rWiBWW €i>€aaiSTii:T mmimS^oimsmi ^null Uttirmitg pitotg THE GIFT OF .'?n^..^.,^..,siolLs..M,.. ..K.A.^r\b.?w :.\?\,\4i-\av.. Cornell University Library arV19357 Twenty lessons in inorganic cliemisti 3 1924 031 295 508 olin,anx Cornell University Library The original of tliis book is in the Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924031295508 TWENTY LESSONS INORGANIC CHEMISTRY: EMBRACIKG IBB CovKSE OF Instruction in Chemistry eeoijired for the First Stage OR Elementary Classes of the Science and Art BeparTment. W. G. YALENTIN, F.C.S. op London and Berlin, principal assistant in the rotal college of chemistry, scibkcs schools, south kbnsinoton, SSit^ dngrabitigs on SEoaI>. NEW YORK: P. PUTNAM'S SONS, 182 FIFTH AVENUE. A.l'^rW'^U' PEEFACE. This little book has been prepared in order to ease the teacher's task of conveying, ia Twenty Lessons, sound chemical instruction to their pupils, and to help the latter to get as quickly as possible over the difficulties which the study of chemistry presents. It is based upon the plan sketched out in the Science and Art Directory, which there is really little fault to find with, except, perhaps, on the ground that it expects too much from young pupils, such as are usually found attending the elementary stage of instruction. I have confined myself all but exclusively to the simple experiments traced out by Dr. Frankland. A glance at the table of contents will show that I -have gone a step further, and have added instruction in the few other non-metallic elements which are not included in the syllabus, but are, in my opinion, capable of completing the interesting relations of the natural groups which the non-metallic elements form, and thus of contributing materially to the enjoyment of the beauty and symmetry which pervades chemical science. I have made them serve, moreover, as a natural basis for conveying the all-important theoretical instruction in volume combination, and combination according to atomic proportions by weight. These additions are, however, printed in Appendices and in difierent type from the main portion of the text, and their study is left optional. The experiments are explained with great care, and reduced to the simplest possible form, Man^y a practical hint will 4 PEEFACE. be found interwoven in the text, the observance of whicli ■will make secure of success. This, I hope, will render the book a safe guide also to the many who have of necessity to be their own teacher. It is not enough, as every teacher knows, to exhibit experiments before a class, unless they are made subservient to explain the theory of the science, and to place it on a sound basis. All theoretical explanation should be based upon experiments which fix it upon the memory. This is the plan which I have laid down for my guidance. Pupils will thus learn with ease and rapidity, and acquire in a short time a sound knowledge of Elementary Chemistry, upon which it will be possible to base the more extensive know- ledge, which the syllabus for the Second or Advanced Chemical Course of instruction prescribes. By using the simple form of chemical notation, which is all but generally adopted by chemists in this and other countries, and giving at the same time due regard to the theory of atomicity, I hope I have succeeded in remov- ing a stumbling-block. By accepting as basis the theory of varying atomicities in the non-metallic elements treated of, I trust the reproach of useless complication of the theo- retical teaching of beginners will to a great extent fall. The theoretical explanation thereof is, to some extent, based upon the clear exposition which will be found in Von Bichter's Introduction to Inorganic Chemistry, to which little German work I am in many other respects greatly indebted. W. V. KoYAL College of Chemistet, Sqvth Kensototon, May 1879. CONTENTS. LESSON I. FAGE Hydrogen — Decomposition of Water by Sodium— Preparation of Hydrogen from Zinc and Hydrochloric Acid — Properties of Hydrogen — Summary, ..... 9 LESSON II. Electrolysis of Water— Voltaic Electricity— Volume Propor- tions of Hydrogen and Oxygen — Proportions by Weight — The Crith — Summary, . .... 19 LESSON in. Preparation of Oxygen — Its Properties — Storage of Gases — Oxides of Metallic and Nou-metaUic Bodies — Combustion — Summary, ^..^ . . . . . .26 LESSON IV. Physical State of Matter — Physical and Chemical Changes — Mechanical Mixtures — Chemical Compounds — Elements — Metals and Non-metals — Composition of Air — Electro- positive and Electro-negative Elements — Summary, . 36 LESSON V. Chlorine, Preparation of — Properties of Chlorine — Chlorides — Chlorine a Bleaching Agent, and (indirectly) an Oxidising Agent. Appendix: Bromine, Iodine, and Fluorine, Pre- paration of, . . . . . . .47 LESSON VL Hydrochloric Acid, Preparation of — Properties of — Electroly- sis of Hydrochloric Acid— Metallic Chlorides, Preparation of. Appendix: Hydrobromic Acid — Hydriodio and Hy- drofluoric Acid, Preparation and Properties of, . . 5S LESSON VIL Constant Combining Proportions— ^Atoms and Molecules — Atomic and Molecular Weights — Molecular Volumes — • Specific Gravity of Gases — Equal Gas Volumes contain the same number of Molecules — Chemical Formulae — Sym- bolic Chemical Notation — Summary, . . .66 CONTSNIS. LESSON Vlll. Pkdi (Sulphur, Extraction of— Crude Sulphur, Roll Sulphur, an! Flowers of Sulphur — AUotropic forma of Sulphur: Octa- hedral, Prismatic, Plastic, and Amorphous — Chemical Properties of Sulphur — Sulphuretted Hydrogen, Prepara- tion and Properties of Hydroaulphurio Acid — Metallic Sulphides. Appendix : Selenium, AUotropic Modifications of — Selenietted Hydrogen — Tellurium — Tellurides — Tel- lurietted Hydrogen — Summary of Sulphur Group, . 72 LESSON IX. Nitrogen — Ammonia, Properties of — Electrolysis of — Sal- ammoniac — Ammonium. Appendix: Phosphorus, Proper- ties of — AUotropic Forms of Phosphorus — Phosphoretted Hydrogen — Phosphoninm — Arsenic, AUotropic Modifica- tions of — Arsenietted Hydrogen, Properties of — Arsenides — Antimonietted Hydrogen — Summary, . . .S3 LESSON X. Carbon — Hydrocarbon — Carbohydrates — Carbonates, AUo- tropic Modifications of — Amorphous Carbon — Graphite Diamond — Absorptive Power of Charcoal for Gases — Com- pounds of Carbon and Hydrogen — Marsh Gas, Preparation and Properties of. Appendix : Silicon — Siliciuretted Hy- drogen, Preparation and Properties of — Tin — Summary of Carbon Group, ...... 95 LESSON XI. Quantivalence or Atomicity of Elements — Definition of — Rela- tion between the Hydrogen Compounds of the Carbon, Nitrogen, Oxygen, and Chlorine Group— Grouping Ele- ment— Non-saturated Elementary Groups or Compound Radicals (Semi-molecules) — Constitutional or Structural Formulae — Graphic Formulae — Varying Atomicity — Hy- drogen Valency and Oxygen Valency— Absolute Atomicity, 102 LESSON XIL Oxides of Carbon — Carbon Dioxide or Carbonic Anhydride, the result of Combustion and Respiration — Carbonates, De- composition of by Heat, by Acids — ^Properties of Carbonic Anhydride — How Demonstrated — Condensation of — Liquefaction of — Critical Point of Temperature — Carbon Monoxide, Preparation and Properties of, . , 109 eoKTSKTa, LESSON xm. PAas Ozone, Hydroxyl, and Hydrosnlphyl— Preparation and Pro- perties of Ozone— Testa for Ozone — Gas Volume and Mole cular Weight of Ozone— Hydrogen Peroxide, how Pre- pared — Decomposition of Hydrogen Peroxide — Hydroxy!, a Compound Monad Radical. Appendix: Metallic Hy- drates — Compounds of Metals with Hydroxyl, called Hydroxides — Functions of Hydroxyl and Metallic Per- oxides— Metaloxyls— Definition of Oxy-salts— Hydrosul- phyl— Sulpho-aalts, , . . . .115 LESSON XIV. Boron — Occurrence in Nature — AUotropio Modifications of Boron — Amorphous, Crystalline or Diamond, and Graphi- toidal Boron — Compounds of Boron with Oxygen, etc. — Relation of Boron to the Non-metals and Meta6, . . 122 LESSON XV. Oxygen Compounds of Metalloids— Anhydrides and Acids — Oxygen Compounds of Chlorine — Synopsis of some of the most important Anhydrides and Acids of the Chlorine, Sulphur, Nitrogen, Carbon, and Boron Group— Varying Atomicity of CI, Br, I rendered probable, and Chain Form of Atomicity Grouping abandoned for varying Atomicity Grouping — Preparation of Oxygen Compounds of Chlo- rine, Chlorates, Perchlorates, Hypochlorous Anhydride, and Hypochlorites, ,....', 125 LESSON XVL Oxygen Compounds of Nitrogen, how formed in Nature — Pre- paration of Nitric Acid from Nitre or Chili Saltpetre, Properties of — Aqua Regia — Oxidization of Nitric Acid, with Formation of Lower Oxides of Nitrogen — Preparation . and Properties of Nitrogen Tetroxide — Molecular Volume varying with Temperature — Decomposition of — Nitrates and Nitrites — Oxidising and Reducing Action of NjOj — Nitric Oxide or Nitrogen Dioxide, Preparation and Pro- perties of — Nitric Oxide a Carrier of Oxygen — Molecular Volume Composition irregular — Nitrous Oxide, Prepara- tion and Properties of — Nitrogen, its Preparation from Ammonium Nitrite, ..... 132 CONTENTS. LESSON XVII. Oxygen Compounds of Sulphur— Sulphur Dioxide, Preparation and Properties of — Sulphurous Acid a Powerful Bleaching and Disinfecting Agent — Preparation of Sulphur Trioxide or Sulphuric Anhydride — Views on the Molecular Consti- tution of Sulphuric Acid — Manufacturing Process Illus- trated Experimentally — Sulphites — Sulphates — Hyposul- phites — How Prepai'ed — Decomposition of, . , 143 LESSON XVIIL Definition of Chemistry — Nature and Classification of Chemical Changes — Practice in Reading Formulae and Substituting Atomic Weights for Symbols, , . . , 151 LESSON XIX. Wei^ts and Measures — Conversion of French into English Weights and Measures — Practical Examples, , ,155 LESSON XX. Questions and Exercises on all the Previous Lessons, , ,159 APPENDICES. I. Table of Elements, Names, Symbols, and Co-efficients of Atomicity, . . . . , . . 175 II. Syllabus of Elementary Course in Inorganic Chemistry, Beprinted from the Science Director]/, , , . 177 LESSONS IN ELEMENTAEY CHEMISTRY. LESSON I. HYDROGEN. Exp. 1. — KU a glass cylinder (or large test tube) with water, cover it with a watch-glass or small glass plate, and invert it over a basin of water, taking care not to e31ow any air bubbles to get into the cylinder. Kemove the cover under water; the water in the cylinder or test tube will remain supported by the pressure of the atmos- phere. Next procure a piece of sodium of the size of a small pea, Pig. 1. — Decomposition of Water by Sodium. wrap it up tightly in a small piece of iine soft wire gauze, and hold it by means of a wire fastened to the wire cage or by the aid of a small spoon, as seen in fig. 1, underneath the mouth of the inverted cylinder. Sodium being a soft wax-like metallic body which has a great affinity for oxygen — a constituent of the atmosphere — ignites 10 ELEMENTARY CHEMISTRY. Bpontaneously in air, and has therefore to be kept in petroleum, A liquid body which contains no oxygen. If the eodimn has to be out into smaller pieces, the cutting should be effected under petroleum, and the required piece removed on the point of a penknife to dry blotting paper, and rapidly freed from the adhering petroleum by gentle pressure between the folds of the paper. To avoid accidents from burning, it should on no account be touched with the fingers. Gas bubbles are speedily observed making their way upward through the water, and being lighter they displace the. water. The bubbling (evolution) lasts a few seconds, and the sodium is seen to disappear entirely. By repeating this operation, if necessary, the whole of the water in the cylinder can be displaced, and a sufficient quantity of the gas collected for examination. Now, what do we learn from this experiment 1 From the fact that the cylinder can be turned upside down, without the water running out, we learn (1) that the water is held up by the pressure of the atmosphere, in accordance with Torricelli's law, viz., that a column of water, 33 ft. in height, confined in a tube, closed at one end, would in like manner be held suspended over water. (2) That a gaseous body (hydrogen) may result from the chemical action of a solid (sodium) upon a liquid body (water), and that the chemical change is induced by the affinity which the metallic , body sodium has for oxygen, no matter whether present in air, or as a constituent of water. We have yet to examine the products of the change, viz., the gaseous body and the new compound which the metal sodium formed with the remnant of the water. Since the gas can be left confined over water without perceptibly decreasing its bulk (100 volumes of water are known to absorb only 1'9 volumes of hydrogen), we learn from the experiment (3) that we have to deal with a gas which can be collected over water without material loss; we also perceive (4) that the gas is colourless. On closing the cylinder with the glass plate (best greased) under water, removing it from the water and phicing it again in an upright position, we may keep the gas unchanged, if the glass plate fits tightly. On bringing a lighted taper near the gas, a test invariably applied to gaseous bodies, we learn (5) that the gas is inflammable ; it bums where it is in con- tact with air with a feebly bluish wave-like flame, but gives out a very faint light only. The hydrogen forms water with the atmospheric oxygen, hence its name hydrogen, fiYDROGEN. U 6t generator of water (from the Greek words «>w< = water; ytmia, I generate). We have now, lastly, to examine the Water which is left in the basin. Chemists possess, in test papers prepared from certaia soluble vegetable colouring matters, such as litmus, turmeric, etc., a capital and simple means of testing liquid bodies. When the litmus is turned red, the liquid is termed acid. The blue colour of a solution of litmus can be turned red by the addition of a single drop of a very dilute acid ; and by dipping unsized filter paper into this red fluid we obtain, on drying, a red litmus paper. If this be put into a liquid containing substances, such as soda or lime, the acid absorbed by the paper is neutralised, or rendered inac- tive, and the original blue colour is restored. Bodies which produce such an effect are termed alkaline bodies. Papers prepared with a solution of turmeric — a yellow colouring matter — are turned brown by an alkaline body, and green by an acid body. The water used in the experiment should be tested first, both with red and blue litmus papers. On dipping litmus papers into the water the papers should remain unchanged (neutral) before, but will show a strong alkaline reaction after the experiment. The water left in the basin imparts also a soft soapy touch to the skin, and on evaporating a little in a glass or porcelain dish, it leaves a fixed residue of caustic soda, or sodium hydrate, possessing these properties in an increased degree. Chemists have agreed to use symbols in place of words (generally the first letter of the word, mostly of Latin or Greek origin), and to express chemical changes by symbolic equations; the change whereby hydrogen is produced is thus expressed as follows: — 2OH2 + Naj = Hj + 2NaOH. Water. Sodium, Hydrogen. Sodium hydrate, or or Natrium. Caustic soda. which reads thus: — Water to which metallic sodium has been added yields hydrogen gas, and leaves a weak solution of sodium hydrate, or caustic soda. Other metals, such as potassium, calcium, etc., decompose water likewise at the ordinary temperature, combining with the oxygen, and set- ting free the hydrogen; others, again, only when heated, or 12 ELEMENTARY CHEMISTRY. ■when steam is passed over the heated metal, such as iron, etc., confined in a porcelain tube and heated in a furnace. Other metals, lastly, possess little or no chemical attraction for oxygen, and do not, therefore, liberate hydrogen under any circumstances, e.g., platinum, gold, etc. Exp. 2. — Larger quantities of hydrogen are more economically prepared by acting upon zinc or iron filings with dilute hydrochloric or sulphuric acid. If we pour a little dilute acid over clippings of sheet zinc, or over granulated zinc (prepared by melting zinc and pouring it from a height of about 6 ft. into a vessel full of cold water, or by powdering, in a warm iron mortar, zinc heated to about 200° C, when it becomes very brittle), we immediately observe gas bubbles coming off. The reaction takes place according to the symbolic equation : — Zn + 2HCa = Hj + ZnCl, Zinc. Or, Zn + Zinc. Hydrochloric acid. HjSO* Zinc chloride. ZnS04 Sulphuric acid. Hydrogen. Zinc sulphate. Kg. 2. -PKEEABATIOlf OF HtDROGEN PKOM ZiNC AND Hydeochloeic Acid. If a tumbler be used, and a light brought near, the gas, instead of burning, as described before, explodes with a sharp report. Being mixed with air, it forms, in fact, a highly explosive mixture. To study the ^properties ef hydrogen at leisure, it is best to use an apparatus m which the gas can be generated, from the materials HYDROGEN. 13 mentioned above, in such a manner as to enable us to collect it over water. A convenient apparatus — capable of being employed also in the generation of other gases — may be fitted up as follows : — Procure a so-called Woulfe's bottle, fit it by means of perforated corks with a straight funnel tube and a delivery tube, bent at right angles (as in fig. 2). To perforate a cork employ a small rat-tail file; heat its point to redness iu a flame, and push it straight through the cork; then widen the hole it makes with a round file, till the glass tube to be fitted goes through it tightly, yet easily. This method answers best for small holes. Cork borers made of different-sized metal (steel or brass) tubes are sold which cut clean holes of any size required, if they are kept sharp and are properly handled. If the hole be not quite true, the glass tube is liable to break off in the operator's hands, and bad wounds frequently result from the broken pieces of glass entering the hand. The cork to be perforated should be care- fully selected, and should be softened by pressure with the thumb or cork-squeezer, or by rolling it gently, a few times, under one's boot, before it is bored and fitted to the apparatus.* To bend a glass tube at a right (or any other' required) angle appears at first sight a simple operation. The following points have, however, carefully to be attended to. Heat the glass tubing equally in a flame — best in the flame from a bat's-wing or fish-tail gas-burner — so as to soften it by slowly spinning the tube round between the thumb, the fore and middle finger of each hand, whilst holding it in the luminous part of the flat flame. The glass becomes covered with a film of lampblack, which prevents it from cooling too rapidly when it is withdrawn from the flame. As soon as it is felt that the glass has become soft enough to bend it easily up and down, it may safely be bent to any shape required. If force has to be applied it is a sure sign that the glass has not been properly heated, and that it will crack either during the bending or soon afterwards. The bend should be nicely curved, and the glass should retain its round shape, and not sink in and double up, as it almost invariably does when it is held in a hotter flame, such as the flame of a spirit-lamp, or of a Bunsen gas- burner. To cut glass we have only to make a scratch across with a good three-cornered file, then hold it firmly with the two hands and apply gentle downward pressure, at the same time pulling it gently apart. A sharp and regular break results. The sharp edges should be taken off by heating the ends in a hot flame (such as the flame of a spirit-flame vi Bunsen gas-burner), tUl they are sufficiently melted to allow the cooled glass tube to slip readily through the hole in the cork, and not to tear it, as would otherwise be the case. Moistening the ends with a drop of water (and in the case of india-rubber with a drop of glycerine) also assists greatly. * It cannot be too strongly impressed upon the manipulator that atten- tion to these minutiae is absolutely necessary, in order to secure success in worMng with gases. Perforated india-ruhber corks can now be bought of varying sizes, but they are comparatively expensive, and become hard and brittle after a time, 14 ELEMENTARy CHEMISTRY. Prepare next a delivery tube, bent slightly upwards (as seen in fig. 2) for the ready delivery of the gas; join it by means of a small piece of flexible ilack india-rubber tubing to the tube bent at a right angle. We possess now a very serviceable apparatus which, when done with, should be set aside for other experiments. For the collection of the gas procure a basin of water about three- quarters fiill, or better still a so-called pneumatic trough, provided with a perforated bridge and overflow pipe; also a couple of glass cylinders or good-sized test-tubes. A few glass plates, well greased on one side, * should also be kept ready at hand, wherewith to close the cylinders, whilst they are inverted over the trough, when full of water, and after they have been filled with gas, and removed, ready for use. Next charge the Woolfe's bottle with about an ounce of granulated ziuc, refix the funnel and delivery tube firmly, and intro- duce enough water to cover the lower end of the funnel tube, then add moderately concentrated hydrochloric acid, or dilute sulphuric acid, and the evolution of hydrogen vnll begin at once. To test whether the corks and india-rubber joints are tight, it is only neces- sary to close the delivery tube for a few moments with the finger. The acid is seen speedily to make its way up into the funnel tube. A few drops of water put around the top of the cork would also readily show any escape of gas, when it is put under pressure. If any leakage should be discovered which cannot be stopped by insert- ing the corks more firmly, it is best to reject the corks and perforate sounder ones. Lutings of whatever kind are at best unsightly, and rarely of any use. Some time — dependent upon the size of the generating apparatus — should be allowed for the displacement of the atmospheric air which fills the apparatus. In order to ascertain whether the air has been suflSciently displaced, some of the gas is collected over water in a little test-tube. When quite fuU the tube is withdrawn by closing its mouth, under water, with the thumb. If on appljdng a lighted taper to the gas it bums with a slight explo- sion, it may be taken as an indication that the air has not been suffi- ciently displaced, and that it cannot be collected with safety. This precaution should never be neglected, for with leaky or rotten corks, the gas may come oflf freely, and yet, by relying merely upon the length of time it is allowed to come off, dangerous explosions are of not unfreqnent occurrence, especially also if the limb of the right angled delivery tube is inserted too deeply. It should, in fact, just pass through the cork and no more. In the place of the zinc we may also employ iron scraps, filings, or borings, according to the equation : — Fe + 2HC1 = H, + FeCl, Iron. Hydrochloric acid. Hydrogen. Ferrous chloride. Hydrogen gas generated from zinc has a most disagreeable » Rosjji peiate, ^ prepared for phanpaceiitjcal purposes, answers best, HYDROGEN. 15 smell, wiiicli Is still worse when iron is used. This arises from the presence of carbon (sulphur and phosphorus) in the metals, which elements by entering into combination with the hydrogen, form gaseous compounds, called carburetted (sulphuretted and phosphoretted) hydrogen. Pure hydrogen is inodorous. Having filled several cylinders, we will next examine what are the properties which the gas possesses. Exp. 3. — On applying a light to the mouth of the cylinder, the gag is seen to burn quietly for a few moments with a lambent non- luminous flame; the glass becomes heated. Hydrogen is an inflam- mable gas, as we have already seen in Exp. 1. We will now invert another cylinder full of gas, take off the glass plate and introduce a lighted splinter of wood (best of cedar-wood), or lighted wax taper. Kg. 4 The gas inflames (fig. 3), and burns at the mouth quietly with a bluish flame. As soon, however, as the taper is pushed upwards through the flame into the hydrogen, as shown in fi^g. 4, it is imme- diately extinguished. On withdrawing the taper again, it ignites once more, when it reaches the burning gas at the mouth of the cylinder. The taper may thus be extinguished and rekindled several times in Bucoession, as long, in fact, as the gas lasts. This proves, then, that hydrogen does not support comius- 16 ELEMENTARY CHEMISTRY. tion; it hums, however, but only where it is in contact with the air, i.e., at the mouth of the cylinder. Exp. 4. — Collect hydrogen in a soda-water bottle, filled to about two-thirds with air, and fire it as in a previous experiment; it explodes with a loud report. This shows that if hydrogen and air be mixed — ^best in the proportions of 1 to 2 — they will not combine at the ordinary temperature, but explode when brought in contact with a spark, or light, or some substance hot enough to raise the temperature of the gaseous mixture to the ignition point, i.e., to a degree of heat at which they ignite or catch fire. Repeat the experiment by filling the soda-water bottle over the pneumatic trough with a mixture of 3 parts of air and 1 part of ordinary coal gas, largely composed of hydrogen gas. It will explode in like manner with a loud report. This well illustrates the danger from an escape of coal gas in our houses. There is no danger, as long as the explosive mixture does not come in contact with a flame or heated body. Repeat the latter experiment, taking, however, say 20 parts of air to one of ordinary coal gas. Apply a light ; the mixture no longer fires, or, if it does, produces only a feeble report. Instances of such gaseous mixtures, largely diluted with air, occur in our coal mines. It is safe to use lighted candles in some mines as long as the com- bustible gases, which issue from the coal in the form of blowers, etc., are removed by thorough ventilation. If there is, however, a sudden overpowering rush of gas mixed with fine coal dust, the result must necessarily be an explosion. Exp. 6. — Take two cylinders filled with hydrogen gas. Remove the glass plates and leave one upright for about a minute, and place the other with its mouth downward. Apply now a light to No. 1, there is no report, and the lighted taper can be lowered to the bottom without being extinguished. Bring the taper near the mouth of No. 2; the gas bums at the mouth, and when the lighted taper is moved upwards, it is extinguished. Hydrogen, being a very light gas, has escaped from cylinder No. 1, and atmospheric air has taken its place. Hence the taper continued to bum in it. In the second cylmder the hydrogen, for the same reason, remained confined, and prevented the heavier air from ascending. HYDROGEN. 17 Exp. 6. — Hold a cylinder full of hydrogen to the mouth of another cylinder fuU of air, in the man- ner shown in fig. 5. After a few minutes apply a light to the latter and an explosion takes place. This shows that the cylinder contains now a mixture of hydrogen and air, the hydrogen gas having made its way from the lower into the upper cylinder. Hence it must be lighter than air. Exact experiments have established the fact that hydrogen, is 14'46 times lighter than air, its specific gravity being '06926, as compared with air = 1. Owing to its great light- Fig. 5. ness, it serves with great advantage for filling balloons. Coal gas, although eight times heavier than hydrogen, is much cheaper and more readily procurable, and is now generally employed for such purposes. Fig. 6. Exp. 7. — The delivery tube, bent at a right angle, is connected with a drying tube (containing pieces of well-dried calcium chloride, a substance which possesses great attraction for water), and a glass tube drawn out in a flame to a fine point, and out off so as to have a fine jet, as seen in fig^ 6. The hydrogen ia allowed to escape for a few minutes before it is lit. The gas burns with a pale blue flame, which, however, is exceedingly hot. Introduce the jet into a dry glass tube held upright, and about J inch wide, and from 2 to 3 feet in length. It will be seen to become covered on its inner side with moisture, which after a short time runs down in streaks. At the B 18 ELEMENTAEY CHEMISTRY. same time it gives out a musical note varying, as in organ pipes, with the width and height . A lower or higher note may be produced accord- ing as the burning jet is cautiously lowered or raised. The explanation is that as the air rushes into the hydrogen flame, a number of explo- sions are produced which cause the glass to vibrate. Next burn the gas under a well dried wide-mouthed bell-glass, held slantingly, as seen in fig. 6, and the vessel soon becomes covered with moisture on its inner surface, and drops of condensed water collect and run down. This proves that water is formed by the combustion of hydrogen in air. The oxygen of the air combines with the hydrogen and forms water. Two gaseous bodies unite with each other and form a new (compound) body, gaseous at first, i.e., in the form of steam, liquid when condensed to water. The change is expressed by the symbolic equation : — -t- H^ = OHj Oxygen. Hydrogen. Water, Hydrogen can also be burned, i.e., made to combine with oxygen, by causing it to pass over certain finely divided cold metallic bodies, such as freshly ignited spongy platinum, which has the power of condensing on its surface — immensely increased by its porous condition — both hydrogen and air, and of calling the chemical force, inherent in each, into activity. The spongy platinum glows and becomes intensely heated. Close contact between elementary matter, then, is conducive to chemical changes. The resulting new body is water (steam). The platinum remains unchanged. We are acquainted with numerous organic bodies, or bodies derived from the vegetable kingdom, which contain hydrogen, besides carbon — their fundamental constituent, — such as oil of turpentine, paraffin, petroleum. Based upon the experience gained in the preceding experiments, we may conclude that when they are burned in air, their hydrogen is likewise left behind as water (steam). After what has been explained, the studentshould have no difficulty in proving this experimentally. Of the compounds which carbon forms with oxygen, we shall have to speak hereafter. Summary. — Hydrogen is an ivflammahh gas. It hums in atmospheric air, producing much heat, hut giving out little light. It forms, with oxygen, water (steam). It is the light- est of all known gases. It is colourless, tasteless, inodorous, and cannot support life. LESSON 11. ELECTKOLTSIS OF WATEK, In Exp. 4 we have seen that a compound body, viz., •water (steam), was formed by the chemical union of hydrogen and oxygen. We will now see whether we can break up this body into its component elements in such a maimer as to collect separately both the hydrogen and oxygen. A French chemist, St. Claire Deville, has shown that the decomposition of strongly heated steam begins at 1200° C, and is complete at the temperature of 2500° C. He ascribed the change to the dissociation of the highly heated molecules* or smallest quantities of matter capable of existing in the free state. The experiments which are required to illustrate this change, produced by heat alone, must necessarily remain consigned to the lecture room. If we call to our aid, how- ever, another of nature's agencies for producing chemical changes, viz., voltaic electricity,^ we shall have no difficulty in effecting the desired change. Kg. 7. Exp. 8. — ^Plunge the platinum electrodes of a voltaic battery (con- sisting of two zinc-carbon ceUs at least) into water (fig. 7), to which * From moUs = a mass. t The student should study in some good manual of Natural Philosophy the laws of the electric current, and make himself familiar with the apparatus employed for producing voltaic electricity. 20 ELEMENTARY CHEMISTRY. a few drops of dilute sulphuric acid hare been added, and we observe immediately small gas bubbles arising from the strips of platinum, and escaping through the liquid. One volume of oxygen escapes from the positive electrode connected with the carbon end, and two volumes of hydrogen from the negative electrode connected with the zinc end of the battery. Both gases can be collected either separately or mixed together in the same receiving vessel. Kg. 8. Exp. 9. — A convenient voltameter of a simple kind can be fitted by the student as follows : — Take a wide-necked 4 or 6 ounce bottle; fit a good cork, and perforate it so as to receive two short bits of glass tubing and a delivery tube, bent as seen in fig. 8. Draw out the short glass tubes by heating in a flame, and seal platiaum wires air-tight into the drawn-out ends, to which strips of thin sheet platinum are attached. The bottle is nearly filled with acidulated water, and the drawn-out glass tubes made to dip under the water, so that no part of the platinum surface should come in contact with the mixed gases evolved ffom the platinum electrodes, lest contact action should produce an explosion. A few drops of mercury are poured into the open tubes in order to make contact with the platinum electrodes. When the copper wires leading to the battery are introduced into the mercury, gas bubbles come off readily as soon as connection with the battery is made, and escape through the delivery tube, and may be collected in the usual manner over the pneumatic trough in a cylinder or soda-water bottle, as shown in fig. 8. The gas, so collected, detonates with great violence when a light is applied to it, water being formed, the vessel should therefore for safety be wrapped up in a towel. Exp. 10. — In order to show the volume proportions of the two gases, an apparatus, devised by Dr. Hofmann, fig. 9, may be used with great advantage. It consists of a U-tube, connected from its bend with an equally wide long upright tube, blown out into a bulb D, for reoeiviug the acidulated water. The" two Electholtsis op water. 21 limbs of tlie U-tute end in two narrow tubes, A and B, provided with glass stop-cooks, and should be. full, up to the stop-cooks, with acidulated water. The main tube must be capacious enough to receive the liquid contained in both limbs of the U-tube. The two electrodes are introduced from below into the U-tube. As soon as connection is made with the battery, oxygen comes off at the positive (carbon) pole, and hydrogen at the negative (zinc) pole. The quantity, more- over, of hydrogen is seen to be invariably just double that of the oxygen. The gases may be tested by opening the stop-cocks and applying successively a glowing cedar splint and lighted taper. If the cedar splint bursts into flame, the gas is oxygen; if the lighted taper ignites the gas, it is hydrogen. As often as we repeat the experi- ment we observe invariably the same constant volume proportions, and we are therefore entitled to infer that the two gases are com- bined in water in these proportions. Thus far we are led by the analytical * experiments, i.e., by the resolution of water into its component elements. By the second method, usually followed in chemical investigations, viz., by the synthetical t method, we are enabled to reunite the two gases, in the proportion of one Kg. 9. of oxygen to two of hydrogen by volume, to reproduce water, thus proving absolutely its compound nature. Exp. 11. — For this purpose a mixture of two volumes of hydrogen, and one volume of oxygen, is introduced into a eudiometer tube filled with mercury, and surrounded with a jacket, consisting of a wider glass tube. The space which intervenes is fiUed with a gaseous * From avxkvifis = a loosening. + From yi!j'Si(ris = a putting together. 22 ELEMENTARY CHEMISTHT. tody, such as the vapour of amylie alcohol (boUing at 132° C). The mixed gases acquire thus rapidly a temperature which prevents the water-vapour, which is formed by the explosion, from condensing, and enables us to ascertain in a simple and neat manner the extent of condensation which the mixed gases undergo when they combine with each other to form the molecule of water. We use the ser- viceable modification of Dr. Hofmann's original apparatus, for which we are indebted to Professor Cooke, and which is represented in fig. 10. Pig. 10. Fig. 11. It consists of an iron TJ-tube, a, such as is used for counecting parallel steam pipes. Into the open ends are fitted, by means of good india-rubber corks, a eudiometer tube closed at the top, and provided with platinum wires for exploding the mixed gases, and another upright open tube. The closed eudiometer tube is sur- rounded with a wider glass tube open at both ends, and fixed over the india-rubber cork which connects it with the iron U-tube. Its upper end is closed with a perforated india-rubber cork fitted with a glass tube bent at right angles, and connected with a tube leading ELECTROLYSIS 01* WATEft. 