— Is unimportant. Can be prepared by heating arsenic acid (H3ASO4) nearly to a red heat : 2H3ASO4 = 3H2O -|- AsjOg. (Compare with phosphoric acid). At a red heat it begins to de- compose into oxygen and arsenic trioxide. — It is a deli- quescent white solid, uniting with water to form arsenic acid. 143. Arsenious Acid— HgAsOg (hypothetical). — This acid is known only in solution and through its salts. Its relation to arsenic trioxide is the same as that of phosphorous acid to phosphorus trioxide. It is a tribasic acid ; but arsenites are known corresponding to a monobasic acid, HAsOo. (Compare HMO.^). Arsenites. — Experiment 121. — Heat powdered arsenic tri- oxide with solution of sodic hydroxide until no more will dis- solve, filter, dilute the filtrate, and preserve it for the following experiments. 1 158 ARSENIOUS ACID AND AKSENITES. This solution contains an arsenite of sodium; say NagAsOg. Experiment 122- — To a little of the solution add a few drops of solution of ferric chloride (Fe.^Cle), A reddish brown precipi- tate appears : FejCle + 2Na3As03 = Fe2(As03)2 + GNaCl. Test its solubility in dilute hydrochloric acid, and in ammonia. This precipitate o^ ferric arsenite is harmless when taken into ^' e stomach, provided the contents of the stomach are i ,o acid. Hence^ freshly precipitated ferric hydroxide (Fe2(OH)8) is the best antidote to poisoning by arsenic. It unites with the acid of the stomach to form ferric chloride and precipitates the arsenic as arsenite. The ferric hydroxide can be prepared by the action of am- monia on ferric chloride, but must then be carefully washed, since ferric arsenite is somewhat soluble in am- monia. It is better prepared by the action of calcined magnesia on solution of ferric chloride ; or a mixture of sodic carbonate and ferric chloride may be given. Experiment 123. — Add some cupric sulphate solution to sodic arsenite in a t. t. A green precipitate (Scheele's green) is thrown down : CuSO^ -f NaaHAsOs = CuHAsOg + NajSO^. This green is often used for colouring wall papers, HC1, Arsenic Trt-iodide (Asia) is used in medicine It is pi'epared by carefully heating arsenic and iodine to- gether. (In what proportion'/). In Donovan's solution, it is combined with mercuric iodide (Asia -}- Hgl.,), and forms a clear colourless solution. The other halogen compounds are of little importance (AsBi'y, ASF3, and AsFj). — Clemen's " bromide of arsenic " (so-called) is a solution of arsenic acid and hydrobromic acid, prepared by the action of bromine on arsenic trioxide. 148. Tests for Arsenic. — (See Experiments 118, 128, 130, and 131.) 1. To a solution of arsenic trioxide in dilute hydrochloric acid add a drop of ammonio-rupric sulphate (prepared by adding ammonia to cupric sulphate solution gradually, until the preci- pitate at first formed is just redissolved). A green precipitate (Scheele's green) appears. 2. Beinfich's Test. — Put a thin strip of bright copper in some hydrochloric acid sohition of arsenic trioxide, and boil (in a t. t.). Arsenic is deposited on the copper. Remove the copper, wash it well (without rubbing), dry it by holding it over a flame QUESTIONS AND EXKHOISES. Ifi3 (not too near), put it in a narrow dry t. t. and heat it. Arsenic and the triox'de are sublimed upon the tube. Try this test with some grt jn wall papers, by digesting them with strong hydrochloric acid, diluting with water, and then using the solu- tion as directed above. QUESTIONS AND I<]XEKCISES. I. (Compare arsenic and phosphorus (a) as to physical proper- tits, and (h) as to their compounds. '_'. Show the analogy between oxygen and sulphur, as seen in till- compounds of arsenic. 3. In what proportion should ferric chloride and sodic car- hdiiate he mixed so as to produce ferric hydroxide : FesCli, + SNaaCO + 3U^0 = Fe2(0H)e + GNaCl + aCOj. 4. What data have you for concluding that arsenic is triad and pentad ? f). How much mispickel will (theoretically) give 10 lbs. of arsenic. 0. In what respect does the molecule of arsenic deviate from the general rule ? What other element shows the same deviation ? 7. Is arsenic a metal or a non-metal ? 8. What is the meaning of "isomorphous " ? 9. In testing for arsenic with hydric sulphide the solution is made acid. Why ? 10. In Marsh's test oxidising agents must be absent. Why ? II. Balance the following ec^uations : (1) As + HNOg - n3A8()4 + NO2 + H2O. (2) A82O3 + HNaO = NagAsOg -f HgO. (3) NH4OH -f Fo2Cle = NH4CI -f Fe2(0H)«. (4) NaaHAsO^ + AgNOg = Ag3As()4 + NaNOa + HNO3. 12. Write the formulas for the following compounds : Sodic (Ithi/ib'lc arsenate, ciq»ric hi/dric arsenite, sod'tc thioarstnite, and (( tn monk orthoamenate. 164 CARBON. CHAPTER XIII. CARBON AND ITS COMPOUNDS. 149. Carbon (C^ = 12).— This element has three allotroi)ie modifications : (1) diainond, (2) grapJdte, (3) charcoal (lamp black, tfec.) Diamond and graphite are crystalline ; charcoal is amorphous. 1. Diamonds are f'^-nd in pebbly deposits of ancient rivers, in South Africa, Australia, South America, Ac. It is the purest form of carbon, and its nature remained long unknown, until it was proved to be carbon by burn- ing it in oxygen, — An impure black variety, carbonado^ is used for polishing the diamonds. — Diamond is one of the hardest substances known. When ])ure it is colour- less. Specific weight =3.5 to 3.6. Its crystals are modifications of the cube. Its great lustre is due to its strong refractive power on light. At a high temperature it burns in air or oxygen forming carbon dioxide (CO.,). It has never been prepared artificially, although many attempts have been made. 2. Graphite is found in lumps in granite, ifec, well crystallised ; or in obscurely crystalline masses of plum- bago, or black lead. The best black lead is found in Cumberland, England. Graphite can be artificially pre- pared by crystallising carbon from molten iron. It often occurs in pig iron. It is not pure carbon, but leaMs considerable ash on burning. — It is a black metallic- r'AKiJON. 105 loi>king substiuicc, groasy to tli« touch ; Hpecific weight rr: 2 to 2.6. It hiiriiH with groat difficulty at a higli toiiiperature to form carbon dioxide. It is used for lead pencils, crucihles, for [>olishing gunpowder grains, ifec, and as a lubricant. 3. Amorphous Carbon. — Jjamp-black, gas-carbon, coke, charcoal, and animal black are impure amorphous ciubon. Lamp-black is prepared by burning turpentine, tkc, with a scant supply of air and collecting the soot on woollen cloths. It consists of particles of carbon covered with tar. It is used in the prei)aration of Indian ink, black paint, and printers' ink, and to give a grey shade to calico. — Gas carbon gathers in the upper part of the retorts in which coal is distilled in the manufac- ture of coal gas. It is very hard and resonant, and con- ducts electricity. It is used as the negative element in electric batteries, and in the manufacture of micro- ph(jnes. — Coke remains in the bottom of the gas retorts when the process of distilling is complete. It is hard and dense, and burns (at a high temperature) without smoke and giving an intense heat. It is used in smelting opera- tions and as fuel in engines. — Charcoal is prepared by the destructive distillation of wood or bones. In the latter case it iaacalled ayiimal charcoal, or bone black. Experiment 132.— Heat a small bit of dry wood in a mat- trass, applying a match to the open end. A combustible (jas is evolved, tar and water gather on the sides, and charcoal re- mains as the skeleton of the wood. Try the same experiment with a bit of l)one, horn, or dried meat. Similar results are ob- tained. Charcoal bus the power of absorbing gases and causing tlieir oxidation when they are oxidisable, A piece of lOf) CllAllCOAL. charcoal made from tlic sliell of IIh^ cocoa nut will aWjil, 171 times its volume of ahin>oiiia gas ami 100 times its volume of liydric sulphide. It must first be heated to expel the gases already condensed in its j)ore.s. On ac- count of this pronertv it is used as a filter foi* air, oeii)*' .nade into so-called " res[)irators." Evidently the char- coal in these respirators should be often renewed, or taken out and heaied red-hot, in order to expel the con- densed irases. Experiment 133. -Fill a filter paper (placed in a funnel) about two-thirds full of bone-black. Colour some water with indigo, heat it, and pour it on the filter. Charcoal has the property of extracting colouring mat- ters from solution. Bone-black is used for this purpose in sugar refining. Experiment 134- — Fill a filter with fresh ground charcoal, .•ind pour some hydric suljjhide water on it. If thf" smell has not been uostroyed when the water runs through pour it on again. Charcoal has vhe power of extracting offensive animal and vegetable matters from water. It is used for filter- ing water. Filtei-s should be renewed very often. The charcoal should either be replaced or be taken out and heated red-hot to destroy the substances extrac|jfd from the water, — Charcoal poultices are usod foi purifying foul wounds. They are very efficacious. — Coed is impure amorphous carbon. It is the remains of primeval forests which have undergv>r'^ a slow proces:^ of decay. Thi.s process is now going on in peat l)og^. A^Uhradte is very pure, containing as high us 94 '°/^ carbon. Bitunmioux, or soft coal ccntair mud', hydrogen, oxygen, and nitro- gen, and only uj) to 75 °i^ car'^on. fAi/nitf is coal in COM l»OUNt)S OF CARBON. ICT the })rocess of formation. It ooDtaiiis up to 70 °/^ carbon. Jet is a hard variety of coal wliich takes a good polish. 150. Compounds of Carbon. — Carbon occurs in Tiature combined as well as free. As shown in Experi- ment 1-^'i, it forms an essential constituent of anirnal and vegetable bodies. In fact, it is the element of organic tissues. — It is found in vast quantities, as carbonates, e. g., calcic carbonate (limestone, marble, chalk, &c.), magnesic carbonate (in mountain limestone) ; also in t}»e air as carbon dioxide (COo) ; in marsh gas (CH^), petro- leum, shale, ikc. — The number of the compounds of carbon is so vast tliat a special branch of chemistry. Organic Chemistry, is devoted to their considera- tion. Many of them exist already formed in the bod.es of plant's and animals, and in the crust of the earth ; but many are the product of the labora- tory. The great number of the carbon compounds is due to the property which ( irbon atoms have of unit- ing ivith each other so as to form groups of carbon atoiiis capable of acting as the nuclei of molecules. Thus, carbon and hydrogen can unite in a great number of different proportions, the simplef-t com- pound being that having one carbon atom in the mole- H H H ' . . II cule, H — C — H, the next containing two, h — C — C — h, I II H H H H H H I I I the next th^-ee, h — C — C — — h, and so on. The i I i H H H hydrogen atoms can be replaced oy other atoms I 108 CARKON niOXTDE. Hid loiiiK'd. Tims. aiul groups, and tlius derioatiiiCH H 1 H C CI, H- 1 C OH, etc. 1 1 H ! H 151. Sources of Carbon Compounds— P/an<.s and animals supply compounds of carbon ready formed, and the most fruitful natural sources are the remains of organised bodies. In fact, if we exclude some of the naturally occnring carbonates, it may be stated that all carbon compounds not of aitificial origin are the products of vegetable or animal organisms. Petroleum supplies a great number of compounds of carbon and hydrogen, mostly belonging to the class of parajfins (C,iH2,i + 2)- — By the distillation of coal, coal tar is obtained. This once waste product has developetl during the last 30 years into an almost inexhaustible source of new and valuable compounds. From it ai-e manufactured the aniline and other beautiful colours, artificial essences and perfumes, and substances which in some degree serve as substitutes foi' quinine, tfec. La^^dly, saccharine, said to be 220 times as sweet as sug.\r, has been made from coal-tar products. — Bone-oil and ivood-tar are sources of organic compounds. CAP BON AND OXYGEN. 152. Carbon Dioxide, CO,. — Commonly called carbonic acid. Ojoukrence. — Free in the air and in the crust of the earth, issuing from fissures, as in the celebrated Grotto del Cane. It is found combined in the carbonates. If CARhON DIOXIDK. 161) is !i product of the coiuliustion, ilecay, and fermentation of organic substances. It is also given out l>y animals ill respiration. Preparation. — Experiment 135. — Put some lumps of mar- ble or limestoue in an S-ouuce bottle provided with a gas-delivery tube bent twice at right angles so as to collect a heavy gas by displacement of air. Fill the bottle al)out one-third with dilute liyCO,, and (2) acid, e.g., NaH0O;{. The carbonates of the alkali metals (K._,(JO;,.Na._,CO;i, ka.) are soluble in water; CAHP.ON M(>N<)XII>K. 1^1 ill! other normal carhoiiatas are insoluUlt.'. lUit many of tlie insoluble normal carbonates combine with carbonic acid to form unstable, sparingly soluble acid salts. Thus, calcic carbonate (CaCO.,), magnesic carbonate (MgCO^), ferrous carbonate (Fe(yO;.), tfec, dissolve in water con- taining carbonic acid. The solulnlity is increased by pressure of the gas. Tests. — 1. Carbon dioxide renders lime water turbid : Ca(OH)., -f- CO2 = CaCO.^ + H2O. 2. Carbonates effervesce with hydrochloric acid. (Try with several of the carbonates. ) If the evolved gas be poured into a t. t. containing clear lime water, it renders it turlnd on shaking up« 154. Carbon Monoxide, CO. — Also called cariomc oxide. Preparation.— Experiment 138.— Carefully heat a little dry powdered potasnic ferrocjianUle (K^F^eCoN^) with about 10 times its weight of conceuti ated sulphuric acid, and apply a light to the mouth of the tube. A gas is evolved which burns with a lambent blue flame : K4FeC,.N„ 4- OHaSOj + GH.,(3 - 2X280^ + 3(NHJ2S0^ 4- FeSO^ + GCO. Carbon monoxide is also formed when oxalic acid (CH-.O^) is heated with sulphuric acid : C2H2O4 = CO + CO2 + H2O. Ft is formed 'dien carbon burns in a scanty sup[)ly of air, as in the inner parts of a tire. • - -- Properties. — A colourless gas, of very faint odour; s[). wt. - I). !)(>('). It burns with ii j»ale bluo tlame 172 f'ARIJON HIS rT.PIllDK. (CO + O ^ COo), as soon on tlio top of a coal fire. It can be con«lenso(l to a li({ui(l at — 139,5'^ by a pressure of 35.5 atinos[)heres. It is sj)aring]y soluble in water (3 in 100); easily in ammoniacal solution of cuprous chloride (Cu.^Cl.,). It is u deadly poison, combining with the ha3molglobin of the blood and thus preventing its aeration. As it often escapes combustion in coal and charcoal fires, it contributes greatly to the poisonous condition of ill-ventilated rooms. Open charcoal fires (braziers) are es[)ecially dangerous. 155. Carbon Bisulphide, C8.,.— Preparation. — By i)assing sulj)hur vapour through long tubes filled with red hot charcoal. Properties. — A mobile colourless liquid, of pleasant ethereal smell when pure, but generally having a disgust- ing odour due to impurities. Sp. wt. = 1.29. It does not mix with water. Experiment 139. — Pour a little carbon bisulphide into a t. t. of water. Note the smell. Shake up with the water. Heat a few drops of carbon bisulphide gently in another t. t. It boils readily. Put a light to the mouth of the t. t. Carbon bisulphide boils at 46° C, forming a heavy vapour, very explosive when mixed with air : CSa + 30a = CO2 + 2S()a. It evaporates quickly when exposed to the air and lowers the temperature. (Try a drop on the hand.) It mixes in all proportions with ether and alcohol ; and dissolves fats, oils, india-rubber, phosphorus, iodine, bromine, itc. "YDROCARBONS. A solution of india-uibber in > i . ^^^ fo; ce.entia, n.bbe; ,o ^ iL"^ ''''''^''^'^ - "-, nit'-ogen dioxide fXor h. ' '"^"''"* ^^^^^^^ with '^^.^^ -d in J^^^'r^' -^'\ ^ dazzling .Mte i— us. It is antis: S,W TZ '""^^'^^^'^^ - meat, &c. • ^ ''^' ^"^' ^« "«ed for preserving ^'^"fphomrbonic add H r*i carbonates. . ^'^ '"^^^^>g-"« to carbonic acid and tht Potasmc sulphocarbonate K OS -■"on bi.„,pHMe in .„,„«;, ^fp^il^r^^ "^V ^i-,.,„ K.OS, + 2HC1 . 2KC1 + H.cs'; H.CS3 = H,S + CS,. CARBON AND HYBEoOEN. 156. Hydrocarbons —Thp „, . S>eat that onlv a very Zl] 7 "'''''" "'' «'««« i« bo «- - "-toontainLg lLT„^'';'™•••'°"-dhyd..o- = carbon atom and 4 hydrogen ^"""'« i" the molecule, „_(]__„ , , "' * '""'"». --""I J of these is 174 PARAFFINS. employed in holding the carliou atoms tlicinselvcs together. H H .11 The graphic formula for this molecule is li — C — (J — ii. I I H II II II II III • ■■ • The next would be n — (J — C — C — ii, and so on, tlic I ' I II II H molecules increasing regularly by CH.^ ; so that a general formula, Cf,U'>^ + 2, ean be written. Very many mem- bers of this series are known. Most of them are found in petrcleum oil and in the gas accompanying it. It is called the Paraffin Series : „ Marsh gas, or methane. . . . CH4 Ethane OgHf. Propane C.^Hj, Butane ^4Hi Pentane C5H12 Hexane - . . C,.Hi ^ &c. &c. The different members of this series resemble each other in chemical properties. Paraffin oil (kerosene) is a mixture of the liquid members. Paraffin wax, used in making candles, is a mixture of solid paraffins, the higher members. These substances are obtained by the frac- tional distillation of petroleum, which is a product of the decomposition of primeval forests. Besides the paraffin series there are several other series of hydrocarbons containing a less proportion of hydro- gen, the Olpjines having the general formula Cj^H.jm, — (C0H4, C^jHq, tkc.) ; the Acetyleme Series, UnH.jn- . . Gas . Gas .. Gas Boila at V C. *' 38° C. " 70° C. 2> '^fAKsir GAS. 'liff-;encrCtirLrjc!;tivi",'''1 "^ ""-^ '"■'<^ tho. '"• Marsh Gas, or Methane Cr "■•"t pools, Hsi,., ,„ ,:v;;';^' °'' ---i., .„„ ou.,,. „ ;;™t of wato, ,„.,, ,„, ,,;"'» => bottle L^ d;,,,,,,^. '['- -,..,, an.\:i t::'::'i ■■" -- -.-ntii: A«H g,.e „«■ „,,,., <,„„„^ i-'yi;"'S» Of America „„, ''■f --■bon. I„ .;„:..,:""; ->"-''«- of othe": -'•-) gas i. ,„,d fo.. ,•„.,;;,.:' ^--y'vHnia, this f"-- ages. Jlarsh gas i, tL . , ' '"'™ ''^'^n bu™i„„ "'■"ora- It is ,1 ''*""'<'<' " fi'-e .lam,> " .f ? " i!- also present in „„ •, '"'"P ofcoai ««/ 178 ETHYLENE. argentic nitrate (impurities, HCl and CI); it does not colour a mixture of potassic bichromate and dilute sul- phuric acid green (alcohol, &c.) ; it is not coloured brown by potassic hydroxide or sulphuric acid ; it does not cause bright sodium to tarnish, even when heated (O2H4CI2. &c.). If, when allowed to evaporate on a clean watch glass, chloroform leaves a strongly smelling residue, the alcohol from which it was prepared contained fusel oil. Experiment 145- — I'ry these tests with samples from the druggists. Iodoform (CHI^) is a yellow crystalline solid prepared by adding iodine to a mixture of common alcohol and solution of sodic carbonate heated to 60°. It is insoluble in water, but soluble in alcohol and ether. 159, Ethylene, CH^. — Also called "olefiant gas.' Is a constituent of coal gas. Preparation. — By the action of potassic hydroxide on monochlorethane (CoH^Cl) : C2H5CI + KOH - C2H4 + KCl + H2O. Or, by heating alcohol with strong sulphuric acid : CgHeO = C2H4 + HgO. Properties. — It is the first member of the olejine series. It is a colourless gas, distinguished from the paraffins by the facility with which it unites directly with other sub- stances, ivithout losing hydrogen. Thus, it unites with an equal volume of chlorine to form chloride of ethylene (C^HiCl^^ an oily liquid ; , C2H4 + CI2 = C2H4CI2. Its molecule is unsaturated, and we express this fact by H H II the graphic formula, n — C = C — H, in which the carbon ISOMKRISM. 179 H*^.oins tire represented as united by two bonds. One of tlies'^ can be divided so as to receive 2 atoms of chlorine, H H II — C - C — H. The olejines are all wisaturatcd compounds. I I Cl Cl 160. T'^omerisni. — Ae has been mentioned', methane is capabiv entering into tliose chemical actions only in wliich its hydrogen atoms are rej)laced by other atoms or compound radicals. Thus, an atom of chlorine replaces One of hydrogen to form monochlormethane. This re- placement has been made in a great many different ways, ;ind the same substance is always obtained. It has been concluded that the fc-r hydrogen atoms are exactly alike ill relative position, so that it does not matter which is replaced. It is very important to get this idea clearly at the outset. It has been found also that only one sub- stitution product of ethane having the formula, C-.H^Cl, can be obtained ; and it is therefore concluded that H H I I the six hydrogen atoms in ethane, ii — C — — n, are alike I I H H ill position. But, when a second atom of hydrogen is replaced by chlorine, two substances are obtained, identi- cal in chemical composition (C\,H4Cl.j), but differing in p i-operties. One of these is the substance mentioned in in Art. 151 as ethylene chloride. The only other differ- ent arrangement of the atoms is represented as follows : H H i L n — C — C — Cl, both chlorine atoms being attached to I I II Cl 180 ACETYLENE. the same carbon atom. This second compound can be H ' I prepared from aldehyde (h — C — C = O), by replacing I I H H oxygen by chlorine ; and it is distinguished from the first by the name ethylidene chloride. These two substances are alike in composition, hut different in properties. This is a case of isomerism.. 161. Acetyleno, C.^H.^. — This compound is a colourless gas formed by the incomplete combustion of gases containing hydrocarbons. It has a strong dis- agreeable smell, which is easily observed in the smoke of a candle just blown out. It is produced in consider- able quantity in a Bunsen burner " burning below." (Try it.) It can also be prepared by the action of alco- holic solution of caustic potash on ethylene chloride or bromide : C2H4CI., -f- 2K0H = C2H2 + 2KC1 + 2H2O. It is poisonous when breathed, uniting with the haemo- globin of the blood as carbon monoxide does. As it is formed by lamps when the flame is turned low, this practice should be discountenanced, especially in sick rooms. Acetylene can be formed from the elements by passing a powerfid current of electricity between carbon poles in an atmosphere of hydrogen. This is an important synthesis. POTASSIC KKHKOCYANIItK. 181 CAHHON AND NITKOCKN. 