CORNELL UNIVERSITY LIBRARY Bequest of HERBERT HICE WHETZEL PLANT PATHOLOGY Cornell University Library QD 33.R38 1900 The elements of chemistry; a textbook for 3 1924 002 975 898 ™„, Cornell University Library The original of tliis bool< is in tine Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924002975898 AMERICAN 8CIENGE SERIES, ELEMENTARY COURSE THE ELEMENTS OHEMISTET A TEXT-BOOK FOR BEGINNERS * IRA REMSEN Profeasor of Cfiemistry in the Johns Hopkins Unvoersity NEW YORK HENRY HOLT AND COMPANY 1900. Copyright 1886, BY HENRY HOLT & CO, ROBERT DRUMMOND, PRINTER, NEW YORK. PREFACE. This book is written upon much the same plan as the Briefer Course in the same series. It is, howeyer, mate- rially simpler in many parts, and is in every way better adapted to younger pupils. In the opinion of the author a rational course in chemistry, whether for younger or older pupils, is something more than a lot of statements of facts of more or less importance; a lot of experiments of more or less beauty; or a lot of rules devised for the purpose of enabling the pupil to tell what things are made of. If the course does not to some extent help the pupil to think as well as to see, to reason as well as to observe, it does not deserve to be called rational. Not only must the pupil perform experiments, but he must know why he performs them, and what they teach. A good plan to follow is to talk over a certain part of the subject, showing how to con- struct the apparatus necessary for some of the experiments, and stating in a general way what is to be learned; then to let the pupil perform the experiments with the aid of the book and the teacher; and afterwards to make the experiments the basis for questioning. In this way the pupil will be- come observant, and at the same time he will discover when his experiments have been performed in the wrong way. It is better to go slowly at first so as to allow the pupil time to become familiar with his surroundings and to enable IV PREFACE. him to learn how to work at the laboratory desk. A badly constructed piece of apparatus or an experiment badly per- formed in any way should not be allowed to pass. Experi- ments should be repeated as many times as may be neces- sary to secure accurate work. Chemical theories are treated in a subordinate way, as it is believed that the attention should first be directed to the simpler facts of the subject and the methods by which these facts are learned. A brief statement of a few of the pre- yailing hypotheses is given in Chapter XIV. Whether it will be advisable for the pupils to spend any time in study- ing this chapter will depend upon their age and their men- tal attainments. If all they can do is to learn the statements by heart and repeat them without showing any signs of comprehension, then unquestionably the chapter should be omitted. It should be remembered that the object of the course laid down in this book is not to make chemists, but to help to develop sound minds, and at the same time to awaken interest in a set of natural phenomena of great im- portance to mankind. It is quite possible to teach the sub- ject in such a way as to destroy all interest in chemical phenomena and to make the pupil shudder whenever a chemi- cal formula is mentioned. There is no better way to accom- plish the latter result than by giving prominence to incom- prehensible theories and forcing the pupils to master a lot of equations which represent facts of which they are entirely ignorant. Baltimobe, December 37, 1886. CONTENTS. CHAPTER I. PAGE Chemical Changes— Physical Changes ..... . . 1 CHAPTER II. The Chemistry of the Air „ 16 CHAPTER III. Oxygen 81 CHAPTER IV. Combining Weights 31 CHAPTER V. Nitrogen 37 CHAPTER VI. Water 41 CHAPTER VII. Hydrogen 45 CHAPTER VIII. Water (continued) 53 CHAPTER IX. Compounds of Nitrogen with Hydrogen and Oxygen .... 66 CHAPTER X. Chlorine and its Compounds with Hydrogen and Oxygen. . . 77 VI CONTENTS. CHAPTER XI. Acids— Bases — Neutralization— Salts . . CHAPTER Xn. Carbon 95 CHAPTER XIII. Compounds of Carbon with Hydrogen, with Oxygen, and with Nitrogen 106 CHAPTER XrV. Atomic Theory — Atomic Weights — Molecular Weights — ^Valence — Classification of the Elements 124 CHAPTER XV. The Chlorine Family: Chlorine, Bromine, Iodine, Fluorine. . 133 CHAPTER XVI. The Sulphur Family: Sulphur, Selenium, Tellurium .... 139 CHAPTER XVII. The Nitrogen Family: Nitrogen, Phosphorus, Arsenic, and Anti- mony — Boron and Silicon 153 CHAPTER XVIII. Base-forming Elements — General Considerations 161 CHAPTER XIX. The Potassium Family: Potassium, Sodium, (Ammonium) . . 165 CHAPTER XX. The Calcium Family: Calcium, Barium, Strontium . . . 178 CHAPTER XXI. The Magnesium Family: Magnesium, Zinc, Cadmium — The Copper Family: Copper, Mercury, Silver 185 CONTENTS. VU CHAPTER XXII. PAGB The Aluminium Family — The Iron Family: Iron, Cobalt, Nickel 196 CHAPTER XXIII. Manganese— Chromium — Uranium — Bismuth 206 CHAPTER XXIV. Lead— Tin— Platinum— Gold 209 CHAPTER XXV. Some Familiar Compounds of Carbon 216 CHAPTER XXVI. Other Compounds of Carbon 231 APPARATUS AND CHEMICALS, Fob the benefit of those who have no laboratory at command, and who may wish to make arrangements for going through with the experimental work, the following list has been drawn up. In it is included everything necessary to perform the experiments on a small scale. Should it be desired to fit up a room with conveniences for students, the amount of apparatus necessary would depend upon the number of students, but for each individual the expense would be small, as many of the pieces of apparatus, such as the galvanic battery, burette, weights, scales, etc., need not be multiplied. In place of some of the pieces of apparatus described in the book, ordinary kitchen utensils will answer: thus, for example, instead of the trough for collecting gases, a tin pan or a deep earthenware dish may be used; instead of the water-bath, a stew-pan, fitted with two or three different-sized tin or sheet-iron rings; and in place of glass cylinders for working with gases, wide- mouthed cheap bottles. The publishers do not deal in chemicals and apparatus, nor, they may as well say, receive commissions on them. Any orders should be sent direct to the dealers. Messrs. Eimer & Amend, Nos. 305 to 211 Third Avenue, N"ew York, whom the publishers take the responsibility of recommending as thoroughly reliable, will furnish each of the following articles at the price given. If several pieces of the apparatus in List No. 1 are taken, a discount of 10 per cent will be made; on a complete set 30 per cent discount will be allowed; on three or more sets, 35 per cent. One or more of the articles in List No. 3, if not marked "net" or "30 per cent," will be supplied at 35 per cent discount if ordered with sets of the apparatus in List No. 1. A discount of 10 per cent will be given on a complete set of the chemicals, and of 15 per cent on three or more sets. APPARATUS AND GSBMIOALS. IX For most items less than the whole set, there will have to be a small additional charge for packing. It should be realized, however, that usually the charge for packing one article must be as large as for several. Some articles can, of course, be mailed without any charge for packing. List 'Eo. 1. A list of apparatus and chemicals necessary for performing all of the experiments in Remsen's Elements of Chemistry, with the excep- tion of experiments Nos. 34, 36, 46, 47, 48, 49, 51, 65, 66, 79, 80, and 113. To perform these latter experiments, the apparatus given in List No. 2 is required. APPARATUS. 1 Nest Beakers, 1-3 $0 40 1 Jeweller's Blowpipe, 8 in 15 7 Wide-mouth Flint Bottles, two each, 3, 4, 8 oz., and one 32 oz. 50 1 Bunsen's Burner with regula- tor, or 6 oz. glass alcohol lamp, same price 50 1 5-in. U-tube 85 2 doz. Assorted Corks 20 1 Nest Hessian Crucibles, "threes" 6 1 IM-in- Porcelain Crucible 18 1 25 CO Grad. Cylinder 50 1 Deflagrating Spoon 25 1 each Evaporating Dish, ^ andSHin '*<' 1 LeadDish,2in 25 1 Eound File, 5 in 25 1 Triangular File, 5 in 25 1 Pack White Filters, 4 in 12 4 Flasks: one 4 oz., two 8 oz., onel6oz 80 1 Steel Forceps 20 2 Funnels, 21^ in 24 2 Funnel Tubes, one 10 in., one 15in 35 1 Gas Bottle, 8 oz., with 2-hole B Stopper 40 !4 lb. Assorted Glass Tubing, 4-7 15 2 Sheets each Eed and Blue Lit- mus-paper 20 1 Horseshoe Magnet, 3 in 20 1 Porcelain Mortar and Pestle, 3^in 45 1 Piece Platinum Foil, 1x1 1^ in. . 60 6 in. Medium Platinum Wire 20 1 Plain Eetort, 8 oz 80 1 Stoppered Retort, 16 oz 65 3 ft. Rubber Tubing for gas, ^ in. 39 (Only needed if Bunsen's Burner is used.) 2 ft. Rubber Tubing (for connec- tions) 20 1 3U in. Sand Bath $0 15 1 Hand Scale, with weights 85 1 Test Tube stand 30 12 Test Tubes, 5 in 30 1 Test Tube Brush 5 1 Test Tube Clamp 20 llronTripod 30 2 2-in. Watch-glasses 10 1 5-in. Water-bath 1 00 2 Wire Clamp Supports 2 00 $14 74 CHEMICALS. 4 oz. Acid Acetic, pure (bottle 5 cents extra) $0 10 4 oz. Acid Arsenious 10 16 oz. " Hydrochloric (bottle 15 cents extra) 10 8 oz. Acid Nitric (bottle 12 cents extra) 10 2 oz. Acid Oxalic 10 16 oz. " Sulphuric (bottle 12 centsextra) 10 1 oz. Acid Tartaric 10 2 oz Alcohol, for experiments only (bottle 4 cents extra). . . 10 8 oz. Alum 10 4 oz. Ammon. Chloride 10 8 oz. " Hydrate, concen- trated (bottle 10 cents extra) 10 4 oz. Ammon. Nitrate 10 2 oz. Antimony, powdered 10 2 oz " and Potassium Tartrate 20 2 oz. Barium Chloride 10 4 oz. Calcium Chloride, fused. . . 10 4 oz. " Sulphate 10 4 oz. Carbon Disulphide (bottle 5 cents extra) 10 8 oz. Animal Charcoal,powdered 10 8 oz. Copper Foil 30 4 oz. '■ Sulphate 10 1 oz. " Oxide 15 4 oz. Fluorspar, powdered 10 APPABATm AND GEEMIGAL8. 1 oz. Indigo.... JO 10 1 oz. Iodine (bottle 3 cents ex- tra) 40 4 oz. Iron Filings, fine 10 8 oz. " Sulphide 10 4 oz. " Sulphate 10 4 oz. Lead Sheet 10 4 oz. " Acetate 10 2 oz. •' Nitrate 10 1 oz. " Peroxide 10 2 oz. " Sesquioxide 10 1 oz. Litmus 10 ^ dram Magnesium Ribbon 20 1 lb. Manganese Dioxide, pow- dered 10 1 oz. Mercury Eed Oxide 10 1 oz. Nutgalls, powered 10 2 oz. Parafflne )0 1 oz. Phosphorus (bot.lOo. extra) 15 1 dram Potassium 60 2 oz. *' Bromide 10 4 oz. " Carbon, (bot. 5 cents extra) 10 4 oz. Potassium Chlorate $0 10 4 oz. " Dichromate — 10 2 oz. " Ferrocyanide .. 10 4 oz. '* Hydrate Sticks (bottle 5 cents extra) 20 1 oz. Potassium Iodide (bottle 5 cents extra) 30 4 oz. Potassium Nitrate 10 2 oz. '^ Permanganate. 10 1 dram Sodium (bot. 3c. extra) . , 10 2 oz. *' Acetate 10 2 oz. " Bicarbonate 10 4 oz. " Biborate (Borax) 10 4 oz. " Hydrate (bottle Scentsextra) 20 4 oz. Sodium Nitrate 10 4 oz. " Sulphate 10 8 oz. Sulphur, roll 10 4 oz. Tin, granulated 10 16 oz. Zinc, granulated...., 30 2 oz. " Sulphate 10 S8 00 List N"o. 3, In order to perform experiments Nos. 34, 36, 46, 47, 48, 49, 51, 65, 66, 79, 80, and 113, the following additional apparatus is necessary: 1 Oxyhydrogen Blowpipe $6 CO 2 Gasholders for Oxygen and Hy- drogen. 5 gal 26 50 1 Liebig's Condenser, 15 in 1 50 1 Burptte, 50C.C, ^o 1 70 1 Pinchcook 25 1 Copper Air-bath, 6x8 in 6 00 1 Kellog-Bunsen's Vapor Lamp, complete (a substitute in case gas IS not used as fuel) (net).. 10 00 $59 55 2 <5t. Bunsen's Cells $3 00 2 Platinum Plates, IxJ^ inch 40 1 Charcoal Furnace,18in.(20p.c.), 2 00 or 1 Charcoal Furnace, 24 in., $3 00(30p.c.);orl 10 burnerGas Combustion Furnace . $20 00 1 25-in. hard Glass Tube, 1 in. bore (net) 1 00 or 1 25-in. Porcelain Combus- tion Tube, 1 in. bore. . ..%\ 75 3pt. WoulfE's Bottles, 2-necked.. 1 93 1 bard Glass Tube, drawn out, 12xi^in.bore S5 THE ELEMENTS OF CHEMISTRY. CHAPTER I. CHEMICAL CHANGES— PHYSICAL CHANGES. Some Familiar Changes. — You are all familiar with many changes which are taking place in the things around you. Take, for example, the changes which are called f,re. You see substances destroyed by fire. They disap- pear. You feel the heat produced by the burning. You know that some things will bum and others will not. Again, you all know that iron when exposed to the air is changed, becoming covered with a reddish-brown substance called rust. If fruit- juices or milk be allowed to stand in contact with the air they become sour. If a spark comes in contact with gunpowder there is a flash and the powder disappears, dense smoke appearing in its place. Changes of Another Kind. — If a piece of stone or of iron be brought in contact with something hot it becomes hot itself.- If taken away it becomes cool again. If heated very hot it gives light. When, for example, iron becomes ''red-hot" we can see it in a dark room. Iron may also be changed by contact with loadstone. After it has been rubbed with loadstone it has the power to attract and hold to itself other pieces of iron. Whan a solid body is struck 2 THE ELEMENTS OE 0HEMI8TRT. with another solid a sound is produced. At a low remper- ature water is solid, forming ice. If the ice becomes warm enough, it melts and becomes water. If the water is heated enough it becomes steam. By cooling steam it changes to water, and by cooling water it changes to ice. Two Kinds of Change. — ^When a substance burns it be- comes something entirely different. Iron-rust is not iron. Sour milk is not fresh milk. Gunpowder after the flash is not gunpowder. In these cases, then, the substances which are changed disappear and something else is formed in their place. On the other hand, when a piece of iron which is hot is allowed to cool it is the same thing that it was before it was heated. Eed-hot iron soon ceases to give light if it is taken away from the fire. Water may be cooled down and changed to ice, and the ice heated and changed to water; and the water formed from the ice is exactly the same thing as the water from which the ice was formed. In these cases the substances are not per- manently changed. You see thus that we have two classes of changes presented to us for study: 1st. Those which do not affect the composition of sub- stances. 2d. Those which affect the composition of substances and give rise to the formation of new substances with new properties. Changes of the first kind are called physical changes. Those of the second kind are called chemical changes. Physics and Chemistry. — That branch of knowledge which has to deal with physical changes is known as physics ; and that which has to deal with chemical changes is known as chemistet. Everything that has to do with motion, with heat, light, sound, electricity, and magnet- CHEMICAL CHANGES-PETSICAL CHANGES. 3 ism, is studied under the head of Physics. Ererything that has to do with the composition of substances and changes in the composition is studied under the head of Chemistry. All Physical and Chemical Changes are Related. — Al- though at first sight the different kinds of change already mentioned appear to be quite distinct from one another, ihey are in reality closely related. If a body in motion be stopped suddenly it becomes hot. Many examples of a similar change of motion into heat are familiar: a wire becomes hot when hammered on an anvil ; a coin rubbed on cloth becomes hot. In both cases the cause of the heat is the interference with the motion. The hammer is stopped and becomes hot ; the coin is not stopped, but the motion is interfered with, and we have to push harder in order to move it over the cloth than we should to move it in the air. Again, we know that by means of heat we can produce motion. The steam-engine is the best example of this. We build a fire ; this heats the water in the boiler ; the water is converted into steam, which expands and moves the piston, and the motion of the piston is the seat of all the complex motions which are found in the different parts of the engine. The train or ship moves. What moves it ? Plainly, the heat is the cause of the motion. But we can go a step farther back and ask what causes the heat. The answer is clear. It is the burning of the fuel. But, in burning, the composition of the fuel is completely changed. A change is produced which is not heat. When a piece of coal burns, then, its composition is changing, and as a result of this change heat is produced. The heat is, therefore, produced by a chemical change in the coal, and we may say that the motion of the steam-engine is the 4 THE ELEMENTS OF CHEMISTRY. result of the chemical change taking place in the coal or wood which^ in burning, produces the heat. Heat Causes Chemical Change. — Just as chemical change produces heat, as in the burning of a piece of wood, so heat causes chemical changes. Experiment 1. — In a clean, dry test-tube put enough white sugar to make a layer i to i inch thick. Hold the tube in the flame of a spirit-lamp or a laboratory ourner as shown in the figure. What changes take place ? What do yon notice on the sides of the tube ? What remains behind ? What is its color and taste? Does it dissolve in water? Is it sugar ? Is the change which has taken place chemical or physical ? What caused it ? Experiment 3. — From a piece of glass tubing of about J inch internal diameter cut oflE a piece about four inches long by making a marK across it with a triangular file, and then seizing it with both hands, one on each side of the mark, pulling and at the same time pressing Fig. 1. slightly as if to break it. Clean and dry it, and hold one end in the flame of a laboratory burner until it melts together. During the melting twirl the tube constantly between the finger and thumb so that the heat may act uniformly upon it. After it has cooled down put into it enough red oxide of mercury (mercuric oxide) to form a layer ^ inch thick. Heat the tuoe as in the last experiment. — What change in color do you notice! What is deposited on the sides of the tube ? During the heating insert a splinter of wood with a spark on the end into the tube. What follows? Take it out and put it back a few times. Is there any difference between the burning in the tube and out of it ? What difference ? How do you know that the red substance which you put into the tube has been changed ? Is the change chemical or physical ? What caused the change ? Chemical Change Caused in Other Ways. — In the two experiments just performed heat caused chemical change. Chemical changes can be produced in other ways. The simplest way is by bringing substances together. CHEMICAL CHANGES— PHYSICAL CHANGES Experiment 3. — Examine a piece of calc-spar or marble. Notice whether it is hard or soft. Heat a small piece in a glass tube such as used in Experiment 3. Does it change in any way ? Does it dissolve in water ? In order to learn whether a substance is soluble in water proceed as follows: Put a piece about the size of a pea in a test-tube with distilled water. Thoroughly shake, and then, as heating usually aids solution, boil. Now pour off a few drops of the liquid on a piece of platinum-foil* or a watch-glass, and by gently heating cause the water to pass off as steam. If there is anything solid in solution there will be something solid left on the platinum-foil or watch-glass. If not, there will be nothing left. — Knowing now the general properties of the calc- spar or marble you will be able to determine whether it is changed or not. Treat a small piece with dilute hydrochloric acid. What takes place? After the action has continued for about half a minute insert a lighted match in the upper part of the tube. Does the match continue to burn ? Does the sub- stance in the tube burn ? Is the invisible substance in the upper part of the tube ordinary air? Why not? Does the solid sub- stance disappear ? In order to tell whether it has been changed chemically the hydrochloric acid Fia. 2. must be gotten rid of. This can be done by boiling it, when it passes off in th§ form of vapor, just as water does, and then whatever is in solution wUl remain behind. For this purpose put the solution in a small, clean porcelain evaporating-dish, and put this on a vessel containing boiling water, or a water-bath. The operation should be carried on in a place where there is a good draught, so that the vapors wiU not collect in the working-room. They are not poisonous, but they are annoying. The arrange- * The expensive metal platinum is much used in chemical labora- tories, for the reason that it resists the action of heat and of most substances. 6 THE ELEMENTS OF CSEMISTBT. ment for evaporating is illustrated in Fig. 3. After the liquid has evaporated and the substance in the evaporating-dish is dry, examine it and carefully compare its properties with those of the substance which was put into the test-tube. Is it the same sub- stance ? Is it hard or soft ? Does it change when heated in a tube ? Is there an appearance of bubbling when hydrochloric acid is poured on it ? Does it dissolve in water ? Does it change when allowed to lie in contact with the air ? Experiment 4. — Bring together in a test-tube a small piece of copper and some moderately dilute nitric acid. Hold the mouth of the tube away from your face and do not inhale the vapors. What is the appearance of the vapors given off ? What is the appearance of the liquid in the tube ? Does the copper dis- solve ? Examine the solution, as in the preceding experiment, and see what has been formed. What are the properties of the substance found after the liquid has evaporated ? Is it colored ? Is it hard or soft ? Does it change when heated in a tube ? Is it soluble in water ? Does it in any way suggest the copper with which you started ? Experiment 5. — Try the action of dilute sulphuric acid on a little zinc in a test-tube. An invisible gas will be given off. Apply a lighted match to the mouth of the tube. What takes place ? After the zinc has disappeared evaporate the solution as before. Carefully compare the properties of the substance left behind with those of zinc. Experiment 6.