23 to a flask in which amylio alcohol (fuael oil) is heated to boiling. The vapour passes along the open space intervening between the eudiometer tube and the outer jacket, and out through a side tube &t the bottom to a Liebig's condenser (not shown in full in the drawing). In order to charge the apparatus with an explosive tnixture of hydrogen and oxygen, the eudiometer tube, as well as the iron XJ-tube, is first filled with mercury, and the gas delivery tube from the voltameter, fig. 11, introduced through the mercury into the closed limb. When nearly full the open tube is again firmly fixed in its place, and the mercury level adjusted by means of a side tube let into the iron U-tube, and provided with a short india-rubber tube and a screw clamp for drawing off the mercury. As soon as protracted boiling of the amylio alcohol no longer alters the level of the mercury in the two limbs, the volume of the heated gases is marked by slipping an india-rubber band over the glass jacket, and the open limb is securely closed by an india-rubber plug. The gases are next exploded by passing a spark from an induction coil between the wires of the eudiometer. The violence of the explosion is moderated by the air-cushion which is interposed between the cork and the mercury in the open limb. The explosion over, mercury is poured in to restore the level in both limbs; another india-rubber band is fixed to the new level, and it will then be seen that the gas volume has shrunk to two-thirds of its original bulk; two volumes of hydrogen and one volv/me of oxygen contracted to two volumes of steam. This reduction in volume from 3 to 2 may also be illus- trated to a class by employing cubical canisters, which, pack inside a double cube, or expressed in a symbolic equation, thus : — H H H , , H: Two volumes One volume Two volumes of hydrogen. of oxygen. of steam. A molecule of steam occupying two volumes is therefore made up of two volumes of hydrogen and one of oxygen, and the weight of one volume of steam must be the weight of one volume of hydrogen and half a volume of oxygen ; and as the latter gas is 16 times heavier than the former, determined by actual experiment, 1 -f 8 = 9. The specific gravity of steam is therefore 9, i.e., one measure, say a litre, of steam is nine times as heavy as one measure, or one ■ litre,* of hydrogen gas — the unit of comparison adopted by * The student is referred to the tables of French weights and measures given at the end of this book. 24 ELEMENTAKY CHEMISTRY. chemists for gas volumes — and its actual weigtt will be found by multiplying the weight* of a litre of hydrogen •0896 by 9, viz., -8064 grm. We shall come across simUar contractions of volume, when other gaseous mixtures are made to combine chemically. The resulting molecular volumes are, however (with a few exceptions) always- two volume vapours. These relations are expi-essed, according to Avogadro, by the law that equal volumes of cdl gases and vapours contain (at the same temperature and pressure) an equal number of molecules. Now, if constant volume combinations are admitted (and the experiment has proved it), we have no difficulty in understanding that gases must also combine in fixed cmd constant proportions by weight. Taking the weight of one litre of the elementary matter which we have called hydro- gen as unit, and bearing in mind that two volumes of hydrogen combine invariably with one volume of oxygen, one part by weight of the elementary matter which we call oxygen must weigh 8 x 2 = 16. Water is then composed as follows, the same scheme or formula, OH2, expressing its combination by weight and by volume : — B;/ volume. By weight. , ' , , . _^; 2 vols, of hydrogen. 2 parts by weight of hydrogen. 1 vol. of oxygen. 16 parts by weight of oxygen. Or, in 18 parts of water, say 18 lbs., grammes, etc., there are — 2 lbs. of hydrogen, and 16 lbs. of oxygen. and as the composition of water is constant, we can readily calculate from these figures how much hydrogen or oxygen is contained in any given quantity of water. As it is usual to express the constitution of all compound matter by weight in percentages, we have the proportions : — 18 : 2 :: 100 : a; = IMl of hydrogen, and 18 : 16 : : 100 : a; = 88-89 of oxygen. 10000 * Dr. Hofmann assigned the name cHth, from xpiih, a barley-oom, to the weight of one litre of hydrogen, "0896 grm., at 0° C. and 760 mm. barometrical pressure. ELECTROLYSIS OF WATER. 25 SuUlIliary. — Water is a compound body consisting of two gaseous substances, viz., hydrogen and oxygen. It can be decomposed, or resolved into its component pwrts, {a) by in- tense heat (dissociation), or (b) by voltaic electricity \elec- trolysis). ^ A molecule is the smallest particle of matter capable of existing in a free state. i Equal volumes of all gases contain an equal nvmher of molecules (Avogrado's law). The weight of one litre of am, elementary or compound gaseous body, compared with that of a litre of hydrogen {at 0° G. and 760 mm. pressure), constitutes its volume weight, also called specific gravity. A crith equals -0896 grm., or the weight of one litre of hydrogen ; and lias been adopted for gaseous mutter as the unit of comparison, in the place of air, the old unit. The specific gravity of hydrogen gas referred to air, is found by dividing 14 '4: 6 into 1, viz., ■06926 = sp. gr. of hydrogen, air = 1 . Gaseous elements combine in very simple definite propor- tions by volume amd by weight. These proportions are constant. Symbolic representation of chemical changes expresses by one and the same formula hdth volume combination and com- bination by weight. The unit of combining weights is also that of hydrogen = 1. LESSON III. OXYGEN. Water, we have learnt, consists to the extent of nearly A by weight of oxygen. Now, as water covers the greater part of our globe ; as it forms, moreover, part of most mineral, vegetable, and animal bodies, its importance will at once become apparent. Air, which is a mere mechanical mixture of about ^ by volume of oxygen, with -^ of another gas which we shall presently know as nitrogen, oonfains, next to water, most oxygen. Hence the elementary body, oxygen, is most widely and most largely diffused on our earth. The electrolysis of water has taught us how to prepare oxygen in the free state. To obtain larger quantities of the gas by this method would, however, be both tedious and expensive. It is to air, then, it would appear, at a first glance, that we must look for a plentifvil supply of oxygen j and as mechanical mixtures are known to offer less resistance to physical or chemical agencies than chemical compounds, it is but natural that we should fix upon air as the best source whence to abstract oxygen. Owing to the inertness of nitrogen, and to the eagerness with which oxygen enters into chemical combination with' elementary matter generally, the oxygen of the air is, how- ever, difficultly obtained in the free state, but renders all the more easy such important chemical processes as com- hiistion, oxidation, and respiration. Instead of going to air, then, as a source of oxygen, we select bodies, rich in oxygen, in which it is held with little chemical energy. Such bodies we possess in certain metallic oxides, e.g., the oxides of the so-called noble metals, silver, mercury, etc., or the OXYGEN. 27 peroxides of a few other metals; also in certain salts of oxygen acids, wHoh, on the application of heat or chemical agents, part readily with their oxygen, either partly or wholly. Exp. 12. — When mercury (quicksilver), symbol Hg (from hydrar- gyrum), is heated nearly to boiling in con- tact with air in a small flask (fig. 12), the bright metal becomes covered slowly with a reddish-yeUow film of oxide, and increases in weight. If some of the powder thus ob- tained be next heated more strongly in a hard glass tube or retort fitted with a de- livery tube, it is found to part with a gaseous body, which can be collected over water and examined. As the preparation of a sufficient quantity of this powder, in the manner described, is rather a slow pro- cess, and, moreover, not without danger if the mercury fumes are allowed to escape into the air, it is more expeditious to use the so-called red precipitate, or mercuric oxide, of the shops, identical in composition, although prepared by a different process. Introduce a weighed quantity of the red precipitate into a retort of hard German glass (fig. 13), and connect it, by means of a sound cork, with a delivery tube which dips under water in a pneumatic trough. Apply gradually a strong heat by means of a Bunsen gas-burner or spirit lamp. Gas bubbles come off, which should only be collected when they re-light a glowing cedar splint. After a little time, a metallic coat- ing is observed to form in the neck of the retort, and -globules of a liquid metal (mer- cury) are seen to accumulate. Collect some of the gas over water, and test it with a glowing cedar spUnt. The latter bursts into flame, and bums with a dazzHng light. As air would not re-Ught the splinter nor cause it to burn as brightly, we infer that it is due ijo a gas which the red precipitate "'S- !"• gave off. Brush the globules of mercury together with the feather of a quill pen, and weigh in a small porcelain dish. They wiE weigh less than the origiaal red powder. Somethiag ponderable, then, has been removed from the latter, viz., the gas which was collected over water, and tested as described. 28 ELEMENTARY CHEMISTRY. Tha experiment illustrates two kinds of important chemical changes, viz. — (I). A change by combination: — 2Hg + O2 = 2HgO Mercury. Oxygen. Mercuric oxide. (2). A change by resolution: — 2HgO = 2Hg Mercuric oxide. Mercury. Fig. 13. If the experiment be properly conducted, it will be found that the metal mercury has merely served to fix, and thus abstract oxygen from the air, and that 100 parts by weight of red precipitate leave invariably 92 '59 parts by weight of metallic mercury. The gas supports combustion much more readily than the air from which it was originally derived, but does not burn. It is colourless, inodorous, and tasteless, and is only slightly soluble in water (100 parts of water dissolve at 15° 0. 2 -9 volumes). It received the name oxygen, or acid producer (from "I"! = sour, and ytw«a<=I gene- rate), given to it by the great French chemist, Lavoisier (1774-1781), who fb-st saw and explained the important part which it plays in all processes of combustion and oxidation, and in respiration; because he held (erroneously as we now know) that oxygen entered into the composition of every acid. The symbol adopted is O. Its density is 16, compared with hydrogen =1; or y^.|^ = l*1065 when com- pared with air as unit. OXYGEK. 29 Exp. 13. — Whenever large quantities of oxygen are required, its preparation from mercuric (or silver) oxide is no longer practical. We avail ourselves, then, of an oxygen salt, viz., potassium chlorate, which gives up the whole of its oxygen when heated, especially when it is kept from fusing hy an admix- ture of about iVth of red ferric oxide or black manganic oxide with the powdered chlorate. A small flask or retort (fig. 14) may be used, fitted with a wide delivery tube, as the gas comes off rather rapidly. It is Kg. 14. best stored up for use in a, gas-holder, as seen in fig. 15, or, in the absence of a gas-holder, the oxygen may be tilled over water into so-called Win- chester quart bottles, each fitted with a good doubly- perforated cork and glass tubes; the one straight and reaching to the bottom, and the other bent at a right angle and just passing through the cork; both are closed with a piece of stout india - rubber tubing and screw clamp. By means of these simple contrivsinces a store of oxygen (or any other gas, in fact) may be obtained, which can be discharged when required simply by fixing a funnel tube to the upright tube, and a delivery tube to the bent tube. When water is poured into the funnel tube, the oxygen is forced out, and having no other chance of escape, provided corks and india-rubber tubes fit tightly, it must pass through the delivery tube, the dis- Fig. 15, 30 ELEMENTARY CHEMISTRY. charge being regulated by means of the screw clamps. This serves as a cheap and very serviceable gas-holder for all gases which are not perceptibly absorbed by water (see fig. 21). The chemical change which, the potassium chlorate* under- goes when heated, comes under the class of changes termed resolution of a compound into an element and a less complex iody; expressed by the equation — 2KC10s = 2KC1 + 30j Potassium cUorate. Potassium chloride. Oxygen, The force which produces the change, viz., heat, has as yet not found a symbolic (quantitative) expression. Of the other methods of preparing oxygen we will speak hereafter, suffice it that the beginner be made familiar with the principal methods first. Oxygen combines with every known element, with the exception of fluorine, forming new compound bodies, widely differing in their properties from the origiaal, the change being mostly accompanied by the phenomena of light and heat. When oxygen is made to combine with other ele- mentary matter, we speak of the change as a process of oxidation, and the bodies thus formed are termed oxides. When it is taken away again, by various agencies, we call the change a process of deoxidation or reduction. Substances which burn readily in air, bum with still greater energy in oxygen gas. This may be illustrated in various ways, and if the experiments are regarded by the pupU, not merely as pretty fireworks, to be dismissed from his mind as soon as the flash has died away, much may be learned which will help him to lay a good foundation for a sound theoretical knowledge. For the purpose of conducting these oxidation experiments successfully, the glass vessel in which the oxygen is stored up should not be too small or too fragile. Large glass flasks are expensive luxuries; we would recommend the use of Florence flasks, or, better still, of good-sized pickle bottles, provided with patent stoppers wherewith the gas may be confined safely for any length of time, till it is required by * The ferric or manganic oxide does not take part in the change. OXYGEN. 31 the experimenter. In the absence of a gas-holder, the oxygen may be filled directly into these bottles, over the pneumatic trough. Exp. 14. — Pit up an apparatus coasiating of a stoppered beU-jar resting on a tinned iron sup- port, as seen in fig. 16, in which the water which con- denses and runs down the side of the bell-jar can be collected. Insert adoubly-perforatedcork fitted with two glass tubes, the one for the hydrogen drawn out to d, point, the other for the introduction of the oxygen. A store of hydrogen should be prepared and kept ready for use in a Winchester quart bottle, fitted up as described; in like manner a store of oxygen. Both gases should be carefully dried by passing them over calcium chloride,in a U-shaped . . ~ _, drying tube, before'they enter ^ig- 16.— Combttrtioit of Hydeogen the apparatus. Turn on the ^'^ Oxygen. hydrogen and light the jet. Insert now the cork. The hydrogen burns at first in the air contained in the bell-jar. Now turn on the oxygen jet and regulate it, so that there is always excess of oxygen present. As great heat is produced by the combus- tion of hydrogen in oxygen, the steam which is formed should be condensed by keeping the bell-jar cool by means of a wet towel. To prevent any water getting into the open space between the metal cup and beU-jar, this space should be filled up carefuUy with some stiff rosin cerate. In this manner a quantity of water may be procured in a short time, which can be tested for its purity by means of red and blue litmus papers, upon which it should be without any aqtion, i.e., neutral. When evaporated in a glass capsule or watch- glass, it should leave no residue. This experiment illustrates in a neat manner that hydrogen burns in oxygen and forms water. Exp. IB. — Heat a piece of magnesium wire in air till it bursts into flame. It burns with a brilliant Ught, and forms with the oxygen of the air an oxide of magnesium or magnesia, symbol MgO; the symbol of the metallic body magnesium being Mg. The wire con- tinues to burn after its removal from the flame. The magnesia is collected over a sheet of black paper. It constitutes a white earthy- looking powder, which is but little soluble in water, and has only a feebly alkaline reaction on red litmus paper, 32 ELEMENTABY CHEMISTRY. This proves that the metal magnesium has, at the ordinary temperature, much less affinity for oxygen than either the metals sodium or potassium. Now introduce another ignited piece of magnesium wire into a bottle filled with oxygen. The combustion becomes of a most dazzling brilliancy. The reaction dififers merely in degree and intensity. It is ex- pressed symbolically, thus : — 2Mg Oxygen. 2MgO Magnesium oxide, or Magnesia Some metals which volatilise at a high temperature bum vividly and with a fiame ; their vaporous condition facilitates greatly the chemical combination with oxygen. Exp. 16. — Some zinc turnings are slightly dipped into melted sulphur ; when the sulphur is ignited the turnings are rapidly introduced into a jar of oxygen. The heat produced by the flame of the sulphur ignites the zinc, and the latter burns with a dazz- ling white light (fig. 17), and forms zinc oxide, a powder which is yellow whilst hot, white when cold. The symbol for zinc is Zn, and for zinc oxide ZnO. The change is ex- pressed symbolically, thus: — J?ig. 17. 2Zn Zinc. + Oj Oxygen. 2ZnO Zinc oxide. Exp. 17.- Fig. 18 ■Procure a fine steel watch-spring. Soften it by heating in a flame, and ooU it up as seen in fig. 18. Fasten a piece of tinder firmly to it by doubling up the one end. Ignite the tinder and intro- duce it rapidly into a jar of oxygen; the tem- perature of the wire becomes speedily raised to the ignition point by the burning tinder, and it burns there with a very intense light, throwing off brilliant sparks. To avoid crack- ing the bottle, the bottom should be protected by letting the molten globules of iron oxide fall on a sheet of moist blotting paper. Kne steel wire may also be burned in an ordinary pointed gas flame, fed by oxygen instead of air. On removing the steel wire, however, from the flame, the combustion ceases immediately. OXYGEN. 33 The symbol for this iron oxide is Fe^O^, that of iron being Fe, from the Latin word ferrum, iron. This oxide is mag- netic. It is quite insoluble in water, and therefore without action on litmus paper. The reaction is expressed thus : — 3Fe + 20;, = Fefii Iron. Oxygen. Triferric tetroxide or Magnetic oxide of iron. Exp. 18. — Heat some bright copper turnings in a Bunsen gas flame, they become rapidly covered with a black film, or scales of copper oxide ; symbol CuO, the symbol for copper being Cu, from the Latin word cuprum. The same takes place -when copper is heated in oxygen gas. Copper oxide is insoluble in water, and has no action on litmus paper. The reaction is expressed thus : — 2Cii + 02 = 2CuO Copper. Oxygen. Copper oxide. Exp. 19. — Heat a gold or platinum wire. There is no change either in air or oxygen. Gold and platinum have not the power of combining with oxygen under these circumstances, because their oxides yield, at this temperature, oxygen and leave the metal (compare Exp. 12). We note, then, among metallic bodies a wide difference in the energy with which they combine with oxygen, as we observed already a difference in the rate at which they give it up again. Those metals which exhibit the greatest affinity for oxygen, such as the so-called alkali metals, e.g., sodium, etc., hold it most firmly, and do not even yield it to reducing agents, such as hydrogen. The reverse holds good for the so-called noble metals, e.g., silver, gold. There are other elementary bodies which possess little or no metallic character, i.e., they have little or no opacity, they possess little or no lustre, nor much power of coiaduct- ing electricity and heat. They are known usually by the term non-metallic bodies {metalloids). Such bodies are, e.g., carbon, sulphur, phosphorus, etc. They combine readily with oxygen. We observe, however, the same difference in the degree of affinity which they exhibit for this element. Instead of forming compound bodies which have a strongly pronounced alkaline character or show no reaction, nor dis- C 34 ELEMENTARY CHEMISTRY. r* 1 ■ .11 '■' P 'ilH |l ,] gM^HI solve or combine readily witli water, they have the power of combining with hydrogen to form gaseous compound bodies; and with oxygen they form, for the most part, more than one oxide. Exp. 20. — Heat some sulphur, placed in a so-called deflagrating spoon (fig. 19) fixed into a wooden cover, till it inflames. It burns in air slowly, and with a pale blue flame. Now intro- duce it into a jar of oxygen. It immedi- ately bums vigorously, and with a dazzling blue flame. The product of the combustion is a gaseous compound body which possesses a most suff'ocating odour. Introduce a piece of moist blue litmus paper into the gas. It is turned red instantaneously. On introducing a lighted taper, the light is immediately extin- guished. The gas does not support com- Dustion. It has received the name Fig. 19. sulphur dioxide or sulphurous anhy- dride, its composition is expressed by the equation — 8 + 0^= SOj Sulphur. Oxygen. Sulphur dioxide. Exp. 21. — Dry carefully a small piece of phosphorus between folds of blotting paper without touching it with the fingers ; place it as quickly as possible into the deflag- rating spoon, inflame it by touching it with a heated wire, and introduce it into a jar of oxygen (fig. 20). It bums with a most intense Hght, and the bottle becomes filled with heavy white clouds, which are gradually condensed and absorbed by the moisture which hangs about the glass jar, forming with it a strongly acid liquid which turns _,. „- blue litmus paper intensely red. a ig. zU. rpj^g -(yater acquires an acid taste. The compound- which phosphorus (P) forms with dry air or oxygen is called phosphorus pentoxide or phosphoric anhy- dride. Its formula is PjOg. The product of the action of water upon it is called phosphoric acid. Exp. 22. — Introduce a piece of ignited charcoal into a jar of oxygen and observe the vivid combustion. The carbon (C) is consumed and forms with the gas a colourless gaseous compound called carbon OXYGEN. 35 dioxide or earhonic anhydride, formula OOj. Introduce a lighted taper into the gas which is left, the light of the taper is immediately- extinguished. This shows that carbon dioxide does not support combustion. It is formed according to the equation : — c + 0, CO, Carbon. Oxygen. Carbon dioxide, or Carbonic anhydride. Summary. — Oxygen is a colourless, tasteless, and inodorous gas, somewhat heavier than air {specific gravity = 1 •!). It does not hum, hut supports the comhustion of other bodies more powerfully. It combines chemically with every hrtovin element except fluorine. The compound bodies which if forms, both with metallic and non-metaUic elements, are termed oxides. Tlhe change itself is termed a process of oxidation. It is for the most part accompanied by the phenomena of heat and light. Bodies which burn in air hum with mnxch greater energy in oxygen. Oxygen sustains life when breathed. The nitrogen of the air acts as a diluent. The oxides of metallic bodies are solid bodies, either soluble in water and of a caustic or alkaline nature, or insoluble in water ami neutral. The oxides of non-metallic bodies (metalloids) are either gaseous, solid, or liquid bodies. They dissolve for the most pa/rt in water, and many possess acid properties, especially in combination with water. Bodies to he burnt in air or oxygen have first to he raised to the ignition point, or to the initial temperatwre at which the chemical change can take place, either by their own slow comhustion, or by extraneous means. The a/mount of heat actually produced is the same, no matter whether bodies are burnt quickly in oxygen or slowly in air; the sensible heat is, however, greater when they are burnt in oxygen, no diluent (non-combustible nitrogen) being present to absorb and retain heat. Comhustion is accmnpanied by flame only in the case of bodies which are convertible into vapour pr&oious to their burning. Elements which possess the greatest affinity for oxygen con- stitute the most powerful reducing agents. The operation by which a compound body is resolved into its elements is called a reduction or resolution, LESSON IV. PHYSICAL STATE OF MATTER — PHYSICAL AND CHEMICAL CHANGES MECHANICAL MIXTURES CHEMICAL COM- POUNDS — ELEMENTS METALS AND NON-METALS (METAL- LOIDS) COMPOSITION OF AIR. Everything in. nature, within reacli of our powers of investigation, occupies a certain space, and is weighable (ponderable). It is termed matter. It undergoes changes which do not alter its fundamental nature, but merely impart to it new properties. A bar of iron, suspended in air in a vertical position, acquires, after a time, the power of attracting fine iron filings. It has become a magnet, and is charged with a force which also exists in the earth, viz., magnetism. A glass rod, rubbed with a silk cloth, acquires the pro- perty of attracting light objects, such as chips of paper, or a suspended wooden rod. It has become electric, or charged with electricity — another of nature's forces. A current of voltaic electricity (from several cells), when passed through a spiral of platinum wire, causes it to become intensely hot, and to radiate light. When the current is interrupted the platinum acquires its original state again. Whilst under the influence of these natural forces (and we might extend our illustrations to several more, such as cohesion, attraction and repulsion, gravity, heat, light), matter acquires new properties which are rendered visible by the different phenomena which they exhibit. Iron, glass, platinum, remain unchanged in their substance, i.6., the state of the matter of which they consist is not altered by these forces. They have undergone what is termed a mere physical change. They have not been transformed into matter different from what they were before. The experi- ments described in the three preceding lessons have, on the Physical and chemical changes. 37 other hand, illustrated the transforming action of -what -we termed a chemical change, and it remains now only to point out the conditions favourable to such changes. Exp. 23. — Place a dry piece of freshly-cut phosphorus on a dry tile, support over it, resting on a brick, at about 3 inches distance, the end of a poker, made red-hot. The phosphorus ignites and bums vividly. Place a dry bell- jar over it and collect some of the dense white fumes, consisting of phosphoric peutoxide (compare Exp. 21). They constitute a snowy white, flaky substance, which is deposited on the sides of the jar, and may be scraped together with a glass spatula and kept in a well-stoppered bottle. This experiment brings home to us that the force called heat can act through distance, and produces a chemical change. The force of chemical affinity, on the other hand, requires that bodies be brought into close contact. Exp. 24. — Mix, with a wooden spatula, on a sheet of paper, one part of finely powdered loaf-sugar, with two parts of finely powdered potassium chlorate. Dip a glass rod into strong oil of vitriol (sul- phuric acid), let it drain, then hold the rod slightly inclined over the mixture, and approach it as near as possible without actually touch- ing it. No change takes place. Now touch the powder with the acid, and it immediately ignites and burns away. This proves, then, that chemical force acts only at ia- appreciable distances, such as it is not possible even to obtain by mechanically powdering solid substances together in a mortar. Dry tartaric acid may be mixed with dry sodium carbonate, and kept for years in dry air without any change taking place. But if water be added, effervescence takes place. The state of liquidity tends to promote that intimate contact between the particles of matter which is favourable to chemical action. Besides intimate contact between matter of different kinds, heat, by altering the physical properties of matter, such as bulk, hardness, elasticity, etc., induces chemical action. We will for a moment examine the processes used for manufacturing gunpowder. A very intimate paste is made with water of finely powdered charcoal, powdered sulphur, and saltpetre. This mixture can safely be passed, as long as it is moist, between heavy rollers without any chemical action being produced. When the mixture is, 38 ELEMENTARY CHEMISTKI*. however, dried at 300'' C, or when an electric spark is passed into it, it speedily explodes. This can only be explained by assuming that the cohesion existing between the particles of the same kind of matter counteracts, in the gunpowder mixture, the force of chemical affinity which is to act between the particles of different kinds of matter, although they are most intimately mixed with each other. Heat weakens the cohesion between bodies; hence a rise in the temperature of the paste to 300° C, by weakening the cohesion between the particles of the same kind of matter, enables the chemical force to overcome the resistance which cohesion opposes to the union between the particles of the different kinds of matter. Similar to the action of heat is frequently that of light and electricity. On the other hand, the chemical affinity between the different constituents of a compound body, by the weakening of this cohesion by heat may be outweighed altogether, result- ing, in fact, in a breaking-up (dissociation, decomposition), of the bodies. Heat, light, and electricity are therefore important factors in chemical changes, be they combinations or decompositions. As we proceed in our experimental course, we will learn that most elementary bodies combine more or less readily with each other, some others only difficultly, and by round-about processes, and others not at all. The ultimate cause for their different behaviour is at present entirely hidden from us. It has received the name chemical affinity, and this force acts most vigorously between those bodies which exhibit the least chemical likeness. Any matter which cannot by any known process be split up into, nor built up out of, any other matter, is termed elementary matter, or a chemical dement. Of such elements we know at present 64 — a very limited number, when we bear in mind that everything around us is built up of them, and that about one-half occur in nature in such small quantities, and so locally, that only a very limited usefulness can be assigned to them. Elementary matter, moreover, rarely occurs in the^ee, or so-called native state, instances of which are carbon, sulphiir, gold, silver, copper, etc. ; but the more extensively occurring METALS And NOK-METALS. 39 elements are invariably found in the combined state, except oxygen and nitrogen, which, occur free in the air, though mixed together. The division of all elements into metals and non-metals (although it cannot lay claim to great accuracy), will, for convenience sake, be retained. Compounds which metals form with the non-metals are invariably decomposed by the galvanic current, so that the metal — the positive element — appears at the electro-negative, and the non-metals (metal- loids) — or negative elements — at the electro-positive pole. Upon this fact is based the division into electro-positive and electro-negative elements. In the adjoining table a few of the most important elements are arranged according to their electro-chemical characters, each being positive to any one below it, and negative to any one placed above it. These distributions are therefore entirely relative. + Hydrogen. Potassium. Silicon. Sodium. Antimony. Magnesium. Carbon. Zinc. Boron. Iron. Arsenic. Aluminium. Phosphorus. Lead. Iodine. Tin. Bromine. Bismuth. Chlorine. Copper. Pluorine. Silver. Nitrogen. Mercury. Sulphur. Platinum. Oxygen. Gold. ■ I A strict line of demarcation is, however, not possible; there are elements which have all the appearance of metals, but when their chemical behaviour is taken into account, they must certainly be classed among the non-metals, and vice versa. For our present purposes it will suffice if we turn our attention first to those elements classified as non-metals, and distinguish in the subjoined list the doubtful ones by different type. 40 Elementary chemistry. We have then the following four important groups of negative elements, together with their symbols : — Fluorine, F. Oxygen, 0. Nitrogen, K Carbon, C. Bromine, Br. Sulphur, S. Phosphorus, P. Silicon, Si. Chlorine, CI. Selenium, Se. Arsenic, As. — Iodine, I. Tellurium, Te. Antimony, Sb. Tin, Sn. Bismuth, Bi. Besides these we have Hydrogen, H, which unites in itself the metallic and raetalloidal character, forming the connecting link. Also Boron, B, usually classified with the non-metals, which occupies an isolated position, and differs in its chemical action somewhat from the non-metals. In cases where the names of elements begin with the same letter, as carbon, chlorine, etc., the symbol receives as an addition either the second or some leading letter out of the middle of the word, thus 01 stands for chlorine, Sb for stibium (antimony), Sn for stannum (tin). We shall make frequent use of these symbolic abbrevia- tions, and the pupil is therefore advised to commit them to memory. Most of the above elementary bodies exist at the ordinary temperature in the solid form, such as J, S (Se, Te), P (As, Sb, Bi), C, Si (Sn), B; one exists in the liquid state, viz., Br ; the others, H, F (?), 01, O, N in the gaseous form. All solid elementary matter, with the sole exception of carbon, have been melted or liquefied, though some of them require a very high temperature, such as the metal platinum, and when a higher temperature is applied they are vaporised. The alteration in their physical condition does not afiect their weight. Liquid bodies — both elementary and compound — contract on passing from the fluid to the solid form, and expand when heated. Water alone forms an exception. It reaches its greatest density at 4° 0., and below that tempera- ture it gradually expands again till it reaches the freezing point at 0° 0. (32° F.), when, as ice, it suddenly expands still further. The weight of 1 litre of water (1000 cubic centi- metres) at 4° 0., is 1 kilo or 1000 grms. A litre of ice weighs only 914 grms. Hence ice floats on water. The temperature of the water below the ice remains, however, COMPOSITION Of AIE. 41 constant, viz., 4° C. Hence animals living in ice-bound waters are protected from the most severe winter frosts. The freezing temperature of water, 0° C, or 32° F., or, better expressed, the melting point of ice, which, like that of all other solid bodies, is constant, has, therefore, been adopted as the standard for graduating thermometers. On heating water to boiling temperature, it is converted into steam. At the atmospheric pressure of 760 mm. (30 inches), the tem- perature of steam is equal to 100° C. (212° F.). One volume of water, at 100° C, yields 1696 volumes of steam of the same temperature. There are numerous other important deductions to be made from these physical phenomena. They belong to the domain of Physics rather than to that of Chemistry. If the students are not already acquainted with them, they should not neglect to make themselves thoroughly acquainted with the various physical laws bearing upon the changes which the action of heat produces, especially upon water and air. Solid (as well as liquid) bodies are but little altered in bulk by heat and cold, or by compression. Not so with all gaseous bodies, elementary or compound. Gases contract or expand, at a given constant ratio, under the influence of heat or cold. They can be visibly contracted by pressure, or expanded by removing the pressure. By the united action of pressure and cold, all gases have now beeil condensed and reduced to the liquid, some even to the solid state. Exp. 25. — Place a few fragments of sulphur (brimstone) in a. Florence flask and heat it, gently at first. It liquefies readily. When heated somewhat stronger, it rises in the form of vapour, which con- denses in the upper part of the flask, and can with care be distilled into another Florence flask and recovered as solid flowers of sulphur. Exp. 26. — Place a few small crystals of iodine in a test-tube. Apply heat, gently at first. The iodine crystals melt and volatilise readily, filling the test-tube with a beautiful violet vapour. Mattel', then, can exist in three states of aggregation: solid, liquid, and gaseous, and it depends for its physical con- dition upon heat and pressure, the chemical composition remaining the same. We have now learnt that elementary matter is found in nature in the free and the combined state. There is a class of 42 ELEMENTAKY CHEMISTRY. bodies also in whicli it exists in the form of mere mechanical mixtures. Such a body we have in air. Exp. 27. — Float a small piece of phosphorus, dried between filter paper, in a dry porcelain crucible over water. Have a good-sized bell-jar ready. Ignite the phosphorus and invert the bell-jar rapidly over it. The phosphorus now must burn at the expense of the oxygen of the air confined under the bell- jar. Dense white fumes speedily fill the glass vessel, and are gradually absorbed by the water. A diminution of about one-fifth^in the volume of the air is observed, when the solid white fumes have entirely disappeared. By removing the crucible from the interior of the bell-jar, and slipping a greased glass plate over its mouth, it can be taken out of the water and examined. A lighted taper is as usual introduced into the colourless gas left in the bell-jar. The taper is immediately extinguished. The residuary gas, therefore, no longer supports combus- tion. It is no longer air, and animal life would no longer be sustained by it. On this account it has received the name azote (from a, privative, and Jainxos, belonging to life), given to it by the French, and Nitrogen, i.e., generator of nitre, by English chemists. The symbol is N. It is a colourless, tasteless, and inodorous gas, slightly soluble in water (about 1*5 vols, in 100), and combines directly with a few elementary bodies only. Its main pur- pose in nature appears to be to act as a dilutent to oxygen. Its specific gravity compared with air is '9713, and with hydrogen 14. 1 litre weighs 14 criths. The proportions of nitrogen and oxygen in air have been determined quantitatively, and by different operators, with very great care. Such experiments are of the greatest im- portance and highly instructive, even if they cannot be performed by the beginner with the same accuracy. Exp. 28. — Divide a test-tube, by means of narrow slips of gummed paper, into five equal parts; invert it over water. Introduce next a piece of phosphorus fastened to a wire. The water is seen to rise slowly as the volume decreases, owing to the absorption of the oxygen of the air by the phosphorus. The gas volume left represents the unabsorbed nitrogen gas. It amounts to a little less than four-fifths of the original air volume. Greater accuracy is obtained by employing a graduated eudiometer tube placed over mei-cury, and absorbing the oxygen by means of a coke-ball soaked in an alkaline COMPOSITION OF AIK. 43 solution of pyrogallio acid, or by exploding a mixture of equal volumes of hydrogen and air by means of the electric spark. Experiments such as these should, if possible, be performed by a beginner with the assistance of a teacher. Exp. 29.— KU a hard glass tube (a piece of combustion tubing) loosely with bright copper turnings or borings, and heat the tube in a small charcoal (or, 2 procurable, gas) furnace (fig. 21). Pass a Kg. 21.