''" ' ' '' * {_ REESE LIBRARY OF THE UNIVERSITY OF CALIFORNIA Received __ v^>^ REVISED BY H. G. MADAN, M.A., KcJw J>. 5ef0rJr / x AT THE CLARENDON PRESS MDCCCLXXX [All rights reserved ] PREFACE. THE object of this volume is to furnish a systematic course of study to those who are beginning to learn Chemistry practically. The course commences with a series of exercises upon the preparation and properties of some of the most familiar substances, in which precise directions are given as to the apparatus and materials to be used, and as to the manner in which each experiment is to be made. In the earlier exercises, especially, the directions given extend to minute details; the aim of the authors being to provide, as far as possible, all the guidance that a beginner, working by himself or with only occasional supervision, may require. A few exercises have been introduced on parts of manipula- tion which, from their importance, it seemed desirable to treat separately; but, as a rule, each operation is described where the occasion for its use first arises : and the subjects have been so chosen as to furnish examples of all the usual chemical operations. The attempt has been made to arrange each exercise so as to provide the student with continuous occupation, and economise his time by giving two or three operations which can be carried on simultaneously and to which he should direct his attention in turn. The time re- quired for the completion of different exercises cannot but vary considerably, since some operations, too important not to be included, do not admit of 'being hastened ; but in most cases about two hours will be found sufficient. vi PREFACE. The list of apparatus given at the outset shows what it is desirable that a student should have for the performance of the exercises ; but those who have not access to a chemical laboratory, and who are unwilling to incur the expense of pro- viding themselves with a complete set of apparatus from a chemical dealer, will find in the Appendix a number of sug- gestions for the construction of pieces of apparatus which can be made very cheaply. The authors have endeavoured, by repeating nearly every experiment in exact conformity with their written description, to insure that the student who carefully follows their directions shall command success ; but as they cannot but fear that many errors and omissions may, nevertheless, have escaped them, they will be grateful for any suggestions from those engaged in teaching who may make use of their book. It is only by a large experience of the errors into which beginners are liable to fall, that the many ways of going wrong can be dis- covered and stopped. The question of chemical nomenclature is at present in such a condition that every lecturer or writer must choose for him- self the names he considers least objectionable. The names assigned to substances in this volume are, with a few exceptions (made with a view to consistency), the same as are used in Roscoe's 'Lessons in Chemistry/ and Watts' edition of 'Fownes' Manual.' The illustrations in the text have, with very few exceptions, been drawn directly on the wood from photographs, taken by one of the authors, of the apparatus actually used. PREFACE TO THE THIRD EDITION. IN preparing the present edition, the Editor has, in the first place, to regret the loss of the co-operation of Mr. Harcourt, whose care, accuracy, and discrimination gave to the former editions a value which the present one cannot justly claim to possess. Some more or less important alterations will be noticed in the present issue : chiefly of the following kinds, 1. The succession of the Exercises has been to a certain extent re-arranged, so as to make them follow more nearly in the order in which a beginner would probably study the radicles in the course of his reading. 2. A few additional Exercises, such as those on Weighing and Measuring, and on Chemical Action, and a rather large number of additional experiments have been introduced ; such experiments alone being selected as can be made without much risk, and with the simplest apparatus 1 . 3. Short headings have been placed before most of the experiments, in order that the student may appreciate more clearly what the experiment is intended to illustrate, before he performs it. > Practical Chemistry seems in danger of being made far too much a study of a few reactions of salts, got up for the purpose of detecting them in the course of an analysis. This is, of course, due to the requirements of examiners, to satisfy which 1 Suggestions for an advanced course of experimental work, which requires experience and more elaborate apparatus, will find a more appropriate place in the second volume. Vlll PREFACE. nearly all the very moderate time available for practical in- struction in schools must at the present day be spent. More- over analytical work (in the narrow, technical sense) entails, like Latin verses, less trouble to the teacher and less risk to the pupil than other kinds of practical work; while it un- doubtedly affords, when intelligently pursued, a very excellent training in the application of logical methods. But it may well be doubted whether a more real and valu- able advance in a scientific education is not made by the care- ful preparation and examination of the properties of such a substance as oxygen, or by an exact study of a few examples of oxidation and reduction, than by simply observing, for instance, that chlorides give a white precipitate with silver nitrate which is soluble in ammonia. It is hoped that this book may do something towards tracing, for those at any rate who have time and enthusiasm for the work, an outline of a rather wider range of study. H. G. MADAN. ETON, September , 1880. TABLE OF CONTENTS. PAGE MEMORANDA . . ,. .. .. . -'.."'. . . . XV LIST OF APPARATUS . . .. . , ... I LIST OF SUBSTANCES . . . . "''.' '."'.' . 21 PART I. Experiments on the Preparation and Properties of Substances. SECTION I. Preliminary Exercises. EXERCISE i. Fusion and Granulation . * ' ' . . . . 27 2. Glass Working . . . . . . ... 28 3. Glass Working (continued) . . - .. . '-35 4. Weighing and Measuring . . ... -45 5. Solution, Evaporation, and Crystallisation . * . . 53 ,, 6. Solution of Calcium Hydrate . . . . 5^ 7. Distillation . . '. , . . ' . . 62 8. Chemical Action . . . ... . .68 9. Filtration and Washing of a Precipitate . . . 76 f 10. Use of the Pneumatic Trough . . . . . 79 ii. Use of the Mouth Blowpipe . .. ... . 83 SECTION II. Preparation and Examination of Non-metallic Radicles and their Compounds. EXERCISE i. Oxygen and Oxides .' . 95 2. Hydrogen , . . IO 4 X TABLE OF CONTENTS. PAGE EXERCISE 3. Nitrogen and Air . .115 4. Ammonia . i . . . t, . ,. . 123 5. Nitrates - . . . . . . . .131 6. Nitrogen Tetroxide 139 7. Nitrogen Trioxide and Nitrites 139 8. Nitrogen Dioxide 141 9. Nitrogen Protoxide 146 10. Carbon 151 n. Carbon Dioxide 154 12. Carbonates 162 13. Carbon Protoxide 163 14. Ethylene 168 15. Acetates . . 172 16. Tartrates . 173 17. Oxalates 175 18. Cyanogen 177 19. Cyanides . 179 20. Chlorine 183 21. Chlorides . . . 190 22. Hypochlorites 195 23. Chlorates 197 24. Bromine 201 25. Bromides 202 26. Iodine 203 27. Iodides 206 28. Fluorides 211 29. Sulphur 213 30. Sulphides . . 216 31. Sulphur Dioxide 223 32. Sulphites 225 33. Hyposulphites 226 34. Sulphates 228 35. Phosphorus 231 TABLE OF CONTENTS. XI PAGE EXERCISE 36. Hydrogen Phosphide . .- . * . . . 233 37. Hypophosphites 233 38. Phosphorus Pentoxide . - . " . . . . 235 39. Phosphates. . . .' 235 40. Borates . . 240 41. Silicon Dioxide . . . . . . * . 242 42. Silicates . .242 SECTION III. Preparation and Examination of Metallic Radicles and their Group I. J. Silver * 248 2. Mercury 256 3. Lead . 264 Group II. 1. Copper 269 2. Cadmium 276 3. Bismuth , . . . .. ; -, . * 277 4. Arsenic . . . . . . . . 280 5. Antimony . . 286 6. Tin . -. . .295 7- Gold . . .299 8. Platinum . > . *. . . 302 Group III. ! Iron . . . .-.,.-. . . . .306 2. Cobalt . . . .... . * , . . 316 3. Nickel . 319 4. Manganese . . .. , i. . ;, ... . . . 320 5. Chromium . .. .. 325 Xll TABLE OF CONTENTS. PAGE 6. Aluminium . ''.. , ' . * ' . " -; . ; -. . 332 7- Zinc .'..>: . '. . .- ,. ^ - ^ : ,i . 335 Group IV. 1. Barium ............ 340 2. Strontium . 344 3. Calcium 346 Group V. Magnesium 349 Group VI. 1. Potassium . . , . . 352 2. Sodium 357 3. Ammonium 361 4. Hydrogen , . 365 PART II. Qualitative Analysis of Single Substances. SECTION I. Explanation of the Analytical Course . . . . . .367 SECTION II. Preliminary Examination of the Substance . . . . -379 SECTION III. Examination of a Single Substance for a Metal . . , .398 SECTION IV. Examination of a Single Substance for a non-metallic Radicle . 410 TABLE OF CONTENTS. xiii SECTION V. PAGE Examination of an Insoluble Substance . '. . . . 416 SECTION VI. Example of the Analysis of a Single Substance . . . . 419 APPENDIX A. Suggestions for the construction of Chemical Ap- paratus. . . . . . . 422 APPENDIX B. I. Preparation of normal solutions of Reagents . .- . 439 II. Recovery of Silver, Gold, and Platinum from Residues . 449 APPENDIX C. Short courses of Analysis ..... . -453 APPENDIX D. I. Laws of Chemical Combination ... V -459 II. Chemical Symbols . .. . . . . . . 464 APPENDIX E. TABLES. I. Weights and Measures . '.. . . . .470 II. Thermometric Scales . . . . . . -473 III. Solubility of Salts ....,-.. . -475 INDEX . . . . . . . .... 476 CORRIGENDA. Page 201, line 3, for So read 160. 262, 8, for nitrate read chloride. JKemoranUa. 1. BE orderly and neat in manipulation. Cleanliness stands at the head of the chemist's scale of virtues. All messes must be cleared away with the zeal of a sanitary inspector. Never go to work, or continue to work, with the table covered with a litter of bottles, flasks, basins, and test-tubes; but replace each bottle on its shelf as soon as you have done with it, and have a basin at hand in which to put dirty test-tubes, &c. Always wash your test-tubes twice : once, before they are put away ; and again, with distilled water, immediately before they are used. Probably more puzzling reactions occur from the use of dirty test-tubes than from any other cause. 2. Do not begin work in a hurry. What is expended in time is very often gained in power, in grasp of a subject. Yet, on the other hand, learn to be economical of time. Several filtrations and evaporations, for instance, may be going on at once. The chemist may sometimes, in spite of the proverb, do more than one thing at a time, by allowing things to do themselves. 3. Be economical of materials. In analysing a substance, do not (without the strongest reasons) use up at once the whole quantity at your disposal. Reserve at least one-fourth of it in a corked tube or covered watch-glass, in case unforeseen accidents should occur and the other portion should be lost. In making a gas, the residue left in the generating vessel will often be of use, at any rate interesting as a specimen. It should not,-as a rule, be thrown away, but purified by recrystallisation or otherwise. 4. Never begin an experiment until you have looked over all the preparations for it, to make sure that you have everything that is necessary within reach. You will not then have the mortification of seeing the half-performed experiment fail for want of some requisite which cannot be procured at the moment. 5. Do not think merely of what will do, but what is best, of the means at your disposal. XVI MEMORANDA. 6. Never add one chemical substance to another without con- sidering for what purpose you add it, and what various effects may be produced. 7. Be exact and methodical. Let nothing pass unnoticed, al- though you may not see its significance at the moment. Make written notes of everything that you do, analyses of lectures, sketches of apparatus. Whatever is worth doing is worth re- cording. 8. Do not attempt to devise a modification of an experiment until you have tried it in exact accordance with the directions given. Then, and then only, if you fail, you will find it possible to blame the book and not yourself. 9. Do not expose yourself needlessly to vapours which you know to be injurious, e.g. chlorine, hydrogen sulphide, hydrogen arsenide. Remember that the bad effects may not be perceptible immediately. 10. Finally, do not look upon Chemistry as a mere amusement, as a means of getting up a few explosions, creating a few unsavoury smells, producing a few striking changes of colour. Chemistry is worthy of better treatment; it is no longer a 'black art,' but a refined science, and should be thoughtfully and reverently studied. Nor, again, give up hopes of making discoveries in the science because the land appears to be already highly farmed, and you have not all the refined apparatus which the optician and operative chemist can supply. Records of close and accurate observations of some of the (apparently) simplest phenomena of Chemistry are much needed; and such it is in the power of every student to contribute. &l) Jjemdam. Narem illaudatis vehementer odoribus angis, Aurem terrifico percutis usque sono. Quippe oculum, Chemeia, magistra haud alma, vel ipsum Corripis, et digitos igne petisque caput. Quid manet ? una fides manet inviolata tuorum Semper, et ut crescunt vulnera crescit amor. H. G. M. LIST OF APPARATUS Required for the Course of Practical Work contained in Paris I and II of this Book 1 . [The abbreviation cm. stands for centimetre. mm. millimetre. c.c. cubic centimetre. grm. gramme. For tables of weights and measures see Appendix E.] 1. A Common Metre (or Half-metre) Rule ; the first decimetre divided into millimetres, the rest into centimetres. 2. A Cylindrical Graduated Glass measure ; to contain 200 c.c. ; graduated into spaces of 5 c.c. 3. A Pair of Scales, with beam about 20 or 25 cm. long, sensitive to a weight of i centigramme. The ordinary grocers' scales, if well made, are sufficiently good. 4. A Set of Weights, from 100 grms. to i decigramme. These need not be of the highest accuracy : such sets, including 100, 50, 20, 10, 10, 5, 2, 2, i, -5, -2, -2, -I grm., mounted on a wooden stand, are sold in France for a price equivalent to less than half-a-crown, and can be procured in England at a reason- able cost 2 . 1 In making this List it has been thought right to err rather on the side of completeness than of deficiency. Some pieces of apparatus, e. g. a Bunsen's holder, are not absolutely necessary ; and in several cases the student will be able, by the aid of a few tools and a little ingenuity, to make substitutes for himself. Some suggestions for the construction of economical apparatus will be found at the end of the book, but no direct reference to such substitutes is made in the text, since the student, who is ingenious enough to make a piece of apparatus for himself, will be at no loss to bring it in where it is wanted. 2 Thus, in Paris, they can be obtained from M. Carette, 12 Rue du Chateau d'Eau ; and in England from Mr. Solomon, Red Lion Square. 2 LIST OF APPARATUS. 5. A Pneumatic Trough, about 36 cm. long, 24 cm. wide, and 16 cm. deep, Fig. i. This is an apparatus for collecting and experimenting upon gases, and consists of a cistern for holding water or any other fluid, furnished with a Fig. i. movable shelf placed across it about 5- or 6 cm. below the top. In the centre of the shelf is a hole, which should not be less than 2 cm. in diameter, and immediately underneath this hole is soldered a broad, very shallow funnel, the mouth of which is of the same width as the shelf : the accom- panying figure represents a section of the shelf at this point 1 L This funnel serves to catch bubbles of gas, in case the delivery tube is not exactly under the centre of the hole, and, to direct them upwards through the hole into- a jar placed above it: In addition to these essentials, the trough represented in the figure has a ledge running along the whole length of one side on which jars may stand when filled with gas, and 1 A long narrow opening, extending nearly the whole length of that part of the shelf which is unsupported, is more convenient than a round hole. Its width need not exceed i cm., and on each side of it should be a strip of metal, soldered to the under surface of the shelf, serving to strengthen the shelf and to guide bubbles of gas to the opening. The figure above represents a section of this part of the shelf. LIST OF APPARATUS. 3 also an overflow-pipe a at one corner, the mouth of which is about 3 cm. above the level of the shelf, to convey any excess of water into the supplementary trough b. These troughs are made of japanned tin, and it is a decided ad- vantage to have the inside japanned white, as a much better Fig. 3. Fig. 2. view of the position of tubes, jarsj &c. when immersed in the water, is thus obtained. For the method of using the Pneu- matic Trough, see p. 79. 6. A Retort Stand, Fig. 2, with rectangular iron foot, iron rod about 36 cm. in height, and three brass rings. 7. A Bunsen's Universal Holder, Fig. 3, of stained beech- wood, the smaller of the two sizes which are sold. This, B 2 4 LIST OF APPARATUS. although rather expensive (about 5.?.), will be found a most useful piece of apparatus, both for chemical and physical ex- periments. Its construction will be sufficiently evident from the engraving. Care must be taken not to use undue force in tightening the screws, or the threads may be torn away. If the screws work stiffly, a little black-lead, in preference to tallow, should be applied to them. 8. A Bunsen's Burner, Fig. 4, small size, with rose top. This burner consists of a brass tube, about i cm. diameter, having several holes close to its lower end, which, in the best form of burner, can be closed when desired by a revolving cap. Gas is introduced through a small flattened central jet, the orifice of which is just above the holes. Thus the gas is allowed to mix freely with air which enters through the holes ; the supply of air being increased by the upward rush of the gas, in the same way as the draught in the chimney of a loco- motive is increased by the blast of escaping steam. This mixture of gas and air burns, when a light is held at the top of the tube, with a blue, non-luminous flame, very different in appearance to the usual bright flame of coal-gas. The theory of the burner is this : Coal-gas consists mainly of hydrogen and compounds of hydrogen with carbon. Both these elements unite with oxygen, producing heat in doing so : but oxygen has more affinity for hydrogen than it has for carbon, and hence, when insufficient air is supplied, the oxygen in it combines with all the hydrogen, but with only part of the carbon. The rest of the carbon is separated in the flame, and its particles heated to whiteness give the brilliancy to the ordinary gas-flame. The presence of these particles of uncon- sumed carbon in the flame may be proved by holding a white plate in it for a moment ; the particles are thus cooled down and deposited as soot. If more air is supplied, so as to afford sufficient oxygen to combine with all the- carbon as well as the hydrogen, none of the former element is separated, and the flame loses its brightness but gains in temperature, since more chemical com- bination takes place. Thus we have the ordinary bluish flame LIST OF APPARATUS. 3 of the Bunsen's burner, which deposits no soot upon anything held in it, while its temperature is sufficiently high to melt readily a piece of copper wire held in it \ One or two precautions should be observed in using this burner. i. The supply of air must not be too great. If much more than half the total volume of air required to burn the gas completely, is admitted through the holes, the mixture becomes too explosive, and the flame passes Fig. 4- Fig. 5- down the tube, continuing to burn at the jet below, with a small smoky flame, the heat of which is mainly expended on the tube itself. In such a case, the 'gas must be entirely turned off, and kindled afresh. If the flame is still unsteady and shews a tendency to recede down the tube, owing to a low pressure of gas in the main, the air-holes should be partially closed by turning the cap (or if there is no cap, by plugging up one or more of them with bits of cork). In fact, it is always best to cut off the supply of air 1 The actual temperature of the flame is estimated at more than 2000, but unless it is enclosed in a furnace, a large amount is lost by radiation. 6 LIST OF APPARATUS. altogether before lighting the burner, and then to admit just sufficient air to destroy the luminosity of the flame. In this way even a small flame, 2 or 3 cm. high, can be safely obtained. 2. The supply of gas must not be too great, and it must be thoroughly mixed with the air before reaching the top of the tube. This latter condition is effected by the peculiar shape of the jet. If the flame is white even though the full supply of air is admitted through the holes, the gas should be partly turned off. If the flame still shows luminosity, there is reason to suspect that the jet is out of order, or that the air-holes are clogged by dust or some fused substance which has dropped down the tube. The main tube should be unscrewed and the jet and air-holes examined and cleaned. 3. The hottest part of the flame is a little below the top and near the border. This can be proved by holding a piece of platinum foil in various parts of the flame and observing where it glows most brightly. 4. The interior of the flame has a strong ' reducing ' action (for an explanation of this term see the exercise on the Use of the Blowpipe). This should be borne in mind when dealing with glass containing lead, which will be blackened, owing to the separation of lead, if held in the middle of the flame. The cast-iron cap shown in the figure, when placed upon the burner, divides the single flame into a ring of small jets which distribute the heat over a large surface, and are well adapted for heating an evaporating basin or sand-bath. 9. A Cast-iron Stand, Fig. 5, with screw, on which may be fitted the blowpipe-jet a, the Argand burner , and the fish-tail burner c. The blowpipe-jet is described in the exercise on the Use of the Blowpipe. The Argand burner, although not absolutely necessary, is extremely convenient for applying a gentle heat to a flask (e. g. in making oxygen gas), since it is more under control than the Bunsen's burner, and may be regulated to give the least possible flame. The fish-tail burner is chiefly intended for bending tubes, p. 31. LIST OF APPARATUS. J 10. A Set of Five Wooden Blocks, about 1 2 cm. square, and respectively 2, 5, 7, 10, 12 cm. in thickness. 11. A Test-tube Stand, of the usual form, for supporting test-tubes while in use. It should have twelve holes in one row, and a strip of slate should be fitted in front of the holes, on which may be written the contents of each test-tube when it is placed in the stand. 12. A small Dish, of tinned iron or copper, about 12 cm. in diameter, for use as a sand-bath. 13. Two pieces of fine Iron- wire Gauze, about 12 cm. square. 14. A Mouth Blow-pipe, Fig. 6, about 20 cm. in length. Fig. 6. 15. A small Ladle, with bowl about 7 or 8 cm. in diameter, and an Iron Spoon, or Capsule, about 4 or 5 cm. in diameter, for ignitions. 16. A pair of Crucible Tongs, Fig. 7, about 20 cm. in length. Fig. 7- > 17. A Set of four Cork-borers, from 3 mm. in diameter upwards. These are short pieces of thin brass tube, sharpened at one end, and having a thick collar soldered to the other end, to afford a better hold. For the method of using them, see p. 37 l . ,* When the cutting edge becomes blunt or bent, it should be sharpened on a hone, or by a very fine file, the borer being constantly rotated while the hone or file is passing over it. 8 LIST OF APPARATUS. 18. A piece of Platinum Foil, about 2 cm. x 5 cm. It should weigh about 0.4 grm. This is used chiefly as a support for substances on which we wish to try the effect of a high temperature, in order to test their fusibility, volatility, &c. If the edges of the foil are turned up round a spherical mould, such as the end of a pestle, the foil being laid on the palm of the hand, and the pestle pressed forcibly upon it, we obtain a very convenient capsule for fusions on a small scale, e. g. for the decomposition of barium sulphate by sodium carbonate. It should, however, be a rule ist. Never to use a platinum vessel when a piece of porcelain will do as well. A bit of a broken evaporating dish will serve for almost every purpose, except when silicon, aluminium, or the alkali metals are to be tested for. 2nd. Never to heat in a platinum vessel the following substances : Substances evolving chlorine or sulphur. Caustic alkalies or barium hydrate. Cyanides, chlorates, nitrates. Easily reducible metallic salts, or their corresponding metals, e.g. lead, silver, tin. When a platinum vessel is dirty, try first to clean it by boiling it in a dish with a little strong hydrogen chloride. If this has no effect, spread over the surface some powdered potassium-and-hydrogen-sulphate, and heat it over a Bunsen's burner until the salt fuses, inclining the vessel so that the liquid salt may flow over every part of it. Finally, boil it with water in a dish. When a piece of platinum foil becomes creased or wrinkled, place it between folds of glazed writing-paper on a smooth surface, such as a plate of glass, and pass over it with strong pressure a rounded burnisher, such as the handle of a paper- knife. 19. A piece of Platinum Wire, about 25 cm. long and 0.32 mm. in diameter (No. 26 brass-wire-gauge). This is chiefly for use in blowpipe experiments. 20. Two pieces of Brass or Copper Wire, about 30 cm. LIST OF APPARATUS. 9 long, and i mm. in diameter. These should be filed to a point at one end and then bent, the one into the form of Fig. 8, the other into the form of Fig. 9, and finally a small piece of wax taper about 3 cm. in length should be stuck upon the Fig. 8. Fig. 9. pointed end of each. One wire may be made to serve the purpose of the two pieces, if bent into this shape 1""^ and a piece of wax taper stuck on each end. 21. A Deflagrating Cup, see Fig. 10. This consists of a brass or iron bowl about 1.5 cm. in diameter, screwed to a piece of stout iron-wire which passes rather stiffly through a cork stuffing-box attached to a tin flange. It is intended to hold substances which are to be burnt in gases. 22. A Deflagrating Jar, Fig. 10. This is a wide-mouthed stoppered jar, open at the bottom, about 28 cm. in height and 1 5 cm. in diameter. The top should be ground flat, in order that it may be accurately closed by a glass plate. 23. Two strong cylindrical Glass Jars, for collecting gases ; 10 cm. in height, 3 cm. in diameter, with ground mouths. They should be made of thick glass, since they are used for holding mixtures of hydrogen and oxygen gases which are to be exploded. 10 LIST OF APPARATUS. 24. Three similar Jars, which may be of thinner glass, 20 cm. in height, 5 cm. in diameter. 25. Two circular Glass Discs, 5 cm. in 'diameter, ground on one side. 26. Two Ditto, 8 cm. in diameter. 27. One shallow Stoneware Tray, for holding gas jars, 8 cm. in diameter. 28. One Ditto, 18 cm. in diameter (see Fig. ro). This, though convenient, is not necessary, as a common dinner- iplate may be substituted for 'it. 29. Four Florence Flasks. These may be procured from any oilman, and should be selected of uniform thickness, freefrom air-bubbles, and "with even 'mouths not 'chipped away at one side. In order to cleanse 4hem, put a few lumps of common ' wash- ing soda' into each and heat it gently over a lamp, 'turning it round so as to bring the salt into contact with every part; finally, rinse it thoroughly, first with 'common water and then with distilled water, and place it to drain mouth *ig- 10 - downwards in the ring of a retort-stand. 30. Three "Masks with flat bottoms, holding respectively 200C.C., 250C.C., 400 c.c. 1 31. One plain Retort, holding about 200 c.c. 1 It will be well to have 2 or 3 more of these, at any rate of the 250 cc. size, in case of breakage. LIST OF APPARATUS. II 32. One Stoppered Ditto, of the same size. 33. Two wide-mouthed Stoppered Bottles, of white glass, holding about 700 c.c., for use in experiments on gases. 34. Six Ditto, holding about 200 c.c. 1 35. Two common corked Bottles, with moderately wide mouths, holding about 200 c.c., for use as washing bottles for gases. 36. Two Ditto, holding about 300 c.c., for containing water which is to be saturated with a gas, such as chlorine, sulphur dioxide, or hydrogen sulphide. 37. One Washing Bottle with tubes (Fig. n), holding 600 c.c. This is of great use for washing precipitates on a filter, and also for con- taining a supply of distilled water for general purposes in analysis. Its construction is sufficiently plain from the engraving 2 . When air is blown from the mouth into the upturned tube, a stream of water is forced through the jet at the extremity of the other tube, and may be directed upon a filter, 'Or into a test-tube. If a larger quantity of water is required at once, as in filling an evaporating dish or small flask, the bottle should be inverted so as to bring the blowing-tube lowermost, from which a stream of water will flow while air enters through the other tube. 1 It is a great advantage to have the stoppers of these gas bottles made much more conical than usual. They are then far less liable to become fixed in their places if the volume of gas in the bottle should contract. 2 This washing bottle may be easily fitted up by the student himself. Instructions for doing this are given at p. 35. Fig. il. 12 LIST OF APPARATUS. 38. Two Thistle Funnels, a, Fig. 12, about 32 cm. in length. 39. Three Glass Funnels, respectively 4 cm., 7 cm., 10 cm. in diameter. 40. Three Glass Beakers, respectively 4 cm., 5 cm., 6 cm. in diameter. 41. Twenty-four Test Tubes, of the following sizes : Twelve, 15 cm. in length, i cm. in diameter. Ten 1 8 cm. 1-5 cm. Two 20 cm. 2-5 cm. 42. Six Watch Glasses, 5 cm. in diameter. 