— Hold the end of a piece of magnesium rib- bon about eight inches long in a flame until it takes fire. Then hold the burning substance quietly over a piece of dark paper, so that the light, white substance which is formed may fall upon the paper. Compare the properties of this product with those of magnesium. Experiment 7. — In a small dry flask of about four ounces capacity put a bit of granulated tin or of pure tin-foil. Pour upon it enough concentrated nitric acid to cover it. If no change takes place at first, heat gently, and presently you will have evidence that ehange is taking place. Is there anything in this experiment whiei suggests Experiment 4 ? What is left behind after the action is finished? Compare the properties of the product with thos« of tin. CHEMICAL CHANGES— PHT8IGAL OHANGES. 7 Solution Aids Chemical Action. — In the cases just studied it was only necessary to bring the substances together, when they acted at once. In each case one of the sub- stances used was a liquid. Solids do not, as a rule, act upon one another as readily as liquids act upon solids, for the reason that the small particles of which the solids are made up cannot be brought as closely together as the par- ticles of liquids. Exi'ERiMENT 8. — Mix together in a dry mortar a little dry tartaric acid and about an equal quantity of dry bicarbonate of soda (sodium bicarbonate). Do you see any evidence of action ? Now dissolve a little tartaric acid in water in a test-tube, and a little carbonate of soda in water in another test-tube. Pour the two solutions together. What evidence have you now that action takes place ? Pour water upon the dry mixture first made. Does action take place? What causes the bubbling? Will a matcli burn in the gas ? In which experiment already performed was a similar gas obtained ? Exi'ERiMENT 9. — Mix together in a dry mortar a little dry sulphate of iron (green vitriol) and a little dry ferrocyanide of po- tassium (yellow prussiate of potash). Does action take place? Make a solution of each of the two substances and pour them together. What evidence have you that action takes place? I^our water on the dry mixture. Does action take place ? Summary. — From the experiments it will be seen (1) that heat causes chemical change; (2) that in some cases simple contact of substances is suflBcient to cause chemical change; (3) that solution aids chemical change. In all the cases of chemical action thus far studied one thing was observed, viz., that the substances which were acted upon lost their own properties and new substances were formed. This is true in all cases of chemical action, and the truth may be stated thus: Whenever two or more substances act upon one another 8 TEE ELEMENTS OF OHEMISTBY. chemically they lose their own properties, and new sub- stances are formed with entirely different properties. Difference between Combining Chemically and simply Mixing. — By mixing is meant bringing things together closeljj so that the particles of one shall be in contact with the particles of the other. We mix salt and sugar by put- ting them together in a vessel and shaking them, or by stirring as with a pestle in a mortar. The longer we stir the more closely the substances are brought together. But no matter how long we may stir the mixture, it remains a mixture and contains both sugar and salt. In some cases, by stirring, chemical action can be brought about, but __generally not. ExPEEiMENT 10. — Mix two Or three grams of powdered roll- sulphur and an equal weight of yery fine iron filings in a small dry mortar. Examine a little of the mixture with a microscope. Can you distinguish the particles of sulphur and those of iron ? Pass a small magnet over the mixture. Are particles of iron drawn out of the mixture ? Has chemical action taken place ? Experiment 11. — Pour two or three cubic centimetres of bisulphide of carbon on a little powdered roll-sulpmr in a dry test- tube. Does the sulphur dissolve ? Treat iron filings in the same way. Does the iron dissolve ? Now treat a small quantity of the mixture prepared in Experiment 10 with bisulphide of carbon. After the sulphur is dissolved pour off the solution in a good- sized watch-glass and let it stand. Examine what is left in the test-tube. Is it iron ? After the liquid has evaporated examine what is left on the watch-glass. Is it sulphur ? Experiment 13. — Mix three grams of finely powdered roll- sulphur and three grams of fine wrought-iron filings or pow- dered iron to be had of the druggists. Put the mixture in a dry test-tube. Heat gently at first and notice the changes. At first the sulphur melts and becomes dark-colored. It may even take fire. But soon something else takes place. The whole mass begins to glow, and if you at once take the tube out of the flame the mass will continue to glow, becoming brighter. This wiU CHEMICAL CHANGES— PHYSICAL CHANGES. 9 soon stop; the mass will grow dark and gradually cool down. As soon as it reaches the ordinary temperature, break the tube and put the contents in a mortar. Does the mass look like the mixture of sulphur and iron with which you started ? An exam- ination with the microscope, the magnet, and bisulphide of car bon will prove that, while there may be a little iron left and pos- sibly a little sulphur, most of the bluish-black mass is neither iron nor sulphur, but a new substance with properties quite dif- ferent from those of iron and of sulphur. What has Become of the Iron and the Sulphur ? — In the last experiment a new substance was formed by the action of sulphur upon iron. Neither substance has been de- stroyed, but both have coribined in a much more intimate way than when they were simply mixed together. This kind of combination which causes the properties of the combining substances to disappear is called chemical com- bination. If othing is lost in the act, as has been shown by weighing the substances before and after action. Mechanical Mixtures and Chemical Compounds. — In a mixture the substances are unchanged. They exist side by side. In a chemical compound the substances which are in combination are completely changed. They are so intimate- ly combined that they camiot be recognized by any ordinary means. Compounds and Elements. — Most of the substances found in nature are made up of several others. Wood, for exam- ple, is very complex, containing a large number of distinct substances intimately mixed together. Some of these can be got out separately, but it is impossible to get them all out separately with the means at present at our com- mand. Most of the rocks met with, and the different kinds of earth, as clay, sand, etc., are also quite complex, and it is in most cases difficult to get out the substances contained 10 TEE ELEMENTS OF CEEMI8TBY. in them. By proper methods^ however, it is possible to decompose the complex substances found in nature so as to get simpler ones, and these again can usually be decom- posed into still simpler ones which cannot be decomposed by any means known to us. Substances which we cannot decompose into simpler ones are called elements. Now, al- though there are thousands and thousands of different kinds of substances met with in nature, these are really made up of a comparatively small number of simple sub- stances or elements. The number of elements thus far discovered is between sixty and seventy, but the larger number of these are rare, and we might have a very ex- cellent knowledge of the essentials of chemistry without any knowledge of these rare elements. We shall find that most things we have to deal with are really made up of about a dozen elements, and that most of the chemical changes which are taking place around us, and which we need to study in order to get an insight into the nature of chemical action, take place between this small number of elements. An element is a substance which we cannot decompose into simpler substances. A compound is a substance which can be decomposed into iimpler ones. A compound contains two or more elements held together chemically. Examples of Elements and Compounds. — As examples of elements may be mentioned iron, copper, tin, silver, gold, (sulphur, and lead. As stated in the last paragraph, they are called elements for the reason that they cannot be de- composed into simpler substances. Among familiar com- pounds may be mentioned water, common salt or sodium chloride^ blue vitriol or copper sulphate, chlorate of potash CHEMICAL CHANQB&-PHT8ICAL CHANQES. 11 or potassium chlorate, marble or calcium carbonate, sand or silicon dioxide. Eacli of these compounds consists of two or more elements held together in chemical combina- tion. Water can be decomposed by yarious methods into two substances known as hydrogen and oxygen, and the sum of the weights of the hydrogen and oxygen obtained from a given weight of water is exactly equal to the weight of the water decomposed. Sodium chloride can be decom- posed into the two elements sodium and chlorine, and the weight of the sodium added to the weight of the chlorine exactly equals the weight of the sodium chloride. On the other hand, the composition of an element cannot be changed without adding something to it. Chemical Action. — Just as the earth attracts all bodies to it in some mysterious way which we call gravitation, just as the magnet attracts pieces of iron, so substances are drawn together chemically and, if they come in contact under the proper conditions, chemical action takes place. By this is meant that some change in composition is brought about ; that the substances which are brought together dis- appear and new ones make their appearance. But the quantity of matter remains the same. The elements ar- range themselves differently. Three Kinds of Chemical Action. — The numerous cases of chemical action may be divided into three classes: (1) comiination; (2) decomposition ; and (3) double decompo- sition or metathesis. As an example of combination the case of the action of iron on sulphur may be taken. The two elements combine directly, forming a compound known as iron sulphide. The action may be represented thus: Iron + Sulphur = Iron Sulphide. A good example of decomposition is that of the action of 12 THE BLBMENTS OF 0HEMI8TBT. heat on the red oxide of mercury or mercuric oxide (see Experiment 2). When this substance is heated two things are obtained from it: an invisible gas, oxygen, which passes out of the yessel and which can be detected by the fact that substances burn in it more readily than they do in air ; and a silvery-looting liquid, which is quicksilver or mer- cury. The action in this case may be represented thus: Mercuric Oxide = Mercury + Oxygen. In double decomposition two or more substances act upon one another and give rise to the formation of two or more new ones. Thus when hydrochloric acid acts upon marble (see Experiment 3) two substances, calcium chloride and carbfmic acid, are formed. This may be represented thus: Hydrochloric Acid + Calcium Carbonate (or marble) = Calcium Chloride + Carbonic Acid. Most cases of chemical action which we have to deal with are of the third kind. The Cause of Chemical Action. — It is evident from what we have already learned that there is some power which can hold substances together in a very intimate way, so in- timate that we cannot recognize them by ordinary means. We do not know what causes sulphur and iron to combine, but we know that they do combine. Similarly, we do not know what causes a stone thrown in the air to fall back again, but we know that it falls back. It is true we say that the cause of the falling of the stone is the attraction of gravitation, but this does not give us any information, for, if we ask what the attraction of gravitation is, we can only answer that it is that which causes all bodies to attract one another. So, too, we may say that the cause of the chemi- cal union of substances is chemical attraction. But in so CHEMICAL CHANOBS-PBTSIGAL CHANCES. 13 doing we are only giying a name to something about which we know nothing except the effects which it produces. Importance of Chemical Action. — If this power, what- ever it may be, should cease to operate, what would be the result? As far as we can see all substances known to be chemical compounds would be decomposed into the elements of which they are composed, and there would be only about sixty or seventy different kinds of substances. All living things would cease to exist, and in their place we should have three invisible gases and something very much like charcoal. Mountains would crumble to pieces, and all water would disappear giving two invisible gases. The processes of life in its many forms would be impossible. These considerations will suflSce to show the great impor- tance of the subject of chemistry, and how impossible it is without some knowledge of this subject to form any conception in regard to the most important phenomena of the universe. Occurrence of the Elements. — ^As has already been stated (p. 10), not more than a dozen elements enter largely into the composition of the earth. It has been estimated that the solid crust of the earth is made up approximately as represented in this table: Oxygen 44-48 per cent. Silicon 33-36 " " Aluminium 6-10 " " Iron 2-10 " " Calcium 1-7" " Magnesium 0.1-3 " " Sodium 2-3" " Potassium 1.&- 3 " " While oxygen forms a large proportion of the solid crust of the earth, it forms a still larger proportion (eight ninths) + 14 THK ELEMENTS OW CHEMISTBT. of water, and about one fifth of the air. Carbon is the principal element entering into the structure of living things, while hydrogen, oxygen, and nitrogen also are essential constituents of animals and plants. Nitrogen forms about four fifths of the air. The Names of the Elements. — The names of the elements are. formed in many different ways. The name chlorine is derived from a Greek word meaning greenish yellow, as this is the color of chlorine. Bromine comes from a Greek word meaning a stench, a prominent characteristic of bromine being its bad odor. , Hydrogen is formed from two Greek words, one of which means water and the other to produce, signifying that it enters into the composition of water. Potassium is an element found in potash, and sodium is found in soda. The Symbols of the Elements. — It is convenient to use abbreviations for the names of the elements and com- pounds. Thus, instead of oxygen we may write simply 0, for hydrogen H, for nitrogen N, etc. Very frequently the first letter of the nam: of th: element is used as the symbol. If the names of two or more elements begin with the same letter, this letter is used, but some other letter of the name is added. Thus, B is the symbol of boron, Ba of barium, Bi of bismuth, etc. In some cases the symbols are de- rived from the Latin names of the elements. Thus, the symbol of iron is Fe, from fernim ; of copper, Cu, from cuprum ; of mercury, Hg, from hydrargyrum, etc. The symbols of the more common elements will soon become familiar by use. It is not desirable to attempt to commit them to memory at this stage. List of the Elements and their Symbols. — In the table here given the names of those elements which are most CHEMICAL CBANQBS-PET8I0AL CHANGES. 15 widely distributed, and which form by far the largest part of the earth, are printed in small capitals. The names of those which are very rare are printed in italics. Aluminium Al Antimony Sb Arsenic As Barium Ba Bismuth , Bi Boron B Bromine Br Cadmium Cd GcBMum Cs Calcium Ca Cabbon C Cerium. Ce Chlokihe CI Chromium Cr Cobalt.. Co Columbium Cb Copper Cu JMdymvain Di Erbium E Fluorine F Oallium Ga Glucinum Gl Gold Au Hydeogbn H Indium In Iodine I Iridium Ir Ibon Fe iM/nthanum La Lead Pb Lithium Li Magnesium Mg Manganese Mn Mercury Hg Molybdenum Mo Nickel Ni Niobium Nb NiTHOGBN N Oamium Os Oxygen O Palladium. ... Pd Phosphorus P Platinum Pt Potassium K Bhodium Rh RuMdium Rb Ruthenium Ru Samui/num Sm Scandium 8c Selenium Se Silicon Si Silver Ag Sodium Na Strontium Sr Sulphur S Tantalum Ta Tellurium Te Thallium Tl Thorium Th Tin Sn Titanium Ti Tungsten W Uranium U Vanadium V Ytterbium Yt TtlHum Y Zinc Zn Zirconium Zr What We Shall Study, — In the course which you have begun you will study only the most common elements and their action upon one another. In this way you will be able to learn much about the chemistry of many interesting things, such as burning, the rusting of iron, the growth of plants and animals, the extraction of useful metals from their ores, the manufacture of illuminating-gas, of soap) etc., etc., and at the same time you will acquire a know! edge of the general principles of chemistry which will enable you to take a more intelligent view of the universe than you can without this knowledge. 16 THE ELEMENTS OF OHEMISTRy CHAPTER II. THE CHEMISTRY OF THE AIR. The Air Causes Chemical Changes. — One of the most interesting, most common, and most important chemical changes with which we are familiar is that which is known as burning. No matter how we may begin the study of chemical facts, we are at once brought face to face with the fact that the air takes part in chemical change. Experiment 13. — In a small porcelain crucible arranged as shown in Fig. 3 put a small piece of lead. Heat by means of a laboratory burner, and notice the changes which take place. After the lead is melted stir with a thick iron wire while heating. Continue to heat and stir until the substance is no longer liquid. What is its appearance now ? Let it cool. Is it lead ? What diCerenoe is there between the action in this case and in the case of melting ice and cooling the water down again ? Which is chemical action and which physical action ? Fio.3. Why? Experiment 14. — Heat a piece of zinc in the same way as you have just heated lead. What changes take place ? Experiment 15. — Heat a piece of tin in the same way. What changes .take place ? • What Caused the Changes ? — By heating lead, zinc, and tin in the air, then, they are changed to powders which do not melt. The question will suggest itself, does the heat alone cause these changes or has the air something to do with them ? The air alone jjlainly does not cause tlie changes, for they do not take place until the substances are THE GHEMISTBT OF THE AIR. 17 heated. To learn whether the air has anything to do with them we shall have to heat the substances in such a way as to keep the air from getting at them. This can be done by putting in the vessel something which melts and which will float on the melted metal. Such a substance is ordi- nary borax. Experiment: 16. — Repeat Experiments 13, 14, and 15, adding in each case enough borax to form a complete cover to the metal after both are melted. Do the metals melt ? Are they changed to powders as in the previous experiments ? Many Similar Facts are Known. — The examples given above are only a few of a large number of similar ones mown. Hence the statement that many metals when heated in the air undergo chemical change and are con- verted into powders which do not melt. The powders are formed by the action of the air on the heated metals, for if the air be kept away from the metals the changes do not take place. The Metals Increase in Weight when Heated in the Air. — If you were to weigh the metals used in Experiments 13, 14, and 15 and then weigh the powders obtained, you would find that in each case the powder weighs more than the metal. This fact taken together with the others already learned shows that there is something in the air which at high temperatures combines with the metals tin, zinc, and lead. Burning in the Air. — The phenomenon of burning takes place in the air, and the question suggests itself, has the air anything to do with the burning ? You know that if you shut up a stove completely the fire dies down, and unless the draught-door is opened the fire goes out. If you want the fire to burn more actively you open the draught- 18 THE ELEMENTS OF GHEMISTBT. doors when air is drawn in and the burning is made to take place more rapidly. A fire burns better when air is blown into it with a bellows. A candle is put out when anything is brought down upon the flame in such a way as to keep out the air. When a smouldering fire is covered with ashes it goes out. All these facts, which are well known to every one, make it appear probable that the aii has something to do with burning, but they do not show what. In order to learn this we shall have to experiment carefully, noticing everything that takes place. Experiment 17. — Fix a short bit of candle on a large flat cork or a block of wood. Light the candle and place it with the block on the surface of water contained in a pail or some other appro- priate vessel. Place over it a good-sized glass vessel, either a wide-mouthed bottle or a good-sized fruit-jar, as represented in Fig. 4, so that the candle and cork are in the glass vessel and the mouth of the vessel is beneath the surface of the water. Hold it in this position for a few minutes and ob- serve what takes place. Does the candle continue to burn ? Is all the air contained in the vessel used up when the candle goes out ? Try the experiment a second time, and when the candle is nearly out raise the FiQ. 4. glass vessel so that air can get in. Does this make any difference? "What difference? What do these experiments prove ? A Candle Will Not Burn in the Air that is Left. — If, after the candle has gone out, you place your hand or a ground-glass plate over the mouth of the vessel and turn it mouth upward, and then insert into it a lighted candle on a wire, the candle will be extinguished. You see that the air which is left in the vessel after a candle has burned in it and gone out is not the same as ordinary air. TEE 0HEMI8TBT OF THE AIB. 19 Experiment 18. — Try the experiment just mentioned, candle on the wire should be arranged as shown in Fig. 5. Does the Candle Increase in Weight ? — You know that in burning the candle gradually disappears, and from this you would he inclined to think that it is de- stroyed. But if you were to collect the smoke which is given off and weigh it, you would find that it weighs more than that part of the candle which has burned up. So that instead of there being a loss of matter there is apparently a gain. The Fio. B. Experiment 19. — On one pan of an appropriate balance place a candle, and directly over it suspend a wide glass tube contain- ing pieces of caustic soda, a substance which has the power to absorb most of. the smoke given off from the burning candle. Place a similar glass tube with caustic soda on the other pan of the balance and exactly balance the two pans. Now light the candle, and in the course of a few minutes the pan with the candle on it wUl sink, showing that it is heavier than the other. One Fifth of the Air is Used up when Anything Surns in a Closed Vessel. — By careful experiments which it would be difficult to repeat here it has been shown that only one fifth of the air ^s capable of keeping up the process of burning, while the rest is an inactive substance in which Pje e_ burning cannot take place. If, for example, you could heat a piece of lead or zinc in a closed vessel for a time, then let it cool and open the 20 THE ELEMENTS OF OHEMISTBT. vessel under water, you would find that water would rusli in and fill about one fifth of the vessel, showing that this much air had been used up. If you should weigh the metal before and after heating you would find that it had in- creased in weight, and if you should weigh the air used up you would find that its weighb is exactly equal to the in- crease of weight of the metal. A great many oxperimentB of this kind have been performed, and they have shown that when a substance burns it uses up something from the air and increases in weight exactly as much as the air loses. The Air Consists Mainly of Two Substances. — The air then consists of two substances, only one of which can keep up the process of burning. This one is known as oxygen. The other, in which things cannot burn, is known as nitro- gen. Besides these the air always contains smaller quanti- ties of other substances, particularly ivater vapor, carbonic acid (or carbon dioxide), and ammonia. "We shall soon study these substances and see of what value they are in the air. Oxygen and nitrogen are called elements because no one has been able to decompose them and get anything simpler from them. OXYQUJSr. 