— Pkepaeation- of Nitkogen pkom Aie. measured quantity of air (say a litre) from a glass gas-holder, using water displacement, as already explained, over broken-up sticks of caustic potash contained in the TJ-tube, in order to deprive the air of its carbon dioxide, and from thence slowly over the ignited metallic copper, and collect the residuary gas, in the usual manner over water. The gas, which is not fixed by the copper, will be found to amount to very nearly four-fifths of the original bulk. Its properties are those of nitrogen. 44 ELEMENTARY CHEMISTRY. Quantitative measurements have shown that atmospheric air contains — By volume. By wdgU. Oxygen 2093 23-13 Nitrogen 79-07 76-87 100-00 100-00 Besides these two gases, it contains a small proportion of carbon dioxide (COj) and aqueous vapour, the latter depend- ent upon the temperature. Of COj the quantities vary ac- cording to clear or foggy days, during prevalent dry -winds, etc. It amounts to from 2 to 6 parts in 10,000. The principal reasons which determined chemists to view- air as a meclMnical mixtwre of its constituent gases are : — (1). The relative amounts of the two gases are not those of their combining weights (O = 16, N= 14), nor of any simple multiple thereof. •(2). When a mixture of N and O, in the proportion in which they are present in air, is made, none of the ordinary manifestations accompanying chemical changes, such as heat, contraction of volume, etc., are observed. The mixture has all the properties of atmospheric air, and can be inhaled with the same facility. (3). Air absorbed by water and other liquid bodies differs in composition and proportion to the unequal solubility of N and O in water. Its percentage composition is : — Oxygen. 34-91 parts by volume. Nitrogen 65-09 ,, ,, We see from the preceding experiments* that it is invariably the oxygen which is removed by the various ab- sorbents, such as phosphorus, pyrogallic solution, metallic copper; and that new (oxidised) bodies are obtained. * Before leaving tMssubjeotthe student should, if necessary with the aid of a master, make himself familiar, if possible, with some other mechanical mixtures, such as between solids and solids, liquids and solids, or liquids and liquids, and should learn to effect the separation, by mechanical means, of the following mixtures : — (1) Iron filings from flowers of sulphur (2) sand from iron filings; (3) salt from butter; (4) nitre from gunpowder; (5) oxygen from coal gas; (6) charcoal dust from black oxide of manganese ; (7) mercuric oxide fiom red oxide of iron. COMPOSITION OF AIE. 45 If the copper were weighed before introducing it into the tube, and again after air had been passed over it for some time, and the copper converted into black copper oxide (comp. Exp. 18), it would be found to weigh much heavier; 65 '5 parts by weight would, in fact, be found to combine with 16 by weight of oxygen. The same quantity of copper would, moreover, be found to combine with the same quan- tity of oxygen by weight, as often as the experiment is per- formed; and with the necessary precautions such experiments may become truly quantitative demonstrations of perhaps the most important property of elementary bodies, viz., the property of combining with other elementary bodies in con- stant proportions by weight, which constitutes the basis of our atomic theory. Before considering this further, however, we will gather up some more practical experimental knowledge. Summary. — Matter is acted upon hy the different natwal forces, such as heat, electricity/, m,agnetism, etc., which impwrt to it new properties, without changing its composition. Such chcmges; chiefly changes in the state of aggregation {solid, liquid, and gaseous) are termed physical changes. Changes which give rise to a tramsformation of matter into a new body or bodies, essentially different in properties from, the original bodies, are called chemical changes. Chemical force acts only in appreciable distances, heat at greater distances. Cohesion, acting between the molecules of the same kind of matter, counteracts chemical affinity — the force which draws together the same, but more powerfully different hinds of matter, and opposes itself to their sepa- ration. Elementary matter which cannot be decomposed by any /mown process or force into matter of a simpler kind, d^ering in properties, nor built wp out of amy other matter, is termed a simple substance, or a chemical element. Sixty four elements are known at present. They are divided, without any sha/rp lines of demarcation, info metals and non- metals, amd into electro-positive and electro-negative ele- jnents. All gases can be condensed to the Uquid, some even 46 ELEMENTARY CHEMISTRY. to the solid condition, by the application of great cold and pressure. Mixtures of two or more simple or compound bodies, not accompanied by the phenomena which marh chemical changes, such as heat, light, etc., are termed mechanical mixtures. Air is a mechanical mixture, principally of oxygen and nitrogen, in the proportion of about oneffth to four-fifths. Nitrogen (azote) does not burn, and is a non-supporter of combustion. It cannot sustain animal life. LESSON V. The four elements, chlorine (symbol CI), bromine (symbol Br), iodine (symbol I), and fluorine (symbol F), exhibit such a degree of chemical analogy that they are best treated together. On account of their entering readily into chemical combination with metals to form salts, they have received the name halogens, or salt formers, from kas = salt, and ymxu = I generate, I.— CHLORINE. Exp. 30. — Introduce an ounce or two of powdered black oxide of manganese into a 12-ounoe flask, fitted with a sound perforated cork, Fig. 22. and provided with a safety funnel and delivery tube, as seen in fig. 22. Shake the powder up with sufficient water to prevent its caking and sticking to the bottom of the flask, or else a fracture will 48 ELEMENTARY CHEUISTRT. ensue on applying heat. Connect the generating flaak with a wash bottle. The entry tube should dip right under the water, and the discbarge tube just pass through the cork. Now add concentrated hydrochloric acid, free from arsenic, sufficient to well cover the black oxide of manganese. Mix thoroughly before applying heat. The flask had best be heated on a sand bath containing a layer of dry sand, or over a piece of wire gauze, applying at &st a small flame only from a Bunsen gas-burner, provided with a rose top. The water in the wash-bottle arrests any hydrochloric acid fumes which may be carried over. When the gas is required quite dry, the water in the wash-bottle should be i-eplaoed by oil of vitriol, which arrests the aqueous vapour on account of its great affinity for water. A yellowish-green gas, known as chlorine, comes off readily, which cannot be inhaled with impunity,* even when largely diluted with air. The experiment must therefore be conducted in a closet con- nected with a good chimney draught, or in the open air. To guard against leakage from defective corks and india-rubber joints, the student should invariably examine them by holding a glass rod, dipped into a strong solution of ammonia {liquor ammonice), near the corks and joints, when any escape of chlorine will be indicated by the formation of dense white fumes (ammonium chloride). Cold water, at 10° C. , dissolves nearly three times its bulk of chlorine; in warm water, however, the gas is little soluble. It is therefore coUeoted, as usual, over a pneumatic trough, containing warm water, in cylin- ders or flasks filled with the same ; or, as the dry gas is more fre- quently required, and as it cannot be collected over mercury, because of its action upon this metal, it is washed and dried by passing it through the wash-bottle, containing oil of vitriol, and then collected in dry cylinders or good-sized test-tubes by displacement. This method of collecting gases is applicable especially to gases which differ in their specific gravity considerably from that of air, which are, in fact, much heavier or much lighter than air. If heavier, the delivery tube must reach right down to the bottom of the cylinder, when the lighter air is lifted out by the heavier gas. If lighter, the cylinder is invei-ted over the delivery tube, when the heavier air falls out by its own weight, and is rapidly displaced by the lighter gas. This is called collecting gases by upward or downward displacement. A good arrangement of apparatus! consists in a per- * To counteract the injurious effect produced by inhaUng chlorine, it is recommended to inhale aniline vapour or ammonia gas. t PioMe bottles, fitted with the new patent stoppers, lined with a ring of india-rubber, may also be used with advantage, especially when for lecture purposes giaaa bottles have to be removed to distances. As clilorine gas acts destructively on india-rubber or metals, the stoppers should be paraffined. CHtORINE. 49 forated glass plate, into whicli fits a perforated india-rubber plug, fitted -with a delivery and discharge tube A and B, as seen in fig. 23. The plate is greased, and prevents any escape of noxi- ous gases, such as chlorine, into the air; and as soon as the exit tube is connected with a delivery tube, the excess of the chlorine cau be conveyed into a solution of caustic soda, which absorbs it and fixes it as an odourless compound. When the cylinder is full it is quickly removed, and kept covered with a glass plate, slightly greased, and a fresh dry cylin- der substituted. In this manner half-a-dozen or more cylinders may be filled in a very ex- peditious way, without the chlorine becoming a nuisance to the class. For the perforated glass plate the student may substitute a perforated tinned iron plate, taking care, however, to slightly cover the side exposed to the chlorine all over with a thin layer of paraffin. The chemical change which the hydrochloric acid under- goes, when it is brought into contact with black oxide of manganese, MnOj (the symbol for manganese is Mn), is due to a change by double decomposition, whereby it is converted into MnCl^ and 2OH2. The reaction takes place in two stages ; — Pig. 23; MnOi! + 4HC1 Manganese HydrocUoric dioxide. acid. MnCl^ + 20Hj Manganic chloride. Water. And MnCli = MnClj + CI, Manganous chloride. Chlorine. Manganic chloride, MnCl^, being a very unstable com- pound, is readily split up, on heating, into MnClj and Cl^. The manganous chloride is soluble in water, and the chlorine, assuming its gaseous condition, escapes. Chlorine gas has received its name from the Greek word x:>.apss, yellowish-green. It is a pungent, sufibcating gas, and cannot be inhaled with impunity. It is heavier than air; its specific gravity being 35'5, hydrogen = 1, i.e., 1 litre 50 ELEJIEUTAUY CHEMISTRY. weighs 35-5 criths, or 35-5 x -0896 = 3-1808 gms. Com- pared with air it is ^^ = 2-45. It can be condensed to a yellow liquid, under a pressure of four atmospheres and at the ordinary temperature. At -40° C. it condenses at the ordinary atmospheric pressure. Water saturated with chlorine gas is called chlorine water. It possesses nearly all the properties of chlorine gas, and is used in the laboratory in its stead. The colour of chlorine is not seen by gaslight, but can be shown by burning a bit of magnesium wire. Chlorine is not found in nature, in the free or uncombined state. Its most important natural compounds are common salt, rock-salt, in which it is combined with the metal sodium, as NaCl. It is one of the most chemically active bodies we know ; in fact, it is taken as the type of the non- metallic or negative elements, which are also sometimes called chlorous elements. It enters into combination with nearly all elements, both metallic and non-metallic, and forms with them a numerous and important class of bodies, termed chlorides, which are for the most part soluble in, or decomposed by, water. Exp. 31. — Expose a cylinder full of strong chlorine water to direct sunlight, over a vessel containing chlorine water. Gas bubbles are seen to make their way to the top, and slowly to displace the solu- tion. AUosF this to go on for some hours, and then test the gas with a glowing cedar splint; it will re-light and bum brilliantly in the gas. Hence we infer that it is oxygen. The change is expressed by the equation: — 2OH2 + 2CI2 = 4HC1 + Oj. Sunlight stimulates the chemical affinity of chlorine, just as it stimulated those of oxygen, and the chlorine breaks up water by combining with its hydrogen and forming hydro- chloric acid. The oxygen from the water is libei-ated, and being in what is termed the nascent state, acts as a powerful oxidiser. Chlorine acts, therefore, as a disinfectant, for it immediately decomposes any animal effluvia or miasma with which it is brought in contact, either in the form of gas or dissolved in water, and oxidises any noxious matter into new and harmless products. Por the same reason it acts also as a powerful bleaching CHLOETNE. 51 agent. Many vegetable and animal colouring matters are attacked, when moist, by chlorine,, which, by acting upon their hydrogen, converts them into substances which have little or no colour, with formation of hydrochloric acid. In other cases the chlorine acts by removing the hydrogen from water and setting free the oxygen, which, in the nascent state, oxidises the colouring matters into colourless bodies. This can be shown as follows : — Exp. 32. — Introduce into a cylinder full of chlorine gas flowers of various colours, a slip of litmus paper, carmine paper, cotton cloth dipped into a weak solution of indigo, stuffs dyed with magenta or aniline purple, printed paper, and some inlr writing, and keep covered over with the greased glass plate till the yellowish-green colour has disappeared, when it will be seen that the colours of the flowers have disappeared: violets, e.g., become quite colourless, the blue cotton cloth is turned white, the litmus, the red magenta, and the aniline blue are discharged; the black writipg ink acquired a reddish-brown appearance; the printing ink alone, prepared from oil and lampblack, remained unaffected, the carbon in it resisting the action of the chlorine. Silk or woollen stuffs cannot be bleached by chlorine gas, as the fibres, which are of animal origin, are destroyed by it. Mineral colours in general are not affected by chlorine. For manufacturing purposes a compound of chlorine and lime, known as hleaching powder, is all but exclusively employed. What was done slowly by sunlight, in Exp. 31, may be effected more rapidly by passing a mixture of chlorine and steam through a porcelain tube, filled with fragments of porcelain, and strongly heated over a charcoal fire or in a gas furnace. The chlorine breaks up the steam, both being in a gaseous condition, with formation of hydrochloric acid and oxygen. The two gases are separated by absorbing the hydrochloric acid gas in a wash-bottle containing a dilute solution of caustic soda, and the oxygen collected over water. The same exceedingly great affinity of chlorine for hydro- gen, as well as for metal and non-metals, may be shown in numerous ways. The student is recommended to make the following experiments : — Exp. 33. — Introduce apiece of clean, i.e., unoxidised phosphorus, by means of a deflagrating spoon, into dry chlorine gas. 62 ELEMENTAET CHEMISTRY. The phospliorus inflames and bums witt a pale greenish flame, giving out little light, while suffocating fumes of phosphorus pentachloride, PClg, are formed. Exp. 34. — ^Fill a bell-jar with dry chlorine gas, and burn a jet of hydrogen in it, as was shown for oxygen in flg. 16. Dense white fumes of hydrochloric acid, HCl, are formed, which ultimately put out the hydrogen flame. The fumes turn blue litmus paper iutensely red. Exp. 35. — A mixture of equal bulks of hydrogen and chlorine explodes with great violence when exposed to sunlight. They com- bine gradually in dififused daylight, and not at all in the dark. The actinic light of burning magnesium wire likewise causes the mixture to explode. To make the experiment with safety it is best to pro- cure an apparatus consisting of a narrow glass tube, of about three- eighths of an inch bore, and about 2 feet in length, provided with a glass stop-cock at each end; and charge it by passing, in a dark place, a mixture of equal bulkil of CI and H, through the tube. To show that it is a mixture, open the tube under a dUute solution of caustic soda. The chlorine is absorbed by the soda leaving the tube exactly half full of colourless hydrogen. Charge another tube in the same manner, wrap it up in a case of wire gauze, and explode the gas by lighting near to it a piece of magnesium wire. Open again over dry mercury. The gas volume remains the same. Intro- duce now a drop of water; the moisture absorbs the hydrochloric acid which was formed, and the mercury rushes in and fills the whole tube. The mercury should be admitted very cautiously, as a rush would inevitably fracture the tube. Einse the tube out with a little water; the water reddens blue litmus solution. This experiment proves synthetically, in a very neat manner, (1) that equal volumes of hydrogen and chlorine combine without any diminution in volume, according to the equation: — i 1 i 1 i \\ — One vol. One vol. Two vols. (2) that the resultant gas has all the properties of a power- ful acid; that, in fact, a new body, HCl, has been formed by the direct combination of two gases of widely different pro- perties; and (3) that the new gas is very soluble in water. Now the same facts might be illustrated experimentally in varioiis ways. We will briefly content ourselves by enume- ratLng a few other experiments ; — CHLORINE. 63 Exp. 36. — Introduce a burning taper into a cylinder full of dry chlorine gas. It burns with, a lurid red flame. The chlorine combines with the hydrogen of the taper, but does not combine with the carbon or oxygen, and deposits much soot. The flame soon extinguishes. Exp. 37. — Soak a strip of filter paper in oil of turpentine — a com- pound of carbon and hydrogen — and introduce it into a jar of chlorine. It bursts into flame and deposits much carbon. Exp. 38. — Burn a jet of coal gas in a large cylinder, and invert another cylinder over it f uU of chlorine. The same phenomena wUl take place. It also shows that chlorine is a heamy gals, and can be poured from one vessel into another. To illustrate the ready combination of metallic bodies with chlorine gas, especially when they are in a liquid or finely divided state, make the following experiments : — Exp. 39. — Heat a small thin piece of sodium in a deflagrating spoon, and introduce it into dry chlorine. It bursts into fltinie and bums with a fine golden-yellow flame, thus : — 2Na -i- C\ = 2Na01. Sodium chloride (Neutral). Exp. 40. — Sift some finely powdered antimony or bismuth into A, tall jar filled with dry chlorine. It inflames — especially if the metal be slightly heated — whilst falling through the chlorine atmosphere, and bums with a fine effect, as each particle of the metal combines with the chlorine, forming with it antimony chloride, SbCls, oi bismuth chloride, BiClj. In order to protect the glass from crack- ing, the bottom of the jar should be covered with a layer of dry white sand. Exp, 41. — Another striking illustration consists in filling a tall glass cylinder with so-called Dutch-metal (an alloy of zinc and copper), and decanting into it a cylinder full of dry chlorine. The metals burn brilliantly, and form chlorides (ZnOlj and CuCy. Summary. — Chlorine possesses great chemical affinity fw ■ vnetah and ywn-metals. It forms chlorides. Sunlight of heat favours the chemical action. Chlorine does not exist in nature in an uncombined condition. In the free state it is a transparent, heavy, yellowish-green gas; it does not bum in 54 ELEMENTAltlf CHEMISTRY. air, hilt supports the combustion of substcmces rich in hydrogin. It is a highly poisonous gas. It is somewhat soluble in cold water (two to three volumes), slightly in hot water, and is readily condensed to a liquid. Chlorine acts as a powerful bleaching agent, and indirectly (by the decomposition of water) as a powerful oxidising agent. A mixture of hydrogen and chlorine explodes spontaneously in direct sunlight. APPENDIX.* II.— BROMINE. This element, like chlorine, does not exist in nature in the uncombined state, nor is its hydrogen compound, hydrobromic acid (HBr), the analogue of hydrochloric acid (HCl), a commercial product. To prepare bromine, therefore, from its naturally occurring compounds, from sodium bromide (NaBr), or mag- nesium bromide (MgBrj), we proceed as follows : — Exp. 42.— Heat gently in a small retort, fig. 24, a little sodium bro- mide, together with black oxide of manganese and oil of vitriol, Heavy dark - brown poisonous fumes come off, which should be condensed in a small receiving flask, kept in ice-cold water. They condense to a heavy dark-brown liquid. The reaction is expressed by the equation : — Fig. 24 2NaBr + MnO^ + 2SO4H2 ^ Br^ + SO^Mn -f SO.Nas -f OH, Sodium Manganese Oil of Bromine. Manganese Sodium Water. bronmle. dioxide. Titriol. aolpliate. sulphate. * A knowledge of Br, I, and F, not being required by students prepar- ing for the elementary course of the Science and Art Department exami- nation, I have placed what I consider of importance in the form of an Appendix, which the student preparing for these examinations may either skip or peruse. IODINE. , 53 Chlorine gas can be prepared by an analogous reaction from sodium chloride, thus : — 2NaCl + MnOj + 280^ = Cl^ + SO4MU + SOiNa^ + OH4 Sodium CHorine. Water. It will also be seen that this method pf preparing chlorine gives us the full amount present in the sodium chloride used. Hydro- chloric acid being a very cheap bye-product from the manufac- ture of sodium sulphate, the manufacturer rather sacrifices half of the available chlorine, as manganous chloride (comp. Exp. 30.) This has, however, found some compensation in the revivification and recovery of the manganese binoxide by Weldon's process. Bromine congeals at 7 '3° 0. to a yellowish-green lustrous mass of scaly crystals, resembling iodine crystals. Liquid bromine has a specific gravity of 3'18 (water=l.) It is very volatile even at the ordinary temperature, and emits dense, irritating, and disagreeably smelling fumes. Hence its name bromine, from Iifiifui5=a, stench. It boils at 63° 0. Its specific gravity or vapour density is 80 (H= 1), or 5'39 (air= 1). Bromine is some- what more soluble in water than chlorine. It is also soluble in alcohol, and especially in ether, chloroform, and carbon disulphide. Bromine acts less energetically than chlorine towards other elementary bodies, and is displaced from its compounds, termed bromides, by chlorine : — 2KBr + CI2 = 2KC1 -1- Br^. With hydrogen it combines only on the application of heat, but not in sunlight. When it comes in contact with the skin, it causes bad burns. III.— IODINE. This element is found in nature diffused very extensively, but always in small quantities only, and not in the free state, but combined chiefly with the metals sodium (Nal), potassium (KI), and magnesium (Mgis), from which it can be liberated, lilce chlorine and bromine, by distillation with black oxide of manganese and sulphuric acid. Free iodine being a solid body, is more conveniently liberated from its concentrated saline solu- tions by passing a current of chlorine; the iodine falls out as a greyish-black powder, which can be collected on a filter. Mgl, + CI2 = MgClg + I,. Magnesium Chlorine Magnesium Iodine, iodide. ofloride. 56 ELEMENTARY CHEMISTRY. The iodine thus separated is dried and sublimed, when it is obtained, in fine large rhombic plates possessing a steel-grey metallic lustre. It possesses a powerful odour, resembling that of chlorine. It attacks the skm less violently than bromine, and turns it brown. Its specific gravity is 4'95 (water=l.) It melts at 107° C, and forms a deep-brown liquid. Towards 180° C. it boils, and is converted into a -vaolet vapour; hence its name iodine, from <"Siis= violet-blue. Its vapour density is 127 (^H=l) or 8"7 (air=l.) Iodine is little soluble in water (1 part in 7000), pretty readily soluble in alcohol (tincture of iodine), freely in ether, chloroform, and carbon disulphide, forming with the two latter reddish-violet solutions. In chemical activity it stands third : it is, in fact, displaced from its saline compounds by both chlorine and bromine. It combines also less energetically with other elements, with the metals mostly only on heating. Hydrogen does not combine directly with it, nor does it draw hydrogen from organic com- pounds consisting of hydrogen and carbon. Exp. 43, — Prepare some starch paste by stirring a little ground starch into cold water, and then add it gradually to some water kept boiling during the addition of the starch. Filter, and to a portion of the clear solution add a little potassium bromida solution, to another a dilute solution of potassium iodide, and stir up well. Next add to a third portion chlorine water. No change takes place. Now add to the other two portions a few droits of chlorine water, and stir up. The first, containing the bromine compound, is turned yellowisA, indicating bromine ; the second, deep-blue, showing the presence of iodine, even if present in very small quantities only. Iodine forms well-defined saline compounds with metals, called metallic iodides, some of which have been found of great use in medicine and in photography. In the uncombined state it is particularly beneficial m glandular diseases and in pleurisy. rv.— FLUORINE. This elementary body has not yet been isolated with any degree of certainty. It is found in calcium fluoride (CaFj) or fluor spar, from which it takes its name (^Mo=to now.) It appears to possess the most powerful chemical action of the halogen group of elements. It attacks all the vessels usually tised by chemists, even platinum vessels. The indications we have of its elementary existence bear this out. When dry silver fluoride is heated in dry iodine vapour, fluorine gas, a colour- fLtrOEINfi, 57 lesa very powerful gas is obtained, wMcli wben passed into water liberates oxygen, according to the equation : — OH, F, 2HP 0. If tbe evidence of its elementary character should ever be completed, it will probably be found that fluorine is a gaseous body,_like chlorine, but it evidently surpasses the latter in its chemical energy. Its vapour density, upon theoretical grounds, is 19 (H=l). We will, in conclusion, briefly call "attention to some curious relations existing between the four halogen elements. With the increase of the specific weights — Specific weights.. (19) CI. 35-5 Br. 80 I. 127 a seemingly increased density of matter appears to keep pace, marked by a decreased volatility. Fluorine is a gas (whether condensable to a liquid we know not) ; chlorine can readily be condensed to a liquid; bromine at the ordinary temperature is a liquid, and iodine a solid. The other physical properties of those elements show similar relations ; thus : — Fluorine. Chlorine. Bromine. Iodine. Melting point Boiling point ... . Colourless. -40? C. 1-33 Yellowish green. -7°C. + 63° C. 2-97 Brown. + 107° C. + 180° C. 4-95 Steel-grey. Specific gravity of Colour and it will be remembered that the vapour density of bromine is nearly the mean of those of chlorine and iodine, J" ' = 81 •50. The falling off in the chemical energy, as the volume weights increase from 19 (F) to 127 (I), has already been pointed out. The higher element is displaced from its saline or hydrogen compounds by the next lower. With regard to the compounds whiah the halogens, chlorine, bromine, and iodine, form with oxygen, we shall have to record the reverse action, LESSON VI. HYDROCHLORIC ACID. Exp. 44. — Introduce a few pieces ol fused sodium chloride (common salt), five parts by weight, into a flask (the apparatus used for preparing chlorine, fig. 22, may be used), and pour sulphuric acid, nine parts by weight, diluted* with a little water (two parts) over it. Heat gently, and pass the gas through a wash -bottle, con- taining oil of vitriol, to free it from moisture, t and collect it over mercury or by upward displacement. The reaction ia expressed thus: — 2NaCl + SO4HJ = 2HC1 + SOiNaj Sodium Sulphuric Hydrochloric Sodium sulphate, chloride. acid. acid. Or NaCl + SO4H2 = HCl -t- SOiHNa Acid sulphate, according to the heat which is applied. Hydrochloric acid gas is colourless and transparent. It reddens blue litmus, is heavier than air, and has a great attraction for water. As soon as it issues into moist air it gives rise to dense white fumes, which are very pungent. The fumes do not bleach carmine paper. The dry gas can be condensed at 10° C, and under a pressure of 40 atmos- pheres, to a colourless liquid of specific gravity 1*27. This has the remarkable property that it is without action upon iron, zinc, magnesium, and even on certain carbonates, * Oil of vitriol is a highly corrosive liquid, and great care must be ob- served in handling it. If it is to be diluted with water the strong acid should always be added to the water, and under continued stirring, and not the water to the acid. The reason for this is, that the cold water may absorb the great heat given out when oil of vitriol is diluted. In fact, it is an instructive experiment to see water brought nearly to the boiling point by the addition of a cold liquid. The glass vessel employed should be thin, to avoid cracking by the heat. " t The heat evolved when oil of vitriol is diluted with water wili have shown what an affinity these substances have for each other, and there- fore we use oil of vitriol as a dryer or desiccator (from the Latin aieco ^ I dry, and de ^ from, or away). HYDROCHLOBIC ACID. 59 although the aqueous acid acts readily upon these substances. It solidifies at - 90° 0. The specific gravity or density of the gas is 18-25 (H = 1), or 1-262 (air = 1). One litre weighs 18-25 criths = 1-635 grm. Exp. 45. — Collect some dry hydrochloric acid gas in a well-dried strong globular glass vessel having a long narrow neck. Kemove to a pneumatic trough, by closing it nrmly with the thumb till the neck is under water. Then open it gradually, and allow the water to rush in by degrees, in order to avoid fracture o£ the apparatus. It win be seen that the water fills, or nearly so, the whole vessel, as if it contaiaed a vacuum. Hydrochloric acid gas is readily soluble in water; one volume of water at 0° C. dissolves 480 volumes, and at the ordinary temperature about 450 volumes of the gas. The water constitutes then a weak solution of hydrochloric acid; it tastes acid and reddens blue litmus paper. A stronger solution is obtained by passing the gas for some time through several three-necked Woulfe's bottles about half full of water, and provided with delivery tubes which barely dip into the water, and with safety tubes. Reject the acid from the bottle nearest the flask as impure. Water saturated with the gas at 15° C. contains about 40 per cent, of hydro- chloric acid, and has a specific gravity of 1 -2. It fumes in the air. Wlien heated to upwards of 110° C, it gives off hydrochloric acid gas (20 per cent.). To prepare the gas expeditiously, we have therefore only to heat the concen- trated acid in a small flask, and to pass the gaseous acid through a drying tube containing p-amice stone freshly soaked in oU of vitriol. Hydrochloric acidmay be viewed as the type of an acid body. Exp. 46. — Prepare a dilute solu- tion of sodium hydrate, which we know turns red litmus paper intensely blue ; likewise a dilute solution of hydrochloric acid, and deliver the latter gradually from a pipette; fig. 25, into the solution of the alkali, tinted blue with a few drops of litmus, till the blue colour just disappears. BoU up, and stir well with a glass rod. If the red colour goes again, add another Fig. 25. drop. There will be a point at which the two fluids neutralise one 60 ELEMENTARY CHEIUSTEY. another, ie., at which the solution neither turns blue litmus paper , red, nor red litmus paper blue. The hydrochloric acid, by combining chemically -with the sodium hydrate, forms a salt, sodium chloride (common salt); thus : — KaHO + HCl = NaCl +. OH2 Sodium hydrate. Sodium chloride. It may, therefore, be said that a salt is a compound formed by the mutual action of an acid upon a metallic oadde, tei-med a base. Such bases are for the most part the mono- or protoxides of the metals; in a few cases also the suboxides. They are called basic or salifiable (salt-forming) oxides, having the general formula RgO and RO (R standing for any metal). A few metals, such as iron (Fe), can form oxides, in which the proportion of oxygen is to the metal as 1^ is to 1, or as 3 to 2, giving rise to so-called sesquioxides * of the general formula R2^3- When one and the same metal forms more than one salifiable oxide, we distinguish them by the ter- minals ous, designating the lower oxide, and ic, the higher. All others we will designate^ in harmony with the more generally accepted formulae, by using the name of the metal adjectively. The following examples will make this clear: — CaO Calcium oxide. CaCl^ Calcium chloride. CuO Cuprio oxide. CuClj ..'... Cuprio chloride. Cu„0 .... Cuprous oxide. CujClj Cuprous chloride. PeO Ferrous oxide. PeCl^ Ferrous chloride. FejOs. . . .Ferric oxide, FejClg Ferric chloride. Exp. 47. — Treat a little yellow mercuric oxide (HgO), with hot water. It is insoluble. Add now dilute hydrochloric acid. It dis- solves readily, forming mercuric chloride (HgCl^), which crystallises out, if the solution is sufficiently concentrated. As mercuric oxide has little or no reaction on litmus paper, being a body insoluble in water, it would not be possible to ascertain by means of litmus paper when the reaction is over, especially as the salt itself, when formed, shows an acid reaction. To obtain a neutral salt, it is fre- quently preferable to leave a little oxide undissolved, and to filter off the chloride. It is then readily obtaiaed neutral) * From the Latin sesgui = 1^. HYDROBEOMIC ACID. 61 i:e., ■without any excess of either acid or base. The change may be expressed thus : — HgO + 2HC1 = HgClj + OHj Mercuric oxide. Mercuric chloride. Electrolysis of Hydrochloric Acid. — Hydrochloric acid gas is a very stable substance. It can be heated to 1500° C, before it suflFers a partial decomposition. Its volume com- position has already been proved synthetically (comp. Exp. 35), and it remains now only to prove the same analytically. There is a little difficulty, however, in demonstrating experi- mentally the relative proportions by volume of the two gases, as one of them, viz., the chlorine, is soluble in hydro- chloric acid, and as it acts upon mercury. Exp. 48. — The apparatus devised by Dr. Hofmann (fig. 9), and used in the electrolysis of water (comp. Exp. 9) may be used. Fill the limbs entirely with a concentrated solution of hydrochloric acid, likewise the globe about half full, and connect the wires with a battery. Hydrogen is speedily liberated from the negative platinum electrode, connected with the zinc (in a zinc carbon battery), whilst the chlorine is liberated from the positive platinum electrode con- nected with the carbon. As the platinum foil is speedily dissolved by the free chlorine, it is preferable to employ carbon electrodes; and as the chlorine is considerably soluble in the strong acid, the more so the gi'eater the pressure, the latter should be equalised, by drawing off some of the acid by the tap, provided with a pinch-cock, and the decomposition started for some time, so as to allow of the liquid becoming well saturated, before the gases are collected. The taps should therefore be opened from time to time as long as the gas volumes in the two limbs do not show equal bulks. Test the gases. The one is of a yellovAsh-green colour, and hleaehes carmine paper. It is chlorine. The other is colourless and bv/rna. It is hydrogen. APPENDIX. I.— HYDROBKOMIC ACID. The chemical affinity of bromine for hydrogen is less pro- nounced than that of chlorine. It decomposes, however, the analogue* of water, viz., sulphuretted hydrogen, SHj, and sets free the sulphur. Water, too, can be decomposed in the pre- * i,e., having an analogy or likeness to, 62 ELEMENTARY CHEMISTRY. sence of deoxidising agents, such as phosphorus, or certain reducing salts, such as hypophosphites, sulphites, hjrposulphites. Exp. 49. — Procure a piece of combustion tubing, bent, as seen in fig. 26. Introduce some pieces of red or amorphous phosphorus, moistened with water, into the bend (a), and into the bend (6) a little bromine. Close with a cork, and fit it with a delivery tube. Pig. 26. Warm the bromine gently, and its fumes, on coming into contact with the moist phosphorus, form, momentarily, phosphorous tribro- mide (PBrj), which is immediately decomposed by water; thus: — PBrs + SOHj = PO3H3 + 3HBr. Phosphorous Phosphorous Hydrobromic tribromide. acid. acid. The hydrobromic acid gas is collected over mercury. It is a colourless gas, and fumes strongly in contact with air. It con- denses under great pressure, and solidifies by great cold. Its specific gravity or volume weight is 405 (H=l), or 271 (air=l). One litre weighs 40'5 criths=3'6288 grms. The gas is very soluble in water. A saturated solution has a specific gravity of 1"78, and contains 82 per cent, of HBr. The liquid acid resembles HCl, but is less stable, for it decomposes partially at 800° O. even. Its volume composition is analogous to that of hydr ochlor ic acid, viz.:- D - D = One vol. One vol. Two vols. Vol. weight =1. Vol. weight = 80. Vol. weight^V =40-5. II.— HYDRIODIO ACID. Iodine possesses even less affinity for hydrogen than bromine. It is readily prepared, like HBr, by the action of iodine on sul- phuretted hydrogen gas, or upon moist phosphorus ; thus: — SH2 + I^ = 2HI + S. PI3 + 30Hj = SHI + PO3H3. HYDROFLUOEIC ACID. 63 The gas is readily soluble in water; and as it is also decom- posed by mercury, it can only be collected by displacement. It is 4*43 times heavier than air, hence it displaces air readily. Hydriodic acid gas is colourless, and fumes strongly when exposed to air. Its specific gravity is 64(H=1). One litre weighs 64 criths=5'7344 grms. Under a pressure of fouratmos- pheres, and at 0° C, it condenses to a liquid which solidifies_ at - 44° C. A saturated aqueous solution at 0° C. has the specific gravity of 1'99, and fumes strongly in the air. When submitted to distillation it yields at 127° C. a solution of specific gravity 1'56, containing 57'7 per cent, of HI. Hydriodic acid is a very unstable body. Heated to 180°_C. it decomposes into H and I. Oxygen decomposes it at a higher temperature into water and iodine; thus: — 2HI + = OH2 + Ij. An aqueous solution is slowly decomposed on exposure to air and sunlight. It turns brown, owing to the separation of iodine, which at first remains dissolved in the acid and then crystallises out in fine crystals. Silver or mercury decomposes it, with evolution of hydrogen; thus ; — SHI + Ag2 = 2AgI + Hj. Bromine and chlorine liberate iodine. On account of the ready decomposition of hydriodic acid^it serves as a powerful reducing agent. It is, like HCl and HBr, a two voliune gas; thus: — One vol. One vol. Two vols. Vol. weight = 1. Vol. weight =127. Vol. weight =i|== 64. III.