43. One Glass Spirit Lamp. 44. One Glass Mortar, 6 cm. in diameter, with pestle. Fig. 12. 45. One Porcelain Mortar, 10 cm. in diameter, with pestle 1 . 46. Three Porcelain Evaporating Basins, respectively 6 cm., 9 cm., 12 cm. in diameter 2 . 47. One Porcelain Crucible, with cover, about 3 cm. in diameter. 48. Two common Cornish Crucibles, respectively 6 cm. and 8 cm. in diameter. 49. One Eeduction Tube, b, Fig. 12, about i cm. in diameter. 50. Two Drying Tubes, c, Fig. 12, about 18 cm. in length. 1 This mortar should not be glazed inside. 2 These should be thin in substance (that there may be less risk of their cracking when heated over a lamp), and highly glazed both inside and outside. The Meissen ware is much the best, both as to shape and quality. LIST OF APPARATUS. 13 This form of tube is intended to contain calcium chloride, or other hygroscopic substance, in small fragments, for the pur- pose of removing moisture from gases which are passed through the tube. It is filled in the following way. After removal of the cork, a small tuft of cotton-wool or tow is pushed down into the bulb by means of a glass rod, until it lies across and protects the opening of the narrow tube. The rest of the bulb and the wide tube is then nearly filled with fragments of thoroughly dry calcium chloride, about as large as split peas. Another piece of cotton wool is then lightly pushed in, to keep the calcium chloride in its place, and finally the cork with its short tube is replaced. It is advisable, when the tube is not in use, to keep the ends stopped by little plugs of cork, in order that the moisture of the air may not find entrance. The calcium chloride for these tubes should not be fused, but only thoroughly dried at a temperature of 2Oo-3oo on a sand-bath. It is in this condition much more porous, and exposes a larger surface to the gas than the fused substance. 51. Twelve 'Ignition Tubes,' Fig. 13, about 6 cm. ip length. For directions for making such tubes, see p. 41, Fig. I.I. 52. Two kilogrammes of readily fusible Glass Tubing, free from lead, of different sizes, but chiefly about 6 mm. in external diameter 1 . 53. Half a kilogramme of difficultly fusible Glass Tub- ing, 5 mm. in external diameter, for making 'ignition tubes' (No. 51) and arsenic tubes. 54. Two or three pieces of Combustion Tubing, about 30-35 cm. in length, and 12 or 14 mm. in diameter. 55. Three or four pieces of Glass Rod, free from lead, 1 The French soda glass is usually very good; but some specimens show a great tendency to devitrify when heated. 14 LIST OF APPARATUS. about 50 cm. in length, and 4 mm. in diameter : for stirring- rods. 56. A piece of vulcanized India-rubber Tubing 1 , about 1 metre in length, and 4 mm. in internal diameter : chiefly for use in connecting glass tubes ; for which purpose pieces about 2 or 3 cm. in length may be cut from it, as required. 57. Two or three pieces of similar Tubing, about 60 or 70 cm. in length, and 6 mm. in internal diameter: chiefly for connecting lamps with the gas supply. 58. Three packets of circular Filters, respectively 7 cm., 14 cm., 20 cm. in diameter, suited to each size of funnel (No. 39). 59. One box of Test Papers, containing books of blue litmus, reddened litmus, and turmeric paper. [Blue litmus is turned red by acids, Reddened litmus is turned blue by alkalis, Turmeric is turned brownish red by alkalis. Their use may be illustrated by laying strips of each side by side on a white plate, and putting on them a drop of (i) dilute hydrogen sulphate (sulphuric acid), (2) solution of potassium hydrate (caustic potash).] 60. Two Brushes for cleaning tubes, one about 3 cm. in diameter, for test-tubes ; the other about 5 mm. in diameter for smaller tubes. 60.. A light hammer, of the form known as riveting- hammer. 62. A small Anvil, about 6 cm. square, and 2 cm. in thickness. 63. A pair of cutting Pliers. 64. A 'three-square* File, about 12 cm. in length. 65. A round (or 'rat-tail') File, about 20 cm. in length These files should be fitted into handles. 1 Tubing of non -vulcanized india-rubber, which is also manufactured, adheres more closely to glass than the vulcanized tube, and is in many respects preferable to the latter. It has the disadvantage of losing its elasticity in cold weather, but after being warmed and stretched a little, it regains all its good qualities. LIST OF APPARATUS. 15 66. A Platinum Spatula, about 9 cm. in length, broader at one end than the other. It need not cost more than 6s. or 7^., and will be found most useful. Instead of it, an Kg.. 14.. aluminium or bone spatula* of the same size may be obtained at a much lower price, and will answer for most purposes. 67. A few pieces of Charcoal, for blowpipe experiments. These may generally be selected from the ordinary rough beech-wood charcoal. Sticks about 3. cm. in diameter, free from knots, should be picked' out and sawn across the grain into pieces about 3 cm. in. length, or rather less. When thus cut, they should show a surface free from, cracks and of close, sound texture. 68. A common China Jug, holding about 2 litres. 69. Half a quire of White Blotting-paper, some sheets of glazed writing-paper, and a few cards. 70. Two or three dozen good Corks of various sizes, from i to 6 cm. in diameter.. Those should be selected which are free from fissures and cavities, and in. which the grain runs across not along the cone. 71. Two or three Dusters. The following pieces of apparatus are also extremely useful, and access to* most of them will be assumed in the exercises : 72. A Herapath's Gas Blowpipe,, provided with a pair of double bellows, or with one of the small French india-rubber blowing machines, Fig. 15.. In this form of blowpipe the gas issues from a brass tube about i cm. in diameter, in the axis of which a smaller tube is permanently fixed, through which a blast of air is directed into the centre of the gas- i6 LIST OF APPARATUS. flame. By attaching a larger or smaller nozzle to the air-tube and altering the quantity of gas, any kind of flame may be obtained, from a large brush-like flame 16 or 18 cm. in length, to a small pointed cone of flame, such as is required for ana- lytical experiments. The india-rubber blowing machine alluded to, consists of two parts : ist, The blower, a a pear-shaped vessel of strong vulcanized india-rubber, having a valve fitted at each end enclosed in a small wooden box ; 2nd, The regulator, b a spherical vessel of thinner india-rubber, with two necks, one of which is connected by an india-rubber tube with the valve-box at one end of the blower, while the other neck is similarly connected with the blowpipe air-jet. When the LIST OF APPARATUS. 1 7 blower is placed on the floor and compressed with the foot, the valve at one end closes, and the air contained in the vessel is forced through the other valve into the regulator, which becomes distended and forces the air through the blowpipe-jet. When the blower is relieved from the pressure of the foot, it recovers its shape, the valve nearest the regulator closes and prevents the return of the air, while a fresh supply of air enters through the other valve. When full, the blower is again compressed with the foot so as to force another supply of air into the regulator. This blowing machine is much cheaper and more portable than any form of double bellows, and is very effective. The regulator is usually made too small, and thus there is a slight variation in the strength of the blast. The india-rubber must be of the best quality ; and it is advisable to enclose the regulator in a net, to prevent its becoming so far distended as to burst. Fletcher's blower, and a substitute, which can be made with- out much difficulty, will be described at the end of the book. Although such a blowpipe as that which has just been described is necessary for some operations in glass blowing, and renders the chemist almost independent of a furnace for fusions on a small scale, yet much may be done by the use of the mouth blowpipe supported in a Bunsen's holder (so that both hands may be free) and directed upon a larger gas-flame than usual. A very convenient form of Herapath's blowpipe is now made, which can be fitted on a Bunsen's burner. The air- tube is connected with a piece of india-rubber tube ending in a mouthpiece. No bellows are required, as sufficient air can be supplied by the mouth. 73. A Glass-blower's Lamp : when gas is not available. This in its simplest form consists of a flat tin dish, near the centre of which a tin wick-holder is fixed in a slanting direction, sufficiently large to hold a bundle of strands of lamp- cotton about i cm. in breadth and 3 cm. in length. The dish is filled with lamp-oil, or melted tallow, and the wick is trimmed, c i8 LIST OF APPARATUS. a furrow being formed along the middle of it, in a line with which, and a little above it, the blowpipe-jet is placed. 74. A Clark's Retort and Receiver, Fig. 1 6 ; useful for distillations on a small scale. Fig. 1 6. 75. A Pipette, Fig. 17, for measuring out small quantities of liquid. It consists of a tube drawn out at one end into a jet, and slightly con- tracted at the other end, so as to be readily closed by the ringer. It should hold about 20 c.c. and should be graduated into spaces of 0.2 c.c. To fill it, dip the jet rather deeply into the liquid, and suck the latter up into the tube by applying the mouth to the upper end. When the pipette is nearly full, remove the mouth and immediately press the forefinger (slightly moistened) firmly upon the upper end (see the fig.). Fig 17. Now raise the pipette until the uppermost graduations are on a level with the eye, keeping the jet lightly pressed against the side of the vessel of liquid, but clear of the liquid LIST OF APPARATUS. 19 itself. If the pressure is slightly relaxed, and the finger moved a little sideways, air will enter, and the column of liquid should be allowed slowly to fall until the lowest part of the curved surface of the liquid just touches the top line, when the pres- sure of the finger must be at once restored, to prevent any more air entering. The pipette may now be steadily removed to the beaker or flask into which the liquid is to be measured, and the desired quantity allowed to escape from the jet, which should be, as before, lightly pressed against the side of the vessel. Be careful always to read from the same point, the lowest part of the curve formed by the surface of the liquid, held at the level of the eye. 76. A Thermometer, with cylindrical bulb, graduated on the stem from 10 to + 150 centigrade. 77. A Platinum Capsule : hemispherical, about 3 cm. in diameter. This, which would cost about 5.?., will answer almost every purpose of a platinum crucible. 78. A Bunsen's Screw Pinch-cock, Fig. 18. This is a contrivance for regulating the flow of a liquid through an india-rubber tube. The tube is placed, as shown in the engraving, between the two parallel rods, and may be compressed by turning the screws, until the passage Fig. 18. through it is entirely obstructed. 79. A small round Wicker Basket, with upright sides, about 14 cm. in diameter and 10 cm, in "depth.; for holding test-tubes. 80. A few sheets or cut niters of Swedish Filtering Paper, for separating precipitates, such as barium sulphate or calcium oxalate, which from their finely-divided condition would pass through- the pores of ordinary filtering paper. A number of bottles will also be required for containing c 2 20 LIST OF APPARATUS. substances both solid and in solution. Many substances, such as calcium chloride, from their alterability in the air, will of necessity be purchased in bottles. Inclusive of these, the following stock of bottles will be probably sufficient 1 : 24 wide-mouthed bottles, with corks, 300 c.c. capacity. 24 i oo c.c. 6 with glass stoppers, 300 c.c. 12 100 c.c. 8 narrow-mouthed bottles, looc.c. 4 o 100 c.c. 3 200 C ' C - The common green or blue glass bottles, costing (when stoppered) from %s. to 6s. a dozen, will answer quite as well as the more expensive bottles of white glass. [When a stopper is found to be fixed immovably in the bottle, try to loosen it by tapping it, first on one side then on the other, with a piece of wood such as the handle of a file, pressing the thumb against the opposite side of the stopper and taking care to direct the blows obliquely upwards, rather than directly across the stop- per. If this does not succeed, heat the neck of the bottle by passing it to and fro over the flame of a spirit lamp, turning it constantly round. The neck will expand with the heat before the stopper, and if the latter is now tapped again, -it will almost cer- tainly be loosened. There is, of course, a risk of cracking the bottle if it is heated too suddenly, but as the success of the method depends upon the difference in temperature between the neck and the stopper, the heat should be applied quickly, and only for a short time, If this method fails put a drop of oil or glycerine round the stopper, and leave the bottle for some time in a warm room. The oil will work its way between the neck and the stopper, and the latter may generally be loosened by tapping. If the bottle contains potassium hydrate, a drop of hydrogen sulphate may be substituted for the oil, and will remove the alkaline cement.] 1 It is not absolutely necessary for the beginner to start with so large a stock of bottles. Some substances, e. g. marble, sulphur, manganese dioxide, &c., may be kept in boxes. But bottles are far preferable, on the score both of cleanliness and security. LIST OF SUBSTANCES Required for the Course of Practical Work contained in Parts I and II of this Book 1 . The numbers in the column on the extreme left of the page are intended to give some idea of the relative quantities of the substances which will be necessary. If i be interpreted to mean 10 grammes (about one-third of an ounce), 2 = 20 grammes, &c., the quantities will be sufficient for the purposes of most students, but at least twice the amount should be obtained, if supplies have to come from a distance. Many of the substances are required for use in solution. In Part I, Sect. 1, Exercise 5, will be found the geieral method of dissolving a salt in water; and detailed" directions as to the strength of solutions &c. are given in Appendix B. An asterisk is prefixed to the names of those substances which the student may prepare himself. 9 Alcohol, pure, sp. gr. 0.815. 60 Methylated, for common purposes. 12 Aluminium and Ammonium Sulphate (Ammonia Alum). 3 Ammonium Carbonate, pure. 3 Chloride, pure crystallised 12 common. 9 Hydrate, solution of, sp. gr. 0.96 (or 0.88 2 , Caustic Ammonia). i Molybdate. 9 Nitrate. 1 Those who are working in a regular laboratory will probably obtain the necessary chemicals from the common stock. This list is more particularly intended to assist those who are working by themselves, in selecting the substances they will require. 2 This is the most concentrated, and best ; but care is required in dealing with it. It must be kept in a cool place, with the stopper tied down, and the bottle must be opened cautiously, especially in warm weather. 22 LIST OF SUBSTANCES. 3 Ammonium Oxalate. 2 Phosphate *. 2 Sodium and Hydrogen Phosphate (Micro- cosmic salt). 6 Sulphide, solution of, 2 Antimony, Metallic. 3 Trisulphide, 1 Arsenic Trioxide (White Arsenic). 3 Asbestos, in long loose fibres* 3 Barium Chloride, pure. 2 Oxide (Caustic Baryta), i Bismuth, Metallic. i Cadmium Sulphate. 30 'Calcium Carbonate, pieces of white marble* 9 Chloride, thoroughly dried, in lumps. 3 Fluoride, white fluor spar. 10 * Hydrate, solution of (Lime water) 2 . 3 Hypochlorite (Bleaching Powder), 20 Oxide, freshly burnt white Quicklime, 20 Sulphate (Plaster of Paris). 6 Charcoal, selected pieces. i Animal. 3 Carbon Bisulphide (Bisulphide of Carbon). 3 *Chlorine, solution of (Chlorine water). i Chromium and Potassium Sulphate (Chrome Alum). i Cobalt Nitrate. 1 Cochineal, solution of. 20 Copper, Metallic ; strips of sheet-copper, about 0.5 mm thick. 3 filings. pieces of wire, No. 18 and 26 wire-gauge. 6 Oxide (Black Oxide of Copper). 1 2 Sulphate. 2 Cotton-wool. 1 This salt is preferable, as a test, to sodium and hydrogen phosphate, but is not necessary. 2 For the method^ of making this solution, see p. 58. LIST OF SUBSTANCES. 2$ Distilled Water, see p. 67. 2 Ether. Gold, Metallic ; a book of gold-leaf. 2 Grape Sugar. 6 Hydrogen Acetate, solution of, sp. gr. 1.04 (Acetic Acid). 6 Chloride, pure concentrated (Hydrochloric Acid). 10 * Chloride, pure diluted. 15 Chloride, common concentrated. 1 2 Nitrate, pure concentrated (Nitric Acid). 10 * Nitrate, pure diluted. 30 Nitrate, common concentrated. ' 6 Oxalate (Oxalic Acid). 12 Sulphate, pure concentrated (Sulphuric Acid). 10 Sulphate, pure diluted. 60 Sulphate, common concentrated. * and Silicon Fluoride, solution of (Hydro- fluosilicic Acid). * Sulphide, solution of (Sulphuretted Hydro- gen). 3 Indigo Sulphate, solution of (Sulphindigotic Acid). 2 Iodine. 12 Iron, Metallic; thin wire and one or two strips of thin sheet-iron. * Perchloride. 2 Peroxide (Rouge). 12 Protosulphate. 12 Protosulphide, in lumps. .-, > ' i Pyrites. 1 2 Lead, Metallic ; strips of sheet-lead. 3 Acetate. 3 Nitrate. 3 ,, Protoxide (Litharge). 3 Lead, Red Oxide (Red Lead). 3 Litmus, solution of (Archil). 0.5 Magnesium, Metallic ; wire or ribbon. 24 LIST OF SUBSTANCES. 3 Magnesium, Sulphate. 30 Manganese Dioxide (Black Oxide of Manganese). 12 Mercury, Metallic. 3 Oxide. 3 Perchloride (Corrosive Sublimate). i Protochloride (Calomel). i * ,, Protonitrate. 1 Nickel Sulphate. 2 Phosphorus. i Amorphous (Red Phosphorus). Platinum Perchloride. 0.5 Potassium, Metallic. i Bromide. 20 Chlorate. 3 Chromate (Yellow Chromate of Potassium). 6 Dichromate (Red Chromate of Potassium). 3 Cyanide. 1 Ferricyanide (Red Prussiate of Potassium). 6 Ferrocyanide (Yellow Prussiate of Potassium). 9 Hydrate (Caustic Potash). 3 Iodide. 12 Nitrate (Purified Saltpetre). 2 Nitrite. i Sulphocyanate. i *Silicon Dioxide (Silica). Silver, Metallic ; a book of silver-leaf, i * Nitrate. 1 Sodium, Metallic. 3 Diborate (Borax). 2 Carbonate, pure, anhydrous, 20 Carbonate, pure, crystallised 12 Chloride (Common Salt). 3 and Hydrogen Phosphate. 6 Hyposulphite. 3 and Hydrogen Tartrate. 12 Sulphate. 3 Sulphite. LIST OF SUBSTANCES. 2$ 3 Starch. 2 Strontium Nitrate. 6 Sugar (Loaf sugar). 30 Sulphur ; roll Sulphur, and Flowers of Sulphur. 1 2 Tin, Metallic ; in strips and foil. * Protochloride (Stannous Chloride), solution of. 2 Peroxide (Binoxide of Tin). 2 Turpentine. 12 Zinc, Metallic; pieces of sheet-zinc. The purest form of the metal is the Belgian rolled zinc, scraps of which may be procured from any tinman. Advice on the use of the following Exercises. 1. Read over the whole Exercise, or at any rate a complete section of it, before beginning work ; in order that you may understand precisely what you are going to do. 2. Look out all the apparatus, &c. required. It need not be all actually on the table before you ; in fact, it is generally better that it should not be so ; but everything should be within reach. 3. Have always at hand a general text-book on Chemistry, and refer to it constantly for explanations of chemical re- actions, points of theory, &c. The present treatise is intended as a practical companion to such a book, and not in any way to supersede its use. O F I ?S- : PART I. EXPERIMENTS ON THE PREPARATION AND PROPERTIES OF SUBSTANCES. SECTION I. PRELIMINAR Y EXERCISES. EXERCISE 1. Fusion and Granulation. Apparatus required Iron ladle, with bowl about 7 cm. in diameter ; iron spoon ; pan or jug filled with clean water ; pair of pliers ; cloth ; pieces of metallic zinc. Put a few small pieces of zinc into the ladle, and place the latter upon a clear fire 1 , supporting it on the coals so that the bowl may rest steadily in a horizontal position. Zinc requires a rather high temperature (433) for its fusion, but when the bottom of the ladle becomes heated to faint red- ness the fragments of metal will sink down into a fluid mass. When this takes place, add some more pieces of zinc, press- ing them down into the fused metal by means of the iron spoon. If any of the pieces of sheet-zinc are too large to go conveniently into the ladle, bend them into a more compact form with the help of the pliers. You will find it much easier to effect this when the metal is made quite hot by being held in front of the fire; since a sheet of zinc which is stiff and unyielding at the ordinary temperature becomes remark- ably pliant when moderately heated. Go on adding pieces of zinc until the ladle is about three-fourths filled, and then 1 A Bunsen's burner will answer the same purpose, but not so well. If it is used, the ladle may be supported on an iron tripod, or on the retort stand, the handle being laid across the largest ring, so that the bowl may be just outside the ring (not resting in it, lest the brass of the ring should melt). 28 PRELIMINARY EXERCISES. leave it on the fire for a minute or two longer, in order that the metal may become quite fluid. The earthy-looking sub- stance, or dross, which floats upon the melted metal, consists of a compound of zinc with oxygen, one of the constituents of the air, and is called zinc oxide. This should, at the last moment, be skimmed off with the iron spoon, so as to leave the surface of the melted metal quite bright, like mercury. You will notice, however, that no sooner has the coating of dross been removed than a thin film of it begins again to be formed, owing to the contact of the air with the strongly heated metal. Now take the ladle off the fire at once, and, holding it about half a metre above the jug of water, pour the liquid zinc in as thin a stream as possible into the water. The steam formed when the hot metal touches the water blows the particles of zinc asunder, and they fall to the bottom of the jug in feathery, tumefied fragments, which from the great surface they expose to the action of a solvent are well adapted for use in the preparation of hydrogen gas (Sect. 2, Ex. 2). The metal in this form is called granulated zinc. The water in the jug should be poured away, and the zinc should be collected, dried as far as possible with a cloth, then completely dried by being placed on a plate in front of the fire, and kept for use in a wide-mouthed bottle or jar. EXERCISE 2. Glass Working 1 . i. To make some elbow tubes, for use in experimenting with gases. Apparatus required Pieces of glass tubing, about 6 mm. in external diameter ; pieces of glass rod, rather smaller in diameter ; three-square file; fish-tail gas burner, on iron foot; Bunsen's burner; Herapath's blowpipe. Select a piece of readily fusible glass tubing about 6 mm. 1 In this and the succeeding Exercises only the more elementary opera- tions in glass blowing are treated of, such as must be learnt in order to fit up the apparatus required in Sect. 2. GLASS WORKING. 2 9 in external diameter. Lay it down on the table before you, holding it down with the thumb and forefinger of the left hand, placed 15 cm. from one extremity. Make a small notch in the tube close to this point with a three-square file, slightly pressing the side of the file against the left thumb, which will thus serve as a guide to prevent the edge of the file slipping along, instead of cutting across, the glass. The notch should be made, not so much by a repeated to-and-fro motion of the file, as by one, or at most two, short forward strokes combined with as much downward pressure as the tube will bear, the hand being raised a little as the file goes forward, so that it may follow the curve of the surface of the glass. By this means the file will cut deeper into the glass with less injury to itself, than if the edge were drawn to and fro from point to handle as is usually done ; the effect being then rather a rub than a cut. Now take up the tube, holding it with both Fig. 19. hands thus, Fig. 19 (one hand being on each side the notch, and the thumb-nails pressing against the glass on the side opposite the notch), and break it asunder precisely as a stick is broken. The edges of the freshly-cut glass are extremely sharp and must next be rounded off by holding the end of the tube just within the edge of the flame of a Bunsen's burner a little below the top of the flame, turning it constantly round, 3 PRELIMINARY EXERCISES. and keeping the outer end lowermost, lest vapour should con- dense in the tube, and run down to the hot part, so as to crack the glass. Do not heat the glass so long as to cause the end to sink in, and thus contract the bore of the tube ; as soon as the edge is observed to be fairly rounded, the tube should be removed from the flame and allowed to cool, when the other end may be rounded in the same manner. [It should be noticed, once for all, that in all kinds of glass working, the process of annealing is of the utmost importance. Glass must never be either heated or cooled suddenly, unless the special object is to produce a crack. The material is such a bad conductor of heat, that the end of a piece of glass may be raised to a red-heat, while at a distance of 3 cm. from this portion it remains for some time sufficiently cool to be held in the fingers. In con- sequence of this low conductivity, when heat is applied suddenly to a piece of glass, the parts immediately in contact with the source of heat expand before the heat is communicated to the neighbouring parts, and thus tend to tear the latter asunder. Again, when glass is suddenly cooled, the surface contracts at once, and is torn asunder by the still expanded adjacent portions, which have not had time to lose their heat. The useful applications of this property will be alluded to presently ; but it should be a rule ist, Never to bring a piece of glass into aflame suddenly, but to hold it for half a minute, more or less according to the size and thickness of the glass, in the current of hot air above the flame, constantly turning it round, and heating more of it than is intended ultimately to be brought to a red-heat. 2ndly, After the work is done, to withdraw the glasj 'very gradually from the flame, occupying a minute or so in removing it to a distance of 12 or 13 cm. above the flame; then to leave it to cool very slowly in a position protected from currents of air. It will sometimes be found useful to have at hand a dish of strongly heated sand, into which the hot glass may be plunged and left to cool slowly ; and in all cases it is better to err on the safe side, than to risk the breaking of a tube owing to its particles being in a state of tension from deficient annealing. 3rdly, Always to keep the glass turning while it is in the flame. The heat of a lamp or blowpipe is mainly applied to one side of an object, viz. that which is turned towards the wick ; while almost all operations in glass blowing require that the piece of glass should GLASS WORKING. be uniformly heated on all sides. If this simple rule be not attended to, it will be found impossible to blow a good bulb and even to make a good bend in a tube. Practice alone, however, can give that steadiness of hand, and adhesiveness, as it were, of the fingers to the glass, which will enable the student to rotate a piece of tube which is heated to fusion in the middle, without sensibly distorting the softened part. The portions of the tube on either side of the centre may be regarded as two distinct tubes united by a flexible material ; and the object should be, to keep these two tubes in the same straight line, and to rotate them continuously at the same rate, without laying any stress on the connecting portion. It is generally best to hold the hands under the glass, the up-turned forefinger and thumb being chiefly employed in rotating the tube, while the other fingers sustain it at such points that the portions of glass on either side of the heated part are pretty evenly balanced, and have no great tendency to tilt in either direction.] For bending the ordinary fusible glass tubing, if its external diameter does not exceed i cm., a blowpipe-flame is neither required nor so suitable as the flame of a common fish-tail or bat's- wing gas-burner ; but if gas is not at hand, a spirit lamp with a large flame may be used. Light the gas, or spirit lamp ; then holding the piece of tube by its extremities, bring it about 7 or 8 cm. above the flame, turning it constantly round and moving it laterally so as to heat about 5 cm. of it equally on all sides. The flame of a fish-tail burner is flat, and the glass must be held along, not across it : the object being to heat a considerable length of the tube, so as to make a gradual bend. After a few seconds, lower it gradually into the flame, still constantly turning it round. If the gas-burner be used, the glass will become covered with soot when . immersed in the flame; but this is of no consequence, as the heat of such a burner is never high enough to incorporate the carbon with the glass. When the heated portion becomes soft and yielding, which will take place even before it has acquired a visible red- heat, withdraw it from the flame, and gently bend it to a right angle, avoiding the use of much force. You will probably find some difficulty at first in making the bend in one plane, i. e. so that the bent tube when laid on a flat surface may touch it in 32 PRELIMINARY EXERCISES. every part of its length. The best method of accomplishing this is, to support the tube lightly by its extremities, so that the direction of the bend may be determined mainly by the weight of the tube itself; then, holding it before you so that a line drawn from the eye may pass through both its extremities, gradually approach the hands to each other, as if you were endeavouring to snap the tube in two. Do not attempt to use much force, or to make the bend suddenly, or you will inevitably either flatten the glass on the outer side or wrinkle it up on the inner side ; either fault being fatal to the strength of the bend. It will usually be found necessary to heat the tube again in order to complete the bend ; and it is better, if there are any signs of wrinkling or flattening, not to attempt to bend it further in that part, but to heat another portion of it a little on either side of the partially-made bend, and to complete the curve in that portion. Another method of bending small tubes (not more than 6 or 8 mm. in diameter), which practically succeeds very well, is the following : Heat the tube as above directed until it becomes soft ; then hold it steady, just at the top of the flame, withdraw the left hand, and allow the tube to bend by its own weight as far as necessary. It is essential that the tube should be held perfectly still during the bending, and not rotated in any way by the right hand. The correctness of the angle may be judged of by holding the tube close to, 1 but not actually touching, an ordinary square, or the corner of the table or of a book. When the proper bend is completed, lay the tube on a bit of glass in such a position that the heated portion does not come into contact with any cold surface, and leave it to cool slowly. While it is cooling you may cut off another portion of the same tubing about 24 cm. long, and after rounding the ends, bend it in "a similar way, making the bend, however, not in the middle of the tube, but about 7 cm. from one end. If that end becomes too hot to hold in the fingers it may con- veniently be inserted in a hole made in a small cork, which will then answer the purpose of a handle. The tubes thus GLASS WORKING. 