21 CHAPTEE III. OXYGEN. '^ Occurrence of Oxygen. — Oxygen is the most widely dis- tributed element, and it occurs also in very large quantity. It has been stated that it forms between forty and fifty per cent of the solid crust of the earth, eight ninths of water and one fifth of the air by bulk. Preparation of Oxygen. — "We have oxygen around us in great abundance, but it is mixed with nitrogen, and it is difficult to separate the two so as to get the oxygen. The easiest way to get oxygen is by heating something which contains it. One of the simplest examples of this kind is the oxide of mercury, which when heated gives mercury and oxygen. When mercury itself is heated in the air for some time to very near its boiling point it is gradually changed to a red powder, just as lead and tin and zinc are changed to powders when heated in the air. This powder is a com- pound of mercury and oxygen. When the compound is heated to a high temperature it is decomposed into its elements, mercury and oxygen. Collection of Oxygen. — The oxygen given off from the oxide of mercury is most conveniently collected by causing it to displace water. For this purpose the apparatus should be arranged as represented in Eig. 7. On now Jieating the oxide, the oxygen which is set free necessarily 22 THE ELEMENTS OF CEEMISTBY. passes through the narrow tube and escapes beneath the mouth of the inverted glass vessel which is filled with water. The gas being lighter than water rises and the water is displaced. The oxide of mercury should be heated in a tube made of hard glass closed at one end. Oxygen Made from Potassium Chlorate. — ^Another sub stance which readily gives up oxygen when heated is po- tassium chlorate or, as it is commonly called, chlorate of potash. This is manufactured in large quantities and is easily obtained. It contains the three elements potas- Fio. 7. sium, chlorine, and oxygen. When heated it gives up the oxygen, and a compound of potassium and chlorine, knowi as potassium chloride, very much like common salt, ),■■ left behind. ExPEEiMENT 30. — Arrange an apparatus as shown in Fig. 8. A represents a flask of 100 c.cm. capacity. By means of a good- fitting rubber stopper one end of the bent glass tube B is con- nected with it, and the other end, which should turn upward slightly, is placed under the surface of the water in C. In A put 4 to 5 grams (about an eighth of an ounce) potassium chlorate, and gently heat by means of a lamp. When gas comes off freely OXYGEN. 23 bring the inverted cylinder D filled with watcx" over the end of the tube, and let the bubbles of gas rise in the cylinder. Exam- ine the gas by placing a glass plate over the mouth of the vessel containing it and inverting it. Insert into it a stick with a spark on its end. What takes place ? Is the gas contained in the ves- sel ordinary air ? Fia. 8. Oxygen Made by Heating a Mixture of Potassium Chlo- rate and Manganese Dioxide. — The most convenient way to make oxygen in the laboratory is to heat a mixture of equal parts of potassium chlorate and manganese dioxide or '' black oxide of manganese." This mixture gives off oxygen very readily when heated. The potassium chlorate alone is decomposed under these circumstances, the man- ganese dioxide remaining unchanged. It is not known how the manganese dioxide helps the action. Experiment 21. — Mix 25 to 30 grams (or about an ounce) of potassium chlorate with an equal weight of coarsely powdered 34 THE ELEMENTS OF OHEMISTBT. manganese dioxide in a mortar. Heat the mixture* in a glass retort arranged as shown in Fig. 9, and collect the gas by displacement of water in ap- propriate TBSsels — cylinders, bell- glasses, bottles with wide mouths, etc. Physical Properties of Oxy- gen. — Haying thus learned how to get oxygen^ you may proceed to study its properties. In the first place, the gas is invisible. The slight cloud which ap- pears in the vessels when the gas is first collected is due to the presence of a very small quantity of a substance If the vessels are allowed to stand for a few minutes the cloud will disappear, and the vessels will look the same as if they were filled with air. The gas is tasteless and inodorous. [Inhale a little from one of the small bottles.] It is slightly heavier than the air. When subjected to an extremely high pressure and low temperature it becomes liquid. The properties of oxygen to which reference has thus far been made are its physical prnperties. These are its appearance, taste, smell, relative weight, and changes in its condition, which still leave it in the elementary form or uncombined chemically. Fio. 9. which is not oxygen. * Black oxide of manganese is sometimes adulterated with other substances, and when heated with potassium chlorate it may then give rise to explosions. It should he tested before using by mixing a little with potassium chlorate and heating in a test tube. If the de- composition takes place quietly the substance may be used for thg preparation of oxygen. OXTBBK 25 Chemical Conduct of Oxygen. — In order to get an idea of the way in which oxygen acts upon some simple sub-, stances under ordinary circumstances a few experiments should be performed. We want to learn: What changes oxygen can effect in other substances; what conditions are necessary in order that it may act chemically; what products are formed, etc., etc. The Action of Oxygen at the Ordinary Temperature. Experiment 33. — Turn three of the bottles containing oxygen with the mouth upward, leaving them covered with glass plates. Into one introduce a little sulphur in a so-called deflagrating- spoon, which is a small cup of iron or brass attached to a stout wire which passes through a round metal plate, usually of tin (see Fig. 10). In another put a little charcoal (carbon), and in a third a piece of phosphorus * about the size of a pea. Let them stand quietly and notice what changes, if any, take place. What these Experiments Show. — These experiments show that oxygen does not act upon sulphur and carbon when brought in contact with them, and that the action upon phosphorus is slight. We might perform experiments of this kind with a great many substances, and we should reach the conclusion that at the ordinary temperature oxy- gen does not readily act upon substances. Indeed, as the air contains a considerable proportion of oxygen, it is clear that oxygen does not readily act upon substances at ordi- nary temperatures or action would constantly be taking place * Phosphorus should be handled with great care. It is always kept under water, usually in the form of sticks. If a small piece is wanted, take out a stick -with a pair of forceps, and put it under water in an evaporating-dish. While it is under the water cut off a piece of the size wanted. Take this out by means of a pair of forceps, lay it for a moment on a piece of fllter-paper, which wilj absorb most of the ^ater; then quickly put jt in a spoon, 26 THE ELEMENTS OF 0HEMI8TBT. between the air and many of the substances exposed to it Slow Action of Oxygen at the Ordinary Temperature. — TJpon some substances oxygen does act even at ordinary tem- perature. Some metals, as iron, become coyered with a layer of rust when exposed to the air. This is due partiy, at least, to the action of the oxygen of the air. Wood and other vegetable substances undergo slow decomposition when exposed to the air, in consequence of the action of the oxygen. Animal substances undergo decomposition comparatively readily when exposed to the air. The pro- cess of decay is partly due to the action of oxygen at the ordinary temperature. The Action of Oxygen in Animal Bodies. — The most im- portant illustration of the action of oxygen at low tempera- tures is that which takes place in our bodies and the bodies of all animals. The food which we partake of undergoes many changes; some of the substances uniting with oxygen. Then, too, we take large quantities of oxygen into our lungs in Ireathing. This acts upon various substances which are presented to it in the lungs; it combines with them, form- ing other substances which can easily be got rid of. More will be said in regard to the breathing of animals and plants when the subject of carbon and its compounds with oxygen is taken up. The Action of Oxygen upon Heated Substances. — Sup- pose that before putting them in the oxygen we heat the tiubstances used in Experiment 33, what will then take place? ExPEEiMENT 33. — In a deflagrating-spoon set fire to a little sul- phur and let it burn in the air. Notice whether it burns with ease or with difflculty. Notice the odor of the fumes which are OXYGEN. 27 given off. Now set fire to another small portion and introduce it in a spoon into one of the vessels containing oxygen, as shown in Fig. 10. Does the sulphur burn more readily in the oxygen or in the air? Notice the odor of the fumes given off. ' ^ Is it the same as that noticed when the burning takes place in the air ? EXPEEIMENT 34. — Perform similar experiments with charcoal. e. Experiment 25. — Burn a small piece of phosphorus in the air and in oxygen. In the latter case the light emitted from the burning phosphorus is so intense Fig. lo. that it is painful to some eyes to' look at it. After the burning is over let the vessel stand. Does it become clear ? r ?j*j^ What Took Place in these Experiments ?— In the first place, the substances were simply heated before they were introduced into the oxygen. Nothing was added to them. It is clear, therefore, that while oxygen does not act upon these substances at the ordinary temperature, it does act upon them at higher temperatures. But what does the ac- tion consist in? We can determine this only by a careful study of the substances before and after the action. We must know not only what substances are brought together, iut also what the weight of each is; and we must know what substances are left behind, and the exact weight of these. By means of accurate experiments it has been shown re- peatedly that the substances which burn in oxygen disap- pear as such, and that in each case a definite quantity of oxygen is also used up. The result of the experiments can be stated thus: The weight of the substance turned plus the weight of the oxygen used up is exactly equal to the weight of the product formed. 28 THE ELBMBNT8 OF CHEMI8TRT. Burning is Combining with Oxygen. — Prom what we have learned we may conclude that when a substance hums in oxygen the act consists in the chemical combination of the two. Burning in the Air. — To determine whether burning in the air is the same act as burning in oxygen it is neces- sary to burn the same things in air and in pure oxygen and see whether the products are the same. This has been done a great many times^ and always with the same result. Whether a substance burns in the air or in pure oxygen the same product is formed, and nothing else. It is therefore certain that the act of burning in the air is due to the presence of oxygen. As we have already seen, there is another substance present in the air in large quan- tity, and it is due to this fact that burning does not take place as readily in the air as in oxygen. Combustion. — By the term combustion in its broadest sense is meant any chemical act which is accompanied by an evolution of light and heat. Ordinarily, however, it means the union of substances with oxygen as this union takes place in the air, with evolution of light and heat. Substances which have the power to unite with oxy- gen are said to be combustible, and substances which have not this power are said to be incombustible. Most of the elements combine with oxygen under proper conditions, and are therefore combustible. Most compounds formed by the union of oxygen with combustible substances are incombustible. They contain oxygen and they cannot di- rectly combine with any more. Some Substances which do not Burn in the Air Burn in Oxygen. — The best illustration of this fact is that of iron. This metal, as you know, does not bum in the air. If OXYQEK. 29 it didj all our stoves, iron yessels, and iron buildings would bum up. In pure oxygen, however, iron burns readily. Experiment 26. — Straighten a steel watch-spring '^ and fasten it in a piece of metal, such as is used for fixing a deflagrating- spoon in an upright position; wind a little thread around the lower end, and dip it in melted sulphur. Set flre to this and insert it into a vessel containing oxygen. For a moment the sul- phur wm burn as in Experiment 23; but soon the steel will begin to bum brilliantly, and the burning will continue as long as there is oxygen left in the vessel. The phenomenon is of great beauty, especially if observed in a dark room. ' The walls of the vessel be- come covered with a dark reddish-brown substance, some of which will also be found at the bottom in large pieces. Kindling Temperature. — You have seen that substances do not usually combine with oxygen at ordinary tempera- tures, but that in order to effect the union the temperature must be raised. If this were not the case it is plain that every combustible substance in nature would burn up, for the air supplies a sufficient quantity of oxygen for this purpose. Some substances need to be heated to a high temperature before they will combine with oxygen ; others require to be heated only slightly. Every combustible sub- stance has its Mndling temperature ; that is, the tempera- ture at which it will unite with oxygen. Below this tem- perature it will not unite with oxygen. Watch a stick of wood burning, and watch how, as we say, "the fire creeps" along it. The reason of the slow advance is simply, this : only those parts of the stick which are nearest the burning part become heated to the kindling temperature. They * Old watch-springs can generally be had of any watch maker or mender for the asking. They can be straightened by pulling them between the thumb and some hard substance, such as a glass rod or a round pencil. 30 TEE ELEMENTS OF CHEMI8TBT. take fire and heat the parts nearest them, and so on grad- ually throughout the length of the stick. Heat a Result of Combustion. — ^We know that whenever a thing burns it gives out heat, and generally light. The heat is a result of the act of chemical combination, and the light is due to the heat. Whenever chemical comiination takes place heat is given off. It is caused by the rapid coming together of the particles of the substances which combine, just as a bullet is heated by being rapidly pro- jected against a hard target which stops it. Chemical Energy and Chemical Work. — ^Any substance which has the power to combine with others can do chem- ical ivorh; it possesses chemical energy. Thus all combus- tible substances can do work. In combining with oxygen heat is given ofE, and this can be changed into motion. To go back to the example of the steam-engine, which was re- ferred to in Chapter I., the cause of the motion is the burn- ing of the fuel. Products of Combustion. — The substances formed in com- bustion are in general known as oxides. The compound of zinc and oxygen is called zinc oxide; that of silver and oxygen, silver oxide, etc. COMBINING WEIGHTS. 31 CHAPTEE IV. COMBINING WEIGHTS. Elements Combine in Definite Weights. — A certain weight of tin always combines with a definite weight of oxygen. If equal weights of sulphur and iron be mixed and caused to act chemically by the aid of heat, it will be found that some of the sulphur is left over in the uncombined state after the action is over. If we should take twice as much iron as sulphur, then, after the action, some iron would be left over. An extensive examination has shown conclusively that each chemical compound always contains the same ele- ments in exactly the same proportions. The compound of sulphur and iron always contains exactly 36.36 per cent of sulphur and 63.64 per cent of iron. The compound of tin and oxygen always contains exactly 78. 67 per cent of tin and 21. 33 per cent of oxygen, and so on throughout the list of chemical elements. The Law of Definite Proportions. — These facts were dis- covered by the united efforts of a large number of chemists continued through several years. They are of great impor- tance. They are summed up in the general statement: Chemical combination always takes place between definite masses of substances. This is known as the law of definite proportions. What a Natural Law is. — It is simply a statement of what we have every reason to believe to be the truth. Every 32 THE ELEMENTS OF OEEMISTBT. fact known to us in regard to chemical combination is in accordance with the law of definite proportions. It ex- presses what has been learned by a study of chemical facts. This law, as well as other natural laws, can never be proved to be absolutely true, for the reason that we cannot examine every case to which the law applies. But if, after examin- ing a very large number of cases, we find that the law holds true in them, we may conclude that it is true of all cases. When we say that all bodies attract one another, do we know this to be absolutely true? Certainly not. But we do know that so far as those bodies are concerned which come under our observation the statement is true, and therefore we have reason to believe that it is true of all bodies. Proportions by Weight in which the Elements Combine. — A careful study of the figures representing the composi- tion of chemical compounds reveals a remarkable fact re- garding the relative quantities of one and the same element which enter into combination with other elements. The proportions by weight in which some of the elements com- bine chemically are stated in the following table : Sulphur 1 ; Oxygen 1. Iron 7 ; Oxygen 3. Iron 7 ; Sulphur 4. Magnesium 3 ; Oxygen 3. Tin 59 ; Oxygen 16. Zinc 65 ; Oxygen 16. Tin 59: Sulphur 16. Zinc 65 ; Sulphur 33. Sodium 33 ; Oxygen 8. Sodium 23 ; Sulphur 16. Potassium 89 ; Oxygen 8. Potassium 39 ; Sulphur 16. You see that for iron, tin, zinc, sodium, and potassium the same figures are used, whether you have the compounds of these elements with oxygen or wi'th sulphur. Now, if we COMBINma WEIGHTS. 