1G2. Cyanogen Compounds. — Nitrogen is pre- sent in all organised bodies. If nitrogenous matters such as horn, flesh, &c., be heated with sodium, a compound is o'ntained composed of sodium, carbon, and nitrogen (NaCN), and called sodivm cymiide. When nitrogenous substances are heated with 2)otassic carbonate (KoCO;.), and iron scraps, a fused mass is obtained which yields on lixiviation a yellow crystalline salt, potassic ferrocyanide (K4Fe(CN),.). This fealt gives a fine blue colour (Prus- sian blue) with ferric salts, and is the starting point in the preparation of the cyanogen {blue-generating) com- pounds. All these compounds contain the monad radical — CN, cyinogen, which can be set free, but, like an atom, unites immediately with another to form a molecule (CN)2. The substance cyanogen (CoNo) can be prepared by heating mercuric cyanide (Hg(CN)._,). It is a very poisonous gas, having chemical properties like those of clilorine ; and its compounds with metals are called cyan- ides, e.g. : KCN, Fe CN)2, Ca(CN)2, &c. 163. Potassic Ferrocyanide— K,Fe(CN)c.3H.,0. Commercially known as yellow prussiate of potash . Preparation. — Fuse refuse animal substances with i)otassic carbonate, and lixiviate the fused mass. A solu- tion containing potassic cyanide (KCN) is obtained. To this add freshly precipitated ye^rmts carbotiate (FeCOo). It dissolves : 6KCN 4- FeCOa =-- K4Fe(CN)„ + KgCOg. The solution is eva[)orated and the two salts separated by 1<*^2 UVDHOCVANIC ACID. cystallisation, the potassir carUoiiato Itoing much tlic more soluble of the two. Pkopertiks. — A salt crystal lisiiig in large yellow pi-is- matic crystals. (Examine a crystal, noting its " feel," taste, the ease with which a splinter can be split off, and the flexibility of the s})linter.) It is soluble in about 4 times its weight of water. (Dissolve a small quantity and taste the solution.) It is not poisonous, and in large (loses acts as a mild [)urgative. Experiment 146. — Heat slightlj^ a small crystal of potassic ferrocyauide in a t. t. It falls to a powder and water is con- densed ?n the side of the tube. (From what source does the water come '!) Heat more strongly, and the salt turns brown. It has been decomposed into potassic cyanide (KCN), carbide of iron (FeCa), and nitrogen. (Write the equation.) Keep the residue. » Potassic ferrocyauide belongs to the class of double cyanides^ and is composed of potassic and ferrous cyan- ides, 4KCN.Fe(CN)._,. But these are so united that no ordinary test shows the presence of iron ; and the salt does not possess the characters of a simple cyanide. It is a salt o{ ferrocyanic acid (H4Fe(CN)g). All soluble simple cyanides are deadly poisons. 161. Hydrocyanic Acid, HCN. — Originally called prussic acid. This is one of the most deadlj^ and sudden poisons known. The vapour of the pure acid causes almost instant death, and even when largely diluted with air it causes headache and giddiness for some hours if inhaled for a few seconds. Unfortunately some persons are not able to detect its subtle odour — tha' of crushed cherry stones. Experiments with it must b* t-'VAXlOES. 183 mude very cautio.isJv __,/,,,; 7 . rine water. ^' ^'"'^''^''^''^-^^nmonia and e/do- -l-d i„ ,0 o^. ^.te'lii iT^'fl '■-■°»y»"icle dis. »ith ;) oz. distilled water p •."'''''"'"""oiJ diluted 0^. distilled water until tl^ere TlTi, , ''"""*"' '" « yo o. with distilled water TM^l 7. ^'^'^^ «" 2 / hydrocyanic acid; it is tt,„ , '"" <=0M>iinn '«'*'« of the British Phalacojraf '^*'"'^«-«- 2K,Pe{CiV)„ + cH.Soi = 6KHS0, + FrrFifp't. •Experimeat 147 —4^,1 . ,x„ '^^peri.ent ,46. »d mtr T 't ^f'T *» «» -»>ue f™„ ph„„o »ei.,, and carefully 3m j,'';!'' "'" ^°»^ ^-^ dilute ™a,eac,d can be noticed. [wC" • ^l"' , l'^^""'"- odonr of « nte an equation showi„„ til , <'«»<>l™d in the water ' »luti„„ of potassic ferr: Z, a ;*»;' -'P^uHc acid., "t^ Hydrocyanic acid i. „„t Jj f^^ """■ *•"= 'Wuted sulphuric acid -t ROPERTIES Th "^"'O- The dilute sltl^i « " ""'T^'^^^ ™'''«''' "nd is feebly acid in reac on t T"" °^ '''^ -"^H 'he acid uniting with t: I" J,' ^'-''^ '-°»I'oses: mate (NH,.CHO,) .- "'■"""S «'«momo for. HON + 2H,0 = HCO, NH p "' '""""^««''^« (C.N,) is formed "e»- The cyanides of the a/1 f """'^' P'°f«'- 184 DOURLK CYANIDES. (II^(CN)..) fii'o solu)>l«; in water. Tlio oilier siiin)l(! cyanides are insoluble in water, but ilissolve in solutions of the alkaline cyanides to form double cyanides. Experiment 148. — To a solution of argentic nitrate add a drop of solution of potassic cyanide. A. white precipitate of argentic cyanide (AgCN) is thrown down : AgNOg + KCN = KNO3 + AgCN. Add more potassic cyanide, and the precipitate is dissolved, owing to the formation of a soluble double cyanide (AgCN. KCN). There are two classes of double cyanides : ( I ) those easily decomposed by dilute acids, and from which hydro- cyanic acid is set free, and (2) those from which hydrocy- anic acid is not set free by dilute acids. To (1) belong the double cyanides of potassium with silver, mercury, &c. To (2) belong the ferrocyanides, &c. All the soluble simple cyanides and the double cyanides 0/ class (1) are deadly poisons. The double cyanides of class (2) are not poison- ous. Tests. — 1. To a solution of hydrocyanic acid, or of a cyanide, add argentic nitrate. A white precipitate of argentic cyanide is formed. This is insoluble in nitric acid, and sparingly soluble in ammonia. (Compare AgCl. ) ( Why must a considerable quantity of argentic nitrate be added before a permanent precipitate is obtained with potassic cyanide ?) 2. To a solution of the acid or of a cyanide add a few drops of ferrous sulphate solution, a drop or two of ferric chloride solution, and caustic soda (caustic potash, potassic carbonate, lime water, &c., will answer) : warm gently, and acidify with hydrochloric acid. A blue colour or precipitate is formed (Prussian blue). (1) 2KCN 4- FeSO^ = Fe(CN), + K^SO^. (2) 4KCN + Fe(CN), == K^Fe(CN)o. (3) 3K,Fe(CN)o + 2Fe2Clc = 12KC1 4- Fe^(FeCeNe)3. CYANIC ACID. 185 According to equations (l) animonia. Urea is carbamide. Amides readily combine with water to form ammonium salts. Thus, when u-ea is heated above 100° C, with water, anmionic carbonate is formed : CO(NH,l, + 2H„0 = C0(0NHJ2. This decom})osition can be brought about more easily by heating with alkalis or acids. (Explain Experiment 150.) It goes on at the ordinary temperature during the fermentation of urine. Tests. — 1. Evaporate the liquid to small bulk, and treat with concentrated nitric acid as in Experiment 149. The crystals of urea nitrate (C0(NH,)2.HN08) are tpute easily recognized. 188 URIC! ACID. 2. FiVaporatc, ami add a strong solution of oxalic acid (CatljO^). Crystals of oxalate of urea are formed (iiCUi^l^N).,. Cj HqO^). Estimation of Urea. — The <|uantity of urea in urine can be readily determined by tlio Davy-Knop method, whicli de[)ends on tlie fact that urea is decomi)Osed by sodic liypobromite, and all its nitrogen set free : CO(NH2)2 -f SNaOBr = CO2 + N2 + 3NaBr -|- 2H2O. This decomj)Osition is brought about in an apparatus provided with a graduated tube in which the nitrogen is collected and measured. From the volume of nitrogen obtained from a given quantity of urine, the quantity of urea can be calculated. 167. Uric Acid. — CSH4N4O3. This substance is found in small quantities in human urine, but forms the principal part of the nitrogenous excrement of birds and reptiles. It occurs also in the hum-in body as " chalk stones " in gout, and urinary calculi. Guano is the ex- crement of sea-fowl. It contains much hydric ammonic urate (NH4H.C5H.2N4O3), and from it large quantities of uric acid were formerly prepared for the manufacture of TKiurexide, a red colouring matter, now superseded by aniline red. — If human urine be strongly acidified with hydrochloric acid and set aside for 24 hours small crys- tals of uric acid collect on the sides of the vessel. The buff-coloured sediment of urine is generally uric acid or the acid ammonium salt. As these compounds are about ten times as soluble in hot as in cold water, they dis- appear when the urine is heated. URATES. 189 --'"MOO,,.,. xu:i:r:!:it:--t *-^RATPS TT * • -« the acid Jtri::^":; /'•'"' '"^-'--.-.t. f"""'! m the ,„.i„e andi'''' """' (^'^^^■} « soluble at I5» ift ),,oo to ^onT^ "'"'o'-eHons. It fe '00° in 123 to 125 partslT," '""''' "' ^''*''' ""^ «« ''■ssolves at 20" i„ 700 *„ Son ^''""*'"'« »«'< (KHUr) 'o «0 ,,a,.ts of wate... I ;, T* Pf "' ""'' «' 100" i„ 70 than e.the,- of the above dilu ^ '' °'°'-'' ^"'"hle P'-Tte, and at 100° in 39 7, ! T' 20» i„ about 370 -'te a,-e fi-eely ,„,„ye -/Cl T^''' ^''"' "-™"' I'-'Po.it ,u,c acid when aeidrfied ^^f"'""""-^ "^ "■'"^^ "nportance in the treatment If • '*"' '^ <"■ g^eat Both the.e d.ea.ses are "L to elT "" ^"'"^' ''"'' ^""t- ''<"''. and the treatment adontedr"' ''""'■^"°" "' "'•'« -id or acid salts into n^^'t'r ,/""'°™' "'<" "™ ''« "--e is decreased bratnLi ^ ' ^''<' -''''t, of donates. As can be easil/see^] I ""^ ''"^'"'"'' <">•- ''^st. "y '<'^". i'thium carbonate is the Experiment ^^^ t.,, ^ ,. Ac-d.,y the sol„ti„„ With hydroXic al"" ''"°'™ «-%• - ^--'«e^t:re— ^^ -» -<■ aaa a few drop, evaporated to dryness.) The rejdt f""" " ""»* «"« b" 190 ALCOHOLS. CAKBON, HYDROGKN, AND OXYGEN. 168. Alcohols. — A.llied to the paraffins is a series of compounds which differ in composition from the paraffins by containinfi; an atom of oxygen in the mole- cule. Paraffins. A Icohols. Methane CH4 Methyl alcohol.. . . CH4O Ethane CgH,, | Ethyl " .... CgHoO Propane C^Hf, [ Propyl " .... CgHgO Butane O^H^o j Butyl " . . C4H10O Pentane CflHia Aniyl " .. . . C5H12O <.V5C. &C. These alcohols can be prepared from the monochlor- paraffins (CH3CI, tfec.) by the action of water : CH3.CI + H.,0 = CH3.OH + HCl. Further, when they are acted on by phosphorus penta- chloride (PCI-), they lose an atom of oxygen and one of hydrogen, and gain one atom of chlorine : CH,0 + PCI, = CH3.CI + POCI3 + HCl. From these facts it is concluded that the molecules of the alcohols contain the radical Jiydroxyl ( — OH ). They are thus hydroxides of the radicals, CH3, C2H5, &c. Methyl alcohol CH3.OH Ethyl " C2H5.OH Propyl *' C3H7.OH &C. &G. 169. Methyl Alcohol. CH3. OH.— Occurs in na- ture combined with acids, as in oil of umitergrecii or METHYL ALCOHOL. 191 meJliyl mlicijlate. When wood is destnictively distilled in the preprAiation of wood -charcoal, three other ]>roducts are obtained : (1) A mixture of combustible gases (CH^, «fec.), (2) a watery liquid, and (3) a tarry liquid. From wood tar, creosote and other substances are obtained. The watery liquid (jxijroligneous acid) is strongly acid, an('i from it is obtained v)ood vinegar, or impure acetic acid, and wood spirit, or methyl alcohol. The acid liquor is neutralized with lime, and the methyl alcohol is then distilled off and purified by fractional distillation, &c. It is also prepared in considerable quantities by distilling the waste (" vinasse ") from the beet sugar indu.stry. Propertiks. — Pure methyl alcohol is a colourless liquid, similar to common alcohol in smell, and boiling at 55°. 1. Specific weight = 0.8142. It mixes with water in all proportions, with contraction of volume and evolu- tion of heat. It burns in air with a pale blue flame. It is a good solvent for fats, oils, resins, &c. Experiment 152. — Mix a little methylic alcohol with an ec^ual volume of water, and note the evolution of heat. Experiment 153- — Set fire to a little methyl alcohol in a porcelain diah. CH^O + 80 = CO2 + 2HoO. Commercial methyl alcohol is always impure, and has an unpleasant odoui*. It is used as a solvent, in the manufacture of aniline dyes, and in the preparation of methylated spirit, a mixture of common alcohol with a small percentage of crude methyl alcohol. This is unfit for use as a beverage, and is imported and manufactured free of duty in Gieat Biitain. It is, however, often 192 ETHYL ALCOHOL. purified and used to adulterate liquors. It is probable that many of the cheaper sorts of strong liquors sold in this country are preparations of methylated spirit. Methylic alcohol acts towards acids like a weak base, forming salts, wliich jtre unstable in presence of water. Thus, with hydrochloric acid it forms methyl chloride : CH3.OH + HCl = CH3.CI + B.,0. Compare K.OH + HCl = K.Cl + H,0. The reaction is not f 'nplete unless the water be re- moved as fast as it is ic . ned. The radical methyl CH..) thus plays the part of a monad metal. The salts of alcohol radicals are called ethereal salts. Many of them are volatile and have a pleasant ethereal smell. — When methyl alcohol is oxidised by a mixture of sulphuric acid and potassic bichromate (K.jCroOj) formic acid is pro- duced : CH4O + O, = CHA '+ H,0. 170. Ethyl Alcohol. — CoHgO. This is common alcohol, the intoxicating principle of all spirituous bever- ages. It is also known as spirits of wine. It is pre- pared by the fermentation of sugar. Fermentation. — This is a chemical action brought about by minute plants and animals, called ferments., which grow and multiply in the fermenting liquid. Cer- tain conditions are necessary to the life of tiie ferments, and fermentation ceases when these conditions are absent. (1) The fermenting liquid must contain the elements of food for the fei'ment ; a solution of imre sugar will not fcM'uiont. (2) The tomj)orature must not FERMENTATION. 193 be much above 40® C. nor much below 20° C. (3) There must be a proper proportion of water present. (4) The products of fermentation must not accumulate too much ; and (5) certain substances called antiseptics, which are fatal to the life of the ferment, must be absent. — There are several kinds of fermentation : 1. Alcoholic. — Caused by yeast (saccharomyces), the* products being alcohol and carbon dioxide : CgHiaOe = 2C2H6O + 2CO2. 2. Acetous. — Due to the vinegar plant (mycoderma aceti), which transforms alcohol by oxidation into acetic acid. 3. Lactic. — The lactic acid ferment has the power of transforming sugar into lactic acid. The ferment is pre- sent in sour milk. 4. Butyric. — Sugar is fermented into butyric add by a ferment present in rotten cheese. The germs, or sporules, of these ferments are present everywhere in the air, and wherever they find a suitable liquid they at once cause fermentation to begin. Experiment 154. — Make a solution of commercial grape sugar in 40 or 50 times its weight of water. Put some yeast in the solution and fill three convenient dishes with it, also three test tubes. Invert the latter in the dishes. Keep No. 1 in a warm room. To No. 2 add a little carbolic acid and set it in the same room with No. 1, but not too near it. Set No. 3 in a cold place and surround it with snow or ice. Fermentation soon begins in No. 1, and bubbles of gas rise into the test tube. After a considerable quantity has collected, test it for carbon dioxide. Fermentation does not begin in Nob. 2 and 3. — Distil 14 194 ALCOHOLIC LIQUORS. a few drops of alcohol from ale, receiving it in a cool test tube. Try taste and inflammability. Alcohol is separated from fermented liquors by dis- tillation. Common alcohol contains water, and often fusd oil, which consists principally of amy I alcohol. This is removed by fractional distillation and by filter- ,ing through charcoal. As it is poisonous it is important to Lave it absent from spirits of wine used in medicinal preparations. — Absolute alcohol is alcohol containing not more than 5 % of water. It is prepared by distilling the commercial article from quicklime, which holds the water. The last traces of water are very difficult to re- move. — Much alcohol is now prepared from glucose, a sugar made from starch. When the glucose is made from potato-starch, the alcohol contains a large percen- tage of fusel oil and is highly poisonous. Properties. — A colou. ^«s liquid of pleasant smell, boils at 78°. 3, freezes at — 130°. 5. When evaporated on the hand it leaves no unpleasant smell (if fusel oil is ab- sent). It burns with a pale blue flame, forming carbon di- , oxide and water. (Write the equation.) It is a good solvent for organic substances, especially those insoluble in water ; and is used extensively in the preparation of tinctures, ionic acid — having the same number of carbon atoms in the molecule ; the other gives a ketone and then breaks up into two acids having fewer carbon atoms in the molecule. For this and other reasons, it is believed that the hydroxy 1 is differently situated in the molecules of the two acids. H H H Primary propylic alcohol H — C — C — C — oh ! I I H H H H H H Secondary propylic alcohol . . h — C — C — C — H I I I H OH H A third kind of alcohols is known which, when oxidised, break up at once into acids having fewer carbon atoms in the molecule. These are tertiary alcohols ; e.g. : CHa I Tertiary hutylic alcohol CH3 — C — ch, I o H 198 AMINES — ETIIKR. 1. Primary alcohols are iliose fn which tho hydroxy! is attached to a carbon utorn which is joined to only one, other cj rbon atom. 2. Secowl ar 1/ '^Aco\io\H *»ave tlie hydroxy! attached to a carbon atom which is joined to ino other carbon atoms. 3. Tertidrji alcohols lu^ve the hydroxyl attached to a carbon atom wliich is joined to three other carbon atoms. 173. Amines, or Substituted Ammonias — These are compounds related to the alcohols in the same way as urea is to carbonic acid (Art, 10(5); and they can be prepared by similar methods, viz., by the action of dry ammonia on the chlorides, bromides, or iodides of the alcohol radicals. Thus, Methyl chloride. Methylainine. CH3CI + NH3 = CH3.NH2 + HCl. They can also be regarded as derivatives of ammonia, formed by replacing a hydrogen atom by an alcohol radi- cal. But a second, and a third hydrogen atom may be replaced, so that there are three classes oj amines, pri- mary, secondary, and tertiary, e.g., Tnono-methyl-amine (CH3.NH.2), di-methyl-amine ((CH3).2NH), and tri- methyl-amine ((0113)3^). Many of these compounds are found in nature. They resemble ammonia in their pro- perties, uniting with acids to form salts, e.g , C2H5.NH3CI, ethyl-ammonium chloride, and dissolving freely in water to a strongly alkaline solution. They generally smell like ammonia. 174. Ether. — (C2H5).20. Also known as sulphuric ether. Ethers are oxides of alcohol radicals, and bear the same relation to alcohols as the oxides of the metals da to their hydroxides. ETHER. 199 Preparation.— Ej )eriment 155).— Mix 4 parts of alcohol with 9 of sulphuric aci and heat the mixture until it begins to boil (at 140° (J.). Ether distils over. Note its odour. On the large scale, as soon as the mixture begins to boil, a small stream of alcohol is allowed to ilow into tl)e still, and the temperature is kept at 140° C. Ether and water then distil over together continuously. Explanation. — Alcohol forms with sulphuric acid^ ethyl sulphuric acid, or ethylic hydric sulphate aMg.OH -f H.,S04 = C.,H,,H.SO, + HA Tlie water distils as fast as it is formed. Alcohol decom- poses ethyl sulphuric acid, forming ethyl ether and sul- phuric acid : C,H5.0H + C.H^HSO^ = (C2H5),0 + H.SO^. The process is continuous, the alcohol being run in as fast as the ether and water distil. As far as the ulti- mate result goes, the action can be represented thus : 2C2H5OH = (C,H5)20 + H2O, as a simple dehydration of alcohol. — It is purified by dis- tilling from calcic chloride and lime to remove water and acids. Properties. — A colourless liquid, bright and mobile. It boils at 3 4°. 9, and the vapour forms aa explosive mix- ture with air. Ether should never be boiled over a naked flame, but always in a hot water bath. Specific weight, 0.736. Experiment 160. — Set fire to a little ether in a porcelain dish tilled half -full of water. 200 ALDEHTDES. Put lome ether in » t. t. »nd immerse iu water as hot at the hand can bear it. The ether boils. Ether is sparingly soluble in water, but mixes in all proportions with alcohol. It is a good solvent for fats and oils, resins, alkaloids, : Fat. Soap. Glycerine. CgHsFa + 3NaOH = 3NaF + CaHgCOHJa. The soap is separated as a curd by the addition of com- mon salt to the solution, and the glycerine is recovered from the mother liquor. In many factories the fata and oils are decomposed by heating under pressure with water and 2 to 3 per cent, of sulphuric acid. Aqueous solution of glycerine and fatty acids are obtained in separate layers. The glycerine is drawn off and purified by distilling with steam at 180° C. The acids are neu- tralised with caustic soda to form soap : CgH^F" + 3H2O = C3H5(OH)3 + 3HF. HF -f NaOH = NaF + HgO. Sodium and potassium soaps are soluble in water and in alcohol. Most soaps are insoluble in salt water, but soap made from cocoanut oil and resin (" marine soap ") is soluble in salt water. Lime and magnesium salts de- compose ordinary soaps forming insoluble lime and mag- nesium soaps. Thus, in washing with hard water, there is always a waste of soap. — Lead plaster is a lead soap, made by heating litharge with olive oil (or lard) and a GLTCERFNE. 213 little water. It consists of plumbic oleate and palmitate principally, with some glycerine. Properties of Glycerine. — A thick, sticky, colour- less liquid, of sweet and burning taste. Specific weight = 1.28. It dissolves in water in all proportions, and is hygroscopic. It mixes with alcohol in all proportions. It is a very good solvent for metallic oxides, salts, ifcc; and is used in medicine in preparing glyceritum acidi carbolici, &,c., which are solutions in 4 fluid ounces of glycerine, of 1 ounce of carbolic, gallic, and tannic acids. Glycerine has antiseptic properties, and borate of glyce- rine has been successfully employed in surgery. — Gly- cerine cannot be distilled alone, but decomposes at 280°, giving oflf pungent choking fumes of acrolein (C3H4O). If water be present part of the glycerine distils along with the water. — Glycerine is a triacid alcohol, and is analogous to triacid metallic bases, such as bismuth hy- droxide (Bi(0H)3). It forms three series of ethereal salts, in which one, two, and three hydroxyls respectively are replaced by acid radicals ; e.g., C3H5(OH)2.N03, 03H5(OH).(]SrO3)2, and C3H6(N03)3, the three nitrates of glyv^erine. The latter, trinitrate of glycerine^ is com- monly called nitro-glycerine, and is prepared by the ac- tion of a mixture of concentrated nitric and sulphuric acids on cooled glycerine. When the resulting liquid is poured into water, nitro-glycerine separates out as a heavy oil : C3H5(0H), -f 3HNO3 = C3H5(N03)3 + 3H2O. Dynamite is made by absorbing glycerine in a porous siliceous sand. It is less dangerously explosive than nitro-glycerine, — On account of its attraction fc-r mois- ture, glycerine is valuable in surgery as an emollient. 214 LACTIC ACID. It is also used for preserving fruits, for making copying ink, and as a lubricator. Impurities, — Glycerine is often adulterated with cane sugar and glucose. To detect cane sugar, dissolve iii water, add a few drops of sulphuric acid, and evaporate on the water bath. If cane sugar is present it is black- ened. To detect glucose, heat with solution of caustic soda. If glucose is present the solution turns brown. (Try with samples of glycerine.) Glycerine should be neutral to litmus. Owing to imperfect purification it sometimes contains acids. Test. — 1. If a liquid containing glycerine be made slightly alkaline with caustic soda, a borax bead dipped in it will give a green colour to the Bunsen flame. 2. Heat a little glycerine with concentrated sulphuric acid, and note the smell of acrolein. 178. Hydroxy- Acids. — There are organic acids, the molecules of which have alcoholic hydroxyl. They partake of the nature of both alcohols and acids, but the acid properties predominate. They are called hydroxy- acids. Thus, hydroxy-acetic acid has the formula CHjOH.COOH. There may be two hydroxy Is in the molecule, as in the case of tartaric acid, which is dihy- droxy-succinic acid. 188. Lactic Acid, C2H4OH-COOH.— This is hy- droxy-propionic acid. Ordinary lactic is formed by fer- mentation of milk, which contains a fermentable sugar (galactose). It is present in the gastric juice, and in pickled cabbage and cucumber. It is generally prepared by the lactic fermentation of cane sugar, by means of putrid cheese. Zinc carbonate is added to neutralise the TARTARIC ACID. 216 acid as fast as it is formed. — It is a monobasic acid. Ferrous lactate (Fe( 031X503)2) is prepared by dissolving iron filings in warm dilute lactic acid. It is used in medicine. 