33 bent will serve to fit up a washing bottle or generating flask for gases ; and several similar ones with the branches varying in length may be made at leisure moments from any waste bits of tubing, and will be found generally useful, saving much time in fitting up apparatus for any particular experiment. 2. To make a glass jet and a dropping-tube, or pipette. Cut off a piece of glass tubing (the less fusible the better) about 25 cm. in length and 5 mm. internal diameter. Round off the ends of the tube as directed in p. 29, and heat a portion of it, about 7 cm. from one end, in the flame of a Bunsen's burner 1 (remembering to turn it constantly round), until it becomes quite soft and begins to thicken and contract in diameter : then withdraw it from the flame, and pull the two ends apart by slightly separating the hands, until the drawn-out portion is contracted to an external diameter of 2 mm. Be careful not to use much force in drawing out the glass, or it will be contracted to a fine thread so thin as to be useless. When it is cool, make a fine scratch with a file at the middle, a, of the drawn-out portion, and break the tube at this point. You will then have "two tubes, each ending in a jet, the edges of which should be slightly rounded in the lamp flame, and the aperture, if necessary, reduced by holding it rather longer in the flame, until a large needle would just pass through it. The shorter of these tubes may be kept for use as a jet, in Fig. 20. Sect. 2, Ex. 2. The longer one will form a very useful ' pipette ' for delivering small quantities, such as single drops of a liquid, in testing. For this purpose the narrow end is dipped into the liquid, and the forefinger (moistened slightly) is pressed firmly on the top of the tube (see Fig. 17) : it may then be withdrawn, and the pressure of the air will prevent any liquid escaping, but by relaxing the pressure of the finger one or more drops may be allowed to fall, as required. 1 If the glass is very infusible the blowpipe flame must be used, but a Bunsen's burner will generally be found to give heat enough. 34 PRELIMINARY EXERCISES. 3. To make a stirring rod. For this purpose the heat of a gas or spirit lamp is scarcely sufficient ; it must be intensified by the use of a blowpipe. The best form of this instrument is fully described at p. 16, and it will only be necessary here to explain the method of using it so as to produce the greatest effect. If a Herapath's blowpipe is at hand, the process is simple. Turn on the gas full, and light it at the mouth of the blowpipe. Then work the bellows gently and uniformly, and gradually reduce the supply of gas, until you have a small brush of blue flame about 10 or 12 cm. long. If you have one of the mouth Herapath's blowpipes, de- scribed in the list of apparatus p. 17, it should be fitted into the tube of the Bunsen's burner and the whole raised on blocks to a convenient height above the table. You should then refer to the Exercise on the Use of the Blowpipe, p. 85, and practise the method of keeping up a continuous stream of air, as there described ; remembering not to turn on more gas than is neces- sary to give a small brush of blue flame. [If a spirit or oil lamp must be used, the wick should be trimmed flat and pulled up sufficiently to give a large flame ; then with the trimming scissors separate the wick in two parts, and bend each portion sideways so as to leave a clear passage for the air between them. Arrange the lamp and jet so that the latter may lie, pointing slightly upwards, in the line of the passage just formed in the wick, and on a level with the top of it. Light the lamp, and, introducing the jet just within the flame, commence the blast of air. The flame of the lamp will now be almost entirely deflected in the direction of the stream of air ; and by pushing the jet a little further into the flame, or drawing it back beyond the margin, any kind of flame may be produced, from a quietly-burning pointed blue cone to a large roaring brush of flame; the former being most suitable for the present purpose. If the flame is ragged or irregular, see whether any filaments of the wick stand in the way of the blast, and if so remove them with the scissors. If this does not cure the defect, the blowpipe-jet is dirty or not truly circular, and must be cleaned out by a large needle, or, better, by a small broach.] Having obtained a satisfactory flame, select a piece of glass GLASS WORKING. 35 rod about 5 mm. in diameter, and cut off a piece about 18 cm. long, as directed in the case of the glass tubing. Hold one end of this piece about 5 cm. in front of the visible flame, turning it constantly round by a twisting motion of the fingers, and gradually bring it just within the apex of the flame, which is its hottest portion. The edges of the glass will soon begin to melt, and the sharp angle will disappear as the glass approaches the liquid condition. The heat should be continued until the end is perfectly round, and then the rod should be gradually withdrawn from the flame and allowed to cool slowly, resting on another fragment of glass or on the table so that the hot end may project over the edge. As soon as it is cool, the other end may be drawn out so as to form a blunt point (in shape resembling the pipette) by heating it in the flame until it becomes soft, then pressing upon it the end (previously heated) of a short bit of glass tubing or rod, so as to weld them together, and lastly directing the flame on the rod close to the junction, and drawing it out, when soft, precisely as was done in making the pipette. The rod should then be cut at the narrowest part and the sharp edges slightly rounded by fusion. EXERCISE 3. Glass Working (continued}. Apparatus required. Piece of glass tubing, about 5 or 6 mm. external diameter ; pieces of less fusible glass tubing, of the same diameter (the ordinary German glass will, however, do) ; three-square file ; Bunsen's burner ; fish-tail burner ; corks ; cork-borers ; cork-squeezer, or pliers ; narrow-mouthed bottle, about 600 c.c. capacity ; rat-tail file ; piece of charcoal, about 3 cm. in diameter, and 6 or 7 cm. long. i. To fit up a washing bottle, as shown in Fig. 21. In doing this you will have to apply the experience in glass working which you have already gained, and in addition to learn the method of boring holes in corks. Cut off a piece of glass tubing about 5 mm. in external diameter and 50 cm. in length hold it horizontally in the D 2 PRELIMINARY EXERCISES. hands and heat it (observing the precautions given in p. 30) in the flame of a Bunsen's burner at a point about 15 cm. from the right-hand extremity. As the tube is somewhat long, you will find an advantage in supporting it near the other extremity on a ring of the retort-stand, or other support, fixed at the same height as the burner. This will render it easier to keep the tube turning between the fingers (p. 30), and to maintain it in the proper position when it becomes soft. Allow the heated portion of the glass to become slightly thickened, then raise the tube out of the flame and draw it out slowly and carefully (wait- ing until the glass has so far cooled that a little force is required for the purpose), as was done in making the pipette, p. 33. Allow it to cool slowly, and then cut it in two at the middle of the contracted portion. You have now two tubes, the one 35 cm. an I the other 15 cm. in length, each terminating in a jet. Lay aside the shorter tube Fig 21. for the present, and heat the extremities of the longer tube just sufficiently to round off the sharp edges ; then (using the fish-tail burner) bend it to an acute angle equal to that of the left-hand tube in Fig. 21, making the bend about 8 cm. from the jet. While it is cooling take the other tube, cut off the contracted portion at the end, round off the sharp edges of each end in the Bunsen flame, and bend it (using the fish-tail burner) near the middle to an obtuse angle equal to that of the right-hand tube in the figure. It now only remains to fit these tubes to the bottle by means of a cork perforated with two holes. It will be best however to begin by practising the method of making a single GLASS WORKING. 37 hole in the centre of a cork. Take a good sound cork about 2 cm. in diameter, squeeze it until it becomes soft and elastic (a pair of pliers or nut-crackers may be used instead of a regular cork-squeezer), then take it up thus, Fig. 22, between the second ringer and the thumb of the left hand, and place the sharpened end of the smallest cork-borer against it, as near the centre of one end as you can judge. Urge the cork- borer into the cork with a twisting motion, as if you were using a cork-screw. Some care will be required to make the hole Fig. 22. straight through the cork, so that it may be truly central. Of the proper direction the eye will be the best judge : and when the cork-borer has penetrated some little way, it will be ad- visable to turn the cork a quarter round, in order that it may be seen whether the axis of the cork-borer and of the cork are still in the same straight line. If not, a slight pressure on the cork-borer in one direction or the other, while the boring is continued, will set it straight. When the borer has penetrated quite through the cork it may be withdrawn with a twisting motion, and will bring with it a cylindrical plug of cork, leaving a hole, the sides of which should be smoothed with the round or rat-tail file. The plug of cork remaining in the borer may be pushed out by means of a wire which is usually sold with the set of borers for that purpose. It should 3 8 PRELIMINARY EXERCISES. not be thrown away, as such small corks are often very useful for stopping the ends of drying-tubes, and other purposes. When you have practised in a similar way on one or two other corks, and have learnt to control the direction of the borer, you may complete the fitting up of the washing bottle. Take an ordinary narrow-mouthed bottle holding about 500 or 600 c.c. ; choose a cork slightly too large to fit it (since the cork is reduced in size when it is squeezed), and render it soft and elastic by squeezing it. You have now to make two holes in it in the position of Fig. 23, on opposite sides of the centre, and about midway between the centre and cir- cumference. Take for the purpose a cork- Fig 23 borer rather smaller than the tubing which you have been using, and bore the two holes, with particular care that each hole does not run into the other or pierce the side of the cork. The cork-borer may be slightly oiled, if thought necessary, but this will be seldom requisite if the end is kept properly sharp. The holes should next be smoothed and slightly enlarged by the rat-tail file, until the end of one of the tubes will just enter them when some little pressure is used. Now pass the longer branch of the longest of the two tubes through the cork, with moderate pressure 1 and a twisting motion, until it projects so far as to reach, when the cork is fitted into its place, nearly to the bottom of the bottle. When this is done, pass one of the branches of the other tube through the other hole in the cork, until it projects 3, or 4 mm. on the other side. Fill the bottle with distilled water, fit the cork carrying the tubes tightly into the neck of it, and your washing bottle is ready for use. Blow gently through the up-turned end of the shorter tube, and see whether a fine stream of water issues from the jet of the other 1 If much pressure is used the tube is not unlikely to break, and the splinters of glass may cause a serious cut. The hole should never be so much smaller than the tube as to make it necessary to use much force in passing the latter through it. It is a good plan, also, to wrap the tube in a cloth or handkerchief while it is being passed through the hole in the cork. GLASS WORKING. 39 tube. If the jet is found to be too large, it may be easily reduced in size by holding the tip of it for a second or two in the flame of a Bunsen's burner. Care should be taken not to allow any water to flow down into the jet, while it is being heated, which would infallibly crack it. If no water issues from the jet when you blow air into the bottle, either the aperture is closed up, in which case a small portion of the tip of the jet may be cut off with the file, or there is a leakage of air at the cork. Place a drop or two of water on the cork, and observe whether, on blowing as before, bubbles rise through it. If they do, you may remedy the fault either by pushing the cork more tightly into its place or by melting a little sealing-wax over the top of it, or, if these fail, by taking a new cork altogether, and boring the holes with more care. Never be satisfied with an imperfect apparatus. 2. To seal a glass tube. This is the simplest operation in glass blowing strictly so called, i. e. in which the assistance of the breath is called in, to mould the glass into shape ; and it is one which the student is continually called upon to practise for mending broken test- tubes and making arsenic reduction-tubes. Test-tubes, however, are made of such thin glass that it is by no means so easy as it appears to seal them neatly ; and you will find it best to commence work on a piece of soft glass tube about 5 mm. in external diameter. Cut off a piece of this tubing about 15 cm. in length, round the ends in the Bunsen flame, and having arranged the blowpipe so as to give a large steady flame, hold the tube horizontally and bring it gradually into the hottest part of the flame, so that about i cm. near the middle may be thoroughly 'heated. When the glass becomes quite soft, remove it from the flame and draw it out a little by separating the hands, until it assumes the form of Fig. 24. Now direct the flame against the part which lies a little to the left of the most contracted portion, and draw it out further until nothing but a thread PRELIMINARY EXERCISES. of glass remains to connect the two portions of the tube, Fig. 25. This thread of glass should next be heated just at the point where it joins the tube on the left hand, when it will fuse and divide, running up into a small knob against the thicker portion of the tube. Lay down the right-hand piece of tube (resting it on another bit of glass that it may not burn the table), and proceed to make the end of the other piece smooth and round. This is done by directing the flame upon the small projecting knob, which will soon fuse and partially incorporate itself with the surrounding glass. The whole end of the tube will, however, have become con- tracted and thickened, and must be expanded a little by removing it from the flame and immediately forcing air very Fig. 24. Fig. 25. Fig. 26. gently into it from the mouth, until it takes the shape of Fig. 26. Do not blow too hard at first, or heat more of the tube than is necessary, or you will probably expand the sides of the tube into a bulb, which is not your present object: your intention being simply to distribute evenly the thickened glass at the extremity by driving it forwards rather than outwards, and to mould the end of the tube into the regular round form of Fig. 26. If this is not accomplished at the first trial, bring the end of the tube again into the blow- pipe-flame until it contracts, and blow it out as before, keeping the attention, while blowing, fixed on the heated glass so as to be ready to moderate or stop altogether the supply of air from the mouth, if the glass shows signs of yielding too much. Now anneal the tube as already directed, and finish the other, or right-hand piece of tube, in a similar way, drawing it out and rounding it exactly as before. If the bit of capillary tube remaining attached to it is too short or too slight to be GLASS WORKING. 41 used as a handle in drawing out the glass, it should be cut off, and while the end of the tube is heated in the flame, a bit of waste glass held in the right -hand should be heated and pressed against it, and the flame directed upon the point of junction. The two pieces will then adhere, and by applying the flame a little more to the left the superfluous glass may be melted and drawn off, attached to the bit of waste glass. Moreover, if the remaining knob be too large to be neatly melted into the bottom of the tube, it may, when soft, be touched with a bit of heated glass and drawn off in a similar way. After a few small tubes have been thus sealed, larger tubes may be operated on in the same way, a larger blowpipe- flame being employed. Test-tubes broken at the bottom will be found good materials for practising on, and may be mended by drawing off the broken portion and sealing them as above. The glass of which these tubes are made is so thin that it is not easy at first to avoid over- heating them in some one spot, thus producing a mis-shapen end, which is quite inadmissible in vessels which, like test-tubes, are ex- posed to comparatively sudden changes of temperature. The softened portion should not be drawn out much at first, but allowed to sink in and contract of its own accord, in order to thicken it a little : and especial care must be taken that the bottom is of uniform thickness and well annealed. If there is a crack in the tube, the piece must be broken off by a slight blow; or, better, the crack may be led round the tube as described in the next section, otherwise it will extend itself when the tube is heated. Another very useful form of sealed tube, which may be made by the student himself, is that known as the 'ignition tube/ which serves for heating substances either per se, or with a flux, in the preliminary examination in qualitative analysis. These tubes are of hard infusible glass, about 5 or 6 cm. long and 5 mm. in external diameter; and the manufacture of them will be a moderate test of proficiency, as it will require some dexterity to get rid entirely of the 4$ PRELIMINARY EXERCISES. small knob of glass already mentioned. The end must be very strongly heated, and the breath thrown in with some force, the moment that the glass is removed from the flame. These tubes are shown of the actual size in Fig. 27. It will be seen that the sealed end is slightly expanded so as to form a small bulb. This is done after the knob has been got rid of, by strongly heating a portion of the sides as well Fig. 27. as the end of the tube, and then immediately blowing into it with considerable force. The bulb should not, however, be larger than is shown in the figure, or it will be too thin to be of much use. 3. To divide glass by leading a crack along it. The low conducting power of glass for heat renders it, as has been already noticed, very liable to crack from sudden changes of temperature. From the same cause, however, it is easy to extend a crack, when once begun, in any desired direction by heating the parts of the glass which lie just in front of the crack. The method is extremely simple, and will be found especially Useful in cutting off the necks of flasks when they are chipped or uneven, and in making evaporating basins or capsules out of broken flasks or retorts. Suppose, for instance, a Florence flask has, as is often the case, a neck too uneven to allow of a cork being fitted into it. Arrange the blowpipe to give a rather large flame; take any waste bit of glass rod or tube about 6 mm. in diameter and 7 or 8 cm. in length ; draw it out in the flame as directed in the last section, leaving the end somewhat pointed. Now take the body of the flask in the left hand, the neck pointing upwards, and, having heated the pointed end of the rod to full redness, apply it to the outside edge of the neck, and hold it there for a second or two. It is very probable that a small GLASS WORKING. 43 crack will be thus started, but if not, it may with certainty be produced by removing the heated rod, and immediately touching the spot lightly with a moistened finger or splinter of wood 1 . The crack once begun, press the red-hot end of the rod on the glass a little in front of it, Fig. 28, when it will at once extend itself to the heated spot; and by slowly drawing the rod in the direc- tion required, re-heating it from time to time in the blowpipe -flame, the crack may be led at first a short distance downwards, and then, turning at right angles, horizontally round the neck so as to cut off a ring of glass including the uneven portion. It is generally not possible to carry the crack entirely round the glass until it returns into it- self; a small portion of the glass will remain undivided, but after laying down the rod the ring may be readily pulled off, a very slight inequality marking the point where the crack was incomplete. A rather better form of termination for the rod, especially when the glass to be cracked is somewhat thick, is the Fig. 28. Fig. 29. following, Fig. 29. It is made by heating strongly about 5 or 6 mm. of the end of the rod, and then, the rod being held in a slanting direction, pressing it down on any flat metallic surface. The glass will spread out laterally, and by 1 By making a notch with the file in the place and in the direction in which the crack should be, and applying the heated rod to the end of the notch, it is easy to start a crack at once and in the desired direction. 44 PRELIMINARY EXERCISES. turning the rod half round and pressing it down again in the same way the desired chisel-shape will be obtained. In using it the edge should be kept in the line of the crack required, and moved along the surface with slight pressure. The ad- vantages of this form are: ist, That more of the glass in the desired line is heated at once, so that the crack extends more rapidly, yet under perfect control ; 2ndly, That it is easier to lead the crack in an unswerving straight line, the eye being guided by the line of the edge of the tool, than when a blunt point only is used, precisely as a carpenter finds it easier to cut the side of a mortice by a broad chisel than by a narrow one. Having thus rendered the neck of the flask even, it will be desirable not only to fuse the edge in the flame, but to turn it slightly outward so as to form a border like that of a bottle, which will give it much greater strength when a cork is to be fitted to it. To do this a very simple tool must be first prepared. Select a piece of sound charcoal, free from fissures, about 3 cm. in diameter, and 6 or 7 cm. long. Cut and rasp the end of this to a point like that of a pencil, but more obtuse, the angle at the apex being nearly a right angle. Take the flask in the left hand, and cautiously heat the extreme edge of the neck in the blowpipe-flame until it softens, turning it constantly round and holding it at right angles to the flame so that the latter may Fig. 30. play across the mouth and heat two opposite sides of the glass at once. When the glass begins to soften and sink inwards, take the pointed charcoal in the right hand arid press it gently with a twisting motion into the neck. The edge will spread out, and by repeating the operation a border shaped thus, Fig. 30, will be obtained, which should be annealed with especial care. Test-tubes, &c. may be bordered in the same way, but it is best to use a spirit lamp or Bunsen's burner, and not the blowpipe, for heating the edges, on account of the thinness of the glass. WEIGHING AND MEASURING. 45 EXERCISE 4. Weighing and Measuring. Apparatus required. Balance, and set of weights; Bunsen's holder; test-tube, selected of stout glass, about 15 cm. long, and 1.5 cm. in diameter; beakers; washing bottle; pipette; three-square file; writing diamond. Alcohol (methylated spirit) ; strong hydrogen sulphate (sul- phuric acid) ; piece of glass rod, and strip of lead or copper. General rules to be observed in weighing. 1. Handle the weights very carefully, using a pair of light brass forceps for the smaller ones. 2. Never allow the scales to swing violently about, but keep them steady with the hand while the weights are being put in. 3. Try the weights in a definite order, beginning with the largest, then taking the next smaller, then the next, and so on. 4. Count the weights over twice, once in the scale-pan, and again as they are being put away in their places, and put down results at once in your note-book. Support the balance in the Bunsen's holder 1 , as shown in . Fig. 31. Fig. 31, at such a height that the pans may be about 3 cm. above the table. Place under the pans a flat ruler (a half- 1 It will be advisable to put a weight (such as the Argand lamp) on the base of the Bunsen's holder, to prevent the possibility of its falling forward when heavy weights are put in the scales. 46 PRELIMINARY EXERCISES. metre rule will do very well) so that by tilting it on its edge they may be steadied when required. In the first place see that the beam, when free to swing, comes to rest in a horizontal position. If it does not do so, one of the pans may be dirty, or not hanging fairly from the beam ; but if nothing of this kind is noticeable, the construction of the balance may be at fault, and the equilibrium must be ad- justed by putting a bit of paper, or tin foil, in the lighter scale ; this must, of course, remain there throughout the exercise. Next, examine the weights to see if they correspond with, and are correct multiples of one another. If you have the complete set of 100, 50, 20, 10, 10, 5, 2, 2, i, -5, -2, -2, -i grm. 1 , the following trials may be made. 1. Place a 10 grm. weight in each scale and see whether they balance each other, as they should do. Absolute accuracy can hardly be expected in common balances and weights, but there should be no error so great as i decigramme. 2. Transpose the weights from one scale to the other. They ought still to balance each other ; otherwise the arms of the balance are not of equal length. If the discrepancy is serious, the balance should be rejected altogether. 3. Weigh out carefully i grm. of writing paper; then put the i grm. weight in the same scale as the paper, and see if the 2 grm. weight balances the whole, as it ought to do. 4. Try whether the 2 grm. weight which you have just used balances the other 2 grm. weight. 5. Try whether the 2 + 2 + 1 grm, weights balance the 5 grm. weight. 6. Try whether the 5 + 2 + 2 + 1 grm. weights balance the 10 grm. weight. 7. Try whether the two 10 grm. weights balance the 20 grm. weight. 8. Try the 50 grm. weight against the 20+10+10 + 5 + 2 + 2 + 1 grm. weights. 9. Try the 100 grm. weight against all those just mentioned. 1 Suggestions for making weights to fill up any deficiencies in a set are given in Appendix A. WEIGHING AND MEASURING. 47 If you have not a complete set of weights you may still be able to make some of the above trials, and others will suggest themselves. For instance, if you have i, 2, and 5 grm. weights, 4 grms. of a substance may be weighed out by putting the 5 grm. weight into one scale, and the i grm. weight into the other, and then placing in the latter scale enough of the substance to restore equilibrium. This method is called 'weighing by subtraction/ and is constantly useful. i. Graduation of a test-tube as a measure of cubic centimetres. The original gramme weight was obtained (see Appendix E) by measuring i cubic centimetre of pure water (at 4 C.) and making a piece of metal of such a weight as to balance it. Hence it is easy to obtain a correct measure of i c.c. by putting into a tube enough water to balance the i grm. weight (the small correction for temperature may be neglected) and making a mark at the level of its surface. Select a test-tube of stout glass, about 1-5 cm. in diameter and 15 cm. in length. Place a beaker in one scale of the balance, and support in it the empty test-tube. Counterpoise them by a beaker partially filled with water (or by small shot) placed in the other scale. When you have seen that the scales are in equilibrium, put into the scale containing the counterpoise a i grm. weight, and pour distilled water into the test-tube from the jet of the washing bottle until equilibrium is restored. If too much water is added, the excess may be removed by a glass rod, or by the pipette which you have already made (p. 33). Bring the test-tube up to the level of the eye, holding it vertically against the wall, or some other upright support ; place the thumb-nail just at the level of the lowest part of the curve formed by \he surface of the water 1 , and make 1 This is the best and most sharply-marked level at which to read off a volume of such a liquid as water, and it may be made even clearer by holding behind the tube a white card over the lower half of which has been pasted a piece of black paper; the boundary line between the white 48 PRELIMINARY EXERCISES. a slight mark with a file at this level. The mark will then, as already explained, denote a volume of i c.c. Weigh into the tube in a similar manner, 2 grms., 5 grms., 10 grms., and 20 grms. of water, making a file-mark at each point. Finally, empty out the water and make a shallow scratch with the file at each of the marks, guiding the edge of the file by a strip of card held firmly round the tube. The lines may extend round one-fourth of the circumference of the tube, and the figures i, 2, 5, 10, 20 c.c. may be scratched on the glass close to the proper mark with a sharp point of the file, or, better, with a writing diamond. The tube is now ready to be used whenever a measure for small quantities is required, and also for determining densities, in the manner next to be explained. 