— HYDKOFLtrORIG ACID. This acid is prepared from fluor-spar (CaFg), by the action of concentrated sulphuric acid; thus: — CaPa + SO4H2 = = SO^Ca + 2HF Calcium Sulphuric Calcium Hydrofluoric fluoride. acid. sulphate. acid. But as hydrofluoric acid attacks glass and most metals, with the exception of lead, platinum, and gold, it can only be pre- 64 ELEMENTAET CHEMISTRY. pared if the student possesses a leaden still, connected ■with a leaden U-tube (fig. 27), which must be kept surrounded by ice, for the condensation of the acid. Fig. 27. Hydrofluoric acid, moreover, is very corrosive, it "gives rise to very painful wounds, and should not he inhaled. The student had, therefore, best content himself by making the following experiments only: — Exp. 60. — Prepare a small leaden cup by hammering a piece of strong sheet lead over the round knob of a poker. Cut the rim quite level, so that a small glass plate or watch glass covers it completely. Cover the glass on one side with a thin layer of wax, and scratch some design on the waxed side with a pointed instrument. Next generate some gaseous hydrofluoric acid by treating a little finely powdered fluor spar, in the leaden vessel, with a little oU of vitriol; stir up to a paste, and invert the glass over it. Place the cup on warm sand. The gas which comes off attacks the glass, where it is not protected by the wax covering, and if left exposed for some time the silica of the glass becomes corroded or etched. Remove the wax with a little oil of turpentine, and a pretty design, according to the skill of the operator, is found engraved on the glass. Hydrofluoric acid is a very mobile liquid, which must be pre- served in vessels made of lead, platinum, or gutta-percha. It fumes strongly in air, and boils at 19° C. Its specific gravity is 0'98 at 12° C. Its vapour density is 10; one litre of the gas weighs 10 criths or "896 grm. It is like the other hydrogen acid s, HC l, HBr, and HI, a tw o volume gas; th us: — — + m = f7T"„. m One voL Vol. weight =1. ' One vol. Vol. weight = JL 19. Vol. Two vols. weight=iy' = 10, HYDEOFLUOKIO AOID. 65 We will now briefly sum up the relations and analogies exist- ing between these four hydrogen acids. ^ They all form at the ordinary temperature dense pungent gases, which fume strongly, when exposed to air, i.e., the mois- ture of the air condenses the otherwise colourless gases. Their aqueous solutions yield up only partially the absorbed acids^ when submitted to distillation. They neutralise metallic bases and form the corresponding salts, called haloid salts, analogous to those which the four halogens formed by direct combination with the metal. Their different vapour densities,* viz. : — SF HCl HBr HI .10 18-23 40-5 64 account for their different chemical action. Hydrofluoric acid is the most powerful of these four acid bodies. Hydriodic acid is decomposed at a temperature of 180° C. into its component parts; hydrobromic acid, which is more stable, only at 800° C; and hydrochloric acid, the most stable, not before the tempera- ture reaches 1500° C. It foUows, from these and other con- siderations, that the element fluorine exhibits the strongest chemical affinity for hydrogen; next to it comes chlorine, then bromine, and lastly iodine. A measure for the chemical energy of these, and other elementary bodies, we possess in the deter- mination of the respective amounts of heat which are produced when they are made to combine with hydrogen, or other ele- mentary bodies. Chemists have accumulated already a great amount of experimental data which hold out a fair prospect of arriving, before long, at a more tangible knowledge of chemical affinity. Thus, chlorine has been found to produce most heat, iodine the least amount, when combining with hydrogen. In order to decompose hydrochloric acid, therefore, more heat is required than for decomposing in like manner hydriodic acid. * The terms specific gravity (H = l), vapour density, and volume weight, are used indiscriminately. LESSON VII. CONSTANT COMBINING PROPORTIONS — ATOMS AND MOLECULES — ATOMIC AND MOLECULAR 'WEIGHTS — CHEMICAL FOB- MUL.B — SYMBOLIC NOTATION. It Las been clearly demonstrated (p. 58 and seq.) that gases combine with each other in fixed and constant volume proportions, and that given volumes (say a litre) having £xed and constant volume weights must also combine in Axed and constant proportions by weight. If we accept 1 litre of hydrogen — the lightest of all gases — as volume unit, and the weight of one volume (1 litre) of hydrogen as weight unit, and call it crith, we obtain for the, gases which we have already studied the following arithmetical values : — Atomio Weights. Volume Weiohis. MoLECtriAB Weights. H - 1 H = 1 crith. Hj = 2 critha. CI = 35-5 CI = 355 „ CI2 = 71 Br= 80 Br = 80 „ Br^ =160 I =127 I =127 „ I2 =254 F = 19 F = 19 „ P2 = 38 , 0H5(steam)= 9 „ 0H,= 18 HCl = 18-25 „ HC1= 36-5 , HBr = 40-5 „ HBr= 81 HI = 64 „ HI =128 HF = 10 „ MF = 20 According to Dalton's theory, all matter is made up of extremely minute particles, which cannot be divided any further by either chemical or mechanical means. Such particles of matter Dalton called atoms, from the Greek >rord Stc/usj indivisible, Palton further supposed that the ATOMS AND MOLECULES. 67 atoms of different elements possess different weights, called atomic weights ; but all atoms of the same element possess the same absolute weight, and are equal among them- selves. When such atoms enter into chemical combination, they form the smallest particles of elementary, as well as compound bodies existing in the free state, viz., molecules. Atoms, there- fore, cannot exist in theyre« state, and an atom is accordingly defined as the smallest quantity of an element which goes in or out of combination. They must either combine with atoms of the same kind of matter, or with atoms of a different kind. Compound (molecular) bodies must contain constant quantities of their constituents, and the relative quantities by weight of the elements, as they express the relative weights of the atoms, must be the same in all their com- pounds. The first and second column in the preceding table shows that the volume weights of elementary gases equal their atomic weights, but the volume weight of compound gaseous bodies is only one-half that of the weights which their formulae express. It follows from this that gas volumes of compound bodies contain only half as many atoms, or smallest particles, as are contained in the same gas volumes of the elementary bodies. In fact, 1 vol. of H, which contains a number of atoms of H, combines with 1 vol. of CI, containing a number of atoms of CI, and forms with it 2 vols, of HCl; and one vol. of HOI contains only half the number of particles contained in the molecule HCl. This is contrary to the conclusion arrived at on purely physical grounds, viz., that all gases — simple as well as compound — contain in eqiial volumes equal quantities of smallest particles. By distinguishing two different kinds of smallest particles, viz., molecules and atoms, and assigning to gases not an atomic, but a molecular constitution of smallest particles of gaseous matter consisting of several atoms, the contradiction disappears. It is evident that the molecules of compound bodies consist of atoms j elementary bodies like- wise form, in the combined state, molecules which consist of several — usually of two — atoms. From these considerations, ^mp^e and Avogadro forpiiil^tp^ the }3.w: e^ual vQlw^es of 68 ELEMENTAET CHEMISTKT. all gases contain an equal nvmher of moleeui.es. Several facts, well established by experiment, confirm that elements in the free state consist of several atoms. Such facts are the allotropic modifications of elements of which we shall have to speak later on, the action of metallic peroxides, and, above all, the different chemical action which elements exert when in the nascent state. The free elements, i.e., their molecules, are compounds of the same kind of matter, the chemical affinity whereof is partially satisfied. The moment atom leaves atom, and before the free atoms can enter into fresh molecular combinations, they possess manifestly in- creased chemical energy. Hence the different chemical effect which is produced from that produced by, e.g., mole- cular hydrogen. The student must not imagine because we have confined ourselves to the experimental ground hitherto studied, and made gas densities and volume weights the basis for proving the law of constant combining proportions and atomic and molecular weigLts, that the atomic theory is not capable of being demonstrated iu any other way. It certainly has the advantage — as we as yet lack the knowledge derived from purely physical considerations, such as specific heat, isomorphism, etc. — that it possesses both a chemical, and, at least, one physical basis, viz., the gas densities, and that we can both weigh and measure the respective combining quantities. If all elementary matter could be converted into the gaseous form, and the volume and weight determined as we determined that of the few but important elements hitherto dealt with, we should have no difficulty in deducing their atomic weights with ease and cer- tainty, as well as their molecular weights, which at present are far from having been determined with certainty; and only by indirect means. For solid bodies, we must rely chiefly upon the purely chemical proof of quantitative analysis, which, as it requires a great amount of chemical knowledge and operative skill, as well as a delicate cehmical balance, is not open to the beginner. Analysis (of which we gave the student an insight in Exps. 17 and 27) has most conclu- sively proved that in every chemical compound the consti- tuents possess constant definite weights. Thus in 100 parts CHEMICAL eonUVLM. 69 by -weight of water and the hydrogen acids, there -were found — Ha = 11-11 = 88-99 H= 5-3 P - 94-7 H= 2-7 01 = 97-3 H = 1-2 Br = 98-8 H= 0-8 I =99-2 100-00 100-0 lOOO 1000 100-0 And as experience has taught us that hydrogen enters, of all elements, in the least quantities by weight into chemical compounds, it has now generally been adopted as unit weight, as well as unit Tolume ; thus — 1 litre of hydrogen weighs at 0' and 760 mm -0896 grm. or 1 orith 1 „ oxygen ,, ,, „ 1-4336 „ 16criths 1 ,, chlorine ., „ ,, 3-1808 grms. 35-5 , And according to the standard employed by Prof, William- son — 11-19 litres of hydrogen = 1 grm.* 11-19 ,, oxygen = 16 grms. ll-]9 „ chlorine =35-5 „ Whether we adopt the crith of Dr. Hofmann or the 11-19 litres of Dr. Williamson, we arrive at the same proportional relative atomic weights. Experiments have, moreover, shown that the same proportional weights are found when these metalloids combine with metals. When chlorine, e.g., combines with metals 35-5 parts by weight combine exactly with the following weights of the metals : — Lithium Sodium Potassium Silver 7 23 39-1 108 It has also been found that elements are capable of com- bining with each other in several proportions by weight, and that such proportions? are mostly multiples of the smallest combining quantities. This was termed by Dalton the law of multiple proportions. Phosphorus, e.g., combines with 3 and 5 parts of chlorine or bromine, forming — PCI3 or PClg, PBrg or PBrj, etc. etc. Chemical Notation. — When two or more elements com- bine according to the laws of constant, simple, or multiple * One litre of hydrogen at 0° C and 760 mm. is here taken at -08935 grm. 70 ELEMEIfTART CHEMISTRY. proportions, and their symbols are placed side by side, -we obtain a chemical formula. A figure placed in front multi- plies every element, or group of elements, or the sum of all component parts thereof, thus : — NaCl means that the compoimd consists of 1 atom of Na (sodium), and 1 atom of CI (chlorine). 6NaCl means that the compound NaCl has to be taken 6 times, and that it consists of 6 atoms of Na and 6 atoms of CI. A figure placed behind, or on the right hand side of a chemical symbol, multiplies only that one element, e.g., COj means that the compound consists of 1 atom of carbon and 2 atoms of oxygen. The sign + indicates addition to; the sign — subtraction of one elementary or compound body from another elementary or compound body. The sign = should be interpreted by furnishes or yields rather than by the arithmetical meaning equal to. Chemical changes, (by combination, resolution, displacement, and double decomposition) are expressed symbolically by a chemical equation. Such equations have already been largely employed, and the student should now learn to interpret them by assigning to each the proper meaning in words, and the corresponding combining weights ; next learn to check off each symbolic equation by sub- stituting atomic weights, and see whether the sum of the numerical values before the sign = is exactly equal to the sum of those after. Summary. — All substances are considered according to Bolton to consist of elem,entary atoms. Atoms unite with atoms to form molecules, either of the same or of different kind of matter. Molecules are the smallest particles of mxitter capable of existing in the free state. JEqual volumes of all gaseous or vaporous matter contain an equal numbe/r of molecules. Gas volumes show the same ratio to each other as molecular volumes. Gas volumes are usually referred to the sta/nda/rd litre, H = l. Molecular volumes to that of H2 = 2. The weights of gas volume, or the specific gravity of all gaseous substances, are equal to half their mxileeular weights. Atomic weights a/re referred to the standard crith, H = 1, and gas ATOMS AND MOLECULES. 71 voliMnes of elements whose molecules consist of 2 atoms are equal to their atomic weights ; and ifHis accepted as the unit of weight and volume, 2 parts by weight of hydrogen or its molecular weight (H^) mil occupy 2 volumes. We speak, therefore, although incorrectly, of 2 volume gases, the volume of a molecule or an atom is, however, quite unJcnown. All we know is that equal gas volumes contain the same number of molecules. These fax,ts and hypothetical assumptions constitute what forms the basis of modern chemistry, viz., the atomic mole- cular theory. /* is based upon tlie facts observed as to com/- bining proportions. LESSON VIII. The elements oxygen — already studied — and sulphur, together ■with the two rare elements selenium and tellurium, consti- tute another group of metalloids which present considerable chemical analogy. SULPHUR. Sulphur occurs extensively in nature, both in the free state and in the form of sulphides, or compounds of metals ■with sulphur; also in the form of salts, such as gypsum, heavy-spar, etc., called sulphates. It is like^wise a chemical constitutent of plants and animal bodies. Exp. 51. — Heat in a test- tube a little sulphur ore (usually contami- nated witli gypsum, chalk, or clay). It volatilises partially; the sulphur condenses in the upper part of the test-tube, and the earthy matters are left behind. This illustrates a process of separation by distillation or sublimation, the latter term being applied to solid bodies, containing volatile constituents ■which on the application of heat pass into liquids and vapours, and on cooling are deposited again. On a manufacturing scale, rich ores are heated in heaps sufficiently to melt the sulphur, ■when it runs out and constitutes crude sulphur. This is purified further by distillation from iron retorts, and ■when run into cylin- drical forms constitutes roll sulphur (brimstone.) Wien the sulphur vapours are suddenly cooled in large brick chambers in a current of cold air, they condense to a fine yellow po^wder, called _^owers of sulphur. Exp. 62. — Heat in a test-tube, or hard glass tube, a little powdered iron pyrites (FeSj). Sulphur sublimes in orange-coloured drops. It is found, however, that the iron pyrites parts ■with only one-third of its sulphur : — 3FeSs = FeaSi + S SULPHUR. 73 This illustrates another mode of extracting sulphur. Iron pyrites occurs ia large masses in this and other countries. The physical properties of sulphur are of considerable interest. Exp. 63. — Dissolve some flowers of sulphur in a small flask by adding to it a little carbon disulphide (CSj), and plunging the flask into warm water. Carbon disulphide is a very volatile, easily inflam- mable liquid, which boils at a low temperature (47° 0.), and care must be taken not to let its vapour come near a flame. The sulphur dissolves readily in it to a clear liquid. Pour the solution out into a small glass basin, or watch glass, and set it aside. The CS^ evapo- rates spontaneously, and the dissolved sulphur crystallises out in transparent, lustrous, rhombic, ootahedra, resembling the well-formed crystals of native sulphur. This constitutes one form in which sulphur exists in. nature, viz., as ordinary rhombic, or octahedral sulphur. Exp. 64. — Melt some sulphur in a small beaker or porcelain crucible (fig. 29), imbedded in the hot sand of a small sand-bath, which is gently heated by a Bunsen flame. Allow the melted sulphur to cool slowly, till a crust has formed on the surface. Pierce the crust, on opposite sides near the edge, with a pointed glass rod, and pour out the sulphur, which remained liquid underneath, through one hole, air being admitted through the' other. When quite cold remove the crust carefully, and without disturbing the inside. Fig. 28. Kg. 29. Fig. 30. A network of long, honey-like, transparent prismatic crys- tals (fig. 30) ■will be found which belong to a different crys- tallographic system, viz., the monoclinic. Bodies which are capable of crystallising under varying conditions, in forms belongrog to two different crystallographic systems, are called dimorphous bodies, and the property itself is termed dimorphism (from /mpifv = form, and in, two). The prismatic crystals of sulphur are slightly elastic at first, but become rapidly brittle and opaque, and assume a 74 EtEMElfiAEY CHEMISTRY. somewhat lighter colour. They pass slowly — rapidly at 100° C. — ^back to the first or octahedral modification, and become soluble in carbon disulphide. JFig. 31. Exp. 55. — Heat some flowers of sulphur in a long-neoked Florence flask or retort (fig. 31), over a gas flame. Apply the heat gradually. The sulphur melts at about 115° C. to an amber-yellow liquid. On applying a stronger heat it gets darker in colour, and of a honey-like consistency, and at about 250° to 260° C. it turns to a red-brown, almost black, tint, and becomes so viscid that the flask or retoit may be turned upside down, without any of the melted sulphur running out. When heated to above 300° C, it becomes once more liquid, and begins to sublime. At 440° C. it boils and distils (especially if the retort be covered with wire gauze), in the form of orange-yellow vapours. Allow a continuous thin stream of condensed sulphur to flow into a tall vessel of cold water. Long threads of yellowish- browu sulphur are obtained, which remain for several days soft and elastic before they return to the original hard, opaque, and brittle condition of octahedral sulphur. At 95° C. the latter change takes place instantaneously, with evolution of a perceptible amount of heat. This soft, or as it is termed plastic, sulphv/r, when treated with carbon disulphide, dissolves only partially, and leaves a grey amorphous powder, which is insoluble in carbon disul- phide, and is called cmiorphous (insoluble) sulphur. Com- mercial fiowers of sulphur, prepared by rapid condensation, contain likewise much amorphous sulphur, insoluble in CS^. SULPHUR. 15 When teated to 100° C, insoluble amorphous sulphur returns to the ordinary soluble modification of sulphur. Exp, 66. — Boil some flowers of sulphur with a small quantity of a solution of caustic soda, till a clear solution is obtained. Pour the solution into dilute hydrochloric acid, and stir. White finely divided sulphur falls out, which is called milh of sulphur. This sulphur is likewise amorphous, but is soluble in carbon disulphide, and is gradu- ally reconverted into ordinary rhombic sulphur. The property -which elementary matter possesses of assum- ing, forms differing from each other in physical properties, such as crystalline structure, specific gravity, fusibility, and solubility, is termed the allotropic* state of matter. We know, besides sulphur, several other elementary bodies which possess this property, even in a higher and more pronounced degree, and it is matter for speculation, whether all elemen- tary matter be not capable of allotropic existence. Oxygen, in ozone, of which we shall have to treat presently, selenium, tellurium, carbon, silicon, phosphorus, arsenic, boron, are capable, among the metalloids, of allotropic modifications. The allotropic forms of sulphur exhibit the following physical properties : — Behaviour with Sp. gr. Fusing points, carbon disulphide, 1, Octahedral.. 2-05 115° C. , Soluble. 2, Prismatic..., 1-98 120° C. Insoluble, 3, Plastic 1'95 | Both are converted 1 PartmUy soluble. ^ An^orphous , 1-95 j ^^^iS"^^' [ I--1-M- These allotropic modifications of one and the same element can only be explained by assuming that their molecules con- tain different (varying) numbers of atoms. In evidence of this explanation, we refer to the different vapour densities of sulphur at different temperatures. At 500° C. the sulphur vapour is 96 times heavier than hydrogen. From 700' C. and upwards it decreases in weight, till at 1000° C. it remains constant. It is then only 32 times heavier than hydrogen. Its volume weight is therefore 32, and its molecular weight 2 x 32 = 64, One volume of sulphur vapour at 1000° C, weighs 32 criths, whilst at 500° C. the molecule contains six atoms, which on further heating become * From aXA.9;, another, and i-fiims, fashion. 76 ELEMENTARY CHEMISTRY. dissociated. The dissociation begins at 700" C, and is com- pleted at 1000° C. It may be inferred from this that other elementary matter, in the solid and liquid state, may form even more complex molecules, containing a greater number of atoms. In its cTiemical properties sulphur resembles oxygen very closely; it forms compounds, analogous to the oxygen com- pounds. Metals and non-metals combine directly with sulphur, and form an extensive and important class of bodies termed sulphides. A few experiments will illustrate this : — Exp. 67. — Mix intimately fine iron-filings (7 parts by weight) * with (4 parts of) sulphur, and inject small quantities at a time into a small Hessian crucible, heated over a good Bunsen flame. The sulphur and iron-filings combine chemically and form ferrous sulphide (FeS). Break up the crucible, when cold, and keep the fused mass for use. Small quantities of other metals, such as finely divided copper, zinc, tin, or lead, might be substituted for the iron- filings, and the mixture with sulphur heated in a test-tube. The chemical combination is marked by a flash of light and the evolution of considerable heat. The compounds OuS, ZnS, 8n8, and PbS have their representatives in nature in the minerals copper pyrites, found in Cornwall, zinc-blende or black-jack, tin pyrites, and galena. Sulphuretted Hydrogen. — This is, next to the oxygen compounds, the most interesting compound of sulphur. Exp. 68. — To prepare this gas the apparatus employed in the pre- paration of hydrogen (fig. 2), may be used. A more convenient apparatus, however, consists of a tall and narrow tubulated glass cylinder, known under the name eprouvette, seen in fig. 32, which is charged with small lumps of ferrous sulphide. A disc of perforated sheet lead, placed over the contracted part, prevents the sulphide from falling to the bottom. Another tubulated bottle is charged with dilute hydrochloric or sulphuric acid. The two are connected with each other by means of india-rubber corks, fitted with short pieces of glass tubing, and about 2 ft. in length of f in. bore, flexible india- rubber tubing, bound to the glass perfectly tight with thin copper wire. By opening or closing a screw-clamp, seen in an enlarged scale in fig. 32, and raising or lowering the acid container, the acid can be made to flow into the eprouvette till it reaches the ferrous sulphide, when the evolution of gas immediately begins, or it can be withdrawn from it, when the evolution stops. By working, in a like * Atomic proportions, re=S6, and S=32, or 7 ! 4, BULPHUE. 77 manner, another screw-clamp interposed over the piece of i^dia- rubber tubing which connects the exit tube of the eprouvette and the delivery tube, the same effect can be produced, without having to lower or raise the acid bottle, and the evolution of the gas brought under thorough control. When the apparatus is not in action, one or the other clamp must be kept closed, but not both. Fig. 32. Numerous other forms of generating apparatus have been proposed, based upon the same principle of arresting the chemical action by withdrawing the acid from the ferrous sulphide. The one described is cheap and serviceable. It can be easily cleaned out by disconnecting the eprouvette, and passing a stream of water through, in order to dissolve out any ferrous salt, when it is again ready for use. If used only at longer intervals, the acid should be removed to a well-stoppered bottle, and the whole apparatus well washed, without disturbing the lumps of ferrous sulphide, and the screw-datrvps left open. Sulphuretted hydrogen, being considerably soluble in cold water, has to be collected over tepid water or by displace- ment. Glass cylinders which can be closed air-tight by means of greased glass plates, are employed, and filled with the gas in the manner explained under hydrogen. The experi- ments should be conducted in a closet connected with a good 78 ELEMENTART CHEMISTRY. chimney-draught, or in the open air. When prepared from ferrous sulphide, as described, it usually contains free hydrogen. To prepare the pure gas, it is necessary to em- ploy barium sulphide (BaS), or heat antimony sulphide (Sb2S3) with hydrochloric acid. The chemical reaction is expressed by the equation — FeS + 2HCl(orS04Hj) = SH^ + FeCL, (or SOiFe), Properties, — Sulphuretted hydrogen is a colourless gas ■which possesses the disgusting odour of rotten eggs. It is highly poisonous, and cannot be inhaled with impunity. According to Faraday, birds die in air containing 1 part in 1500, and dogs in air which contains 1 part of the gas in 800 parts of air. It is somewhat heavier than air, its specific gravity is 1-177 (air=l) or 17 (H = l). One litre of the gas weighs 17 criths or 17 x -0896 = 1'5232 grm. Water dissolves from three to four times its volume of the gas, and forms sulphuretted hydrogen water, which reacts slightly acid with litmus paper, and possesses the properties of the gas itself. Cooled to — 74° C, or subjected to a pressure of 17 atmospheres at 10° C, the gas condenses to a colourless mobile liquid of specific gravity 0'9, which freezes at - 85° C. to a white crystalline mass. Exp. 89. — Replace the delivery tube in apparatus (fig. 32), by a glass tube drawn out to a jet, and pass the gas, before it issues, through a drying tube containing dry porous calcium chloride. Bring a light near the jet, and hold a dry bell-jar over it. The gas inflames and burns with a pale-blue flame, with formation of water and sulphur dioxide, known by its pungent smell: — 2SHi, + 3O2 = 2OH2 + 2SO2. If a cold body, such as a thick glass rod, is held in the flame, sulphur is seen to deposit on the rod, and the hydrogen alone is burnt. The same is seen when a lighted taper is brought to the mouth of a jar fuU of sulphuretted hydrogen gas. The gas burns with a pale blue flame at the mouth of the cylinder only, and sulphur is deposited on its sides, owing to an iusufiBcient supply of air. Exp. 60. — Bum a little sulphur in a deflagrating spoon, and lower it into a dry cylinder. When air has yielded all its oxygen to the sulphur to form sulphur dioxide (comp. Exp. 20), the flame becomes extinguished. Remove the spoon, and close the cylinder with a glass plate. Place the cylinder mouth to mouth with another cylinder, contmning dry 8?ilphuretted hydrogen gas, %ud witbdra-sf SULPHUR. 79 the plates. The two gases diffuse and react upon each other. The hydrogen of the latter robs the sulphur dioxide of its oxygen and forms water, and sulphur is, deposited as a fine light yellow amor- phous powder: — 2SHi, + SOj = 2OH2 + Sj. In an aqueous solution (prepared with, unboiled ■water, i.e., water containing air) sulphuretted hydrogen is slowly decomposed, and the solution becomes milky ; thus : — SHj + = OHj + S. It decomposes rapidly, also, if the bottle is not quite fulL Hence the necessity of preserving it in a bottle which is quite full, and closed with a good indiarrubber stopper. Such a solution is called hydrosnlphuric acid. The halogens CI, Br, and I act on it in the same manner as oxygen. Exp. 61. — Place a cylinder of dry chlorine gas mouth to mouth with another containing dry sulphuretted hydrogen gas. The gases immediately react upon each other, with formation of hydrochloric acid and deposition of sulphur. A little sulphur chloride is also formed, if chlorine is in excess. CI2 + SHj = 2HC1 + S. 2 vols. 2 vols. 4 vols. This reaction is conveniently employed for preparing, in a perfectly analogous manner, hydrobromic and hydriodic acids, as will be explained in the Appendix. Sulphur in sulphuretted hydrogen possesses a greater affinity for nearly all metals (and non-metals, as we have just seen) than for hydrogen. Metals, therefore, displace it, with formation of metallic sulphides, e.g., Pb + SH, = PbS -1- H^. Metallic oxides and hydrates are likewise readily acted upon by SHj, with formation of sulphides and water : — CuO + SHj' = CuS + OH2 Copper Copper oxide. sulphide. KHO -f- SH„ = KHS -1- 0H„ Potassium hydrate. Potassium hydrpsulphide. Uepce sulpburetted hj^drogen or bj^dfosulpburic mi ^pts 80 ELEMENTARY CHEMISTET. as a -weak acid, and metallic sulphides or hydrosulpMdes may be viewed as salts of this weak acid. The affinity of sulphur for most metals is -so great, that SHj removes them, out of very dilute solutions even, because it forms with them, for the most part, insoluble compounds. Exp. 62. — Place a few drdpa of each of the following salt solutions into six separate glass cylinders, or good-sized test-tubes, and nearly fill them up with distilled water, and mix well. (1) Lead acetate {sugar of lend). (2) Copper sulphate {blue vitriol)., (3) Cadmium chloride. \ (4) Antimony terchloride. (5) Zinc sulphate (white mtrioT). (6) Magnesium sulphate (Epsom salts). Add a strong solution of SHj to each, and watch the precipitates, as they slowly form, before shaking up. The following changes will take place: — (1) A black precipitate of lead sulphide... PbS. (2) A black ,, cuprio ,, ...CuS. (3) A fine yellow „ cadmium,, ...CdS. (4) A brick-red curdy „ antimony ter ...SbjSj. (5) A white ,, zinc ,, ,...ZnS. (6) Ho change takes place. Sulphur, we have already learned, is a true vapour only at the very high temperature of 1000° C. SHj would, there- fore, consist of 1 volume of sulphur vapour at 1000° C., plus 2 volumes of hydrogen — the three volumes contracting into two, analogous to steam : — + H ir JL Three vols. Two vols. and 1 volume of sulphuretted hydrogen gas contains, there- fore, 1 vol. of H and ^ vol. of S. The molecule must consist of 2 vols, of H and 1 vol. of S; consequently the molecular weight of SHj is made up of 2 x 1 = 2 (H) + 32 (S) = 34. The volume weight, determined by weighing, is 8/ = 17 criths, or 17 x -0896 = 1-5232 grm. TELUJEIUM. 81 APPENDIX. SELENIUM.'. Symbol, Se. Tliis substance is found native to a very limited extent; it is also found associated with certain iron pyrites. It is deposited partly in tlie flue-dust, partly in the mud of the leaden chambers in sulphuric acid works. Like sulphur, it can exist in different alio tropic modifications, viz. : — Amorphous (reddish-brown powder). Specific gravity, 4'26; soluble inCSj. OryetaUine (dark-grey mass with metallic lustre). Specific gravity, 4'8; insoluble in CSa. It also exhibits changes analogous to those exhibited by sulphur. Selenium mel^s at 217°,_ boils at about 700°, and gives off dark-yellow vapour, the density of which decreases as the temperature rises, till at about 1400° C. it remains constant. It has then a density of 79'5 (H=l), and its molecular weight is 159. Its atomic weight is 79"5. Selenium closely resembles sulphur also in its chemical pro- perties; it burns with a reddish-blue flame, forming selenium dioxide (SeO^), which has a peculiar smell, resembling that of decaying horse-radish. It forms a gaseous hydrogen compound, selenietted hydrogen (SeHj), which is colourless, and possesses a most _ disagreeable smell. The gas is poisonous. Its aqueous solution is decomposed by air with separation of selenium. TELLURIUM. Symbol, Te. This substance is of very rare occurrence. It exists either native, or in combination with metals (Au, Ag, Pb) as tellurides. It possesses all the properties of a metal; it crystallises in rhombohedra, of specific gravity 6"25, is white as silver, lustrous, and conducts heat and electricity. Tellurium melts at 800°, and volatilises at a white heat, and can be distilled. _ Its vapour is greenish-yeUow, like chlorine. It burns in air with a blue flame tinged with green, and forms tellurium dioxide (TeOj). Its hydrogen compound, tellurietted hydrogen (TeHj), is a colourless very poisonous gas, and of a disagreeable odour. Tellurium has the atomic weight 128 assigned to it. Summary, — The elements 0, S, Se, and Te, constitute a 82 ELEMENTARY CHEMISTRY. natural grawp of elements which exhibit considerable analogy, more so the last three. Oxygen, which has the lowest atomic weight, differs most widdyfrom the others {analogous to fluorine in the chlorine group). Their chemical activity seems to he determined by their atomic weights; thus: — = 16, S = 32, Se = 79-5, Te = 128 (or 125); as compared with F = 19, CI = 35-5, Br = 80, I = 127. An increase diminishes their volatility, and seems to give rise to denser molecules, with higher specific gravities, higher melting and boiling temperatures, as will be seen from the following table: — Oxygen. Sulphur. Specific gravity, . ... 1 "95 and 2 '05 Melting point, 115° Boiling point 440° Gas volume, 16 32 Oxygen, which as late as the beginning of this year figwred among the nonrcoercible gases, has been condensed since, and the vacancies left in this column will, there is every reason to hope, soon be filled up. The other three elements are solids. It should be remembered, however, that S, Se, and Te, in the free or molecular state, consist, in all probability, of a greater number of atoms, i.e., they form denser molecules. With a rise in the atomic weights they exhibit, instead of metalloidal, metallic characters. TeUuriwm has all those physical pro- perties which constitute a metal. Selenium possesses them, in a less degree in its crystalline modification. In their chemical OfCtivity they exhibit, however, very sUght gradations. All combine unth hydrogen to form hydrides, viz: — 0H„ SHj, SeHj, TeHj. Water alone is a neutral liquid at the ordinary temperature; ail others are gaseous, and exhibit weak acid properties. Air or oxygen decomposes their aqueous solutions, with deposition of S, Se, and Te. Water is not decomposed. When heated strongly the decomposition of their elements takes place in a like ratio, ie., water or stea/m last. Selenium. Tellurium. 4-2 and 4-8 6-2 217° 500° C. 700° White heat, 79'5 ... LESSON IX. The elements, nitrogen, phosphorus, arsenic, cmtimony, and bismuth, constitute' another group of elements -which exhibit a marked analogy between each other, and which, in its three last members, approaches nearer to the metals than any other group of metalloids. I.— NITEOGEN. Amiaoilia. — The element nitrogen, which was described when we studied the composition of atmospheric air (comp. Exp. 27), is one of the most inert bodies in nature. In the free state, as in air, it exists, side by side with oxygen, without entering into chemical combination. Under the influence of various powerful agencies, such as electricity, light, heat, etc., it does enter into combination, but always very slowly, and to a limited extent only. Its compounds with hydrogen and oxygen, on the other hand, are among the most interesting bodies, and possess a strongly pro- nounced chemical character. The intervention of water seems to be necessary to produce combination, as we have not yet succeeded in extensively inducing direct combination between nitrogen and hydrogen, or nitrogen and oxygen, and the product is a proportionally unstable compound, viz., ammonium nitrite, as well as nitrate ; two salts of which we shall have to treat further, when we come to the oxygen compounds of nitrogen. Although present in the air and in the soil in small quantities only, these salts constitute the great fertilisers from which plants derive their nitrogen — one of the constituents most essential to plant life. Nitro- gen, again, selects the hydrogen, when plants or animal nitrogenous bodies undergo slow decomposition by decay or putrefaction, and separates as ammonia (NHj), composed of J atom of nitrogen and 3 atoms of hydrogen. 