189. Tartaric Acid, QJ^^O^. — This is dihydroxy- ... . ^ , ^ , . CH.OH— COOH succinic acid, and its expanded formula is I CH.OH— COOil It is at the same time a diabasic acid and a diacid alcohol. There are three isomeric tartaric acids, and our chemical theory is inadequate to explain their isomerism. Ordinary tartaric acid is found in the juice of grapes, berries of the mountain ash, cucumbers, potatoes, &c. Ppeparation. — From tartar or argol, which is impure potassic hydric tartrate deposited in wine casks and vats during fermentation. (It is less soluble in alcohol than in water.) From this salt, purified by crystallisation, the acid is prepared as follows : " Boil 45 oz. cream of tartar (potassic hydric tartrate) with two gals, water; add 12| oz. prepared chalk gradually, stirring constantly: 2KHT + CaCOs = KgT + CaT + H2O + COj. (T = C4H4O6.) Then add 13J oz. calcic chloride in 2 pints of water : K2T + CaCla = Caf + 2KC1. Allow the calcic tartrate to subside, pour off the liquid (What does it contain?), wash the precipitate with dis- tilled water until tasteless, and pour on it 1 3 fluid ounces sulphuric acid diluted with 3 pints of water. Boil for half an hour and filter : CaT + HaSO^ = OaSO^ + HaT. J16 8EIDLITK POWDEH. £yapor>>/^e the filtrate at a gentle heat to specific weight 1.21, allc to cool, and Bepa''ate the deposited gypsum (CaS04,2H.jO). Again evaporate till a film forms ou the surface, cool, and drain the crystals of tartaric acid which form." (B.P.) (Potassic hydric tartrate is spar- ingly soluble, the normal tartrate quite soluble, calcic tartrate insoluble in water. Explain the steps of the above process). Properties. — Large colourless crystals or a white granular powder, of acid taste, soluble in water (2 parts in 1 of water), and in alcohol, but not in ether. Experiment 168. — Examine the appearance and tawte of a crystal of the acid, then heat on mica. It browns and chars with the smell of burning sugar ; with a stronger heat it burns away completely. Experiment 169. — Carefully add solution of tartaric acid to some solution of potassic carbonate (coloured with litmus) until the solution is neutral. (What salt is present ?) Then add more tartaric acid, stirring all the time with a glass rod. A white granular precipitate of the acid tartrate forms. (Write equations. ) Experiment 170. — To a strong solution of hot sodic car- bonate in a porcelain basin add, a little at a time, cream of tartar (7 .HT) until it causes no eflfervescence. Evaporate to crystalhsation. Sodie potassic tartrate, or Hochelle salt (KNaT), is formed : Na.CO, 4- 2KHf = 2KNaT + HaO + CO, Rochelle salt is one ingredient of seidlitz powder. The blue paper contains usually 3 parts Rochelle salt and 1 part sodic hydric carbonate; and the white, 1 part tar- taric acid. When ihe solutions are mixed the tartaric TARTAR EMETIC. 217 acid decomposes the carbonate, while the Kochelle salt takes no part in the action : 2NaHC0, + Haf - NajT + 2H3O + 2C0a. (From this equation calculate the proportions of car- bonate and acid which must be used in order that there may be excess of neither.) Tartar Emetic is antimonyl potasaic tartrate (SbO.K.T), prepared by boiling cream of tartar with antimony trioxide : feoaOg + 2KHT = 2SbOKf + BjO. The radical antimonyl (SbO) acts the part of a monad metal. Tests. — 1 . To neutral solution of a tartrate add calcic chlo- ride or to a solution of tartaric acid add lime water ; calcic tar- trate (CaT) is precipitated. Wash the precipitate on a filter, break the filter, wash the precipitate into at. t., and add sodic hydroxide ; the precipitate dissolves. 2. To tartaric acid or solution of a tartrate add acetic acid and potasaic acetate and stir. Fotassic hydric tartrate ib pre- cipitated as a white granular powder. 3. Tartaric acid or tartrates in solution, when heated with a considerable proportion of concentrated sulphuric acid, turn brown or black at once. 4. To neutral or alkaline solution of a tartrate add a few drops of potassic permanganate solution, and heat, The colour disappears. Note. — Solution of tartaric acid in water undergoes slow decomposition owing to the growth of a fungus. Spirits of wine prevent this. 218 CITRIC ACID. 190. Citric Acid, CgHgO^.Hp. This is a tribasic ( COOH acid and monacid alcohol, C3H4.OH \ cooH. It is found in the juices of limes, lemons, currants, raspberries, gooseberries, .f>^y The saccharoses seem to be analogous to ethers — they all unite with water to form, glucoses ; CANE SUGAR. 221 (Compare this with the relation of ethyl ether to ethyl alcohol.) This takes place under the influence of fer- ments, and by boiling with dilute acids or alkalis. 1. Cane Sugar (Gi;rilI16Ilt 187. — Dissolve a piece of filter paper in a little >ig sulphuric acid, dilute, boil for some time, and test with . ehling's solution. Gun-cotton, pyroxylin, or nitro-cellulost, is the trinitrate of cellulote, CoHyOaCNOaJj, prepared by the action of a mixture of concentrated sulphuric and nitric acids on cotton or wood. It is very explosive, containing as it does an oxidisable and ai) QUESTIONS AND EXERCISES. 231 oxidising part. (Explain). — Celluloid is a preparation of nitrates of cellulose and camphor, prepared by a method similar to that for gun-cotton. It softens when heated and can l)e moulded into any shape. — Collodion is a solution in alcohol and ether of nitrates of cellulose. It is used in photography. QUESTIONS AND EXERCISES. 1. Compare carbon dioxide and carbon bisulphide, as to their compounds. 2. What causes the eflfervescence of soda water ? 3. How would you prove by an experiment that carbon di- oxide is formed by the burning of a candle ? 4. Show that most of our materials for fires and lights are from a vegetable source. ' 5. Write graphic formula for acetylene (C2H2). \\^ith how many atoms of chlorine would you expect its molecule to com- bine ? 6. Show how green vitriol, ferric chloride, and sodic carbonate may be usei as an antidote to poisonous cyanides. 7. Accou nt for the smell of ammonia about stables and water closets. 8. A quantity of urine (70 c. c.) is decomposed by sodic hypo- bromite, and yields 8 c. c. of nitrogen. How riany grains of urea per gallon ? 9. Write formulas for methyl nitrate, sulphate, and ortho- phosphate ; and for ethyl bromide, acid suipJiafe, and sulphite. 10. What is the practical distinction between primary, secondary, and tertiary alcohols ? 11. Calculate the specific weight of ether vapour (air = 1). 12. Given zincic carbonate and acetic acid, prepare zincic acetate. Try it practically. 13. What chemical actions accompany the souring of milk ? 14. What is " invert sugar " ? Why so called ? 15. Why is toast more easily digested than bread ? 232 COAL TAR. CHAPTER XIV. CARBON AND ITS COMPOUNDS (Coxcluded). 199. Ooal Tar. — About thirty years ago coal tar was an offensive waste product of gas manufacture, and the problem was how to get rid of it. To-day it is the pubstance for which the coal is distilled in many fac- oories ; and the gas manufacturers regard it as one of the chief sources of their revenue. This change is due to the discovery of the aniline dyes, the raw materials for their manufacture being obtained from coal tar. — The tarry liquid which collects in the condensers of the gas- works is redistilled fractionally. There distils over fii-st a light oil which floats on water ; this contains benzene (CgHg), toluene (CyHg), carbolic acid (CgH^O), &c. Later there distils a heavy oil containing xylene (CgHio), mesitylene (C9H12), cymene (CiqHi^), naphthalene, anthra- cene, &c. 200. The Benzene, or Aromatic, Series.— We have already studied unsaturated hydrocarbons, such as ethylene and acetylene, the marked characteristic of which is the readiness with which they combine with such substances as chlorine to form saturated compounds. The benzene compounds are unsaturated as far as their composition goes, but they are characterised by the difficulty with which anything is added to their mole- qules. They yield substitution^ rather than addition, BENZENE. 233 products, and in this respect resemble saturated hydro- carbons. The chiof members of the series are ab follows : Boiling ■ ' points. Benzene, CqH^ 81° Toluene, CyHg Ill Xylenes (3 isomers), C 8 Hi about 140 TMesitylene ] 163 ^ Pseudocumene VC9H12 151 I^Cumene J 166 201. Benzene (Benzol). — CgHfi. Preparation. — From the light oil of coal tar. This is washed first with caustic soda solution to dissolve out carbolic acid and other acid impurities, and afterwards with dilute sulphuric acid to remove basic substances. It is then distilled fractionally, and the part coming over between 80° and 90° is used for the preparation of benzene. — It can also be prepared by heating benzols acid with lime : . CeHs.COOH + CaO = C^B.^ + CaCO 3' This method is analogous to that for the preparation of methane. Properties. — A colourless liquid of specific weight 0.89. It boils at 80".5, and has a pleasant aromatic odour. It burns with a brightly luminous flame. Experiment 188. — Pour a little benzene into a basin of water and set fire to it. Ezperimont 189. — Pour a few drops of benzene into a t. t. of water heated nearly tc the boiling point. Observe that the benzene boils. Benzene is solid at 0°C. — It is a good solvent for fats, 234 BENZOL BINO. oils, and resins. — When benzene is acted on by chlorine, substitution products are formed. There is only one monochlor-benzene (CgHgCl). If the atoms of carbon in the molecule were connected as they are supposed to be in the hydrocarbons already studied, we should expect the hydrogen atoms to be diflferently situated and thus to permit the formation of isomeric derivatives by the replacement of the hydrogen atoms. Now mono- chlor-benzene has been prepared in a variety of ways, some of which lead to the conclusion that different hydrogen atoms have been replaced by chlorine ; but the products are identical. It is plain, then that the six hydrogen atoms are similarly situated in the mole- cule. Kekul^, of Bonn, has devised a structural for- mula showing this. It is called the benzol ring, and although it only pictures an hypothesis, yet it has proved a powerful lever in the hands of experimenters. (6)H h(1) I I c c / \ (5) H— C C— H (2) c c (4)H H(3) The molecule is represented as being symmetrical, each carbon atom being united to a hydrogen atom, to another carbon atom by a single bond, and to a third by a double bond. (Study this formula, and observe that the hydro- gen atoms are represented as similarly situated.) When two hydrogen atoms of the benzene molecule SUBSTITUTION PRODUCTS. 235 are replaced, three isomevic di-suhstitution products are formed. If the hydrogen atoms represented in the above formula be numbered consecutively from 1 to 6, it is easily seen that (2) and (6) are similarly situated with regard to (I), so that replacing (1) and (2) with, say, Cl's, gives the same formula as is obtained by re- placing (I) and (6). In the same manner (3) and (5) are similarly situated; but, with regard to (1), (4) is differently situated from (2), (3), (5), or (6). Only three different formulas of di- substitution products are possible, and this result is in accordance with the facts. By a oeries of beautiful experimental investigations, the relative positions of the substituted atoms have been determined, and names have been assigned accordingly. Thus (1) (2) (or (1) (6))'di-substitution products are called ortho, e.g., ortho-dichlorbenzene ; (1), (3) products are called meta, and (1), (4) para. 202. Nitro - substitution Products. — When strong nitric acid acts on benzene, one or more of the hydrogen atoms are replaced by the monad radical — NOj [nitroxyl). Thus : (1) CeHe + HNO3 = CeH^.NOa + H,0. (2) CeHe + 2HNO3 = CeH,.(N02)2 + m^O. Only one mononitrohenzene is known, but three isomeric diniti'ohenzenes have been obtained. (How many tri- nitrohenzenes are possible according to theory 1) MoNONiTROBENZENE (CgHg.NOj) is manufactured on the large scale in the preparation of aniline (CgHg.NHj). It is a yellow, oily liquid smelling like oil of bitter almonds. It is often sold as " artificial essence of mir- 236 ANILINE. bane," or "artificial oil of bitter almonds ; " but as it is poisonous and different in its physiological action from the true oil, it should never be used in medicine in place of the true oil. — Mononitrobenzene boils at 205° C. Its specific weight is 1.2. It is insoluble in water. By the action of nascent hydrogen it is reduced to aniline (CeH5.NH,) : CeH^.NOa + SH^ = CeHg.NH^ + 2H2O Nitrobenzene is used to perfume cheap soaps and confec- tionery, as well as in the manufacture of aniline. It is sometimes mixed with oil of bitter almonds as an adulteration. Its presence can be detected by reducing to aniline by means of zinc and hydrochloric acid, and then treating with filtered solution of bleaching powder, with which aniline forms a beautiful purple colour. Experiment 190- — Mix a few drops of benzene with a little concentrated nitric acid. Warm very gently and note the smell of nitrobenzene. 203. Aniline (Phenylamine). — C6H5.NH2. Was first prepared from indigo [anil). It is found in small quantities in coal tar, wood tar, and bone oil. Preparation.— By the action of nascent hydrogen on mononitrobenzene. The hydrogen is evolved from iron and acetic or hydrochloric aoid. (Write the equations). Properties. — Aniline is a colourless liquid of specific weight 1.036. It boils at 184°.5. It is soluble in 31 times its weight of water, and the solution has p weak alkaline reaction. It is more freely soluble in alcohol. — Aniline unites with acids to form salts : CeHg.NHa + HCl = CeHg.NHaCl. Compare with NH3 + HCl = NH^Cl. CARBOLIC ACID. 237 Aniline is a substituted ammonia, or amine, of the aroma- tic series. Commercial aniline always contains toluidine (CyHy.NHa^ a higher member of the same series; and, when it is oxidised by means of arsenic acid or potassic chlorate, the beautiful colour rosaniline (Q.^^■^^^.^ is formed This is the first of the aniline dyes, the dis- covery and manufacture of which have revolutionised tlie dyer's art. They are comparatively innocuous when pure, but arsenic acid is used in their manufacture, and through carelessness or ignorance it is sometimes imper- fectly separated. Tests. — 1. To an aqueous solution of aniline add some tiltered solution of bleaching powder. A purple colour results. 2, Dissolve a drop of aniline in strong sulphuric acid. (What is formed ?) Stir in a porcelain dish with a drop of potassic bichro- , mate solution (KaCrgOy). A blue colour is produced. 204. Carbolic Acid (Phenol). — Q.U^.OYL. This is in reality a tertiary alcohol, but it has very weak acid properties. — It is found in small quantities in urine. It is a product of the distillation of wood, coal, bones, &c. Preparation. — From the heavy oil of coal tar. This is treated with caustic soda solution, which dissolves the carbolic acid, forming sodic carbolate, or phenolate, (CgHg.ONa). The solution forms a layer separate fiom the oil. It is decanted, and is then decomposed by hy- . « drochloric acid : CoHs.ONa + HCl = CeHg.OH + NaCI. ' The carbolic acid is purified by distillation. Properties. — A colourless, crystalline solid, crystal- lising in long needles. It has a strong, somewhat tarry smell, not unpleasant when the carbolic acid is pure. It 238 CREOSOTE. melts at 35°, and boils at 180^ It is dehquesconfc, uniting with a small proportion of water to form a liquid. This liquid is sparingly soluble in water (1 in 15), but mixes with ether and alcohol in all proportions. Experiment 191. — To a little solid carbolic acid add a drop or two of water. They combine to form an oily liquid. Add a little more water. The two do not mix. (Which is tlie heavier?) JSow add much water, and the carbolic acid dis- solves. Note taste and smell of this Hquid. It is very poisonous, and the strong solution burns the skin. It has a burning taste. The antidotes are olive oil, castor oil, and a mixture of slaked lime witn 3 times its weight of sugar, rubbed up with a little water. — Carbolic acid is extensively used as an antiseptic in surgery, &c. It was introduced into general use by Lister, of Edinburgh, who devised a system by which surgical operations were carried on in an atmosphere containing no living putrefactive germs. The antiseptic spray was combined with a minute cleanliness hitherto unknown in surgery, and in all probability to this is due in a great measure the success of Listerism. t Test. — Mix the liquid with one-fourth its volume of am- monia solution and add a few drops of clear bleaching powder solution. The merest trace of carbolic acid will cause a blue colour to appear. 205. Creosote. — Pure creosote is obtained by distil- ing beech and other hard woods. It consists mostly of is- omeric cresolsy CgH^"^^^. It resembles carbolic acid in smell and taste. Carbolic acid is often sold as creosote ; and the so-called " coal-tar creosote " is merely impure carbolic acid. PICRIC ACID. 239 To distinguish carbolic acid from creosote : 1. Dissolve in glycerine and add water. Carbolic acid remains dissolved. Creosote is precipitated by the water. 2. Add to the liquid to be tested alcoholic solution of ferric chloride. Carbolic acid gives a brown colour ; creosote, green. 3. With aqueous ferric chlorid*^, carbolic acid turns blue ; creosote is unchanged. 206. Picric Acid ( Trinitrophenol, or Carbazotic Acid).—C,li,{OB.).(NO,),. Preparation. — Experiment 192. — Dissolve some carbolic acid in dilute nitric acid and add drop by drop about half the volume of strong nitric acid. Dilute with cold water, and picric acid is precipitated. Properties. — A yellow crystalline solid sparingly soluble in cold, easily in hot water, and in alcohol or ether. It has a bitter taste and is poisonous. It explodes when heated rapidly. Amnionic picrate (NH^.CgHaNgO;) is used as an explosive. Picric acid has strong colouring power, and is a good dye for silk and wool. 207. Benzylic Alcohol— CeHg.CHaOH. — Found in balsam of Tolu and Peru, and in storax, as ethereal salts of benzoic and cinnamic acids. When oxidised it gives first benzoic aldehyde (CeHg.COH), and then benzoic acid (CgHg.COOH). 208. Benzoic Aldehyde.--CeH6.C=0. A com- ponent of amygdalin, a glucoside found in bitter 240 BITTER ALMOND-OIL. almonds, in laurel leaves, cherry kernels, io OaO + C.H.(COOH).=Ca003 + o,H.COOH «o *he cooler part, of the tubo" ttotlrf'"^'^ "^^""^ PilOPERTIES - A v.* tahery needles, of arlllrdot\^^^^^^^ scales or It dissolves easily in alcohol. ' at 121^ c. Experiment 194— Tr^f^ J. , ;-« quantity of wator^H j Tie? ! «'"» •'-«'i'= -M in a T^»t with htn>ns. Heat a stju „ ^ '? ^"""^ 'he solution ■"■oa. "nd inhale the fuaea J"''*"''' »* henzoio acid on Benzoates R -e mostly solubler wltef " "°"°'"'"<'' =">" '^^ »alta Experiment IQfJ— p«i^ porcelain dish witriit^n "7" Vt«™ »' '■"monia i„ a 242 SACCHARINE. crystals of amnionic benzoate (NH^.C^HjOj) are left. It is necessary to add a little ammonia from time to time during evaporation so as to keep the solution alkaline. When salts of ammonia are evaporating a little ammonia always escapes. Animonic benzoate is used in medicine. When taken into the system it is eliminated in the urine as hippuric acid, rendering the urine strongly acid. — Sodic benzoate (Na.CyHgOa) can be prepared in the same way as am- monic benzoate. It is used as a medicine. Experiment 196. — Dissolve in a little water the ammonic benzoate prepared in Experiment 195. To a small portion of the solution add dilute hydrochloric acid. Benzoic acid is pre- cipitated. To another portion add neutral solution of ferric chloride. Ferric benzoate (Fe.^Bzg) is precipitated. Examine it carefully, noting its colour, &c. Tests. — See last experiment. * 210. Saccharine. CeH^ZgQ ^NH. {Benzoyl sul- phonic imide. — This substance is related to benzoic acid. Benzosidphonic acid has the formula CJjH^HgQ ^g. If the two hydroxyls are replaced by the dyad radical =NH, the formula for saccharine is obtained. — This re- markable substance was discovered a few months ago by Dr. Fahlberg, Properties. — A white crystalline solid, " 220 times as sweet as cane-sugar." It has antiseptic properties, and is said to be harmless when taken into the system, passing away in the urine unchanged. It is difficultly soluble in cold water, more freely in hot water, in alco- hol, and in ether. It is proposed to use it instead of cane-sugar in cases of diabetes mellitus. dALLW ACID wijitergreen." It j. ^ ^^H ''), or " oil of «" - •>, the oxidHt.ro'rzr '™"' '-"■•''°'- -"•. - monobasic acid, p„„«,f,.,, ~./ gl"eosule._^^ i, „ -Pecta to carbolic acid,C: 'r' ""'!"■'"''<' '" --o "ssoes. ' ""S "ot so injurions to the 212. Gallic Acid /-T^-i , K various barks, ic. «'"'°'*''''' *» oak-galls, Preparation —Fm listened with water"" T,T' "'''«" "- Powdered. ^'■egaliic acid is then di so v :~' A"^- « -«'^^' P«oPERT,t-s._A ]i<,hf . * """'""S ^»t<"-. dissolves in joo p,,,f ', J^f ' 7»tellme solid. It >'''"<"•; it is f,.eely soln.l ' '' '" ^ ?"■•'» of hot ^'Kerineand in etir"Si- ^^ -« ^P-'ngl, t' ^«3ts.-,. With . ■ K """"'""•" ""'"• "-k precipitate, .olallrjif ^<= """''"^ " «<- a Mue- ^•"<.oe.„otc„.,,.,3„,„ti„„,,,,^^„^^^_.^^^^ . 213. Tannic Acid n tt ^ ««• . *'•* of gallic acid, !id Us :^'"^V .'""' " - ««%- "^^-''^o -id b, ti. subsi^:?: ::r r ^™"' '^' o,„. ^ nioJecuIe of water • 90 TT rx Tannic acid. ^C'HeO, - H,0 = c,,H, O ^PREPARATION -Fr -'- 3 or 4 da,s andThef 'xt^rtf "' ^'"^■"^ «'- » ^^fci'tcfcing witli ether. 244 TERPEN ES. pROPKKTiES. — A white or yellowish solid, of acid, astringent taste, soluble in water, and in a nuxtiire of water with alcohol or ether. — Tanidyi is the glucoside, present in oak-galls, «'ieon seems able to replace cIX„! ^ '^^'" '^"•^'- "'"' "'■■'»y organic compound, •'' ""'•''''" "^'o-'t in 232. Silicon Dioxide _^,n ".":' '^''h'lrous sUicic acid T • '^''° """'"' "««, silicon knoH-a. ' ^' '^ «'« only oxi.le of «»'. J-per, cbalceC diatl " '?"'" ^^"''' '^''^<- ^«"- Uniee. with L : S oT ' f r "" '- ''- *o «.-eat .iWson of minerals, S i~' ^'-'^ ^orms -TilOPERTlES .P 'mating .*V«'«oJ";HroT-r' ft'' "'"-'-'"' by »'«oh,ble in water and in : ,' \ ''«■"' ^^^ Powder^ («^)- /^ « easily i ,:^' Xr ""''' '^''"•^'"'- ft decomposes sodic carbonatf k'' "'"'" '" """"onia. -- dissolved in water rsoli^'V''^^'^'' "''' '' ■■■'loa are used in glass and ,0 "°"' ^orms of -H- and cemenl; o, ;e,„rr"f"*""' '" ""-"^ '--- pestles used if t:LSingt::tiS;- 000 rM.,. . 233. Silicic Acid and Silicates. Experiment 206.-Fnse a litti , 258 SlLIClC ACID. weight of anhydrous sodic carbonate (Na.