2. Determination of Densities. 1 Density ' means, strictly speaking, ' quantity of matter ' ; and equal bulks of different substances contain very different quantities of matter. This is generally found out by weighing them. Thus the weight of i c.c. of water is, of course, i grm.; the weight of i c.c. of silver is found to be 10-5 grms. Hence we say that silver has loj times the density of water 1 . In practice, water is usually taken as the standard of com- parison for liquids and solids, and the ' density ' or ' specific gravity' of a substance is the number which expresses how many times a certain bulk of it is heavier or lighter than the same bulk of water. A. DENSITY OF LIQUIDS. In the case of liquids the process is very simple. A vessel is (i) counterpoised so that its own weight may be neglected; (2) filled up to a particular level with water, and weighed ; and black being made to coincide nearly with the lowest part of the curve. The latter then appears black and perfectly sharp against the white back- ground. 1 In illustration of this, a piece of good cork may be cut with a sharp knife into a cube each side of which measures i cm., and then weighed : it will be found to weigh nearly one-fourth of a gramme. A cube of lead of the same dimensions (filed and scraped as true as possible) will weigh between n and 12 grms. WEIGHING AND MEASURING. 49 (3) filled up to the same level with the liquid and again weighed. Then we have only to find the proportion between the weight of the water and the weight of the liquid by the rule- of-three sum ; Weight of water : weight of equal volume of liquid : : I : density of liquid. The measure you have made is particularly convenient for this purpose, since it is easy to obtain with it a definite volume of any liquid, and it is clear from the way in which you have graduated it, that the number of cubic centimetres of the liquid taken will express the weight in grammes of the same volume of water, thus saving the trouble of weighing the latter. Thus if the volume of the liquid is 5 c.c. we know at once without weighing that this volume of water weighs 5 grms. Density of Alcohol, &c. In the first place see that the tube is properly counter- poised : then measure in it 10 c.c. of common alcohol, and weigh it carefully. Put down the weight at once in your note-book. Then, since it is clear that 10 c.c. of water weigh 10 grms. (neglecting the slight correction for temperature) we shall have the proportion, Weight of loc.c. of water : wt. of loc.c. of alcohol : : I : density of alcohol. After rinsing out the tube with water, and drying it, you may find the density of strong hydrogen sulphate (common sulphuric acid) in a similar way ; but it must be borne in mind that the substance is very corrosive, and should be handled carefully. A strong solution of common salt may be sub- stituted. . * s '$r B. DENSITY OF SOLIDS. In the case of solids there would seem, primd facie, to be a great difficulty in getting a volume of the substance exactly equal in size to a given volume of water. It may be done readily, however, with the measuring tube in the following way. E 50 PRELIMINARY EXERCISES. i. Density of glass. Dry the tube, and, after seeing that it is properly counter- poised, put into it a bit of glass rod about 8 or 9 cm. in length and about as thick as a pencil. Find the weight of the glass, and write down this weight at once on a piece of paper. Thus : (i) weight of glass in air = Then fill up the tube (the glass still remaining in it) with water, to the level of the 20 c.c. mark, see that no air-bubbles cling to the glass, and weigh the whole. By this last weighing you have found the weight of a mixture of the solid + water measuring 20 c.c. And if you subtract from this the weight of the solid, the remainder will be the weight of the water you have added to make up the total volume to 20 c.c. Thus: weight of solid + water = weight of solid alone = weight of water added = Now, if the solid was not there, but its place supplied by water, we should have 20 c.c. of water, which would, of course, weigh 20 grms. And it is easy to see that the difference between 20 grms. and the actual weight of the water you added will be the weight of the water which would be there if the solid was not, i.e. the weight of a volume of water equal in size to the solid. Hence, the next step in calculation will be weight of 20 c.c. water = weight of water added = (ii) weight of water equal in ) volume to the glass j ~ Then, since you know already the weight of the glass in air, you have lastly to work out the proportion, weight of water (ii) : weight of equal vol. of glass (i) : : i : density of glass. WEIGHING AND MEASURING. 51 In the same way you may ascertain the density of a piece of copper wire, or of a number of shot, remembering that it is advisable to take a good large piece of the substance ; otherwise the errors of the balance and weights will be so relatively large as to make the results uncertain. The density of many solids is, perhaps, more usually taken by another method, in which recourse is had to Archimedes' principle, that 'a solid when immersed in a liquid loses a weight which = that of the liquid which would occupy its place, i.e. the weight of a volume of the liquid equal to it in size.' All that is required, therefore, is (i) to weigh the solid in air, (2) to immerse it in water and weigh it again in that position. The difference between the two weights will be the weight of a volume of water equal in size to the solid, and the density can then be found by the usual proportion sum. In illustration of this method, the density of a bit of stone or glass (a marble or a solitaire ball), or of a copper coin may be taken as follows : Arrange the balance as usual; except that,, since the chains or cords by which the scale is hung ar$ likely to get in the way, it will be well to keep them farther out by attaching to them, about 2 or 3 cm. below the ring from which they are hung, a wire frame of the shape shown in Fig. 32, made of three pieces of brass or copper wire about 9 cm. long twisted together; each arm being about 4 cm. long. Such a frame may be made for each scale, and may remain permanently attached to the balance, as it will be found of great use in pre- venting the chains getting entangled. Support over one scale a beaker upon a glass plate resting E 2 PRELIMINARY EXERCISES. Fig. 33- on a ring of the retort stand, as shown in Fig. 33, care being taken to leave just room enough for the scale to rise and fall freely below the retort ring. Hang the solid, of which the density is to be taken, in a secure noose of the finest cot- ton or silk, and tie it to the centre of the three-armed frame above mentioned, so that it may hang freely in the middle of the beaker. Weigh it in this position, and note down the weight at once. Then fill the beaker with water, brush away with a piece of wire any air bubbles which may cling to the solid, and weigh it again. Put down the weights thus : weight of solid in air = weight of solid in water = weight of equal volume of water = Then calculate the density by the usual proportion sum. The calculation may be expressed in the following rule Weight of solid in air . .. , = & , . . . - = density of solid. Loss of weight in water The principle of Archimedes suggests a neat method of taking the densities of liquids, which may sometimes be found useful. It is simply, to weigh a piece of glass or other suitable solid ; (i) in air, (ii) in water, (iii) in the liquid of which the density is required. Then, as already explained, Loss of weight in water = weight of volume of water equal to the solid. Loss of wt. in the liquid = wt. of vol. of the liquid equal to the same solid. Thus we have ascertained the weights of equal volumes of water and the liquid, from which the density of the latter is found in the usual way. You may, in illustration, take the density of alcohol by this method, using the solid of which the density has just been found ; and of which, therefore, the weight in air and water is already known. Compare the result with that which you previously obtained. SOL UTION, E VA PORA TION, AND CRYSTALLISA TION. 53 EXERCISE 5. Solution, Evaporation, and Crystallisation. Apparatus required Porcelain mortar and pestle ; scales and weights ; Bunsen's holder ; flask, with flat bottom about 300 c.c. capacity ; glass measure; retort-stand; sand-bath, with sand; argand, or spirit lamp; funnel, 7 cm. in diameter; filters, 14 cm. in diameter; beaker; porcelain dish, 12 cm. in diameter; watch-glass; glass rod; washing bottle, filled with distilled water ; spatula ; cloth ; writing-paper ; blotting-paper ; alum ; sodium sulphate. Place the mortar on a clean sheet of paper, and put into it two or three lumps of common alum. Reduce these to a coarse powder by first striking them with the pestle until they are broken up into small pieces and then completing the pulverisation by rubbing these fragments with a circular move- ment of the pestle (not unlike the motion used in stirring a liquid, but combined with downward pressure), occasionally shaking down to the centre portions of the salt which adhere to the sides of the mortar. When this is done, take two half sheets of writing-paper, turn up two opposite sides of each, so as to form a trough, and place one in each scale of the balance; they should then be found to counterbalance each other. Into one scale-pan put weights amounting to 30 grms., and into the other bring some of the powdered alum, using a card or spatula for transferring it. Continue to add the salt until the beam turns, then remove any excess of the powder little by little, until the beam remains level, showing that there is the same weight in 'each scale. Now take out of the scale the paper with the powder in it, and transfer the latter to a flask, as in Fig. 34. Place the measure on a level table, and pour distilled water into it until the lowest part of the curved surface of the water is seen to touch the division which marks 150 c.c. The eye should be placed on a level with this division and neither above nor below it, or it will be impossible to obtain a correct measurement. Pour the measured water into the flask and 54 PRELIMINARY EXERCISES. set the latter on the sand-bath, in which should be placed enough sand to form a stratum about i cm. deep, or rather less. Support the sand-bath on the largest ring of the retort- Fig. 34- ^ stand, and place under it the argand burner, the flame of which should nearly, but not quite touch the bottom of the sand-bath. While the solution of the alum is going on, you may get ready a filter, or strainer, to separate any particles of dirt which may be in the liquid. Take a circular piece of filter- ing paper about 14 cm. in diameter, fold it in half, and then again at right angles to the first fold, so that the circle is reduced to a quarter-circle consisting of four thicknesses of paper. Open this out, so as to form a conical cavity, Fig. 35. having three folds of the paper on one side and one on the other ; and place it in a funnel slightly larger than the filter thus folded. Fig, 35 will serve to explain the mode of folding the filter. The filter should fit the funnel pretty accurately, and may require to be opened out a little more, or, on the SOLUTION, EVAPORATION, AND CRYSTALLISATION. 55 other hand, contracted so as to form a more acute cone ; but in all cases care should be taken not to injure the point, which, although it requires most strength, is generally the weakest part, since all the creases meet there. Set the funnel in a ring of the retort-stand, and place under it a beaker or other vessel. Pour a little distilled water upon the filter, directing the stream not into the point, but down the thicker part of the side, and allow the water to drain off into the beaker. Meanwhile see if the whole of the alum has by the aid of the heat dissolved in the water, and if not, shake the flask to bring fresh portions of the liquid into contact with the undissolved portion. When the solution is complete, take away the lamp ; take the flask out of the hot sand and put in its place a porcelain dish ; turn round the ring holding the funnel, raising or lowering it if necessary, until the tube of the funnel just touches the side of the dish near its rim. Now, grasping the neck of the flask with a cloth, pour its contents along a glass rod, Fig. 36, so as to fall on one side of the filter; pouring slowly ( 'at first, until the filter becomes fully saturated with the solution, but afterwards keeping the filter nearly full. When all the liquid has run through, remove the funnel and filter, and replace the lamp in order to evaporate the solution ; " i. e. to drive off the water until only enough is left to retain the salt in solution at a temperature near the boiling- point. The liquid is then said to be 'saturated' at that temperature. To see when this is the case, dip from time to time a clean glass rod into the solution, place a drop of the liquid on a glass plate or watch-glass and stir it with the rod as it cools. If it deposits minute cfystals on cooling, the proper point has been reached. The lamp should then be removed, and the porcelain dish taken carefully from the sand with the fingers (protected by a glove or cloth), and deposited in a cupboard or on a folded cloth laid on the table. Cover it loosely with a piece of paper supported under- neath by a short glass rod or tube laid across the dish. The whole should now be left quite undisturbed for two or three hours at least, in which time a good crop of crystals ought PRELIMINARY EXERCISES. to be formed by the slow cooling of the solution. Meanwhile, if time permits, you may crystallise some sodium sulphate in exactly the same way, weighing out 60 grms. of the salt, and Fig. 36. dissolving it in 100 c.c. of water. (The solution may be left to crystallise in a beaker, if no other large porcelain dish is at hand.) When the dish containing the crystals is quite cold, pour SOLUTION, EVAPORATION, AND CRYSTALLISATION. 57 off the remaining solution, or ' mother liquor ' as it is called, into a beaker, holding a glass rod in contact with the lip of the dish, so that the liquid may run down it and not down the out- side of the dish. After the last drops have drained away, shake out the crystals on a folded sheet of white blotting-paper, dry them by pressing them gently and repeatedly with fresh pieces of blotting-paper, and examine their shape. [If no good, well-defined crystals are obtained, put the whole of the crystals into the beaker containing the mother liquor, and heat until they are re-dissolved ; then hang in the solution a loop of lamp-cotton or worsted, or a small splinter of coke, to serve as a nucleus upon which crystals may form and be free to grow on all sides.] Notice the totally different form of the crystals of the two salts ; the alum crystallising in shapes derived from the octo- hedron, a solid figure obtained by joining two four-sided pyramids base to base; the sodium sulphate crystallising in long four-sided prisms, like flattened rods. Notice also the different behaviour of the salts when a crystal of each is exposed to dry air for some time * : the alum remains nearly unaltered, while the sodium sulphate ' effloresces,' as it is termed, or becomes converted into a white opaque substance, by giving up a certain amount of water which it contains, and which seems essential to its crystalline form. The water thus combined with the salt is called ' water of crystallisation/ Mix in a clean porcelain dish the solutions of alum and sodium sulphate which were poured off the crystals, evaporate the mixture, as before, on the sand-bath, and leave it again to crystallise. You will now obtain a crop of crystals of both salts, and each will be found to have crystallised in its own characteristic form. If, however, the evaporation has not been carried very far, the alum (which is the least soluble of the two salts in cold water) will crystallise alone. This method, of 1 The effect may be quickly shown by putting one or two of the crystals of each substance into a small wide-mouthed gas bottle, together with a small lump of quicklime loosely wrapped in paper, which will by its affinity for water maintain the dryness of the air. 58 PRELIMINARY EXERCISES. partial crystallisation, is continually employed for the purpose* of, separating a crystallisable salt from impurities which are more soluble than itself. EXERCISE 6. Solution of Calcium Hydrate (Lime water). Apparatus required Retort-stand ; sand-bath and sand ; argand, or spirit lamp ; Bunsen's burner ; scales and weights ; porcelain dish, 8 cm.' in diameter; stoppered bottle, holding about 200 c.c. (a small wide- mouthed gas bottle will do) ; glass rod ; two watch-glasses ; test-tube, about 1.5 cm. in diameter; litmus and turmeric paper; writing-paper; cloth ; washing bottle, filled with distilled water ; lumps of quicklime. The salts which you have selected for the last experiment are not only very soluble in water, but also more soluble in hot than in cold water \ You may take calcium hydrate as an example of a substance which dissolves only in small proportion in cold water, and is still less soluble in boiling water. Place about 5 grms. of good quicklime, in lumps, in a porcelain dish, and pour over it 4 or 5 drops of distilled water from the washing bottle. The lime, if it is freshly burnt, will become very hot and fall to pieces 2 , forming a white impalpable powder. The water disappears entirely, its elements having united with the elements of the quicklime to form a single substance, calcium hydrate 3 . at o, at 33, at 100,- 1 100 c.c. of water dissolve 5.22 ; 22 ; 421 grms. of alum. 12.0; 322; 244 of sodium sulphate. Hence we see that, while sodium sulphate is more soluble in hot than in cold water, its solubility does not increase regularly with the temperature, reaching a maximum at 33, and then slightly decreasing. 2 If it does not become hot in the course of a minute, the reason is that it has absorbed moisture and carbon dioxide by exposure to the air. A lump Or two may be put into the hottest part of a common fire, until it has become thoroughly redhot, then taken out, covered with dry sand and allowed to cool. It must be kept in a well-stoppered bottle. 3 The evolution of heat is due to two causes : (i) The chemical com- bination which is taking place. It is a good example of the universal law that heat is evolved during chemical combination. (2) The fact that a liquid (water) is entering into combination, while a solid (calcium hydrate) is the sole product. For in all cases in which a liquid becomes a solid, heat is evolved. SOLUTION OF CALCIUM HYDRATE. 59 Add more water in successive small portions, until all the lumps of lime have been broken up, and the mass is thoroughly moist : then transfer it with the help of a glass rod or spatula to a stoppered bottle holding about 200 c.c. The last portions may be rinsed in by the aid of a stream of water from the jet of the washing bottle. Fill the bottle nearly to the neck with distilled water, and, after inserting the stopper, shake the liquid for a minute or two, then leave it undisturbed for a quarter of an hour. You will notice that the salt does not dissolve, like the alum, to a clear fluid (although you have added about forty times its weight of water), but that the greater part of it subsides to the bottom of the bottle. Leave the bottle until the next day, occasionally shaking it thoroughly. You will find that even then there is a large quantity of calcium hydrate remaining undissolved .; indeed, you will require some positive proof that any of it has been dissolved. Take out the stopper, wipe the inside of the neck of the bottle with a clean cloth, and pour some of the liquid into a test-tube, inclining the bottle very gently so as to avoid disturbing the sediment. Hold the test-tube up to the light, in order to see if there are any solid particles floating in the liquid. If such is the case, the liquid may be filtered into another test-tube. The following experiments should be tried with the clear solution : 1. Dip a clean glass rod into the liquid, and taste what adheres to the rod. You will find that it is not tasteless, like pure water, but has acquired a sharp caustic taste. 2. Try its action on test-paper. Lay strips of blue litmus, reddened litmus amd turmeric paper on a white plate, and place on each, with a glass rod, a drop of the solution. It will not alter the blue litmus, but will turn the reddened litmus blue and the turmeric a brownish red. A substance which does this is said to have an ' alkaline re- action.' 3. Pour a few drops into a watch-glass ; place the latter upon the sand-bath, supported as before on a ring of the retort- stand, and evaporate the liquid to dryness. For. the sake of 60 PRELIMINARY EXERCISES. comparison you may evaporate in another watch-glass (placed on the same sand-bath) a little of the distilled water which you have been using. When all the water has been driven off, you will find that in the former case a solid white residue is left on the watch-glass, in the latter case there is no residue whatever, or at all events a mere trace. The occurrence of such a residue is a conclusive proof that something has been dissolved by the water. 4. While the evaporation is proceeding, you may heat over a Bunsen's burner the test-tube containing the remainder of the solution of calcium hydrate. [The operation of heating a test-tube in the naked flame requires some care, otherwise the tube may crack, or its contents may be thrown out, owing to the sudden formation of large bubbles of vapour at the bottom of the tube. Hold the tube in a slanting position, turning it round between the fingers and moving it to and fro in the flame 1 , so as to distribute the heat over as large a surface as possible. Remember, moreover, that the test-tube should not, as a rule, be more than one-third full, and that no heat must be applied to the part of the tube above the level of the liquid ; otherwise, if the colder liquid should reach this part, the tube will be almost certain to crack. When the liquid has nearly reached the boiling-point, remove the tube from the direct flame and hold it at the side or above the flame, occasionally shaking it to promote the formation of bubbles of vapour.] Observe that the liquid, as the temperature rises, becomes milky, a solid substance being formed in it. This is owing to the fact that calcium hydrate is much less soluble in hot than in cold water 2 . A solution, therefore, of calcium hydrate, which is saturated at the ordinary temperature, will deposit a portion of the substance when it is heated. Cork the tube 1 If the tube becomes too hot to be held between the fingers, a simple and convenient holder is obtained by folding half a sheet of writing-paper into a band about 2 cm. in breadth. This should be passed round the tube near its mouth, and held (close to the tube) between the forefinger and thumb. The jaws of a Bunsen's holder, Fig. 3, taken out of the socket, also form an excellent holder. 2 100 c.c. of water dissolve at 15, 0.173 grms. ; at 100, 0.083 grms. of calcium hydrate. SOLUTION OF CALCIUM HYDRATE. 6 1 and cool it by immersing the lower portion of it in cold water, shaking it occasionally. The greater part of the turbidity will, after some little time, disappear : the calcium hydrate being again dissolved. 5. This solution of calcium hydrate (or ' lime water/ as it is often called) is chiefly used to detect the presence of carbon dioxide (carbonic acid) since when it is brought in contact with this gas, it becomes cloudy, owing to a white insoluble substance, calcium carbonate or chalk, being formed. Hence it is called a * test ' * for carbon dioxide. You may illustrate this use of it, and at the same time prove that carbon dioxide is present in the breath, by putting a little of the solution into a small beaker, and blowing into it for a few seconds through the long branch of an elbow tube, when the clear liquid will gradually become milky. Pour off the rest of the solution of calcium hydrate into a clean bottle, inclining the bottle which contains the solution very gently, in order to avoid disturbing the solid substance at the bottom. This operation is called ' Decantation,' and will be again alluded to in Exercise 9. Be careful to cease pour- ing before any turbid solution finds its way into the second bottle (if any floating particles are noticed, the whole must be filtered) ; close the latter with a good cork or stopper, and, after placing a label on it, put it away for use in future experiments. 1 A test means an experiment, or a material for an experiment by which we examine an unknown substance to find out what it is. 62 PRELIMINARY EXERCISES. EXERCISE 7. Distillation. Apparatus required Stoppered (or plain) retort, about 200 c.c. in capa- city ; retort-stand ; sand-bath with sand ; argand, or spirit lamp ; thistle funnel (Fig. 12, a); small flask; porcelain mortar; Bunsen's holder; funnel, 10 cm. in diameter ; beaker ; test-tube-stand ; test-tubes in basket ; watch-glass ; washing bottle with distilled water ; wooden blocks ; blot- ting paper; lamp- cotton, or tow; cloth; solutions of barium chloride, silver nitrate, ammonium oxalate, hydrogen nitrate (dilute), ammonium hydrate, calcium hydrate. Distillation is the process of converting a volatile liquid into vapour, condensing the vapour again into a liquid, and collect- ing the product or ' distillate/ It is very frequently used in chemical work for separating a more volatile from a less volatile substance. For example, alcohol may be thus separated from water, and water itself may be, as will be seen in the following exercise, separated from earthy impurities which unfit it for use in the laboratory. An apparatus for distillation consists of three parts ; 1 . A boiler ; for which, in laboratory work, a glass retort is generally used. 2. A condenser; for which the long neck of the retort, kept cool by being wrapped in paper soaked in cold water, will serve sufficiently well 1 . 3. A receiver ; such as a glass flask. The arrangement of the apparatus is shown in Fig. 37. Select a stoppered retort with a long neck ; place it upon the sand-bath (containing a little sand), supported upon the largest ring of the retort stand at such a height as to allow the lamp to be placed under it. Put over the tubulure the smallest retort-ring, to hold the retort steady in its place. This will be most conveniently done if the rod of the retort-stand is placed behind the retort, as shown in the figure. Pass the 1 A 'preferable form of condenser, known as 'Liebig's condenser,' is de- scribed in Appendix A. DISTILLATION. 63 r beak of the retort into a clean flask, placed in a slanting posi- tion in the porcelain mortar, and support the latter on wooden blocks at such a height that there may be a gradual fall from the point at which the neck joins the body of the retort to its outer extremity. Now fill the retort about half full (not more) of common Fig- 37- water, using a funnel passed through the tubulure and taking care that no water passes down the neck of the retort. [If you have to use a plain retort, the water must be put in before it is arranged in its place. For this purpose, lay a folded cloth upon the table and place the retort upon it, supporting its neck in a vertical position by a Bunsen's holder; then pass a thistle funnel down the neck and pour through this the proper quantity of water.] Now light the lamp and put it under the sand-bath. While the water is being gradually heated, the arrangement for con- densing the steam should be set up in the following way. 6 4 PRELIMINARY EXERCISES. Take a piece of blotting-paper about 14 or 15 cm. broad and about three-fourths as long as the neck of the retort ; fold two of its adjacent corners inwards so as to give the paper the fol- lowing outline ; wet it thoroughly, and place it over the neck of the retort with the folded cor- ners underneath, so that while the narrower part of the paper lies upon the broader part of the neck, the narrower part of the neck may be completely enveloped by the paper, the two unfolded corners (pressed close together) hanging down some way below it. Next, take a strip of blotting-paper about locm. in breadth and somewhat shorter than the first strip, fold it, in the direction of its length, into the shape of the letter A, and place it like a saddle upon the first wrapper. Just beyond the lowest end of the folds of paper, twist round the neck of the retort a few strands of lamp-cotton or of tow, thoroughly wetted, the end of which should hang down 10 or 1 2 cm. The object of this is to prevent the water which trickles down the paper from passing any farther down the neck, of the retort and entering the receiver. Underneath the end of this piece of cotton is to be placed a beaker or basin to catch the waste water. Directly over the upper extremity of the paper-wrapping support in the Bunsen's holder a large funnel, the neck of which has been partially plugged up by a bit of paper or tow, so that water will only issue from it in drops. This should be tried before the funnel is arranged in its place, by holding it over a basin or sink, pouring in some water, and pushing in or pulling out the plug of tow until the drops follow each other not too quickly to be counted. After fixing the funnel in the Bunsen's holder (which should have a weight put on the wooden base behind to prevent any chance of its toppling over) fill it with common water, and see that the drops fall slowly and regularly from its beak upon the upper end of the blotting-paper, and that the water, after saturating the paper, finds its way into the beaker, and not into the receiver. You will now see the use of the upper strip of paper ; it serves as a channel to guide the drops of DISTILLATION. 