83 were to determme the composition of all compounds which contain zinc, we should find that the relative quantity of zinc present could, in nearly all cases, be expressed by the figure 65. Similarly the quantity of sodium in sodium compounds could be expressed by the figure 33, and that of potassium in potassium compounds by 39. Combining "Weights of the Elements. — For every element a certain number can be selected, such that the proportions by weight in which this element enters into combination with others can be expressed by the number or by a simple multiple of it. These numbers are called the comMning weights. It is not by any means an easy matter to deter- mine which numbers are most convenient for all cases; and if the selection is to be determined solely by convenience, there may be difEerences of opinion as to what is most con- venient. We shall see a little laj;er that while the numbers primarily express the combining weights and nothing else, and are based solely upon determinations of the composition of chemical compounds, they have come to have a deeper meaning, and are now determined by methods which you cannot well understand until you have gone further into chemistry. The facts which it is of the highest impor- tance that you should understand now are : (1) That chemical action takes place between definite weights of substances ; and (2) That the relative weights of the elements which enter into combination with one another can be expressed by numbers called the combining weights. Symbols of Chemical Compounds. — You have learned that the chemist uses a kind of short-hand to express the names of the elements. Instead of the name oxygen he writes the symbol 0, etc. Now these symbols stand not only for 8 34 THE ELEMENTS OF GHEMI8TRT. the names but also for the combming weigbts of tbe ele- ments. Thus, stands not only for tbe name oxygen but for 16 parts by weight; Fe stands for 56 parts by weight of iron, etc. To express a compound in the short-hand, the symbols of the elements contained in it are simply placed side by side. Thus, common salt or sodium chloride consists of the elements sodium and chlorine, which are combined in the proportion of their combining weightiS. The symbol of the compound is NaOl, which means a com- pound of the elements sodium and chlorine in the propor- tion 33 of sodium and 35.5 of chlorine. How Chemists Express Chemical Reactions. — The symbols are of great convenience when it is desired to express what has taken place in a chemical reaction. Thus you have seen that when the compound mercury oxide, HgO, is heated, it is decomposed into mercury and oxygen, a fact which is clearly expressed by the equation HgO = Hg + 0, which tells not only the fact that decomposition takes place but the proportions by weight in which the substances take part. Thus, the compound, HgO, contains the elements in the proportion of 200 parts of mercury to 16 parts of oxygen. When 316 parts of this compound are decom- posed 200 parts of mercury and 16 parts of oxygen are obtained. A Chemical Problem. — Suppose you wished to know how much oxygen is contained in 50 grams of mercury oxide, how could you determine it? You know that in 216 parts of the compound there are 16 parts of oxygen; or, that in 316 grams of the compound there are 16 grams of oxygen. How many grams of oxygen are there in 50 grams of the OOMBININQ WEIGHTS. 35 compound? Plainly the answer is given by solving the expression 316 : 50 :: 16 : the miniber_of grams of oxygen contained in 50 grams of the oxide. Law of Multiple Proportions. — Two elements frequently combine in more than one set of proportions. Thus, while ordinarily iron and sulphur combine in the proportion 56 of iron to 33 of sulphur, they also combine in the propor- tion 56 of iron to 64 of sulphur. Tin combines with oxy- gen in two proportions, forming two distinct compounds. In one 118 parts of tin are combined with 16 parts of oxy- gen; in the other 118 parts of tin are combined with 33 parts of oxygen. The elements potassium, chlorine, and oxygen combine in several proportions as represented here : Potassium 39 39 39 39 Chlorine 35.5 35.5 35.5 35.5 Oxygen 16 33 48 64 It will be observed that while in the compounds men- tioned the quantities of oxygen and sulphur united with bhe same element or elements vary, these quantities are closely related to one another. In the case of iron and sul- phur there is twice as much sulphur, relatively, in one compound as in the other. So, also, in the compounds of tin and oxygen there is twice as much oxygen combined with a given quantity of tin in one case as in the other. Finally, in the four compounds which are made up of potassium, chlorine, and oxygen the quantity of oxygen varies, being twice as great in the second compound as in the first, three times as great in the third, and four times as great in the fourth. These facts, and others of the same kind, are summed up in the Law of Multiple Propor- tions, which may be stated thus: 36 THB ELEMENTS OF CHEMISTBT. If two elements, A and B, combine in different propor' tions, the relative quantities of B which comhine with any fixed quantity of A bear a simple ratio to one another. Symbols of Compounds of Elements Combined in More than One Proportion. — ^As has already been stated, when two elements combine in the simplest proportion the symbol of the compound is made by putting the symbols of the elements side by side, as in HgO, NaCl, etc., etc. If it is desired to represent compounds of the same elements com- bined in different proportions, use is made of small figures placed below the line, as iu the symbols SO^, CO,, H^SO^, etc. , etc. The meaning of the figures is simply this : In the compound SO, sulphur and oxygen are combined in the proportion of the combining weight (33) of sulphur and twice the combining weight (16) of oxygen, or 32 parts of sulphur to 33 parts of oxygen, which happens to be the same as 1 part of one to 1 part of the other. The symbol HjSO, represents a compound made up of hydrogen, sul- phur, and oxygen in the proportion ttvice the combining weight of hydrogen (1), the combining weight of sulphur (33) and four times the combining weight (16) of oxygen ; or 3 parts hydrogen, 33 parts sulphur, and 64 parts oxygen, making all together 98 parts of the compound. Peoblem.^How much sulphur is there ia 60 grams of the com- pound HsSOi (sulphuric acid) ? How much oxygen ? How much hydrogen ? NITMOGEN. 37 CHAPTER V. NITROGEN. Occurrence of Nitrogen. — You have already learned that about four fifths of the bulk of the air is nitrogen. This element is also found in combination in a large number of substances in nature. It is found in the nitrates, as salt- petre or potassium nitrate, KNO3, and Chili saltpetre or sodium nitrate, Na!N"03. It is also found in the form of ammonia, ■which is a compound of nitrogen and hydrogen of the formula NH3. jimmonia occurs in small quantity in the air, and is formed under a variety of conditions, which -will be referred to when the substance is considered. Nitrogen occurs, further, in most animal substances in chemical combination. Preparation of Nitrogen. — The most convenient way to prepare nitrogen is to burn a piece of phosphorus in a bell- ]ar over water. The reasons why phosphorus is better for the purpose than most other substances are (1) because it burns, that is combines with oxygen, easily ; and (2) be- cause the compound which it forms with oxygen (the pro- duct of combustion) is a solid and dissolves in water. If the product of combustion were a gas this would remain mixed with the nitrogen after the combustion. Experiment 37. — Place a wide-moutbed jar over water in a larger vessel of water. In the middle of a flat cork about three inclies in diam«ter fasten a small porcelain crucible, and float this on the water in the trough. Put in it a piece of phosphorus 38 THE ELEMENTS OF CHEMI8EBY. about twice the size of a pea, and set fire to the phosphorus. Quickly place the jar over it on a support which will prevent the jar from sinking more than an inch or two in the water. At first some air will be driven out of the vessel on account of the expan- sion due to the heat. After the burning has stopped cover the mouth of the jar with a glass plate and turn it mouth upward. Try the effect of introducing successively several burning bodies into the nitrogen, as, for example, a candle, a piece of sulphur, phosphorus, etc. Other Substances besides Phosphorus may be TTsed.— Any- thing that has the power to combine with oxygen may be used in the preparation of nitrogen from the air. Metallic copper is convenient, and is not unfrequently used. It is only necessary to pass air over heated copper, when the metal combines with oxygen, forming the solid copper ox- ide, CuO, leaving the nitrogen uncombined. Properties of Nitrogen. — ^You have seen that nitrogen is a colorless, tasteless, inodorous gas. It does not support combustion, nor does it bum. [Suppose nitrogen were combustible, what would be the composition of the atmos- phere ?] Nitrogen not only does not combine with oxygen readily, but it does not combine with any other element easily except at a very high temperature, and then with only a few. Just as it does not support combustion, so also it does not support breathing. An animal would die in it, not on account of any active poisonous properties possessed by it, but for lack of oxygen. In the air it serves the use- ful purpose of diluting the oxygen. If the air consisted only of oxygen, all processes of combustion would certainly be much more active than they now are. "What the effect on animals of the continued breathing of oxygen would be it is difficult to say, as but few experiments pn this subject have been made. NITBOQEm 39 Jitrogen and Oxygen are Mixed together, not Chemi- cally Combined in the Air. — It is not an easy naatter to prove this statement satisfactorily, but the evidence is so strong that no chemist doubts it. (1) If nitrogen and oxygen are mixed together, the mixture acts just like air. When they are mixed there is nothing to show that chemical action takes place. You have seen that the combination of two substances gives rise to heat. When nitrogen and oxygen are mixed together there is no change in the temperature of the gases. (2) Substances known to be chemical compounds do not vary in composition; that of the air does vary slightly. (3) Air dissolves somewhat in water. If air which has been thus dissolved be pumped out and analyzed, it is found to have a composition different from that of ordinary air. Instead of containing 1 volume of o.xygen to 4 vol- umes of nitrogen, it will contain 1 volume of oxygen to 1.87 volumes of nitrogen. The relative quantity of oxygen is much larger in air which has been dissolved in water than in ordinary air= This is due to the fact that oxygen dissolves more readily in water than nitrogen does. If the gases were in chemical combination the compound would probably dissolve without chang3 of composition. Summary. — The air consists of nitrogen and oxygen in the proportion of 4 volumes of the former to 1 volume of the latter. Oxygen supports combustion; nitrogen does not. Oxygen supports respiration; nitrogen does not. Oxygen and nitrogen are elements. They are not chemically com- bined in the air. Oxygen is made by heating substances which contain it, as, for example, mercury oxide and po- tassium chlorate. Nitrogen is made by burning phos- phorus in a closed vessel containing air. 40 TEE ELEMENTS OF CHEMISTRY. Eiements combine in definite proportions by weight (law of definite proportions). In each element a number may be selected by means of which the proportion by weight in which it enters into combination may be expressed (combining weights). If an element combines with another in more than one proportion^ the quantities which enter into combination with a fixed quantity of the second element bear a simple ratio to one another (law of multiple proportions). WATEB. 41 CHAPTER VI. WATER. Occurrence of "Water in Nature. — The wide distribution of water on the earth is familiar to every one. But water also occurs in forms and conditions which prevent it from being easily recognized. Thusj all living things contain a large proportion of water, which can be driven off by heat. If a piece of wood or a piece of meat be heated, water passes off. Experiment 28. — In a dry tube heat gently a small piece of wood. What evidence do you obtain that water is given off ? Do the same thing with a piece of fresh meat. Large Proportion of Water in Animal and Vegetable Substances. — The proportion of water in animal and vege- table substances is very great. If the body of a man weighing 150 pounds were put into an oven and thorough- ly dried there would be left only about 50 pounds of solid matter, all the rest being water. As all meat, vegetables, and food-stuffs in general contain a similar large propor- tion of water, it is evident that water is an important arti- cle of commerce. When you buy four pounds of beef you pay for about three pounds of water and one pound of solid matter. Water of Crystallization. — ^Many chemical compounds when deposited from solutions in water often appear in regular forms called crystals. These frequently enclose w^ter in chemical combination^ and this wa.ter is necessary 42 THE ELEMENTS OF CHEMISTBT. in order that the substance may exist in the form of crys- tals. Water thus held in combination is called water of crystallization. Experiment 29. — Dissolve some ordinary alum in water (6-8 ounces alum to 200 com. water) by the aid of heat. Filter through a plaited filter and allow the filtered solution to cool. Crystals of alum will be deposited. Pour off the liquid above and place a few of the crystals on a piece of dry filter-paper. After the water is all absorbed from them and they appear dry, put them in a dry test-tube and heat gently. What evidence have you that water is contained in the crystals ? EXPEEIMENT 30. — Perform a similar experiment with some gypsum, which is the natural substance from which " plaster of Paris" is made. Experiment 31. — Heat a few small crystals of copper sulphate or " blue vitriol." In this case the loss of water is accompanied by a loss of color. After all the water is driven off, the powder left behind is white. On dissolving it in water, however, the so- lution will be seen to be blue ; and if this solution be evaporated until the substance is deposited, it will appear in the form of blue crystals. Efflorescent and Deliquescent Substances. — Some sub- stances which contain water of crystallization give it up very easily when exposed to the air. Such substances are called efflorescent. Experiment 32. — Select a few crystals of sodium sulphate or Glauber's salt which have not lost their lustre. Put them on a watch-glass, and let them lie exposed to the air for an hour or two. They soon lose their lustre, and become white and powdery on the surface. Some compounds if deprived of their water of crystalli- zation will take it up again when allowed to lie in an atmosphere containing moisture. Such substances are called deliquescent. As the air always contains moisture, it is only necessary to expose such compounds to the air in order to notice the change. It is well shown by the WATUS. 43 compound calcium chloride, OaOl^. This substance has a remarkable power of attracting water and holding it in combination. Experiment 33. — Expose a few pieces of calcium chloride to the air. Its surface will soon give evidence of being moist, and after a time the substance will dissolve in the water which is ab- sorbed. Water is a Compound, — That water is a compound and not an element can be shown by passing an electric current through it. If the ends of the wires connected with a galvanic battery be put in water a short distance apart it will be noticed that bubbles of gas rise from each wire. As these gases cannot well come from the wires, the most probable supposition is that they are formed from the water. ExPEEiMENT 34. — To the ends of the copper wires connected with two cells of a Bunsen's or Grove's battery fasten small plati- num plates, say 35 mm. (1 inch) long by 12 mm. (i inch) wide. Insert these platinum ends into water contained in a shallow glass vessel about 15 em. (6 inches)wide and 7 to 8 cm. (3 inches) deep, taking care to keep them separated from each other. No action will take place, for the reason that water will not conduct the current, and hence when the platinum ends are kept apart there is no current. By adding to the water one tenth its own volume of strong sulphuric acid it acquires the power to conduct the current. It will then be observed that bubbles rise from each of the platinum plates. In order to collect the gases the ap- paratus may be arranged as shown in Pig. 11. A and B repre- sent glass tubes which may conveniently be about 30 cm. (1 foot) long and 35 mm. (1 inch) internal diameter. They should be marked by means of a file, or by etching, so that equal divisions can be recognized. Tubes thus marked so that the divisions in- dicate cubic centimetres are most convenient, and are easily ob- tained of dealers in chemical apparatus. The tubes are first flUed with the water containing one tenth its volume of sulphuric acid, and then placed with the mouth under water in the vessel C. The platinum plates are now brought beneath the iuverted 44 THE ELEMENTS OF 0HEMI8TBY. tubes. The bubbles will rise in tbem and displace the water. Gradually the water will be completely forced out of one of the tubes, while the other is still half full of water. The substance which we have thus collected in each of the tubes is an invisible gas. After the first tube is full of gas, remove it by placing your thumb over the mouth. Turn it mouth upward, and at once ap- ply a lighted match to it. A flame will be noticed. The gas ^J> ? they are the figures best adapted to expressing the relative weights of these elements which enter into combination. A similar connection exists between the relative weights of equal volumes of some other elementary gases and their combining weights, as will be seen later. All Combining Weights are Referred to that of Hydro- gen. — The figures called the combining weights express the relations between the weights of the different elements which enter into combination. When we say that the combining weight of hydrogen is 1 and that of oxygen is 16, we mean that the weight of oxygen which generally enters into combination is sixteen times as great as the weight of hydrogen which enters into combination. The figures 2 and 32 would express this relation Just as well; so would 6J and' 100; but the simplest figures which can be used are 1 for hydrogen and 16 for oxygen. Having adopted these, all other combining weights are referred to these. Hydrogen a Liquid, — At a very low temperature and high pressure hydrogen becomes liquid. hybboqen: 51 Chemical Properties of Hydrogen. — Under ordinary cir- cumstances hydrogen is not a particularly active element. It does not unite with oxygen at ordinary temperatures, but, like wood and most other combustible substances, needs to be heated up to the kindling temperature before it will burn. You have seen that it burns if a lighted match be applied to it. The flame is colorless, or very slightly blue. As burned under ordinary circumstances the flame is col- ored, in consequence of the presence of foreign substances; but that it is colorless when the gas is burned alone can be shown by burning it from a platinum tube, which is itself not acted upon by the heat. Experiment 42. — If there is no small platinum tube available, roll up a small piece of platinum-foil and melt it into the end of a glass tube, as shown in Fig. 17. Connect the burner thus made with a bottle or gasometer containing hydrogen, and after ll the gas has been allowed to issue | In from it for a moment * set fire to 1 1 m it. ■ In a short time it will be seen MM that the flame is practically color- ' ^^^i^^s^ nHnT ^^i^^^^ F less and gives no light. That it li^^M^^™*"^™**^^ is hot is shown by holding a piece of platinum wire or a piece of some other metal in it. The Burning of Hydrogen. — Hydrogen burns. You have already learned that burning consists in combining with oxygen. On the other hand, substances which burn in the air are extinguished when put in a vessel containing hydro- gen. This is the same as saying that a body which is com- * Always be caulious in working with hydrogen. The danger con- sists in the fact that a mixture of hydrogen and oxygen or hydrogen and air is extremely explosive. It requires a flame or spark to explode it. Always let the gas escape for a time, and collect a test-tube full and light to see if it will bum quietly, before applying a flame to it. 52 THE ELEMENTS OF GHEMJ8TBT. bining with oxygen does not continue to combine witb oxygen wben it is put in an atmos- phere of hydrogen, and does not com- bine with hydrogen. This is ex- pressed by saying that hydrogen does not support combustion. Experiment 43. — Hold a wide-mouthed bottle or cylinder filled with hydrogen with the mouth downward. Insert into the vessel a lighted taper held on a bent wire, as shown in Fig. 18. The gas takes fire at the mouth of the vessel, but the taper is extinguished. On withdrawing the ta- per and holding the wick for a moment in ■ ■ the burning hydrogen, it will take fire, but on putting it back in the hydrogen it will be again extin- guished. Other burning substances should be tried in the same way. WATER. m CHAPTER VIII. WATER {Oontinued). Composition of Water. — In Chapter VI. you learned that hydrogen and oxygen are both set free when an electric current is passed through water. It remains to be seen whether these are the only elements contained in water. If water consists only of hydrogen and oxygen, then when these elements combine water should be formed. But when hydrogen burns it combines with oxygen. Is water formed when hydrogen bums ? Experiment 44. — Pass hydrogen from a generating-flask or a gasometer through a tube containing some substance that will absorb moisture, for all gases collected over water are charged with moisture. You have seen in Experiment 33 that calcium Fig. 19. chloride has the power to absorb moisture. It is extensively used in the laboratory fof the purpose of drying gases, and it may be used iu the present experiment. It should be in small pieces 64 TEE ELEMENTS OF CHEMISTS Y. about the size of a pea, not powdered. After passing the hydro- gen through the calcium chloride, pass it through a tube ending in a narrow opening and set fire to it. (Take the precaution mentioned in the foot-note, page 51.) If now a dry vessel be held over the flame, drops of water will condense on its surface and run down. A convenient arrangement of the apparatus is shown in Fig. 19. A is the calcium chloride tube. Before lighting the jet hold a glass plate in the escaping gas, and see whether water is deposited on it. Light the jet before putting it under the bell-jar; otherwise, if hydrogen is allowed to escape into the vessel it will contain a mixture of air and hydrogen, and this mixture is explo- sive. Hydrogen and Oxygen do not Combine at the Ordinary Temperature. — If they did, hydrogen would take fire the moment it comes in contact with the air. If we mix the gases together and allow the mixture to stand unmolested, it remains unchanged. If, however, we should bring a spark or a flame in contact with the mixture a violent ex- plosion would occur, and a careful examination would show that the explosion is caused by the combination of the two gases. The combination causes heat. The heat causes the gases to expand greatly and suddenly, and the noise is caused by this sudden expansion. The expansion is fol- lowed by a contraction. Experiment 45. — Mix hydrogen and oxygen in the proportion of about 3 volumes of hydrogen to 1 volume of oxygen in a gas- ometer or large bottle. Fill soap-bubbles, made as directed in Ex periment 41, with this mixture and allow them to rise in the air. As each one rises bring a lighted taper in contact with it, when a sharp explosion will occur. Great care must be taken to keep all flames away from the vicinity of the vessel containing the mix- ture. Measuring the Volumes of Hydrogen and Oxygen which Combine to Form "Water. — The last experiment simply showed that when a flame comes in contact with a mixture cffip WATER. 