^COg). Coutinue heating tintil a clear li(|uid is obtained. Pour this out on a piece of clean iron, and, when it has cooled, break it up and dis' solve it iu water by boiling for some time. Tn tliis oxperiment ftodic silicate (NsiySiO.,) is formed : NaaCOg + SiOj = NaaSiO^ -f CO2. (Have you observed the escape of the carbon dioxide 1) Experiment 207. — To a little of the solution of sodic silicate add dilute hydrochloric acid ; collect the gelatinous precipitate on a filter and wash it with hot water. It is silicic acid. Heat a little of it on mica and obtain silica. Try the solubility of silicic acid iu alkalis, and in acids. Write the equation for the de- composition of sodic silicate by hydrochloric acid. Silicic acid has not been obtained of any definite com- position free from water. There are numerous classes of silicates, corresponding to a great number of theoretical acids; e.g., ortho-silicates, salts of an acid, H^SiO^; and meta-silicates, from HoSiOa. — Silicic acid is insoluble in water, but an unstable solution, which easily gelatinises, can be obtained by careful manipulation (compare dia- lysed iron). — The silicates of the alkalis are soluble in water (soluble glass) ; all other silicates are insoluble. Mica, felspar, garnet, serpentine, and clays, are exam})les of natural silicates. Felspar is a double silicate of aluminium and potassium. By the action of air and water it is decomposed into potassic carbonate and hy- drated aluminium silicate, or clay. In this way a fertile soil is gradually formed by the " weathering" of felspar.— The silicates are most conveniently represented as com- posed of oxides of metals united with one or more mole- cules of silica, e.g., Na-P.SiOa, 3Mg0.2SiO.^, &c. ""- "f silict.,. ,f the'.;, t- r^'"';"'', '--Pi'-.te wit,, ,„,„. ''^' '"»'«! for. " "'■"•"'J' «i'l. "ilica nee.l not 234. Fluosilicic Acid.-H,8iF, ;''h about t..o;t,S"r;,tf!rr^'"'"" '^'■■'^ -" ' Wio mixture i„ a t. t. or (Usk '^7"'-'^'''' ./''""• »/«»■ (Oap , ,, --it. a„„ .nunciatei/t;^;--;- strong -■•"■urL „! » t; t. h»lf-full of water. h1 I ^"^ """ '''l'P"'« '"to :7'r"' '""•'"- through the : Lr: ^- , ^"."'vi^iwo t-... i, 3..i«ta„eo. Collect s,„„e of this a^ '1,™* ' """'"' " ""''y "''ito ;;■' to « li«l.t white „„waer. U^J^^ "V" '"""• ^' ''"- the water.-The .lelivery tube In Tl "" "" ■''''"•tion of experiment must then eea,,e. "°°'"°' °'"'''«' "P. »...! the Jn tins ex|>eri,„ent, three chemical -.cti . , - -presented b, the following e^'uiC '' ''''""' 2 t^abO, + 2HF. Silicon (2)4HF + sio *«*^"";--ie. OrthoHilcic pi„ .... /Qj Qcj-n . acid *'»').silicie (^; 3S1F4 + 4H2O = H 4^ . "'"'• ■' . the end „f th„ experi,ne u « - b1 «r"" "'^ "'"^ »■'- acid, ablution of ..osiJLcS^i^ilir"- "itOPERTfES -A f Ao«W., a're soluble i"ln?'t "''• *^°^' "^ *« (K=siF,, and wi::.r;; ;;~/«- I ^aoii^ ^ ) are only sparingly '260 BORON — nonic ^cin. soluble. For this reason fluoKilicic acid is used to sepa- rate these metals froui others present v/ith them in solu- tions. — i'Y^^osilicic acid is silicic acid with fluorine instead of oxygen^ 6 atoms of fluorine replacing 3 of oxygen. 235. Boron (B'» = 11).— The chief compound; of this element occurring in nature are borax {N'a,.J^^O^. ICH.^O), and boric, or boracic, acid (H^BOg). Borax is found principally' in the plains of Thibet, and in the borax lakes of California. Eerie acid issues along with steam from fissures in the sides of volcanic hills in Tus- cany. — The element, boron, is of little importance. It can be pre}>ared by methods similar to those used in the preparation of silicon, which element it resembles in its properties. 236. Boric Acid. — H3BO3. Derived from the la- goons of Tuscany, into whicli tiie boric acid comes from volcanic fissures or from holes bored for the purpose. Prkparation. — The water of these lagoons is evapo- rated by the heat of the steam which issues from the earth, until tiie acid crystallises out. The crystals are collected, dried, and purified by recrystallisation. Before tJie discovery of the presence of borio acid in the Tuscan lagoons, it was prepared fr&dti borax, by treating a hot saturated solution with strong hydrochloric acid. T^e boric acid crystallised out on cooling : iNaaB^O^ 4 2HC1 -j- 6H2O - 2NdCl -j- 4H3BO3. Since tli*- discovery ol' the borax lakes of California, buiic ac'l is again made in this way . BORAX. 261 ■txperiment 209— Dissn]u» a P<>.-cdaiu ,lish a.ul set (ire t„ it I 'f »'™l""'c mhM.m i„to fame Boric .aci,, volatilise., with aklt, '^''•°" "'""'"' "' "«' t"e hot flame. i,„parti„g the 1" , ' "'"' '" ''"-"I"«-l in ^.ueous solution, an., tr/its actfor; hi;;:",;::;'- -"""'= ""• r-entad a. co,„pou,.cI« of" r^""' V "" '"' ■"■ «'io«*, e.g., 3Mg0.4B.,0.. ''^''''''' ^'"^ *<"«» "".s the borax of co:n„,erce !!^ 'I '"'"''• ^™'" «™-oH,,ofg.e.j;zrre:r;2:r""7^ 4H3BO3 + Na^CO, = N. R n . -TROPERTIES.— Bor V -o ^ ::--"••- -,.io.n. ,,,- ^---. J 262 TESTS FOR BORIC ACID. Experiment 212. — Heat a small piece of borax in a dry t. t. Water condtMi.ses in the tube (Whence has it come?), and the borax swells up. Heat a little borax on a platinum wire, until it fuses to a clear bead, then allow it to cool, moisten it, touch it to some powdered cupric sulphate, fuse it again, and note the colour when it has cooled. When borax is heated, it loses its water of crystallisa- tion, and, if tlie temperature is high enough, fuses to a clear liquid. At high temperatures the borax bead dis- solves metallic compounds, forming borates which give characteristic colours to the beads. Borax is used in this way to test small quantities of solid substances. — Borax is soluble in glycerine;, and a glycerine of borax is used as a lotion and gargle. Tests for Boric Acid and Borates.— 1. Mix the sub- stance with strong sulphuric acid and alcohol in a porcelain dish, and set the alcohol on fire. It burns with a green Hame. Or, fuse some of the substance on a platinum wire, moisten it with strong sulphuric acid or glycerine, and hoM it in the Bunsen flame. It gives a green colour to the flame. 2. Acidify the solution with hydrochloric acid, dip in it a strip of turmeric jyaptr, and dry the paper at a gentle heat. It is turned brown. 3. Add a few drops of ])aric chloride (BaCla) to a solution of a borate. A white precipitate is formed. It is ,olubI'> in hydrochloric acid. QUESTIONS AND EXERCISES. 1. Compare silicon and carbon, (a) with regard to chemical, and (b) with regard to physical, properties. 2. What is soluble glass ? 3. Explain the term jlnosilicic, acid. 4. Balance the following ecpiation : K.,SiFe + Al = KF + A1.,F., + Si. - METALS. 263 5. It is found that alkaline solutions eat away glass. Explain. 6. Mention an acid and a base which will dissolve sand. 7. How can it be proved that silica is an acid-forming oxide ? 8. With what does the delivery- tube become choked up in Experiment 208 ? 9. Boric acid (H3BO3) is tribasic. Write the formula for normal sodic borate. Is this the ordinary salt ? 10. Borax is an acid salt, and yet its solution is alkaline. Account for this. 11. How can borax be used to test for glycerine ? 12. In the preparation of boric acid from borax, sodic chloride is formed. How is the boric acid separated from it ? CHAPTER XVI. THE METALS. 238. General Ohaiacters. -Tho only charactei- istic common to all metals is the power of taking the place of the hydrogen of acids to form salts, or in otlier words, the power of forming bases. But most metals have a bright and peculiar appearance called metallic lustre ; as a rule, they are specifiically heavier than water ; they are good conductors of heat and electricity ; and most of them are malleable and ductile. 239. Ores of Metals. — The noble metals (i.e., the least oxidisable) are generally found uncombincd (native) ; native copper also occurs. Sometimes the baser metals are found free ; but in most cases they occur combined with other elements, from which they are separated by the processes of metallurgy. Common metals such as lead, iron, tin, ikc, are found very gener- 2G4 METALLURGY. ally as sulphides and oxides. In many cases salts of the metals are found in nature. If the metals of the alkalis be excepted, it may be stated as a general rule tliat metallic ores are insoluble in water. — The processes by which metals are obtained from tlieir ores are various. A common way, applicable to oxides and some oxygen salts, is to heat to a high temperature with some form of carbon (coal, charcoal, &c.). In many cases sulphides are first roasted to convert them into oxides, and then reduced by means of coal or charcoal. In other cases sul[)hides are partially oxidised at a comparatively low temperature, and then heated to a higher temperature, at which the oxygen and remaining sulphur combine, set- ting the metal free. Lead and copper aie obtained in this way : (1) PbS + 30 = PbO + SO2. (2) PbS -f- 2PbO = 3Pb + SO2. 1. Metals reduced by heating the ores with coal, char- coal, &c. : Na, K, Rb, Sn, Cd, Zn, Fe, Mn, Sb, Cr, Ni. 2. By pa7'tial oxidation arid subsequent Jusiori : PI), Cu, Bi. 3. By heating with sodium or potassium : A), Mg, Ca, Be. 4. By electrolysis of fused salts : Ba, Ca, Sr, Li, Cs. 5. By distilling in a current of air : Hg. G. Native : Cu, Ag, Au, Pt, Hg, &c. This is only a general statement, and not intended to be exhaustive. 240. Alloys. — Metals usually combine with eacli other when fused together. In many cases the combina- ALLOYS. 265 tion takes place in definite proportions, and chemical com- pounds are formed. In other cases, the proportions may be varied, and it is not easy to decide whether or not there is any chemical action. Compounds of metals with each other are called alloys. The properties of alloys are not the mean between those of the metals present. Alloys generally melt at lower temperatures than any of the constituents. Thus, Rose's fusible metal (tin, 1 [)art ; lead, 1 part; and bismuth, 2 partS) melts at 1)5° C. ; while tin melts at 235°, lead at 334°, and bismuth at 270°. Many alloys are in common use, e.g. Solder, tin and lead in various [)roportions. « Brass, 65 parts zinc, and 137 parts coppcu-. Gold coin, 1 1 parts gold and 1 part copper. Silver coin, 40 parts silver and 3 parts copper. Gun metal, 9 parts copper and I part tin. Bell metal, 4 parts copper and 1 i)art tin. Type metal, 4 parts lead and I part antimony. Briti rmia jnetal, copper, zinc, tin, antimony. Pewter, 4 parts tin, and 1 part lead. Bronze, tin, copper, and zinc. German silver, 5 parts copper, 2 parts nickel, and 2 })arts zinc. Wood's fusible metal (melting at G8°), 8 parts lead, 5 [)arts bismuth, 4 parts tin, and 3 parts cadmium. Amalgams are alloys of mercury with other metals. 241. Compounds of Metals.— The compounds of metals are classified into (1) binarif compounds, including oxides, sulphides, chlorides, bromides, iodides, fluorides. 266 OXIDES OP METALS. (fee. (Note the ending — ide) ; and (2) oxygen salts, ttc, such as sulphates, sulphites, nitrates, phosphates, : — Li.^O, NaaO, KgO, Rb.^O, Cs^O ; Ag,0, Hg,0, Cu^O ; Tl^O, Au,0. . (b) General formula MO ;— CaO, SrO, BaO ; PbO, HgO, CuO, SnO; FeO, MnO, ZnO, NiO, CoO, CrO ; PtO, &c. (c) General formula M.fin, : — Sb.^Og, Bi.^Og, Au^Oj, Tl,03; FeA, AlA, Mn.Og, Co A, ^^r.p.,. This includes nearly all the basic oxides (the rarer metals being left out of consideration). — It will be observed that some metals have more than one basic oxide. Some dyad metals (Hg, Cu) have oxides in which they seem to play the part of monad metals. There is reason to believe, however, that the molecules of the corresponding chlorides must be represented as fol- lows: HgjClj, and Cu^Cly. The metals must, then, be dyad in these compounds, and the structural formulas Hg\ Cu . for the oxides and chlorides are | O, \ ^O, and Hg— CI Cu— CI I , I . — Gold and thallium are monad and triad. Hg— CI Cu— CI Thus gold forms aurous oxide, AugO, and auric oxide, AujOg. — Iron, cobalt, and manganese, have two basic oxides, e.g. ferrous oxide, FeO, and ferric oxide, Fe,,0;,. In the lower oxides these metals are dyad. The specific OXIDES OB^ METALS. 267 weight of ferric chloride in the gaseous condition shows Fe/S tiiat its forniuhi is Fe.^Clg, or grapliicallv | >^{ . Ferric ' Fe { ci Ici Fe =0 oxide must then be represented as | ^ O, and in the Fe =0 ferric compounds iron is tetrad. So witli m^inganose, cobalt, aluminium, and cliromium, which have also basic sesquioxides. The first group of sesquioxidos, Sb.jO;), (kc, correspond to chlorides, SbCl.,, &c., so that the metals must be represented as triad, e.g. O — Sb - O - Sb = O. — There are hydroxides corresponding to most of the basic oxides. 2. Acid-forming Oxides. — The basic oxides of imper- fect metals, such as antimony, have also weak acid charac- ters ; but there are also distinct acid-forming oxides of tliese metals, e.g. antimony pentoxide, Sb.^Oj. Chromium, manganese, &c., also form acids. The acid- forming oxides always contain a greater proportion of oxygen than the basic, and, as a rule, readily give up their oxygen to reducing agents, becoming transformed to basic oxides. 3. Indifferent Oxides, — These are such oxides as manganese dioxide (MnO.^), having neither acid nor basic properties. They generally contain a greater proportion of oxygen than the basic oxides, and are hence often called joer-oxides. 243. Sulphides of Metals. — These correspond closely to the basic oxides of the metals, e. g., LigS, Na.jS, &c. The imperfect metals have sulphides corresponding to their acid-forming oxides, e. g., Sb.^8-, SnS.,, ifec. As a 268 CHLORIDES, etc. — OXYGEN SALTS. rule, wlien a basic oxido of a motal is soluble in wat(!i', the corresponding sulphide is also soluble, — and so for insolubility. Thus, both the oxides and the sulphides of lithium, sodium, potassium, &r., are soluble in water. 244. Chlorides, &C. — There are chlorides corres- ponding to the basic oxides of the metals. In writing the formulas of chlorides, it must be remembered that 2 atoms of chlorine replace 1 atom of oxygen. Thus, given the formula of aluminic oxide, Al.^Og, the formula for aluitdnic chloride is written, Al^Clg. It could be written more simj)ly, AICI3, but, for reasons similar to those stated above for ferric chloride, the simpler formula is doubled. The formula for bismuth trioxide is Bi-.O^; replacing O3 by CIj, we get as the formula for the chlor- ide, Bi.,Clg, but its specific weight in the gaseous state shows that its molecule contains only half the number of atoms represented here, so that the formula for bisinuth trichloride is BiClg. 245. Oxygen Salts. — The oxygen salts of the metals have been already noticed along with the various acids. To derive the formula of an oxygen salt from the formula of an oxygen acid, it is necessary to know the atomicity of the metal, and, also, whether or not two atoms of the metal play the part of a single atom as in the case of mercurous salts (Hg._,(N03)2, tkc), and the ferric, salts (Fe.2(N03)o, tfec). For example, given the formula of sulphuric acid as H.2SO4, and knowing the at micity of calcium to be 2, it is easy to write the for- mula for calcic sulphate, viz,, CaS04. Again, bismuth is triad ; and, therefore, 1 atom of bismuth replaces 3 of liydrogon. In order to replace the hydrogen of su! ANALYSIS — PKECIPITATION. 2G9 pliiiiic Jicid by hisinuth, vo must take SPLSO^. The G iitoms of hydrogen ai( ;quivalent to 2 of bisinutli ; and, tlierefore, the formula for bismuth sulphate is Bio(S04):5. The atomicity of iron in the ferric salts is 4, but 2 atoms of iron are united in the molecules of ferric salts so that their joint atomicity is 6 ; i.e., Fe., replaces 6H. The formula for ferric sulphate is thus Fe._,(S04)3. — To many oxygen salts there are corresponding sulphur salts, e.g., K2CS3. 246. Classification of Metals — Analysis. — The method of classification to be adopted here is that which is employed in the jn'ocess of examining unknown substances to discover the elements of which they are composed. These processes constitute analysis in the broad sense of the term. The substances are not always — indeed, not generally — decomposed into their ele- ments, but such evidence is obtained as enables the ana- lyst to be certain of the presence of the elements. This is qualitative analysis. If the quantities of the elements in a compound, or the quantities of the elements and compounds in a mixture, are to be determined, this is clone by quantitative analysis. A great deal of the work in both qualitative and quantitative analysis consists in preparing insoluble compounds of the metals (and acids) by precipitation from solutions. In order to understand the operations of analysis it is necessary to know the solubilities of chemical substances. Such knowledge is also of great importance to the prescriber of medicines. A physician who is not well acquainted with this part of chemistry is very likely to produce '' muddy mixtures." Precipitation. — When two chemical compounds are brought together in solution, there is usually chemical 270 CLASSIFICATION OP METALS. action, consisting in exchange of parts of tlie molecules. If this exchange causes the formation of an insoluhle substance, the latter is precipitated, or thr'own to the bottom. Experiment 213. — Mix solutions of cupric Huliihatc. (Cu8(),) and baric chloride (BaCla). A white precipitate of Itaric ml- phate (BaSO^) falls, while cuprir chloride (CuClg) remains in solution. Such a cliemical action is called a double decomposition, because the two salts decompose each other, the metals changing places : CuSOJ _ (BaSO^ Bad, I ~ |CuCl., Group Reagents. — Insoluble compounds can gener- ally be obtained by precipitation. We have seen in studying groups of compounds, such as chlorides, sul- phides, carbonates, &c., that each group may be classified into (1) soluble, and (2) insoluble. Thus, there are three insoluble chlorides (PbCL,, AgCl, HgyCl.,), and the rest are soluble. If a complex solution containing salts of all the metals were treated with hydrochloric acid, these three chlorides would be formed and precipitated. Thus, a separation would be effected of lead, silver, and mer- cury from the rest of the metals. Hydrochloric acid is a group reagent ; and, in analysing substances, the first step is to determine by the use of group reagents to what group or groups the substances under examination belong. GROUPS OF METALS. I. Lead,* silver, and mercury (mercurows salts). Chlorides precipitated by hydrochloric acid. . * Plumbic chloride is sparingly soluble, so that lead appears in Crroups and II. QUESTIONS AND EXERCISES. 271 II. Lead, mercury (nierciiric salts), copper, cadmium, bismuth, mitimony, \avseuic\, tin, gold, platinum, and some rare metals. Siilj)hides precipitated by hydric sulphide from neutral or acid solutions. III. Iron, cJiromium, aluininium, zinc, manganese, cobalt, and nickel. Sulphides precipitated only in pre.s- ence of an alkali. Amnionic sulphide is the group re- agent. IV. Calcium, strontium, and barium. Precipitated as carbonates from solutions (in presence of amnionic chlo- rides) by amnionic carbonate. V. Magnesium. Precipitated as phosphate, by sodic phosphate. Magnesium is often included in Group IV. VI. Lithium, sodium, potassium, ammonium, rubi- dium, and ccesium. Salts mostly soluble. Groups I., II., and III., include the common metals in everyday use. They are the heavy tnetals. Group IV. is made up of the metals of the alkaline earths. Group VI. includes the metals of the alkalis. QUESTIONS AND EXERCISES. 1. Metala generally feel cooler than other substances. Why is this ? 2. What is an ore ? 3. Are alloys compounds or mixtures? 4. What class of metallic compounds does the ending -ide mark ? 5. Why write the formula for chromic chloride Cr.^Clo, and not CrClg ? 6. Mercury is a dyad metal, but it has an oxide HgjO. How is this explained ? What non-metal forms numerous compounds in the same way ? ^ A. *«)* ...%. vj ,i«. *:i> *t IMAGE EVALUATION TEST TARGET (MT-3) Jo 1? ^o ''mH^D "m 1.0 M I • * 11.25 ■am !!! Hi ■ 10 M 2.0 lA. IIIIII.6 Photographic Sciences Corporation 23 WEST MAIN STREET WEBSTER, N.Y. 14580 (716) 872-4503 iV iV <^ '^ .A ^^ V ^^^- ^1* ^^^ O^ '^^ rv <^ '/»^ 272 « METALS OF GllOUP I. » 7. Bismutli has an oxide, the formula of which is Bi^O.;. Ferric oxide is represented by Fe^O.,. The first is caJled his- tnuth trioxitlc ; the second, iron sestjuiox'uk. Is there any rea- son for this difference of momenclature ? 8. Write the formulas for the chlorides corresponding to SnO, Or^O.,, K2O, BiaOa, BaO, CuO, GuaO, Ag.,0, and AU2O3. 9. The formula for oxalic acid is H20y04. It is dibasic. Write the formulas for the normal oxalates of barium, sodip'*!, ammonium, iron (ferrous and ferric), chromium, and copper. 10. Will the groj'p reagent of Group II. precipitate the mem- bers of Group I. as sulphides '! Try. 1 1 . Have you observed any regularity in the atomicities of the groups of metals? Write the formulas for the oxides of Groups IV. and VI. CHAPTER XVII. METALS OF GROUP I. Lead, Silver, and Mercury. 247. General Characters.— The metals of this group are heavy and soft (mercury is liquid). They are easily reduced from their ores by lieating with charcoal. Their sulp/ddes are black and insohible in water and in dilute acids. The oxides are earthy compounds in- soluble in water. The chlorides (except mercuric chlo- ride), bromides, iodides, carbonates, and phosohates, are insoluble in water. . LEAD (Plumbum). 248. Lead.— (Pb"= 20G.4. Specific weight =11.352. Melting point = 334° C. Specific heat = 0.0315). The «» LEAD. 273 cliief ore of lead is galena (PbS). It is very common in Canada, occurring in crystalline masses, of a brilliant, metallic appearance. Experiment 214. — Examine a specimen of galena, noting ita colour, hardness (scratch with a knife), specific weight, &c. Mix a little of the powdered mineral with sodic carbonate, mijibten, and heat it on charcoal before the blow-pipe, or on a cliarred splinter in the reducing flame of the Bunsen burner. Extract the metallic bead, and examine it carefully as to its hardness, malleability, &c. It is lead. Galena generally contains silver, sometimes only in small traces, but often in considerable proportion. Preparation. — The galena is partially oxidised by heating in air, and then more strongly heated to set the lead free. (Art. 239). Experiment 215. — Put a piece of zinc in a solution of plum- bic acetate, and allow it to remain for some time. Pouv otF the iii^uid, dry the metal which remains, and melt it by heating it ill a closed porcelain crucible with a little charcoal dust. Ex- amine it. It is lead. Properties. — A heavy, dull metal, soft, tough, easily tarnislied. A small quantity of antimony or arsenic alloyed with it renders it hard and brittle. Lead is easily set free from compounds in solution by the action of iron, zinc, ariiigly soluble in pure water. 255. Plumbic Iodide.— Pblj. (In what experi ment has this been already formed ?) Experiment 229.— To some solution of plumbic acetate aeated sulphur baths, which convert the soluble salts into plumbic sulphide, and this can be rubbed oflf the skin. 280 SILVER. 200. Tests. 1. If the solution is not too dilute, kijd rochluric acid gives a white precipitate insoluble in a further (j[uautity of the acid and unchanged by ammonia. 2. Sulphuretted hydrogen gives a black precipitate (PbS) in- soluble in solution of ammonic sulphide, partly dissolved, partly whitened by strong nitric acid. . ■ 3. Sxdphuric acid gives a white precipitate (PbS04). 4. Potassic iodide (KI) gives a yt3llow precipitate (Pbla). 5. Potassic bichromate (K2Cr207) gives a yellow precipitate (rbCr04). 