84 EliEMENTAET CHEMISTRT. Exp. 63. — Heat in a test-tube, provided with a cork and delivery tube, some highly nitrogenised body, such as white of egg, glue, isinglass, etc., together with soda lime (i.e., quicklime slaked with a solution of sodium hydrate). A pungent gas comes off (besides some tarry empyreumatio products) which turns red litmus paper blue, and which can be fixed by an acid, such as sulphuric acid. This illustrates approximately another chemical decompo- sition, which now yields us the greater part of our supply of ammonia, viz., the process of distilling coal for gas in our gas- works. The immense coal deposits, in various parts of the earth, are derived from fossilised plants ; and although the percentage of nitrogen in coal does not amount to more than from "75 to 1"5 per cent., yet, on account of the vast quan- tities of coal which are annually carbonised for the produc- tion of coal-gas, it furnishes us considerable quantities of ammonia in the so-called " ammoniacal liquors," looked upon as a mere bye-product in gas-works. When the crude coal- gas is washed with a hydrochloric acid solution, its ammonia becomes fixed and converted into ammonium chloride by the direct combination of these two bodies; thus : — NH3 + HCl = NH4CI. Ammonia. Ammonium chloride. The solution is evaporated, and a white salt, commonly called sal-ammoniac, is left. This forms now our chief source of ammonia. Exp. 64. — Gently heat, in a small flask provided with a cork and delivery tube, a mixture of slacked lime and powdered ammonium chloride. A pungent colourless gas comes off, which is dried by passing it over quicklime contained in the eprouvette (fig. 33), and which must be collected over mercury or (imperfectly) by displace- ment in an inverted cylinder, as the gas is so much lighter than air. Calcium chloride forms a compound with ammonia, and cannot, therefore, be employed for drying it. The chemical change is the reverse of the one just explained. The HOI in the ammonium chloride (NHg, HCl) is attracted to the fixed alkali (lime), with which it forms calcium chloride, and ammonia, being a volatile com- pound, is set free; thus : — 2NH4CI + Ca(0H)2 - CaCla + 20H3 + 2NH3. AMMONIA. 85 Collect in dry bottles or cylinders by displacement. Test whether the gas is combustible by applying a lighted taper. The flame is at first slightly enlarged, and then extinguished. Fig. 33. The enlargement is due to a very slight and evanescent com- bustion of the gas, because its igniting point, like that of nitrogen, is higher than the temperature produced by its combustion. The gas has, therefore, to be heated before it can burn. Exp. 65. — ^A dry bottle is charged by displacement with tlie dry gas, by letting the delivery tube pass right up into the bottle (as seen in fig. 33), and is then stoppered with a good cork, provided with a short glass tube, capped with an india-rubber tube and compres- sion-olamp, and plunged into cold water. The water rushes in with great force on loosening the clamp, as it would into a vacuum (fig. 34). By colouring the water red, with a little litmus solution and a drop of weak acid, it changes the colour to blue as the ammonia is absorbed. Ammonia gas is exceedingly soluble in water, and its 86' ELEMENTAE? CHEMISTRY. solution reacts strongly alkaline. One part of water absorbs (at 0° C. and 760 mm. bar. pressure), 1050 volumes of am- monia ( = -877 parts by -weight); at 15° C, 730 volumes. A strong aqueous solution of ammonia is called " liquor am- monioe." Fig. 34. Exp. 66. — Fit a short piece of |-incli bore porcelain tube, of about 1 foot in length, with entry and delivery tubes, the latter drawn out to a jet, for passing a current of dry ammonia gas, and place the tube in a charcoal furnace (comp. fig. 21). Apply a light to the gas as it issues from tlie jet. It wiU not burn readily, but a pale green- ish flame will play over the top of the light. Now apply heat gradually to the porcelain tube. As the initial temperature is raised at which the gas issues, it may be made to bum; on slowly cooling the tube, by taking oflf the ignited charcoal, the flame wUl gradually die away. Ammonia gas is broken up by being passed through the hot porcelain tube into hydrogen, which bums, and nitrogen, water, ammonium nitrite,, and nitrogen dioxide, being formed. This may be shown by passing the gas into water, acidulated with a little hydrochloric acid, to absorb any undecomposed AMMONIA. 87 ammonia, and collecting over a dilute acid solution over a pneumatic trough. The gas so collected is found to consist, when submitted to analysis, of a mixture of 1 volume of nitrogen and 3 volumes of hydrogen. It has lost the pro- perties of ammonia gas ; it is no longer soluble in water, and shows a neutral reaction, instead of being alkaline. ' Fig. 35. Exp, 67. — Pass some dry ammonia gas over metallic sodium placed in a bulb-tube (as seen in fig. 35), and heat the bulb-tube gently* The rAetal sodium partially displaces the hydrogen, forming a com- pound called sodamide (NHjjNa). The Uberated hydrogen bums freely at the drawn-out end of the tube; it has all the properties of hydrogen. The same fact, viz., that ammonia contains hydrogenj might be proved in various other ways, for instance, by passing chlorine through a concentrated solution of ammonia^ when it is broken up; thus : — 8NH3 + 3CI2 = 6NH4CI + 2Ni tjnless, however, excess of strong ammonia be alwaya present, there is a risk of forming nitrbgen trichloride (NCI3) — a compound which is fearfully explosive — and the experi- ment should, on no account, be attempted by the beginner. s& ELEMENTAKT CHEMISTRY. Kg. 36. of H and 1 volume of N; H One voL + The electrolysis of NHg inay also be effected in a Hofmann's apparatus (fig. 36). Diy ammonia gas is decomposed over mercury by passing electric sparks through it for some time. The decomposi- tion is slow, but after a time the gas volume is seen to increase from 2 volumes to 4 volumes. Another pretty experiment to illustrate the composition of NHg may be made by employing a two- limbed apparatus, the shorter limb closed with a good indiarrubber cork, through which passes a short glass tube, provided with a glass stop-cock, in order to admit the dry gas. Copper wires pass through the india-rubber cork which closes the eudiometer limb. They are connected with a spiral of platinum wire, which holds a short piece of stout copper wire freshly oxidised in a flame. When a galvanic current is sent through, the copper oxide becomes strongly heated. The hydrogen gas reduces the CuO with formation of water which condenses, and nitrogen gas which is left. Three out of the 4 volumes disappear. This proves that ammonia consists of 3 volumes thus : — H H H Jl_3 Three vols. Two vols. The molecular weight is 14 + 3 = 17. The volume weight or specific gravity of the gas is y = 8-5 criths, or 1 litre weighs 8-5 x -0896 = '7616 grm. Ammonia gas condenses, PHOSPHORUS. 89 at 10° C. and 6-5 atmospheres, to a colourless mobile liquid of specific gravity 0-613 at 0° C, which solidifies at - 80° C. The gas, as well as its aqueous solution, possesses strong basic characters; it constitutes a strong (volatile) alkali, and neutralises acids, forming with them salts which resemble the salts of the fixed alkali bases, potassium, or sodium hydrates; e.g. — NH, + HCl = NH4CI [KOI] 2NH3 + SO4HJ = S04(NH4)2 [SO4KJ, etc. There is, moreover, evidence that the group of elements NH^ can exist, in combination with mercury, as an unstable amalgam, and that it acts chemically, like the metals K, Na, etc. It has, therefore, received the name ammonium, and may be conveniently expressed by the symbol Am, as AmCl, ammonium chloride, etc. APPENDIX. 11— PHOSPHOEUS. This elementary body possesses such a marked affinity for oxygen, that it is never found in the free state in nature, but always in combination with oxygen in the form of salts, called phosphates, the principal amongst them, the calcium phos- phate, being of paramount importance, both in the economy of the vegetable and animal kingdom. It is, in fact, from this salt, which constitutes the greater part of our bones, that we derive phosphorus by a process of partial reduction. _ The liberated phosphorus escapes in the form of vapour, which is condensed by proper appliances under water. When purified by redistillation, it is obtained as a pure, wax-like, faintly- yellow, semi-opaque, solid body, of specific gravity 1'83 at 10° C., and is generally sold in the form of sticks preserved under water, At the ordinary temperature it is soft and tough, at 0° C. it becomes brittle. It melts at 44° C, and is then of a yeUowish- syrupy consistency, and boils at 288° C. It volatilises, however, far below its boiling point, and as its vapour is spontaneously inflammable, the greatest care must be observed in handling this substance. Friction even may set it on fire. Phosphorus is insoluble in water, little soluble in alcohol and ether, veiy easily soluble, however, in carbon disulphide, from which 90 ELEMENTARY CHEMISTRY. solution it crystallises, out of contact of air, in rhombic dodeca- hedral crystals. This constitutes its first allotropie modification, viz., crystalline or yellow phosphorus. Its name is derived from the Greek word ipurfaph, because it glows in the dark in air and other gaseous matter containing oxygen. This phenomenon appears, therefore, to be due to oxidation. When ordinary phosphorus is heated in iron vessels, with exclusion of air, to 300° C, for a few minutes even, it undergoes a change. The soft yellow phosphorus becomes a dark red and amorpkous powder, and acquires materially diflferent (physical) properties. The same change begins to take place slowly at 250° and upwards, and if a little iodine is added to the ordinary yellow phosphorus, it passes into another, the so-called red aUotropic modification, even below 200° C. Eeddish-brown amorphous phosphorus has a specific gravity of 2"14, and is insoluble in carbon disulphide, it does not glow, and is not poisonous, Hke ordinary phosphorus. It does not melt even at a red heat apd strong pressure, and volatilises (above 260°) only slowly and partially, tne vapours changing back into ordinary phosphorus. This constitutes a source of danger in its manu- facture. The employment of amorphous phosphorus in the manufacture of lucifer matches, etc., has been the means of great saving of life. It is now used in the laboratory with great advantage in many reactions where ordinary yellow phos- phonis used to be employed. A third aUotropic modification, so-caUed metallic phosphorus, is obtained by melting lead and amorphous phosphorus in a sealed tube. The molten mass, when cold, exhibits on its surface lustrous black metallic-loohing phosphorus crystals, which have the specific gravity 2"34. This aUotropic modifica- tion is even more inactive (chemicaUy) than red phosphorus. The vapour of phosphorus is 4'4 times heavier than air, hence its vapour density is 62 (H=l), and its molecular weight 124. The atomic weight of phosphorus, 31, has been conclusively established, however, by actual analysis, and the molecule of phosphorus vapour consists, tlierefore, of 4 atoms ; P4 = 4x31 = 124. Unlike the sulphur vapour, which contains 6 atoms at 500° C, and 2 atoms only at 1000° C, no simpler atomic expression than 4 has as yet been established by heating phosphorus vapour as high even as 1040° C. Its vapour density IS therefore irregular, and differs from most other gases in forming a 4 volume molecule _P II p_ ■p 11 p" Its volume weight is 2x31=62 criths, and 1 litre of phosphorus vapour weighs 62 X ■0896 = 5-555 grm PHOSPHOEETTED HYDROGEN. 91 Phosphoretted hydrogen.— Phosplioms forms with hydrogen three different hydrogen compounds, PHs, P2H4, P4H2, the prin- cipal one, PHs, being perfectly analogous in composition to that which nitrogen forms, viz., NH3. Exp. 68. — Heat gently, in a small tubulated retort, a concentrated solution of sodium or potassium hydrate, together with a few small pieces of phosphorus. The NaOH breats up under the influence of phosphorus, which possesses a powerful affinity for oxygen, and forms with it an oxy-acid, which remains behind in combination with the alkali metal as a salt, sodium hypophosphite, and with the hydrogen, phosphoretted hydrogen compounds, which escape, and when they come in contact with the air, inflame spontaneously. To perform this experiment with safety, a slow current of coal-gas should be passed through, as indicated in fig. 37, till the air is dis- placed, and the gas collected over warm water to prevent the delivery tube becoming choked up with condensed phosphorus. Each gas bubble ignites as soon as it issues into the air, and forms pretty wreaths of white smoke (PoOj). This spontaneous ignition is due to a slight admixture of figuia PjH^. Kg. 37. PS3, when free from P2H4, inflames only when heated to 100° C. It is a colourless gas, having a highly offensive odour of garlic, and is very poisonous. Its vapour density is 17 (H=l), or 1'185 (air=l). Its molecular weight is 2x17=34, and 1 litre of PH3 weighs 17 criths = 17 x •0896 = 1-5232 grm. Phosphoretted hydrogen resembles ammonia, also, in being of a weak basic nature. It combines with HBr and HI, and 92 ELEMENTARY CHEMISTEf. forms crystalline compounds, analogous to ammonium cHoride j chus : — PH3 + HI = PHJ Phosphonium iodide. In whicli the group of elements, PH4, phosphonium, analogous to NH., acts like a quasi metal. When decomposed with KOH, it yields pure wow-inflammable phosphoretted nydrogen : — PH4I + KOH = KI + PHs + OHj. III.— ARSENIC. Symbol, As. — This element acts chemically like phosphorus, forming compounds which are quite analogous to the phos- phorus compounds. The same applies to the fourth element, antimony (symbol, Sb), and its compounds. In their physical properties, however, they approach the metals, more especially antimony: and in the last element of the group, bismuth (symbol, Bi), the metallic character prevails, and the chemical recedes. This is shown by the fact that it does not enter into composition with hydrogen, like all the other members of the group, yet forms analogous chlorides, etc. Arsenic exhibits two aUotropic modifications— (1) amorphous arsenic, a black non-lustrous mass, of specific ^avity 4'71, brittle and easily powdered ; (2) crystalline arsenic, obtained by the continuous heating of arsenic to 210°-220° C. It forms steel-grey hexagonal rhombohedra, showing a strong metallic lustre; their specific gravity is 57. Arsenic volatiKses at 180° C, without first melting. Its vapour is of a lemon-yellow colour, and its density is 150. Its molecular weight is, therefore, 300. It is a four-volume vapour, like that of phosphorus. The atomic weight of arsenic having been found gravimetrically equal to 75, it follows that the gas molecule of As, like that of P, consists of 4 atoms (As =4 x 75= 300). One litre weighs 150 criths, or 150 x •0896 = 13'44 grms. Arsenic combines directly with metals, and forms with them arsenides, analogous to sulphides, e.g., FeSj and FeAsj, al- though the arsenic shows in its various other compounds the character of the elements of the nitrogen, and not of the sulphur group. As arsenic (as well as antimony and bismuth) are usually studied under the metals, we vpill only briefly refer to the hydrogen compounds, AsHs and SbHs, which are of a composi- tion powerfully analogous to NH3 or PHj. AESENIO. 93 Exp. 69. — Arsenletted hydrogen (AsHs) is prepared pure by treat- ing an alloy of zino and arsenic (AsjZnj), with hydrochloric acid, when the following reaction takes place:— AsjZns + 6HC1 - 2ASH3 + SZnClj. As the gas is so extremely poisonous, it is advisableto dilute it with another non-poisonous gas, viz., hydrogen. This is done by generating hydrogen, as usual, from zinc and dUute hydro- chloric or sulphuric acid. A few drops of a 'solution of white arsenic (AS2O3) in hydrochloric acid are added, when the evolu- tion of a mixture of H and AsHs proceeds vigorously. Most of the properties of arsenietted hydrogen may be studied just as well with this as with the pure gas. It is a colourless gas of peculiar garlic odour and very poisonous, even when consider- ably diluted with hydrogen. It should, therefore, be prepared in a good draught cupboard. The pure gas condenses to a liquid at - 40° C. Its density is 39 (H= 1), or 2-69 (air= 1). It is not spontaneously inflammable, like PH3, but bums when lit with a livid flame, forming AS2O3 and OH2. Heat breaks it up into As and H. When the gas is passed through a heated glass tube, a mirror of metallic arsenic is deposited close behind the heated spot, especially if the glass tube has been narrowed a little. A cold porcelain dish held into the flame lowers the temperature suddenly below the ignition point of the arsenic, and the porce- lain becomes covered with a black mirror or shining spots. This reaction is utilised for the detection of arsenic. When arsenietted hydrogen is decomposed into its component elements (by passing the electric spark through it into a eudio- meter), it yields 3 vols, of H and 1 vol. of arsenic vapour. The atomic weight of arsenic, as determined gravimetrically, and from its volume weight, is 75, and the molecule of AsHs is, therefore, 75-1-3=78, and its density V*=39. Antimonietted hydrogen (SbHj), is prepared in an analogous manner. It yields a mirror which is less lustrous than the arsenic mirror, and is insoluble in a solution of bleachin^-powder, arsenic being readily soluble, because it becomes oxidised to arsenic trioxide (As^Os). Summary. — The elements of the so-ccdled nitrogen group, viz., N, P, As, Sb, Bi, exhibit both in their physical, as well as in their chemical, properties, similarly mwrhed gradations as did the elements of the other groups already studied. With the increase in their respective atomic weights we pass from, the gaseous, nitrogen, which diners the most widely from the 94 ELEMENTARY CHEMISTET. Others, hy the wax-like semi-liquid phosphorus and semi- metallic arsenic, to the metallic antimony, and to ike even more pronownced metal, bismuth; and if we glance at the sub- joined tabular arrangem,ent, we are forced to admit that such an increase amounts to a condensation of matter with a corre- sponding decrease in the fusibility and volatility, and a gradual passing from, the metalloidal to the metallic condition. With the exception of Bi, they all form volatile hydrogen compounds. NiTBOGEN Phosphobus AnsEsia. Anti- Mosry. BiSMWTH. Atomic weight.. 14 31 75 122 208 Specific gravity. — From 1-83 to 2-34. 44° 0. 4-71 to 5-7 6-7 9 '8 Melting point ... 180° C. 430° C. 265° C. (volatile without fusing.) Vapour density — (air=l) •972 4-32 10-3 Hydrides NH3 PH3 AsHs SbH, Basic or alkaline character Strong. Weak. None. None. There eodst some organic phosphorus, arsenic, and antimony compounds, however, in which compound radicals, such as C3.^ = methyl, C^^ = ethyl, etc., take the place of one atom of hydrogen. With the increase in the molecular weight of these compounds their stability increases; thus: — Triethylphosphine. Triethylarsine. As(C,H5)3 Triethylstibine, Sb(CjHB)3 are stable bodies, and form powerfully basic or alkaline bodies in their respective oxides, such as P(C2Hg)3, (CjHgHO), etc. The groups of dements, 'S{G^^^, phosphoniwm; As(C2H5)^, a/r- sonium; Sb(02H5)^, stibonium,' moreover, closely resemble NH^, ammonium,, in their chemical deportment. LESSON X. Carbon, silicon, and tin constitute another group of elements, in which the metalloidal character is illustrated by carbon, the metallic character being represented by tin. I.— CAEBOlSr. This elementary matter is one of the most important with which we are acquainted. In the free state it is met with in the form of diamond and graphite. It is chiefly found, however, in combination with other elementary matter, such as hydrogen, giving rise to a class of compounds, called hydrocarbons, e.g., paraffin, petroleum, pitch, rosin, etc.; again with oxygen and hydrogen, forming a numerous class of bodies, called carbohydrates, e.g., starch, sugar, etc.; and, lastly, in combination with nitrogen, oxygen, hydrogen, sulphur, and phosphorus, in many organic substances, de- rived from the animal and vegetable kingdoms, in which the carbon forms the essential constituent. In fossilised vege- table organic matter, such as peat, brown coal, pit coal, anthracite, etc., carbon is likewise the principal constituent, varying in amount from 50 to 94 per cent. In the mineral kingdom and in atmospheric air carbon is> found equally abundant as carbon dioxide, COj; either in the free state, as in air, or in combination with bases, as salts, called carbonates, such as limestone, chalk, marble, dolomite, etc. Carbon, in the free state, occurs in various allotropic modi- fications. The three principal varieties are: — (1) Amor- phous carbon, (2) graphite, and (3) diamond. In all of them the carbon is a solid body, which has not been liquefied or vaporised, at the highest temperature even, such as is produced between the poles of a strong galvanic battery. This can only be explained by the hypothesis that the carbon piolecule consists of a number of complex atom groups of 96 ELEMENTARY CHEMISTRY. carbon. No proof is possible, as the molecules of most solid and liquid bodies cannot be determined in the present state of our chemical knowledge. The three modifications of carbon resist chemical action considerably; they burn, however, slowly and difficultly in oxygen, and form carbon dioxide. (1) The purest amorphous carbon* is soot or lampblack, obtained by burning hydrocarbons, such as turpentine, etc., in a limited supply of air, when the hydrogen alone burns, and collecting the soot in large chambers. Gas carbon is a hard, compact, metallic-looking carbon, which forms as a crust in gas retorts. It is a good conductor of electricity, and is used in galvanic batteries and for making electric candles. Coke, charcoal, animal charcoal or bone charcoal, mineral charcoal, found in layers between coal schists, peat, brown coal, and pit coal, are familiar examples of amorphous carbon. Their specific gravity varies with the compactness, e.g., pit coal =1-2 to 1'3; anthracite = 1 "7. (2) Qraphite is sometimes found crystalline; mostly, how- ever, as an amorphous, greyish-black, metallic-lookiag, soft mass, also called plumbago or black-lead. It is largely em- ployed for making lead pencUs. Its specific gravity is 2-25. It is a good conductor of heat and electricity. When pig- iron, rich in carbon, cools, artificial graphite (kish) separates in the form of lustrous hexagonal plates. (3) Diamond is the hardest of known substances, and is highly prized as a gem, on account of its rarity, its great re- fractive power, and its brilliant lustre. Its specific gravity is 3-5. It resists the action of air, but burns when heated in oxygen, 12 parts by weight yielding 44 parts of carbon dioxide. It is a non-conductor of electricity. When heated strongly in the arc of a powerful galvanic battery, it softens a little and swells up, losing at- the_ same time its brilliancy, and changes to a graphitoidal mass, resembling coke, capable of conducting electricity. Exp. 70. — To illustrate the manufacture of wood charcoal, intro- duce some well-dried chips of pine or iir-wood into a short piece of hard glass tube, sealed up at one end before the blowpipe, and blown into a bulb. To prevent the running back of any condensed moisture * The student should, if possible, have samples before him, when ho studies the aUotiopic forms of carbon. CABBOK. 97 and tarry matter, the tube should be bent in the blowpipe flame at a slight angle, and should be fitted with a narrow delivery tube dipping under water, as seen in fig. 38. Apply heat gradually, by means of a rose-burner, as long as any gaseous matter comes off. Collect the gases (so-called wood gas) over water, making use of a pneumatic trough. Apply a light; they burn with a luminous flame, and produce a white light. Examine the residue in the bulb. It consists of wood charcoal. On a manufacturing scale iron retorts are employed, and the water and tar collected. Fig. 38. Exp. 71. — Shate up some offensively smelling water, say from a stagnant pool or farmyard drain, with freshly burnt powdered char- coal. Let it stand over it for about an hour, and then filter through good porous filter paper. In order to pre- pare a filter, fold up a square of paper about 4 in. by 4 in., first into half (fig. 39), and then again into a quarter of its original size, then cut off the comer opposite the centre by running the scissors at an equidistance from it, so as to leave it in the shape of a quadrant of a circle. * Open up the paper, leaving three thicknesses on one side and one on the other, and drop it into a glass funnel, if the funnel is shaped true, i.e., sloping at an angle of 60°, and a little larger than Fig. 39. * Tin plate filter cutters can be purchased, which much facilitate the true cutting out. O 98 ELEMENTARY CHEMISTEY. is required to hold the paper, the paper will fit it all round and adhere all over the glass, when wetted with water. The polluted water will run through clear and bright, and will have lost its offensive- ness. Wood charcoal, and still more so animal or bone charcoal, obtained by burning bones in iron retorts, and breaking up into small granular pieces, possesses the power of decolourising and deodorising coloured and offensively smelling liquids, because these bodies con- dense within their por s gases and vapours. Wood and bone charcoal are therefore extensively used in sugar-works and in making water- filters. Exp. 72. — Collect a little ammonia gas over mercury in a small test-tube. Push up through the mercury a piece of freshly-burnt wood charcoal. The gas is rapidly absorbed, and the mercury fills the tube. One vol. of wood charcoal lias the power of absorbing 90 vols, of NHj, 55 vols, of SHj, or 9 vols, of 0. It gives them up agaia under the receiver of an air-pump, or when heated to 100° C. This property of wood charcoal has been utilised in the construction of respirators. Compounds of Carbon with Hydrog'en. — Carbon is found united with hydrogen in numerous natural compounds, some of which are solid, others liquid or gaseous. The study of these bodies belongs to the domain of organic chemistry, sometimes termed the chemistry of the carbon compounds. We shall confine ourselves to the study of one naturally occurring hydrocarbon, viz., mcursh gas (CH^) ; it is one of the most important of the compounds w^hich carbon forms wdth hydrogen. It is easily obtained in an impure state, mixed with nitrogen and carbon dioxide, by stirring up the mud of stagnant pools in which vegetable matter — leaves, etc. — has undergone gradual decomposition (decay), and may be collected by tilling a bottle with water, inverting it over the water in the pool fastened to a stick, and causing the gas bubbles, as they come to the surface, to enter the bottle. When closed under water with a tight-fitting stopper, the bottle may be removed to the laboratory and examined. A similarly constituted gaseous mixture escapes from the seams of coal in coal mines, and is frequently seen in mining dis- tricts to issue from the ground, and when set on fire to blaze away ajid light up the neighbourhood at night time. Unless removed frpift tjif -workings of coal Diines b^- efficient ven1/U30 s< ^O ^0=^ \0— OH Sulphur dioxide. Sulphur trioxide. Sulphuric acid, 0=:N— 0— 0— 0— N=0 = N— 0— OH Nitrogen pentoxide. Nitric acid. Whichever view may be taken, it is as yet not possible, without accepting two classes of structural formulae — so-called atomic formulae, as well as mere molecular aggregations — to express satisfactorily compounds containing water of crystallisation, double salts of the halogen radicals, etc. But so many relations, bearing upon multiple combination of elementary matter, are rendered clear, that the atomicity theory, dealing only with facts, undoubtedly deserves a place in modern chemistry. * In order to illustrate the views on the qnantivalence of elementary matter, examples of compounds have to be introduced which have not teen studied in the previous Lessons. LESSON XII. OXIDKS OF CARBON. It has been shown (p. 44) that air contains traces of a gaseous body called carbon dioxide or carbonic anhydride (COg), usually to the extent of -OS to '05 per cent. what gives rise to this carbon compound ? Combustion and respiration. Exp. 74. — In order to prove its presence in air,'expose some clear lime water in a shallow glass vessel. A white film of calcium carbonate (COjOa) forms by the com- bination of the carbonic anhydride (COj) with the lime (CaO). Exp. 75. — Place a Httle clear Ume water in a glass cylinder, and burn a wax candle over it for a few minutes. A white precipitate of chalk or calcium carbonate forms, which causes the solution to become milky. All our ordinary fuels produce OOg by their combustion (comp. also Exp. 22). Exp. 76. — Fit up a Faraday's apparatus, as shown in fig. 40. Introduce into each flask some clear solution of lime water, and cause the air to pass through the solution contained in the right-hand side flask, so as to deprive it of its COj, be- fore it enters the lungs, by closing with the forefinger the exit tube of the left-hand side flask. Now open this tube and close the entry tube with the forefinger of the right hand, and exhale so that the breath is deprived of its carbonic anhydride by passing through the lime-water contained in the flask on the left. After a few breathings the lime water becomes milky in both flasks, more so, however, in the last than in the first, and if con- ^"S-*^ S # ^ij l^w Fig. 40. tinned for a few minutes, a considerable amoimt of a white preoipi- 110 ELEMENTARY CHEMISTET. tate is obtained, which clearly shows that the gas coming from our lungs is mnch richer in carbonic anhydride than the air which we inhale. Life is sustained by the oxygen, of the air which we breath, and which oxidises, under the influence of the blood corpuscules, the food with which it is brought in contact. The bodily heat is sustained, and the products of oxidation, viz., water and carbonic anhydride, are thrown off by the lungs. Exp. 77. — If the white precipitate obtained from the last experi- ment be filtered off and dried, it yields a soft white powder, called chalk (COjCa), which is neutral to test paper. Ignite a little of it in a hard glass tube, sealed up at one end — a so-called ignition tube. The CO2 leaves the CaO, and becomes once more gaseous. This can be shown by pouring the gas into a test-tube which contains some clear lime water, when a white film forms on the surface, or by shaking it up with the lime water, when the latter becomes milky. "When cold, moisten the residue in the tube with a drop of water. The mass becomes hot, and reacts strongly alkaline. The carbo- nate was converted into quick-lime, which became slaked when the water was added, and converted into the hydrate. Nearly aU carbonates lose their COj when strongly heated. Exp. 78. — Treat another portion of the chalk powder with a little dilute hydrochloric acid. It effervesces strongly and dissolves, forming a soluble calcium salt, viz., CaClj. When the gas is passed into lime-water, it reproduces with it what the acid destroyed, viz., COsCa. The same may be illustrated also by employing old mortar. When COj is, however, passed somewhat longer through the solu- tion, the white precipitate disappears again, calcium carbonate being soluble in CO^ with formation of a soluble bicarbonate. On heating the solution CO^ escapes, and COjCa is reprecipltated. This illustrates the formation of boiler deposits, most of our natural waters containing lime (and magnesia) salts as bicarbonates. It has thus been shown that carbon dioxide results from regpiration as well as combustion. Plants decompose carbon dioxide under the influence of sunlight, and by the aid of a green body called chlorophyll, which is the active agent in plant life. They assimilate the carbon and give off oxygen. The carbon unites with water and ammonia, and helps to build up that infinitely varying pmnber gf pla^tsf TrWeb ve see a,r9w4 us, TJie acomaula- OXIDES OF CAEBOIT. Ill tion of carbon dioxide, which, as we have already learnt, does not support life, is thus prevented, and the eqmlibriuin between animal and plant life maintained. Exp. 79.— In order to study the properties of this important gas, it is best prepared by the action of an acid upon limestone or marble, according to the eciuation : — ■ COsCa + 2HC1 Calcium carbonate. OaCl^ + CO2 + OHs,. Calcium chloride. The apparatus (figs. 2 and 32) may be employed, and the gas col- lected over water, or by displacement, being more than half as heavy again as air (specific gravity=l'524). Collect several cylinders full of it, and set them aside, ready for use, by closing the mouth with a greased glass plate. Some pretty experiments can be made to illustrate the heaviness (density) of carbon dioxide. Among these are : — (1) Floating soap bubbles, like corks, upon water, on the surface of the gas, in a wide cylinder. Kg. 41. (2) Suspending a light beaker glass from the one arm of an oi'dinary pair of apothecaries' scales (fig. 41), and counter- poising it accurately by means of small Shot, and then in- verting a cylinder containing CO^ gradually over it. The l)e,a^er js veighe4 4own, because tbe COg is- wwh heaviei" 112 ELEMKSTTARY CHEMISTRY. than the air which it displaces. It can, in fact, be poured from, one vessel into another. This may be shown by throwing a strong beam of light on a white screen in such a manner as to illuminate the movements of the gas. (3) Placing a small night-light into a cylinder, filled with air, and pouring the COj from another cylinder into it. The light becomes extinguished as soon as the gas reaches it. If several small wax tapers are fixed at different heights to a wire frame, and the burning tapers lowered into an empty cylinder, and COj quickly poured into it, the lights will be extinguished one after another as the gas falls to the bottom. Two things are illustrated by this experiment, viz., that the carbon dioxide is heavier than air, and that it does not support combustion, being itself the product of combustion of carbon. Exp. 80. — Saturate some distilled water with carbon dioxide, and introduce a strip of blue litmus paper. The paper becomes of a port- wine tint. Contrast it with the red produced upon a strip dipped into very dilute hydrochloric acid. Carbon dioxide shows feebly acid properties. Water dis- solves at 14° C. its own volume of the gas; at 0° 0. it can dissolve 1"79 vols. Under a pressure of 2 atmospheres it dissolves 2 volumes, of 3 atmospheres 3 volumes, and so on. When the pressure is taken off, the gas comes off again and causes effervescence. This explains the nature of effervescing drinks, such as soda-water, champagne, etc. Good spring waters contain carbon dioxide, which imparts to them their refreshing taste. When a tumbler of spring water is brought into a warm room, gas bubbles are seen to collect on the inside of the glass, which simply consist of CO2. The water after a time becomes flat, and loses its re- freshing taste. Carbon dioxide can be condensed under a pressure of 36 atmospheres, and when cooled to 0° C. to a mobile colourless liquid, which is not miscible with water, and which boils at - 78° C. The specific gravity of liquid COj is at - 10° C. = 0'99, at 0° C. = 0'94. It expands, therefore, more than any gas we know, although the co-efficient of expansion of liquid bodies is usually smaller than that of gaseous bodies. The OXIDES OF CARBON. 113 same has been observed in tbe case of other gaseous substances ■which are converted into liquids by pressure. Above 30 '9° C. carbon dioxide may be compressed into a smaller bulk than that which liquid COj would occupy, but cannot be condensed into a liquid, no matter what pressure be put upon it. All other coercible gases show, in like manner, a so-called critical point of temperature, at which they can no longer be condensed to a liquid by pressure alone, but only by pressure and cold. When the pressure is taken off from liquid carbon dioxide, a portion evaporates so fast, that it deprives the rest of so much heat, as to cause it to freeze and to turn it into a snowy white mass. Its tem- perature sinks then to - 79° C. When solid it is a bad con- ductor of heat, and evaporates only slowly. It may be held in the hand, nay, even placed on the tongue, as it is always surrounded by a layer of gas, and. is never brought into actual contact with the skin. When compressed, however, into a compact mass, it causes very painful blisters. Ether mixed with solid COj, lowers the temperature of the latter rapidly to -110° C. Its volume composition is best shown by burning a given weight of diamond or graphite in oxygen, and weighing the COj gas, or by burning carbon in a given volume of oxygen. The gas volume, after cooling, remains the same : — C -(- 0, = CO, 2 vols. 2 vols. The density is, therefore, ^ — ■, or 22 criths (H = 1), or 1 '524 (air = 1). Its molecular weight is 44. Exp. 81. — Pass carbon dioxide (comp. fig. 21) over dry pieces of charcoal, packed pretty tightly in an iron tube (or combustion tube), and heated to redness in a furnace. Collect the gas which comes off over water, containing some solution of caustic soda, in order to absorb any COj left undecomposed. The charcoal burns at the ex- pense of half the oxygen of the COj, and forms CO or carbon mon- oxide. The gas volume becomes doubled. CO, H- C = 2C0 2 vols. 4 vols. Apply a light and the carbon monoxide bursts into flame, burning with a feebly luminous blue flame where it is in contact wili air or oxygen. S 114 ELEMENTARY CHEJIISTRY. It resembles in this respect hydrogen. A mixture of CO and air or oxygen combine with a loud explosion, when fired. It is, like hydrogen, a non-supporter of combustion; a lighted taper introduced into the gas is extinguished. It acts as a poison, when inhaled, even in small quantities. Carbon monoxide results, wherever combustion of carbonaceous matter goes on with an insufficient supply of air or oxygen. Exp. 82. — In oxalic acid, whioli consists of carbon monoxide and dioxide, as well as water, we possess a convenient store of the gas. When the crystals of oxalic acid are gently heated with about ten times their weight of oil of vitriol, they are deprived of water, and the molecules of CO3 and CO set free as gas. The COj can be sepa- rated from the CO by absorption with a solution of sodic hydrate. The apparatus illustrated in fig. 22 may be employed, and the CO, which is almost insoluble in water, collected in the usual manner over water. The reaction mlay be expressed thus: — C2O4H2 = CO2 -I- CO -t- OHj. Exp. 83. — ^Pure carbon monoxide may also be prepared by heating well-dried potassium ferrocyanide (yellow prnssiate) with about 9 Sarts by weight of concentrated sulphuric acid. The generating ask should be provided with a wide delivery tube and the flame lowered, when the reaction is started, as the gas comes off rather violently. Collect as usual over water. Pour lime water into a cylinder filled with the gas, and shake up. Ko milkiness or precipi- tate is produced. Next inflame the gas, and shake up again, and a white precipitate is speedily produced, showing that carbon dioxide is now present. Carbon monoxide * is a colourless inodorous gas. Its density is 14 (H = 1) or -967 (air = 1) ; its molecular weight is 28. It is almost insoluble in water, but can be absorbed by an ammoniacal solution of cuprous chloride (CujCl^). It is a constituent of coal gas. In blast furnaces it performs important functions, by acting as the principal reducing agent upon metallic oxides, e.g. : — Fefis + SCO = Fca -f 3C0j, and by its producing, next to hydrogen, the greatest amount of heat on combining with a second atom of oxygen. * As the term carbonic oxide appears to be misleading, the ending io being usually employed to designate higher, the ending ous lower oxides, etc., it is preferable to adopt the denominations mon- and di-oxide. LESSON XIII. OZONE, HYDKOXYL, AND HYDROSULPHYL. Exp. 84. — When oxygen or air is left in a good-sized flask for about two hours in contact with some pieces of freshly-out phosphorus, which are kept half immersed in water, it acquires a peculiar odour, and its chemical activity is increased. This is shown by its readily turning moist iodised starch paper blue. The same is observed when oxygen is passed over moist pieces of phosphorus in a glass tube. It had also been observed that vivid lightning during a thunder-storm, or the discharge of electric sparks from an ordinary frictional electric machine, or a Ruhmkorff coil, or better still from a powerful induction apparatus, produced a most penetrating chlorous odour, which Schoenbein, in 1840, pointed out as an allotropic modification of oxygen, analogous to the allotropic forms which sulphur, etc., acquires under favourable conditions. It was called ozone, from o|) Not isolated, but CI2O4, a y^h^il I neutral body, is known, CIO3H Chloric acid, /ni n ^ C which equals half of CIO4H Perchloric acid. (CIA)) (CIA+CIA)- ♦ The atomicity of the difieient metals will be found in an Appendix. OXYGEN COMPOUNDS OF METALLOIDS. 