55 of hydrogen and oxygon an explosion occurs. To stow what else takes place the experiment must be performed in a closed -vessel. This experiment has been performed many times. As it would be difficult for you to repeat it you will have to be satisfied with a description of the apparatus used and a statement of the result obtained. A tube is used which is marked on the outside so that the volume of gases contained in it can be seen, and has two small plati- num wires passed through it at the closed end, nearly meeting inside and ending in loops out- side, as shown in Fig. 20. It is called a eudio- meter. It is filled with mercury and inverted in a trough containing mercury. A quantity of pure hydrogen is now passed up into the tube and its volume accurately measured. Then Just half this volume of oxygen is introduced, and after the mix- ture has stood for a few minutes, so that the gases can become thoroughly mixed, an electric spark is -> passed between the wires inside the tube by con- necting the loops with the poles of a small Ruhm- korfE coil or with a Leyden jar. The explosion takes place noiselessly and with very little danger. If the interior of the tube was dry before the ex- plosion, it will be seen to be moist afterwards. The ^^' ^' liquid water which is formed occupies almost no space as compared with the space occupied by the two gases before combination. Now, if the experiment be performed with the two gases in diifferent proportions, it will be found that only when they are mixed in the proportion of 3 volumes of hydrogen to 1 volume of oxygen do they completely disappear when exploded. If there is a larger proportion of hydrogen present, the excess is left over. If there is a 66 tbe elements of chemistbt. larger proportion of oxygen presentj the excess of oxygen is left over. Thus it is shown that when hydrogen and oxy- gen combine to form water, they do so in the proportion of 2 volumes of hydrogen to 1 volume of oxygen. Formation of Water by Passing Hydrogen over Heated Oxides. — Water may be formed by passing hydrogen over a compound containing oxygen and heating. A convenient substance for the purpose is the compound of copper and oxygen known as copper oxide or black oxide of copper. It contains its elements in the proportion represented by the formula CuO. At ordinary temperature hydrogen does not act upon this substance. At a high temperature the hydrogen combines with the oxygen, forming water, and the copper is left behind as such. The reaction is represented thus : CuO + 2H = H,0 + Cu. Experiment 46. — Arrange an apparatus as shown in Fig. 21. o Fig. 31. ^ is a "Wolff's flask for making hydrogen. To remove impurities the gas is passed through a solution of potassium permanganate contain|d in the wash-cylinder B. The cylinder contains con- centrated sulphuric acid, and the U-shaped tube D contains gran- ulated calcium chloride, both of them serving to remove moisture from the gas. The pure dry hydrogen is now passed through the hard glass tube E, which contains a layer of copper oxide. After the apparatus is filled with hydrogen the burner under E is WATER. SI lighted, and the copper oxide heated to low redness. Soon mois- ture will be seen in the end of the tube and drops of water will collect in the vessel G. How this Experiment Shows the Composition ofWater. — The copper oxide loses its oxygen and of course loses weight. If, therefore, you should, weigh the copper oxido before the experiment, and afterward the copper, and should also collect and weigh the water formed, you could from the figures obtained easily calculate the relative weight of oxygen contained in water, thus : Let X = weight of tiibe + copper oxide before the experiment; y = weight of tube + copper after the experiment. Then x— y = weight of oxygen taken from the copper oxide. The water formed is collected in a small tube containing calcium chloride. Let a = weight of calcium chloride tube before ; 6 =; weight of calcium chloride tube after. Then h — a— weight of water formed. If the experiment is carefully performed, it will be found that T is very nearly equal to f, which means that by weight oxygen forms eight ninths of water. Oxidation and Reduction. — Any substance which like hydrogen has the power to abstract oxygen from com- pounds containing it is called a reducing agent. The pro- cess of abstracting oxygen from a compound is called re- duction. Reduction and oxidation arc opposite processes. Applications of the Heat Evolved by the Combination of Hydrogen and Oxygen. — The heat evolved when hydrogen combines with oxygen is very great, and it is utilized for various purposes. To burn hydrogen in the air is, as we have seen, a simple matter, but to burn it in oxygen re- 58 THE ELEMENTS OF CHEMISTRY. quires a special apparatus to prevent tlie mixing of the gases before they reach the end of the tube where the com- bustion takes place. The oxyhydrogen blow-pipe answers this purpose. It is simply a tube with a smaller tube pass- ing through it, as shown in Pig. 33. Fio. 23. The hydrogen is admitted through a and the oxygen through b. It will be seen that they come together only at the end of the tube. The hydrogen is first passed through and lighted; then the oxygen is passed through ■ slowly, the pressure being increased until the flame ap- pears thin and straight. It gives very little light, but it is intensely hot. ExPEEiMENT 47. — Hold in the flame of the oxyhydrogen blow- pipe successively a piece of iron wire, a piece of a steel watch- spring, a piece of copper wire, a piece of zinc, a piece of platinum wire. The Oxyhydrogen Blow-pipe Used in Working Platinum. — The metal platinum is used for many purposes, particularly for making chemical apparatus. The vessels are made from molten platinum, and the metal is melted by means of the oxyhydrogen blow-pipe. The Lime-light or Drummond Light.— When the flame of the oxyhydrogen blow-pipe is made to strike against some substance which it cannot melt nor burn up, the substance becomes heated so high that it gives off intense light. The substance commonly used is quicklime. WATEEt. 69 Hence the light is generally called the lime-light. It is also known as the Drummond light. Experiment 48.— Cut a piece of lime of convenient size and shape, say an inch long by three quarters of an inch wide and the same thickness. Fix it in position so that the flame of the oxy- hydrogen blow-pipe will strike upon it. The light is very bright, but by no means as intense as the electric light. Properties of Water. — Though, as we know, water is widely distributed over the earth, we never find it perfectly pure. All natural waters contain foreign substances in solution. These substances are taken up from the air or from the earth. Pure water is tasteless and inodorous. In thin layers it is colorless, but in thick layers it is blue. This has been shown in the laboratory by filling a long tube with distilled water. When looked through it appears blue. The beautiful blue color of some mountain lakes is the natural color of pure water. On cooling water contracts until it reaches the tempera- ture of 4° 0. At this point it has its maximum density. When cooled below 4° it expands, and the specific gravity of ice is somewhat less than that of water. Hence ice floats on water. Natural Waters. — The purest water found in nature is rain-water, particularly that which falls after it has rained for some time. That which first falls always contains im- purities from the air. As soon as the rain-water comes in contact with the earth and begins its course toward the sea it begins to take up various substances, according to the character of the soil with which it comes in contact. Mountain streams which flow over rocky beds, particularly beds of sandstone, which is very insoluble in water, contain exceptionally pure water. Streams which flow over lim^ 60 THE ELEMENTS OF CHEMISTRT. stone dissolve some of the stone^ and the water becomes ''hard." The many varieties of mineral springs have their origin in the presence in the earth of certain sub- stances which are soluble in water. Common salt occurs in large quantities in different parts of the earth. As it is easily soluble in water^ many streams contain it; and as all the streams find their way into the ocean, you see one reason why the water of the ocean is saltij.- Effervescent Waters are such as contain some gas, usually carbonic-acid gas, in solution and give up a part ol it when placed in open vessels. Chalybeate Waters contain some compound of iron. Sulphur-water contains a compound of hydrogen and sulphur, called hydrogen sulphide or sulphuretted hydrogen (which see). Impure Waters. — As streams approach the habitations of man they are likely to become contaminated. The drain- age from the neighborhood of human dwellings is very apt to find its way into a near stream. This condition of things is most strikingly illustrated by the case of a large town situated on the banks of a river. It frequently happens that the water of the river is used for drinking purposes, and it also frequently happens that the water is contami- nated by drainage. Water when once contaminated by drainage tends to become pure again by contact with the air in consequence partly of the action of the oxygen. Hence river- water may become fit for use after having been impure. If it is to be used for drinking purposes, however, it is not well to rely too much upon this process of purifi- cation. Wells should not be dug too near dwellings and farm- houses, as the drainage may find its way into them beneath WATER. 61 the surface of the earth. This is a frequent source of danger, as some diseases are communicated from one person to another by means of contaminated drinking-water. Distillation. — Water may be purified by means of distil- lation. This consists in boiling the water, and then con- densing the vapor by passing it through a tube which is kept cool by surrounding it with cold water. By means of distillation most substances in solution in water can be got rid of. Substances which are volatile, however, will of course pass over with the water vapor. Aboard ship salt water is distilled and thus made fit for drinking. In chem- ical laboratories ordinary water is distilled in order to purify it for fine work with chemical substances. A simple ap- paratus to illustrate the process of distillation is that shown in Fig. 23. Fio. 23. The water to be distilled is placed in the flask A. The flask is connected by means of a bent glass tube B with the long tube OG. This in turn is surrounded by the larger tube or jacket D. The side tube E is connected with a faucet by means of the rubber tube G. The water is allowed to flow slowly into the jacket and out at F, whence 62 TME ELEMENTS OP GBEM18TBT. it passes through the rubber tube H to the sink. When the water in A is boiled, the vapor passes into the tube CO. Here it is cooled down, and takes the form of liquid, which runs down and collects in the flask K called the receiver. The apparatus therefore consists of three parts : the distil- ling-flask, the condenser, and the receiver. Experiment 49. — Dissolve some copper sulphate, or some other colored substance, in a litre of water, and distil the water. Uses of Water in Chemistry. — Water is the best solvent. A greater number of substances dissolve in it than in any other liquid. Chemical operations are frequently carried on in solution. That is to say, the substances which are to act chemically upon one another are first brought into solution. The object of this is to get the substances into as close contact as possible. If we rub two solids together, the particles remain separated by sensible distances, no matter how finely the mixture may be powdered. If, how- ever, the substances be dissolved and the solutions poured together, the particles of the liquid move so freely among one another that they come in intimate contact, thus aiding chemical action. In some cases substances which do not act upon one another at all when brought together in dry condition act readily when brought together in solution. (Experiments 8 and 9.) Solution. — In a solution the particles of the solid dis- solved are in some way attracted and held in combination by the particles of the liquid. There is a limit to the amount of any substance which can be held in solution at a given temperature. The substance dissolved is distributed uniformly through the solution, no matter how dilute or how concentrated the solution may be, provided it has stood long enough, or has been thoroughly mixed by stirring. WATEB. 63 In representing by an equation a reaction whidi takes place between substances in solution, it is not customary to take account of the water which acts as a solvent. Summary. — You have thus learned that (1) Water can be decomposed into hydrogen and oxygen by means of an electric current; (2) The gases are obtained in the proportion of eight parts by weight of oxygen to one part by weight of hydro- gen, or one volume of oxygen to two volumes of hydrogen; (3) "When hydrogen is burned water is formed; (4) When hydrogen and oxygen are mixed together they do not combine under ordinary circumstances; (5) When a spark or flame is brought in contact with the mixture, violent action accompanied by explosion takes place; (6) The action is caused by the chemical combination of the two gases; (7) They combine in the same proportions as those in which they are obtained from water by the action of the electric current; ■(8) Water can be made by passing hydrogen over heated copper oxide; (9) By weighing the copper oxide before and after the experiment, and determining the weight of the water formed, the proportion of water which consists of oxygen is found to be eight ninths. Formula of Water. — All the facts taken together prove that the composition of water is what it has been stated to be. Now, using the accepted combining weights of hydro- gen and oxygen, viz., 1 and 16, the simplest formula which expresses the composition of water is H,0. This expresses the fact that water is composed of 3 parts by weight of 64 TEB ELEMENTS OF CHEMISTRY. hydrogen and 16 parts by weight of oxygen, or 1 part of the former to 8 parts of the latter. If 8 were adopted as the combining weight of oxygen the formula of water would be HO. Comparison of Hydrogen and Oxygen. — Hydrogen and oxygen are different kinds of matter, Just as heat and elec- tricity are different kinds of energy. Heat can be con- verted into electricity, and electricity into heat, but one element cannot by any means known to us be converted into another. They appear to be entirely independent of each other. If we compare hydrogen with oxygen we find very few facts which indicate any analogy between the two elements. In their physical properties they are, to be sure, similar. Both are transparent, colorless, inodorous gases. On the other hand, oxygen combines readily with a large number of substances with which hydrogen does not com- bine. Oxygen, as you have seen, combines easily with car- bon, sulphur, phosphorus, and iron. It is a difficult matter to get any of these elements to combine directly with hy- drogen. Further, it is a general truth that substances which combine readily with hydrogen do not combine read- ily with oxygen. The two elements have opposite chemi- cal properties. "What one can do the other cannot do. Opposite Chemical Properties are Favorable to Combina- tion. — Not only do hydrogen and oxygen, with their oppo- site properties, combine with great ease under the proper conditions, but, as we shall see later, it is a general rule that elements of like properties do not readily combine with one another, while elements of unlike properties do readily combine with one another. Ozone. — When electric sparks are passed for a time through oxygen it is changed in a remarkable way. It ac- WATER. 65 quires a strong odor and is much more active than the substance which we call oxygen. The odor of the gas is noticed in the neighborhood of an electric machine in ac- tion, and is said to be noticed during thunder-storms. The substance which has the odor is ozone. It is formed in a number of chemical reactions, as when phosphorus acts on air in the presence of water. By cold and pressure it has been obtained in the form of a dark-blue liquid. Ozone is present in small quantities in the air. Relation between Oxygen and Ozone. — When a certain volume of oxygen is converted into ozone the volume of gas is decreased to two thirds. By heating ozone above 300° 0. it is converted into ordi- nary oxygen, and its volume increased from two to three. It is clear that ihe element oxygen can be converted into something else without the addition of anything to it. This might lead you to think that it is not an element. But the substance formed from it has exactly the same weight and can be changed back to oxygen without any- thing being added to it. It follows that the change must take place within the oxygen itself. Hydrogen Dioxide, H^Oj. — Besides water, hydrogen and oxygen form a second compound with each other. This is hydrogen dioxide, H^O,.* It is prepared by treating ba- rium dioxide, BaO^, with sulphuric acid. It is a liquid which decomposes easily into water and oxygen. The ease with which it gives up oxygen makes it a good oxidizing agent. It is now manufactured on a large scale, and is used in medicine. * The reason for writing this formula H2O3 and not HO will he seen later. THE ELEMENTS OF 0SEMI8TMY. CHAPTER IX. COMPOUNDS OF NITROGEN WITH HYDROGEN AND OXYGEN. Destructive Distillation of Animal and Vegetable Sub- stances which Contain Nitrogen. — Whenever a compound containing carbon, hydrogen, and nitrogen is heated in a closed vessel, so that the air cannot reach it, and it cannot burn up, the nitrogen passes out of the compound, not as nitrogen, but in combination with hydrogen, as ammonia. Nearly all animal substances contain carbon, hydrogen, oxygen, and nitrogen, and many of them give off ammo- nia when heated in the way described. Heating in this way is called destructive distillation. Similarly, com- pounds containing carbon, oxygen, and hydrogen, even though they be thoroughly dry, when heated give ofE oxy- gen in combination with hydrogen as water (see Experi- ment 1). The coal which is used for making illuminating- gas contains some hydrogen and nitrogen in chemical com- bination, and when the coal is heated in a closed vessel ammonia is given off. Natural Decomposition of Animal and Vegetable Sub- stances which Contain Nitrogen. — The decay or slow nat- ural decomposition of r.nimal and vegetable substances ex- posed to the air is familiar to every one. It is caused by the action of hosts of minute living things (called microbes) act- ing together with the oxygen of the air. Some animal sub- stances give off ammonia when they decompose in the air. COMPOUNDS OF NITBOQEN. 67 "When animal substances decompose under proper condi- tions either a nitrite or a nitrate is formed; the former is derived from nitrous acid, HlfO^, the latter from nitric acid, HN"0,. In some countries where the conditions are favorable to the process immense quantities of nitrates are found, chiefly potassium nitrate or saltpetre, KNO3, and sodium nitrate or Chili saltpetre, NaKO^; so called because it is found in Chili in large quantities. Prom the nitrates nitric acid can easily be obtained. How Compounds of Nitrogen are Made. — The principal compounds of nitrogen are those which it forms with hy- drogen and oxygen. They are made either from ammonia or nitric acid by methods which will be described. Ammonia, N H,. — The conditions under which ammonia is formed have been mentioned. The chief source at pres- ent is the " ammoniacal liquor" of the gas-works, which is the water through which the gas has been passed for the purpose of removing the ammonia. By adding hydro- chloric acid to this liquid ammonium chloride, commonly called sal ammoniac, is formed. This is the most common compound containing ammonia, and it is therefore used in the laboratory for making ammonia. Preparation of Ammonia. Experiment 50.— To a little ammonium chloride on a watch- glass add a few drops of a strong solution of caustic soda, and notice the odor of the gas given ofif. Do the same thing with caustic potasli. Mix small quantities of quicklime and ammonium chloride in a mortar, and notice the odor. Has ammonium chlo- ride this odor ? To prepare ammonia mix slaked lime and ammonium chloride in the proportion of 3 parts of the former to 1 part of the latter, and gently heat the mixture. It has been shown that besides the ammonia, which is given off in the 68 THE ELEMENTS OF CHEMI8TBT. form of gas, calcium chloride, OaCl,, and water are formecl in the reaction. It is represented thus: 2NH,01 + CaO,H, == 2NH3 + CaCl, + 2H,0. ExPEEiMENT 51.