6. Insoluble compounds are detected by reducing on charcoal with sodic carbonate, dissolving tlie metallic bead in nitric acia, and making the above tests. SILVER (Argentuvi). 261. Silver. — (Ag' = 107.06. Specific weight -- 10.5. Melting point = 1040° C. Specific heat = 0.057.) Occurrence. — Native, often in large masses ; tlic; principal ores are silver glance (Ag^S), rubi/ silver (AgaSbSg), silver copper glance (Ag.^S.Cu.^S), and horn silver (AgCl). Preparation. — 1. Silver is extracted from argenti- ferous lead by Pattinson's process, wliicli consists in melting the lead and then cooling it slowly. Pure lead crystallises and sinks to the bottom. This is ladled out, until the remaining molten lead contains a considerable percentage of silver, when the process is finished by cupeUation. The lead is melted in bone-ash cupels, or shallow vessels, and subjected to a blast which oxidises the lead and leaves the silver. ELECTHOl'LATING. 281 2. Ainalgamatio7i Process. — The silver is extructed with mercury, which is distilled, leaving the silver free. 3. The silver is dissolved out o'^ its ores by acids, sodic thiosulphate, &c., and then procipitated by scraps of copper. Properties. — A pure white metal, the best conductor of heat and electricity known ; very tough and ductile ; and very soft when pure. Note. — Keep all residues from experiments with silver. Experiment 232 — Cut small pieces of silver from a silver coin, and try their soiubility in dilute hydrochloric, nitric, and sulphuric acids. Try the strong acids with the aid of heat. Silver is soluble in nitric acid, argentic nitrate being formed. It is insoluble in hydrochloric, and in dilute sulphuric acid ; but it dissolves in strong, hot sulphuric acid, with the formation of argentic suli)hate (Ag.2S04) and sulphur dioxide : 2Ag + 2H2SO4 = AgaSO^ + 2H2O + SO2. Silver is easily reduced from its comj)ounds. Experiment 233. — Put a scrap of zinc in a small (quantity of argentic nitrate solution in a porcelain basin. After a short time, a dark powder is formed in its place. Fuse this on char- coal with the blow-pipe. A bright silver bead is obtained. Dissolve it in nitric acid, and keep the solution to test. Silver is much used for plating inferior met;ds. This is now generally done by means of electricity, in the process known as electroplatirig. The object to be plated is fastened to the negative wire of a galvanic battery, and immersed in an aqueous solution of the double cyanide of silver and potassium (AgCN.KCN), 282 LUNAR CAUSTIC. through which the electric current is paH8e used in the preparation of cor- rosive sublimate (HgCl.,). • . 274. Mercuric Chloride, HgCU, or corroAve sub- limate^ is prepared by subliming a mixture of mercuric sulpliate and common salt, a little manganese dioxide being added to make sure of the absence of mercurous salts. (How?): HgSO^ + 2NaCl = HgCla + NagSO^ Propertiks. — Heavy colourless crystals, having a biting mc allic taste (Examine a specimen) ; soluble in water (7 > ts in 100), more so in alcohol, and still more so in ether. It volatilises more readily than calomel when heated. The medicinal dose is ^j^ to \ of a grain. In larger doses it is a violent poison. The antidotes are white of egg, flour, &lq. Stannous chlmnde (SnCl.j) may be given : SnClg 4- SHgCla = SnCl^ + HgaCla (How does this prevent the poisonous action ?) Experiment 242. — Mix solutions of mercuric and stannous chlorides. What is the precipitate formed ? Experiment 243. — To solution of corrosive sublimate add lime water. A yellow precipitate is formed : HgCl, 4- Ca{OH), - Hg(OH), -f CaCl.,. This is the yeUoxo wash of the Pharmacopana. MERCURIC IODIDE. 289 Corrosive sublimate is an excellent antiseptic, even in very dilute solution, and is largely used instead of car- bolic acid. 275. Mercuric Oxide. — HgO. There are two varieties, the differences depending on the fineness of division. Red oxide of mercury is prepared by heating mercury with mercuric nitrate : Hg + Hg(N03)2 = 2HgO + 2N0a. It is a heavy, red powder, soluble in those acids which form soluble mercuric salts. (What is the effect of a strong heat upon it 1) — The yellow oxide is prepared by precipitation. A solution of mercuric chloride is treated with solution of caustic soda, and the precipitate of mer- curic hydroxide (Hg(0H)2) is washed, and dried at 100°. This method of preparing the hydroxides and oxides of the heavy metals is very generally employed. In several cases, the soluble base used as a precipitant is ammonia instead of soda. 276. Mercuric Iodide, Hglj. Also called red iodide of mercury. Experiment 244. — To solution of mercuric chloride add solu- tion of potassic iodide drop by drop. A yellowish precipitate appears, but immediately turns red : 2KI 4- HgCl, = Hgl^ + 2KC1. Add more potassic iodide. The precipitate of mercuric iodide redissolves, a soluble double salt {Hgl2.2KI) being formed This solution, with caustic soda added to it, constitutes NesM- kr's reagent, a very delicate test for ammonia, used in water analysis. Try it with a drop of ammonia dissolved in about half a litre of distilled water. A brown colour or precipitate ap- pears : NH3 4- 2Hgl2 + 3NaOH = NHgJ + 3NaI + SHjO. 20 290 WHITE PRECIPITATE. Mercuric iodide is a brilliant cryst^Uine powder of a vermilion colour. It turns yellow when heated care- fully. It is very slightly soluble in water, sparingly in alcohol, quite freely in ether and in aqueous solution of potassic io'Mde. It resemb' s corrosive sublimate in its poiscmous action. 277. Infusible White Precipitato, or mercuric ammonium chloride, NHgHjCl. Experiment 245- — Add ammonia solution to solution of mercuric chloride. A white precipitate falls ; HgCla 4- 2NH3 = NHgHjCl + NH^Cl. 278. Fusible White Precipitate, or mercuric di- ammonium chloride, Hg(NH3Cl)2, is prepared by adding solution of mercuric chloride to a boiling solution of am- monic chloride and ammonia. — These two compounds diflfer as their names indicate. The infusible precipitate decomposes without fusing when heated ; the fusible precipitate fuses and then decomposes. 279. Mercuric Sulphide, HgS, is found in nature as a heavy red mineral, cinnabar. It can be prepared by subliming mercury and sulphur together, when it is obtained as a red or black powder, vermilion, or jEthiops mineral. Or, it can be prepared as a black powder by precipitation. Experiment 246- — Add hy'dric sulphide to solution of mer- curic chloride. A white precipitate ai)pear8 (2HgS.HgClo), but this rapidly passes through shades of colour until it becomes black (HgS). (Write the equation). Divide the precii)itate into three parts and try its solubihty ( 1 ) in ammonic sulphiile, (2) in boiling dilute nitric acid, and (3) in aqua regia. He suits (1) (2) (3) MERCURIAL POISONING. 2S1 280. Tests for Mercuric Compounds. 1. See Experiment ?46. 1,\ Sodic hydroxide solution gives with solutions of mercuric salts a yellow precipitate (Hg(0H)2) not rediasolved whtn more of the reagent ia added. 3. Btannoua chloride (SnCl^ > gives a white precipitate (HgaClj), turning grey (Hg) with more of the reagent. 4. A bright copper wire is silvered when put in a mercuric solution. This applies to mercurous solutions also. General Test for Insoluble Mercury Compounds. — Mix with dry sodic carbonate and charcoal powder, and heat in a matrass. Metallic mercury is obtained as a mirror in the tube. — All mercury compounds volatilise when strongly heated. 281. Mercurial Poisoning. — The soluble com- pounds of mercury are violent irritant poisons. A characteristic symptom is the increased flow of saliva {salivation). The insoluble compounds are not so poison- ous, but are still dangerous. Even metallic mercury in a finely divided state will cause symptoms of poisoning, especially when it is breathed as a vapour. Therefore, it is dangerous to boil mercury, or to sublime compounds of mercury, into the atmosphere of an inhabited room. As mercury and its compounds are very extensively used in arts and manufactures, as well as in many patent and quack medicines, numerous cases of poisoning occur. The antidotes are albuminous substances, such as white of egg, flour, &c., and stannous chloride. 292 QUESTIONS AND EXERCISES. QUESTIONS AND EXERCISES. 1 . Is there any reason why ^-aiu water should not be stored in J.ead-liued tanka ? 2. In what liq d<\s is lead soluble, and in what insoluble ? 3. Muntion some liquids which will, and some which will not dissolve litharge. 4. A white crystalline solid is given you. How would you determine whether it is sugar of lead? 5. What proportions of plumbic acetate (Pb(C2H30.^)2.3HM()) and litharge (PbO) must be combined to form the subacetate of lead? 6. Why should solution of subacetate of lead be kept well closed from the air ? 7. What chemical action takes place when white lead is taken into the stomach ? 8. In what acids is mercury soluble ? 9. Why is mercurous chloride called calomel ? 10. What chemical compounds are present in black wash ? In yellow wash ? 11. Write formulas for mercurous sulphate, mercurous bromide, and mercuric cyanide. 12. How would you prepare a specimen of mercuric hydroxide^. 13. Black mercuric sulphide becomes red when rubbed. Can you account for this ? 14. Explain the action of stannous chloride as an antidote to poisoning by corrosive sublimate. Woiild stannic chloride (SnCl^i) do ? 15. Argentic cyanide is insoluble in water, but soluble in solution of potassic cyanide What happens when a drop of argentic nitrate solution is added to a considerable quantity of potassic cyanide and shaken up with it ? CHAPTER XVI 293 II. METALS OF .iftoUP n. [lead, Mercury] Pn.. ^ y< Un, [Areemci, Oold, PUuinum, ,fe. feclissolved by a f„,.tl,p,. ' ' ' '""'"'"« of them are "*'** can be prepared hy CLTT !'='^'""'>'>- ~ The "■e earthy substances insoluble ° '^^''"•o^ides. They stances insoluble in water ^'""^''"'^ ''■•e '"arthy sub. T'"« group is subdivided into two • A- Mefcals having siilnh.vi • , ""'"'ine sulphides :%;!'" ""°'"'"« '» -'"tions of 7'^- In analysis, me S/Xl ""'";'""' "'"' *- class, "" ^"s are included in this R Metals havi'n^ snlnl.;,i ^"'ne^iphides:', riiV^o'f'^ '" ^lutions of ««, and some rare metX ' ''"■''"'"J' ^''^''' P^'- A. COPPER ^P„^,„ -» J. Copper (Cu" = fiq I „ Mdting point = 1090O n q f "" "^"'S^" = 8.92 ^- Specific heat = 0.0952). ' 294 COPPER. Occurrence, — Free ; soiuotiines in great musses. The ores of copper are very iiunierous. The commonest one is copper pyrites, or chalcopyrite (CuFeS^). Copper is found in the liver and kidneys of man and of domestic animals. Preparation. — The smelting of copper is a very com- plicated process, but it is the same in principle as that of lead, viz., a partial oxidation of the sulphide and sul)- sequent fusion at a higher temperature. Poor ores are worked up by dissolving in acids and precipitating with iron. Experiment 247. — Pip the poiut of * knifo blade in a little solution of cupric sulphate. It becomes coated with copper : CUSO4 4- Fe = FeSO^ + Cu. Properties. — A red metal, heavy, very tough, malle- able, and ductile. Next to silver it is the best conductor of heat and electricity. Its solubility in nitric and sul- phuric acids has been already proved. (See Arts. 86 and 1 15). Experiment 248. — Try the solubility of copper in hydro- chloric acid, strong and dilute. Put a piece of brighb copper wire in dilute acetic acid, so that it is half covered with the acid. Leave it for a day, and then examine it. Test the acid for copper. Verdigris, or basic cupric acetate, has been formed. Experiment 249. — Put pieces of bright copper wire in test tubes or beakers containing (I) distilled water, (2) dilute solu- tion of common salt, (3) butter or fat, and (4) solution of sugar. After 24 hours, examine the condition of the copper and test the solutions for copper. Copper is gradually dissolved by water, especially when the water contains ammonium salts or chlorides. Vinegar, fats, oils, and syrups, with the aid of air and BLUR VITRIOL. 295 moisture, dissolve copper. Thus occur frequent cases of poisoning, from copper kitchen utensils, taps for liquors, 284. Compounds of Copper. — Copper resem))les mercury in forming two classes of compounds, (I) cup- rous, in which two atoms of copper act as a dyad radical ("u- I , and (2) cupric, in which one atom of copper replaces (_'u — two of hydrogen. — The cup'ous salts are so easily oxidised that it is difficult to keep them. Cuprous oxide (Cu.^O) has been already noticed. (See Sugars). Cuprous chloride (CU.2CI2) is remarkable as being a solvent for acctvlene and carbon monoxide. 285. Cupric Sulphate.— CUSO4.5H2O. Also called blue vitriol and blue stone. Preparation. — Copper pyrites is roasted so as to form cupric oxide (CuO) and ferric oxide (Fe.203). The cupric oxide is then dissolved out by hot sulphuric acid, in wliich ignited ferric oxide is insoluble. The solution is evftporated, and the salt crystallised. The commercial salt always contains a little ferrous sulphate (FeSO^. THjO). Blue vitriol is obtained as v. secondary product in the refining of silver by precipitation on copper. (In what way has it been already prepared 1) Properties. — Cupric sulphate is generally sold in large blue crystals. These are soluble in water (2 parts in 5). Experiment 250. — Carefully heat a crystal of cupric sulphate in a t. t. It turns whit«3, and water gathers on the sides of the tube. The crystal falls to a powder, because it has lost its water of crysiallisaiion. When the t. t. is cool, pour a few 296 CUPRIC OXIDE. drops of water ou the atii jJrouM xalt. Note signs of heat. Anhydrous cupric sulphate is used in tenting li(iuida for water. Tt turns blue when acted on by water. Experiment 261. — Dissolve a little cuj ric sulphate in water, and test the solution with blue litmus paper. 1'he basic part (if the salt is comparatively weak. Taste the solution. Test it for sulphuric acid. Blue vitriol is used in medicine as a caustic, and also as an emetic. In small doses (up to 2 grains) it is not j poisonous, but acts as a tonic and astringent. In large)' doses it is poisonous, unless it exerts its emetic action. Antidotes, white of egg, hurett(Hl hydrogen, the zinc salt reniainijig in solution. The sulphide is dis- solved in strong hydrochloric acid, and the carbonate (CdCO.,) is obtained by precipitating with sodic carbonate. By heating the carbonate, pure cadmium oxide is formed, and this is then reduced by heating in iron tubes with charcoal. PiioPKHTiES.-- A white metal, somewhat like tin. It crackles when bent. It is harder than tin, malleable and ductile, and takes a good polish. (Cadmium is soluble in hot dilute hydrochloric acid, and in suli>huric acid. It is very easily dissolved by nitric acid. (1) Cd -f 2H01 - CdCla -f H2 (2) Od -f H2SO4 = CdSO^ -f H2 (3) 3Cd + 8HNO3 = 3Cd(N03)2 + 2N0 + 4H2O. 290. Compounds of Cadmium.— Cadmium has only one oxide ^OdO), a brown solid, mentioned abovu- The salts of cadmium are mostly colourlesSj and resemble those of zinc both in chemical properties and in physio- lojrical action. Solutions of the normal salts have an acid reaction. • 291. Cadmic Nitrate, CdCNOa).^, is prepared by dissolving the metal in nitric acid and evaporating the solution. It is a deliquescent white salt, used for pre- paring other salts, and in chemical experfments. CADMU: IODIDE. 299 292. Oadmic Sulphate, .'UMHO^.H!!/), w prepared from the nitrate or cliloride. Experiment 253. — "our Holutiou of cadmic nitrate or cldoride into sodic carbonate nolution : Cd(NO„)a -f NaaCO„ = OdCOg -f 2NaN0„. Kilter off the precipitate of cadmic carbonate, waah it, and dis- Holve it in dihite sulphuric acid, taking care not to use too much. Evaporate to cryatallisation, and examine the cryHtals : CdCOa + HjSO^ = CdSO, + H,() -f CO,. This method of pasHing from one soluble Halt of a metal to another is often employed. Sometimes the hydroxide is pre- cipitated instead of the carbonate. Sulphate of cadmiiun is a colourless salt^ resembling sulphate of zinc in its physiological actions, but it is more powerful. It is used as a wasli for diseases of the eye. It is soluble in about one and a half times its weight of water, 293, Oadmic Iodide, Cdl.^, is pre[)ared by digesting the metal with iodine and water, until the colour of the iodine diduppears. \ solution is obtairied which, on evaporation, deposits thin pearly j)lates of the iodide. It is soluble in about an equal weight of water. — Cadmium iodide is used in medicine in the form of an ointment. It is also used in jdiotography in preparing the sensi- tive plates, as it is one of the few iodides soluble in alcohol and ether. A solution in alcohol and ether is mixed with a collodion solution and spread in a thin layer upon the plate. The liquids quickly evaporate and leave a thin layer of collodion impregnated with cadmium 300 BISMUTH. iodide. When this is dipped in a bath of argentic nitrate, double decomposition takes place : Cdia -^ 2AgN03 - 2Agl -|- Cd(N03)3. Tnis is the sensitive plate. 294. Tests. 1. To a cadmium solution add hijdric sulphide. A yellow precipitate of cad mic' sulphide (CdS) is formed. This is insoluble in yellow ammonic sulphide. It resembles arsenic trisulphide (As^Sg) and stannic sulphide (SnS^), but these are soluble in ammonic sulphide. Cadmic sulphide is soluble in hot dilute sulphuric and nitric acids. 2. To a solution of a cadmium salt add ammonia gradually. A white precipitate of cadmic hydroxide, Cd(0H)2, appears, but redissolves in more of the reagent, forming a colourless solution. BISMUTH. 295. Bismuth. (Bi"' ^ = 210.— Sp. wt. = 9.8.— Melting point = 270°.— Sp. heat = 0.0305.) Occurrence. — Rather rare, chiefly in the free condi- tion. It is found often with ores of cobalt. Preparation. — Generally as a by-product in smalt works, being separated in the metallic state from the sulphide of cobalt by smelting with iron scraps. The commercial metal nearly always contains arsenic. For medicinal use it must be freed from this by melting with a little saltpetre, which oxidises the arsenic, but does not attack the bismuth. Properties. — A hard, lustrous, brittle metal, of a reddish tint. It expands on solidifying, and gives this property to its alloys, some of which are used in stereo- typing. It decomposes steam at a red heat. It oxidises I BISMUTH NITRATE. 301 slowly in the air. Bismuth is not dissolved by cold dilute hydrochloric or sulphuric acid. Experiment 254. — Dissolve a little bismuth in hot, strong sulphuric acid : 2Bi + 6H2SO4 = Bi2(S04)3 + 3SO2 + 6H2O. It dissolves easily in nitric acid and in aqua regia. — Alloys of bismuth, lead and tin, made to melt at par- ticular temperatures, are used as safety plugs for boilers. 296. Compounds of Bismuth. — Bismuth unites with oxygen in four proportions (Bi.^O.,, Bi203, BijO^, BiaOg), but only one of the oxides, viz , the trioxide^ (BijOg) is of importance medicinally. It is a basic oxide. Tho pentoxide (BijOg) is acid-forming. The others are indifferent. 297. Bismuth Trinitrate, Bi(N03)3.3H20. Also called nitrate of bismuth. Experiment 255- — Dissolve a little bismuth in nitric acid diluted with about three-fourths its volume of water : Bi -f 4HNO3 = Bi(N03)3 -f NO + 2H,0. Evaporate the solution to crystallisation. Colourless delique- scent crystals are obtained. Any arsenic present remains dis- solved in the mother liquor. 298. Bismuth Subnitrate, or basic nitrate of bis- muth, BiN 03(0 11)2!. Also called white bismuth. Preparation.— Experiment 256.— Add a few drops of water to the crystal i of trinitrate obtained in Experiment 255, so as to form a solution, and pour it into a beaker of distilled w?*" r. A white precipitate falls : Bi{N0,)3 4- 2H2O = BiNO^iOH), + 2HNO3 t The composition of this salt varies with the amount of water used in its preparatio .1. 302 BISMUTH TRIOXIDB. (Many salts of weak bases can be thus decomposed by water.) Filter oflF, wash, and dry the precipitate. Keep the filtrate. Properties. — A heavy white powder, insoluble in water, but soluble in moderately strong nitric acid. It is again precipitated from this solution by the addition of water. Experiment 257- — Dissolve a little bismuth subnitrate in a few drops of nitric acid and a drop or two of water. Then add more water. Experiment 258. — Dissolve a little bismuth subnitrate in sulphuric acid diluted with an equal volume of water. To this add a few drops of ferrous sulphate solution. A black colour or precipitate is formed (BiaOa). Subnitrate of bismuth is much used in medicine. It is not poisonous, but it sometimes contains the tri-nitrate or arsenic compounds, and then gives rise to symptoms of poisoning. It should be carefully distinguised from the trinitrate. It is also used as a cosmetic, and to givo an iridescent glaze to porcelain. 299. Bismuth TriOXide, BijOg, is prepared by boil- ing subnitrate of bismuth with solution of caustic soda : 2BiN03(OH)2 + 2NaOH = 2NaN03 + BiaOg + SHjO. The precipitate is collected on a filter, washed, and dried. Properties. — A lemon-yellow powder, insoluble in water, but soluble in nitric and hydrochloric acids, with the formation of the trinitrate and the trichloride (BiClg) respectively. It is a basic oxide. — It is used instead of the subnitrate in many cases, and is to be preferred on account of its purity. 300. Bismuthyl Carbonate.— 2(BiO)2C03 . 11,0. BISMUTHYL CARBONATE. ' 303 Preparation. — Experiment 259- — Pour solution of bis- muth trinitrate into cold solution of amnionic carbonate, A white precipitate falls : 3(NH JaCOg 4- 2Bi(N03)3 = (BiO)2C03 -f GNH.NOg + 2CO2. Collect the precipitate on a filter and wash it. Properties. — This salt, commonly called carbonate of bismuth, is a white powder, insoluble in water, but soluble in nitric acid with effervescence. It is also soluble in sulphuric acid, and the solution should not respond to the test for nitric acid. If it does, the carbonate has contained subnitrate. The carbonate of bismuth is often administered in place of the subnitrate, on account of its more ready solubility in the acid juices of the stomach, and also because of its antacid properties : (BiO)2C03 + 6HC1 - 2BiCl3 + CO2 + 3B.^0. In this salt the radical ~ Bi = O plays the part of a monad metal. Other salts of bismuthyl are known, e.g., bismuthyl chloride (BiOCl), formed when the trichloride of bismuth is acted on by much water : BiClg + H2O = BiOCl + 2HC1. 301. Tests. 1, To the filtrate from Experiment 256 add hydric sulphide. A brovn-black precipitate of bismuth trisidphide (Big S3) falls : 2Bi(N03)3 + 3H2S = BiaSg + GHNO3. It is insoluble in yellow ammonic sulphide, but soluble in hot dilute nitric acid. 2. Solutions of bismuth salts give with ammonia a white pre- cipitate (Bi(0H)3), not dissolved by more of the reagent. If this precipitate be filtered off and dissolved in as little as possible of 304 ANTIMONY. hydrochloric acid, the solution is turned milky on the addition of much water. This precipitate is not dissolved by tartaric acid. 3. Potassic iodide gives with bismuth solutions a brown pre- cipitate (Bilj,). 4. Caustic potash gives a white precipitate (Bi(0H)3), insoluble in excess. 5. Insoluble bismuth compounds can be tested by dissolving them in nitric acid and diluting with water. (Experiment 256.) The precipitate obtained is insoluble in tartaric acid. (Com- pare Aniimony.) B. ANTIMONY {Stibium). 