65 water and to distribute them regularly over the paper-wrapping underneath. The water in the retort will soon begin to boil, and the steam, passing over into the colder parts of the neck, will be reconverted into water which will collect in drops and run down into the receiver. When twenty or thirty drops have thus distilled over, withdraw the receiver (holding the neck of the retort steady with one hand), and pour away the liquid which it contains ; since the first portions which come over are liable to contain impurities derived from the neck of the retort. When the last drop has drained away, replace the receiver in its former position and continue the distillation until about three-fourths of the water in the retort has passed over. Pour, from time to time, some cold water into the large funnel so as to keep it nearly full. Be particularly careful to regulate the heat so that the water may not boil so violently as to splash over into the neck of the retort, and thus be carried down into the receiver. If, in spite of care, it boils unsteadily, with < bumping/ owing to the sudden formation of large bubbles of steam in contact with the more strongly heated portions of the retort, it will be advisable to remove the lamp, to wait until the temperature of the water has sunk a few degrees, and then to introduce into the body of the retort a fragment or two of charcoal, or a bit of crumpled platinum foil. This will, in consequence of its numerous points and edges, ma- terially assist the formation of smaller bubbles of steam, and when the lamp is replaced the boiling will go on more quietly. While the distillation is going on, you may examine the quali- ties of the water which you are using, in the following way : Place four clean test-tubes in the stand, and fill each about one-third full of the same water which you have taken for distillation. [In pouring a solution from a bottle into a test-tube, it should be a rule never to allow drops of the liquid to run down the side of the bottle. Apart from the unsightly appearance of a bottle encrusted with crystallised salts, the labels are likely to be obliterated or washed off, and shelves and tables will be damaged. These incon- veniences may be entirely avoided by the simple method of pouring 66 PRELIMINARY EXERCISES. which is illustrated in Fig. 38. The test-tube, into which the liquid is to be poured, is held near the top between the third finger and little finger of the left hand. The stopper, grasped by the forefinger and thumb of the same hand, is loosened and wetted with the solu- tion by slightly inclining the bottle; it is then taken out, drawn across the neck, so as to leave a wet track, for the liquid to follow, and held against the neck of the bottle, while the test-tube is Fig. 38- brought directly under it. The stopper then (like the glass rod in Fig. 36, p. 56) forms a prolongation or lip down which the liquid runs, not a particle finding its way down the side of the bottle. Besides the greater facility with which drops may be measured out, this method has the further advantage, that the stopper is never out of the hands, and hence there is no danger of the solution being contaminated by impurities taken up by the stopper from a dirty table.] (a) Add to the contents of one test-tube five or six drops of dilute hydrogen nitrate (nitric acid), and then one drop of solution of barium chloride; shake the test-tube, and hold it up to the light. If a white cloudiness or precipitate is pro- duced, it is a proof that the water contains a SULPHATE. () Add to the contents of another test-tube five or six drops of dilute hydrogen nitrate, and then one drop of solution of silver nitrate. If a white cloudiness or precipitate is pro- duced, the water contains a CHLORIDE. (c) Add to the contents of the third test-tube three or four DISTILLATION. 67 drops of solution of ammonium hydrate (ammonia), and then one drop of solution of ammonium oxalate. If a white cloudiness or precipitate is produced, the water contains a CAL- CIUM salt J . (d) Add to the contents of the remaining test-tube about i cc. (a small tea-spoonful) of solution of calcium hydrate (lime-water). If a white cloudiness or precipitate is produced, it is, as you have already seen, p. 61, a proof that the water contains CARBON DIOXIDE. By this time sufficient distilled water will have collected in the receiver to be examined by the same tests, in order to see whether the process of distillation has freed it from im- purities (if any have been found). Place four clean test-tubes in the stand, pour into each some of the distilled water, and repeat (a), (&), (c), (d) experiments. The water should give no cloudiness or precipitate in any of the above experiments, and if a few drops are poured into a clean watch-glass and evaporated to dryness on the sand-bath no solid residue should be left; otherwise it is most likely that the water in the retort has boiled too rapidly, and a portion of it has splashed over, or has been carried over as spray into the receiver. Before the water in the retort has wholly evaporated, you should stop the distillation by removing the lamp, and with- draw the receiver, resting the beak of the retort temporarily upon the edge of the mortar. The retort and the rest of the apparatus should now be cleaned and put away for future use. If there is any deposit in the retort which cannot be removed by water alone, a few drops of dilute hydrogen chloride (hydro- chloric acid) will at once dissolve it 2 . 1 If the water which you have used is fresh spring water, and if, from experiment (c), you have discovered that a calcium salt is present, you will probably find that, as the distillation proceeds, the water in the retort becomes turbid, and a white deposit is formed. The reason of this will be explained in the exercise on Carbon Dioxide. * It will be scarcely worth your while to attempt to distil for yourself all the water you will require. You will in all probability be able to obtain it at the nearest chemist's shop at a cost of 2d. or 3 iodide, ( Iodine, 2*4 parts ) 332 parts. 454 parts. [Set aside the mixture in the mortar for use in the next exercise.] CHEMICAL ACTION. 75 Radicles Simple and Compound. Salts. The above examples have been selected to show the action which occurs between elements whether isolated or in com- bination. But it is very often the case that groups of elements take part in a chemical action and are transferred from one compound to another just as if they were single elements. Such closely associated groups, as well as the elements them- selves, are called ' radicles/ as being the common root (radicula) or basis of a series of compounds. Thus we find that the class of substances called ' nitrates ' all contain nitrogen and oxygen associated in the proportion of 14 parts by weight of nitrogen to 48 parts by weight of oxygen. This group is called the ' nitrate ' radicle. Similarly the substances called 'ammonium salts' all contain nitrogen and hydrogen associated in the proportion of 14 parts of nitrogen to 4 parts of hydrogen. This group of elements is called the 'ammonium* radicle; and the elements thus con- nected may be transferred from one compound to another without apparently losing their hold on one another. The compounds formed by the union of two or more radicles, one being more electropositive than the other (i. e. separated by electricity at the negative pole of a battery), are called ' Salts ' in the most general sense of the term. 2. The following may be taken as an example. Place in a test-tube 10 c.c. of solution of ammonium chloride, and add to it a few drops of solution of silver nitrate. A white substance insoluble in the liquid will appear, and on being shaken up will collect together in flakes and fall to the bottom, forming what is called a l precipitate/ The action which has taken place may be thus represented : Before Decomposition. After Decomposition. Substances taken. Composition. Substances obtained. Silver / /Nitrogen, 14 partsx \ Ammonium nitrate, < \Oxygen, 48 parts/ > nitrate, 1 70 parts. ( Silver, 108 parts \>^^ .^i 80 parts. Ammonium i /Nitrogen, 14 parts x ^^*^^^^ \ Silver chloride, M Hydrogen, 4partsJ^_ > chloride, 53.5 parts. ( Chlorine, 35.5 parts ~~ ) 143.5 parts.. 76 PRELIMINARY EXERCISES. Thus the compound radicles AMMONIUM and NITRATE com- bine, forming a salt (ammonium nitrate) soluble in water which therefore remains in the liquid; while the two simple radicles or elements SILVER and CHLORINE combine, forming an in- soluble salt (silver chloride) which is precipitated as a white powder *. These radicles have, in many cases, not yet been isolated. No one, for example, has ever seen the ammonium radicle or the nitrate radicle. We can transfer them from one compound to another, but we have not been able to arrest them in their passage. They are like groups of figures in a money account, which have a definite value and may be transferred from the debtor to the creditor side without being actually exhibited in cash. The elements or ' simple radicles ' may possibly be themselves compound, but even if their compound nature is discovered they will not cease to be radicles. In fact, if we consider Chemistry as ' the study of the com- position and properties of radicles and of the ways in which they act on each other to produce substances permanently differing from themselves/ we shall have a description of the science which is independent of any possible modification of the atomic theory, and of any discovery of the compound nature of the so-called elements. EXERCISE 9. Filtration and Washing of a precipitate. Apparatus required. Porcelain mortar; washing bottle with distilled water; funnel 8 cm. in diameter; niters 14 cm. in diameter; flask about 250 c.c. capacity ; test-tubes and stand ; glass rod ; evaporating dish ; solution of silver nitrate. You obtained in the last Exercise (p. 74) a mixture of 1 If this is left in the light you will observe that it becomes darker in colour. This is a good example of the action of another force, light, in analysis ; it has separated chlorine from the silver, leaving the latter either as subchloride or as metallic silver, forming a dark powder. The whole art of Photography depends on this or similar chemical actions of light. FILTRATION OF A PRECIPITATE. 77 mercury iodide and potassium chloride. You have next to learn how these may be separated from each other by taking ad- vantage of the fact that one of them (mercury iodide) is insoluble in water, while the other (potassium chloride) is soluble. In consequence of this, when water is added to the mixture the potassium chloride will dissolve, and the solution may be separated from the precipitate of mercury iodide by decantation and subsequent filtration. Add 50 c.c. of distilled water to the mixture in the mortar, and grind the whole together with the pestle : then pour the contents of the mortar into a beaker, rinsing out the last portions with a jet of water from the washing bottle. Leave it undisturbed for a few minutes that the precipitate may subside. Meanwhile, fit a filter about 14 cm. in diameter, folded as already directed (p. 54) into a funnel about 7 or 8 cm. in diameter, taking care that the filter fits the funnel closely and does not project beyond its rim. Wet the filter with distilled water and allow it to drain for a few moments ; then support the funnel in the neck of an empty flask, and pour the liquid from the beaker down the side of the filter, using a glass rod to direct the stream, and taking care not to disturb the precipitate more than you can help. When the greater part of the liquid has been poured off, fill up the beaker again with distilled water, stir up the precipitate with a glass rod 1 , and leave it to subside. When the liquid above the precipitate is tolerably clear, pour it off again into the filter, still retaining the bulk of the precipitate in the beaker. Repeat this operation of filling the beaker with water, allowing the precipitate to subside, arid then pouring off the clear liquid, two or three times. This process is called ' washing by decantation/ and is especially adapted for cases where we have a powdery, quickly-subsiding precipitate. Finally, transfer the whole of the precipitate to the filter, by stirring it up with a little water, pouring it quickly into the 1 It will be found an advantage to fit upon the end of the glass rod a short ferule of india-rubber tubing, to avoid scratching or breaking the beaker while stirring. 78 PRELIMINARY EXERCISES. filter and again rinsing the beaker with more water. What has passed through the filter (technically called the ' filtrate ') is, of course, a solution of potassium chloride, and need not be preserved. It may happen that the first portions of the liquid which mn through the filter are turbid. If this is the case, they should be poured back into the filter, another flask or beaker being placed to catch the fluid. If however the filtrate is still turbid, there is reason to suspect that there is a hole in the filter itself. In such a case it will be best to return the precipitate to the flask by making a large hole through the apex of the filter, by means of a glass rod pressed vertically downwards, and washing down the precipitate by a strong stream of water from the washing bottle. Another filter should then be fitted to the funnel and the precipitate transferred to it as before. The washing of the precipitate must now be completed on the filter, in order to free it from all traces of the solutions from which it was formed. This is done by pouring over it a gentle stream of water from the jet of the washing bottle, until the funnel is nearly, but not quite, full ; the level of the water being on no account allowed to rise above the edge of the filter. When the washing water has entirely run through the filter, you may pour on a fresh supply, taking care to direct the stream on the sides of the filter, so as to wash the precipitate down towards the lowest point. The washing of the precipitate can only be considered complete when no potassium chloride can be detected in the filtrate. The presence of a chloride in a solution may be detected, as we have already seen (p. 66) by adding solution of silver nitrate, which gives a white precipitate. The filtrate should therefore be tested from time to time by allowing a little of it to run into a test-tube and adding a drop of solution of silver nitrate. The cloudiness produced will get less and less on successive trials, and finally the filtrate will remain quite clear on addition of the test. When this is the case the mercury iodide may be considered sufficiently washed, and the funnel may be covered with a piece of paper turned down at the sides USE OF THE PNEUMATIC TROUGH. 79 so as to form a cap, and put to dry (resting on its side in an evaporating dish) in a warm place. When dry, the mercury iodide may be detached from the filter, shaken into a short test-tube or small bottle, and kept (duly labelled) for use in a future exercise (see under MERCURY). [Meanwhile it may be noticed that this substance when mixed with gum forms a splendid scarlet paint, the only drawback of which is its want of permanency. In illustration of this, the filter with the remains of the precipitate adhering to it, may be spread out flat on a piece of wire gauze and be heated gently over a lamp. It will be found to turn yellow, and at a slightly higher temperature, to volatilise. If the yellow substance is rubbed with a glass rod it will turn scarlet again.] EXERCISE 10. Use of the Pneumatic Trough. Apparatus required. Pneumatic trough; two cylindrical gas jars, 5 x 20 cm. ; one ditto, 3 x 10 cm. ; test-tubes ; india rubber rings ; corks ; cork borers ; pipette ; jug of water ; cloth. Fill the trough with clean water up to the level of the over- flow-pipe, or about 2 cm. above the shelf, and place it before you on the table, the broad fixed ledge being farthest from you, and the movable shelf being placed near the left-hand end of the trough. Take one of the large cylindrical jars, and, holding it nearly horizontally in the right hand, plunge it into the water, the mouth of the jar being held a little higher than the closed end, in order that the air may more readily escape. When the jar is filled with water and wholly immersed in the trough, bring the closed end uppermost and raise the jar vertically until its mouth is on a level with the shelf, and then move it laterally until it rests over the hole in the shelf : taking care to keep the mouth always below the surface of the water. So long as this condition is fulfilled, you will find that the jar remains full of water, the column of water being retained in it by the pressure of the air on the surrounding water. Next, 8o PRELIMINARY EXERCISES. take a similar jar, holding it vertically, mouth downwards, the closed end being grasped by the right hand, and bring its mouth about 3 or 4 cm. below the water-level in the trough. It will now represent a jar full of gas, which is to be transferred or decanted into the other jar. This is effected by a manipula- tion quite analogous to that by which we pour water from one vessel to another, the only difference being due to the fact that instead of pouring water downwards through air, we have to pour air upwards through water. Hold the jar containing water steady with the left hand, bring the mouth of the other jar under the hole in the shelf, and gradually depress its closed end so that the air contained in it may ascend bubble by bubble through the hole into the jar placed over it. The level of the water in the latter will fall until the jar is completely filled with air. The reason for steadying it with the left hand will now be evident, since it will show a tendency to topple over owing to the upward pressure of the water; and it is best never to fill a jar completely with gas, but only so far that the level of the water inside and outside the jar may be the same. It can easily be filled completely, when required, from another jar. Repeat the experiment, decanting air from the one jar into the other until you can do so without allowing a single bubble to escape. It is not necessary that the jar should rest on the shelf, but it may be held in the left hand, as in Fig. 49, p. 109, its mouth being retained about 2 cm. below the water-level, and the mouth of the jar of air brought close to its edge, and a very little to the right of it, since the bubbles of gas have a forward as well as an upward direction. You may, in the next place, fill the small jar with air and decant its contents into the larger one. Then try to decant the air back from the large jar into the small one. This will not be found so easy, since the bubbles of air from the mouth of the jar are so large that unless the jars are held steady and the decantation is very gradual a waste of gas is likely to occur, and must occur if the disproportion between the mouths of the jars is very great. You will know that none has been lost if the small jar is just filled with the air decanted from the larger one. USE OF THE PNEUMATIC TROUGH. 8 1 [When gas is to be transferred to a test-tube, it is better to decant it first into a jar of intermediate size, and then into the tube ; or, the object may be effected in the following way. Fill the tube in the usual way with water, and insert into its mouth, still held downwards below the water-level, the up-turned beak of an inverted funnel about 7 cm. in diameter. Retain the funnel in its position by placing the little finger under the rim, the tube being held upright between the thumb and the other fingers. If, now, air be decanted from a larger jar, bubble by bubble, into the funnel, the bubbles will rise into the tube without any loss, the displaced water making its escape between the mouth of the tube and the funnel, which latter should not be held too closely in contact with the former.] Additional Experiments. A. Effect of change of temperature on the volume of a gas. Take a test-tube about 2.5 cm. in diameter and 15 or 20 cm. in length ; place round it, about the middle, a small india-rubber band ; fill it with water, and place it inverted upon the shelf of the trough. Decant air into it from a small test-tube until, when your eye is brought on a level with the india-rubber ring, the lowest part of the curve which is formed by the surface of the liquid appears just to touch the upper edge of the ring l . Heat a little water in a test- tube nearly to boiling, and pour it over the tube containing the measured volume of air. The surface of the water in the tube will rapidly sink below the ring, showing that the air has expanded with the heat ; but when a little water at the ordinary temperature is poured over the tube, the air will contract to its original volume. If you can obtain any ice or snow, you may place some in a flask and add some water ; when the latter has been cooled down nearly to the freezing-point it should be poured over the tube containing the air. The surface of the liquid will now rise above the ring, the air contracting in volume as the temperature is lowered. Try a similar experiment with coal gas, decanting the requisite quantity into the tube from an india-rubber tube connected with the gas supply. The same experiment might be tried with any other gas, and you would find it to be a universal law that the volume of a gas Increases as its temperature is raised, and decreases as the temperature is lowered. Exact determinations of the amount of this variation in volume 1 See p. 47, note. G 82 PRELIMINARY EXERCISES. were first made by Gay Lussac, who established the following law, applicable to all true gases, whatever their nature, FOR EVERY INCREASE IN TEMPERATURE OF IG A GAS EXPANDS f fa ( =0.00366) OF THE VOLUME IT OCCUPIES AT OC. B. Effect of change of pressure on the volume of a gas. This is not quite so simply demonstrated at the pneumatic trough, since it is impossible to effect much variation in the length of the column of water which gives the pressure ; and hence only a small, but still perceptible, difference in volume is obtained. The experi- ment may, however, be made in the following way. Fit a good cork to a test-tube about 1.5 cm. diameter: bore a hole in it (? 37)> an d fit into the hole a straight piece of glass tubing about 20 cm. in length, and 6 or 7 mm. in diameter (the pipette you have made (p. 33) will do very well). Take out this tube, when fitted, and insert the cork tightly into the test-tube. Slip over the small tube a narrow india-rubber ring (cut from a piece of tubing), and sink it vertically in the trough almost to the bottom ; then, holding the test-tube by the rim (lest the warmth of the hand should alter the volume of the enclosed air), fit the small tube into the cork, raise or lower the apparatus until the level of the water in the tube and in the trough is the same, and adjust the ring to this level. The air enclosed in the tube is now at the same pressure as the external air ; both pressing on the surface of the water with the same force. Owing to the difference in diameter between the large and the small tube, a slight alteration in the volume of the air in the former will cause a considerable difference in the level of the water in the latter. Now slip under the extremity of the tube a gas jar, wholly immersed in the trough, and raise the whole out of the trough, the gas jar serving as a deep pneumatic trough. Set the jar on the table, and raise the tube until its extremity is only just below the water-level : you will observe that the water in the tube falls below its former level, showing that the volume of the air in the apparatus has increased. This enclosed air is obviously under less than the whole pressure of the external air, since the pressure of the latter is partly balanced by the column of water in the tube. Next, sink the tube in the jar until it touches the bottom : the water will rise above its original level in the tube, showing that the enclosed air has contracted in volume. This air is now exposed to more than the pressure of the external air, the latter being aided by the column of water in the jar which is above the level of the water THE USE OF THE MOUTH BLOWPIPE. 83 in the tube *. We have thus an evidence that the volume of a gas increases as the pressure to which it is exposed is lessened, and decreases as the pressure is augmented. By measuring the pressures to which gases may be subjected, and the corresponding volumes, the follow- ing law, applicable to all gases, was established by Marriotte, THE VOLUME OF A GAS VARIES INVERSELY WITH THE PRESSURE UPON IT. The practical lesson to be learnt from these experiments is that in measuring gases over the pneumatic trough especial care must be taken to deal with them under equal conditions of temperature and pressure (or to make allowance for any differ- ence) : otherwise the apparent volumes will not represent the real quantities we wish to take. The jars should not be held more than is necessary in the warm hands, and the volumes should be read with the water as nearly as possible at the same level inside and outside the jar. EXERCISE 11. The Use of the Mouth Blowpipe. Apparatus required Blowpipe ; blowpipe lamp ; piece of platinum wire ; piece of platinum foil ; two or three pieces of charcoal ; small glass mortar ; watch-glasses ; crucible tongs ; test-tube ; knife ; sodium diborate ; sodium carbonate ; potassium dichromate ; potassium cyanide ; strontium nitrate ; solution of cobalt nitrate ; manganese dioxide ; tin peroxide ; dilute hydrogen chloride. 1. General principles of its use. The mouth blowpipe consists, in its simplest form, of a tapering tube, usually bent near its smaller end to a right 1 Much greater variations in pressure can be obtained by connecting the end of the tube with a funnel by means of a long india-rubber tube; both this and the funnel being filled with water by immersing them in the trough (care should be taken to get rid of all air bubbles). If the funnel is then raised or lowered, the column of water in the tube is added to or subtracted from the pressure of the air, as above explained. It may be convenient to note that a column of water i metre in height very nearly = y ff of the average air-pressure. G 2 84 PRELIMINARY EXERCISES. % angle, and terminating in a fine jet. But as the moisture of the breath soon collects in the tube and interrupts the flow of air, a much superior form of blowpipe is that which was introduced by Dr. Black, and which is represented in Fig. 40. Fig. 40. All moisture is condensed in the wider part of the tube, while the movable nozzle can be readily unscrewed and cleaned out, if it should become stopped up by soot or oxide. Before the instrument is used, the nozzle should be carefully examined to see that the aperture is clear, round, and not very large, otherwise the cone of flame will be ragged, irregular, and brush- like. The best fuel to be used with the blowpipe is undoubtedly ordinary coal gas, where it can be obtained. The most efficient form of burner is that represented by Fig. 41. It consists merely of a short piece of brass tube about i cm. in diameter, flattened out at one extremity until Fi g- 4 1 - it s edges form a narrow rectangular aperture about 0.5 mm. broad, inclined at an angle of 70 to the axis of the tube. This tube, which need not be more than 3 cm. long, may be screwed into the same iron foot which serves as the base of the argand burner J . The orifice of the burner should not be more than 10 cm. above the table, in order that the greatest steadiness may be secured by resting the arms on the table, while the right hand holds the blowpipe and the left hand 1 If gas is not available, an oil lamp, a tallow lamp, or a spirit lamp fed with a mixture of ten parts spirit of wine and one part turpentine, may be used ; or finally, but not preferably, a wax candle. The lamp should have a flat wick, which just before use must be carefully trimmed smooth and divided along the middle with the trimming scissors, so as to leave a furrow along which, and about 2 mm. above it, the blast of air from the blowpipe must be directed. THE USE OF THE MOUTH BLOWPIPE. 