— Arrange an apparatus as shown in Fig. 34. Fia. 24. In the flask put a mixture of 100 grams slaked lime and 50 grams ammonium chloride. Heat on a sand-bath. After the air is driven out, the gas will be completely absorbed by the water in the first Wolff's flask. Disconnect at A, and connect with another tube bent upward. Collect some of the escaping gas by displac- ing air, placing the vessel with the mouth downward, as the gas is much lighter than air. The arrangement is shown in Kg. 35. The yessel in which the gas is collected should be dry, as water absorbs ammonia very readily. Hence also it cannot be collected over water. In the gas collected introduce a burning stick or taper. Does the gas burn? Does it support combustion ? In working with the gas great care must be taken to avoid breathing it in any quantity. After enough has been collected, connect the delivery-tube again with the series of Wolff's flasks, and pass the gas through the Fia. 25. water as long as it is given off. Properties of Ammonia. — Prom the observations made in the experiment just performed you see that ammonia is a COMPOUNDS OF WITBOGEIT. 69 colorless, transparent gas. It lias a very penetrating char- acteristic odor. In concentrated form it causes suffocation. It is but little more than half as heavy as air. It is easily compressed to the liquid form by pressure and cold. When the pressure is removed from the liquefied ammonia it passes back to the form of gas. In so doing it absorbs heat. These facts are taken advantage of for the artificial preparation of ice. Carry's ice-machine is used for this purpose. Ammonia does not burn in the air, but does bum in oxygen. It is absorbed by water in very large quantity. One volume of water at the ordinary temperature dissolves about 600 volumes of ammonia-gas, and at 0° C. about 1000 volumes. Spirits of Hartshorn. — The solution of ammonia in water is what we commonly have to deal with under the name ammonia. In ordinary language it is called "spirits of hartshorn." The solution loses all its gas when heated to the boiling temperature. Nitric Acid, HlSTOj. — To effect the direct union of nitro- gen with oxygen and hydrogen is not easier than to effect the direct union of nitrogen and hydrogen to form ammo- nia. The silent and continuous action of minute living things in the soil is always tending to transform the waste products of animal life into compounds closely related to nitric acid. In general, by oxidation the nitrogen of ani- mal substances is converted into nitric acid, while by re- duction it is converted into ammonia. Preparation of Nitric Acid. — Nitric acid is obtained from a nitrate like potassium nitrate, KNO,, or sodium nitrate, JfaNOj, by treating with sulplmric acid. 2NaN03 + H,SO, = Na.SO, + aHNO.. Sodium „^^ sulphuric , sodium ^ nitric nitrate ^"^ acid S'^* sulphate *"'* acid. 70 TEB ELEMENTS OF CBEMISTET. You see that the hydrogen of the sulphuric acid changes place with the sodium of the nitrate. Experiment 53. — Arrange an apparatus as shown in Fig. 26. Fio. 26. In the retort put 35 grams sodium nitrate (Chili saltpetre) and 1 5 grams concentrated sulphuric acid. On heating gently, nitric acid will distil over and be condensed in the receiver. In the latter stage of the operation the vessel becomes filled with a red- dish-brown gas. The acid which is collected has a somewhat yellowish color. Pure Nitric Acid is a colorless liquid. It gives ofE color- less fumes when exposed to the air. When boiled it under- goes slight decomposition into oxygen, water, and compounds of nitrogen and oxygen. One of these compounds is col- ored, and it is this which is noticed in the last experiment and whenever strong nitric acid is boiled. Ifitric acid suffers a similar decomposition when exposed to the action of thD direct rays of the sun. In consequence of this de- composition bottles containing strong nitric acid sometimes COMPOUNDS OF NITBOaEN. 71 contain a reddish-brown gas above the liquid after standing for some time. Strong nitric acid acts violently on many- substances, particularly those of animal and vegetable origin, decomposing them. It causes bad wounds in con- tact with the flesh; it eats through clothing ; it burns wood; it dissolves metals; and it is altogether one of the most active of chemical substances. In working with it it is necessary to take the greatest care. Ordinary or Commercial Nitric Acid contains only about 68 per cent of the chemical compound HlSTOj. The rest is mostly water, though there are several impurities present in small quantities. How to Make Strong Nitric Acid.*— Pure, strong nitric acid may be made by mixing commercial nitric acid and commercial strong sulphuric acid and distilling. Experiment 53. — Mix together 400 grams ordinary concen- trated sulphuric acid and 80 grams ordinary concentrated nitric acid. Distil the mixture from a retort arranged as in Experiment 52, taking care to keep the neck of the retort cool by placing filter- paper moistened with cold water on it. Use the acid thus ob- tained for the purpose of studying the properties of pure nitric acid. Nitric Acid Gives up Oxygen Eeadily. — Nitric acid is much used on account of the ease with which it gives up oxygen. Many substances burn up in strong nitric acid. Experiment 54. — Pour concentrated nitric acid into a wide test- tube, so that it is about one fourth filled. Heat the end of a stick of charcoal of about the size of a lead-pencil, and, holding the other end with a forceps, introduce the heated end into the acid. It will continue to burn with a bright light, even though it be * The experiments with strong nitric acid may be performed or not as the teacher thinks best. They had better not be performed by the pupils, and should not be performed by any one who is not experi- enced in working with chemical substances. 72 THE ELEMENTS OF 0EEMI8TBY. placed below the surface of the liquid. The action is oxidation. The charcoal in this case finds the oxygen in the acid and not in the air. Great care must be taken in performing this experiment. The charcoal should not come in contact with the sides of the test-tube. A large beaker-glass should be placed beneath the test-tube, so that in case the tube should break, the acid would be caught and prevented from doing harm. The arrangement of the apparatus is shown in Fig. 27. The gases given off from the FiQ. 37. tube are offensive and poisonous. Hence this as weU as all other experiments with strong nitric acid should be carried on either out of doors or under a hood in which the draught is good. ExPEEiMENT 55. — In a small flask put a few pieces of granulated tin. Pour on this just enough strong nitric acid to cover it. Heat gently over a small flame. What takes place ? What is the appearance of the substance left in the flask ? It is mo.stly a com- pound of tin and oxygen. (See Experiment 7.) Action of Nitric Acid upon Some Metals. — Generally when an acid acts upon a metallic element like silver, copper, lead, etc., the hydrogen of the acid is liberated and the metallic element takes its place. Thus when nitric acid COMPOUNDS OF NITROGEN. 73 acts upon silver the action takes place as represented in the equation Ag + HNO, = AgNO, + H. Silver aiid ^^^l ei-e ^^-^ and hydrogen. The substances thus formed are called nitrates. At the same time the hydrogen and a part of the oxygen are taken out of the acid, and compounds of nitrogen and oxygen are formed which are represented by the formulas NO^, NO, and NjO. The first of these, nitrogen peroxide, NO,, is a colored gas, and as some of it is always formed when nitric acid acts upon metals in the air, the presence of the red- dish-brown gas observed in the experiments already per- formed with nitric acid will be readily understood. Experiment 56. — Dissolve a few pieces of copper-foil in ordi- nary commercial nitric acid diluted with about half its volume of water. The operation should be carried on in a good-sized flask and either out of doors or under a good hood. What action takes place ? After it is over what is the appearance of the liquid in the flask ? Pour it out and evaporate to crystallization. Com- pare the substance thus obtained with copper nitrate. — Heat specimens of each. — Treat small specimens with sulphuric acid. — Do the substances appear to be identical ? What reasons have you for considering them identical ? Aqua Regia is made by mixing together concentrated nitric and hydrochloric acid. It is an excellent solvent. It is called aqica regia because it dissolves the king of metals, gold. Similarly nitric acid is called aquafortis, or strong water. In olden times all liquids were regarded as kinds of water, and all gases as kinds of air. The Oxides of Nitrogen. — Nitrogen combines with oxygen in five proportions. The names and symbols of the com- pounds formed are here given. 74 THE ELEMENTS OF GEEMI8TRT. Nitrous oxide NaO Nitric oxide NO or NsOa Nitrogen trioxide NaOj Nitrogen peroxide NOj or NjO, Nitrogen pentoxide NaOs A Good Illustration of the Law of Multiple Proportions. — The combiuing weight of nitrogen being 14, the above sym- bols represent the fact that in the compounds of nitrogen and oxygen the quantities of oxygen combined with 28 parts of nitrogen are 16, 33, 48, 64, and 80 ; or 16, twice 16, three times 16, four times 16, and 5 times 16 parts of oxygen are combined with 38 parts by weight of nitrogen. This series of compounds is an excellent illustration of the law of multiple proportions, which is one of the most im- portant and interesting truths of chemistry. — [What is the law of multiple proportions? How does this series illus- trate it?] Nitrous Oxide, N^O. — This compound is formed by reduc- tion of nitric acid when the acid acts upon metals under favorable conditions of concentration and temperature. It is usually prepared by heating ammonium nitrate. The decomposition takes place as represented, thus: NH.NO, = N,0 + 2H,0 ^T^a^"" Ideated gives -t^- and water. Experiment 57. — In a retort heat 10 to 15 grams crystallized ammonium nitrate until it has the appearance of boiling. Do not heat higher than is necessary to secure a regular evolution of gas. Connect a wide rubber tube directly with the neck of the retort, and collect the gas over water, as in the case of oxygen. Properties of Nitrous Oxide. — It is colorless and transpar- ent and has a slightly sweetish taste. When inhaled it causes a kind of intoxication, which is apt to show itself in the form of hysterical laughing. Hence the gas is com- COMPOUNDS OF NITBOQEN. 75 monly called laughing-gas. Inhaled in larger quantity it causes unconsciousness and insensibility to pain. It is therefore used in certain surgical operationSj particularly in pulling teeth. It supports combustion almost as well as pure oxygen. Experiment 58. — Insert into it a piece of burning wood, a can- dle, and a small piece of phosphorus. Nitric Oxide, NO. — This gas, as has been stated, is formed when nitric acid acts upon some metals, as copper. It seems probable that two changes take place: (1) The copper displaces the hydrogen of the acid, and copper nitrate is formed; and (2) The hydrogen acts upon the nitric acid, reducing it and forming nitric oxide. These two stages may be represented thus: 3HNO3 + Cu = Cu(]Sr03), + 2H; aHKO, + 6H = 4H,0 + 3N0. and hydrogen give water and and Nitric acid nitric oxide. Experiment 59. — Arrange an apparatus as shown in Fig. 28. In the flask put a few pieces of copper-foil. Cover this with water. Now add slowly, waiting each time, ordinary concentrated nitric acid. When enough acid has been added gas will be given off. If the acid is added quickly it not infrequently happens that the evolution of gas takes place too rapidly, so that the liquid is forced out of the flask through the funnel-tube. This can be avoided by not being in a hurry. What is the color of the gas in the flask at first ? What is it after the action has continued for a short time? Collect over water two or three vessels full. Properties of Nitric Oxide. — Nitric oxide is a colorless, transparent gas. Its most re- 76 THE ELEMENTS OF CMEMISTBY. markable property is its power to combine directly with oxygen wlien the two are brought together. The reaction is represented by the equation NO + = NO,. The product is nitrogen peroxide, and this at ordinary temperatures is a reddish-brown gas. Experiment 60. — Turn one of the vessels containing colorless nitric oxide with the mouth upward and uncover it. What takes place ? Explain the appearance of the colored gas in Experiment 59, and the fact that it afterward disappeared. "What was in the vessel at the beginning of the operation ? Bo not inhale the gas. Perform the experiment with nitric oxide where there is a good draught. Experiment 61. — Into one of the vessels containing nitric ox- ide insert a burning candle. Does the gas burn ? Does it sup- port combustion ? Nitric oxide does not burn and does not support com- bustion. Nitrogen Peroxide, NO,. — This is the reddish-brown gas formed in the experiments with nitric oxide. It has a dis- agreeable smell and is poisonous. It is used in large quan- tities in the manufacture of the extremely important sub- stance sulphuric acid, as will be explained farther on. CHLORINE ANB ITS COMPOUNDB. 77 CHAPTEE X. CHLORINE AND ITS COMPOUNDS "WITH HYDROGEN AND OXYGEN. Introductory. — A little later you will see that oxygen and nitrogen are members of families of elements. The other members of the oxygen family resemble oxygen in many respects, and the other members of the nitrogen family resemble nitrogen. Hydrogen, strange to say, does not belong to any family but stands by itself. Another family is the chlorine family, of which chlorine is the best- known member. Occurrence of Chlorine. — Chlorine, though widely dis- tributed in nature, does not occur in very large quantity as compared with oxygen and hydrogen. It is found chiefly in combination with the element sodium as common salt or sodium chloride, which is represented by the symbol NaCl. It is also found in combination with other ele- ments, as potassium, magnesium, etc. In small quantity it occurs in combination with silver, forming one of the most valuable silver ores. All the chlorine with which we have to deal is made from common salt. Preparation of Chlorine. — We cannot decompose sodium chloride directly into its elements. In order to get the chlorine out of the compound in the free state it is neces- sary first to get it in combination with hydrogen in the form of hydrochloric acid, HCl This is very easily ac- 78 TBE ELEMENTS OF CBEMISTUY. complished by treating salt witli ordinary sulphuric acid. The reaction is represented thus: (1) 2NaCl + H,SO, = Na,SO, + 2H01. Sodium -„^ sulphuric _■„. sodium „_ j hydrochloric chloride ^^ acid Sive gulpjiate ™i'iissiate of potash, K^FeCjlSTj + 3HjO, is formed. When this is simply heated it decomposes, yielding potassium cyanide, KCN". Prom the potassium compound it is not difficult to make mercury cyanide, Hg(CN)j. By heating mercury cyanide it breaks up, yielding mercury and cyanogen gas: Hg(CN), = Hg + 0,1^,. [What analogy is there between this reaction and that which takes place when mercury oxide is heated?] Properties. — Cyanogen is a colorless gas, easily soluble in water and alcohol. It is extremely poisonous. Hydrocyanic Acid, Prussia Acid, HCI^. — This acid occurs in nature in combination with other substances, — in bitter almonds, the leaves of cherry, laurel, etc. It is prepared from potassium cyanide, just as hydrochloric acid is pre- pared from sodium chloride. The reaction is: 2K0H + H,SO, = K,SO, + anCK COMPOUNDS OF CABBON. 123 Properties — Hydrocyanic acid is a volatile liquid. It has a very characteristic odor resembling that of bitter almonds. It is extremely poisonous. It dissolves in water, in all proportions, and it is such a solution which is known as prussic acid. Other Compounds of Carbon. — That part of Chemistry which has to do with the compounds of carbon is commonly called Organic Chemistry. It is more convenient to con- sider this subject after the chemistry of the other common elements has been studied. The last part of this book will treat of some of the more common and better known com- pounds of carbon. 124 TBE ELEMENTS OF 0EEMI8TBT. CHAPTER XIV. ATOMIC THEORY — ATOMIC WEIGHTS — MOLECULAR WEIGHTS — VALENCE — CLASSIFICATION OF THE ELEMENTS. The Laws of Chemical Action. — You have learned that there are two laws always governing chemical combination. These are the laws of definite and multiple proportions. These laws are simply statements which sum up what has been found to be true in all cases examined. They are statements of facts discovered by actual experiment. We may Know a Fact without Knowing its Cause. — It is one thing to know a general fact, and quite another to know the cause of the fact. We know that all bodies are attracted by the earth, and that they fall when thrown into the air. But we do not know why this is so. So, too, though we know that substances combine according to the laws of definite and multiple proportions, it does not neces- sarily follow that we know why they combine according to these laws. Hypothesis and Theory. — When a law has been discovered by careful study of the facts, the next thing to be done is to imagine a cause. We try to imagine a condition of things which, if it existed, would lead to the results discov- ered. If we succeed in imagining such a condition of things we suggest an hypothesis. If, now, we test this hy- pothesis in every way that suggests itself, and find that all facts discovered are in accordance with it, we then call it a ATOMIC TEEOBT-YALBNOE. 125 theory. An hypothesis is a guess in regard to the cause of certain phenomena. A theory is an hypothesis which has been thoroughly tested, and which is applicable to a large number of related phenomena.* The Atomic Theory, — The atomic theory was suggested to account for the laws of definite and multiple proportions. The theory is simply this: That all kinds of matter are made up of indivisible par- ticles called atoms; and that the atoms of the different elements have different tveights. Now if, when substances act upon one another, the action takes place between these atoms, and consists either in a union or separation of the atoms, then it is easy to understand why compounds are formed according to the law of definite and multiple proportions. If two elements whose atoms have weights which are to each other as 3 to 9 combine so that one atom of the one combines with one atom of the other, then the compound which is formed will contain the elements in the proportion of 2 parts by weight of the one to 9 parts by weight of the other ele- ment. If they combine so that one atom of the first element combines with two atoms of the other, then the resulting compound will contain the elements in the pro- portion of 2 parts by weight of the one to 18 parts by weight of the other element. * Hypotheses and theories are of great value to science, if founded upon a thorough knowledge of the facts to which they relate. They hecome dangerous when used by those who are not familiar with the facts. The student who has not received a thorough scientific train- ing should remember that theories and hypotheses, to be of value, must be suggested, not by a superficial but by a thorough knowledge of the facts. 126 TBB ELEMENTS OF GRBMISTST. Atomic Weights. — The weights of the elements which have thus far been referred to as combining weights are, in accordance with the atomic theory, the relatire weights of the atoms, or the atomic weigJds. The symbols of the elements represent atoms of the elements. Thus, H repre- sents an atom of hydrogen, an atom of oxygen, etc. As hydrogen enters into combination in smaller proportion than any other element, its combining weight or atomic weight is taken as the unit. "When we say that the atomic weight of oxygen is 16, we mean simply that the atom of oxygen is 16 times heavier than that of hydrogen. Molecules. — As the symbols of the elements represent atoms, so the symbols of compounds represent combina- tions of atoms. The symbol of hydrochloric acid, HCl, represents, according to the theory, the smallest particle of this substance that can exist. It is made up of an atom of hydrogen and an atom of chlorine, which are combined chemically. The symbols HNO^, H^O, N'H, are intended to represent the smallest particles of the compounds that can exist. The smallest particle of nitric acid consists of 1 atom of nitrogen, 1 atom of hydrogen, and 3 atoms of oxygen. These smallest particles of compounds are called molecule". The molecules are made up of atoms. The weight of a molecule is equal to the sum of the weights of the atoms of which it is composed. Avogadro's Law. — A careful study of the conduct of gases has led to the conclusion that equal volumes of all gases under the same conditions of temperature and pres- sure contain the same number of molecules. This is known as Avogadro's law. The Relative Weights of Molecules Determined by Weighing Gases. — If Avogadro's law is true, then by ATOMIC TEE0B7— VALENCE. 