302. Antimony (Sb»*-^- = 120. Sp. wt. - 6.7 to 6.86. Melting point = 425°C. Sp. heat = 0.0523).— The chief ore of antimony is stihnite (SbjSg). This occurs in black, shining, crystalline masses. Preparation. — Stibnite, purified by fusion, is reduced by heating with iron : SbgSg -f 3Fe = 2Sb + 3FeS. Properties. — A silvery metal, generally in masses of laminated crystals, hard and brittle ; it can be ground to a powder in the mortar. When heated in air, it burns, forming the tetroxide (SbgO^). It is soluble in nitric acid and in aqua regia. It is also soluble in hot, strong sulphuric acid, antimonic sulphate being formed : 2Sb -f 6HaS0^ - Sb2(S04)3 -f 3SO2 + 6H2O. In this salt antimony plays the part of a trivalent metal. — Antimony black is finely divided antimony prepared by reducing the metal from a solution of the chloride by / ANTIMONY TRISULPHIDE. 305 means of zinc. It is used for giving to plaster casts, (fee, the appearance of iron or steel. — Antimony is a con- stituent of many useful alloys. (Art. 240.) 303. Oompounds of Antimony. — Antimony combines with oxygen in three proportions. The trioxide (Sb.^0;,) is both basic and acid-forming ; the pentoxide (SbyOg) is acid-forming, antimonic acid (H3Sb04) and the antimonates being similar to the corresponding compounds of phosphorus and arsenic; the tetroxide >Sb204) is also acid-forming. 304. Antimony Trisulphide, SUS;,, is found in nature as stibnite. The mineral is purified by fusion, and is used as the starting point in the^ preparation of antimony compounds. It is also called black antimony and crude antimony. — It is a greyish-black crystalline powder, soluble in hot, strong hydrochloric acid, with evolution of hydric sulphide. Experiment 260- — Heat a little black sulphide of antimony with strong hydrochloric acid. Keep the solution : SbgSg + 6HC1 = 2SbCl3 + SHgS. Experiment 261- — Boil a little sulphide of antimony with solution of sodic hydroxide. It dissolves : 2Sb2S5 + 4NaOH = NaSbOj + SNaSbSg + 2H2O. Add dilute sulphuric acid until a precipitate appears : NaSbOa + SNaSbSj, + 2H2SO^ = 2Na2S04 -f 2SbaS3 + 2H2O. The substances formed when antimony trisulphide is dissolved iu caustic soda are sodic antitnonite (NaSbO.^) and sodic sulphanti- monite (NaSbSa). When the acid is added the trisulphide is again precipitated, but it is orange-red. Prepared in this way it always contains a little of the trioxide, and is called sulphurated antimony, or golden sulphide of antimony. 21 306 POWDER OP ALGAROTH. 305. Antimony Trichloride (SbCl.,) is prepared as in Experiment 260. By evaporating such a solution the trichloride is obtained as a crystalline, colourless, solid, melting at 72° (" butter of antimony "). It is very deliquescent. Expe ' Jient 262. — Dilute a small part of the solution pre- pared iu Experiment 260. A white precipitate of antimony I chloride, or powder of Algaroth (SbOCl) is formed : SbCla -h HaO - SbOCl + 2HC1. Filter, and test the filtrate for antimony and for hydrochloric acid. To two other portions add considerable quantities of strong hydrochloric acid and tartaric acid respectively, and dilute them as before. To a strong solution of antimony trichloride add a little dilute hydrochloric acid. A precipitate forms ; the dilute acid has the same eflFect as water. Add more acid and the precipitate is redissolved. Antimony trichloride is a powerful caustic. It is a corrosive poison, acting like a strong solution of hydro- chloric acid. (Explain this.) 306. Antimony Trioxide (SbgO ), also called flowers of antimony, is prepared by diget^ting powder of Algaroth (SbOCl) with sodic carbonate, and washing with hot water. — It is a greyish-white powder, insoluble in water, sulphuric and nitric acids, but readily soluble in alkalis, and in hydrochloric and tartaric acids : SbaOg + 6HC1 = 2SbCl3 + 3H2O. When heated strongly in air it fuses and, absorbing oxygen, becomes changed to the tetroxide (SbaOi). — Antimonial powder is a mixture of 1 part of antimony trioxide with 2 parts of calcic phosphate (Ca3(P04).2). 307. Tartar Emetic, SbO.K.C^HiOg, is antimony I potassium tartrate, already mentioned (Art. 189). TARTAR EMETIC. 307 Experiment 263. — DissoW** some tartar emetic in as little as possible of hot water. Dilute the solution. It does not turn milky. The explanation is as follows : — The antimony is already combined as a soluble antimonyl compound. (What experiment above does this explain ?) It will have been observed that antimony shares with bismuth the tendency to form so-called oxysalts, in which a radical, in this case, aritimonyl, - Sb = O, acts the part of a univalent atom. Experiment 264- — Examine a specimen of tartar-emetic care- fully. Taste it. Heat a small portion on mica or platinum. It chars and burns, leaving a white solid. In large doses trHar emetic is a [)oison. Antidotes^ freshly precipitated ferric hydroxide, tannic acid, or any vegetable infusion containing tannin, e.g., tea. 308. Tests. 1. To a solution of an antimony salt, acidified with hydrochloric acid, add hydric sulpJiide. An orange precipitate falls. Filter off the precipitate and test the solubility of parts of it in yellow ammonic siilphide and in hot strong hydrochloric acid. It dissolves in both. Dilute the hydrochloric acid solution. — The ammonic sulphide solution contains amvionic sulpfiantimonite (NH^SbS^). Treat it with hydrochloric acid, and the sulphide is reprecipitated. 2. Test for antimony as in Marsh's teat for arsenic (Art. 146). Antimony has a gaseous compound with hydrogen, stihine, or nntimoniuretted hydrogen (SbH,). Spots are obtained, similar to those of arsenic, but they are turned orange by am- monic sulphide, and are not dissolved by bleaching powder solution. (Compare ^r«ewic.) 3. Put a scrap of zinc in a solution c£ tartar emetic, collect the precipitated antimony, and test its solubility in hot hydro- chloric acid. It is insoluble. (Compare Tin.) 308 TIN. 4. Strong solutions of antimony trichloride give a white pre- cipitate with water or dilute hydrochloric acid, 8^ = KjO. 2Cr03). — This salt is the starting point in preparing chromium compounds. Preparation. — Chrome ironstone is roasted, ground, and heated with lime and potassic carbonate, with con- stant stirring so as to allow oxidation to go on. The object of the lime is to economise alkali, and to prevent fusion, so that the air may penetrate into the mass : CrgOa + 2K2CO3 + 30 = 2K2Cr04 -j- 2CO2. CraOa + 2CaO + 30 = 2CaCr04. When oxidation is complete, the potassic and calcic chromates are dissolved in water, and to the solution potassic sulphate (K2SO4) is added to precipitate calcium : KaSO^ + CaCrO^ = CaSO^ -|- K2Cr04. To the strong solution of potassic chromate thus obtained sulphuric acid is added to form the less soluble bichromate: 2K2Cr04 + H2SO4 = K^Gt^O^ + K2SO4 + H2O. The object of this operation is to separate the chromium salt from the impurities present in the solution. Properties. — Potassic bichromatf crystallises in large garnet red prisms, soluble in water (8 parts in 100). It is a strong oxidising agent, especially in the presence of acids. An instance of this has been already described (Aldehyde). Experiment 283. — To a solution of potassic bichromate acidified with sulphuric acid add sulphuretted hydrogen. The red colour changes to green, and sulphur is precipitated : INSOLUBLE CHROMATES. 331 KgCraO^ + 4H2SO4 + 3H2S = K2SO4 + CraCSOJg + 7H2O + 3S. In this action chromium trioxide is an oxidising agent, and the hydrogen of hydric sulphide is oxidised to water. Leaving the acid out of considei-ation the action can be represented more simply : 2Cr03 + 3H2S = CraOj -f- 3H2O + 3S. Experiment 284. — To 50 c. c. of saturated solution of potassic bichromate add 5 or 10 drops of sulphuric acid, and then sul- phurous acid until the coloui is bright green. Evaporate to a small bulk and set aside. The solution contains chrome alum (K2SO^.Cr,(SOJ3.24H,0): K2Cr207 -f HaSO^ + SSOa = K2S04.Cr2(S04)3 + H2O. Potassic bichromate, on account of its oxidising power, is a corrosive poison. The antidote is ferric chloride, which forms the sparingly soluble ferric chromate. Alkaline sulphites should also be antidotal, (Whyl) Potassic bichromate is used in the preparation of other chromates. The following are insoluble in water but soluble in dilute acids : baric (BaCr04), plumbic (PbCrO^), argentic (A-gjCrOi), mercurous (Hg2Cr04), ferric (Fe2(Cr04)3), and others. Experiment 285. — Add solution of potassic bichromate to solutions of the following salts, note the colour of the precipitates and test their solubility in acetic and nitric acids, viz., baric chloride (BaCla), plumbic acetate (Pb(C2H302)2). argentic nitrate ( AgNOg ), and merctirous nitrate (HgalNOg) 2). Normal chromates are precipitated, and acid is set free in each case. (Write the equations.) Plumbic chromate (PbCr04) \l used as a paint {chrome yellow). Chrome red is a basic chromate of lead pre- pared by boiling the normal chromate with lime water. 332 CHROME ALUM. Experiment 286. — t)ip a piece of white cotton in dilute solu- tion of pi imbic acetate, soak it well, wring it, and then dip it in dilute solution of potassic bichromate. It is dyed yellow, and the colour is fant, being precipitated within the fibres of the cotton. Boil the cotton with lime water ; it becomes orange red. 340. Chromic Acid. Experiment 287. — To a cold saturated solution of pota38ic bichromate add one and a half times its volume of concentrated sulphuric acid, taking care to stir well. Set in a cool place. Chromium trioxide (CrOg) separates oui* in beautiful red crystals. Chromium trioxide dissolves in water, forming a strongly acid Bolution, but no definite acid has been separated from this. The normal chromates are analogous to the sulphates in composition, e.g. K2Cr04, PbCr04, (fee, so that chromic acid may be supposed to have the formula HgCrO^. Potassic bichromate is then an anhydrous acid salt. 341. Chrome Alum (K,S04.Cr,(S04)3.24H20). This salt is prepared as in Experiment 284. It is a by- product in some operations in which potassic bichromate is used as an oxidising agent, e.g. in the manufacture of alizarine. It is soluble in water, and crystallises from cold solutions in violet crystals isomorphous with those of common alum. If a crystal of common alum be placed in a saturated solution of chrome alum it grows by addi- tion of layers of the chrome alum. Solutions of chrome alum undergo a peculiar change on being heated. The colour changes from violet to green, and this solution does not crystallise. It slowly returns to its former condition. This property is common to all chromic CHROMIC HYDROXIDE. 333 galls. — Chrome alum is used in tanning, dyeing, and calico-printing. 342. Chromic Hydroxide (Cr,(OH)«). Experiment 288. — Add ammonia to a solution of chrome alam. Collect the precipitate of chromic hydroxide on a filter and wash it. Try the soluhility of portions of it in hydrochloric acid, caustic soda, and ammonia. Heat part of it on mica. Chromic hydroxide is of a dirty green colour. It dis- solves in hydrochloric acid, forming chromic chloride (CrjClg). It is also soluble in caustic soda, forming a green solution from which it is reprecipitated by boiling. When heated it loses water, and chromium sesquioxide (CraOg) remains. This oxide is used as a paint (chrome green). Guignet's green has the composition, Cr203.2H20. It is also sold as chrome green. 343. Tests. Chromaies. 1. Baric chloride gives a yellow precipitate insoluble in acetic acid, soluble in nitric acid. 2. Acidified solutions of chromates are turned green by hydric sulphide. 3. Solutions of chromates are reduced by ammonic sulphide, which precipitates chromic hydroxide, so that this group reagent is a test for chromates as well as for chromic salts. 4. Insoluble chromates can be tested for by the borax bead, to which they give an emerald green colour. Chromic Salts. 1. Ammimia precipitates chromic hydroxide, insoluble in excess. 2. AmmOTiic sulphide gives a dirty green precipitate of hy- droxide : Cr^CSOjg + 3(NH JaS + SH^O = Cr2(OH)e + SCNHJ^SO^ + SH^S. 334 ALUMINIUM. 3. Caustic soda gives a green precipitate soluble in excess, re- precipitated by boiling. 4. Insoluble chromium compounds can be detected by the borax bead, or by heating in the oxidising flame with a sodic carbonate bead, to which they give a yellow colour, due to the formation of sodic chromate. If the bead be dissolved in water the yellow colour appears strongly. ALUMINIUM. 344. Aluminium (Al'^ = 27.3. ~Sp. wt. = 2.67.— Melting point = 700°.— Sp. heat = 0.2143). Occurrence. — Compounds of aluminium form a very considerable proportion of the earth's crust, being found in clay, granite, gneiss, mica, felspar, &c. Preparation. — From bauxite, a hydroxide of alum- inium and iron. Aluminium chloride (AljClg) is obtained by a series of operations, and from this the metal is set free by sodium. Lately the metal has been obtained more economically by electrolysis. Properties. — A light, tin-white metal, malleable, ductile, and sonorous. When pure it does not tarnish in air, but the impure metal soon tarnishes ; and this is one difficulty in the way of the economical manufacture of the metal. It decomposes water at 100°, and dissolves easily in most acids and alkalis. Obviously, it cannot be used for cooking utensils. It is very useful wherever lightness and durability are required, as in optical instru- ments, &c. Aluminium, bronze is an alloy of aluminium with 90 % of copper. It has the appearance and many of the qualities of gold. ALUMINA. 335 345. Alumina (AI2O3). This is the only oxide of aluminium. Occurrence. — As corundum, ruby, sapphire, emery, (fee. ; and combined in many silicates, &c. Preparation. — Experiment 289.— To a solution of alum add ammonia. Collect on a filter, and wash, the gelatinous pre- cipitate of aluminic hydroxide, Ala(0H)9 : 6NH4OH + Al2(SOj3 = Al2(0H)e + 3(NH4)2S04. Heat a portion of the precipitate on mica. It decomposes into water and aluminic oxide : Al2(0H)6 = AlaOs + SHaO. Properties. — A whit« powder, insoluble in acids after it has been ignited. Crystalline alumina is next to diamond in hardness, and in the form of emery is used in grinding and polishing hard substances. Aluminic hydroxide^ Al2(0H)g, is a, weak base, and also a weak acid. . - Experimont 290. — To ia solution of alum add caustic soda, a little at a time. Aluminic hydroxide is precipitated and re- dissolved: Al2(0H)e + 6NaOH = Ala(0]Sra)e + eHjO. Aluminic hydroxide dissolves in solutions of caustic soda and caustic potash, forming aluminates. It does not dissolve in solution of ammonia. — It has the power of extracting colouring matters from solution, and is used as a clarifier, decolouriser, and as a mordant in dyeing. 346. Aluminic Salts. Aluminium salts are mostly colourless, and, when the acid is a strong one, of an astringent, acid taste. They resemble ferric and chromic salts in composition, e.g. AljClg, Al2(S04)3, Al2(N03)g, &c. 336 ALUMS. Like chromium and iron (in ferric compounds), aluminium does not form salts of such weak acids as carbonic. 347. Alums. Aluminic sulphate (Al2(S04)3) com- bines with potassic sulphate (KqSO^) and water to form potash alum, K2S04.Al.j(SOj3.24H20. It also unites with ammonic sulphate to form ammonia alum (^Yi^)^^O^.A.\{%0^)^.UVL^O. The alums are a group of compounds similar in properties and composition, and exactly alike in crystalline form. A crystal of any one alum will increase in size when placed in a saturated solu- tion of any other ; the alums are isomorphous. A gen- eral formula may be written thus : MaS04.M'2(S04)3.24Hj,0. M = K, NH4, Na, Rb, Cs, Ag, or Tl. M' = Al, Fe, Cr, In, or Ga. Preparation. — Potash and ammonia alum,s are the ones in common use. They are prepared mostly from shale, which contains clay (a silicate of aluminium) and iron j)yrites (FeSj). The shale is burned in heaps, when aluminic and ferrous sulphates are formed. By lixivia- tion a solution of aluminic sulphate is obtained. To this potassic or ammonic sulphate is added, and the alum is obtained by evaporation, and purified by recrystallisation. Properties. — Potash and ammonia alums are colour- less solids, generally sold in large crystals. They are exactly alike in appearance, and can only be distin- guished by a chemical test. They have an acid, sweetish, astringent taste. They are soluble in water (12 parts in 100), the potash, a little more so than the ammonia, alum. They effloresce slowly in air, owing to the action PORCELAIN. 337 of the ammonia of the air in forming basic salts. — Potasli ahim is now the one generally sold. Experiment 291. — Heat a crystal of potash alum in at. t. ^ and observe the loss of water of crystallisation. The white powder which remains is anhydrous alum, or burnt alum {alumen tidum). 348. Aluminic Sulphate (Al2(SO,)3.l8H20). This salt, known as concentrated alum, or alum cake, is pre- pared on the large scale by the action of sulphuric aci of manganese are pyre i^ite, or black oxide of ma/nganese (Mn02), hraunite (Mn-^Og), hausmannite (MugOi), psilomelane (BaO.MnOa), and r hodocrozite 342 MANGANESE DIOXIDE. (MnCOg). The metal is of little importance. It can be prepared by reducing manganous oxide (MnO) with charcoal at a very high temperature. It decomposes warm water. Its presence in iron renders that metal very hard. 360. Oxides of Manganese. Mang^mese unites with oxygen in four proportion, forming owo basic, — manganous oxide (MnO), and manganic oxide (Mn.^Og) ; and two indifferent oxides, — red oxide of manganese (MugOi^ and manganese dioxide (MnO.^). It unites with oxygen and hydrogen to form two acids — manganic (H2Mn04), and permanganic (HMn04). There is some evidence of the existence of an oxide (M.i\.f)^) corres- ponding to permanganic acid : 2HMn04 = H2O + MnaO^. 361. Manganese Dioxide (MnO.^). This sub- stance is found in large quantities as the mineral pyro- lusite, or black oxide of manganese. It is the most important compound of manganese, being used in the manufacture of bleaching powder and glass, and in the preparation of oxygen, chlorine, potassic permanganate, &c. Properties. — A brownish black solid. When heated, it gives off one-third of its oxygen : SMnOg = MugOi + O2. Strong hot sulphuric acid causes it to lose half its oxygen : MnOa -f H2SO4 = MnSO^ + O + H2O. The action of hydrochloric acid has been already studied. (Art. 92.) — Manganese dioxide is sometimes fraudulently MANGANATKS. 343 mixed with coal dust and charcoal powder. This makes it explosive when heated : 2Mn02 + C - 2MnO + CO2. 362. Manganous Salts- In these salts manganese is bivalent (MnCl^, MnSO^, &c.). The soluble salts can be prepared by dissolving manganese dioxide or man- ganous hydroxide (Mn(0H)2) in the acids ; and the insoluble salts by precipitation. Manganous salts are usually pink or rose-coloured, and are not easily oxidised to manganic salts, (Compare with ferrous and ferric salts.) Experiment 296. — Heat a little manganese dioxide with con- centrated sulphuric acid. Observe the evolution of oxygen. A solution of manganous sulphate (MnS04) is obtained. There is usu^'Jly a reddish residue oi ferric oxide, nearly always present in manganese dioxide as an impurity. The solution contains ferric sulphate as an impurity. This can be removed by heating the impure manganous sulphate to redness, and thus decomposing the ferric sulphate. Manganous sulphate can then be dissolved out. 363. Manganic Salts. Unlike the corresponding salts of iron and chromium, manganic salts very readily lose oxygen, &c., and become converted into manganous salts. For example, MnaCSOJa + H2O = 2MnS04 + O -f- H2SO4. 364. ManganateS- The manganates are similar to the sulphates and chromates in composition, and are also in many cases isomorphous with these salts. The most important manganates are potassic (K2Mn04), and sodic (NajMnO^). Preparation. — Experiment 297. — Fuse manganese dioxide 344 PERMANGANATES. in a porcelain basin with one and a half times its weight of caustic potash, and stir for some time with a glass rod so as to expose the mass to the oxidising action of the air : 2Mn02 + O2 + 4K0H - 2K2Mn04 + 2H2O. Lixiviate the blue mass with water. A solution of potassic man- ganate is obtained, (Keep the solution.) By using caustic soda a solution of sodia manganate can be prepared in the same way. Properties. — The magnanates of potassium and sodium form dark green solutions from, which the solid substances can be obtained by evaporation. They are stable only in the presence of free alkali. (See Exp't 298.) Condys green disinfecting fluid is an alkaline solution of sodic manganate, generally containing permanganate in small proportion. The manganates are powerful oxidising agents, and to this they owe their valuable disinfecting and deodorising properties. — Manganic acid (H2Mn04) is not known apart from its salts. 365. Permanganates. These are salts of perman- ganic acid (HMnO^). The potassium and sodium salts are of most importance. PhEPARATION. — Experiment 298.— To the clear solution of potassic marganate (Exp't. 297) add carefully dilute sulphuric acid until the cc lour change: to purple. This takes place as soon as the free alkali is neutralised : 3K2Mn04 + 2H2O = 2KMn04 + MnOa + 4K0H. If this solution is evaporated, it deposits first potassic sulphate, and then potassic permangandte (KMnO^). Properties. — Potassic permanganate crystallises in needle-shaped crystals of a dark purple colour, and a somewhat steely lustre. It is soluble in water (I part in 15) and has e lormous colouring power. PI'RMANGANATES. 345 The permanganates are strong oxidising agents, and are of great value as disinfectants and deodorisers. Condy'a redjiuid is a solution of more or less pure sodic permanganate. (NaMnO^). Experiment 299. — To a solution of potassic permanganate add sulphurous acid. The colour disappears : 2KMn04 + 5SO2 + 2H2O = KaSO^ + 2MnS0, -f 2HaS0^. Test this solution for sulphuric acid. — Decolorise acidified solu- tions of potassic permanganate with other reducing agents, e.g., ferrous sulphate, hydric sulphide, amnionic sulphide, &c. (Write the equations). Potassic and sodic permanganates oxidise many or- ganic substances, especially those which are offensive and noxious. Experiment 300- — Bubble the air from the lungs through a dilute solution of potassic permanganate, using a glass tube. The purple colour disappears and a reddish precipitate of hy- drated dioxide of manganese (MnO(OH)2) is thrown down. — Re- peat the experiment, first acidifying the solution with dilute sulphuric acid. The colour is discharged, and no precipitate ap- pears. 366. Tests. Manganous Salts. 1 . Ammonia gives a white precipitate of manganous hydroxide (Mn(OHa)), soluble in excess. 2. Ammonic sulphide gives a salmon-coloured precipitate of manganous sidphide (MnS), soluble in dilute hydrochloric acid. 3. Caustic soda gives a white precipitate of manganous hydroxide, insoluble in excess, and oxidising to brown manganic hydroxide (MnaOa(OH)a) when shaken up with air : 2Mn(0H;a + O = MngOaCOHja + HaO. 4. Insoluble compounds can be tested by heating with a sodic 346 COBALT. carbonate bead iu the oxidising zone of the Bunsen flame. Th(; bead is coloured green by the formation of sodic manganate. The borate bead is coloured amethyst by manganese compounds. Manganates and Permanganates. 