127 Anhydrides. . Acids. The anhydrides have not ^^^ Hypobromous acid, been isolated. ^''^^g Bromio acid. BrOiH Perbronuo acid. I2O5 Iodic anhydride, IO3H Iodic acid, (IjO^) . . . .Not isolated. IO4H Periodic g,cid. II. SULPHUB GeOUP. SO3 Sulphur dioxide, or sul- SO3H2 Sulphurous acid. phurous anhydride. SO3 Sulphur trioxide, or sul- SO4H2 Sulphuric acid. phuric anhydride. III. NlTBOGEN GeOUP. N2O3 Nitrogen trioxide, or NOjH Nitrous acid. nitrous anhydride. NjOj Nitrogen pentoxide, or NO3H Nitric acid. nitric anhydride. IV. Caebon Geoup. COj Oarbon dioxide, or car- COjHj Carbonic acid. bonio anliydride. v. BoEON Geoup. B2O3 Boric trioxide, or boric BOjH Metaborio acid. anhydride. 'The acids of the halogens 01, Br, I, as well as the nitrogen acids, contain only one hydrogen atom, which can be replaced by metals; they are therefore monobasic acids. Assuming that O is always a dyad, and 01 a monad, their formulse can be expressed by connecting their atoms in chain form; thus: — Anhydrides. Acids. CI— 0— CI CI— (0— H) \ ^ ' « ^ J Hypochlorous anhydride. Hypochlorous acid. CI— 0—0— 0— CI CI— 0— (0— H) V ) V V Chlorous anhydride. Chlorous acid. CI— 0— 0— (0— H) V J Chloric acid. CI— 0— 0— 0— (0— H) t ^ ' Perchloric acid. 128 ELEMENTARY CHEMISTRY. If we view the H as present in the form of hydroxyl (OH), we get the acid radicals (GWy, (Cl'"02)', (CrO,)'. In the anhydrides, we have two of these compound radicals linked together by an oxygen atom, and when this atomic group is acted upon by water, they break up thus : — OClXn ^ r>/H CIO(OH) „^ 2C10(0H) Chlorous acid. The salts of these acid radicals could also be obtained by the direct action of the hydi-oxyl group, and then displacing the hydrogen by an equivalent quantity of a metal; e.g.: — CIA + Oi,Hj = 2(C10jOH). Trom considerations derived from a comparison of the compounds of the halogens with hydrogen and with oxygen, we must assign to CI, Br, I a variable atomicity, in fact, varying from 1 to 3, 5 and 7. It is known that their afiBnity for hydrogen gives rise to compounds in which the chemical activity diminishes with the increased atomic weight, from fluorine (19) to iodiae (127); whilst that of their oxygen compounds increases. The oxygen compounds which iodine forms are the most stable, those of Br and CI proportionally less stable. We also know that in the hydrogen compounds chlorine displaces both bromiae and iodine, and that bromine displaces iodine, whilst in the case of the oxygen compounds of these elements, iodine displaces bromine or chlorine. The stability of the oxygen compounds increases also with the increase in the number of atoms of oxygen contained therein. Chlorates, bromates, and iodates, and more so even perchlorates, perbromates, and periodates, constitute most energetic and stable compounds, quite different in their behaviour from hypochlorites or chlorites, etc. When the chain form of atomic grouping is abandoned for the varying atomicity gi-ouping, these facts are explained in a natural manner. We write the CI", CI"", Cr, and CI™ compounds as follows : — CI"— (OH), C1""0(0H), C^OjCOH), andCl^-OalOH) d"— 0— H, 0=01"""— 0—H, 0=3 01"— 0—H, = Cl™-0-H, and, in like manner, the bromiae and iodine compounds. OXYGEN COMPOUNDS OF CHLOKINK. 129 OXYGEN COMPOUNDS OF CHLORINE. Exp. 90, — Pass a current of cUorine gas through a hot concentrated solution of potassium hydroxide (KOH). The following reaction takes place : — 6K0H + 3CL = 5KC1 + CIO3K + 30H.. Potassium Potassium chloride. chlorate. The two salts are unequally soluble in cold water. The chlorate is difficultly soluble, and crystallises out from the hot solution in lustrous plates. A cheaper method consists in substituting milk of lime, Ca(0H)2, for the potassium hydrate. The reaction takes place in two stages: — (ClOaljCa + eOHj Calcium chlorate. which calcium chlorate is decomposed by potassium chloride (KOI) into potassium chlorate and calcium chloride; thus: — (0103)aCa + 2K;C1 = 2CIO3K + iCaCl,. The latter is also so much more soluble in OHj, that the potassium chlorate separates out all but pure. One or two recrystallisations from distilled water will render it free from traces of chloride. Potassium chlorate is very largely employed in the arts, e.g,, for preparing a dipping mixture for lucifer matches (which consists usually of antimony trisulphide (SbgSg) and potassium chlorate), which causes them to explode, when struck against a coating of red or amorphous phosphorus. Exp. 91. — Heat some potassium chlorate, to about 330° C, in a small retort. It yields at first a part of its oxygen only, according to the equation — 2C10,K = CIO4K + KCl + Oj. Potassium Potassium chlorate. perchlorate. There is a stage when the saline mass fuses quietly. On further heating, it evolves the whole of its oxygen, and leaves only potassium chloride. I 130 ELEMENTARY CHEMISTRY. It is this property of parting readily vnth oxygen which renders potassium chlorate a valuable and useful salt in the laboratory. It constitutes a ready oxidising agent on account of its relative instability, as well as of the instability, amount- ing to explosiveness, of the lower oxides of chlorine, especially , of the chlorine tetroxide. Cl.Os + Cl,05 = 201,04. Exp. 92. — Generate this gas in stout glass cylinders, in which a small quantity of oil of vitriol is placed, by dropping a few pinches of well-dried and finely-powdered potassium chlorate into the acid. A heavy yellowish-green gas, having the composition of CljO^, comes off with a crackling noise, lifting out the lighter air from the cylinder, which may be kept loosely covered with a piece of card-board. When the gas is seen to have filled the cylinder completely, a red- hot iron wire may be introduced. The gas is decomposed at once," usually with a sharp explosion. Exp. 93. — The same may be shown by placing at the bottom of a deep test-glass (best in the form of a deep champagne glass), a small piece of yellow phosphorus, covered with water, and dropping a few large crystals of potassium chlorate upon the phosphorus. By the aid of a funnel tube drawn out to a narrow point, a little oil of vitriol is then poured down directly upon the crystals, without mixing with the water. Chloric tetroxide, or chloric peroxide, is liberated, which on coming in contact with the phosphorus is decomposed, and the phosphorus bums ■ndth flashes of light. The experiment described in Lesson IV. (Exp. 24), of deflagrating a mixture of sugar and potassium chlo- rate by means of a drop of oil of vitriol, might also be repeated, to illustrate the oxidising action of potassium chlorate. Exp. 94. — The lowest oxide of chlorine, CljO, hypochlorous anhydride, is obtained when dry chlorine gas is passed over freshly precipitated dried mercuric oxide in the cold, according to the equation — HgO -f SCQj = HgCl, -t- OCI2, and can be collected by condensing in a narrow U-tube immersed in a freezing mixture. It constitutes a very unstable liquid, which decomposes in a very short time jntp pljlorwe and oxjrgen, 'Wfttey form^ OXYGEN COMPOUNDS OF CHLOEINE, 131 ■with it hypoclilorous acid CI(OH). It is a more powerful oxidising and bleaching agent than chlorine itself, as wiU be seen from the following equations : — CI2 + OH2 = 2HC1 + 0, but 2C1(0H) = 2HC1 + 20. It is usually met -with in the form of sodic hypochlorite (ClONa), which is sold under the name of Eau de Javelle, and is used as a disinfectant. LESSON XVI. OXYGEN COMPOUNDS OF NITEOGEN. When organic nitrogenous bodies undergo decomposition, they give rise, as we have seen in Lesson IX., to ammonia compounds, which are oxidised into nitrous and nitric acid, ammonium nitrite, and nitrate. The air contains nitric acid, or some lower oxides of nitrogen, the formation of which, to a great extent, is due to electrical discharges in the air, and in all probability likewise to the action of ozone upon atmo- spheric ammonia. Exp. 96. — Pass electric sparks briskly through moist air, contained in a tri-tubulated glass globe (fig. 42), in which the air can be put under pressure by connecting the open tube 5;/^ of the vessel with a force- pump. As soon as the sparks have passed for a few minutes, red fumes ap- pear in the globe, and blue litmus paper is turned red, showing that an acid body is produced, viz., nitric Kg. 42. acid. Eain water, especially the first few drops which fall during a thunder-storm, contains nitric and nitrous acids, as is shown by good test paper. The quantity producible by the electric spark is, however, only very small. It is from a natural product, viz., nitre, or Chili saltpetre, that nitric acid is usually extracted. Exp. 96. — Heat gently in a retort (fig. 43) potassium nitrate or saltpetre, together with sufficient sulphuric acid to cover the salt, and to fill the retort about one-third full. No crystals ought to be left hanging about the retort neck. Euddy fumes come off, which condense and can be collected in a receiving flask, kept cool by partial immersion in a basin of cold water, and by covering it with a wet cloth. OXYGEN COMPOUNDS OF NITROGEN. 133 The liquid iu the receiving flask turns blue litmus intensely red. It consists of nitric acid, coloured somewhat yellowish- brown by the fumes of the lower nitrogen oxide (N2OJ, which dissolves in it. Strong nitric acid suffers, even at a mode- rate temperature, a de- composition into OHj, N2O4) and 0. Excess of sulphuric acid should, therefore, be employed, so as to drive off the acid at a lower tempera- ture, and to leave the acid salt (SO^KH) be- hind, because the deoom- Kg. 43. position of the nitre into S0^K2 cannot be effected entirely in a glass retort, except by employing a high temperature. Equation I. expresses the proportions employed for a labo- ratory experiment; Equation II., the proportions employed by the manufacturer, who uses large iron vessels, and earthen- ware condensers, and sodium nitrate, or Chili saltpetre, because the latter is cheaper. An acid containing ruddy fumes, answering equally well for most of his purposes : — Equation I. NO3K + SO4H2 = SO4HK + NO3H Equation II. 2N03Na + SO4H2 = SOiNajj + 2NO3H. Pure nitric acid is miscible with water in any proportions. The ordinary concentrated acid of commerce, of specific gravity r42, contains about 68 per cent, of NO3H, and dis- tils at 120°'5. Fuming nitric acid, of specific gravity 1'52, is rarely required by the beginner. Nitric acid parts with its oxygen the more readily the more concentrated it is. It contains upwards of three-fourths of its weight of oxygen, and is, therefore, a strong oxidising agent. It is principally used to dissolve metals, which do not dissolve, or only slightly, in hydrochloric acid : such, e.g., as silver, mercury, lead, bismuth, or copper, and forms with these metals salts called nitrates, readily soluble in water. 134 ELEMENTAKT CHEMISTRY. A portion, of the acid is invariably decomposed into lower oxides of nitrogen, accompanied by a copious evolution of ruddy fumes. This means that they are first oxidised before they can be converted into their respective salts. It is also largely used to oxidise non-metaUie bodies, such as P, S, I, etc. To illustrate this oxidising action of nitric • acid, the students should perform the following experiments : — Exp. 97. — ^Prepare a mixture of powdered charcoal (15 parts by weight), and potassium nitrate (75 parts), and set fire to it. It bums with violent deflagration. The product o£ the oxidation is carbonic anhydride. Exp. 98. — Put some copper filings into a test-tube, and add a few drops, at a time, of concentrated nitric acid, as long as ruddy fumes come off. The copper is dissolved to a blue liquid, turning azure blue when ammonia is added in excess. It has, in fact, been con- verted into a copper nitrate NjOgCu", or (N03)jCu". Similar reac- tions are produced when tin filings are employed. The tin is left behind as a white powder (SnOj). These two metals are usually employed when we have to test for nitric acid. Exp. ^9. — Add concentrated nitric acid to real gold-leaf. No chemical action takes place. Shake up in another test-tube a few leaves with concentrated hydrochloric acid. It is likewise without action. Now add the contents of the two test-tubes together and apply a gentle heat, the gold leaves dissolve readily. Platinum foil acts in like manner, as also the spongy platinum. This proves that both metals, when ia the pure or unalloyed state, are not attacked chemically by either of these acids, but dissolve readily when acted upon by a mix- ture of the two — best in the proportion of 1 vol. of NO3H and 3 vols, of concentrated HCl — called aqua regia. Both acids are broken up, the hydrogen of the HCl and the oxygen of the NOgHO combining to form water, and the acid rem- nants, NO2 and CI, form new compounds, viz., NOjCl and NOCl, which act like chlorine itself, and form the chlorides of the metals, viz., AuClg and PtCl^. We repeatedly had occasion to remark on the oxidising action of nitric acid being accompanied by the evolution of ruddy fumes. These fumes consist for the most part of a OXYGEN COMPOUNDS OF NITROGEN. 135 mixture of the lower oxides of nitrogen of N^0^, NgOg, N2O2, and NgO, according to the concentration of the acid, the nature of the metallic bodies, the temperature and violence of the chemical reaction, and the presence of metallic nitrates, as Ackworth and Armstrong have recently shown. It is not within the limits of this little work to go fully into these interesting changes at this elementary stage, espe- cially as they could not be traced properly without a know- ledge of gas analysis. The following experiments should, however, be performed if possible by the students themselves : — Exp. 100. — Put a, little finely -powdered dried lead nitrate into a, bulb-tube, blown out of a piece of narrow combustion tubing before the blowpipe* flame. Then clean the neck of the tube carefully and draw it out, about 2 or 3 inches from the bulb, in two places; next bend it in a small bat's-wing flame, so as to obtain a tJ-tube, joined without a cork or india-rubber connection to the bulb-tube * A cheap and serviceable blowpipe may be constructed as follows : — Take a piece of glass tubing, about a quarter of an inch in bore, which fits readjly into the tube of a Bunsen burner, and bend it at right angles as in flg. 44. Next procure a good size cork and perforate it vertically along its axis, and also half way through at right angles, so that the two perforations meet. Now insert, a piece of glass tubing, about a quarter of an inch diameter, and 3 to 4 inches long, into the axial per- foration, so as to reach not quite half way through the cork. Then draw out another piece of the same bore glass tubing, after flrst heating in a bat's-wing burner, so as to taper off very gradually. Cut it off and insert it into the perforation from the opposite open end of the cork, BO as to cause the end with the fine jet nearly to reach to the mouth of the above short glass tube or 'gas exit. Attach to the wide end of the glass tube so drawn out an india- rubber tube, ending in a bone mouth-piece, through which the air if a a required to form a blowpipe flame *^'S- **■ can be blown. Insert the short bend of the right-angle tube into the side opening in the cork, the long end being fixed in the Bunsen burner, and the gas can be conveyed into the inside of the cork to circulate round the inner tube and pass out, together with the air blown in, in the form of a regular blowpipe jet, as well-defined as could be desired. 136 ELEMENTAET CHEMISTRY. ■which serves as the retort, as seen in fig. 45. When heat is applied the lead nitrate usually decrepitates, and small pieces may even be carried into the drawn-out portion of the receiving vessel, and pre- vent the gases (0 and NjOj from escaping freely, or block up their escape altogether, when, of course, the bulb-tube containing the Fig. 45. fused salt would inevitably burst. The tT-tube must be placed into a freezing mixture of ice and salt, when the greater part of the N2O4 gas would be condensed, the oxygen may be tested with a glowing cedar splint, and escapes into the air. The decomposition takes place according to the equation : — (N03),Pb" Lead nitrate. PbO Lead oxide. Nitrogen tetroxide. + Oxygen, Nitrogen tetroxide, or as it was erroneously called, hypo- nitric acid, exists only at a low temperature, and Buffers OXYGEN COMPOUNDS OP NITROGEN. 137 gradual decomposition, on -warming, into the simpler molecule, NO2, ■which, on cooling in a freezing mixture, forms once more N^O^. It is, in fact, an interesting case of dissociation at low temperatures. The body is solid at - 26° C, and forms then a colourless crystalline mass, which melts at — 13° to a colourless liquid. At 0° C. it acquires a yellowish colour owing to beginning dissociation, and this increases in inten- sity till at 26° C. the body boils, and is converted into a yellowish-brown vapour, which darkens in colour as the tem- perature rises to 150° C, when the dissociation is complete, and when the vapour density is 23. The theoretical molecular weight of NjO^ being = 92, the volume weight, or the vapour density, ought to be ^ = 46. Hence NjO^ has been disso- . ciated into two simpler molecules having a vapour density of 23. A small quantity of cold water decomposes nitrogen tetroxide into nitrous anhydride and nitric acid, according to the equation : — 2Nj04 + OH2 = NjOj + 2N0.,H- Nitrous anhydride With more water, or with strong bases such as potassic hydrate, it forms nitrous and nitric acid, or the respective salts; thus: — 1. N2O4 + 2K0H = NO3K + NOjK -t- OH2. Or, (NTO2 2. .^ O + 2K0H = N'Os(OK) -1- N'"0(OK) + OH^ Nitrogen Potassium Potassium Potassium tetroxide. hydrate. nitrate. nitrite. In the second equation we may view the liquid te- troxide as a mixed anhydride, of nitric and nitrous an- hydride : — 2N2O4 = N2O5 + Nfis analogues of chloric tetroxide. 2CI2O4 = CI2O5 + ClaOj oomp. p. 126. 138 ELEMENTARTf CHEMISTRTf. Warm water decomposes it into nitric acid and nitric oxide j thus: — SS^Oi + 20H2 = 4NO3H + NjOj- Nitrous acid (NOjH) does not exist in the free state. Its best known salt, potassium nitrite, is prepared by acting upon fused nitre with lead or copper filings. The metals are easily oxidised. By treating the mass with water, and filtering off the insoluble oxides, potassium nitrite (NO2K) can be prepared, from which the acid is liberated on the addition of sulphuric acid — ^the reddish-brown fumes which come off, consistrag of NjOj (nitrous anhydride), and its products of decomposition, NOg and NO. Exp. 101. — Similarly coloured fumes are obtained when strong nitric acid is made to act upon arsenious anhydride (trioxide or white arsenic, AsjOj), or starch, and can be condensed on cooling in a freezing mixture to a greenish liquid^ which appears to consist of UjOj and NjOj. When this liquid is gently heated, it gives off fumes which, on cooling in a freezing mixture, condense to a blue liquid, and consist principally of the trioxide or nitrous anhydride It may suffice to collect some of this gas by displacement in order to study (1) its oxidising action, by causing it to act upon a strip of unsized filter paper dipped into potassium iodide (KI), and starch paste. Iodine is liberated, which immediately combines with the starch, forming with it a characteristic blue compound of iodide of starch; thus : — 2KI + N2O3 = K,0 + N^Oj + Ij. The least traces of NjOg can thus be detected, and reversely, traces of an iodide. Another pretty illustration of the oxidising action of NjOj consists in treating a weak solution of magenta (a gorgeous red colouring matter), or of indigo dissolved in oil of vitriol, with NgOg, when the colours disappear, the oxide being reduced to a lower oxide (N2O and 'N2^2)- To illustrate (2) its reducing action, we may employ a weak and slightly acidulated solution of potassium perman- ganate, which exhibits a beautiful pink tint. As soon as the coloured solution is shaken up in a cylinder containing OXYGEN Compounds op nitrogen. 139 N3O3 it loses its colour, and the oxygen from the potassium permanganate passes over to the .NgOg, and converts the latter into the highest oxide, viz., N^Oj.* The same effect is produced when a solution of potassium nitrite is added to a weak solution of potassium perman- ganate, and the NgOg liberated by dilute sulphuric or acetic acid. Exp. 102. — Treat some copper filings or turnings in a Woolfe's bottle (fig. 2) with, nitric acid, diluted with about half its bulk of water. A gas is evolved, which is indicated by the formation of ruddy fumes. After a few minutes' action, the gas within the bottle becomes quite colourless. This is a sign that the air has been dis- placed by a gas which, on issuing into the air, turns again reddish- brown. The gas is collected as usual over a pneumatic trough, containing, however, wann water, rendered slightly alkaline by means of a few drops of sodio hydrate. A perfectly colourless gas is then obtained. Several cylinders are filled, and when closed under water by means of a greased glass plate and removed, can be examined at leisure. When some folds of blue litmus paper are introduced into a cylinder full of the gas, and the glass plate rapidly replaced, we Ibbserve that, on first removing the plate, and thus admitting air, ruddy fumes immediately form, which turn the blue litmus paper in the upper part of the cylinder red, whilst the paper in the lower part remains blue in the colourless portion of the gas. This experiment proves that the colourless gaseous body obtained by the action of nitric acid upon copper is not an acid body, but that by contact with the air it is converted into an acid gas, as is shown by its action upon blue litmus. None of the three oxides of nitrogen hitherto studied gave these reactions. Hence this oxide can only be one of the remaining two oxides of nitrogen, viz., it must be either NgOj or NgO. Quantitative determinations have shown that it is composed of two atoms of nitrogen and two atoms of oxygen, and must therefore be called nitrogen dioxide (NjOj), or nitric oxide, the lowest oxide (NjO) being called nitrous oxide. * The reaction is expressed by the ec[Uations: — MnjOsKj = 2MnO + KoO + SO available for oxidation. Potassiimi permanganate. SNjOa + 100 = SN3O5. 140 ELEMENTARY CHEMISTRY. The action of nitric acid upon copper is expressed by the following equation : — 3Cu + 8NO3H = 3(N03)jCu" + NjOj + 4OH2 Copper Nitric Nitrate. oxide, < and the deoxidation of the nitric acid molecule which we have traced from NjOg to NjO^, and to NjOg, is in this reaction arrested when "^fi^ ^^ reached. It is, however, never so well-defined and clear a change as this equation would imply, for the nitric oxide contains frequently so much nitrous oxide, that a taper burns in it brilliantly, whilst a burning taper is extinguished immediately in nitric oxide gas. An analogous change takes place when lead or mercury are acted upon by nitric acid. They are converted into nitrates according to the equations: — 3Pb + 8NO3H = 3(N03),Pb" _ + N,0, + 40Hj 3Hg + 8NO3H = 3(N03),Hg" ' + N,0, + 40Hj The remarkable affinity of NjOj for oxygen, enables us to convey oxygen (from air) to bodies which, without its inter- vention, would not combine with oxygen. It acts as a carrier of oxygen. The first combines with it to form the higher oxides (NjOg and NgO^, and yields it again to bodies which are eager to take it up. Thus in the manufacture of oil of vitriol, we can readily burn sulphur to sulphur dioxide, or sulphurous anhydride, but it requires a carrier of oxygen, like nitric oxide, to cause a third atom of oxygen to combine with the SOj and convert it into SO3. Exp. 103. — To illustrate this to a class, invert a cylinder full o£ colourless N jOa over water,, remove the glass plate, and blow some air or oxygen into it. Deep ruddy fumes are seen to form instan- taneously. On next introducing some sulphur dioxide gas, the ruddy fumes disappear. The changes may be expressed as follows : — N,0, + = N,03 SO, -1- K.O, = SO3 -t- N,0„ and 2S0j -t- Ns04 = 2SO3 + N,0,. OXYGEN COMPOUNDS OF NITEOGEN. 141 Exp. 104. — Into another cylinder full of N^O, introduce a burning taper ; it is immediately extinguished. This shows that nitric oxide does not support combustion. The same happens if feebly burning sulphur or phosphorus is plunged into the gas. A glowing piece of charcoal dies likewise away in it. Intensely burning phosphorus, however, decomposes NaOj, and burns in it almost as brilliantly as in oxygen itself. The cause for its burning less brilliantly is evidently the presence of the inert nitrogen, which fixes much of the heat produced by the combination of the phosphorus with the oxygen. It acts, in fact, as a heat diluent. Temperature (as well as pressure) influences the amount of light given off by burning bodies. Exp. lOB. — Introduce a few drops of carbon disulphide into another cylinder fuU of nitric oxide, and give it time to diffuse and become well mixed with the gas. On applying a light the CSj burns in the NjO,, with a quiet luminous flame, the rays of which exert a chemical action similar to the actinic rays of sunlight. It is used for photo- graphing in dark places or at night. The molecular composition of nitric oxide is NgOj = 60; its volume weight is = 15, or 1 litre of the gas weighs 15 criths, i.e., 15 X -0896 = 1 "344 grm., and the gas shows the same anomalous molecular composition as N^O^. It is little soluble in water, but is readily absorbed by an aqueous solu- tion of ferrous sulphate, and is given off again on warming the solution. Metallic sodium decomposes it into Ng and O2. There remains one more oxide of nitrogen, viz., nitrous oxide (NjO), which is best prepared by heating ammonium nitrate, a salt prepared by neutralising a solution of ammonia, or ammonium carbonate, with dilute nitric acid. The solu- tion is next evaporated in a porcelain dish over a rose-bumer, and the crystals fused gently, and then poured out on an iron plate, allowed to cool, and reduced in a mortar to a coarse powder. Exp. 106. — Heat some of the powder in a Florence flask or small retort (fig. 14). The salt melts, boUs, and gradually breaks up into nitrous oxide (or laughing gas), and steam, and is collected over water. The decomposition takes place according to the equa- tion : — NO3NH4 = N,0 + ■ 2OH2 Ammonium Laughing Water, nitrate, gas. 142 ELEMENTARY CHEMISTET. Nitrous oxide is a colourless gas, •with a sweetish, taste. Its molecular weight is 44, and its volume weight 22. One litre of the gas weighs 22 criths, or 22 x 0896 = 1-9712 grm. Nitrous oxide is not acted upon by air or oxygen. It sup- ports combustion almost as vividly as oxygen itself. A glowing splinter of wood bursts into flame when plunged into nitrous oxide; phosphorus burns with a luminous flame; feebly burning sulphur introduced by means of a deflagrat- ing spoon is put out, because it produces little heat, but when it once bums briskly it will go on burning with increased brilliancy, almost as if placed in oxygen itself, with a pale, rose-coloured flame. It is without action upon N^Oj, no ' ruddy fumes are formed, and no contraction in volume takes place; not so when oxygen is mixed with the latter gas. Hence we can readily distinguish nitrous oxide from oxygen. When nitrous oxide gas and hydrogen are mixed in equal volumes and exploded, they form Nj and OHj ; the explo- sion is, however, less violent than that of H and 0. When passed through a red-hot tube, NO breaks up into nitrogen and oxygen. When the pure gas is inhaled it produces a kind of exhilarating intoxication, which is sometimes accom- panied by immodetate laughter. Hence its name laughmg gas. It has been found to act as an ammsthetic or agent for suspending the mental and sensorial functions during dental and surgical operations. Ammonium nitrite heated in like manner yields nitrogen and water, according to the equation : — NOjNH^ = N, + 2OH2. Instead of ammonium nitrite, which is difficult to prepare, we may use a mixture of ammonium chloride and potassium nitrite, when the following reaction tdkes place : — NH4CI + NOjK - ECl + Nj -h 20H,. By substituting potassium nitrate, we obtain in like manner nitrous oxide gas; thus: — JIH4C1 t i^OjK ^ p:cj t N?0 + gOH,, LESSON XVII. OXYGEN COMPOUNDS OP SULPHtTE, In Lesson VIII., Exp. 59, it has been shown that the results of the combustion of sulphuretted hydrogen gas in air, are ■water and sulphur dioxide; thus: — SH2 + 03 = OH3 + SO2, Sulphur dioxide resulted also from the combustion of sul- phur, or metallic sulphides, in air : — S + O2 = sdi,. In either of these cases, sulphur dioxide is always mixed with nitrogen. To prepare pure sulphur dioxide, the sul- phur must be burnt in oxygen. It is found most convenient, however, to deprive sulphuric acid of part of its oxygen, by such deoxidising agents as carbon, or of metals which do not act upon the water in the sulphuric acid molecule, but upon the SO3, and are capable to break up the latter into SO^, which escapes, and 0, which goes to the metal forming an oxide, which is immediately dissolved in the excess of sul- phuric acid with formation of a metallic sulphate. Exp. 107. — Introduce about half an ounce of copper clippings or turnings into a flask provided with a funnel tube and delivery tube, as seen in fig. 46. Add some concentrated sulphuric acid sufficient to well cover the copper turnings, and apply a gentle heat. A copious evolution of a gas takes place, which is first passed through a Woolfe's bottle containing water to arrest any sulphuric acid'fumes which may be carried over, and then through a second bottle containing dis- tUled water, in which sulphur dioxide is soluble. The solution in the first bottle supplies us with impure sulphurous acid. When the gas is no longer absorbed by the two bottles, it may be passed through the left-hand delivery tube, on opening the screw clamp, into a solution of caustic soda, contained in a cylinder, in which it is freely g,bsofbed, " ' " . - . • lU ELEMENTARY CHEMISTRY. The saturated solution of sulphurous acid is kept in a; ■well- stoppered bottle for further use. It reddens blue litmus paper, and is recognised by its pungent smell and bleaching action. Fig. 46. The reaction takes place according to the equation : — Cu + 2S04Ha - SO.Cu" .+ SO, + 20H- Copper sulphate. Sulphur dioxide. When SOg is prepared by heating in a Florence flask coar.se pieces of charcoal with oil of vitriol, carbon dioxide, as well as sulphur dioxide, are generated, which can be separated with diflS.culty only; thus : — 2SO4HJ + C =1 2S6a + CO2 + OH,. Another method of preparing SOj, viz., by the action of sulphuric acid iipon small lumps of sulphur, yields pure gas, if the temperature is not raised too high so as to volatUise the sulphur. OXYGEN COMPOUNDS OP SULPHUR. ■ 143 In the place of metallic copper, in. Exp. 107, -we might have employed several other metals, such as silver, mercury, etc., which, like copper, do not decompose water. Exp. 108. — Collect by displacement or over mercury, some sulphur dioxide or sulphurous anhydride iii a glass jar. Introduce a bunch of roses, and stopper up the jar. The flowers become bleached, but the colours are not destroyed; for on adding a dilute alkali (ammonia), or very dilute sulphuric acid, they are restored. A solution of the gas in water may also be added to an infusion of rose leaves, or other vegetable colouring matter, such as an infusion of logwood, or red Exp. 109. — Add a little freshly prepared solution of sulphurous acid to a solution of potassium permanganate. The gorgeous pink tint of the latter is discharged, and cannot be restored by acids nor alkalies. The change is due to oxidation. The permanganate, being the oxidising agent, converts the SOj into SOg, whUst in the case of vegetable colouring matters, the sulphurous acid appears to form colourless compounds with them. Stains of fruit, port, or claret, e.g., can be removed from linen by treat- ment with SOy The bleaching of sulphurous anhydride is thus markedly distinct from that of chlorine, and is resorted to when the latter acts injuriously, as in the case of woollen materials, of silk, straw, sponge, isinglass, etc. Sulphurous acid is a powerful disinfectant, for the reason shown in Exp. 60. An alcoholic solution of SOj is employed with advantage in sick-rooms, and is one of the most power- ful disinfectants. Sulphurous acid arrests also fermentation in beer, wine, cider, etc., and its lime salt is now generally employed by brewers to arrest the after fermentation of beer, and to prevent its turning sour. Sulphur dioxide is a colourless gas of suffocating odour. Its density is 32 (H = l) Its molecular weight = 64. It condenses readily (- 15° C., or at the ordinary temperature under 2 atmospheres pressure) to a colourless liquid of specific gravity 1'49, which solidifies at - 76'' 0. Liquid sulphurous anhydride absorbs much heat when it evaporates, and is therefore used for liquefying other gaseous bodies, and for solidifying liquids. Water, e.g., can be made to freeze by immersing a test-tube into it containing water. Water absorbs abou.t 50 volumes of sulphur dioxide, and gives it up K 146 ELEMENTAKY CHEMISTRY. again when it is heated. The solution shows all the pro- perties of the gas. It reddens litmus, or is gradually converted into sulphuric acid by the action of the oxygen of the air, or quickly by the addition of chlorine water or nitric acid. The following equation expresses the changes : — SOA + O CI, 3S0, + 2NO3H = SOA + 0H„ + SO4H, + 2HC1 + 20H, = 3SO4H3 + N2O, SO2 possesses great aflBnity for oxygen. Both gases com- bine when they are passed over spongy platinum, or platinum black, prepared by heating platinic chloride (PtCl^) till the chlorine is driven off. The porous condition of this body facilitates, by a kind of catalytic action, the combination of the oxygen with the sulphurous anhydride. Exp. 110. — Prepare a little platinised asbestos by moistening asbestos with a solution of platinic chloride, and heating it in a Bunsen flame. Introduce it into a short piece of combustion tube drawn out, as seen in fig. 47, and heated to a low red heat. Pass next a current of well-dried sulphur dioxide (prepared from copper and sulphuric acid) and oxygen over it, mixed in the proportion of 2 volumes of the former and 1 volume of the latter. In order to dry and mix the gases, they are passed through the drying bottles, charged with sulphuric acid, into the three-necked Woolfe's bottle, which is empty, before they are sent over the platinised asbestos. Kg. 47. Dense white suffocating fumes issue from the drawn-out jet of the tube, as soon as they come in contact with the moisture of the atmosphere. (Both SOg and O are colouriess OXYGEN COMPOUNDS OF SULPHUR 147 gases.) When a jar is held over the fmnes, which has been wetted by a little barium chloride, the fumes are immediately fixed as a white precipitate of (SO^Ba) barium sulphate. The reaction is explained as follows : — SOj + SO3 Sulphurous Oxygen, anhydride. Sulphuric anhydride. SO3 + OH2 SO3OH,, or SO4H2 ^ ^-_— ' V^ Y ' Sulphuric Water a,nhydride. (from the air). Sulphuric acid. BaCl^ + SO4H2 = S04Ba" + OHj. Barium chloride. Barium sulphate. Exp. 111. — Another mode of converting SO^ into SO3, viz., by adding a solution of peroxide of hydrogen, or hydroxyl, to an aqueoua solution of sulphur dioxide, is of great theoretical interest. The combines with the SOj and forms SOg, leaving OH2 as the hydroxyl remnant. Or by viewing the combina- tion between the SOg inolecule and the Ogllj molecule as a direct one, and thus giving rise to a new molecule in which all the elements are held together by the grouping element sul- phur, it satisfies at once all the requirements of the atomicity theory. The new compound body is expressed symbolically by the equation : — SO2 + O2H2 = SOaHjOj, or S0j(H0)2 Sulphur Hydroxyl. Sulphuric dioxide. acid. and its graphic expression is then as follows : — O n-il/O-H * It is well that the student should be taught that various formnlar expressions are possible, according to the origin and formation o| the sulphuric sjci^. 