127 ■weighing equal volumes of gaseous substances we can learn the relative weights of the molecules of these sub- stances. Atomic Weights Learned from Molecular Weights. — If we knew the molecular weight of all compounds we could easily determine the atomic weights of the elements. It would only be necessary to select the smallest quantity of an element which occurs in any of its compounds. Thus, for example, if we were to examine all known oxygen com- pounds that can be studied in the form of gas or vapor, we should find that the smallest quantity of oxygen found in any molecule is represented by 16. Valence. — The formulas of the compounds thus far con- sidered have all been determined by exactly the same methods. On comparing the formulas of the simplest hydrogen compounds of chlorine, oxygen, nitrogen, and carbon a curious difference is observed. The formulas are CIH, 0H„ NH3, CH,. According to the atomic theory these expressions mean that the molecule of hydrochloric acid consists of 1 atom of chlorine combined with 1 atom of hydrogen; the mole- cule of water consists of 1 atom of oxygen combined with 2 atoms of hydrogen; the molecule of ammonia of 1 atom of nitrogen and 3 atoms of hydrogen; and the molecule of marsh-gas of 1 atom of carbon and 4 atoms of hydrogen. It appears, therefore, that the atom of oxygen can hold in combination twice as many hydrogen atoms as the atom of chlorine can; that the atom of nitrogen can hold three times as many; and the atom of carbon four times as many. Other atoms differ from one another in the same way. 128 THE ELEMENTS OF 0BEMI8TRY. That property of an element by virtue of which its atom can hold in combination a definite number of other atoms is called valence. Kinds of Elements. — The smallest power, as far as the number of other atoms which it can hold in combination is concerned, is that of the chlorine atom. As one chlorine atom can hold but one hydrogen atom in combination, so one hydrogen atom can hold but one chlorine atom. Either the hyilrogen atom or the chlorine atom may be taken as an example of the simplest kind of atom. An element like hydrogen or chlorine is called a univalent element; an element like oxygen whose atom can hold two unit atoms in combination is called a iivalent element; an element like nitrogen whose atom can hold three unit atoms in combination is called a irivalent element; and an element like carbon whose atom can hold four unit atoms in combination is called a quadrivalent element. Most elements belong to one or the other of these four classes. [Calcium forms with chlorine the compound OaCl^. What is the valence of calcium ? Potassium and sodium form chlorides of the formulas KCl and NaCl respectively. What is the valence of these elements ? Sulphur forms with hydrogen a compound of the formula SH,. What is the valence of sulphur ?] Displacing Power of the Elements. — In the formation of salts you have seen that the hydrogen of acids is displaced by metals. In such cases one atom of a univalent metal takes the place of one atom of hydrogen, one atom of a bivalent metal takes the place of two atoms of hydrogen, etc. Thus potassium and sodium are univalent. In the formation of potassium nitrate from nitric acid, HNO,, one atom of potassium displaces one atom of hydrogen in CLASSIFICATION OF THE ELEMENTS. 129 the molecule of nitric acid, forming the salt KNO,. So also sodium nitrate is NaNO^. In the molecule of sul- phuric acid, H,SO^, there are two atoms of hydrogen. To displace these, two atoms of a uniyalent element are re- quired. Thus, potassium sulphate is K,SO,, and sodium sulphate is Na^SO,. Examples of salts containing bivalent metals are the following: zinc sulphate, ZnSO,, in which one atom of bivalent zinc has displaced the two atoms of hydrogen of the sulphuric acid ; barium sulphate, BaSO,, in which one atom of bivalent barium has displaced the two atoms of hydrogen of sulphuric acid. When a bivalent metal forms a salt with an acid like nitric acid, which con- tains but one atom of hydrogen in the molecule, it is be- lieved that one atom of the metal acts upon two molecules of the acid, thus : p,^ , HNO3 _ p,, i NO3 , f. Cu + 2HNO3 = Cu(N03), + H,. The formula of zinc nitrate is similar, viz., Zn(SO^^. In the case of trivalent elements the matter is a little more complicated, but still simple enough if it be borne in mind that a univalent atom displaces one atom of hydrogen ; a bivalent atom displaces two atoms of hydrogen ; a trivalent atom displaces three atoms of hydrogen, etc. Classificatiost of the Elemeistts. Acid Properties and Basic Properties. — The chemical properties which force themselves upon our attention most prominently in whatever field of chemistry we may be working are those which are known as acid properties and 9 or 130 TEE ELEMENTS OF CHEMI8TBY. basic properties. As has already been pointed out, these two kinds of properties are the opposite of each other. No matter how much chemistry may grow, it is certain that the distinction between these two kinds of properties will always be recognized as important. Acid-forming Elements and Base-forming Elements. — In general, both acids and bases contain hydrogen and oxygen. There are some elements whose compounds tvith hydrogen and oxygen have basic properties, and others whose com- pounds with hydrogen and oxygen have acid properties. This important fact may be used as the basis of a partial classification of the elements. According to this, we have (1) acid-for'iidng elem.ents and (3) base-forming elements. Examples of the first class are chlorine, nitrogen, and sul- phur. Examples of the second class are sodium, calcium, magnesium, etc. The last mentioned are generally called metals, and the acid-forming elements are generally called non-metals. Families of Elements. — Another important fact which is soon recognized in studying the elements is that they fall into families according to their chemical properties, the members of the same family showing striking resemblances among one another. Thus, there is the chlorine family, which, includes, besides chlorine itself, bromine, iodine, and fluorine. Further, there is the sulphur family, con- sisting of the closely related elements sulphur, selenium, and tellurium ; besides other families. In all these cases the resemblance between members of the same family is striking. Families of the Acid- forming Elements. — First, we shall have the following families to deal with : CLASSIFICATION OF TEE ELEMENTS. 131 Chlobine Family. Sulphub Family. Nitroobn Family. Cabbow Family. Chlorine, Sulphur, Nitrogen, Carhon, Bromine, Selenium, Phosphorus, Silicon. Iodine, Tellurium. Arsenic, Fluorine. Antimony. As the object of your present study is to get a general idea of the principles of chemistry^ it will not be necessary to go into details in dealing with these families. One member of each family, except the sulphur family, having been treated comparatively fully, the other members may be treated briefly. The members of the sulphur family re- semble oxygen somewhat, but also differ from it in many respects. It will thus be possible to get a clearer idea of the principles of chemistry than by attempting to study a large number of facts. 132 THE ELEMENTS OF 0HEMI8TBT. CHAPTER XV. THE CHLORINE FAMILY: CHLORINE, BROMINE, IODINE, FLUORINE. Introduction. — The three members of this family which show the most marked resemblance are chlorine, bro- mine, and iodine. Fluorine is not known in the uncom- bined state. Its compounds, however, resemble the com- pounds of chlorine, and henco the element is generally included in this family. Bromine {At. Wt. 80). — This elemenb occurs in nature in company with chlorine. Chlorine, as has been stated, occurs mostly in combination with sodium, as sodium chloride, or common salt. In several of the great salt- beds there is some bromine in the form of sodium bromide, l^aBr, and in some places it occurs as potassium bromide, KBr. Preparation of Bromine. — The method is the same as that made use of for extracting chlorine. In order to get chlorine out of common salt, the salt is first converted into hydrochloric acid, and this is then oxidized. So, too, in order to get bromine out of sodium bromide, the bromide must first be converted into hydrobromic acid, and this then oxidized. The reactions are 2NaBr + H,SO, = ISTa^SO, + aHBr ; 3HBr + = H,0 + 2Br. THE CELOBINE FAMILY. 133 Properties of Bromine. — Bromine is a heavy dark-red liquid at ordinary temperatures which is easily conyerted into a brownish red vapor. It has an extremely dis- agreeable odor. Hence its name from a Greek word mean- ing a stench. Its properties are, in general, like those of chlorine. It acts violently upon organic substances. It attacks the skin and the membranes lining the passages of the throat and lungs. Wounds caused by the liquid com- ing in contact with the skin are painful and heal with dif- ficulty. It must, therefore, be handled with great care. It combines with many elements directly and with great energy, its compounds with other elements being called bromides. While acting in general in the same way as chlorine, it is a somewhat weaker element, so that chlorine drives it out of its compounds and sets it free. Experiment 82. — Mix together about a gram of potassium bromide and two grams of manganese dioxide. Pour upon the mixture in a good-sized test-tube sufficient dilute sulphuric acid to cover it. Heat gently. What do you observe ? Perform this experiment where there is a good draught. Hydrobromic Acid, HBr. — The only compound which bromine forms with hydrogen alone is hydrobromic acid. This is in all respects very much like hydrochloric acid. Experiment 83. — In a test-tube put a few crystals of potassium bromide. Pour on them a few drops of concentrated sulphuric acid. The white fumes of hydrobromic acid and the reddish- brown vapor of bromine are noticed. Treat a few crystals of potassium or sodium chloride in the same way. "What difference is there between the two cases ? The explanation of the difference observed is that sulphuric acid decomposes hydrobromic acid, set- ting bromine free, while it does not decompose hydrochloric acid. Compounds with Hydrogen and Oxygen. — With hydrogen and oxygen bromine forms compounds which resemble very closely those which chlorine forms with the same elements. 134 TEE ELEMENTS OF GHEMI8TBY. The principal ones are hromic, HBrOj, and Jiypolromous acids, HBrO, which are like chloric and hypochlorons acids. Iodine, I {^At. Wt. 137). — This element occurs in nature in combination with sodium^ in company with chlorine and bromine, but in smaller quantity than either. It is also found in larger quantity in sea-plants. It is obtained largely from the latter source. On the coasts of Scotland and Prance the sea-weed which is thrown up by storms is gathered, dried, and burned. The organic portions are thus destroyed [what is the meaning of the word destroyed used in this sense?], and the mineral or earthy portions are left behind as ashes. The incombustible residue is called kelp. It contains sodium iodide. At present, in some parts of the ocean, sea-weed is cultivated for the sake of the iodine which it yields. Chili saltpetre, or the natural sodium nitrate found in Chili, contains some sodium iodide, and of late this has furnished a considerable quantity of the iodine of commerce. Preparation of Iodine. — Iodine is prepared from sodium iodide, just as chlorine and bromine are prepared from their compounds with sodium and potassium. Properties of Iodine. — At ordinary temperatures iodine is a grayish-black, crystallized solid. It melts easily and boils, forming a violet-colored vapor. Experiment 84. — Mix about 1 gram potassium iodide with about twice its weight of manganese dioxide. Treat with a little sulphuric acid in a test-tube. Heat gently. G-radually the tube will be filled with the beautiful colored vapor of iodine. In the upper part of the tube some of the iodine will be deposited in the form of crystals of a grayish-black color. Iodine dissolves slightly in water, easily in alcohol, and easily in a water solution of potassium iodide. THE OHLOBINE FAMILY. 135 ExPEKiMENT 85. — Make solutions of iodine in water, in alcohol, and in a water solution of potassium iodide. Use small quantities in test-tubes. When a solution containing /?-«e iodine is treated with a little starch-paste the solution turns blue^ in consequence of the formation of a complicated compound of starch and iodine. Bromine and chlorine do not form blue compounds. Advantage is taken of this fact to distinguish between iodine and other members of the family. Experiment 86. — Make some staroli-paste by covering a few grains of starcli in a porcelain evapo rating-dish with cold water, grinding this to a paste, and pouring 200-300 cc. boiling hot water on it. After cooling add a Httle of this paste to a dilute water solution of iodine. What change takes place ? Now add a little of the paste to a diluted water solution of potassium iodide. Is there any change of color ? Add a drop or two of a solution of chlorine in water. What takes place ? Explain what you have seen. Does chlorine alone form a blue compound with starch ? Hydriodic Acid, HI, is analogous to hydrochloric and hydrobromic acids. It is set free from the iodides by treat- ing them with sulphuric acid; but it is even more unstable than hydrobromic acid, and hence breaks up into hydrogen and iodine. The iodine is set free, while the hydrogen acts on the sulphuric acid, as it does in the case of hydro- bromic acid. Experiment 87. — Treat a few small crystals of potassium iodide with sulphuric acid. [What do you notice ?] Compare with the results obtained when potassium bromide aud sodium chloride are used. Fluorine oceujs in nature in large quantity, and widely distributed, but always in combination with other elements. It is found chiefly in combination with calcium, as fluor- spar, or calcium fluoride, CaF^, and in combination with Bodium and aluminium, as cryolite, a mineral which oc- 136 THB ELEMENTS OF GHEMISTBY. curs abundantly in Greenland, and has the composition SNaF . AlPj, being a complex compound of sodium fluoride and aluminium fluoride. The element fluorine has not been obtained in the free state. Hydrofluoric Acid, HF, is made from fluor-spar by treat- ing it with sulphuric acid. The action is of the same char- acter as that which takes place when hydrochloric acid is liberated from sodium chloride: OaF, + H,SO, = CaSO, + 3HP. It is a colorless gas, with strong acid properties. It greatly irritates the membranes lining the throat and lungs, and hence care should be taken not to inhale it. It acts upon glass, dissolving it, and must therefore be kept in vessels of rubber, lead, or platinum, upon which it does not act. Etching on Glass. — The acid is used for etching on glass, particularly for marking scales on thermometers, barome- ters, and other graduated glass instruments. A solution of the gas in water is manufactured for this purpose and kept in rubber bottles. Experiment 88. — In a lead or platinum vessel put a few grama (5-6) of powdered fluor-spar, and pour on it enough concentrated sulphuric acid to make a thick paste. Cover the surface of a piece of glass with a thin layer of wax or paraffin, and through this scratch some letters or figures, so as to leave the glass ex- posed where the scratches are made. Put the glass with the waxed side downward over the vessel containing the fluor-spar, and let it stand for some hours. Then take off the glass, scrape off the coating, and the figures which were marked through the wax or paraffin will be found etched on the glass. Comparison of the Members of the Chlorine Family. — In considering, first, the physical properties of these elements, you notice that all, with the exception of fluorine, form THE CHLORINE FAMILY. 137 colored gases or vapors. At ordinary temperatures chlorine is a gas, bromine a liquid, and iodine a solid. In regard to their chemical conduct, it may be said that, in general, fluorine is the most active; chlorine comes next in order, then bromine, and lastly iodine. Their Compounds. — The compounds formed by the three elements chlorine, bromine, and iodine with hydrogen and oxygen have analogous compositions, and are formed by analogous reactions. Thus, there are the hydrogen com- pounds: HCl, HBr, and HI; and the compounds with hydrogen and oxygen: HCIO, HBrO. — HCIO,. — — HCIO3, HBrO,, HIO3. HCIO,, HBrO,, HIO,. Relations between the Atomic Weights. — On comparing the atomic weights of chlorine, bromine, and iodine, it will be seen that the atomic weight of bromine, which is 80, is nearly the mean of the atomic weights of chlorine and iodine. 35.5 -f 137 = 162.5; At. Wt. of At. Wt. of chlorine. iodine. and — ^ == 81.35, which is nearly the atomic weight of bromine. Relation between the Properties of the Elements and their Atomic Weights. — The properties of the three ele- ments chlorine, bromine, and iodine vary with the varia- 138 THE ELEMENTS OF CHEMISTRY. tions in their atomic weights, or with the weights of their atoms. The gradation in properties takes place in the order chlorine^ bromine, iodine, and this is also the order in which the atomic weights increase. This may be a mere coincidence, but We shall find that in the other fami- lies there are similar indications of a close connection be- tween the weights of the atoms of the elements and their physical and chemical properties. TEE aULPEUM FAMILY. 133 ,;/ .CHAPTEE XYL \ THE SULPHUR FAMILY: SULPHUR, SELENIUM:, TELLURIUM. Sulphur, S {At. Wt. 33).— The principal member of the family is sulphur. In nature it is frequently found ac- companied by small quantities of selenium, and sometimes by tellurium. It has been known in the elementary form from the earliest times, for the reason that it occurs abun- dantly in this form in nature. It is found particularly in the neighborhood of volcanoes, as in Sicily, which is the chief source of the sulphur of commerce. It occurs, fur- ther, in combination with many" metals as sulphides, — as in iron pyrites, FeS,; copper pyrites, PeCuS^; galenite, PbS, etc. ; in combination with metals and oxygen as sul- phates, — for example, as calcium sulphate, or gypsum, CaSO^ -f 3H5O; barium sulphate, or heavy spar, BaSO,; lead sulphate, PbSO,; and in a few vegetable and animal products in combination with carbon, hydrogen, and, gene- rally, with nitrogen. Extraction of Sulphur from its Ores. — When taken from the mines, sulphur is mixed with many earthy substances from which it must be separated. This separation is ac- complished by piling the ore in such a way as to leave passages for air. The piles are covered with some material to prevent free access of air, and the mass is then lighted below. A part of the sulphur burns, and the heat thus furnished melts the rest of the sulphur. The molten sul- 140 TEE ELEMENTS OF CEEMISTBY. pliur runs do\(n to the bottom of the pile, and is drawn off from time to time. [If the pile were not protected from free access of air what would become of the sulphur? What analogy is there between this process and that made use of in making charcoal? What are the essential differences between the two processes?] How Sulphur is Refined. — The crude brimstone first ob- tained is afterwards refined by distillation, and it is this distilled sulphur which is met with in commerce under the names "roll brimstone," "stick sulphur," and "fiowers of sulphur." The distillation is carried on in earthenware retorts connected with large chambers of brick-work. When the vapor of sulphur first comes oyer into the con- densing chamber it is suddenly cooled, and hence deposited in the form of fine powder. This is what is called "flowers of sulphur." After the distillation has continued for some time the vapor condenses in the form of a liquid, which collects at the bottom of the chamber. This is drawn off into wooden moulds and takes the form of "roll brim- stone" or "stick sulphur." Properties of Sulphur. — Sulphur is a yellow, brittle sub- stance which at — 50° is almost colorless. It melts at 111°, forming a thin, straw-colored liquid. When heated to a higher temperature it becomes darker and darker in color, and at 300° to 350° it is so thick that the vessel con- taining it may be turned upside down without danger of running out. Finally, at 440° it boils and is then con- verted into brownish-yellow vapor. Experiment 89. — Distil about 10 grams of roll sulphur from an ordinary glass retort. The retort need not be connected with a condenser. Notice the changes above described. Collect the TEE BVLPSVB FAMILY. 141 liquid sulphur whicli passes over in a beaker-glass containing cold water. Crystals of Sulphur. — When molten sulphur solidifies, or when it is deposited from a solution, its particles arrange themselves in regular forms called crystals. But, strange to say, the crystals formed from molten sulphur are en- tirely different from those deposited from soluti ^ns of sul- phur. Substances which crystallize in two distinct forms are called diniorpJiotis. Carbon, like sulphur, crystallizes in two different forms [what are they?], and is hence di- morphous. Experiment 90. — In a covered sand or Hessian crucible melt about 20 grams of roll sulphur. Let it cool slowly, and when a thin crust has formed on the surface make a hole through this and pour out the liquid part of the sulphur. The inside of the crucible will be found lined with honey-yellow needles. Take out a few crystals and examine them. — Are they brittle or elas- tic? What is their color? Are they opaque, transparent, or translucent ? — Lay the crucible aside, and in the course of a few days again examine the crystals. — What changes, if any, have taken place ? Solution of Sulphur. — Sulphur is insoluble in water, slightly soluble in alcohol and ether. It dissolves in the liquid compound of carbon and sulphur known as carbon disulphide, CS„ and from this solution it is deposited in crystals quite different from those obtained in Experiment 90. ExPEBiMENT 91. — Dissolve 3 to 3 grams roll sulphur in 5 to 10 cc. carbon disulphide. Put the solution in a shallow vessel, and allow the carbon disulphide to evaporate by standing in the air. What is the appearance of the crystals ? Are they dark yellow or bright yellow ? Are they brittle or elastic ? [State in tabular form the properties of the two allotropic forms of sul- phur.] 149 TBB BLBMBNm OP GMEMISmY. Chemical Conduct of Sulphur.