1. Hydric sulphide reduces them, and precipitates manganous sulphide if the solution is alkaline. 2. Ammonic sulphide reduces them, and precipitates manganouR sulphide. COBALT. 367. Cobalt (Co " '^ = 58.6.— Sp. v t. = 8.5.— Melting pt. = 1100°.— Sp. heat = 0.10696.)— Cobalt occurs combined with nickel, iron, arsenic, and sulphur. It is always accompanied by nickel. It is also found in meteoric iron, and is present in the atmosphere of tlio sun. It is an unimportant metal. Cobalt ores are used chiefly in the manufacture of smalt, a powdered blue glass used as a paint. 368. Oxides of Cobalt. Cobalt forms three oxides, parallel with those of iron. They are cohaltous (CoO), cobaltic (Co.^Og), and cohaltcso-cobaltic oxide (C03O4, or C0O.C02O3). They are all stable. 369. Salts of Cobalt. There are two series of salts, cohaltous and cobaltic. The latter are very unstable, being readily reduced to the former. — Cohaltous salts (C0CI2, C0SO4, Co(N03)2, &c.) are violet or blue when anhydrous, but rose coloured when hydrated. 370. Cobaltous Nitrate (Co(N03)2.6H20) is a reddish, crystalline salt, prepared by dissolving cobaltoso- cobaltic oxide or cobaltous carbonate in nitric acid, and NICKEL. 347 evaporating the solution. It is freely soluble in water, and the solution has an acid, astringent taste. — Cobiltous nitrate is used in testing substances by means of the blowpipe. (Art. 350, i). It is decomposed by a strong heat : 30o(N03)2 = C03O4 + 6N0a + Oj. 371. Oobaltous Chloride ( CoCl,. 6 H,0) is a rose- coloured salt prepared by the same method as that used for the nitrate. Its solution has an acid reaction, and ia used as a sympathetic, or invisible ink. Experiment 301. — Write with a solution of cobaltous chloride 80 dilute that the writing is invisible when dry. Hold the paper near a flame. The writing appears in blue characters. (Explain.) 372. Tests. 1. Ammonia gives a blue precipitate (basic salt) soluble in ex- cess to a brownish solution. 2. Amnionic sulphide gives a black precipitate of robaltous ■lulpfdde (CoS) * insoluble in cold dilute hydrochloric acid, but soluble in aqua regia. 3. Caustic soda gives a blue precipitate insoluble in excess and turning reddish when shaken up with air. 4. Insoluble compounds are tested by the borax bead, to which cobalt gives a deep blue colour. NICKEL. 373. Nickel (Ni"- 1'^- = 58.6. Specific weighs = 8.9. Melting point = 1500°. Specific heat = 0.10863). Nickel is found generally along with cobalt. The * In reality the hydro-sulphide, Co(SH)a. 348 SALTS OF NICKEL. principal ore is kup/er-nickel (NiA.8). Nickel ores gen- erally contain cobalt, copper, iron, and arsenic. It is a white metal, somewhat like steel in appearance, hard, ductile, and not easily oxidised by air. It decom- poses steam slowly at a red heat, and is soluble in dilute! acids. On account of its permanence in the atmosphere it is used for electro[)lHting other metals. — Nickel coim\ are made of an alloy of 75 parts of copper with 25 of I nickel. This alloy is hard and wears well. — Genmnl silver is an alloy of copper, nickel, and zinc in various proportions. It is harder than copper, but more easily attacked by acids. 374. Oxides of Nickel. Nickel forms two oxides, nickelous (NiO), and nickelic (Ni^Og). Nickelous oxide I is basic, while nickelic is indifferent. (Compare witli iron, .■'■■ v • ;.■ • ^ »■ ■■•-'■■ • 6. Why must ferric hydroxide be freshly precipitated when used as an antidote to arsenic ? -v ,.. - . - 7. In what respects are iron and chromium alike ? In what respects do they diflfer ? 8. The third equation in Art. 339 represents calcic sulphate (CaS04) as being precipitated from aqueous solution. Is this strictly correct ? 9. Is there any resemblance between chromium and sulphur ? 10. Chrome yellow dissolves in solution of caustic potash. What substances are formed ? 11. Does chrome alum contain aluminum? Why is it called " alum" ? Write the formulas of all the alums which have been mentioned. 12. Why cannot aluminium be used for making cooking uten- sils ? 13. How would you distinguish aluminium bronze from gold ? 14. Write the formula for eois'mm alum ? METALS OP GROUP IV. 351 15. Whiit is the composition of kiMtnt alum ? 16. Can aluina be represented by a simpler formula than that given in Art. 347 ? 17. Common alum is a good antidote to lead salts. Explain. 18. How would you distinguish a solution of aluminic from one of zinc sulphate ? 19. What is zinc white ? 20. What resemblance is there between manganese and sul- phur ? 21. Calculate the percentage of oxygen in potassic permanga- nate. What weight of potassic permanganate will oxidise the sulphurous acid obtained by burning 10 g. of sulphur ? 22. Explain the explosive nature of a mixture of charcoal, manganese dioxide, and potassic chlorate ? 23. Write a short essay on the general resemblances r.nd dif- ferences among the metals of Group III. with regard to ;he salts which they form. 24. Explain the antiseptic properties of a solution of potassic permanganate. Will it disinfect the atmosphere ? / 25. How would you prepare cobaltous nitrate from cobaltous sulphate? 'j - 26. What differences have you noticed in the chemical charac- ters of nickel and cobalt ? -, - , , CHAPTER XX. METALS OF GROUPS IV. AND V. Calcium, Strontium, Barium ; Magnesium. 379. General Characters. — Calcium, strontium, barium, and magnesium are the metals of the alkaline earths. Formerly, any insoluble earthy substance which 352 MRTALS OF GROUP IV. t remained unchanged \vhon heated was called an earth; so that substances such as lime, silica, phosphates, (be, were classed under this terra. Then it was noticed that some of these earths, viz., lime, strontia, baryta, and mag neaia were somewhat soluble in water, and had alkaline properties. They were therefore called alkaline earths, and were held to be elements until metals were obtained from them. The metals have very strong chemism and are difficult to separate from their compounds. Cal- cium, strontium, and barium are prepared by the elec- trolysis of their fused chlorides or cyanides. Magnt'- sium can be prepared in the same way, ^ ut is prepared on the large scale by reducing its chloride by means of sodium. These metals oxidise so readily that they must be protected from the action of the air by naph- tha. They are bright, easily fusible, and decompose water at ordinary temperatures. They are all dyad, and each has only one basic oxide (CaO, SrO, BaO, MgO). These oxides unite directly with water, forming spar- ingly soluble hydroxides (Ba(0H)2, Sr(0H)2, Ca^OH),, and Mg(0H)2 ; — in the order of their solubility begin- ning with the most soluble). The sulphides (CaS, SrS, BaS, MgS) are decomposed by water, and cannot be pre- pared by precipitation. They are prepared by heating the sulphates with charcoal, e.g. : CaSO^ + 4C = CaS + 4C0. The carbonates (CaCOg, SrCOg, BaCOg, MgCOg), sulphates (MgSO^, CaSO^, SrSO,, BaSO^, in the order of their solubility : — magnesic sulphate is freely soluble.), and phosphates (Qa2,{V0^\, to poisoning by acids, and also to correct acidity oi the stomach. 356 CALCIC SULPHATE. 384. Calcic Chloride (CaCl,.6H20). Preparation. — Experiment 308- — Dissolve in a porcelain dish a few fragments of calc spar in hydrochloric acid, and evaporate the solution on the water bath until it forms a pellicle on the surface. Then heat it over the Bunsen burner, placing the dish so far above the flame that it may not be touched by it. When the salt is quite dry, apply the flame to the dish until moisture ceases to come off". Leave this fxined ca^ric chloride, (CaCla) exposed to the air for 24 hours, and observe the result. Properties. — Calcic chloride is a colourless salt very soluble in water. The fused chloride contains no water of crystallisation. It is very hygroscopic, and is used for drying gases. Solution of calcic chloride is used as a test reagent, and also as a medicine. 385. Calcic Sulphate (CaSO^). Occurrence. — Crystallised as gypsum, alabaster, or selenite (CaS04.2H20), and anhydrite (CaS04). It is present in sea and other waters. Preparation. — Experiment 309.— To solution of calcic chloride add dilute sulphuric a i, fil^or, and wash the p'c- cipitate with hot water. (Write the equation.) The precipitate is gypsum. Properties. — Gypsum is a white solid of sp. wt. 2.3. Experiment 310. — Heat a small quantity of gypsum in a t. t. and observe. Heat a larger quantity in a porcelain basin until moisture ceaseS to escape. Let cool, and mix the anhydrous salt with water on a piece of broken porcelain or smooth wood. (What proportion of water should be used tc form gypsum?) Observe change after a few minutes. Anhydrous calcic sulphate is called j^laster of Paris, or sometimes simply plaster. It is used as a cement, for making plaster casts, &c., and in surgery for making stiff BLEACHING POWDER. 357 bandages. - (jryj)sum is less soluble in hot than in warm water. It is most soluble at 35°C. Experiment 311. — Heat a saturated solution of gypsum to boiling. One part of gypsum requires 500 of water to dissolve it. 386. Bleaching Powder. {''Chloride of Lime:') This substance has been already referred to at p. 105. It is probably a mixture of calcic hypochlorite and chlor.'de in molecular proi)ortions, Ca OCl)^ + CaCl^ ; but it always contains calcic hydroxide. Preparation. — Slaked lime is spread on a series of shelves in large closed compartments, and exposed to the action of chlorine gas. The chlorine is generated by the action of crude hydrochloric acid on manganese dioxide : 4HC1 + MnOa = MnCla + CI2 + 2H2O. Its action on the slaked lime may be represented as follows : .. : 2Ca(OH)2 -I- 2012 - Ca(OCl)2.CaCl2 + 2H2O. Properties. — A white powder, having a chlorous smell. The odour is due to the liberation of hypochlorous acid by the action of the carbon dioxide and moisture of the air : Ca(0Cl)2 + H2O + CO2 - CaCOg + 2HC10. It is one of the best known decdorisei*s and disinfectants, and is esp(?cially useful because of the volatility of hypo- chlorous acid, a substance which deodorises and disinfects the atmosi>here into which it escapes. Expenment 312.— l^jxatnine a specimen of bleaching powder, 358 CALCIC PHOSPHATE. noting its colour and odour. Shake up about 10 grains of it with 50 to 100 cubic centimetres of water and filter. The filtrate contains calcic chloride and hypochlorite. It is the Liquor calcls chloratm of the pharmacopoeia. Add a few drops of it to a solution of sulphate of indigo. Try with acidified litmus solution, and with potassic bichromate solution . Experiment 313. — Pour some dilute sulphuric and hydro- chloric acid over small portions of bleaching powder in watch glasses, and note evolution of chlorine : CaCla + Ca(OCl).^ + 2H^S04 = 2CaS04 + 2CI2 + 2H.^0. CaOla + Ca(0Cl)2 -|- 2HC1 = 2CaCl2 -f- 2CI2 -f 2H2O. When bleaching powder is heated, the hypochlorite is decom- posed into chlorate and chloride : 6Ca(OCl)2 = Ca(C103)2 + 5CaCl2. 3«7. Calcic Phosphate {p-Si^{VO,\). This com pound has been already studied. (Arts. 128 and 132.) Occurrence. — It is found in the minerals apatite (3Ca3(P04), + Ca[Cl2, F,]*), phosphorite (Ca3(PO,)2), tsombrerite (Ca3(P04)o.2HoO), &c., and in bones. Bone ash contains about 80 % of calcic phosphate. Preparation. — Experiment 314.— Digest bone ash with dilute hydrochloric acid, filter, dilute to double volume, add ammonia to alkaline reaction, filter, and wash the precipitate with hot distilled water. The hydrochloric acid acts on the phosphate to form calcic chloride and calcic tetrahydric phosphate : CaalPOJa + 4HC1 = CaH4(P04)2 + 2Cani3. The ammonia reprecipitates the calcic phosphate : CaH^CPOJa + 2CaCl2 + 4NH3 = Ca3(P04)2 + 4NH4CI * When sj'iiibola are put within sqnare brackets and separated by a comma, it signifies that the elements are present in varyinjf proportions. MORTARS AND CEMENTS. 359 It is plain that any impurities in the bone ash which are soluble in hydrochloric acid may be precipitated along with calcic phosphate. Properties. — A light, white powder, insoluble in water, soluble in dilute hydrochloric, nitric, or phosphoric acid. From this solution calcic phosphate is again pre- cipitated when an alkali is added. (Experiment 314.) Thus, an acid solution of calcic phosphate might be mis- taken for an aluminium salt; but the former gives a white precipitate (calcic oxalate) on the addition of sodic acetate and amnionic oxalate, while the latter does not. 388. Mortars and Cements. — Ordinary mortar is a mixture of slaked lime ((^a(0H)2), sand (SiO.^), and water. It hardens by the formation of calcic carbonate, carbon dioxide being absorbed from the air. The process of hardening continues for years. There appears to be no combination of the lime with the silica. — Hydraulic mortar, or Roman cement, is prepared by carefully heat- ing a mixture of lime and clay. It hardens under water, and the hardening seems to be due to the formation of silicate of lime and alumina. Portlaoid cement is made by carefully heating a levigated mixture of clay and chalk. These cements deteriorate when kept exposed to the air, because the lime in them unites with carbon dioxide. 389. Tests. 1. Solutions of calcium salts give a white precipitate with ainmonic carbonate. If tlie solution is acid it must be neutralised with ammonia. The precipitate is soluble with effervescence in nitric acid. 2. Sodic phosphate gives a white precipitate with neutral or 360 STRONTIUM. alkaline solutions of calcic salts (in practice the solution is made alkaline with ammonia) : aCaCla + 2Na2HP04 + 2NH3 = Ca3(P04)2 + 4NaCl + 2NH4CI. 3. Ammonic oxalate gives a white precipitate of calcic oxalate even with very dilute solutions of calcium salts : CaCl2 + (NHJaCaO^ = CaCaO^ + 2NH4CI. This precipitate is soluble in dilute nitric or hydrochloric acid, but is insoluble in acetic acid. ■ , 4. Calcium compounds insoluble in water can be tested by dissolving in hydrochloric acid, adding sodic acetate (so that the acidity may be due to acetic acid), and then adding ammonic oxalate. Or, they may be tested by moistening them with strong hydrochloric acid end bringing them by means of a plati- num wire into the Bunsen I'ame. A bi'ick red colour is imparted to the flame by calcium compounds. STRONTIUM. 390. Strontium (Sr»- = 87.2). — Compounds of strontium are found in considerable quantities in nature. The most commonly occurring are celestine (SrS04), and strontianite (SrCOg). The inetal is prepared by electro- lysis. — Strontium compounds have not yet found a place in the pharmacopoeia. The nitrate (Sr(N03).2) and other salts are used in making fire-works. Tliey give a fine red colour to flames. Experiment 315. — Mix a little atrontic nitrate with powdered charcoal and sulphur, put the mixture on a piece of mica or por- celain and touch it with a hot wire. (What causes the rapid combustion ?) The soluble salts are prepared by dissolving strontia- nite in the acids, or by reducing celestine to strontic sul- • BARIUM. 361 phide (SrS), and dissolving this in the respective acids. StroiAtic oxide (SrO), and hydroxide (Sr(0H).2) are simi- lar to the corresponding calcium compounds, but the hydroxide is more soluble than calcic hydroxide. Stron- tium compounds are mostly colourless. The sulphate (SrS04) is less soluble than calcic, but more so than baric, sulphate. 391. Tests. 1. Amiiionic carbonate gives a white precipitate (SrCOg) with neutral or alkaline solutions of strontium salts. The precipitate is soluble with eflFervescence in dilute nitric acid. 2. Sodic phosphate (with ammonia) gives a white precipitate (SrgfPOJ,). 3. Ammonic oxalate gives a white precipitate of strontic oxalate (SrCjO^), soluble in nitric and sp/iringly soluble in acetic acid. 4. Calcic fiulphate gives a white precipitate (SrS04) after some time : CaSO, -f- SrCl^ = SrSO^ + CaCl,. 5. Insoluble strontium compounds can be tested by moistening with strong hydrochloric acid and bringing on a platinum wire into the Bunsen flame. A carmine red colour is imparted to the flame. The test is more delicate if the substance be held for a few moments in the reducing flame, then moistened with hydro- chloric acid, and held in the oxidising flame. BARIUM. 392. Barium (Ba» = 136.8).— The principal com- pounds of barium found in nature are witherite (BaCO,), heavy spar (BaS04), and psilo7nelane{\M.n, BajO.MnOj). The metal can be prepared by electrolysis of the fused chloride or cyanide. 362 BARIUM CHLORIDE. . 393. Oxides of Barium. — Barium, like calcium and strontium, unites with oxygen in two proportions, forming the monoxide (BaO), and the dioxide (BaOj). 1. Barium monoxide (BaO) is prepared by heating the nitrate : Ba(N03)2 = BaO + 2NO2 + 0. It unites with water, and forms barium, hydroxide, or baryta (Ba(0H).2). This compound is more soluble than either calcic or strontic hydroxide. Baryta water, used in analysis, is a solution of barium hydroxide. The hydroxide is prepared on the large scale from heavy spar, for use in suijar refininj;. It forms an insoluble com- pound with cane sugar. 2. Barium dioxide (BaOj) is a white solid prepared by heating the monoxide to a red heat in a current of oxygen. It is used in the preparation of hydrogen dioxide. 394. Baric Chloride (BaCl,.2H,0). Preparation. — By dissolving baric carbonate or sul- phide in hydrochloric acid : BaCOg + 2HC1 = BaCla + H3O + CO2. It is also prepared from heavy spar, which is firet reduced to sulphide (BaS), and then decomposed by hydrochloric acid : BaSO^ + 40 = BaS + 4C0. BaS + 2HC1 = BaCla + HgS. Properties. — A white crystalline solid, soluble in water (35 parts in 100), sparingly soluble in alcohol. Experiment 316. — Examine carefully a specimen of barium chloride, noting taste, &c. Dissolve it in a little distilled water, and to a small portion of the solution add about twice the volume BARIUM NITRATE. 363 of strong uibiic acid. Baric chloride is only sparingly soluble in strong nitric acid. To another portion add magiiesic sulphate. Baric sulphate is precipitated : MgSO^ + BaClg - BaSO^ + MgClj. Baric chloride, in common with the other .soluble com- pounda of barium, is very poisonous. Solution of mag- nesium sulphate is a good antidote. (How does it act 1) 395. Baric Nitrate (Ba(N03)a). Is prepared by the same methods as those used in preparing the chloi'ide. It is much used in pyrotechny, being mixed ^vUh char- coal and sulphur to form "green fire." ; Experiment 317. — Mix carefully with little friction small quantities of baric nitrate, sulphur, and ground charcoal. Put the mixture on a piece of mica, a flat stone, or a piece of porce- lain, and touch it with a red hot wire. 396. Tests. 1. Ammonic carbonate gives a white precipitate (BaCOg), soluble with eflfervescence in dilute nitric acid. 2. Sodic phosphate (with ammonia) gives a white precipitate (Ba3(P0,),). 3. Ammonic oxalate gives a white precipitate (baC.^O^), soluble in ddute nitric, sparingly soluble in acetic acid. 4. Calcic sulphate gives at once a white precipitate (BaSO^). Baric sulphate requires -400,000 parts of water for its solution. 5. Insoluble compounds are tested for as in Art. 391 (5). Barium compounds give a greenish colour to the flame. MAGNESIUM. 397. Magnesium. (Mg"=23.95). ' Occurrence. — Magnesium compounds are very abun- 364 MAGNESIUM SULPHATE. dant and widely distriV)uted. Mountain limestone, or dolomite, ([Mg, Ca] CO.,,) forms whole ranges of moun- tains. Other commonly occurring compounds are mag- nesite (MgCOg), kieserite (MgS04.H20), carnallite (MgCl... KC1.6H.,0), spinelle (MgO. AljOg), asbestos ([Mg,(Ja]SiO.,), Epsom salts (MgS04.7H20) &c. Magnesic phosphate (Mgg' P04)2) is found in the V>ones, &c., of animals. Preparation. — By heating together a mixture of mag- nesium chloride, calcium fluoride, and sodium. The sodium displaces the magnesium : MgCla + 2Na = Mg + 2NaCl. The metal is purified by distillation. Properties. — A soft, silvery metal ; it tarnishes in moist air; sp.wt. = 1.75 ; melts at red heat, and boils above 1040*^ ; when heated in air it catches fire and burns with a dazzling white light. The magnesium light is used in photography, signalling, &c. Experiment 318. Bum a piece of magnesium wire, dissolve the white ash (MgO) in a drop of dilute sulphuric acid, evaporate on a watch glass, and obtain crystals of Epsom salts. 398. Magnesic Sulphate (MgSO^.TH.O).- Mag- nesium sulphate is generally sold as Epsom salts, crystal- lised with seven molecules of water to the molecule of sulphate. It occurs in nature crystallised with one molecule of water, as kieserite (MgSO^.HjO.) Preparation. — Epsom salts are now prepared mostly from kieserite, by heating in water. The sparingly soluble kieserite apparently combines with more water and becomes changcjd to the much more soluble hei^tahy- drated salt. This is then purified by ci-ystallisation. MAGNESIUM CARBONATE. 365 Properties. — A colourless, crystalline solid, isomorph- ous with zinc sulphate (ZUSO4.7H2O), which it resembles very closely in appearance ; it has an un])leasant bitter taste. It is soluble in water, 35 parts in 100. Experiment 319. Compare specimens of Epsom salts and crystallised zinc sulphate, noting general appearance and taste. Dissolve them separately in water, and add ammonium chloride and a drop of ammonia to each. Magnesium sulphate is used in medicine as a purgative. It is a " saline purgative," i.e., it acts by promoting the diffusion of water into the intestinal canal. 399. Magnesic Carbonate (MgCOa).— Found in nature in large quantities, as magnesitfi. It was formerly used in preparing Epsom salts. The carbonate of mag- nesia of the pharmacopoiia is a basic salt (4MgO. 300.2. 5H,0). Preparation. — By the action of solution of sodic car- bonate on solution of magnesic sulphate. Experiment 320- To a hot solution of magnesium sulphate add hot solution of sodic carbonate. Basic carbonate of mag- nesium is precipitated. Filter, wash the precipitate, and dry it in a glass or porcelain dish. Note the appearance of the dried salt. It is the heavy carbonate of magnesia, or magnesia alba ponderosa. Repeat the experiment, but use cold solutions, and boil for a few minutes after precipitating. The dried precipitate is very light. It is magnesia alba levis. Properties. — The carbonates of magnesia are white powdery solids insoluble in pure water, but soluble in dilute acids (with effervescence), in solutions of am- monium salts, and in water containing carbonic acid. Experiment 321. — To solution of magnesic sulphate add ammonic carbonate ; a white precipitate falls (unless the am- IMAGE EVALUATION TEST TARGET (MT-3) /. r^. y 4, c^/ t/j fA 1.0 I.I 2.0 1.8 L25 liU 111.6 Photographic Sciences Corporation ^ c\ \ 23 WEST MAIN STREET WEBSTER, N.Y. 14580 (716) 873-4503 ^9> i; '^^^ ^m 't-.^'.