148 ELEMENTARY OHEMISTRT. Exp. 112. — To illustrate to a class the process of manufacture of sulphuric acid now in general use (the so-called chamber acid, or oil of vitriol), the foUowing apparatus is required : — 1. A large flask or balloou A, to serve in the place of the leaden chamber, and provided with a good india-rubber cork, per- forated with four narrow holes, and fitted up with glass tubes, as seen in fig. 48. Fig. 48. 2. A steady supply of sulphurous anhydride, prepared by the action of SO4H2 upon copper or mercury in flask (6), and con- veyed to the bottom of the balloon. 3. A steady supply of N^Oj gas, prepared in flask (c) from copper turnings, and somewhat dilute nitric acid, and likewise con- veyed by a tube to the bottom of the balloon. 4. A supply of steam from a small flask (d), in which water is kept steadily boiling. 5. A well regulated supply of air, which is best supplied through another (fifth) tube (not shown in fig. 48), from the gasholder described on p. 43. A straight safety tube allows any excess of gases or air to escape when the apparatus is well adjusted. The action may be shown by OXYfiBN COMPOUNDS OF SULPHUE, 149 firat passing N^Oj, -which, on the admission of air, fonns reddish- hrown fumes. When the sulphur dioxide is next admitted, the fumes are seen to vanish, and a compound of the composition SO^ ] Trn" is formed, which is deposited on the glass in the form of a white crystalline body. When steam comes in contact with them, they resolve themselves into S02(HO)2, nitric oxide, which, by combining with 0, converts a fresh quantity of SOj into SO3, being alternately reduced and oxidised ; thus : — 2SO2 + N2O4 + 20H, = 2SO4H2 + N2O,. After some time a considerable amount of strong sulphuric acid can be ^obtained, if the chemical reactions are properly regulated. If a solution of sulphurous or sulphuric acid is added to a metal, oxide, carbonate, etc., it combines with them, forming salts called sulphites and sulphates, by the replace- ment of the whole of the hydrogen, neutral salts are obtained; e.g.: — 2SO3H2 + COaNaa = SOaNaa + COa + OHj. Or, SO4H3 + 003^2 = SO^Nas + CO2 + OHj. ■whilst acid salts are obtained, when only half the hydrogen is replaced — 2S03H2 + Na, = aSOsHNa + H„ S04H2 + NaHO = SOjHNa + OH2. All acids which are bibasic, i.e., contain two atoms of replaceable hydrogen (or 2II0), can form two series of salts, viz., primmry or acid, and secondary or neutral salts. 150 ELEMENTARY CHEIIISTEY. By the action of sulphur upon sulphurous acid, a siilphui acid is formed which contains 2 atoms of sulphur; thus : — SO3H2 + S = S2O3H2, and has received the name of hyposulphurous acid — the " hypo" of the photographer. It forms a series of salts called hyposulphites, the most important of which is sodium hypo- sulphite (SSOgNaj). The more correct view of this acid seems, however, to be to replace one hydroxyl group in sulphuric acid by hydro- Bulphyl(SH); thus:— LESSON XVIII. DEFINITION OF CHEMISTRY — CHEMICAL CHANGES — CLASSIFICATION OF CHEMICAL EEACTIONS. According to the Eegulations of the Science and Art Department, it becomes incumbent upon any one competing in the May examinations, for the prizes yearly given, that he should be fairly prepared to answer any questions on the subject-matter discussed and explained in the seventeen preceding Lessons. To do this successfully it requires, more- over, a certain training in the way how to answer questions. We will devote this Lesson to give the pupil as many practi- cal hints and instructions as will enable Mm to pass (always assuming that he has carefully attended to the previous Lessons) a successful examination, when perhaps otherwise he might be full of knowledge and yet not be able to express himself clearly in writing, or not grasp the questions cor- rectly. We have strictly adhered to the subject-matter laid down for the pupil's guidance in the syllabus,* and we believe that, if the pupil has performed himself, or seen performed before him, the 109 experiments sketched out by the examiners (and a list of which will be found also in Appendix IL), he cannot very well fail in the examination. Every tutor knows, however, that a certain amount of training, how to work the answers to the questions, is a very desirable thing. This need not and should not be done merely — as we know it is sometimes done — by answering questions given by the examiners in pre- vious years. The pupils might thus acquire a smattering of chemistry, which it is the examiners' busiaess to distinguish and sift from sound and systematically acquired knowledge, and give his award accordingly. It has yet another aspect. There are annually a number of examination papers worked by pupils who have not the knowledge requisite to carry * This syllabus will be found in Appendix II. 152 ELEMENTAEY CHEMISTRY. them through the examination. These pupils have evidently never measured their strength beforehand, and the result is failure and disappointment to pupils and teachers. I think, on these grounds, that we shall not be accused of encouraging cramming. A certain amount of the chemical knowledge which a beginner has to acquire is not the worse for being well committed to memory, or, as it may be called, " crammed up." The very questions given by the examiners show that some memory work is encouraged, as long as the pupils understand what they are about. Definition of Chemistry. — Chemistry has been defined as the science which treats of the composition of all kinds of > matter, and of those changes in composition which result from the action either of different kinds of matter upon each other, or the external forces upon one and the same kind of matter.* Chemical changes depend upon the affinities inherent in every kind of matter; they are modified by temperature, and by the state of aggregation — solid, liquid, or gaseous — of the simple and compound bodies. We know of no better means of assisting beginners than by making everything clear, both experimentally and on paper, and following up the chemical changes by reducing, what appears at first sight complicated and cumbrous, to a few typical changes, among which every chemical reaction readily ranges itself. There are only five chemical changes known. These are — (1) A change by Combination. (2) ,, Eesolution. (3) „ Displacement. (4) „ Double Decomposition; and, lastly, (5) „ Eearrangement of the elements composing a molecule, within the molecule itself, giving rise to isoTMric bodies. The first class of the changes are numerous, and depend Upon the chemical affinity existing between elementary bodies. They give invariably rise to compound bodies in single or multiple proportions. The action is purely synthetical. * Frankland: Zecture Notes, page 1. CHEMICAL CHANGES. 153 Typical examples we have, e.g., when a metal combines with a non-metal, etc. : — Na + " CI = NaCl. Fe + S = FeS. SO, + o = so,. NH3 + HCl = NH4CI. The second class comprises changes due to analytical action, as when a compound hody resolves itself into its component elem,ents, or into an element and compound body, and, lastly, into two or more less complex compound bodies Typical examples are — HgO = Hg +0. SFeSs = Fe3S4 + Sj. .KCIO3 = KCl + O3. COHO = ^°' + CO + OH,. The third class comprises changes which arise when any element, or group of elements, displaces another element, or grovp of elements, in a compound hody. Typical examples of such changes we have, e.g., when a more electro-positive element displaces a less electro-positive element : — Cl» + SNal = 2NaCl + 1, (free). Zn + 2]SrO,Ag = NsOfiZn -1- Ago (precipitated). Fe + S04CU = SO^Fe + Cu CnO + H, = Cu + OH,. 2PbO + c = 2Pb + CO,. SO4H, + Zn = SOiZn + H,. COaCa + 2HC1 = CaCla + CO, + OH,. The fourth class comprises perhaps the most numerous class of chemical changes, viz., when a mutual exchmige of elements or groups of elements, in two or more bodies, takes place. They are designated changes by double decomposition. A. great number of chemical bodies trace their origin back to an exchange of this nature. Typical reactions are — CuO + 2HC1 = CuCl, + OH,. ZnS + 2HC1 = ZnCl, + SH,. NO3K -I- SO4H, = SO4HK + NO3H. NaCl H- SO4H2 = SOiHNa + HCl. NOgAg + NaCl = NOjNa + AgCl. 154 ELEMENTARY CHEMISTRY. The fifth class of chemical changes is of a very limited extent among inorganic compounds, and finds its representa- tives all but exclusively among organic bodies which can form isomeric compounds. As typical we may view the well-known change which soluble white of egg undergoes when heated. It becomes a hard white body. It wiU be found good practice if the pupil is held to classify every chemical change which he comes across, as he goes through the previous Lessons, according to these four divi- sions, and acquires thorough practice in expressing it by an equation; and, if need be, makes it mathematically clear by substituting atomic weights for symbols. The division to which the change belongs may be briefly indicated by employ- ing the bracketed letters. (C) for change L, i e. , Combination. (E) ,, II., i.e., Resolution. (D) ,, III., i.e., Displacement. (DD) ,, IV., i.e., Double Decomposition. It frequently happens that well-prepared pupils do not make the marks which their knowledge, in the teacher's opinion, entitles them to make ; and as the examinations of the Science and Art Department are of necessity written examinations, teacher and pupil should bear in mind that a kind of practice in answering questions is required, which is most essential to success. Suppose a question consists of more than one part, a portion of the marks will have to be assigned to each part, and if it be not properly answered these marks will of course be l(jst and the total diminished. Dissecting questions into parts, and assigning marks to each part, should, therefore, form part of the preparation for an examination. If the pupUs are examined in this manner before the actual examination comes on, the teacher should have no difficulty to satisfy himself who of his pupils wUl pass and who will not. LESSON XIX. WEIGHTS AND MEASUEES. It is generally acknowledged that the decimal or metric system is so much simpler, and lends itself so much more readily to all scientific calculations, that it has been all but generally adopted by scientific men, and has in many countries been legally adopted for all measurements of ordi- nary occurrence in daily life. We will shortly explain the principles of the metric system, which the French have adopted since the Revolution of 1789. They called the TO'.'innr.'innT P^'^ °^ *^^ earth's quadrant (extending on the meridian of Paris, from the equator to the pole, and which had been determined by the most eminent of their mathe- maticians with great accuracy) a metre, and fixed upon it as their unit of length. A metre is equal to 39 '37 English inches, * or a little more than an English yard. The subdivisions of the metre are distinguished by the Latin prefixes deci-, centi-, and Tnillv-, so that a decimeter is ^ of a metre, a centimeter y^^, and. a millimetre -^wm '^^ * metre. The multiples are indicated by the Greek prefixes decor, hectO; and kilo-, so that 10 metres are equal to 1 decametre. 100 „ „ 1 hectometre. 1000 ,, ,, 1 kilometre. The kilometre is almost the only term used in practice. It is used as a measure of distance by road; 16 kilometres are equal to nearly 10 English miles. The metre serves likewise as the measure of capacity. A cubic metre, i.e., a cube, each side of which has the dimen- sion of 39-37 English inches, weighs 1000 kilograms of water. It is equal to 0-9842 of an English ton, i.e., 2240 * Accurately, 39-37079 EngMi incites. 156 ELEMENTART CHEMISTRY. English pounds. This would constitute a rather unwieldy- unit of capacity. A decimetre, or a cube of 3-937 English inches, each side, is a more serviceable unit. It is called a litre, and is equal to 1-7637 imperial pints, or 61-024 cubic inches. A litre of water at- 4°C., weighs exactly 1 kilogram, or 1000 grams, equal to a little less than 2 J lbs. avoirdupois, and constitutes the common weight in France. Being equal to 1000 cubic centimetres, 1 cubic centimetre weighs 1 gram, and this latter forms the usual unit for the more delicate weighings with our chemical balances. A gram is equal to 15'4:32 English grains. It is further subdivided into — Tenths of a gram, or decigram 0-1 grm. Hundredths of a gram, or centigram '01 grm. Thousandths of a gram, or milligram 001 grm. The same prefixes are used for the divisions and multiples of the litre as were used for the metre. Instead of the term mUlilitre, or YirW °^ ^ litre, we use, however, almost invariably cubic centimetres, abbreviated C.C.j hectolitre ^b mostly employed as a wine measure. For chemical purposes the following table, in which the measures of surface are omitted, will answer all our pur- Mbasures op Length. Millimetre -001 of a metre -0394 inch. Centimetre -01 „ -3937 „ Decimetre -1 ,, 3-9370 inches. Metre 1 metre 39-37 „ Decametre 10 metres 393'7 „ Hectometre 100 ,, 328-00 feet. Kilometre 1000 „ 3280-9 ,, Measures of Capacity. ™Wtre.. ..^."^'" \ '"01 °* ^ ^*'^ '"^^ cubicinehes. Centilitre -01 „ -61 „ Decilitre -1 ,, 0*176 imp. pints. litre 1 cubic decimetre 1 -76 „ Decalitre 10 ,, 2-2 gallons. Hectolitre 100 „ 22-009 „ WEIGHTS AND MEASUREg. 157 Milligram •001 = Centigram Decigram Gram •01 •1 1 Decagram 10 Hectogram , 100 Kilogram 1000 Myriagram 10,000 Quintal 100,000 Tonneau 1,000,000 Wbishts. ^tStterl ■015^3grainavoir. 10 „ •15432 1 „ 1 '54323 lcub.centimet.15'43235 grains. 10 „ -02204 lb. avoir. 1 decilitre -22046 , „ 1 litre 2-20462 „ 10 Utres 22-04621 „ 1 hectolitre 220-46. 1 cub. metre 2204-6 „ Assuming that the pupils are well acquainted with English weights and measures, we will now only give some practical examples how to convert French into English weights : — 1. Find the contents of a tank expressed in litres or cubic decimetres. The tank is 4 feet by 4, and 3 feet deep; its cubical content is therefore — 4 X 4 X 3 = 48 cub. feet 48 cub. feet are equal to 12 x 12 x 12= 1728 cub. inches x 48 = 82944 ciib. inches. 61-024 cub. inches =1 litre. 8??#= 1359-2 litres. 61-024 2. A cylindrical gas-holder is 4-9 metres high, and 89 square metres area; how many litres of gas will it hold? 4-9 X 89 = 436-1 cubic metre contents. 1 cub. metre =1000 cub. decimetres or litres. Therefore 1000x436-1=436100 litres. 3. Find the percentage composition of hydric potassic sul- phate (SO.HK). S = 32 23-53 O4 = 64 47 06 H = 1 -73 K =_39 28-68 136 10000 Total molecular weight of the sulphate = 136. by rule of three we get — In 100 parts. Therefore 136 : 32 136 : 64 136 : 1 136 ; 39 100 : K = 23-53. 100 : y or simply 2 x 23-53 = 47-05 100 : s = -73. i 100 ; X or simply the difference from 100 =28 'OS, 158 ELEMENTAKT CHEMISTRY. 4. What is the percentage compositioii of nitric tetroxide Per cent. Nj, = 28 30-43 O4 = 64 69-57 92 100-00 The molecular -weight of NjO^ is 2 x 14, or 28, and 4x16, or 64, or equal to 92. Rule of threfe calculation — 32 : 100 : : 28 : a; = 30-43. 92 : 100 : : 64 : a; = 69-57. 5. When the percentage composition of a compound is given, you are requested to find the empirical formula. Rule (1). Divide the percentage number by the respective atomic -weight of the element, and carry the calculation to three decimal places. Rule (2). Divide each of the numbers thus found by the lo-west, and, if necessary, reduce to their simplest relation in whole numbers. Example. — Found in 100 parts — 2-04 _ 2-04 _ z^ = 2 Hydrogen 2-04 1 1-02 ■ Sulphur 32-65 00.65 1-02 Oxygen ■ 65 31 65-31 ^ 4.Q3 ^ 4;08 ^ 4 16. 1-02 The formula, therefore, is HjSO^ LESSON XX. QUESTIONS AND EXEiciSES. LESSON I. J 1. What are the properties of hydrogen gas? How are they best demonstrated before a class? Give description and sketches of apparatus employed. , 2. How would you demonstrate that water is formed by the com- / bustion of hydrogen in air ? 3. Explain the action which spongy platinum exerts when hydrogen is passed over it in contact with air. 4. How many milligrams of hydrogen are evolved when 460 milli- grams of sodium {Na=23) are thrown into water? Express the decomposition by an equation. (Exam. 1877. ) * 5. I throw a fragment of sodium upon water; show by an equation j what chemical change takes place, and give the names of the sub- stances produced. (Exam. 1868.) 6. I burn a jet of hydrogen in air; what chemical effect is pro- / duced? (£xam. 1872.) 7. I have two cylindrical jars of hydrogen; I hold one of them mouth upwards and the other mouth downwards; at the expiration of half a minute I plunge a lighted taper into each jar. Describe exactly what you would expect to take place in each case. (Exam. 1872.) 8. In dissolving zinc in hydrochloric acid, and ooUeoting the hydro- gen evolved, 250 cubic centimetres of the gas measured at 0° C. and 760 mm. pressure were obtained. How much zinc was dissolved? (Exam. 1871.) LESSON IL 1. What precautions have ts be observed in fitting up a volta- meter for the decomposition of water ? 2. Describe an experiment for proving that water is a compound body, and state precisely the conclusions to which the experiment leads you. (Exam. 18*r7.) * It win be found that some of the questions quoted from the various Examination Papers differ but slightly from each other, and the pupil wUl have an opportunity of studying how questions of the same or of a, similar nature may be put in different language. 160 ELEMENTART CHEMISTET. 3. Describe the apparatus (exolnsive of the battery) required to electrolyse water acidulated with sulphuric acid, and make a sketch of it. What are the names and relative volumes of the gases given off, and how would you demonstrate their characteristic properties ? ^Ezam. 1873.) 4. Explain how you would demonstrate, experimentally, that water is formed by the combustion of hydrogen in air. (Exam. 1870.) 5. What is the percentage composition of water ? (Exam. 1876. ) ' 6. How would you demonstrate experimentally the volume com- position of water ? (Exam. 1870.) 7. What is the meaning of the terms electrolysis, analysis, synthesis, dissociation, molecules, constant volttme proportions? ^ What constitutes an explosive mixture ? 8. Six litres of hydrogen are burnt in air, and the steam which is produced condensed. How much water, by weight, can be obtained theoretically, and what volume of steam, expressed in litres, will this be equal to ? 9. What is a crith, and how is it employed by chemists ? (Exam. 1874.) 10. How much water would be produced from 28 lbs. of oxygen and 5 lbs. of hydrogen, and would either of the elements be in excess? (Exam. 1868.) LESSON III., 1. What are the properties of oxygen ? Describe briefly how you would illustrate each by a simple experiment. 2. How would you prepare oxygen gas ? Explain your process by an equation. (Exam. 1868.) 3. You have given to you some red precipitate' (mercuric oxide). State (1) whether you consider this substance to be a sim{)le or a com- pound body; (2) whether it undergoes any chemical change when sub- mitted to the action of heat; and if so, (3) what is the nature of the change, and how it can be expressed symbolically. (Exam. 1874. ) 4. You have given you some potassic chlorate (chlorate of potash) and black oxide of manganese, and are required to make and collect oxygen from these materials. Describe minutely how you would do this, and make a sketch of the apparatus which you would employ. What are the chief properties of oxygen? (Exam. 1872.) 5. You have some mercury, a glass flask, and a piece of hard glass tube, and are required to make pure oxygen gas. How will you do it? (Exam. 1869.) 6. I have two receivers flUed with oxygen gas; in one I bum a fragment of sulphur, in the other a fragment of phosphorus. Describe what takes place in each case, and state whether the volume of gas QUKSTIONS AND EXERCISES. 161 in the receivers •will be diminishecl or augmented, or will remain unaltered. (Exam. 1868.) 7. What are the resulting products when hydrogen, carbon, sul- phur, and phosphorus are burnt in oxygen ? Express the reactions by equations. (Exam. 1874.) ;' 8. How would J^ou show that bodies increase in weight when they are burnt ? Give examples. Explain more fully what takes place when a candle burns in air, and how you would show the increase in weight experimentally. 9. Air contains 23 per cent, of its weight of oxygen. How many grams of phosphorus are needed to bum out the whole of the oxygen in 100 grams of air when the highest oxide of phosphorus is formed — P=31? (Exam. 1878.) 10. Why does oxygen not combine with platinum and gold when these metals are heated in a current of oxygen gas ? 11. Describe a simple gas-holder, and give, if possible, a drawing. 12. Illustrate changes by combination and by resolution, by chemi- cal equations. Explain why one of the same body, on the application of heat, may undergo alternately these two changes. 13. What is the density of a litre of hydrogen or oxygen compared with air ? Show how you can arrive at the combining or atomic weight of oxygen when the hydrogen is made the unit of comparison. 14. What meaning do you a,ttach to the terms oxygen, oxidation,, oxide, alkaline or caustic, acid, actual and sensible heat, reduction, ignition point, flame, metal, metalloid, nolle metalsi LESSON IV. 1. What is the diflferenoe between a mixture of two elements and a compound of two elements ? (Exam. 1874.) 2. A wooden lath is suspended horizontally by means of a thread; a dry glass rod or tube is now briskly rubbed with warm silk and then brought near to one end of the suspended lath. What is the result? (Exam. 1876.) 3. What happens when a glass rod, moistened with concentrated sulphuric acid, is brought very near to a small heap of a mixture of sugar and potassic chlorate, but so as not to, touch the heap? (Exam. 1876.) 4. Divide the following substances into dements and compounds: — Diamond, graphite, charcoal, glass, lime, ozone, iron, gold, water, ammonia, and flint. (Exam. 1876.) 5. Why is atmospheric air declared to be a mixture and not a com- pound? (Exam, 1874.) 162 ELEMENTARY CHEMISTRY. ' G. Descrilie two methods for the preparation of nitrogen, expr^as- ing the reactions by equations, and giving drawings of the apparatus. (Exam. 1877.) 7. How would you separate — 1. Sand from sugar ? 2. Chalk from common salt ? 3. Charcoal from nitre ? 4. Glass from boric acid ? 5. Sulphur from water ? (Ezam.'l873.) 8. Classify the following substances into elements and com- pounds : — Common salt. Mercury. Oxygen. Iron. Sulphur. Laughing gas. Gypsum. Ozone. Ammonia. Water. Corrosive sublimate. Lime. Why is hydrogen regarded as an element and hydrochloric acid as a compound? (Exam. 1869.) 9. Classify the following elements into metals and non-metals, and into positive and negative elements : — (Exam. 1873. ) Aluminium, Iodine. Phosphorus. Calcium. Iron. Potassium. Carbon. Lead. Silicon. Chlorine, Manganese, Silver. Copper. Mercury. Sodium, fluorine. Nitrogen. Sulphur. Hydrogen. Oxygen. Zinc. 10. What elements can I get out of each of the following mate- rials ?— (Exam. 1872.) Water, Hydrochloric acid. Diamond. Ozone. Ammonia. Brimstone. 11. Classify the following substances into elements and com- pounds: — Steam, ice, sulphur, hydroxyl, ammonia, common salt, marble, and carbonic anhydride. (Exam. 1878.) 12. Classify the following substances into elements and com- pounds: — (Exam. 1871.) Glass. Soda. Silver. Diamond, Hydroxyl. Quicksilver. Lime. Zinc. Borax. Charcoal, Sugar. Chlorine. 13. Classify the chief elementary substances into metals and non- metals, and into positive and negative elements. (Exam. 187S.) 14. Classify 22 of the most important elements into metals and Bon-metaJs; also into yositiy? »nd negative elwentg, (Etam, 1871.) QUESTIONS AND EXEKCISES. 163 15. What meaning do you attach to the terma chemical element, chemical compound, chemical affinity, mechanical mixture, positive and negative elements, chemical force, nitrogen ? 16. What is the volume composition of atmospheric air ? Know- ing the density of and N, how would you find the percentage composition by weight of air ! 17. Describe the three states of aggregation in which matter can exist. Give illustrations and state what are the diflferent physical conditions upon which they depend. , 18. What are the properties of nitrogen gas, and how would you demonstrate them experimentally ? 19. What are the physical conditions necessary to cause (1) solid elementary bodies to pass from the solid to the liquid and to the gaseous form; and (2) the gaseous bodies to the liquid and to the solid form ? Give a few illustrations. 20. Describe an experiment which furnishes proof that elementary bodies combine in constant proportions by weight. 21. Give the names and symbols of the non-metallic elements. (Esam. 1S6S.) LESSON V. 1. How would you prepare chlorine, and how would you show that a jet of hydrogen bums in chlorine? Give a sketch of all the appara- tus which you would employ. (Ezam. 1873.) 2. In 100 parts by weight of common salt [how many parts by weight of chlorine ? (Exam. 1867. ) 3. What happens when steam is passed through a red-hot porce- lain tube, and when a mixture of steam and chlorine is passed through the same tube? (Exam. 1877.) 4. A piece of sodium was completely converted into chloride by the absorption of 200 cubic centimetres of chlorine, measured at 0° C, and 760 mm. mercurial pressure; what was the weight of the sodium? (Exam. 1873.) • 5. How much chlorine, by weight (in grammes) and by measure (in cubic centimetres), can I obtain from one litre of hydrochloric acid gas, measured at 0° C, and 760 mm., mercurial pressure. (Exam. 1871.) 6. I bum a jet of hydrogen in chlorine; what chemical change takes place? (Exam. 1872.) 7. You are required to make oxygen from chlorine and water. Describe exactly how you will do it, and give a sketch of the appa? ratjis vhich ^ou propose to employ, (Ejjajn. 187I-) ' " 164 ELEMENTARY CHEMISTRY. 8. I mif together cUorine and hydrogen, and expose the mixture to sunlight; what happens! At the termination of the experiment, I add ammonia to the product. "What is the name and formula of the compound formed ! (Exam. 1871.) 9. If a mixture of manganic oxide (peroxide of manganese) and hydrochloric acid be heated, what chemical change takes place? Give the name and'properties of the gas which is evolved. (Exam. 1869.) 10. Describe (minutely, and not merely by equations) two processes for the preparation of chlorine. Give an equation and a sketch of the apparatus in each case. (Exam. 1878.) 11. How would you collect dry chlorine gas without making a nuisance, and what test would you apply in order to find out any slight escape of the gas ? 12. What are the properties of chlorine gas, and how would you demonstrate them by a few simple experiments ? 13. Explain the meaning of the terms chlorine (bromine, iodine, and fluorine), chlorides, disinfecting or bleaching agent, oxidising agent. 14. Enumerate some experiments showing the greater chemical affinity of chlorine for metals and non-metals, compared with that of oxygen. 15. Define gas collection by upward or downward displacement. LESSON VI. 1. Describe the principal properties of hydrochloric acid gas. 2. If you had given to you some common salt and sulphuric acid, and were required to fill a glass jar with HCl, describe how you would do it, and give a sketch of the apparatus you would employ. (Exam. 1872.) 3. How would you distinguish chlorine gas from hydrochloric acid gas? 4. How would you show experimentally that hydrochloric acid consists of hydrogen and chlorine ? (Exam. 1876. ) 5. Hydrochloric acid is stated to be composed of equal volumes of chlorine and hydrogen, united without condensation. How would you prove experimentally that this is the case {a) by analysis; (6) by synthesis? (Exam. 1878.) 6. What is the percentage composition of hydrochloric acid? (Exam. 1871.) 7. What meaning do you attach to the terms "acid," "base,'' and "salt?" (Exam. 1868.) 8. What is the meaning which chemists attach to the term neutralise, and how would you illustrate this meaning experimentally? QUESTIONS AtfD EXERCISES. 165 9. How are metallic oxides divided, and what is the chemical notation employed to designate the different oxides ? 10. What precautions have to be adopted (1) in preparing a satu- rated aqueous solution of hydrochloric acid gas; (2) in making dilute sulphuric acid from oil of vitriol; (3) in conducting the electroljrsis of hydrochloric acid; and (4) in preparing at once a neutral chloride from any insoluble metaUio oxide and hydrochloric acid ? LESSON VII. 1. Define the terms "atom" and "molecule" in their modern acceptation. (Exam. 1869.) 2. Knowing the weight of a litre of hydrogen gas to be "0896, or one crith, how would you arrive at a knowledge of the specific gravity or volume weight of the following gases : — Chlorine: Steam. Bromine. Hydrobromic acid gas. Oxygen. Hydrochloric acid. Nitrogen. Phosphorus tribromide. 3. I know the weight of a litre of several gases ; how can I find their respective specific gravity? The weights are as follows : — 1-4336 grm .., -8064 3-1808 grms 5-7344 11-3792 grms 1-6352 4. I take equal volumes (measured at the same temperature and pressure) of hydrogen, nitrogen, hydrochloric acid gas, steam, and carbonic anhydride (carbonic acid), and find that the nitrogen weighs 56 grammes. Required the weight of each of the other gases. (Exam. 1869.) 5. How do we arrive at a knowledge of the volume weight of a simple as well as a compound gas ? and, knowing the volume weights, how do we deduce these from the atomic weights of elementary gaseous bodies ? 6. In a balloon you have 15,620 cubic metres of hydrogen gas; ascertain by two different methods how much the gas will weigh in grms. (One cubic metre = 1000 litres; one litre =1000 cubic centi- metres, abreviated CO.; and one cubic centimetre of water at 4° C weighs 1 grm.). 7. Define (1) Avogadro's law, (2) multiple proportions, (3) the principles of chemical notation. 8. Practice reading of chemical formulas and equations. LESSON vin. 1. Describe the changes produced in brimstone by the continued application of heat. 166 ELEMENTARY CHEMISTRY. 2. How does snlplmr occur native, and how does it crystallise rmder different con(Utions ? (Exam. 1874.) 3. Ejqjress by an equation the action of hydrochloric acid upon trisulphide of antimony. (Exam. 1S67.) 4. You have given to you iron filings, sulphur, and hydrochloric acid, and are required to make sulphuretted hydrogen; how will you proceed? (Exam. 1868.) 5. Explain what takes place when sulphuretted hydrogen is passed into solution of sulphurous acid. (Exam. 1S76. ) 6. Describe the allotropic modifications of sulphur. 7. State how you would extract the sulphur from a sample of sulphur ore, and in what form is the sulphur usually brought into the market ? 8. Define the terms sulpMde, roll sulphur, flowers of sulphur, iron pyrites, suhlimaiion, dimorphism, aUotropism. 9. Describe fuUy a process for preparing sulphuretted hydrogen gas, and give a drawing of the apparatus. 10. What are the properties of sulphuretted hydrogen, and how would you briefly demonstrate them experimentally ? 11. How would you show experimentally the action of sulphuretted hydrogen upon several dilute salt solutions containing lead, copper, cadmium, antimony, zinc, magnesium? 12. What changes does sulphuretted hydrogen gas undergo when it comes in contact with oxygen, chlorine, bromine, iodine ; and what are the new compounds which are produced? 13. What is the atomic and molecular weight of SOj and SH^ com- pared with hydrogen; and what is the weight in grms. of one htre of the respective gases ? 14. How would you extract sulphur from iron pyrites (FeSj) ? 15. If I bum a piece of sulphur in a closed flask filled with atmo- spheric air, what substances shall I find in the flask at the end of the operation, and what wUl be the relation between the volume of the gases originally contained in the flask, and that of the gases found there at the close of the experiment? If I repeat the experiment in a flask filled with pure oxygen instead of atmospheric air, what difierence shall I find in the composition and volume of the resulting gases? (Exam. 1871.) 16. If I bum a piece of sulphur in a bottle filled with air, and another piece in a bottle fiUed with oxygen, what shall I find in each of the bottles after the combustion is finished? Give equations. (Exam. 1878.) 17. How would you prove that the gaa obtained by pouring sul- phuric acid upon ferrous sulphide contains both sulphur and hydro- gen? (Exam. 1878.) QUESTIONS AND EXERCISES. 167 , LESSON IX. 1. How would you prepare ammonia gas, and fill a jar with it? Give a sketch of the apparatus. (Exam. 1875.) 2. If you were required to prepare pure ammonia gas, how would you proceed, and what apparatus would you employ? (Exam. 1870.) 3. Describe minutely what occurs when hydrochloric acid gas and ammonia gas are mixed together. Give a sketch of the apparatus which you would employ to show this experiment. (Exam. 1873.) 4. How would you ascertain that ammonia is a compound contain- ing nitrogen and hydrogen? (Exam. 1877.) 5. What takes place when a lighted taper is immersed in gaseous ammonia ? (Exam. 1874. ) 6. Explain the meaning and derivation of the terms nitrogen, sal- ammoniac, liquor ammonios, fired and volatile allcali, am/moniacal liquor, soda-lime, sodamide. 7. What are the most important properties of ammonia gas, and how would you briefly demonstrate them experimentally? 8. How would you prepare and coUeot dry ammonia gas? 9. How would you show by an experiment that glue, white of egg, isinglass, etc., contain nitrogen among their elementary con- stituents? 10. Describe two methods for preparing nitrogen from ammonia. 11. How can you prove experimentally that NHj contains one atom of JS" and three atoms of H ? 12. What is the specific gravity of ammonia gas, that of hydrogen being taken as imity? (Exam. 1870.) 13. What takes place (1) when ammonia gas is passed through a porcelain tube heated to redness ; (2) when chlorine is passed into a strong aqueous solution of ammonia, and what precaution has to be observed in the latter experiment ? LESSON X.' 1. How does the element carbon occur in nature ? 2. Explain the action of heat upon wood, coal, coke, bones, graphite, in a bent bulb-tube or small retort. 3. Describe the allotropio foi-ms of carbon. How would you prove that these different substances consist of the same element ? (Exam. 1877.) 4. I heat as strongly as possible a fragment of each of the follow- ing substances in a glass tube through which a current of air is pass- ing : — Sulphur, phosphorus, boron, charcoal. What chemical changes take place ? (Exam. 1876.) 168 ELEMENTAHt CHEMISTRY. 5. Two volumes of marsh gas, and four volumes of oxygen are exploded in a. eudiometer tuoe; what volume of gaseous products will be left ? Express by an equation. (Exam. 1872.) 6. Grey cast-iron contains minute black scales ; of what material are these scales composed, and what are its properties ? I heat bonea to redness in a close vessel, from the interior of which air is excluded. I repeat the operation with wood instead of bones. What are the names and properties of the materials left in the vessel, and how are these materials related to the black scales found in the grey cast- iron? (Exam. 1869.) 7. Explain the decolourising and disinfecting action of wood char- coal and of bone-black, and what industrial appHoation is made of these properties. 8. Describe an experiment which proves that diamond, wood charcoal, graphite, and coke are composed of the same elementary matter chiefly, viz., carbon. 9. Describe the preparation of marsh gas from sodium acetate and soda-lime, and explain its volume composition and chief properties. Give an equation. 10. What is the density of marsh gas compared' with hydrogen ? 11. Describe an experiment to illustrate the indestructibility of matter in the case of a burning candle. Give a, drawing of the apparatus you would use. (Exam. 1878. ) 12. Define the meaning of the terms animal or bone charcoal, mineral charcoal, gas carbon, kish, wood cMrcoal, graphite, plum- bago, hydrocarbon, carbo-hydrate, marsh gas, f/re-damp, destructive distillation. 13. Why are the gases left after an explosion in a coal mine so destructive to human life ? 14. In what proportions must marsh gas and air be mixed in order to bum quietly, and without explosion, when a, light is applied to the mixture ? LESSON XL 1. What is meant by the atomicity or quantivalenoe of an element 1 (Exam. 1870.) 2. What is meant by the atomicity or equivalence of an element ? Give the atomicity of all the non-metallic elements. (Exam. 1868. ) 3. What is the atomicity or equivalence of the following elements : — Chlorine, calcium, magnesium, silver, tin, lead, and arsenic? (Exam. 1869.) 4. Give the atomicity of each element in the following compounds : — HCl— (OH)s— NH3— COj— SOa and SHj. (Exam. 1877.) QUESTIONS AND EXEECISES. 169 5. Draw the graphic formula of water, hydrochloric acid, hydroxyl, metaboric acid, nitric acid, and sulphuric acid. (Exam. 1S77. ) 6. What do you mean by the term "compound radical?" Illus- trate your answer by writing out the names and formulae of a few compound radicals. (Exam. 1873. ) 7. Explain the terms grouping dement, non-saturated molecule, com- pound radicals, constitutional formulce, graphic formulae, atomicity. . 8. What is understood by hydrogen valency and oxygen (halogen) valency? Give illustrations and examples. 9. Write out the symbols and graphic formula of the following molecular compounds: — Marsh gas, hydrochloric acid, arsenietted hydrogen, ammonia, sulphuretted hydrogen, water, methyl, hydroxyl, hydrogen persulphide, sodium hydroxide, nitrogen trichloride, methyl chloride, silver chloride. 10. Enumerate compound bodies, which exhibit varying atomicities. 11. What are the molecular formulse of the following elementary bodies:— 01, Br, I, 0, S, As, P, H, Hg, Zn, Cd? 12. Explain the valency of the grouping elements in the follow- ing compound bodies:— 1„0„ SO3, SOj, OH., CH,, NH,, Is^H.Cl, C0„ OS,. LESSON XIL, 1. How would you prepare carbonic anhydride (carbonic acid) ? Give a sketch of the apparatus, and describe the properties of this gas. (Exam. 1872.); 2. What takes place when carbonic anhydride is passed into — 1st, distilled water ; 2nd, baryta water ; and 3rd, water containing some freshly precipitated calcic carbonate (carbonate of lime) ? (Exam. 1870. ) 3. Lime water is shaken up in a jar filled with carbonic oxide; what occurs? The carbonic oxide is then inflamed, and the lime water once more shaken up with the contents of the jar. What now takes place ? (Exam. 1875. ) 4. You are required to prepare carbonic oxide. Give a descrip- tion of one process, a sketch of the apparatus, and an equation show- ing the nature of the chemical change. (Exam. 1874. ) 5. A solid substance contains both a. carbonate and an easily decomposable sulphide. State how you would prove the presence of these two bodies. (Exam. 1874.) 