— Sulphur combines with oxygen when heated to a sufficiently high temperature. The product is sulphur dioxide, SO^. [Is there any anal- ogy between carbon and sulphur in this respect ?] It com- bines readily with most metals, forming sulphides. Its combination with iron has already been shown in Experi- ment 13. It also combines with copper, the act being accompanied by light and heat. Experiment 93. — In a wide test-tube heat some sulphur to boilmg. IntroducG into it small pieces of copper-foil or sheet- copper. Or hold a narrow piece of sheet-copper so that the end just dips into the boiling sulphur. What evidence have you that action takes place ? Hydrogen Sulphide, Sulphuretted Hydrogen, H^S. — When hydrogen is passed oyer highly heated sulphur the two ele- ments combine to form hydrogen sulphide. [Is there any analogy between this process and the formation of water by the burning of hydrogen?] This compound of sulphur and hydrogen occurs in nature in solution in the so-called "sulphur waters," which are met with in many parts of this country as well as in other countries. It also issues from the earth in some places. It is formed by heating or- ganic substances which contain sulphur, just as water is formed by heating organic substances which contain oxy- gen, and ammonia by heating such as contain nitrogen. It is formed, further, by decomposition of organic substances which contain sixlphur, as, for example, the albumen of eggs. The odor of rotten eggs is partly due to the forma- tion of hydrogen sulphide. [How is it that paraffin, p. 107, heated with sulphur gives off hydrogen sulphide ?] Preparation of Hydrogen Sulphide. — It is made in the laboratory by heating a sulphide with an acid. "When sul- TEE SULPHUB FAMILY. 143 pliuric acid acts upon iron sulphide, hydrogen sulphide is given off thus: PeS + H,SO. = FeSO, + H,S. Hydrochloric acid acts in a similar way: PeS + 2HC1 = Fed, + H,S. Experiment 93. — Arrange an apparatus as shown in Fig. 36. Put a small handful of sulphide of iron, FeS, in the flask, and pour dilute sulphuric acid upon it. Pass the gas through a little water contained in the wash-cylinder A. Pass some of the gas into water. What evidence have you that it dissolves ? — Collect some by displacement of air. It is heavier than air (specific grav- ity 1.178). Should the vessel be placed with the mouth down or up ? Set fire to some of the gas contained in a cylinder. If there is free access of air the sulphur burns to sulphur dioxide, and the hydrogen to water. Fig. 36. Properties of Hydrogen Sulphide. — Hydrogen sulphide, or, as it is commonly called, sulphuretted hydrogen, is a colorless, transparent gas. It has a disagreeable odor, somewhat resemhling that of rotten eggs. It is poisonous 144 THE ELEMENTS OF CBEMISTBY. when inhaled in any quantity. It dissolves in water, form- ing a solution which, has the odor of the gas. Most metals when heated in the gas are converted into sulphides. Thus, when it is passed over heated iron this reaction takes place: Fe + H,S ^ FeS + H,. [What takes place when water vapor is passed over heated iron ?] Precipitation of Sulphides. — Many of the sulphides are insoluble in water. Hence,, when hydrogen sulphide is passed through solutions containing metals in the form of soluble salts, the insoluble sulphides are thrown down, or 'precipitated. Experiment 94. — ^Pass hydrogen sulphide successively through solutions containing a little lead nitrate, zinc sulphate, and arsenic prepared by dissolving a little white arsenic, or arsenic trioxide, AsaOs, in dilute hydrochloric acid. What do you observe in each case? — The substances formed are respectively the sulphides of lead, zinc, and arsenic. The reaction in the case of zinc sulphate is represented thus: ZnSOi + HjS = ZnS + HjSOj. Chemical Analysis. — In dealing with chemical substances the first thing we have to determine is their composition, or, in other words, we have to analyze them. For this purpose we must first know the properties of the elements and their conduct towards chemical substances. To facili- tate the process of analysis the mixture to be examined s usually brought into solution and then treated successively with certain substances, the effect being observed in each case. Suppose we had a solution containing most of the metallic elements in the form of salts. If we were to pass hydrogen sulphide through this solution, some of the met- THS SULPHTTB FAMILY. 14S als would be precipitated as sulphides, while others would remain in solution, as their sulphides are soluble. The precipitated sulphides could then be filtered off and exam- ined, and the filtered solution also could be further exam- ined. Hydrogen sulphide is constantly made use of in the laboratory for the purposes of analysis. Compounds of Sulphur with Oxtgek, and with Hydeogen and Oxygen. Formation of the Compounds of Sulphur. — When sulphur burns in the air, the dioxide, SO^, is formed. Under cer- tain conditions the dioxide combines with more oxygen, forming the trioxide, SO,. When sulphur dioxide acts upon water, sulphurous acid is formed: SO, + H,0 = H,SO,. [What analogy is there between the acid thus formed and carbonic acid?] When the trioxide combines with water, sulphuric acid is formed: SO. + H,0 = H,SO.. Sulphur Dioxide, SO^. — This compound is formed by burning sulphur in the air or in oxygen. It issues . from volcanoes in large quantities. It is best prepared by heat- ing copper with sulphuric acid. We should naturally expect the copper simply to take the place of the hydrogen of the acid, thus: Cu + H,SO, = CuSO, + 2H. Probably this action takes place first. But the hydrogen 10 146 THE ELEMENTS OF CHEMI8TBT. acts upon the sulphuric acid, reducing it and forming sul- phur dioxide: H,SO, + 2H = 2H,0 + SO,. [Compare the action of copper on sulphuric acid with that of copper on nitric acid. What analogy is there be- tween the two cases?] Experiment 95. — Put eight or ten pieces of sheet-copper, one to two inches long and about half an inch wide, into a 500-cc. flask; pour 15 to 30 cc. concentrated sulphuric acid upon it. On heating, sulphur dioxide will be evolved. The moment the gas begins to come off, lower the flame, and keep it at such a height that the evolution is regular and not too active. Pass some of the gas into a bottle containing water. Collect a vessel full by displacement of air. It is more than twice as heavy as air. See whether the gas will bum or support combustion. Properties of Sulphur Dioxide.^ — Sulphur dioxide is a colorless gas of an unpleasant, suffocating odor, familiar to every one as that of burning sulphur-matches. Water dissolves it readily. It bleaches readily, and stops fermen- tation. Experiment 96. — Burn a little sulphur in a porcelain crucible under a bell-jar. Place over the crucible on a tripod some flowers. In the atmosphere of sulphur dioxide the flowers will be bleached. Uses of Sulphur Dioxide. — It is used extensively for the purpose of bleaching wool, silk, straw, paper, etc.; and, further, to preserve liquids which have a tendency to under- go fermentation. If left in the air, fruit- juices become sour in consequence of fermentation. As sulphur dioxide prevents fermentation, the juices are kept sweet if treated with something which gives ofE the gas, as, for example, a sulphite. The principal use of sulphur dioxide is in the THE SULPHUR FAMILY. 147 manufacture of sulphuric acid. For this purpose it is made in enormous quantities. Sulphurous Acid and Sulphites. — The solution of sulphur dioxide in water has acid properties, and contains the acid H,SO,. By neutralizing the solution with bases, the sulphites, or salts of sulphurous acid, are obtained. The sulphites are analogous to the carbonates in composition, and suffer the same decomposition when treated with acids. When a carbonate is treated with an acid, carbon dioxide is given off. So, also, when a sulphite is treated with an acid, sulphur dioxide is given off: ¥a,S03+ H,SO, = Na,SO, + H,0 + SO,; Na,SO, + 2H01 = SKTaOl + H,0 + 80,. Sulphuric Acid, H^SO,. — Salts of sulphuric acid are found in nature, as gypsum, heavy spar, etc. It cannot easily be prepared from its salts, as hydrochloric and nitric acids are prepared, and is made exclusively by oxidizing sulphur dioxide in the presence of water, or, in other words, by oxidizing sulphurous acid. The reactions involved in the manufacture of sulphuric acid are: S + 0, =. SO,; SO, + H,0 = H,S03; H.SO, + = H,SO,. The last reaction cannot readily be effected directly by the action of the oxygen of the air, but an extremely interest- ing method has been devised by which the oxygen of the air is constantly transferred to the sulphurous acid. How Nitric Oxide Acts in Oxidizing Sulphurous Acid. — The method depends partly upon the power of nitric oxide. 148 THE ELEMENTS OF CHEMISTRT. ~S0, to combine directly with the oxygen of the air to form nitrogen peroxide, NO,. Nitrogen peroxide gives up half its oxygen to sulphurous acid, and is itself thus reduced to nitric oxide. If, therefore, sulphur dioxide, water, and nitrogen peroxide be brought together, the first action is represented thus: SO, + H,0 + NO, = H,SO, + NO. Now, if air be supplied, the nitric oxide will be converted into the peroxide: NO + = NO,. The peroxide acting upon a further quantity of sulphur dioxide and water is again reduced, and so on indefinitely. It will thus be seen that, starting with a small quantity of nitric oxide, it should be possible to convert a large quantity of sulphur dioxide into sulphuric acid. Manufacture of Sulphuric Acid. — In the manufacture of sulphuric acid sulphur or iron pyrites, FeS,, is burned. In the former case, the only product of the combustion is sulphur dioxide; in the latter case, the sulphur forms sul- phur dioxide, and the iron is converted into an oxide, Fe,0,. The sulphur dioxide thus formed is conducted into large chambers lined with lead, for the reason that sulphuric acid does not act upon lead, while it does act upon most other common metals. Instead of starting with nitric oxide, nitric acid is passed into the chambers, and water in the form of steam. The first action between the nitric acid, steam, and sulphur dioxide is this: 3HN0, + 3S0, + 3H,0 = 3H,S0, + 3N0. THE SULPHUB FAMILY. 149 From this point sulphur dioxide, water, and nitric oxide are brought into action, and the chief reactions are those described above. A Leaden Chamber. — The arrangement of a leaden chamber is shown in Fig. 37. The furnace in which the sulphur or iron pyiites is burned is represented by /. Steam from the boiler b is forced into the chamber through Fig. 37. jets. The nitric acid is formed from Chili saltpetre and sulphuric acid in the furnace n. A good draught is kept up by means of a high chimney. Ordinary Sulphuric Acid: Oil of Vitriol. — The acid ob- tained from the chambers is evaporated in lead pans, and afterwards in platinum or glass. The strong acid thus obtained is the concentrated sulphuric acid of commerce, which is commonly called oil of vitriol. It is an oily liquid, usually somewhat colored by impurities. The jijifre acid is a colorless liquid at ordinary temper- atures. When cooled down it forms crystals. It decom- poses the salts of most other acids, setting the acids free and f orining sulphates. You have already had illustrations of this power in the liberation of nitric and hydrochloric acids from their salts by treatment with sulphuric acid. [Give the equations representing the action which takes 150 THE ELEMENTS OF OHEMISTRT. place when common salt and potassium nitrate are treated with sulphuric acid.] Sulphuric Acid Combines with Water. — Sulphuric acid has a very strong tendency to absorb water and form com- pounds with it. A great deal of heat is formed in this action. This fact has been repeatedly illustrated in ex- periments already performed; and attention has been called to the necessity for caution in mixing the liquids. The acid acts upon organic substances containing hydrogen and oxygen, and extracts them in the proportions to form water. A piece of wood is charred, if put in the acid, in consequence of the abstraction of hydrogen and oxygen. [How is wood charred in the preparation of charcoal? Is there any analogy between the preparation of charcoal in the ordinary way and by the action of sulphuric acid?] Wounds caused by sulphuric acid are painful and heal with difficulty. Importance of Sulphuric Acid. — Sulphuric acid is the most important manufactured chemical substance. Most chemical industries depend upon it. Among the many uses to which it is put are the making of "soda" or sodium carbonate, which is necessary for the manufacture of soap and glass; the making of phosphorus; of artificial fertilizers; the refining of petroleum, etc., etc. In 1883 there were manufactured 300,000 tons of sulphuric acid in the United States, and over 900,000 tons in Great Britain. Monobasic and Dibasic Acids. — Sulphuric acid differs markedly from nitric and hydrochloric acids in one respect. It has the power to form two different salts with the same metal, in one of which there is relatively twice as much of the metallic element as in the other. If to a given quan- tity of sulphuric acid there be added only half the quantity THE SULPHUR FAMILY. 151 of caustic potash required to neutralize it, a salt is formed which crystallizes. It has the composition represented by the formula KHSO,. If nitric acid be treated in the same way, only half the acid is acted on, and this forms ordi- nary potassium nitrate, KNO3, the rest of the acid being left unacted upon. In the case of sulphuric acid two reactions are possible, viz. : H,SO,+ KOH = KHSO, + H,0; H,SO, + 2K0H = K,SO, + 3H,0. In the case of nitric acid only one reaction seems to be possible : HNO3 + KOH = KNO, + HO,. Acids which, like sulphuric acid, have the power to form two salts with the same metal are called dibasic acids. Acids which, like nitric acid, have the power to form only one salt with the same metal are called monobasic acids. This power is connected with the number of replaceable hydrogen atoms contained in the molecule of the acid. An acid containing two replaceable hydrogen atoms in its molecule is dibasic ; one containing only one replaceable hydrogen atom in its molecule is monobasic. Acid, Neutral, and Normal Salts, — A dibasic acid yields two classes of salts : (1) those in which all the hydrogen is replaced, and (2) those in which half the hydrogen is re - placed by metal. The former are called normal salts, the latter acid salts. Normal salts are generally neutral, and are sometimes called neutral salts. Carbon Bisulphide, OS,. — Sulphur forms with carbon a comppuud called carbon disulphidCj whioh has the compg- 152 THE ELEMENTS OF OHEMISTBY. tion CSj. It is made by bringing carbon and sulphur to- gether at higb temperatures. It is a liquid which boils at 47°. That it dissolves sulphur has been shown in Experi- ments 11 and 91. It also dissolves many other substances. Selenium, Tellurium, and their Compounds. — These ele-' ments are rarely met with. In general their properties are very similar to those of sulphur, and they form compounds analogous to the principal compounds of sulphur. Relations between the Atomic Weights of Sulphur, Sele- nium, and Tellurium. — The relation between the atomic- weights of the members of the sulphur family is like that already noticed between the atomic weights of the members of the chlorine family. It is shown thus : 32 + 135.2 = 157; At. Wt. ot At. Wt. of sulphur. teUuriiun. and — ^— = 78.6, which is nearly 79, the atomic weight of selenium. THE NITBOGEN FAMILY. 153 CHAPTER XVII. THE NITROGEN FAMILY: NITRO&EN, PHOSPHORUS, ARSENIC, AND ANTIMONY. BoEOS" AND Silicon'. Phosphorus, P {At. Wt. 31). — Phosphorus occurs in the form of phosphates, or salts of phosphoric acid. The chief of these is calcium phosphate, which is the principal con- stituent of the minerals phosphorite and apatite, and of the ashes of bones. Phosphorus Made from Bones. — It is made from bone-ash, which contains a large proportion of calcium phosphate. The ash is first mixed with sulphuric acid. Then the compound thus obtained is mixed with charcoal and heated, when phosphorus distils over. It is cast into sticks under water, and kept under water. Properties. — It is colorless or slightly yellow and trans- lucent. At ordinary temperatures it can be cut like wax, but it becomes hard and brittle at lower temperatures. It melts at 44°, and boils at 390°. Unless carefully protected from the light its appearance changes. It becomes opaque and dark in color, and finally dark red. This change can be hastened by heating the phosphorus in a sealed tube to 250°. Ordinary phosphorus is insoluble in water, but solu- ble in carbon disulphide. In contact with the air it gives off fumes which emit a pale light visible in a dark room. It takes fire when rubbed or cut, and must hence b^ 154 TEE ELEMENTS OF CHEMISTRY. handled with great care. It should always be cut under water, and neyer held in the hand. It not only combines with oxygen easily, but with other elements, such as chlo- rine, bromine, and iodine. Experiment 97. — Bring together in a porcelain crucible or evaporating-dish a little phosphorus and iodine. It will be seen that simple contact is sufficient to cause the two substances to act upon each other. Direct combination takes place, and the action is accompanied by light and heat. Phosphorus is very poisonous. Its vapor produces a disease of the bones. Red Phosphorus. — The red substance formed when ordi- nary phosphorus is left in the light, or heated without ac- cess of air, is a second variety of phosphorus, known as red phosphorus. This differs from ordinary phosphorus as much as graphite differs from the diamond. Ordinary phosphorus is very active, combining readily with oxygen; it is soluble in carbon disulphide; and is poisonous. Red phosphorus, on the other hand, is inactive. It does not change in the air, and requires to be heated to a compara- tively high temperature before it will combine with oxygen; it is insoluble in carbon disulphide, and is not poisonous. It is converted into the ordinary variety when heated to about 300°. [Make out a tabular comparison of the pro- perties of the two allotropic forms of phosphorus. ] Uses of Phosphorus. — The principal use of phosphorus is in the manufacture of matches. Ordinary friction-matches are tipped with a mixture of phosphorus, glue, and potas- sium chlorate. " Safety-matches" are usually tipped with potassium chlorate and antimony sulphide. The surface upon which they are rubbed is made of red phosphorus, black oxide of manganese, and glue. Mixed with flour, phosphorus is frequently used as a rat-poison. THE NITROGEN FAMILY. 155 Compounds of Phosphorus with Oxygen and with Hydro- gen and Oxygen. — When phosphorus is burned in the air or in oxygen it is converted into the oxide, PjO^. This combines with water in different proportions, forming two distinct acids, known as rnetapho!, 311 Mixture, mechanical, 9 Molasses, 332 Molecular formulas, 136 weights, 136 Molecules, 126 Morphine, 242 Mortar, 182 Multiple proportions, 35 Naphtha, 107 INDEX. 271 Naphthalene. 240 Narcotine, 243 Neutralization, 88 Nickel, 304 Nicotine, 242 Nitrates, 73 Nitric acid, 67, 69 oxide, 74, 75 Nitrobenzene, 237 Nitro-cellulose, 235 Nitrogen, 37 family, 153 in air, 20, 39 oxides. 73 pentoxide, 74 peroxide, 74, 76 trioxide, 74 Nitroglycerin, 337 Nitrous acid, 67 oxide, 74 Nomenclature, acids, 93 bases, 93 salts, 94 Octane, 107 Oil of bitter almonds, 238 Oleo-margarin, 327 Opium, 242 Organic chemistry, 316 Osmium, 214 Oxides, 30 Oxygen, 21 preparation, 21 properties, 24 Oxyhydrogen blowpipe, 58 Ozone, 64 in air, 65 relation to oxygen, 65 Palladium, 314 Paper, 235 Paraffin, 107' Pattison's process, 191 Pentane. 107 Petroleum, 106 Phenol, 238 Phosphorite, 153 Phosphorus, 153 oxide, 155 red, 154 Photography, 194 Pig iron, 300 Pitchblende, 308 Plaster of Paris, 181 Plathaum, 314 chloride, 314 Plumbago, 96 Porcelain, 198 Potash, 165 Potassium, 165 chlorate, 86, 169 chloride, 86 chromate, 306 dichromate, 307 ferrocyanide, 133 hydroxide, 167 hypochlorite, 86 iodide, 166 nitrate, 167 Propane, 107 Propylene, 108 Puddling, 201 Pyroxylin, 334 QuAKTZ, 159, 160 Quartzite, 159, 160 Quinine, 341 Radicals, 339 Seduction, 57 Rochelle salt, 175 Rouge, 304 Rubidium, 177 Ruby, 197 Ruby copper, 187, 18B Rust, 301 Safety-lamp, 131 Safety- matches, 154 Saltpetre, 167 Salts, 91 acid, 151 neutral, 151 nomenclature, 93 normal, 151 Sand, 159 Saponification, 336 Sapphire, 197 Serpentine, 185 Selenium, 153 Siderite, 199 Silica, 159 272 INDEX. Silicates, 169 Silicon, 159 oxide, 160 Silver, 191 bromide, 194 chloride, 194 iodide, 194 nitrate, 193 plating, 193 Slag, 300 Slaking, 179 Slow oxidation, 26 Soaps, 333 Soapstone, 185 Soda, 171 Sodium, 169 borate, 173 carbonate, 171 chloride, 169 hydroxide, 170 hyposulphite, 195 nitrate, 170 phosphate, 173 sulphate, 171 Solder, 313 Soldering, 173, 313 Solution, 7 Solvay method, 172 Spectroscope, 176 Spirits of wine, 218 Stalactites, 181 Stalagmites, 181 Stannic compounds, 313 Stannic chloride, 313 Stannic sulphide, 313 Stannous compounds, 313 Stannous chloride, 213 Starch, 236 Stearin, 223 Steel, 201 Stibine, 159 Strontium, 183 Sugar of lead, 233 milk, 334 Sugar-refining, 233 Sulphites, 145 Sulphur, 139 dimorphism of, 141 dioxide, 145 trioxide, 145 Sulphuretted hydrogen, 143 Superphosphate of Um^ 183 Symbols, 33, 34, S5 Tahkln, 339 Tanning, 340 Tellurium, 153 Tempering, 201 Thallium, 177 Theory, 134 Tin, 312 dichloride, 313 oxide, 313 salt, 313 sulphide, 313 tetrachloride, 313 Tin-stone, 313 Toluene, 108 Turkey-red, 341 ULTBAMABUfB, 198 Uranium, 308 Valence, 137 Verdigris, 333 Vitriol, blue, 190 green, 303 white, 187 Wateb, 41 analysis, 44 hard, 117, 181, 333 maximum density, 59 of crystallization, 41 as a solvent, 63 synthesis of, 54, 56 uses in chemistry, 63 Water-gas, 46, 118 Water-glass, 174 Weldon's process, 78 Wood- spirit, 318 Wood-vinegar, 321 Wrought-iron, 200 Xylbke, 108 Zinc, 186 blende, 186 oxide, 186 sulphate, 187 HOLDEN'S ELEMENTS OF ASTRONOMY By Edward S. 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