^ ^'^^^ ^ -^%^ 366 MAGNESIA. monic carbonate consists mostly of the acid salt, in which case a little ammonia must be added). Add ammordc chloride ; the precipitate is dissolved. Experiment 322. — Put a little magnesia alba in a consider- able quantity of distilled water in a flask or beaker, and pass carbon dioxide through the water for some time. If the car- bonate does not dissolve completely, filter. Boil a little of the clear solution ; it becomes milky owing to the pre " "^itation of magnesic carbonate. The solubility of magnesic carbonate increases with the pressure of the carbon dioxide. Liquor magmsice, carhonatis is a solution made by using carbon dioxide under considerable pressure. It contains about 1 3 grains of " carbonate of magnesia " to the fluid ounce. 400. Magnesic Oxide (MgO). — Magnesium forms only one oxide. It is known in pharmacy as magnesia, or magnesia usta. Preparation. — By heating strongly the carbonate of magnesia. A light or heavy magnesia is obtained cor- responding to the carbonate used. Experim 3Ilt 323. — Heat a small quantity of magnesia alba for some time in a porcelain crucible. Try the action of hydro- chloric acid on the residue. It dissolves without eflfervescence, if the heating has been continued long enough: MgU + 2HC1 = MgCla + HaO. Properties. — A light white powder, almost insoluble in water (1 part dissolves in about 55,000) ; soluble in acids, salts of magnesium being formed ; tasteless ; when moistened, turns red litmus blue. It is thus a well- marked basic oxide. It is a good antidote to arsenic poisoning; it forms insoluble arsenite or ai'senate, and neutralises tlje acid of the gastric juice. QUESTIONS AND EXERCISES. 367 401. Tests. 1. Ammonic carbonate gives a white precipitate, bohible in acids, and in solution of ammonium chloride. The carbonates of barium, str&ntrum, and calcium are not soluble in solution of ammonium chloride. 2. Sodic phosphate (with ammonia) gives a granular white pre- cipitate (Mg.NH^.PO^), which forms in lines on the walls of the t. t. when the solution is stirred with a glass rod : MgSO^ 4- NHj + Na.HPO^ = Mg.NH^.PO, -f- Na^SO^. 3. Compounds insoluble in water are dissolved in hydrochloric acid and tested by (1) and (2). QUESTIONS AND EXERCISES. 1. In what way does calcic carbonate act as an antidote to acids ? To zinc chloride ? 2. What substances does quick lime absorb from the atmos- phere ? 3. What weight of water will 10 lbs. of quick lime absorb ? What volume of air at 20°C saturated with water vapour will supply this amount of water ? 4. Explain the " setting " of plaster of Paris. 5. Why does bleaching powder become moist when exposed to the air ? Why must it be kept in well closed vessels ? 6. Calculate the weight of limestone to furnish 1 ton of lime. What volume of carbon dioxide would be driven from it into the atmosphere in the process of burning ? 7. What substances are formed by the action of hydrochloric acid on barium sulphide (BaS) ? Write the equation. 8. How would you distinguish a specimen of zinc sulphate (white vitriol) from one of Epsom salts ? 9. When potassic hydroxide Rolution is added to solution of magnesic sulphate a white precipitate falls. What is it ? Write the equation. 368 METALS OF THE ALKALIS. 10. How would you prepare baric nitrate from baric chloride ? 11. Baric sulphate is often used by painters as a substitute for white lead. Why is it preferable ? 12. What substances are formed when solutions of sodic sul- phate and baric nitrate are mixed ? CHAPTER XXL METALS OF GROUP VI. Lithium, Sodium, Potassium, Rubidium, CcEsium, \Ammonium\ 402. General Characters. The metals of this group form freely soluble hydroxides, called alkalis (from alkali, the Arabic name for the plant from the ashes of which potash was first prepared). The Tnetals of th" alkalis form a series, similar in properties, but showing that gradation always found in chemical series. Thus the hydroxides increase in basic character from lithium to caesium ; the oxidisability of the metals increases in the same order, while ttoir melting points increase from csesiuni to lithium. The metals are all univalent, and are difficult to separate from their compounds. Each forms only one basic oxide (NajO, KjO, Li.^O, .«- 3 O.S 4* 5 I ■ o 0) t-i C o 1) --e iM 1-2 5 3 4) c ox; P. * - s SO CLS S 3 (i O 4) O -o =,. «_^ 00 f^ 09 0) «8 CO hogO S ®-»^ ■r3 X M C « 00 s o O T3 C 3 s, a 8 s m a> c tiD rtl s o a o -kj OJ i.' ■p< T3 ?. ^ u A 4) ^ £ s 4J e c« 1) u > 4> ^ U 41 P. s O o H H AN'ALYTrCAL TAFU.R.S. 40 i 402 ANALYTICAL TABLES. H m H § Xi G H g O fci ^ o C I— I » ^ O c I, w S3 H 05 cn a> C o o B I 0) e 'S I be B 0) O B s B O 0) cS J3 O et O <» 0) o o a a s B -s B O 01 O 5-t (/3 d O p. o a o 1 1 ^ tf OS 6 a> eS C Sao G1] S P . § «^ « B O o O O t^ a -•iq s « c o :?K 3.fc ''^ 00 « c o u »t c o o 03 09 3 be c 1 o H 0) 5 -So *■ 404 ANAhYTICAT/ TABLES. PQ < 01 1 c 0) -s s e o '■C a I 3^ a" o2 S ■5. o i o ;zi » T3 I. §: CO O >. o 05 o O (z; ♦J I. iJ-O s i" « « " 21- -Z &? !*; c . o a o o N -»3 O ;z; o jz; ^ .a o tient wht. ppt. ed on heating, Add to O. S. Perma dissolv O c 4) » - OJ o IS f s 5q a &e 5 9** e«.2-S ;2'x.-* ^fc^g O &3 0) s .«)-? r** ~ 0) r** ~ Sq9 t-i 55 a— .>!' "= '^ -- a 2: c . I 9 I a 4 '% i •S 355 B 3! 5 1 2 Ic 0. *«•* 9 >^ u itf o n) X "O •«-> § .a 01 X! d S! o o ^ -*? •o 1 0) Xi ■^ w b m o «H o ^ -w 3 T5 m « Q ^ O ■+* c C 0) 01 > d r APPENDIX. TABLE OF SOLUBILITIES. 100 parts (by weight) o) water at 15°G dissolve of NAMES. Acetic Acid Alcohol, ainyl •' ethyl " methyl Alum, ammonia < " chrome " potash Ammonia Ammonium carbonate . . . . Ammonic chloride " chloroplatinate " nitrate " oxalate " sulphate Antimony trichloride " trioxide Argentic chloride " nitrate.. .. . .. . ** oxide Arsenic acid '• trioxide Baric carbonate ♦' chloride ' ' fluosilicate " hydroxide " nitrate •• phosphate •• sulphate Benzene Benzoic acid " aldehj'de Bismuth trichloride " trinitrate " subnitrate Boracic acid Borax Bromine Cadraic chloride " sulphate Calcic carbonate " chloride " citrate FORMULAS. CjH.Og CsH,,d C,H,6 CH.O (NH,.)j,Al„(SO,)..24HgO KaCrj(SO«)«. 24H2O KjAlaCSOJi. 24H;,0 te°'::;;:;:::::::: (Nrf.),PtCl« NH.NO., (muhc.,o,.H.,o (NH,),S6, SbCl,, Sb^O, Ajrci AgNO, A^^O H,As04 ASvO, BaCdg BaC1^.2H20 BaSiFg Ba(OH\ Ba(NO.,), Ba.,(P6j2 BaSO^ • CeHg C.Hj.COOH CgHj.COH BiCla Bi(N03),.3H^O BiN03(6H)2 HjBO,, N'a^B^Oj.lOH^O Br.'. CdCl^ CdSO^ CaCOg CaOl., Ca3(C«H,0,),.4H,0 PARTS. all proportions. 25.00 all proportions. all proportions. 11.4 14.3 12.3 59.7 27.6 35. 0.666 200 4.22 75.5 loot* 0.001 (1) 0.00 loot 0.033 loot 3.33 0.0071 45. 0.0263 3,4 8.1 0,00 0.00025 0.1 ' 0.6 3 32 loot loot 0.00 3.00 5.3 3.226 140 58 0.0018 75. 0.1 (?) * loot means very soluble. 406 APPENDIX. NAMES. Calcic hydroxide *' oxalate " phospliate " sulphate '• tartrate Camphor Carbolic acid Carbon bisulphide " dioxide " monoxide Chloral hydrate Chlorine Chloroform Citric acid jobaltous chloride " nitrate " sulphate Cupric nitrate " sulphate Dextrin Ether (ethylic) . Ferric chloride " sulphate Ferrous " *' amnionic sulphate Gallic acid Glycerine Hydrochloric acid hydrocyanic " Hydrogen " peroxide Iodine Iodoform Lithic carbonute " chloride " urate Magnetic chloride " oxide *' am. phosphate . . " sulphate Manganous carbonate '* chloride " sulphate Marsh gas Mercuric chlorfde " oxide Mercurous chloride " nitrate " oxide " sulphate Morphine " chloride. Nickel sulphate Nitric acid Nitrobenzene Nitrogen " monoxide Oxalic acid FORMULAS. Ca,OH)^ CaC,04.2H20 Ca,(P04)„ CaSO.. 211^0 CaC.H40«.iH.,0 c.„H,„o.... : CeH^.OH CS^ CO J, CO Cj,HCl.,O.H^O cf....:..... CHCl, c«hA.h.o C0CL.6H0O Co(NO,)j6Hi,0 CoS0..7H^O Cu(N0.,)5j 3H^O CuSO^.SHaO... CgHioO. (C,H.),6 Fe,cr« Fejj(S04)„ FeSO^.TH^O Fe(NH4MS04)^6H20. C,He04.H,0 C,H,(OH}., HCl... HCN H H.O, I CHI3 LijjC'O, LiCl..' Li,C,H,N.O., MgCf, MgO MgNH^PO^.eH^O . MgSO^.TH^O...... MnCO., MnClsUH^O MnS04.4H20 OH4 Hg.Cl, HgO Hg.Cl, Hgj'NO,), Ug.^0 Hg.SO, C.jH.»NO,,.H.,0.., C,,H,»N0;.HC1.., N1SO4.7H2O HNO., C«H,.NO, N N..O C.:Ha04.2HaO PARTS. 0.137 0.00 0.00 0.238 O.Oltt 0.1 6.67 0.1 0.19744 0.00305 100 (?) 0.751.5 0.1 (•!) 133.00 loot loot 33.5 loot 39.5 loot 11.00 loot loot 70. 19 1.00 all proportions. 7572 all proportions. 0.00017 all proportions. 0.182 0.01 (?) 0.8 I 10 (?) 130. 0.0018 0.0067 67.5 0.013 200.00 130.00 0.00286 6.98 0.00 0.00 loot 0.00 0.2 0.05 6.00 67.0 all proportions. 0,1 (?) 0.0023 0.1633 11. APPENDIX. 407 NAMES. Oxygen.. Phosphoric atud Plumbic ac^etate " bromide " carbonate " chloride '• iodide •' nitrate *' sulphate Potassic bichromate " bromide. " carbonate " hydric carbonate " chlorate *' chloronlat.nate • . " chloriae " chromate . . . . . " cyanide " fluosilicate " ferricyanide . .. . " ferrocyanide . . . . " hydro -xide " iodide " nitrate " oxalate " hydric oxalate.. . *' permanjfanate . . . '* sulphate " tartrate " hytlric tartrate. . •' sodic •• " urate . . " acid urate Quinine " sulphate " bi -sulphate Salicylic acid Sodic acetate " carbonate " hydric carbonate. . " chlorate " chloride "* hydroxide " nitrate *' phosphate " sulphantimonate . . . " sulphate *' thiosulphate Stannic chloride ......... Stannous chloride Starch Strontic carbonate *' chloride. '* hydroxide " nitrate " phosphate " sulphate Strychnine FORMULAS. PARTS. O H.^PO. Pb CjH.v)^ .,.H.,0. PbBr ....". ...?.. '... PbCO; PbCl.; Pbl, PbNO., .^ PbSO/. K.,Cr^Oj KBr K„CO., KHCO., KCIO,,". KjPtClfl KCl KjCrO,. KCN... ,SiF„ ..,Fe(CN>«. .311^0. K, k; K^FeiCN g. KOH Kl KNO,, K.,C.,04.H:;0 KHd.Oi.HaO KMnO^ K2SO4 KjC^H.O^ KHC^H.O« KNaC^H.O„.4HaO K,C,H N.O., KHCsH^N.O., c.,„h;,nA-"3H,o.... C,„H,.N,0,>^.H„SO, C2.,H,,N,0,.H2SO,. . C-HfiO., NaC.,H.,0...3H..O Na.,0o;.l6H2O' NaHCO, NaClOa". NaCl.." NaOH NaNO, Na.,HP04.12H20 Na;;8bS4.9H.,0 Na;;SO4.10H:,O Na.,S203.5H;0 SnCL,.". ...." SnCl.,.2H20 C«H,oOft SrCO., SrCl ■ SnOH). SnNOJa. Sr.,'PO,)., SrSO« ...*.... C„.H,,N,0,. 0.0057 l(K)t ."iH.OO 0.05 t?) 0.002 0.9 0.082 53.00 0.0044 10.3 100 ?) KM). 4 25.00 6.00 1.10 32.8 62.0 loot 0.12 40.5 30.00 213. 140. 26. 33. 4.8 6.6 9.2 151.5 0.453 59. 2.24 0.125 0.05 0.14 10.0 0.5 (?; 30. 60 10.5 95. 35.76 loot 84. 14. 34.5 35.96 116. loot 270. 0.(M) 0.00554 50.00 457 55. 0.00 0.0145 0.05 408 APPENDIX. NAMES. FORMULAS. PARTS. Strychnine chloride Cj.,H2.,N.,02.HCl 5. (h 300. Sucrai'. Cane ** Grape 75. " Milk C,2H220,,.HjjO 20. Sulphur 0.00 Sulphuretted hydrogen Sulphur dioxide H.,S 0.4918 SO a 14.33 Sulphuric acid H2SO4 all proportions. 7.0 {1, 138- Tartar emetic Tartaric acid 2iKSbOC4H40„ .HjjO C,H,0 Turpentine (oil) P* T?"" 0.05 H) Urea .• CON.H. 100.00 Uric acid C;,H^N^O, 0.0067 Zinc carbonate znc6,.*. "..:.........:. 0.00 " chlorde ZnCl.." .' loot '• oxide ZnO." 0.00 " sulphate ZnSO^.TH^O .50.5 INDEX. A. Acetates, 205. Acetone, 201. Acetylene, 180. Acetylene series, 174. Acid, acetic, 193, 204, " antimonic, 305, " arsenic, 159 " arsenious, 156, 157. '' benzoic, 239, 240. " boric, or boracic, 260, 2C2 broinic, 111. " butyric, 193, 207. nuosilicic, 259 •; formic, 192, 202, 203. " gallic, 243. " hippuric, 240, 242. nydriodic, ll4. " hydrobromic, 110. " hj'drochloric, 101. " hydrocyanic, 182, 183. ^, hydrofluoric, 117, 257. hypobronious. 111. '\ hypochlorous, 104, 105. hypophosphorous, 151. I) ti i< <( It <( i< It << << <( << «< << i< It hyposulphuruus, 127, Iodic, 116. lactic, 193, 214. manganic, 344. me«onic, 250. raetaphosphoric, 146. 149 muriatic, 101. nitric, S3, nitrous, 94. oleic, 207. orthophosphoric, 146. osmie, 315. oxalic, 171, 203, 208, 211 palmitic, 207. perchloric, 108. phosphoric, 35, 86, 146, 147 phosphorous, 146, 150. picric, 86, 239. propionic, 197. prussic, 100, 182. pyrophosphoric, 149. salicylic, 243. selenic, 140, 312. selenious, 140. silicic, 257. 258. stearic, 207. succinc. 211. fl3l.l34 sulphuric, 85. 127, 129, 13(», Add, sulphurous. 35, 125, 126, 128. tannic, 243. '' tartaric, 214, 216. thiosulphuric, 134. uric, 188. 7 valerianic, 196, 207. Acids, 35, 153 " dibasic, 132. " haloid, 103. Air, composition of, 72. Air, impurities of, 75. Albuminoids, 254. Alcohol, amylic, 194, 196. benzylic, 239. ' butylic, 196. ;; ethylie, 177, 192, 193, 195. methylic, 190. propylic, 196. salicylic, 248. Alcohols, 190. " diacid, 208. " isomeric, 197. Aldehyde, acetic, 195, 200, benzoic, 239. " cinnamic, 245. ^1 salicylic, 248. valerianic, 196. Aldehydes, 200, Alkaline earths 352, Alkaline reaction, 80. Alkalis, 368. Alkaloids, 249, " artificial. 263. Allotropv, 53. Alloys, 264. Alum, ammonia, 336. " chrome, 332. " iron, 326. " potash, 336. Alums, 332, 336. Alumina, 335. Aluminium, 334. " bronze, 334. " chloride, 334. " sulphate, 337. Amalgams, 284. Amides, 187. Amines, 198, 249. Animonia, 76, 80. Ammonio-cupric sulphate. 162 Ammonium, 82, 383. '* benzoate, 242. bromide, HI. 410 INDEX. « Ammonium carbonate, 385, '* chloride. 384. " cyanate, 185. " formate, 183. «• hydroxide, 383. •• nitrate, 87, 00. " oxalate, 210. " phosphate. 386. " picrate, 239. sulphate, 384. sulphide, l(K), 386. Amyifdalin, 239, 247. Amyl nitrite, 196. " acetate, 197. Amyloses. 220, 227. Anmsthetics, 177, 200. Analysis, 138. 269, 393. Aniline, 236. dyes, 232, 237. Anthracene, 247. Antidotes, 145, 254. Antimony, 101,304. •' butter of. 306. " pentoxide, 305. " sulphate, 304. " tetroxide, 3()4, 305, •• trichloride, 306. " trioxide, 217. 305, 306. " trisulphide, 136,305. Antimoniuretted hydrogen, 307. Antimony 1, 217, 307. chloride, 306 " potassic tartrate, 217, 306. Antipyrine, 253. Antiseptics, 193, 238. Apatite, 142, 358. Aqua Fortis, 83. Argentic salts (nee silver). Argol, 215. Aromatic series, 232. Arsenic, 61, 155. •* antidotes to, 158. *' flowers of, 156. '* pentoxide, 1.56. •• sulphides, 160. trichloride, 132, 162. " tri- iodide, 162. " trioxide, 155, 156, 157, 159. Arsenical wall paper, 162. Arseniuretted hydrogen, 161. \tmosphere, 67, 68. , omic heat, 48. " weights, 47, 48. theory, 44. Atomicity, 62. Atoms, 44, 47. Atropine, 25a. Avogadro's Law, 45, B. Balsams, 244. Barium, 361. Barium dioxide, 64, 362.' " fluosilicate, 259. nitra>L, 363. sulphate, 132, 361. Barometer, 67. Bases, 36, 37. Basicity, 86, 87, 203. Beer, 194. Beet sugar, 379. Benzene, 2:53 Benzene series, 232 Bismuth, :iOO. *' carbonate, 303. " chloride. M'L " oxide, 301. " nitrates, 301. " trioxide, 302. " trisulphide, 303. Bismuthyl carbonate, 302. chloride, 303. Black ash, 371. wash, 285. Blue vitriol, 295. Bleaching, 100. 106, 125. powder, 105, 138, 1 77, 202, .S.^7 Bf'iling points, 23. B ,;e ash, 143, 147, 358. bla<:>k, 14h. oil, 143, 168. Bones, 142. Borates, 261. Borax, 260, 261. Boron, 260. trioxide. 261. Boyle's Law, 69. Brimstone, 121. Bromides, 111. bromine, 98, 108. Brucine, 252. « Brunswick green, 296. Burtictt's disinfecting fluid, 340. Butter, 206. c. Cadmium, 297. " amalgam, 284. compounds, 298, 299. Cffisium, 388. Calcium, 353, acetate, 204. " carbonate, 3.55. " chlorate, 381. " chloride. 3.56, citrate, 218, 219. fluoride, 117, 118. " hydroxide, 354. " hvpophosphite, 151. oxalate, 209. " oxide, 353. •' phosphate, 358. sulphate, 98 132. 356. " thiosulphate, 123. INDEX. , Calomel, 285. Calculations, chemical, 50 Camphor, 245. Caramel, 222 Carbohydrates, 220 Carbon, 164. bisulphide, 113, 144 172 ^^ compounds, 167. .. dioxide, 43. 75, 77, 168. monoxide, 43, 171. Carbonates, 170 171 Carbonyl chloride, 187 Carboxyl, 203. Celluloid, 231. Cellulose, 230. Cerium and its comfwunds, 349. Charcoal, 35, 165, 166. Chalk, 355. Charles' Law, 70 Chemical action, 1, 6. Chemism, 38. Chemistry, l. n>!i ,°^8^a"'c,lfi7, 185. Chloral, 201. Chlorates, 107, Chlorides, 101,' 103. Chlorme, 98, 99. ;] ojddes, 104. r.u. o.\5'gen acids, 105. Chloroform, 177, 178, 202 Chromates, 331, 332 Chrome alum, 331, 332. yellow, 279, Chrommm, 329 II chloride, 333 ^^ hydroxide, 333. sesquioxide, 333. trioxide, 332. Chromyl chloride, lie Cmchonine, 251 Clay. 258, 337. SriS." ^'■"""''' ""^ ^'■'"'"'''" 1«2- Coal tar, 232. . Cobalt, 346. chloride, 347 '* nitrate, 346. Cocaine, 252 Collodion, 231. Combination by volume, 45 Combining weights, 42, 57 Combustion, 34, 38. 59, 76." Compounds, 6. Conine, 250. Conservation of matter. 41 Condy's fluids, 344, 345 " Copper, 293. Copperas, 321 Coprolites, 142. Corrosive sublimate, 288 Cream of tartar 215 Creosote, 191, 238, 239. Cresols, 238. 411 Crystallisation, 3, 24, 27 Crystalloids and colloids. 326 Cupric nitrate, 86. '■ oxide, 296. sulphate, 295. Cuprous chloride, 172, 296 iodide, 11.5. " oxide, 222, 296. Cyanides, 181, 183, 184. Cyanogen, 181. D. decomposition, doable, 270 l^eflm+e Proportions. Law of, 42. 44 Deliquescence, 27 ' Dextrin, 225, 229, Dextrose, 225, 248. Dialysis, 63, 326. Diamonds, 164. Diffusion, 62, 63 Digitalin, 248. Dimorphism, 356. Dissociation, 131. Distillation, 3, 80. Donovan's solution, 162 Dulong & Petit, Law of. 48 Dynamite, 86, 213 Earths, 352. Effervescing powders. 219 Efflorescence, 27 Electricity, 29. 390. Electrolysis, 392. Electroplating, 281. 313. Elements and Compounds, 5. 6 E ements. Table of the, 39. ii-lutriation, 2. Emery, 335. Epsom salts, 120, 3()4. Equations, chemical, 49. Equivalents. 42. Essence of mirbane. 235 Essences, artificial, 197. Ether, acetic, 195. " ethyl (sulphuric), 198, 200. '' nitrous. 195. ' ^' Ethers, 198. Ethylene, 178. Evaporation, 21, 23, 24 Explosion, 60. Fatty acids, 202. 207. Fats and oils, 207. Fehling's test, 223 226 Ferments, 76, 192. Fermentation, 192, 193. Ferric arsenite. 158. 'I chloride. 158, 324. hydroxide, 158, 325, 327 412 INDKX. Ferric nitrate, 322, 326. " oxide, 320, 327. " Hulphate, 322, 326. " sulphocyanate, 186. tartrate, 328. Ferrous ai senate, 159, 323. '* bromide, 324. " carbonate, 181, ;;23. iodide, 324 *• lactate, 215. " nitrate, 326. '• oxalate, 210. " oxide, 320, 322. " phosphate, 160, 324. sulphate, 321. " sulphide, 136. Filtration, 2. Flame, 176. Fluorides, 117, 118. Fluorine, 117. Fluor spar, 117, 259. Fluosilicates, 259. Formulas, 48, 49. 62. Freezing and melting, 18. Freezing mixtures, 26. Fusel oil, 194, 196, 197. Fusion, 4. G. Galena, 120, 273. Gas liquor, 80. Gas, olefiant, 17& Gases, 2. " Lawof Diffusion, 64. " Molecular weight of, 47. ♦' Solubility in water, 34. " volume of, 51, 70, 71, 72. German silver, 348. Glass, 274, 377. " etching of, 118. " soluble, 258. Glauber's salt, 371. Glucose, 194, 220, 225, 226, 244. Glucoses, 225. Glucosides, 227, 247. Glycerine, 203, 211. 213. " of borax, 262. Glycogen, 229. Glycol, 208. Gold, 312. Goulard's extract, 276. Gram-molecule, 51, 71. Graphite, 164. Green vitriol, 321. Group reagents, 270. Guano, 188. Gum, British, 229. •• benzoin, 240, 241. Gums, 230. Gun-cotton, 80, 230. Gun -powder, 88. Gypsum, 24, 98, 120, 356. H. Halogens, 98. Heat. 12. " expansion by, 14. latent, 20, 23, 26. " specific, 21. Hydrocarbons, 173. " saturated. 176. " unsaturated, 178. Hydrogen, 55, 58, 60, 61. " dioxide, 64, 65. " persulphide, 139. sulphide, 136. Hydroxides, 58, 190. Hvdroxy-acids, 214. Hydroxyl, 58, 190. Hydroxylamine, 83. Hypochlorites, 105, 106. Hypophosphites, I'^l, 152. Hyposulphites, 127. I. Indigo, 128. 134, 246. Infusion, 27, 28. . ' Iridium, 315. Ink, 244. 347. Inosite, 227. v Innlin, 228. Iodides, 112, 116. Iodine, 98, 112, 113, 126, 135. " chlorides, 116. " pentoxide, 116. Iodoform, 178, 195. Iron, 56, 318. dialysed, 325. " galvanised, 320. rust, 320. pyrites, 120, 121, 124, 155, 321. Isomerism, 179, 180. Isomorphism, 159, 332, 336. Jalapin, 249, Jet, 167. J. K. Kairine, 253. Kaolin, 337. Kelp, 108, 112. Ketones, 197, 201. L. Lactose, 223. Lamp-black, 165. Latent heat, 20, 23. Lau£:hing gas, 90. Lead, 272. " acetates, 103, 206, 276, 276. " black, 164. ** bromide. 111, J INDEX. 413 Lead chloride, 103, 277. 'I '•hromate, 331.' hydroxide, 88. , iwlide, 11.5. nitrate, 85, 87. 95, 276. oxtdes. 274, 275. phosphate, 147. ^^ plaster, 212. 278 poisonin^r, 279. red, 274. 276. sulphate. 132, 278. ' white, 276. Ledoyen's disinfecting fluid 276 Levulose. 22.5. 227. ' Lime, chloride of, 357 millc of, 355. quick 353. slaked, 354. Liquids, 2. Liaterisni. 238. Litharfire, 205, 274. Lithium and ooinpound.s, 387. Litmus, 35. . oi. M. Maceration, 27. Mag-nesia, 366.' alba, 365. Magnesium, 363. carbonate, 365. citrate, 219. )' oxide, 366. sulphate, 98, 364. Manganates. 343. Manganese, 341. ;' dioxide,'33, 99, 341, 342. salts, 343. Mareh gas, 175. Marsh's test, 161. Massicot, 274. Matter, three states of. 2 Mercurial poisoning, 291 Mercuric chloride, 288 iodide, lis. 162, 289. nitrate, 287 oxide, 32, 112, 287, 289. su phate, 285. 287, 288. sulphide. 290. Mercurous bromide, 111. chloride, 103, 285, iodide, 115. 286. nitrate, 103. 285. sulphate 132. Mercury. 283. Metallurgy, 263. Metals, 39, 263. I' classifieation of, 269 compounds of, 265. Methane, 175, 176. ethyl, 192. «' amine, 198. *' chloride, 198. << It « « ^Jt'tjiyj salicylate, 191, 24.1 Methylated spirit, 191 Microcosmic salt, 148, 386. Minium, 274. Mi-xtures, separation of, 2. Mohr s suit, 323. Molasses, 221. Molecules, 45, 46. Morphine. 250, Mortars and cements, 3.59 Mucilages, vegetable, 230 ' [90. Multiple proportions'. Law of. 43, 44] N. Naphthalene, 246. Nessler's reagent, 289. Neutralisation. 88 Nickel, 347, 348. Nicotine, 250. Nitrates, 85, 86, 88. Nitre, (see Saltpetre) Nitrites, 94. Nitrobenzene, 2.35, 240 Nitrogen, 72, 79. compounds in air, 76. dioxide, 92, 93, 129, 173 monoxide, 90, 91 I pentoxide. 9.5. " tetroxide (peroxide). 95 trioxide, 93. Nitroglycerine. 86, 213. Notation, chemical, 47, o. Oil of bitter almonds, 236, 240 cinnammon, 245. cloves, 245. vitriol, 129, 130. wintergreen, 243. Oils, drying. 274. Oils, essential, 245. Olefines, 174, 178 Olein, 212. Orpinient, 160. , Osmium, 315. Osmose, 63. Oxalates, 210. Oxides, 35. Oxidising agents, 65. Oxygen, 32, 33, 34, 73. Oxymel, 223. Oxy -salts, 307. Ozone, 52. Palladium, 315. Palmitin, 212. Paraffin oil, 174. p '' wax. 137, 174. Paraffins, 168, 174. Paris green, 1,58. 414 INDKX. « Pearl ash, 37». Percolation, 28. Penuan^'anates, 344. Peroxides, 2(i7. Petirolemn, 168. Phenol, 237. Phosphates, 142, 148. Phosphine, 152. Phosphoretted hydrofjen, 150, 152. Phosphorus, 35, 142, 143. "' oxides of, 145. " pentachloride, 153, 100. " pentoxide, 43, 146. " testa for, 146. tribroniide, 110. trichloride. 150, 158. trioxide,. 43.146. Phosphoryl, 153. Photoj,'raphy, 136, 299. Plaster of Paris. 356. Platinum, 60, 3i3. Plumbago, 1(J4. Plumbic compounds (see Lead). Poisons, 395. Porcelain, 337. Potash lye, 381. Potassium, 378. [330. " bichromate, 33, 65, 115, 143, bromide, 110, 382. carbonate, 379. acid carbonate, 380. chlorate, 32, 99, 104, 107, 381. chloride, 98. cyanide, 182. ferrlcyanide, 328. ferrocyaiiide, 171, 181. fluosilicate, 107, 256, 259. hydroxide, 380. hypobromite, 111. iodide, 112, 115, 278, 383. manganate, 343. nitrate, 381. perchlorate, 108. permanganate, 344. sulphate^ 83. sulphocarbonate, 173. sulphocyanate, 185. Potato oil, 196. Pottery, 337. Powder of Algaroth, 306. Precipitation, 269. Proteids, 254. Prussian blue, 181, 246, 328. Ptyalin. 223. Pure substances, 2. Q. Quantivalence, 62. Quicksilver, 284. Quinine, 251. <( It i< <( (f i< <• etate, 175, 206. " antimonite, .305 " arsenate, 159. INDKX. ScKliuin arsenite, 158. benzoate, 242. biborate, 261. broiuifle, 376. carbolate, 237. ^^ f-arbonate, 112, 371 bi-carbonate, 373. chloride, 369. cyanide, 181. hydroxide, 57, 373. „ hypochlorite, 1{)6. ,, bypoaulphite. 128. nianganate, 343. nitrate, 83, 374. nitrite. 94. oxalate, 209. ,^ oxides, 369. phosphate, 375. ^^ silicate, 258. sulphantiuionite, 305. sulphate, 370. bi-sulphate, 84. sulphide, 376. ,1 sulphite, 1-26. 375. thiosulphate 135 Solids, 2^^''"''"'^*^' 1^«' 207. Solubility, 25. Solution, 3, 24. chemical, 25. latent heat of, 26 saturated, 25. supersaturated, 26, Specific heat, 21.