6. What are the properties of CO and COj? Enumerate them in tabular form in two columns. 7. How would you illustrate experimentally that OOj is a heavy gas, i.e., heavier than air? 8. What is the chemical action which plants exert upon carbonic acid gas ? 170 ELEMENTARY CHEMISTrV. 9. Explain the processes of respiration and combustion, and show that both give rise to the formation of carbonic acid gas. 10. What is the action of heat upon carbonates ? 11. How are boiler deposits formed ? Explain the liquefaction of COj. What is understood by the so-oaUed " critical point of tem- perature," and how can COj be solidified? 12. What is the density of COj, and how many litres of the gas win have to be prepared in order to fill a gasholder constructed to hold 25 kilos, of the gas ? 13. What happens when COj is passed over heated charcoal con- tained in a red-hot porcelain tube? Give equation. 14. Describe several methods for preparing carbon monoxide. Give equations. 15. What are the properties of carbon monoxide, and what func- tions does the gas perform in a blast furnace ? 16. How are COj and CO separated from each other ? 17. What is the volume and molecular weight of CO^ and of CO? 18. How much carbon will be required to convert five litres of car- bonic anhydride into carbon monoxide, and what will be the volume of the gas so obtained ? 19. Write out the graphic formulse of carbon monoxide, carbon dioxide, and oxalic acid. 20. You have given to you a cylinder of hydrogen and one of car- bon monoxide, and are requested to find out, by applying a light, which cylinder contained the carbon monoxide and which the hydrogen. LESSON XIII. 1. Mention the composition of ozone, state its properties, and describe how you would prepare it. (Exam. 1870. ) 2. What takes place when electric sparks are passed through dry oxygen? (Exam. 1877.) 3. Some moist phosphorus is placed in a jar filled with atmospheric air, and a slip of paper, which has been dipped into water containing starch and potassic iodide, is suspended in the jar. State what occurs. (Exam. 1875.) 4. How is hydroxyl (peroxide of hydrogen) prepared? what are the relations of this substance to water and slaked lune, and to what useful purpose has it been applied ? (Exam. 1869. ) 5. What do you understand by the term "compound radical?" Give some examples of iuorganic compound radicals, and write out the constitutional formulEe of a few bodies, illustrating the functions of these radicals. (Exam. 1869.) Questions and exehciseS. Itl 6. Define a compound radical, and give a few examples. Amongst the following substances pick out those which are compound radi- cals:— KCl, NHj, OH, SO5, OKH. (Exam. 1875.) 7. What is the graphic formula for baric peroxide, ozone, hydrogen peroxide, hydrosulphyl ? 8. What takes place when hydroxyl is heated, or when silver oxide or spongy platinum is brought in contact with HjOj ? 9. Which are the most delicate tests for ozone and for hydroxyl ? 10. What is the volume weight of ozone ! and the molecular weight of hydrogen peroxide ? 11. Write out the symbolic and graphic formulse of the hydroxides of Zn, Ag, K, Ba, Sb, Sn ; also the formulae of a few metaloxyls and metalsulphyls. LESSON XIV. 1 . How does boron occur in nature, and how would you prepare boric anhydride from borax ? (Exam. 1871.) 2. How is metaboric acid prepared, and what salts does boric and metaborio acid form ? Give examples of the salts of sodium, calcium, and magnesium. 3. State how the element boron is obtained from borax, and what are the aUotropio forms of boron. Describe their preparation and properties. 4. What compounds of boron prove that boron is a triad element ? Give the constitutional and graphic formulas. 5. How would you test for boron in a compound of boron ? LESSON" XV. 1. Describe how the highest oxygen compounds of the non-metals are converted from the anhydrides to the hydrates or acids, and how the latter are forming either mono, di, and tribasic (or hydric) acids. Give illustrations . 2. How are salts of monobasic acids formed with monad, dyad, and triad metals ? Give illustrations. 3. Express symbolically and graphically the formulae of the chlorine compounds with oxygen, and with oxygen and hydroxyl, connecting their constituents in chain form, and also according to varying ato- micity grouping. 4. How is potassium chlorate prepared on a manufacturing scale, and what use has this salt found in the arts ? 5. What decomposition does potassium chlorate undergo when sub- mitted to heat (1) by itself, (2) with powdered sugar, (3) with oil of vitriol ? 6. How is sodium hypochlorite prepared ? 172 ELEMENTARY CHEMISTRY. 7. Express chloric peroxide, hypoohlorous anhydride, both sym- bolically and graphicaUy. 8. How is potassium perohlorate prepared, and in what manner does it differ in its properties from the chlorate? Give equation. LESSON XVI. 1. Explain the process of manufacturing nitric acid from sodio nitrate (nitrate of soda). What is the theoretical quantity of pure nitric acid obtainable from one ton of sodic nitrate ? (Exam. 1869.) 2. You have some nitric acid and metallic copper given to you, and are required to prepare nitrogen gas from these materials; how wiUyoudoit? (Exam. 1871.) 3. State exactly how you would .prepare nitrogen and nitric oxide. Give equations. (Exam. 1869.) 4. What changes take place when zinc dissolves in dilute nitric acid ? (Exam. 1876. ) 5. Metallic copper, sodic chloride, sulphuric acid, saltpetre, and solution of ammonia, are given to you, and you are required to pro- duce therefrom (o) nitrous oxide, and (6) nitric oxide. How would you proceed in each case ? (Exam. 1874. ) 6. You have some ammonic carbonate (carbonate of ammonia) and nitric acid, and are required to make and collect laughing gas from these materials. How would you do it? Describe minutely the apparatus you would employ and make a sketch of it. What are the chief properties of laughing gas ? (Exam. 1871.) 7. I put some gold leaf into a jar of nitric acid, and into one of hydrochloric acid; what takes place ? I mix the contents of the two jars; what then occurs ? (Exam. 1876.) 8. Mention the colour of the following liquids: — 1. Solution of potassic nitrite acidified with nitric acid. 2. Solution of potassic permanganate. 3. Dilute sulphuric acid tinted with magenta. If solution No. 1 be added to solution No. 3, what alteration of tint is observed, and what produces the change? If solution No. 1 be added to solution No. 2, what change of colour occurs, and why? (Exam. 1873.) 9. Enumerate the compounds which hydrogen forms with oxygen and with oxygen and hydroxy!. 10. Describe the decomposition which lead nitrate undergoes when heated by itself in a little bulb retort. Give equations. 11. What is the volume weight and molecular weight of nitrous and nitric oxide, as well as nitric peroxide or nitrogen tetroxide ? 12. Explain how N^Oj can act as a carrier of oxygen, and also what use it has found in the manufacture of oil of vitriol. QUESTIONS AND EXERCISES. 173 LESSON XVII. 1. Express in an equation the results obtained on heating fragments of copper with concentrated sulphuric acid. Name the products and describe the properties of the gas obtained. (Exam. 1868.) 2. You have given to you some sulphur, water, and nitric acid. Describe how you would make sulphuric acid from these materials. (Exam. 1871.) 3. Describe some experiments which illustrate the bleaching action of sulphurous acid (1) upon vegetable colouring matters, (2) upon potassium permanganate. Give instances of its diein/ecting action. 4. How would you demonstrate that the affinity which sulphurous anhydride possesses for oxygen is not satisfied by direct combination with oxygen, but only by a kind of catalytic action, induced by spongy platinum. 5. Describe by words and equations the action of H2O3, chlorine water (bromine iodine), upon sulphurous acid. ' 6. Describe fully, and by equation, the various reactions which take place in the manufacture of sulphuric acid. 7. Give formulsB of neutral and acid sulphites and sulphates. 8. Explain the action of dilute sulphuric or hydrochloric acid upon a concentrated solution of sodium hyposulphite, and express the same by an equation. LESSON XVIII. 1. What happens when sulphuric acid is poured upon (1) rock- salt, (2) chalk, (3) saltpetre? Give equations. (Exam. 1877.) 2. What changes take place when the following salts are heated with concentrated sulphuric acid: — (1) Common salt, (2) nitre, (3) borax, (4) yeUowprussiate of potash? Give equations. (Exam. 1874. ) 3. Water, sodium, hydrochloric acid gas, and iron, being given to you, describe four methods for preparing hydrogen. Sketch the apparatus you would use in each case. (Exam. 1874. ) 4. I add sulphuric acid to a white salt, and effervescence occurs. What may this be caused by, and what tests must I apply to ascer- tain the nature of the gas which is evolved ? (Exam. 1878.) 5. Into separate test-glasses, containing dilute hydrochloric acid, I put the following substances: — Zinc, chalk, marble, common salt, charcoal, iron, and gold. Mention the chemical changes which take place, and give equations. (Exam. 1878.) 6. State which of the following substances are solid, liquid, or gaseous at the freezing point of water: — Sulphurous anhydride, ammonia, sulphuric ai£ydride, chlorine, nitric oxide, nitric acid, Bulphuretted hydrogen, andhydroxyl. (Esam. 1876.) 174 ELEUGNTABT CHEMISTRY. 7. What chemical effect is produced when a strong solution of hydrochloric acid in water is added to each of the following sub- stances: — Zinc, iron, challc, sUver, sodic carbonate, gold? (Exam. 1876.) 8. I put slips of litmus and turmeric paper into (1) dilute nitric acid, (2) solution of potash, (3) solution of ammonia, (4) solution of carbonic anhydride, and (S) solution of potassium chloride. Describe what occurs in each case. (Exam. 187S.) 9. You have given to you distUled water, oil of vitriol, nitric acid, copper turnings, iron filings, and metaUio lead. State what salts you could prepare from these materials, and describe briefly how you would make them. , Explaiu the chemical changes by equations. (Exam. 1870.) 10. Tou have given you zinc, sulphuric acid, caustic potash, and water, and are required to prepare hydrogen from these materials by two distinct processes. State how you would proceed, and show by an equation the chemical change in each case. (Exam. 1869.) LESSON XIX. 1. What is the percentage composition of ammonium chloride? (Exam. 1876.) 2. What is the chemical formula of a body having the following percentage composition ? — S 32-65 O 65-31 H 2-04 100-00 (Exam. 1876.) 3. A normal or neutral salt of sulphuric acid, and a dyad metal, contains 21-05 per cent, of sulphur and 36-84 per cent, of metal; what is the atomic weight of the metal ? (Exam. 1868. ) 4. Where has free hydrogen been observed in nature? A balloon requires 5 cubic metres of gas to inflate it, how many kilograms of sidphuric acid must be converted into zinc sulphate (sulphate of zinc) in order to evolve sufficient hydrogen to 311 it ? (Exam. 1872. ) 5. How mnch, by weight, of each element is contained in 100 lbs. of a compound whose formula is P2O7N4H15 ? (Exam. 1872.) 6. How much, by weight, of each element is contained in 100 lbs. of a compound whose formula is S04N2Hg ? (Exam. 1871.) 7. Calculate the percentage composition of potassium chlorate (chlorate of potash) — (K=39. 01=35-37. 0=16). (Exam. 1878.) 8. One litre of nitrogen gas, measured at 0° C, and 760 mm. mer- curial pressure, weighs 14 criths; what is the weight in grains of one cubic metre of the same gas, measured at the same temperature and pressure? (Exam. }879.} APPENDIX I. TABLE OF ELEMENTS. NAMES, SYMBOLS, AND CO-EPFICIENTS OF ATOMICITY — ATOMIC WEIGHTS ChYDEOGBN = UNIT). Aluminium ^Xu»aiv .27-5 Antimony (Stibium) SU"""" 122 Arsenic ^sm.naY ; 75 Barium Ba« 137 Bismuth Bi'""'" 210 Boron B"> 11 Bromine Br' 80 Cadmium Cd' 112 Caesium Cs' 133 Calcium Ca» 40 Carbon C".... 12 Cerium Ce""^" 92* Clilorine CI' 35-S Chromium Cr"''"""'' 52-4 Cobalt Co'""""' 59 Copper (Cuprum) Cu" 63-3 Didymium Di" 96* Erbium Er" 112-6 Eluorine P 19 Gallium Glucinum (Beryllium) Gl" 9'4 Gold (Aurum) Au'" 197 Hydrogen H' 1 Indium In" 113'4 Iodine I' 127 Iridium •. i],ii,i7andri 193 Iron(Ferrum) pe","'"'*'' 56 Lanthanum '. La" 92'8 Lead (Plumbum) pyuudiv £07 Lithium Li' 7 Magnesium Mg" 24 Manganese ]VinU,iTana,i 55 Mercury (Hydrargyrum) Hg" 200 JiIoljsrbde»Tj«i,.........,..,......„.-..Mo"'"»°'"„. „.,.,.•..,. 99 176 ELEMENTARY CHEMISTRY. Nickel Ij;u.na,, 59 Niobium Ifbrnmav 94 Nitrogen ]Sfi.iii»dT 14 Osmium Os"' "• " ""^ "" 199'2 Oxygen 0" 16 PaUadium Pd"'"'" 106-6 Phosphorus pi.ui..aT 3I Platinum ptvi.ndi, I97.4 Potassium (Kalium) K' 391 Ehodium Ehu, 1. a-d « io4-4 Rubidium Kb' 85-4 Euthenium H^ii, h, w .»d viu io4-4 Selenium SeU,i»»dTi 79 Silicon. Si". 28 Silver (A:^entum) Ag' 108 Sodium (l^triumj Na' 23 Strontium' Sr^ 87-5 Sulphur giih^Ddri 32 Tantalum Ta'"""^' 182 Tellurium Te"'""*" 128 Thallium Tl""'*'" 204 Thorium Th-' 231 Tin(Stannum) Sn""'^" 118 Titanium Ti'""^'' 50 Tungsten (Wolfram) -y^i.^dvi j84 Uranium ■gr""'"' 120 Vanadium Vd"'""" 51-3 Yttrium Y" ; 61-7 Zinc Zn« 65 Zirooaium Zr". 89'6 APPENDIX II. I. — Syllabus op Elementary Course in Inorganic Chemistry. (From the "Science Directory.") Pupils presenting themselves for examination wUl be expected to possess a knowledge of the following subjects : — Definition of chemistry. Simple and compound matter. Different modes of chemical action. Combining weights. Volume weights. Principles of chemical nomenclature. Symbolic notation. Graphic notation. Chemical formulae. Chemical equations. Atomicity of [elements. Simple and compound radicals. Definition of a compound radical. Clas- sification of all elements into metals and non-metals, into positive and negative elements. Classification according to atomicity. French and English systems of weights and measures. Conversion of English into French weights and measures. The crith and its uses. Hydrogen. — Its preparation and properties. Chlorine. — Preparation of chlorine from hydrochloric acid. Analysis and synthesis of hydrochloric acid. Properties and reactions of hydrochloric acid. Oxygen. — Its preparation and properties. Allotropio oxy- gen or ozone. Formation and reactions of water. Prepara- tion and properties of hydroxy! Compounds of chlorine • with oxygen and hydroxyl. Boron. — How it occurs in nature. Its allotropic modifi- cations. Boric anhydride. Boric acids. Carhon.—l.i& preparation and allotropic forms. Prepara- tion and properties of carbonic oxide and carbonic anhydride. M 178 ELEMENTARY CHEMISTRY. Niirogm. — Its preparation and properties. Compounds of nitrogen with oxygen and hydroxyl. Compound of nitrogen ■with hydrogen. Ammonia. Ammonic salts. Sulphv/r. — Its properties and allotropic modifications. Compounds of sulphur with positive elements. Compounds of sulphur with oxygen and hydroxyl. II. — Extract fkom a Kepoet by Dr. Feankland. In conclusion, I have to state that it would, in my opinion, be desirable to call the attention of such science teachers as give instruction in chemistry to the circumstance, that the unsatisfactory results of the examinations, in the elementary stage of inorganic chemistry, are obviously due chiefly to the want of sufficient experimental illustrations in the classes. It would be well to bring to the notice of such teachers that the performance of the following experiments, at least, ought to be witnessed by every pupil who comes up in the elemen- tary stage, and that, for the future, it will be assumed that such has been the case : — 1. Ignition of platinum wire and of magnesium wire in air, to show effect of chemical action in the second case. 2. Transformation of liquids and gases into solids, and vice versA, by chemical action. 3. Ignition of phosphorus by red-hot bar of iron, placed at a dis- tance of several inches. 4. Attraction of a suspended wooden rod by an electricaUy-excited glass tube, held at a distance of several inches. 5. A glass rod moistened with concentrated sulphuric acid held close to a small heap of a mixture of sugar and potassic chlorate pro- duces no effect, but inflames the mixture as soon as the rod is brought into actual contact with it. 6. An example of direct chemical union: — Combination of hydrogen and chlorine by heat. 7. Chemical displacement: — Precipitaition of copper from a solution of cupric sulphate by a bright plate of iron. 8. Mutual chemical exchange: — Add solution of potassic iodide to solution of mercuric chloride. 9. Re-arrangement of elements in a compound: — Coagulation of albumen by heat. 10. Eesolution of a compound into its elements, or into two or more less complex compounds: — Heat mercuric oxide and show oxy- gen and mercury produced. 11. Electrolysis of water, with demonstration of properties of the separated gases. APPENDIX. 179 12. Preparation of hydrogen by the action of sodium upon water. 13. Preparation and collection of hydrogen from zinc and dilute sulphuric acid. 14. Preparation and collection of hydrogen from zinc and solution of caustic soda. 15. Burn jar of hydrogen mouth upwards, and another with the mouth downwards. 16. Pour hydrogen upwards from one jar into another. 17. Extinguish a burning taper in hydrogen. ' 18. Preparation and collection of chlorine from manganic oxide and hydrochloric acid. 19. Bleach carmine paper in the gas. 20. Electrolysis of solution of hydrochloric acid. Collect gases separately, and show their properties. 21. Bum jet of hydrogen in chlorine. 22. Prepare hydrochloric acid gas from common salt and sulphuric acid. Collect over mercury or by displacement of air. 23. Show by test papers alkalinity of solution of potash, acidity of solution of hydrochloric acid, and neutrality of liquid produced by the mixture of these solutions in suitable proportions. 24. Extinguish taper in hydrochloric acid gas. 25. Show solubility of hydrochloric acid gas in water. 26. Prepare and collect oxygen from mercuric oxide, potassic chlorate, a mixture of potassic chlorate and manganic oxide, and by the transmission of chlorine and steam through a red-hot tube. 27. Burn a taper in oxygen, and show re-kindling from glowing wick. 28. Combustion of phosphorus in oxygen. 29. Combustion of bundle of steel wire iu stream of oxygen. 30. Explosion of mixture of oxygen and hydrogen. 31. Show formation of water from jet of hydrogen burning in oxygen. 32. Show neutral reaction of water. 33. Show formation of ozone by action of moist phosphorus upon air. Show action of ozonised air upon paper imbued with starch and potassic iodide. 34. Preparation of hydroxyl by passing a stream of carbonic anhy- dride through water containing baric peroxide in suspension. 35. Heat hydroxyl in test-tube, and show evolution of oxygen. 36. Add argentic oxide to hydroxyl, and show production of oxy- gen and metallic sUver. 37. Wash with solution of hydroxyl paper, discoloured with plumbic sulphide. 38. Wash with solution of hydroxyl white oil paint similarly dis- coloured. 39. Prepare chloric peroxide (CI2O4) in test-tube, and explode it with a hot wire. 40. Add sulphuric acid to a mixture of phosphorus and potassic chlorate, under water. 180 ELEMENTARY CHEMISTET. 41. Prepare hypoohlorous acid by agitating cMorine with mercuric oxide and water. i^Oc 42. Transmit current of chlorine through boiling milk of lime, add potassic chloride to filtered product, and then crystaUise out potasaic chlorate. 43. Preparation of boric acid from borax and hydrochloric acid. 44. Flame of a solution of boric acid in alcohol. 45. Preparation of charcoal from wood in test-tube. 46. Show crust upon lime-water after exposure to air. 47. Add hydrocmoric acid to pieces of old mortar, and show that carbonic anhydride is evolved. 48. Breathe through lime-water. 49. Bum candle in glass cylinder fiUed with air, and show forma- tion of carbonic anhydride by lime-water. 50. Prepare and collect carbonic anhydride from limestone, chalk, or marble, and hydrochloric acid. 51. Show that soap-bubbles, filled with air, float on carbonic an- hydride. 52. Pour solution of litmus into jar of carbonic anhydride. 53. Immerse lighted taper in jar of carbonic anhydride. 54. Pass carbonic anhydride through an iron tube filled with char- coal and heated to redness. Show the inflammability of the carbonic oxide produced. 55. Prepare and coUeot carbonic oxide from a mixture of oxalic acid and sulphuric acid. 56. Prepare and coUeot carbonic oxide from a mixture of sulphuric acid and yellow prussiate of potash. 57. Inflame jar of carbonic oxide, and immerse lighted taper in the gas. 58. Agitate lime-water with carbonic oxide, and show that no tur- bidity is produced; inflame the gas, agitate again, and demonstrate the production of carbonic anhydride. 59. Prepare nitrogen by burning phosphorus in atmospheric air. 60. Prepare and collect nitrogen from ammonic nitrite, or from a mixture of potassic nitrite and ammonic chloride. 61. Prepare and coUeot nitrogen by passing chlorine into'strong solution of ammonia. 62. Immerse a burning taper in nitrogen. 63. Pass electric sparks through air in a small vessel containing litmus paper. 64. Show neutrality of nitrogen. 65. Prepare and collect nitrous oxide from ammonic nitrate. Show production of amnionic nitrate from nitric acid and ammonic car- bonate. 66. Show that feebly-burning sulphur is extinguished in nitrous oxide, and that sulphur strongly ignited continues to bum in the gas with augmented bnlliancy. 67. Immerse a burning taper in nitrous oxide. 68. Prepare and collect nitric oxide from copper and nitric acid. Appmmt. iSi 69. Add nitric oxide to air in a jar over ■water. 70. Immerse a burning taper in nitric oxide. 71. Show that feebly-burning phosphorus is extinguished in nitric oxide, and that strongly-ignited phosphorus burns in it brilliantly. 72. Preparation of nitrous anhydride from nitric acid and arsenious anhydride. 73. Show the reducing action of nitrous acid by adding a solution of potassic permanganate to an acidified solution of a nitrite. 74. Show the oxidising action of nitrous acid by adding a solution, of a nitrite to acidulated water tinted with magenta. 75. Prepare nitric peroxide (N2O4) by mixing nitric oxide and oxygen. 76. Prepare nitric acid from potassic nitrate and sulphuric acid_ 77. Prepare nitric acid by the direct combination of nitric peroxide and hydroxyl. 78. Pour nitric acid upon copper clippings. 79. Deflagrate a mixture of nitre and charcoal. 80. Add strong nitric acid to gold-leaf. 81. Add strong hydrochloric acid to gold-leaf. ' 82. Mix the two last-named liquids together and show that the gold-leaf then dissolves. 83. Prepare gaseous ammonia from a mixture of ammonio chloride and slaked lime. Collect over mercury or by displacement. 84. Demonstrate solubility of ammonia in water. 85. Immerse a taper in gaseous ammonia. 86. Bum a stream of gaseous ammonia at the end of a hot tube. 87. Show alkalinity of ammonia. / 88. Demonstrate volatility of ammonio chloride. ' 89. Show production of ammonic chloride from gaseous ammonia and hydrochloric acid gas. 90. Prepare plastic sulphur. . 91. Melt sulphur in test-tube and show changes as the temperature increases. 92. Prepare and collect sulphuretted hydrogen from ferrous sul- phide and dilute sulphuric acid. 93. Burn jet of sulphuretted hydrogen, and hold over the flame a glass rod moistened with ammonia. 94. Show acidity of sulphuretted hydrogen. 95. Decompose sulphuretted hydrogen- by sulphurous anhydride. 96. Decompose sulphuretted hydrogen by chlorine. 97. Pass sulphuretted hydrogen gas through an aqueous solution of each of the following substances: — Arsenious acid, cupric sulphate, plumbic acetate, tartar emetic, and zincic sulphate. 98. Prepare sulphurous anhydride by the action of copper upon sidphurio acid. Collect over mercury or by displacement. 99. Show action of sulphurous anhydride on litmus paper. 100. Condense sulphurous anhydride in glass tube immersed in a mixture of snow and salt. 101. Immerse taper in sulphurous anhydride. 182 ELEMENTARY CHEMISTKY. 102. Demonstrate solubility of sulphurous anhydride in water. 103. Bleach infusion of rose leaves by sulphurous acid, and then restore the colour by addition of dilute sulphuric acid. 104. Convert sulphurous acid into sulphuric acid by — 1, E?cposing its aqueous solution to the air; and, 2, By heating its aqueous solution -with nitric acid. 105. Demonstrate the formation of sulphuric anhydride by passing sulphurous anhydride and oxygen over ignited spongy platinum. 106. Show the formation of sulphuric acid by the direct union of sulphurous anhydride and hydroxyl. 107. Prepare sulphuric acid by mixing sulphurous anhydride, oxygen or air, nitric peroxide, and steam, in a flask. 108. Add one volume of concentrated sulphuric acid to two volumes of strong syrup of white sugar placed in a capacious vessel. 109. Demonstrate the spontaneous decomposition of free hyposul- phurous acid, by adding dilute sulphuric acid to a solution of sodic hyposulphite. ' According to g 45 of the Directory, special extra payments are made on account of students who show a good knowledge of experi- mental chemistry or laboratory practice. This knowledge is at present tested by questions set with the ordinary examination paper in May. In the elementary stage the course of laboratory instruction to which the questions are confined is the preparation of the elements and compounds above enumerated, and the methods of experimen- tally demonstrating their properties, These questions are, as much as possible, so framed as to prevent answers being given by pupUs who have obtained their information merely from books and oral instruction. INDEX. Acid, boric, 122. „ chloric, 129. „ chlorous, 126. „ hydriodic, 62. „ hydrobromic, 61. 5, hydrochloric, 58. „ hydrofluoric, 63, „ hydrosulphuric, 80. t, liypochlorous, 131. „ metaboric, 122, „ nitric, 133. ,, nitrous, 138. ,, sulphuric, 147. ' „ sulphurous, 144. Acid salts, definition of, 133. Acids, formation from anhydrides, 128. ,, monobasic, constitution of, 128. Action, chemical, modes of, 152. Aflanity, chemical, 38. Air, atmospberic, 42. „ composition of, 44. Alkalies neutralised by acids, 59. Allotropism, 75. Ammonia, S3. „ absorption by water, 85. „ combination with acids, 87. „ composition of, 87. „ decomposition by beat, 85. „ „ by potassium, 87. Ammonia gas, preparation of, 84. „ properties of, 87. „ sources of, 84, Ammonium, 87. „ amalgam, 89. „ chloride, 84., ., nitrate, preparation of, 14-1. „ „ decomposed by heat, 141. „ nitrite, decomposed by heat, 142. Ammonoxyl, 127. Anaesthetic, use of nitrous oxide as an, 142. Anhydride, sulpburic, 147. ,, sulpburous, 146. Anhydrides, conversion into acids by water and hydroxyl, 149. Animsd charcoal, 96. . , , a decolourising agent, 96. Antimonietted hydrogen, 93. Antimonoxyl, 120. Aqua regia, 134. Arsenietted hydrogen, 93. Atmosphere, composition of, 44.' Atom, definition, of, 67. Atomicities, classification of elements by, 175. Atomicity, absolute, 107. „ varying, 107. Atomic theory, 68. „ weight, 66. „ weights of elements, table of, 175. Base, definition of, 60. Borates, 122, Borax, 122. Boric acid, 122v Boron, 122. Bromine, 54. „ etymology of, 55. Calcium carbonate, 109. „ fluoride, 63. \ Carbon, allotropy of, 95. „ combustion in oxygen, 35, 96. „ oxides of, 35, 113. Carbonates, 95. decomposed by dilute acids, 110. Carbonic anhydride, 35, 111. „ action oulime-water, 114. „ absorption by water, 112. „ molecular weight of, 113. „ preparation of, 111. „ properties of, 112. , , volume weight of, 112. Carbonic oxide,' preparation from car- bonic anhydride, 113, ,, preparation from oxalic acid, 114. ,, preparation from potas- SLC ferrocyanide, 114. „ properties of, 114. Chalk, 109. Charcoal, 9Q: Chemical action, modes of, 151. „ affinity, definition of, 39. „ change distinguished from phyi sical change, 36. Ohemistiy, definition of, 151. Chili saltpetre, 132. Chlorates, 129. 184 ELEMENTAUY CHEMISTRY. Chlorates, action of salphuric acid upon, 130. Chloric acid, 126. „ peroxide, 130. Chlorides, nature of metallic, 60. „ preparation of, 53, 60. Chlorine, 47. „ action on meta^, 53. ,, „ water, 50. Chlorine and hydrogen, 52. ,, „ exploded by sun- light, 50. Chlorine, bleaching by, 50. ,, combustion of taper in, 53. „ compounds of, witb oxygen, 53. „ etymology of, 49. „ maniLfactureol from, oxides of manganese, 49. „ moIecxUar and volume weight of, 50. ,,, prepai-ation of, 47. ,, properties of, 60. „ water, 50, Chlorites, 128. Combination by volume, 104. Combining proportions, 104. „ weight, relative, 102. Combustion, 35. Compound radical, definition of, 106. Constant cbemical combiniog propor- tions, 66. Constitution of salts, 60. Copper, action of nitric acid on, 140. „ action of sulphuric acid on. Hi. Critb, 24. Density, or specific gravity of gases, 66. Displacement, chemical change by, 152. „ collection of gas by, 48. Divalentic, explanation of term, 105. Dyads, 105. Kau de Javelle, 131. Electrolysis of hydrochloric acid, 61. „ water, 21, 22. Element, definition of, 40. Elements, table of, 175. Explosion of hydrogen and air, 16. „ „ oxygen, 20. Eluorine, 56. Fluor-spar, 56. Foimuiie, molecular, 66. Gas-holder, 29. „ jars, 32. Gold, dissolved by aqua regia, 134. Graphic notation, 106, 120. Graphite, 96. Grouping elements, 105. Halogen, etymology of, 67. Halogens, 67. Haloid saltBf 65. Herepatb's blowpipe lamp, 135. Hydric peroxide, or hydroxyl, 116.' Hydriodic acid, 42. Hydro-acids, 65. Hydrobromic acid, 61, Hydrocarbons, 95. Hydrochloric acid, 58. „ ■ absorption bywater, 59. „ action on metallic oxides, 60. „ composition byvolume, 52. „ electrolysis of, 61. „ gas, preparation of, 68. , , liquid, 59. „ properties of, 59. „ synthesis of, 52. „ volumetrical composi- tion of, 52. ,, gas, dry, preparation of, 49. Hydrofluoric acid, 63. Hydrogen, 9. ,, ' antlmonietted, 03. ,, araenietted, 93. „ displacement by sodium, 9. ,, etymology of, 11. ,, fiame, 15. ,, phoaphoi'etted, 92, „ preparation of, 10. 1 „ properties of, 11. „ sulphuretted, 76. „ the unit of atomicity, 103. Hydroaulplitiric acid, action on solutions '^ of metals, 80. „ preparation of, 76. „ propel-ties of, 78. , solution of, 79. „ volume weight of, 78.' Hydrosulphyl, 121. Hydroxyl, 119. „ preparation of, 116. „ its oxidising power, 118. „ its action on anhydrides, 118. Hypochlorites, 130. „ as bleaching agents, 130. „ as disinfectants, 131. Hypochlorous acid, 131. Iodides, preparation of, 56. Iodine, 65. „ etymology of, 55. Iron pyrites, 73. „ sulphide, preparation of, 76, Laughing ga^, 142. „ preparation of, 142. „ properties of, 142, „ volumes, 142. liime-water, 109. Magnesia, 32. Magnesium, burning in air, 31. INDEX. 185 Magnesium^ burning in oxygen, 32. ' Mechanical mixture, 42. Mercuiy, oxidation of, 27. Metal, definition of, 39. Metalloids, classification of, 89. , , distinction of from metals, 89. Metalloxyls, 120. Modes of chemical action, 151. Molecule, definition of, 25. < Monad, compound radicals, 106. Multiple proportions, 69. „ law of, 69. Negative electrode, 20. ,, elements, 40. Neutralization, explanation of term, 60. Nitrates, occurrence in nature, 132. Nitre, 132. „ cubic, 132. Nitric acid, 133. „ action on metals, 134. 5, „ orgaiiiciTiatter,134, „ J, phosphorus, 134. „ ,, sulphur, 134. „ properties of, 133. Nitric oxide, 140. „ a "carrier" of oxygen, 140. „ action of air on, 140. „ composition of, by volume and by weight, 140. Nitric peroxide, 140. „ composition of, by volume and by weight, 137. Nitrites, 138. Nitrogen, 43, 142. „ function in air, 143. „ preparation of, from air, 143. „ properties of, 44. Nitro-hydrochloric acid, 134. Nitrous acid, 138. „ oxidising and reducing ac- tion of, 138. Nitrous anhydride, 138. „ composition of, by volume and by weight, 138., Nitrous oxide, 142. , composition of, by volume and by weight, 142. „ preparation and properties of, 142. ^ Non-metallic elements, list of, 40. Non-metals or metalloids, distinction of, from metals, 39. Notation, chemical, 69. „ graphic, 106. Normal salts, definition of, 149. Oil of vitriol, 150. Oxalic acid.action of sulphuric acidon,114. Oxide, carbonic, 113. „ „ its properties, 114. „ „ its preparation, 113. jt nitric, 140. Oxide, nitrous, 142. Oxides, metallic, action of hydrochloric acid on, 60. „ salifiable, 60. Oxygen, 26. ,, combu.9tion in, 82, „ from mercuric oxide, 28, „ preparation from potassic chlo- rate, 29. „ properties of, 35. Oxy-salts, nomenclature of, 126. Ozone, an allotropic form of oxygen, 116. „ preparation of, 116. „ properties of, 116. Peroxide of hydrogen (hydroxy!), 116. Phosphoretted hydrogen, 91. Phosphoric anhydride, 34. Phosphorus, 89. ;„ action of potash on, 91. „ combustion in o^gen and air, 34. „ properties of, 90. Pipette, 59. Platinum black, or spongy platinum, 146, Plumbago, 96. Plumbic nitrate, decomposition of by heat, 140. Pneumatic trough, 12. Potassic chlorate, preparation of, 129. „ feiTocyanide, carbonic oxide pre- pared from, 114. ,, sulphate, 133. Quantivalence of elements, 105. Questions and exercises, 159. Radicals, compound, definition of, 1.06. Keducing agent, sulphurous acid as a, 147. Relative combining weights, 66., Sal-ammoniac, 84. Saltpetre, 132. Chili, 132. Salts, acid, 149. „ haloid, 65. -. - ,, oxy, nomenclature of, 126. Selenium, 81. Silica, 100, Silicates, 100. Silicic acid, 101.. „ anhydride, 100. ,, hydrate, 100. Siliciuretted hydrogen, 101. Sodic biborate, 122. ,, chloride, 60. ,, hydrate, 60. „ hypochlorite, 131. „ nitrate, or cubic nitre, 132, „ sulphate, acid or hydric, 150. Sodium, action on hydrochloric acid gas, „ action on water, 9. 186 ELEMENTAUT CHEMISTRY. Steam, compoaitioti by volume, 23. Sulphates, preparation from sulphurous anhydride and metallic peroxide, 147. Sulphides, 76. „ native, 76. Sulphites, 150. ,, acid or hydric, 150. Sulphur, 72. „ aJlotropic forma of, 75. ,, and ii-on, 73. „ and oxygen, 34. „ changes on heating, 73. „ distillation of, 74. , , extraction from iron pyrites, 72. „ flowers of, 72. „ occurrence of, in nature, 72. If properties of, 75, „ roll, 72. Sulphuretted hydrogen, molecular for- mula, 80. „ hydrogen, molecular weight, 80. „ hydrogen, preparation of, 78. „ hydrogen, propertiesof, 78. „ hydrogen, solution of, 79. Sulphuric acid, 150. „ action, on metallic hy- drates, 149. „ preparation on small Bcale, 150. „ viewed as a compound of sulphurous anhydride and hydric per- oxide, 147. Sulphuric acid viewed as a compound of sulphuric anhydride and water, 147. Sulphuric anhydride, 147. „ synthesiB of, 147. Solphuroiis acid, 147. 1) a reducing i^ent, 145. Sulphurous acid, action oil hydrio per- oxide, 147. „ action on hydrosul- phui-ic acid, 78. ,, action on nitric per- oxide, 149. Sulphurous anhydride, 146. „ preparation of, 144. ,, properties of, 145. Symbolic formulae, 106. Table of names, atomic weights, and symbols of elements, 175. „ non-metallic elements, 40, Theory, atomic, 70. Tin, action of nitric acid on, 134. Tincal, 122. Use of the crith, 24. Vitriol, oil of, 150. Volumes, combining, 66. Volumetrical composition of hydrochloric acid, 52. „ composition of steam, 23. Water, composition of, by volume, 23, ,, composition of, by weight, 24. „ decomposed by voltaic action, 24, ,, electrolysis of, 21. Weights and measures, 164. White arsenic, 92. YelloTt^ pruBsiate of potash, its deoompo- sition by Bulphuiic acid, 1144 Zinc, burning of, in air, 32, „ in oxygen, 82. WILLIAM COLLINS AND COMPANY, PHINTERS, GLASGOW, PUTNAM'S SERIES OF SCHOOL HISTORIES. These volume "have been prepared with great care by leading instructors, and are comprehensive as well as concise. They are of interest to the general reader, while planned especially for the needs of the class-room. HISTORY OF ENGLAND. For Junior Classes. By L. Schmitz, LL.D. With Illustrations and Historical Map. 16mo, cloth, $1. "Dr. Schmitz'a Tolume is sensibly written." — Athenmtm. " Dr. Schmitz has the pen of a ready writer. He has the art of conipreSMng what he has to say in a few words, and yet rendering his narrative lively nnd pictui-esqne. It is attractively illnstvated, and a capital historical map of the Britii^h Isl^iida adds to its value.'* — National Schoolmaste}', HISTORY OF SCOTLAND, Witli Historical Map and Illustrations. 16mo, cloth, $1, " This well printed and bound achool-book has been written on one of the best models, and is adapted from oiio of the most reliable of our histories— to wit, Sir Walter Scott's ,' Tales of a Grandfather.' We have no little satisfaction in recom- mending it to teachers and parent's throughout the country. "-r-ffreenocA Telegj'ax>h, HISTORY OF GREECE. By L. Schmitz, LL.I). Illustrated, with Map. 16mo, cloth, 75c. " This little work is likely to be the History of Greece for junior classes for some time to come." — Schoolmaatcr. " The work before us is a valuable addltioii to our school histories of Greece, and It beat's a character somewhat unique, in that it is a reliable history for junior classes. An excellent fe:i,ture in this work is that a continuation is given in the appendix from the date where the history ceases, B.C. 146, to the accession of King George in 1S62. This part of the book has been written by A. Grenadios, late Professor in the University of Athens. A laige coloured map of Ancient Greece adds to the value of the yfork."— National Sckootmaster, HISTORY OF ROME. By L. Schmitz, LL.D. Illustrated, with Map. IGmo, cloth, 75c, '* A clear, scholarly, correct presentation of tho scope of the wonderful history of that wonderful people." — Prof. J. P. Lacroix. HISTORY OF INDIA. By W. C. Peaece. Illustrated, with Map. 16mo, cloth, $1. HISTORY OF FRANCE. By StJTHEELAND Menzies. Illustrated, with Map. 16mo, cloth, $1. "A carefully studied, comprehensire, and picturesque narrative," — Indianapolis Journal, LANDMARKS. OF MODERN HISTORY. By Rev. C. S. Dawe, B.A., London. 16mo, cloth, $1. " For senior pupils who have mastered the outlines of British history, this volume would. prove an interesting source of study: and for pupil teachers and otheiB anxious to obtain a bird's-eye view of historical factSj the ' Landmarks ' will form a very convenient text-book." — Schoolmaetej'. -