85 holds the support containing the substance to be examined. The blast of air should be directed obliquely downwards, parallel, in fact, with the orifice of the burner. The following figure (Fig. 42) will serve to make the position clear. Fig. 42. The first thing to be learnt in the use of the blowpipe is the method of keeping up a regular, continuous blast of air for several minutes without interrupting the ordinary process of respiration. This is by no means difficult. In the ordinary double organ bellows, we can distinguish two essential parts ; (a) the lower compartment or ' feeder/ which by its alternate expansion and contraction supplies air intermittently ; and (t>) the upper compartment or ' reservoir,' which receives and stores up the air thrown in by the feeder, and sends it out in a con- tinuous stream at a uniform pressure to the pipes. When the 86 PRELIMINARY EXERCISES. blowpipe is properly used, the lungs and the mouth are acting respectively as the feeder and the reservoir of the bellows ; the muscles of the cheeks acting as the weights placed on the reservoir to secure a constant pressure on the gas; the tongue, slightly drawn back and applied to the roof of the mouth, representing the valve between the feeder and the reservoir; and the nostrils representing the aperture through which air enters the feeder. These analogies being borne in mind, the following general directions will, it is thought, be sufficient to guide the student in learning the use of the blowpipe ; a few minutes' practice being of more value than a prolonged description. Begin by distending the cheeks with air from the lungs; keep them thus distended while you breathe freely through the nose. In doing this you will have unconsciously placed the tongue in the position it should occupy as a valve between the mouth and the lungs. Now insert the blowpipe between the lips, and expel the air from the mouth through the jet by compressing the muscles of the cheeks. When the stock of air in the mouth is nearly, but not quite, exhausted, introduce a fresh supply of air direct from the lungs, interrupting the ordinary respiration for a moment only, and slightly relaxing the muscles of the cheeks, so that they again become distended with air. A difficulty will probably be found at first in keeping the pressure constant just at the moment at which air is thus thrown into the mouth from the lungs. A very little practice, however, will enable you almost unconsciously so to balance the action of the muscles of the chest and cheeks, that the latter yield exactly in proportion as the former impel air into the mouth, and thus no variation is perceptible in the blast of air from the jet. When, after one or two trials, you find that you can produce a fairly uniform stream of air for a minute or so, you may bring the jet into the lamp-flame (which should be about as large as the flame of an ordinary candle) in the position above described, and use the blast of air to deflect the flame. The appearance of the latter (see Fig. 43, p. 88) will THE USE OF THE MOUTH BLOWPIPE. 87 sufficiently indicate the regularity and pressure of the stream of air. It should appear as a well-defined cone of blue light, burning noiselessly, surrounded by a faint nebulous yellowish envelope, which reaches for some distance beyond the apex of the cone. If it flickers, and burns with a roaring noise, either the jet is not introduced sufficiently far into the flame, or the aperture is too large, or the pressure of air too great. If it is irregular in outline, the aperture of the jet is not round, and must be cleaned out and rounded by introducing a large needle ; or, if you are using a lamp with a wick, the latter may not be evenly trimmed, the projecting filament breaking the current of air. If the flame appears as a luminous tongue, either the aperture of the jet is too small, or the stream of air is not propelled with sufficient force ; or, finally, the flame itself is too large. The blowpipe-flame is used for three distinct objects. ist, and always, to subject substances to a higher temperature than the lamp alone would give. 2nd. To promote the union of oxygen with substances capable of combining with it ; in other words, to ' oxidise ' them. 3rd. To abstract oxygen from substances which readily part with it ; in other words, to ' reduce ' them. The possibility of employing the blowpipe for the last two purposes will be evident if we examine the structure of the lamp-flame before it is deflected by the blast of air. It will be readily seen to consist of three distinct parts, as shown in Fig. 43- 1. A dark central portion, #, composed, of gaseous com- pounds of hydrogen and carbon, unburnt as yet, since no oxygen can reach them, but raised to a high temperature by the surrounding portions of the flame. 2. A luminous zone, b, depositing soot on cold bodies placed in it, consisting of the gaseous hydrocarbons in the act of com- bining with the oxygen of the air ; their hydrogen being wholly burnt to water, their carbon only partially burnt to carbon dioxide ; the remainder of the carbon being set free and raised 88 PRELIMINARY EXERCISES. to a white heat by the temperature of combustion, thus impart- ing to the flame all its luminosity. This carbon is itself con- sumed as it reaches the exterior of the zone. 3. A scarcely visible, ill-defined external envelope, c, con- sisting of the gaseous or vaporised products of combustion, viz. carbon dioxide and water, mixed with a great excess of air strongly heated owing to its proximity to the zone of com- bustion. Fig. 43- It is obvious that a substance placed in the centre of the flame and gradually brought to the exterior will be successively subjected to reduction, simple ignition, and oxidation. 1. The heated hydrocarbons which compose the central portion will, if the substance contain oxygen loosely combined, abstract that oxygen and be converted into carbon dioxide and water. 2. As the substance approaches the exterior of the flame it will arrive at an area of perfect combustion, where the hydro- carbons meet with just enough oxygen to burn them completely, and where, consequently, the temperature is highest. 3. Finally, when it arrives at the extreme border of the flame, it is in contact with excess of highly heated air, or diluted oxygen, which will combine with it if combination is possible under such conditions. The cone of flame produced by driving a blast of air from the blowpipe through the lamp-flame (see Fig. 43) is precisely similar in its constitution ; its powers being intensified, not THE USE OF THE MOUTH BLOWPIPE. 89 changed in kind, by a judicious adjustment of the relative proportions of gas and air. We have, then, the following general rules for the use of the blowpipe, * 1. To effect reduction ; more gas and less air will be needed, the object being to burn the gas only partially, and thus to compel it to obtain the oxygen necessary for com- bustion from the substance submitted to its action. Admit more gas, therefore, until the flame is about 7 cm. high, and, holding the blowpipe-jet at the border of the visible flame, blow a gentle stream of air through it, so as to deflect the flame in the form of a long luminous tongue, within the tip of which (between a and b in the figure) the substance to be reduced must be held, wholly immersed in the flame, and thus exposed to the same conditions as the ore in the body of a smelting furnace, surrounded by ignited fuel and combustible gases. 2. To effect oxidation ; more air and less gas is neecled, the object being not only to burn the latter completely, but -also to provide, over and above, a supply of highly heated oxygen, and thus to expose the substance to conditions similar to those which exist on the hearth of a cupelling furnace. Diminish the supply of gas until the flame is only 5 or 6 cm. in height ; introduce the blowpipe-jet about i mm. within the border of the flame, and blow more strongly so as to produce a well- defined blue cone, surrounded by a faintly luminous envelope, and hold the substance to be oxidised near the point marked c in the figure, about i cm. in front of the tip of the blue cone. 3. To expose a substance to the highest attainable temperature, it must be held at the point b in the figure, i. e. just at the tip of the blue cone mentioned above. Here the combustion is complete, and hence we have the maximum temperature which can be produced by the union of the gases 1 . 1 It must be understood that, where an oil or spirit lamp is used, the raising and lowering the wick will have the same effect as increasing or diminishing the supply of gas to the burner. 90 PRELIMINARY EXERCISES. [The supports for substances to be exposed to the blowpipe- flame are principally of the following kinds. 1. Platinum foil or wire: the former in strips about 2 cm. broad and 5 cm. long, held in a pair of crucible tongs or forceps; the latter, No. 26 brass wire-gauge, in pieces about 6 or 8 cm. long, terminating in a small ring about 2 mm. in diameter, formed by bending the end of the wire round any small cylindrical body ; the tip of the blowpipe-jet answers very well. Platinum foil is used as a support when substances are to be heated per se, to test their fusibility or volatility 1 . The loop of platinum wire serves to hold a bead of melted borax when we wish to examine the colour imparted to it by certain metals. 2. Charcoal, in the form of flat pieces of beech or elm charcoal, which should be carefully selected free from cracks and of close even texture. Good pieces may always be found among ordinary charcoal, sold for burning, and should be cut across the grain with a fine saw into pieces about 1.5 cm. thick. A cross section is always to be preferred to a longitudinal one, since the former absorbs the flux more readily, and does not split when heated. With the point of a knife, or a spatula, cut a small conical hole in the charcoal, as shown in section in Fig. 44, so as to form a small Fig. 44. crucible for containing the substance ; taking care that the surface of the charcoal extends some little way beyond the hole, so that any incrustation may be retained for examination. The charcoal may be conveniently held in a pair of crucible tongs, their bent points being turned upwards, as in Fig. 42. 3. Pieces of hard, difficultly fusible glass tubing, about 6 cm. in length and 3 mm. in diameter internally, sealed at one end and expanded into a small bulb. The shape and method of making these tubes is given at p. 42. 4. Pieces of similar tubing about 8 or 9 cm. in length, open at both ends. Such supports are extremely useful, when the effect of simply 1 Pieces of broken porcelain, such as the fragments of an evaporating dish, will almost always serve in place of the platinum foil, when it is not essential that silica or alumina should be excluded. Platinum foil should be used only when nothing else will serve the purpose, since it is not easy to keep it clean, and it is soon acted on and pierced with small holes which render it useless. THE USE OF THE MOUTH BLOWPIPE. 9 1 heating a substance is to be tried, as a preliminary to its actual analysis ; especially where there is reason to expect that any volatile products may be formed, since these will be retained in the cooler part of the tube for future examination. In general, however, the heat of a Bunsen's burner, or even a good spirit lamp, will be sufficient in such cases. Indeed, no glass tube will long withstand the intense heat of the blowpipe -flame without softening and enclosing the substance under examination. The pieces of platinum wire for blowpipe use may be conveniently preserved in the following way : Fit a cork to a wide-mouthed i oz. bottle ; then with a sharp cork -borer cut two or more holes in the cork, about 5 mm. in diameter. Push out of the borer the small cylinders of cork extracted from the holes, and make a pin-hole along the axis of each. Pass one end of the piece of platinum wire through the pin-hole and bend it into a hook on the other side of the cork to secure the wire in its place. Lastly, fill the bottle nearly to the neck with dilute hydrogen chloride; cork it, and fit into each hole a cork cylinder with wire attached, so that the end of the wire may be immersed in the dilute acid. By this means the wires will be kept always clean and ready for use ; while the cork cylinders will serve as convenient handles and prevent the wires from being lost. Fig. 45 represents a bottle thus fitted.] 45- 2. Examples illustrating its use. In the first place, light the lamp and see that it burns with a steady flame, about 6 cm. high, and that the wick, if it is an oil lamp, is properly trimmed and divided down the middle. If the flame wavers, owing to draughts in the room, a screen of some kind must be arranged to protect it. Next examine the blowpipe-jet, and clean it out, if necessary, with a needle, until 92 PRELIMINARY EXERCISES. it deflects the flame into a steady pointed cone. Arrange the lamp at such a height that the hand which holds the substance in the flame may rest steadily on the table, while the other hand holding the blowpipe may also be firmly supported either on some part of the stand of the lamp itself (Fig. 42, p. 85) or on a wooden block placed close to it. A little of each of the substances required should be placed in watch-glasses near at hand. A. Simple ignition. 1. Make a ring, O (actual size), at the end of one of the bits of platinum wire by bending it round the tip of the blowpipe jet, moisten it with a drop of distilled water, dip it into the sodium carbonate, and hold it in the hottest part of the blowpipe-flame : notice the intense yellow colour imparted to the flame by the salt, which is highly characteristic of the metal sodium. [The platinum wire must be rendered perfectly clean between each experiment by washing it with a few drops of dilute hydrogen chloride, and heating it strongly until it does not of itself impart any colour to the flame.] 2. Moisten the wire with strong hydrogen chloride, dip it into the powdered strontium nitrate, and hold it in the flame as before. The strontium present will impart to the flame a characteristic crimson colour. 3. Heat the loop at the end of the platinum wire, and dip it into powdered sodium diborate (borax) placed in a watch- glass. A portion will adhere to the wire, and must be again brought into the blowpipe-flame. It will at first swell up and give off water, but will finally fuse into a colourless transparent bead (of sodium metaborate), which undergoes no change on being further heated. When the bead is cold, moisten it slightly with solution of cobalt nitrate, and again heat it slowly before the blowpipe, holding it in the hottest part of the flame, i. e. at the apex of the blue cone. When all action appears to have ceased and the bead is as clear as at first, withdraw it from the flame and allow it to cool. It will now be seen to have acquired a deep blue colour, if the cobalt salt has been taken in the right THE USE OF THE MOUTH BLOWPIPE. 93 proportion. If the bead appears nearly black, too much of the cobalt nitrate has been added, and the wire after being again heated must be tapped on the edge of the table, so as to shake off the greater part of the still fluid bead, then dipped into the borax and again fused before the blowpipe. If the blue colour is very faint, a little more of the cobalt nitrate must be taken ; but the delicacy of the reaction is so great that it is hardly possible to take too little of the substance. [To clean the wire, heat the bead strongly till it melts, and immediately shake it sharply off into the sink or upon a plate : melt some more borax upon the wire, and shake the bead off in the same way. On again making a bead, it will be usually found sufficiently colourless for other experiments.] [Other examples of the use of the blowpipe in ignitions will be found under the heads of SILICATES, CHROMIUM, and ALUMINIUM.] B. Oxidation and Reduction. [In the preceding experiment it is immaterial into what part of the flame the substance is introduced, since the colour imparted to borax glass by cobalt is the same whether the oxidising or reducing flame be employed to melt the bead. In the following experiments, however, the distinction between the two flames must be carefully observed, and the bead should be kept steadily for at least half a minute in the one or the other flame, as directed.] i. Form a borax bead as above, and, having added to it a trace of manganese dioxide, heat it in the oxidising flame, holding it i cm. at least in front of the visible flame. The bead will acquire an amethyst colour. Now heat it again, but this time in the reducing flame, holding it so that the luminous portion shall completely envelope it, and taking care that it does not, even for a moment, remain in the outer border of the flame. It will now be found that the amethyst colour has nearly or completely disappeared, and the bead is as colourless as at first. But if it be again held in the oxidising flame, the colour will return. The reason is this, Manganese unites with sodium borate to form two distinct compounds, one containing more oxygen 94 PRELIMINARY EXERCISES. than the other. That which contains most oxygen is deeply coloured : the other is colourless. By heating the substance in the oxidising flame, we determine the formation of the first, or highly oxidised salt ; but when this is transferred to the reducing flame, oxygen is taken away from it and the colour- less salt is formed. 2. Prepare a charcoal support, as described p. 90. Mix together in a mortar equal parts of tin dioxide and potassium cyanide, and transfer a small quantity of the mixture to the hole in the charcoal, taking care that none is spilled over the surface of the support. Bring the mixture into the reducing flame of the blowpipe, holding the charcoal slightly inclined towards the jet, so that the flame may play directly into the hole. The mass will readily melt, and bright globules of metallic tin will make their appearance, while the flux will be gradually absorbed by the charcoal. Maintain the heat steadily until the scattered particles of metal have run together into one globule, and the flux has disappeared ; then withdraw it quickly from the flame and let it cool. Try the malleability of the metal by detaching it with a knife from the charcoal, placing it in the mortar and pressing the pestle strongly down upon it. It will be found to spread out under the pestle into a flat plate, not crumbling to powder or even tearing at the edges. 3. Make a hole in another part of the charcoal support, and place in it the piece of tin which you have just obtained. Fuse it in the reducing flame, and notice that its surface can be kept quite bright so long as it is held in that flame. Remove it into the oxidising flame, lowering the gas flame and slightly increasing the blast of air. It will now become tarnished, a crust of white oxide being formed, which appears to grow out of the metal. Bring it again into the reducing flame, and a bright globule of metal will be again formed. The reduction should be assisted by the addition of a minute quantity of potassium cyanide. [Other examples of oxidation and reduction will be found under the heads of COPPER, IRON (borax-beads), BISMUTH and CADMIUM (reductions on charcoal)]. OF SECTION II. PREPARATION AND EXAMINATION OF THE PROPERTIES OF THE PRINCIPAL NON-METALLIC RADICLES AND THEIR COMPOUNDS. [An asterisk is prefixed to those experiments which illustrate properties of the substance which are considered especially applic- able for its detection in the course of qualitative analysis.] 1. OXYGKEN and OXIDES. Apparatus required Pneumatic trough ; argand burner ; fish-tail burner, or spirit lamp ; Bunsen's burner ; retort stand ; sand-bath ; piece of wire gauze ; corks ; cork-borers ; rat-tail file ; three-square file ; Florence flask ; glass tubing, about 5 mm. in external diameter ; porcelain mortar ; two small porcelain dishes ; scales and weights ; sheets of writing-paper ; deflagrating jar; deflagrating cup; one wide-mouthed stoppered bottle, holding about 700 c.c. ; two ditto, holding about 200 c.c. ; two cylindri- cal gas jars, 20 x 5 cm. ; ground-glass disc, 8 cm. in diameter ; taper on wire (Fig 9) ; cedar matches ; piece of watch-spring ; German tinder, or fusee ; crucible tongs ; jug of water ; blotting-paper ; potassium chlorate ; manganese dioxide ; clean sand ; sulphur ; box of test-papers. Oxygen is generally obtained by the action of heat on some compound containing it. Thus when mercury oxide was heated (p. 69) it was found to give off oxygen; and this method is of interest as being the one used by Priestley in his discovery of oxygen. But practically another substance, po- tassium chlorate, is nearly always used in the preparation of the gas. This salt contains potassium chlorine and oxygen, and when it is heated the whole of the oxygen in it (about one-third of its weight) is evolved, and a compound of potassium and chlorine l (potassium chloride) remains. This may be tried on a small scale as follows. 1 2 KC10 3 = 96 PREPARATION AND EXAMINATION OF Place a few crystals of potassium chlorate in a dry test- tube, supported in a slanting position in a Bunsen's holder (as in Fig. 39), and apply heat. The salt will fuse into a liquid, and at a temperature just above its melting-point, will give off a gas, with effervescence, which may be shown to be oxygen by its power of re-kindling a glowing match introduced into the tube. Continue heating the salt for half a minute, then remove the lamp, and when the fused mass in the tube is cool, warm it with a little water, and test the solution with a drop of silver nitrate. A white precipitate will be produced, which we have seen already (pp. 66, 75) to indicate the presence of a chloride. [The reaction may be expressed as follows J : Substance taken. Composition. Substances obtained. / Potassium, 39 parts \ Potassium Potassium \ ( chloride, chlorate, < Chlorine, 35.5 parts ( 74.5 parts. 122.5 parts. / \Oxygen, 48 parts Oxygen, 48 parts.] A very pure gas may be obtained by this method, but the temperature at which the decomposition takes place is so high that ordinary glass flasks cannot support it without softening. It is found, however, that if the salt be mixed with manganese dioxide, the decomposition takes place at a much lower tem- perature, and with greater rapidity. The manganese dioxide does not, apparently, give up any of the oxygen which it con- tains : at any rate, it is found at the close of the action to be unaltered in composition, and may be employed repeatedly with fresh portions of potassium chlorate. In the first place the materials for the preparation of the gas should be got ready, as it is important that they should have time to dry thoroughly. If this precaution be neglected 1 The student is advised to write out all the chemical actions which he meets with, in some such form as the above. When he has studied the properties and combinations of two or three of the elements he will be .better able to appreciate the grounds of the atomic theory, and the system of symbols by which all chemical changes may be concisely yet fully expressed in the form of equations. OXYGEN AND OXIDES. 97 the flask in which they are to be heated is not unlikely to crack during the experiment, owing to the moisture condensing in the neck and dropping down upon the hotter portions of the glass. Weigh out on paper (as directed in Exercise 5, p. 53), 25 grms. of crystallised potassium chlorate ; reduce the crystals to powder in a mortar ; then place the salt in a porcelain dish on the sand-bath to dry. Weigh out, similarly, 6 grms. of manganese dioxide, and place it also in a porcelain dish on the sand-bath near the potassium chlorate, stirring them both occasionally with a glass rod. In the next place, you have to prepare an apparatus for generating and collecting the gas. Since heat is required to decompose the potassium chlorate, a flask supported in a re- tort-stand will serve to contain the materials ; and since oxygen gas is scarcely soluble in water, it may be collected over the pneumatic trough filled with water ; a bent glass tube will serve to convey the gas from the flask to the trough. Take a clean Florence oil-flask, selecting one which has a smooth even mouth; roughen the sharp edges of the mouth with a file ; or, if a Herapath's blowpipe is at hand, turn the edges outwards so as to form a spreading lip, as directed, p. 44. Cut off a piece of the glass tubing about 65 cm. in length, and round the edges in the usual way: then (using the fish-tail burner) bend the tube to an acute angle, making the middle of the bend not more than 8 cm. from one extremity; and lastly make a slight bend in the opposite direction as near the other extremity as possible, so as to give the tube the shape shown in Fig. 46. Fig. 46. The object of this second bend is to facilitate the escape of H 98 PREPARATION AND EXAMINATION OF the bubbles of gas by giving them a forward and upward direction. It will be found convenient to use a cork handle (p. 32), in case the end of the tube should become too hot to be held in the ringers. When the glass is quite soft, hold the tube out in front of you, so that the eye may be in the plane of the first bend ; it will then be easy to turn up the end which is nearest to you, so that both the bends may lie in the same plane but in opposite directions. Next, choose a sound cork very slightly larger than the neck of the flask, squeeze it until it becomes soft and elastic, and bore a hole through it for the delivery tube, using a cork-borer which is rather smaller than the glass tubing which you have used. The end a should now be fitted with gentle pressure and twisting motion into the cork, through which it should pass completely and project slightly at the opposite end. Do not attempt to use much force in pushing the tube into the cork, or you may break the tube and be cut with the splinters of glass ; but enlarge the hole with the rat-tail file, until the tube will enter it without much difficulty. The potassium chlorate and manganese dioxide may now be taken from the sand-bath, and set aside to cool for a minute or two, during which time the pneumatic trough may be filled with water up to a level about 2 cm. above the shelf. It is well to have a jug of water at hand, in case more should be wanted. Take the deflagrating jar, slightly grease the stopper and fit it tightly in its place ; then immerse the jar sideways in the water, raising the open end a little, so as to allow all the air to escape. When the last bubble is gone depress the open end, and raise the jar by its neck (taking care to keep the lower end below the water-level), until it can be moved laterally to its place on the shelf. Fill the two cylindrical jars with water and place them inverted on the shelf. The large bottle should be filled with water from a jug, the (greased) stopper inserted and held in its place with one hand, while with the other the bottle is inverted, and its mouth brought below the level of the water in the trough, when the stopper may be withdrawn, and the bottle OXYGEN AND OXIDES. 99 moved to the shelf. It is better not to overcrowd the shelf with bottles and jars, which, when filled with water and inverted, are rather unsteady, and hence the other bottles should, after being filled with water, be placed near the trough, to be brought to the shelf when required. Now mix the potassium chlorate and manganese dioxide in the mortar with a few circular strokes of the pestle, add to the mixture an equal bulk of fine dry sand 1 , and grind the whole until thoroughly mixed; then shake it out on a sheet of paper, and transfer it to the flask. After wiping the neck of the latter, fit the cork with the tent delivery tube into its place with care- ful pressure, and support the flask on a piece of wire-gauze bent into a shallow cup, and resting on the largest ring of the re tort- stand. The smallest ring should be passed over the neck of the flask to secure it in an upright position, and the latter should be fixed at such a height that a lamp may be easily placed beneath it, and that the end of the delivery tube may pass under the shelf of the pneumatic trough, and be about 3 or 4 cm. below the surface of the water. The whale apparatus will then be arranged as in Fig. 47, next page. Before beginning to heat the mixture in the flask, you should ascertain whether there is any leakage owing to the cork being unsound or badly fitted. Place the warm hand on the flask for a few seconds, and observe whether, owing to the expansion of the air in the flask, the level of the water in the delivery tube is depressed below the level of the water in the trough, and finally a bubble or two of air escapes, and also whether on removal of the hand the water only returns by degrees, as the air cools, to its original level in the tube. If no depression of the level takes 1 Unless this addition of sand is made, it often happens, especially if there is rather more than the due proportion of manganese dioxide in the mixture, that there is a sudden rush of gas at the last, a low incandescence spreading through the half-fused mass. It is well to be prepared for this, and to take away the lamp at the moment when you perceive any tendency to a rush of gas. Of course the only possible risk would arise from the delivery tube not being sufficiently large to carry off the rapid current of gas, or becoming obstructed by particles of the mixture mechanically carried over with the gas. When sand is added, however, as above directed, the decomposition proceeds with perfect regularity from beginning to end, and much less attention to the lamp is required. H 2 100 PREPARATION AND PROPERTIES OF place, there is a leak in the cork-joint, which must be stopped before anything further is done. If the fault is not cured by pressing the cork farther into the neck of the flask, it will- generally be best to take a new cork altogether. When you have proved that the apparatus is air-tight, you may proceed to heat the flask by a gas or spirit lamp. The best form of gas lamp for the purpose is an argand, or other form of ring-burner, since it distributes the heat over a larger surface, and can be made to give a very small flame if required. Fig. 47- The first effect of the heat (which should be applied cau- tiously and gradually) will be to expand the air in the flask, which will escape in bubbles through the water in the trough. In a short time the stream of bubbles, which had slackened, will become more rapid, showing that gas is being evolved from the mixture. As soon as this takes place, slide one of OXYGEN AND OXIDES. IOI the cylindrical jars along the shelf until its mouth is over the hole and the bubbles can rise -freely into it. The heat must be carefully regulated, so as to keep up a moderately rapid stream of bubbles. It will be scarcely worth while to test the first jarful of gas, which will certainly be mixed with air. Fill the jar again with water, and place it as before to receive the gas. When it is full, slide it off the shelf with one hand, and with the other bring a ground-glass plate upon its mouth, while under water ; raise the jar out of the water, still keeping the glass plate pressed against its mouth, and place it mouth upwards on the table. Now light a cedar match at the lamp, blow it out, and while its end is still glowing, plunge it into the jar of gas. If it is re-kindled, bursting sharply into flame, the gas is suffi- ciently pure for experiments. If this is not the case, return the jar at once to the trough, fill it again with gas, and test it in the same way. When you have thus ascertained that the gas is pure, you may proceed to fill the jars and bottles with it, bringing each in succession over the hole in the shelf, and when it is full of gas sliding it (without raising its mouth above the level of the water) to one end of the shelf, and bringing another into its place. In order that the pneumatic trough may not be in- conveniently crowded with bottles, you may remove them one at a time, when filled with gas, to the table, after inserting the stopper tightly, under water. When the deflagrating jar has been filled, slip under its mouth a shallow tray (a common plate or saucer will answer the purpose) ; then, keeping the tray horizontal and the mouth of the jar resting in it, raise both out of the water and place them on the table. The water remaining in the plate will thus act as a valve to prevent the gas in the jar from escaping. As soon as the jars and bottles are filled with oxygen, take out the cork from the flask, and raise the delivery tube at once out of the water, withdraw the lamp, and set the flask aside to cool. The porous, half-melted mass which it contains may be readily washed out by a little warm water. It consists of a mixture of potassium chloride, manganese dioxide, and sand, 102 PREPARATION AND PROPERTIES OF and will not be worth preserving. The flask will be found scarcely, if at all, injured, and after being cleaned and dried may be used again for the same purpose. The properties of the gas should next be examined in the following manner. 1. Its action on test-paper. Take strips of blue litmus and reddened litmus paper, and moisten them with distilled water: then introduce them for a moment into the large bottle of oxygen, replacing the stopper as soon as possible, as the bottle of gas is to be used for another experiment. You will observe that the colour of neither test-paper is changed \ Oxygen is therefore a ' neutral ' substance. *2. Its relation to ordinary combustion. Place one of the cylindrical jars, its mouth upwards and closed with a glass plate, on the table before you, near the lighted lamp. Loosen the stopper with the left hand ; take in the right hand the piece of wax taper attached to a bent wire, and light it at the lamp; then withdrawing the stopper intro- duce the taper into the bottle of gas. Notice that it is not extinguished but burns with a whiter, more intense flame. Its action on a glowing match, causing it to burst sharply into brilliant combustion, has been observed already, and need not be tried again. The thick cedar matches are preferable for this test, as they retain a glowing end longest. 3. Its union with non-metallic radicles, such as sulphur. Place the large bottle of gas on the table before you. Take the deflagrating cup and adjust its position by sliding the rod through the flange so that it may, when placed in the bottle, hang in the position shown in Fig. 10, p. 10, about 5 or 6 cm. from the bottom of the bottle 2 . Place in it a piece of sulphur, rather larger than a pea. Loosen the stopper of the bottle of gas with the left hand, hold the deflagrating cup for a few 1 If the evolution of gas has been rapid, chlorine and chlorine oxides may be present in sufficient quantity to be recognised by their odour (pure oxygen being inodorous), and to redden and bleach the litmus-paper in a short time. - It may be adjusted with sufficient accuracy by holding it against the side of the bottle. OXYGEN AND OXIDES. 103 moments in the flame of the lamp, until the sulphur melts and finally catches fire, and then immerse it in the bottle. The sulphur, which was burning in the air with a faint lambent blue flame, will immediately begin to burn much more brilliantly, while white clouds are formed in the bottle. When the com- bustion is over, take out the cup, and observe the pungent suffocating smell of the gaseous combination of sulphur and oxygen (sulphur dioxide) which has been produced. Dip a piece of moistened blue litmus paper into the bottle and observe that it is strongly reddened. The sulphur dioxide has combined with the water to form an ' acid ' substance (hydro- gen sulphite, or ' sulphurous acid '). Thus, though oxygen is neutral itself, it forms compounds which when combined with water have an acid reaction. Acids, however, do not all contain oxygen, as was formerly supposed. They are, in fact, ' hydrogen salts ' ; i. e. salts in which the electro-positive radicle (see p. 75) is hydrogen. 4. Its combination with metals, such as iron. (c) Take a piece of thin watch-spring (readily obtained from any watch-maker) about 20 cm. in length; soften it by hold- ing it in the lamp-flame until it becomes red-hot and loses its elasticity : when it is cool, straighten it and push one end into the flange of the deflagrating cup, securing it, if necessary, by a small wedge, such as the end of a match. Bend up the other end of the spring so as to form a small loop, thus _D, in which place a bit of German tinder or (which will do quite as well) a bit of one of the common cigar-lights made of touch- paper, and sold in strips. Loosen the stopper of the deflagra- ting jar with the left-hand, while with the right hand you take up the flange with watch-spring attached. Light the tinder at the lamp, and immediately take out the stopper, and steadily lower the watch-spring into the gas, until the flange rests on the neck of the jar. The tinder will continue to burn, and the watch-spring, becoming red-hot, will also enter into brilliant combustion, sending out sparks and fusing into globules of iron oxide, which will fall off into the water in the tray. Be careful to take out the watch-spring as soon as the combustion comes 104 PREPARATION AND PROPERTIES OF near the neck of the jar, or the latter may be cracked by the heat. [The beauty of the combustion is almost entirely due, not to the iron, but to the carbon present in the steel watch-spring ; as may be shown by repeating the experiment, substituting for the spring a piece of pure iron wire (' binding wire ') coiled into a spiral by being wound round a test-tube or glass rod about i cm. in diameter. In this case the metal will simply burn with a steady glow, emitting few or no sparks according to the purity of the iron.] Reserve the remaining bottles of oxygen for use in future Exercises, placing a written label on each, to show what it contains. 2. HYDROGEN. Apparatus required Pneumatic trough ; two gas jars, 20x5 cm. ; one ditto, 10 x 3 cm. ; flask, with flat bottom, holding about 250 c.c. ; bent delivery tube, used in the last Exercise ; thistle funnel ; corks ; cork- borers ; rat-tail file ; retort-stand ; piece of wire-gauze ; taper on wire ; glass disc, 8 cm. in diameter ; gas tray, 8 cm. in diameter ; Bunsen's burner; Bunsen's holder; 4 rvm g tube; glass tubing, 6 or 7 mm. in dia- meter; india-rubber tubing, for connectors; glass jet (p. 33); large beaker or funnel ; glass tube about 30 cm. long and 2 cm. in diameter ; jug of water ; cloth ; granulated zinc ; strong (common) hydrogen sul- phate ; distilled water ; plaster of Paris. Hydrogen is usually prepared by the action of the force of chemical affinity upon certain compounds containing it. An experiment has already been made (p. 71) which shows that when zinc is caused to act upon hydrogen chloride, the latter is decomposed, the zinc combines with the chlorine, while hydro- gen gas is liberated. If hydrogen sulphate (common sulphuric acid), diluted with water, is acted on by zinc or iron, a precisely similar change takes place ; and this is the usual process for preparing hydrogen. The apparatus required is shown in Fig. 48. Get ready the pneumatic trough as for the preceding exercise. Instead of bottles it is best to use plain cylindrical jars, ground at the mouth, about 5 cm. in diameter and 20 cm. high. Fill HYDROGEN. 105 two of these with water and arrange them on the shelf of the trough. Now take the bent delivery tube, used in the prepara- tion of oxygen ; select a sound cork which will, after being squeezed, fit the neck of the flask ; bore two holes in it (Fig. 23, p. 38), one large enough to admit the delivery tube, the other adapted to the tube funnel. If none of your cork-borers will Fig. 48. make holes of the precise size required, use the next smaller cork-borer, and enlarge the holes with the rat-tail file. Fit the short branch of the delivery tube into the cork until its end just appears on the opposite side ; then with a screwing motion pass the tube of the funnel through the other hole in the cork until the lower extremity, when the cork is fitted into the neck of the flask, would reach nearly to the bottom. Place in the 106 PREPARATION AND PROPERTIES OF flask 30 gnus, of granulated zinc, sliding the pieces down the neck, held slanting (not dropping them in, lest they should break the flask) ; support the flask in the retort-stand on wire- gauze *, and fit the cork firmly into its place. The flask should be supported at such a height that the end of the delivery tube may be just below the hole in the shelf, and not unnecessarily deep in the water. Pour through the funnel enough distilled water to cover the zinc to the depth of t cm., and try whether the joints are tight by placing the warm hands on the flask for a few seconds. This will expand the air within, which will raise a column of water in the funnel tube, depressing, of course, the water in the delivery tube to an equal extent. If on withdrawing the hands this column remains steady for a moment, and only sinks gradually to its former level, the joints may be considered good. If however the column either does not rise at all, or sinks rapidly when the warmth is withdrawn, there is a leak somewhere in the cork. You may try to remedy this by pressing the cork further into the neck of the bottle 2 : if this does not succeed, drop a little sealing-wax on the top of the cork and spread it evenly with a hot wire. This will almost certainly prove a cure ; but do not proceed with the experiment until the joints will stand the above test. [The action may be expressed as follows 3 : Substances taken. Composition. Substances obtained. Zinc, <^ ^ Hydrogen, 65 parts. ^^^^^ 2 parts. Hydrogen / Hydrogen, 2 parts--" -x Zinc sulphate, \ /Sulphur, 32 parts \ sulphate, 98 parts. '\Oxygen, 64 parts/ 161 parts.] Now pour about 2 c.c. (a tea-spoonful) of strong common 4 1 Although the flask does not, in the present case, require to be heated, yet it is advisable to place under it a piece of wire-gauze which serves as an elastic cushion. 2 A small leak may often be stopped, by simply moistening the cork and tubes with a few drops of water. 3 Or by the following equation : Zn + H 2 SO 4 = H 2 + ZnSO 4 . 4 The pure acid should not be used for this purpose : it should be reserved for analytical experiments. HYDROGEN. 107 hydrogen sulphate down the tube funnel, and shake the flask, so that the acid and water may mix. When this reaches the zinc an effervescence will commence, owing to the liberation of hydrogen. After a moment or two a little more acid may be poured through the funnel, so as to keep up a rapid stream of bubbles from the delivery tube; but especial care should be taken not to add too much at a time, lest the action should become too violent, partly from the undue strength of the acid, partly owing to the heat evolved from the mixture of the acid with the water. If the liquid in the flask should show a tendency to froth over, pour some distilled water down the funnel, to dilute and cool the acid. It is often the case that the action is slow at first, but it is better to give it a little time than to add acid recklessly l . Fill three jars with the mixture of air and hydrogen which first escapes from the flask, and reject their contents before proceeding to collect the gas for your experiments. This precaution is of more importance here than in the case of oxygen, because (as will appear) air forms with hydrogen a mixture which explodes upon contact with a light, and you may have an awkward, if not dangerous, mishap, if you unintentionally experiment with such a mixture instead of pure hydrogen. After sacrificing this quantity, however, you may safely collect some jars of the gas, precisely as directed in Exercise i, sliding the jars over the hole in the shelf, and when each is full removing it to the side shelf of the trough. It is best not to fill the jar completely with gas (as it may topple over), but only so far that the water in the tray and in the jar may stand at the same level. Add from time to time a little more strong hydrogen sulphate, to keep up the stream of gas, but manage so that the action may be subsiding while the last jar is being filled, so as to prevent unnecessary waste of gas. When the jars are full, leave the flask and tube in their 1 Pure zinc and some varieties of granulated zinc do not always act readily on the acid. If, after all, only a slight effervescence occurs, pour into the funnel one or two drops of solution of platinum perchloride and wash it into the flask with a little water. This will, owing to the galvanic action between the reduced platinum and the zinc, greatly increase the evolution of the gas. 1O8 PREPARATION AND PROPERTIES OF position for the present, and examine the following properties of the gas : 1. Its action on test-paper. This may be sufficiently tested by holding strips of blue and red litmus paper over the bubbles as they rise from the delivery tube. The gas will be found to be neutral, like oxygen. *2. Its relation to ordinary combustion. Transfer one of the jars of gas (using a gas tray) from the trough to the table. Take the taper attached to the bent wire (Fig. 8, p. 9) and light it : then with the other hand raise the jar of gas steadily from the water, keeping its mouth still down- wards, and immediately pass the lighted taper up into it. The gas will take fire with a slight noise where it is in contact with the air, and burn with a pale almost invisible flame ; but the taper on being pushed further into the gas will be extinguished. Now withdraw the taper and turn the mouth of the jar upwards ; the flame will pass quickly down the jar, and the gas will be found to have disappeared entirely. The jar may now be refilled with gas, for use in other experiments. 3. Its lightness as compared with common air. Transfer another of the jars of gas from the trough to the table. Take a small gas jar (empty) and hold it inverted in one hand, as shown in Fig. 49. Raise the jar of gas out of its tray with the other hand, bring its mouth close to the edge of the small empty jar, and steadily depress the closed end, as in the figure, proceeding exactly as if you were pouring a liquid upwards from it into the smaller jar. Set down the small jar, which is in your left hand (mouth downwards), in the tray of water ; light the taper affixed to the wire and bring it into the upturned mouth of the other jar. The gas will be found to have escaped entirely, the taper burning as in the outer air. Now raise the mouth of the small jar above the level of the water in the tray, and pass up into it the lighted taper. A slight explosion will take place, as the gas catches fire, thus demonstrating that the hydrogen has really HYDROGEN. 109 ascended and displaced the air in the jar, precisely as it dis- places the water in filling a jar at the pneumatic trough. Fig. 49. 4. Its combination with oxygen, to form water. (a) Fill with water both the jars used in the last experiment, and place them on the shelf of the pneumatic trough. Fill the smaller jar with hydrogen from one of the remaining jars of gas, and decant its contents into the larger jar. Fill it again with gas, and again decant its contents, as before. You have now two measures of hydrogen in the larger jar. Next, take one of the bottles of oxygen which you reserved (p. 104), invert it, and bring its mouth below the water-level in the trough ; take out the stopper, and decant into the small jar sufficient oxygen to fill it. Decant this measure of oxygen into the jar containing the two measures of hydrogen, depress the jar in the trough, and shake it laterally to mix the gases (taking care that no air enters); then fill the small jar with the mixed gases, close its mouth with a glass plate, remove it from the trough and place it on the table, mouth upwards, retaining the glass plate in its position with the left hand. Light a match, with- draw the glass plate and apply the lighted match to the mouth 110 PREPARATION AND PROPERTIES OF of the jar. The explosion which follows, though loud, is quite unattended with danger if a small strong jar is used as above directed. Do not, on any account, apply a light to the mixed gases in the larger and thinner jar, since you may have a serious accident if the jar should break. [You may, if time allows, try two or three similar experiments, varying the proportions of hydrogen and oxygen (taking, for in- stance, two measures of oxygen and one of hydrogen), and you will find that the explosion, which accompanies the chemical com- bination, is loudest when one measure of oxygen is mixed with two measures of hydrogen. This is found to be the exact proportion in which the two gases are combined in water 1 . And if the gases are mixed in any other proportion, the excess of one or the other remains uncombined.. You may, further, try a few similar experiments, using air instead of oxygen. You have noticed, in Experiment 2, that when a lighted taper is passed into a jar of hydrogen the gas takes fire at the mouth of the jar, where it is in contact with the air. This is due to its combination with the oxygen which is one of the constituents of air. Now, you will find that when air and hydrogen are mixed, and a lighted match applied to the mixture (this may be done in the larger jar), an explosion takes place, less violent than in the case of oxygen and hydrogen, but loudest when five measures of air are mixed with two measures of hydrogen 2 . But we have just seen that two measures of hydrogen unite with one measure of oxygen to form water. Hence five measures of air contain one measure of oxygen 3 .] That water is the product of the union of oxygen with hydrogen will be best shown by causing the combination to take place more slowly ; for instance, by allowing a jet of hydrogen to burn in air. (<5) Raise the delivery tube out of the water, and support the end of it upon a wooden block placed on the table (the flask being still retained in the retort-stand). Attach to it one of 2 If you have no jar large enough to contain seven measures of the gases, put an india-rubber ring round the small jar about 2 cm. from its mouth, and reckon the contents of the jar to this level as I measure. 3 The composition of air will be further illustrated in the next Exercise. HYDROGEN. Ill the elbow-tubes which you have already made, stretching over the ends of both a short piece of india-rubber tubing, slightly moistened to make it slip over the glass more easily. To the other branch of the elbow-tube, which should point vertically upwards (Fig. 50), adapt in a similar way the glass jet you have already made (p. 33). Pour a little more acid on the Fig. 50. zinc, if the stream of gas has ceased ; and since air may have entered the flask, it will be advisable to test the purity of the gas before lighting it at the jet, in order to avoid the chance of an explosion. To do this, hold over the jet -a small test-tube, bringing the jet nearly to the closed end of the tube. We have seen that hydrogen can be poured upwards, therefore the tube will soon fill with gas. After about ten seconds raise the tube slowly from the jet, close its mouth immediately with the thumb, remove it to some distance from the jet, and, still holding the mouth downwards, apply a lighted match to it. If the gas burns quickly, with a shrill noise, air is mixed with it ; and it will not be safe to light it at the jet. Other trials should 112 PREPARATION AND PROPERTIES OF be made, and when the gas catches fire with only a slight noise, the flame passing slowly along the tube, it is pure and you may proceed with the experiments. Pour a little more acid on the zinc in the flask, if necessary, and light the hydrogen issuing from the jet. When it burns steadily with a flame about 2 cm. high 1 , hold over it a clean dry beaker or bottle, and notice that a dew is at once deposited on the glass, soon collecting into drops of a colourless liquid, which is pure water. It will be hardly worth your while to collect any quantity of water, but you may at any rate satisfy yourself that the product of the combustion is tasteless, and that when the outside of the glass is gently warmed by moving it to and fro over the lighted jet of gas the deposit volatilises without leaving any residue. (c) When the current of gas has slackened, but is still burning at the jet, another experiment may be tried which shows in an interesting way that the flame, under certain conditions, although apparently steady, is really expanding and contracting ; is, in fact, rather a series of flames quickly suc- ceeding one another, than a continuous flame. Hold a glass tube, about 30 cm. in length and 1.5 or 2 cm. in diameter, over the jet, and depress it gently until the flame is entirely within the tube. At a certain point the flame will become elongated and a musical note will be produced varying in pitch with the length of the tube, and also, for the same tube, with the size of the flame. This sound is due to the fact that the air in the tube is set in vibration by the extremely rapid succession of explosions caused by the combination of the hydrogen as it issues from the jet with the oxygen of the surrounding air 2 . 5. Its diflusibility. Put out the flame, and hold a piece of blotting-paper close 1 The flame will shortly become yellow, owing to a trace of sodium, contained in the glass of the jet, becoming volatilised. 2 Hydrogen and oxygen only combine when mixed in certain proportions. This mixture takes time to form, but when it is formed the combination is sudden. A distinct interval then occurs before the due mixture is again formed ; this is exploded by the heat of the previous combination ; another pause occurs, then another explosion, and so on. HYDROGEN. 113 above the jet from which the gas is still issuing. Bring a lighted match near the upper side of the blotting-paper, just over the jet. The gas will catch fire, showing that it has passed quickly through the pores of the paper, as through a sieve. Additional Experiments. 6. Action of platinum in causing the combination of oxygen and hydrogen. This will be more fully explained hereafter, but it may be tried in a simple way thus, Take a small tuft of asbestos, and coil a platinum wire once or twice round it to serve as a handle: then moisten it with a drop of solution of platinum perchloride and hold it, first above and then in the flame of a Bunsen's burner until the salt is decomposed and a gray deposit of finely divided platinum left on the asbestos. Allow this to cool, and then hold it just above the jet, in the stream of gas. It will become red hot, showing that it is causing the combination of hydrogen with the oxygen of the air, and the gas will shortly catch fire. 7. Proof that water is formed when hydrogen and oxygen combine. It must be observed that we have not yet rigorously proved that water is formed during the burning of hydrogen in air, since no pains has been taken to dry the gas, which of course contains moisture derived from the liquid in the flask. In order that the experiment may be decisive, the hydrogen must be passed over some drying material before it is burnt at the jet. Take off the glass jet and india-rubber connector, and fit the end of the elbow tube into the cork at the end of a drying tube (Fig. 10 c. p. 12) filled with fragments of quicklime or of calcium chloride. Support the drying-tube in a vertical position by the Bunsen's holder, and fit the jet upon its upper end. After testing the purity of the gas, as already directed, you may light it at the jet, and hold a beaker over it, as in experiment 4 b. If moisture is now deposited on the beaker, it must have been i 114 PREPARATION AND PROPERTIES OF formed during the combustion, since the gas has been dried, and the air contains too little moisture to form any deposit on the glass. 8. Lightness of hydrogen. Make a solution of soap by dissolving in a small evaporating dish a bit of common soap as large as a pea in 5 or 6 c.c. of water. Remove the glass jet, and touch the end of the tube with a finger dipped in the soap solution. A bubble will soon be blown, which when it leaves the tube will ascend rapidly. One or two trials with soap solution of various strengths and more or less warm may be required to get a good result \ [If you possess one of the small fish-skin balloons sold by opti- cians, the lightness of hydrogen gas may be further demonstrated in the following way : In the first place ascertain that there are no holes in the balloon by expanding it with air and holding it between your eye and the light, turning it round to examine every part of it 2 . If any holes are visible, they may be mended by touching the margins with weak gum-water and covering them with small patches of gold-beaters' skin. A short piece of quill should be inserted in the neck of the balloon, and secured in its place by folds of thread. Take off the glass jet from the apparatus used in the preceding experiment, and, having carefully squeezed and sucked out as much as possible of the air from the balloon, stretch the india-rubber connector over its neck, and proceed to fill it with gas, pouring a little more acid on the zinc whenever the current of gas becomes slow. When the balloon is full, you may allow it to ascend in the room, after insert- ing a small plug of cork into the neck, and attaching a long piece of thread to the quill, in order to have the movements of the balloon under control.] 9. Diffusion of hydrogen through plaster of Paris. Take a piece of glass tube about 25 cm. long, and i cm. internal diameter (a piece of combustion tube will do) and fit a 1 A solution which keeps well and forms good bubbles may be made as follows. Dissolve 5 grins, of pure sodium oleate (made by gently heating 5 grms. of sodium hydrate' with 25 grms. of oleic acid) in 80 c.c. of distilled water: when cold add 5 c.c. of glycerine and mix thoroughly. The solution should be slightly shaken up before bubbles are blown with it. 2 These balloons are very liable to be attacked by insects. They should be kept in a wide-mouthed bottle with a small bit of camphor. HYDROGEN. 1 15 cork to one end. Pour about 10 c.c. of water into a small porcelain dish, and add enough plaster of Paris to form a thick cream, stirring it thoroughly with a glass rod. Before it sets, plunge into it one end of the glass tube (the cork being with- drawn) until it rests on the bottom of the dish, and support it upright in a Bunsen's holder until the plaster has got moderately hard. Then carefully detach it from the surrounding plaster, and push the cork a little way into the tube so as to drive the plug of plaster before it. Take out the cork, and dry the plaster thoroughly by a gentle heat; leaving it for several hours in a drying cupboard, or before a fire. When it is quite dry, insert the cork and fill it with hydrogen by placing it over the end of the drying-tube, in the same manner as the test-tube was filled, p. in. While it is filling, pour some water into a large beaker and add a drop of indigo sulphate to colour it. In about a minute, if there is a fair stream of gas, the tube will be sufficiently full. Its lower end should now be immediately dipped into the water in the beaker and the cork withdrawn from the upper end. The hydrogen will diffuse out through the plaster plug so much faster than the air diffuses inwards that the water will rise in the tube and nearly fill it. After trying the above experiments, you may take the apparatus to pieces, wash the tubes, and set them aside to dry. The liquid which is in the flask is a solution of zinc sulphate, and may be filtered into an evaporating dish, and evaporated as directed in Sect, i, Ex. 5, (p. 55) until it deposits crystals on cooling. The zinc sulphate thus obtained is very pure, and may be reserved for use in the laboratory. ^ ; 3. NITROGEN" and AIR. Apparatus required Pneumatic trough ; porcelain dish 6 cm. in dia- meter; gas tray ; deflagrating jar ; two gas jars, 20 x 5 cm. ; one gas jar, 10 x 3 cm. ; small gas bottle ; beaker ; glass disc ; taper on wire ; jug of water ; cloth ; blotting-paper ; crucible tongs ; knife ; test-tubes ; piece of fine brass wire ; graduated measure ; porcelain mortar ; india-rubber rings ; watch glass ; corks ; cork borers ; elbow tubes ; phosphorus ; tow ; turpentine ; test papers ; calcium chloride ; lime water ; ether. Nitrogen occurs in air, simply mixed with oxygen ; and in I 2 Il6 PREPARATION AND PROPERTIES OF order to obtain a supply of it we have only to withdraw the oxygen by the action of some substance which has an affinity for it and not for nitrogen. Phosphorus is, on the whole, the best substance for the purpose, since it readily combines with oxygen and the compound formed (phosphorus pent- oxide) is very soluble in water, and is therefore quickly with- drawn when the experiment is made over the pneumatic trough, leaving the nitrogen nearly pure. Fill the pneumatic trough with water, and float a small porcelain dish on the water, retaining it over the movable shelf. Take a stick of phosphorus from the bottle with the crucible tongs *, place it in a gas tray full of water, and cut off with a knife (still holding it under water) a piece about twice as large as a pea. Dry the piece of phosphorus thoroughly, by gently pressing, not rubbing, it between folds of blotting- paper ; then place it at once, using the (dried) crucible tongs, in the floating dish. Take the stopper (which should be greased) out of the deflagrating jar, and, holding the jar in one hand over the phosphorus, light the latter by touching it with a burning match, and immediately lower the jar over the burning phosphorus until it rests upon the shelf of the trough, and insert the stopper. The level of the water in the jar will at first be depressed, owing to the expansion of the enclosed air by the heat of combustion, but it will soon rise above the level of the water in the trough, showing that one of the constituents of the air is being withdrawn. When the phosphorus ceases tp burn, allow the jar to remain undisturbed for five minutes, until the white fumes (which consist of a compound of phos- phorus with oxygen, phosphorus pentoxide) have been for the most part absorbed, and meanwhile fill all the gas jars with water and place them inverted on the shelf of the trough. Fill also the large beaker, which is to be used precisely as a gas jar, its large, spreading mouth rendering it easier to avoid loss in decanting gas from the deflagrating jar. When the white fumes have nearly cleared away, depress the deflagrating jar in the trough and shake it laterally until the 1 See note, p. 72. NITROGEN. 117 small dish is filled with water and sinks to the bottom, when it may be withdrawn. Decant some of the nitrogen first into the beaker (remembering not to fill it quite, lest it should topple over) and then from the beaker into the three gas jars. The properties of the gas may now be examined as follows. 1. Its action on test paper. Raise the mouth of the smallest gas jar above the water of the trough (still keeping it inverted, since nitrogen is rather lighter than air), and pass up into it strips of moistened blue and red litmus paper. The gas will be found to be neutral, like hydrogen and oxygen. 2. Its relation to ordinary combustion. (a) Slide one of the larger jars of gas off the shelf of the trough, cover its mouth with a glass plate, lift the jar out of the water, retaining the plate in its position with one hand, and place it on the table mouth upwards \ Light the piece of taper affixed to the wire, remove the glass plate from the mouth of the jar, and plunge the lighted taper into the gas. Observe that the taper is extinguished while the gas itself does not catch fire ; thus showing it to differ from oxygen, in which the taper continued to burn, and from hydrogen, which extinguished the taper, but was itself inflamed. (6) Twist a small piece of tow round the end of the copper wire in place of the taper, so as to form a ball about i cm. in diameter. Remove another jar of nitrogen from the pneumatic trough, and place it mouth upwards on the table, as in the last experiment. Pour a few drops of turpentine on the ball of tow, set it on fire, and immerse it in the jar of gas. The flame will be as instantly and completely extinguished as the small flame of the taper in the last experiment. These are all the experiments which can readily be tried with nitrogen, which in the free state appears as an inactive gas, showing very slight chemical affinities. [Reserve a jar or bottle full of nitrogen for use in the next series of experiments.] 1 This position is most convenient, although the nitrogen will escap^ rather more quickly than from an inverted jar. Jl8 COMPOSITION OF Composition of air. We may obtain proofs of the composition of air in two ways : (a) By analysis ; i. e. by separating it into substances which we can prove to be oxygen and nitrogen, and observing the quantities of each which are obtained from a given amount of air. (<5) By synthesis ; i. e. by mixing oxygen and nitrogen in the proportions indicated by analysis and observing whether the resulting product has the same properties as air. A. Analysis of air. For this purpose we may conveniently employ phosphorus : not, however, kindling it and thus causing it to withdraw the oxygen quickly, but allowing it to act at the ordinary tempera- ture for several hours. The cylindrical measure will do pretty well instead of a regular gas measuring-tube, if one of the latter is not at hand. Fill a small test-tube about half full of water, put into it enough phosphorus to form a stratum about i cm. deep, and place the tube in a beaker of nearly boiling water until the phos- phorus is melted. Make a small loop at the end of a piece of fine brass wire about 30 cm. long, by coiling it round a glass rod or pencil, plunge the looped end of the wire into the liquid phosphorus, and cool the tube by holding it in cold water. When it is quite cold, pull out the wire with the lump of phosphorus attached to it (this may require the tube to be dipped into hot water again for a moment, to loosen the phosphorus from the sides) and put it into a dish of water until wanted. Put the graduated cylindrical measure mouth downwards into a porcelain mortar nearly full of water, pushing up into it the end of a piece of india-rubber tube. Suck air out of the jar through the tube until the water level inside stands exactly at the mark 200 c.c. ; then pinch the tube to prevent air entering or escaping, and withdraw it from the jar. Incline the jar a little and introduce the lump of phosphorus, pushing it up by AIR. 119 means of the wire nearly to the closed end of the jar. Restore the jar to its vertical position and leave it undisturbed in a safe place for 12 or 14 hours 1 . [Meanwhile the other experiments on air maybe proceeded with.] At the end of this time, pull out the phosphorus attached to the wire, and read the volume of the remaining gas. To do this it will be best to transfer the jar to the pneumatic trough, and lower it in the water until the level inside and outside the tube is the same. You will find that out of the original 200 c.c. of air, only 160 c.c. (approximately) remain; and this residual gas may be shewn to be nitrogen by decanting some into a gas jar and passing up into the jar a lighted taper. And since the white fumes formed during the action of the phosphorus are known to consist solely of a compound of phosphorus and oxygen, the (200160=) 40 c.c. of gas which have dis- appeared, may be assumed to be oxygen. Then the percentage composition of air by volume can be found by the proportion sum 200 : 40 : : 100 : percentage of oxygen, and zoo percentage of oxygen = volume of nitrogen and other gases in 100 parts of air. B. Synthesis of air. Take one of the larger cylindrical gas jars, and graduate it into five parts in the following way. Try first whether the large jar will hold not less than six of the small jars full of water. If it holds less than this, slip an india-rubber ring over the small jar, about i cm. from, the mouth, fill the jar with water up to the level of the ring and try whether about six times this reduced volume will fill the larger jar. One or two trials will be sufficient to ascertain the proper volume, which is to be the unit of measurement. Now fill the measure up to" the proper point with water, pour the water carefully into the larger jar, and mark the level at which it stands by a small india-rubber ring slipped over the jar. Add another measure of water, and 1 It should not be left for more than a day, otherwise the air which diffuses through the water will vitiate the results. 120 COMPOSITION OF mark the level similarly with another ring. Proceed thus until five measures of water have been poured into the larger tube. You have now a tube graduated with fair accuracy, which should be filled with water and placed inverted on the shelf of the pneumatic trough. Decant into it sufficient nitrogen, from the bottle which was reserved, to fill it to the level of the fourth division : then add one measure of oxygen (from one of the bottles reserved in Exercise i), cover the mouth of the jar with a glass plate, and invert it once or twice (retaining the glass plate firmly in its place with one hand) so as to mix the gases thoroughly. Place the jar mouth upwards on the table and immerse in it a lighted taper. The latter will not burn brilliantly as in oxygen (p. 102) or be extinguished as in nitro- gen, but will continue to burn as it did in the external air *. Other experiments would show that the mixture possessed all the properties of common air, and thus we have a proof by synthesis that 5 volumes of air consist (approximately) of 4 volumes of nitrogen and i of oxygen. Besides oxygen and nitrogen, perceptible quantities of carbon dioxide and water vapour are present in air. Their presence may be shown as follows : 1. Carbon dioxide. Pour a little lime water into a watch glass, and leave it exposed to the air for ten minutes or more. A white film will form on the surface, proving the presence of carbon dioxide in the air of the room. 2. Water vapour. Pour a few drops of ether into a large dry test-tube and make it evaporate quickly by blowing air into it through an elbow tube (best with a pair of bellows, since the warmth of the breath interferes with the cooling effect 2 ). 1 The brilliancy may be slightly increased, since air is not entirely freed from oxygen by the action of phosphorus under the above conditions, and hence the mixture would contain rather more than the proper amount of oxygen. 2 If ether is not at hand, a little pounded ice (or snow) and salt may be put into the tube. Or a freezing mixture may be made by mixing 8 grms. of finely powdered sodium sulphate with 5 c.c. of strong common hydrogen chloride. AIR. 121 The outside of the tube will become very cold, and cool the air near it ; and a deposit of dew or even ice will appear on it, proving that water vapour is present in air, and only requires to be cooled down to a certain point in order to be condensed and show itself in a visible form. The chief sources of both of these are very similar ; viz. the combustion of candles, fires, &c., and the breathing of animals. These may be illustrated in the following way. i. Carbon dioxide. (a) Put a little lime water into a small gas bottle, and shake it up. It will not become cloudy, since the amount of carbon dioxide in the air contained in the bottle is extremely small. Now light the taper affixed to a wire, place it in the bottle, and allow it to burn there, laying the stopper loosely on the mouth of the bottle, to prevent entrance of air. When it goes out, remove it from the bottle, insert the stopper and shake up the lime water, which will become milky, proving that carbon dioxide has been formed ; the carbon of the wax having combined with the oxygen of the air. An experiment showing that carbon dioxide is produced in respiration has already been made, p. 6 1 : it may be repeated in a more exact way, as follows. Adapt a cork to a large test-tube (taking care to soften the cork thoroughly by squeezing it, or it may break the tube) ; bore two holes in the cork and fit into them elbow tubes as shown in Fig. 5 1 . The long branch of one elbow tube should reach nearly to the bottom of the test-tube, the short branch of the other should only just pass through the cork. Fill the test-tube about half full of lime water, and suck air through the liquid for a few seconds, applying the mouth to the extremity of the short elbow tube. No turbidity will be produced, the quantity of carbon dioxide in the air being very small. Now, having taken a deep breath, apply your ; ! Fig. 5 1. 122 COLLECTION OF GASES BY DISPLACEMENT. mouth to the other elbow tube (the long branch of which passes into the liquid), and blow air from the lungs through the lime water. The latter will almost immediately become turbid, showing that much carbon dioxide is present in air which is expired from the lungs \ 2. Water vapour. (a) Hold a beaker over the flame of a lamp or candle ; its surface will become covered with moisture, owing to the com- bination of the hydrogen of the gas or wax with the oxygen of the air. (l>) Strew a little powdered calcium chloride upon a glass plate and breathe upon it. It will become liquid, showing that abundance of moisture is present in the breath. COLLECTION OF GASES BY DISPLACEMENT. This is a method of collection which depends upon the difference between the density of a gas and that of common air. It is especially useful in cases where the gas to be collected is so soluble in water that it would be impracticable to collect it over that fluid. In such cases a trough filled with mercury might be used, but the great expense of this would place it beyond the reach of most of those for whom these exercises are intended. When we pour water into a vessel, the water, being heavier than the air contained in the vessel, descends to the bottom and displaces the air, which is driven out at the top. Precisely the same thing occurs when we lead a gas heavier than air into an open jar. The gas does not mix with the air at once, but collects at the bottom of the jar and gradually rises, driving the air before it, and finally overflowing the edge of the jar like other fluids. It is obvious that a gas lighter than air may be similarly collected by simply reversing the position of the receiving vessel, placing it mouth downwards, and -leading the gas into its upper part ; as has, in fact, been already done in filling a test-tube with hydrogen (p. in). 1 The reason why carbon dioxide does not accumulate in the air will be alluded to under the head of CARBON DIOXIDE. AMMONIA. 123 Two points must, however, be attended to in order to obtain by this method jars of gas even approximately pure. 1. It is necessary to pass into the jar at least twice the volume of gas required to fill it; since diffusion must take place between the fluids with greater rapidity in proportion as their densities are less, and hence the boundary-line between the gas and air is never so sharply marked as in the case of water and air. 2. All currents of air in the room must be avoided as much as possible ; the tendency of such currents being to stir up the gas, and produce a more rapid mixture with air than diffusion alone would cause. COMPOUND OF NITROGEN AND HYDROGEN. 4. AMMONIA. Apparatus required Florence flask ; corks ; cork-borers ; elbow tubes, one with long branch; drying tube, fig. 12, c ; india-rubber connector; retort-stand ; Bunsen's holder ; wooden blocks ; sand bath ; argand burner ; porcelain mortar ; scales and weights ; porcelain dish ; test- tubes ; taper on wire ; gas jar, 20 x 5 cm. ; one large and four small gas bottles ; glass disc ; pan of water ; beaker ; flask with flat bottom, holding about 250 c.c. ; piece of platinum wire about 15 cm. long ; card ; glass rod ; ammonium chloride (sal ammoniac) ; quicklime ; small bits of flannel (or silk) and calico ; box of test-papers ; strong solution of ammonia ; hydrogen chloride ; hydrogen sulphate ; indigo sulphate. Nitrogen and hydrogen can only with great difficulty be caused to unite directly ; but when organic substances, such as leather, wool, or gelatine, which contain both elements, are decomposed some of the nitrogen and hydrogen unite to form ammonia. The following experiment illustrates this : Place a small bit of flannel (or silk) in a moderate- sized test- tube, support it in a slanting position as in fig. 39, p. 69, and heat it rather strongly. The substance will become blackened or ' charred/ showing the presence of carbon : water will condense in the tube, proving that it contains hydrogen and oxygen; 124 PREPARATION AND PROPERTIES OF while strong-smelling volatile products will be given off among which are ammonium carbonate and ammonia. The latter may be recognised (i) by its alkaline reaction on a strip of reddened litmus paper moistened and held in the tube : (2) by the white fumes (of ammonium chloride) formed when a glass rod dipped in strong hydrogen chloride is held in the issuing vapours. If a piece of paper or calico (substances which contain no nitrogen) are heated in the same way, the vapours evolved will give no alkaline reaction or white fumes when tested as above. Coal contains nitrogen, and the compounds of ammonia obtained from it in the manufacture of coal-gas are combined with hydrogen chloride (as illustrated in the second of the above tests) and form ammonium chloride (' sal ammoniac '), which is the usual source of ammonia, since it readily yields the gas when gently heated with quicklime. The chemical change may be expressed as follows l : Ammonium ( Nitrogen (28 parts) 28 ) Ammonia chloride j Hydrogen (8 parts) -= = ^^ 6 ) (34 parts). (107 parts). ( Chlorine (71 parts) -v^ ^ 2 Water Calcium oxide Oxygen (16 parts) -^ -16 (^ parts). Calcium (56 parts). Calcium (40 parts) 40 ( chloride (in parts). Weigh out 15 grms. of sal-ammoniac, and reduce it to powder in the mortar. The salt in its sublimed state is so tough as to render this rather difficult 2 , and more may be effected by direct blows of the pestle, especially if aided by a thrust and slight twist of the arm at the moment of impact, than by the usual rubbing motion. Place the powdered salt in a basin and set it to dry on the sand-bath over the lamp, occasionally stirring it to prevent its caking together. Mean- while reduce 20 grms, of quicklime to fine powder in the mortar 3 : 1 Or by the equation, 2(H 4 N)Cl+CaO =CaCl 2 +H 2 O + 2H 3 N. 2 It should be bought in a state of powder if possible. 3 If the quicklime is very hard and difficult to powder, it may be slacked as directed, p. 58, care being taken to use as little water as possible, so that the calcium hydrate may be perfectly dry. AMMONIA. then cover the mortar with a plate, to protect the lime from the moisture and carbon dioxide of the air. An apparatus should now be fitted up as shown in Fig. 52. Adapt a cork to a clean dry Florence flask, and fit into the cork an elbow tube each branch of which is about 8 cm. long. Fill the drying tube with fragments of quicklime about as large as split peas in the manner described at p. 13. Fit the end of the elbow tube into the perforated cork of the drying tube, and support the flask in the Bunsen's holder l at such a height that the lamp will go easily underneath it. Fig. 52. The ammonium chloride may now be taken from the sand- bath and set aside to cool ; the cooling may be hastened by spreading it out on a sheet of paper. 1 A notch should be cut across the cork at the end of each jaw of the holder (if this has not been done already) in order to grasp the neck of the flask more securely. 126 PREPARATION AND PROPERTIES OF Next, adapt a large flat cork to the smallest ring of the retort- stand, and bore a hole in it, through which the long branch of the other elbow tube should be passed so that its end may be about 12 cm. above the cork. Clamp the retort-ring in the position shown in the figure ; one, at least, of the larger rings being fitted on above it, for the purpose of steadying the bottles while they are being filled. The retort-stand must now be supported on blocks at such a height that the drying tube may be horizontal when its end is connected with the elbow tube by a short bit of india-rubber tubing, as shown in the figure. The ammonium chloride will by this time have cooled, and should be mixed quickly and thoroughly with the quicklime in the mortar. The mixture should be shaken out on a half-sheet of paper and transferred at once to the flask, in the manner shown in Fig. 34, p. 64 (the cork with elbow tube being left resting on the Bunsen's holder). Having restored the flask to its place and fitted the cork tightly into its neck, place one of the smaller bottles inverted over the up-turned end of the elbow tube so that its mouth rests lightly upon the cork in the retort-ring (see the engraving). The flask may now be gently heated by the argand burner with a small flame. If the spirit lamp must be used, it should be moved to and fro under the flask, the flame being never allowed to rest in one place, otherwise the flask is apt to crack ; an accident which is not unlikely to happen in any case, as the substance to be heated is a solid of low conducting power, and not a liquid, which would distribute the heat by convection. While the bottle is being filled you may grease its stopper and those of the other bottles, and also fit a good cork to the neck of the larger gas bottle for use in Expt. 5. The gas comes off at a comparatively low temperature, and from its lightness collects in the highest part of the bottle, driving the air downwards before it, which will escape between the edge of the bottle and the cork. To ascertain when the bottle is full of gas, hold a piece of turmeric-paper (moistened by being breathed upon) near its neck and slightly above its AMMONIA. 12 7 mouth. If the gas is overflowing, it will quickly and decidedly redden the test-paper. Remember, however, that a very little ammonia is sufficient to act on the paper ; and hence it is advisable to leave the bottle in its place for about half a minute longer after the above effect has been observed, to ensure its being really full of gas. The bottle should then be slowly raised until clear of the delivery tube, and the stopper inserted at once. Another bottle may then be placed in the same position and filled in like manner. When all the bottles have been filled with the gas, withdraw the lamp, disconnect the elbow tube from the drying tube, and place the flask (still fitted with the cork and elbow tube) in a draught-cupboard or in the open air. The chief properties of ammonia may now be examined, as follows : *1. Its peculiar odour and its alkaline action on turmeric paper will have been noticed already. 2. Its lightness has been sufficiently proved by its collection by upward displacement. 3. Its rapid diffusibility. Place an empty gas jar, mouth upwards, on the table, and drop into it strips of wetted reddened litmus and turmeric paper. Bring over the mouth of the jar a small bottle of ammonia inverted, remove the stopper and place the mouths of the jars in contact for a few seconds. The gas, in spite of its low density, will diffuse downwards through the air ; the reddened litmus will become blue and the turmeric red; thus showing at once the alkaline reaction of ammonia and its quick rate of diffusion. 4. Its relation to ordinary combustion. Support a small bottle of ammonia on the smallest ring of the retort stand (the cork being taken out) in the same position as when it was being filled. Withdraw the stopper and pass a lighted taper slowly up into the bottle. The taper will be extinguished, but the gas will show a ten- dency to burn with a greenish flame at the mouth of the bottle. [The feeble inflammability of ammonia in air may be shown by restoring to its place the flask, fitted with elbow tube, which was put 128 PREPARATION AND PROPERTIES OF aside just now, heating it so as to generate a little more ammonia, and bringing the flame of a Bunsen's burner close to the extremity of the tube from which the gas is issuing. A yellowish-green flame will be seen.] 5. Its solubility in water. Fill the supplementary pan of the pneumatic trough (or a basin) with water. Place a dry glass plate on the table, bring over it a small bottle of ammonia, mouth downwards, remove the stopper, and bring the mouth of the bottle at once down upon the glass plate. Then, still keeping the bottle inverted and plate closely pressed against its mouth, plunge it below the surface of the water in the pan and withdraw the glass plate. The water will rise in the bottle especially if the latter is gently shaken, and will fill it entirely if the gas is unmixed with air. There will usually be a small residue of air, and you will thus gain an idea how far you have been successful in filling the bottle by displacement. The water in the bottle will be found to have gained the smell and alkaline reaction of the gas, and to have a caustic taste. It has, in fact, combined with the ammonia, not merely dissolved it, and the liquid is a solution of ammonium hydrate (the common ' solution of ammonia' which you will often have occasion to use in testing). [Another experiment illustrating the solubility of ammonia may be made, if time permits, as follows. Take the cork which was recently fitted to the large gas bottle : bore a hole in the centre and fit into it a glass tube about 18 cm. long, ending in a jet (the pipette already made, p. 33, will do very well), so that the jet may project about 5 cm. within the bottle. Fill a beaker with water and add to it a few drops of solution of litmus together with one drop of dilute hydrogen chloride to make the litmus red. Twist a small piece of moistened tow round the tube just below the jet (this is for the purpose of beginning the absorption). Put the beaker on the iron base of the retort stand, and clamp the smallest retort ring at such a height that when the cork rests on it the end of the tube may reach nearly to the bottom of the beaker. Now invert the large bottle of ammonia, take out the stopper and quickly fit the cork into its place (still keeping the bottle inverted), and plunge the outer end of the tube into the beaker of coloured water. The AMMONIA. 129 pressure of the external air will force the water up the tube, as the ammonia is absorbed and a vacuum made in the bottle, and a fountain will be formed, the red litmus becoming blue under the action of the ammonia.] *6. Its combination with other radicles. Ammonia shows a great tendency to combine directly with salts of hydrogen (i. e. the substances called acids), associating their hydrogen more closely with itself to form the radicle ' AMMONIUM/ containing 1 4 parts by weight of nitrogen com- bined with 4 parts of .hydrogen (instead of with 3 parts as in ammonia). Thus, when ammonia is brought into contact with hydrogen chloride the two gases combine to form the salt 'ammonium chloride'; the substance, in fact, from which you prepared the gas. Dip a glass rod into strong hydrogen chloride and hold it just above the mouth of a bottle of ammonia, lifting the stopper for a moment only to let a little of the gas escape. White clouds of ammonium chloride will be formed when the gases mix. Having cleaned the glass rod, dip it into strong hydrogen acetate (acetic acid) and allow a little ammonia to mix with its vapour in the same way. Similar white clouds of * ammonium acetate' will be noticed. This reaction is very useful as a test for ammonia ; and hydrogen acetate is slightly preferable to hydrogen chloride for the purpose, since the latter itself gives slight white fumes in moist air, which might lead to a mistake. Other experiments illustrating the formation of ammonium salts will be found under the heads of NITRATES, CHLORIDES, and AMMONIUM. 7. Its union with oxygen, under the influence of platinum. Platinum, as noticed under HYDROGEN, has a peculiar power of causing chemical combination : and when a piece of it is heated and put into a mixture of ammonia and air, the oxygen of the air combines with both the nitrogen and the hydrogen of the ammonia (and not with the hydrogen alone, as in Expt. 3). 130 AMMONIA. Form a piece of platinum wire, of the kind used for blowpipe experiments, about 15 cm. long, into a close spiral, by coiling it round a glass rod or pencil, and attach it to a strip of card sufficiently wide to fit rather tightly into the neck of a flask about 400 c.c. in capacity. The coil should hang down freely in the centre of the flask, about i cm. from the bottom, the card forming a diaphragm or partition in the neck, as shown in Fig. 53. Withdraw the coil from the flask, pour fa few drops of a strong solution of am- monia into the latter, and shake it so as to diffuse the ammonia gas through the air contained in the flask. Heat the platinum spiral to redness in a Bunsen's burner, and while it is still red-hot, plunge it into the flask. The coil will continue to glow for some time, and white fumes of ammonium nitrite will be almost immediately formed. The heated platinum wire has determined the union of the con- stituents of ammonia with the oxygen of the air. If, when the coil of wire has ceased to glow, the flask is gently heated by waving it for a few seconds over a lamp, more ammonia gas will be evolved from the liquid, and the platinum will again become red-hot. After the lapse of a minute or two, take out the coil of wire, add 2 or 3 c.c. of water, and shake it up in the flask ; then pour the liquid (which will be slightly yellow, owing to the presence of nitrogen tetr- oxide) into a test-tube, add enough dilute hydrogen sulphate to render the solution strongly acid to test-paper (when the smell of nitrogen oxides will be perceived), then add one drop of solution of indigo sulphate, and heat the mixture. The blue colour of the indigo will disappear, proving, under the conditions of the experiment, that a nitrite or nitrate is present. 53- [Before putting away the drying tube, the quicklime in it should be examined and any of it which appears slaked by the moisture NITRATES. 131 should be taken out and thrown away. A bit of glass rod should then be put into the hole in the cork, and the other end of the tube stopped with a plug of cork, to prevent entrance of moisture.] COMPOUNDS OF NITROGEN AND OXYGEN. Nitrogen forms five well-defined compounds with oxygen, a list of which will be found in Appendix D, and should be written out in the note-book. They or their compounds will be taken in descending order, beginning with compounds related to the highest oxide, nitrogen pentoxide. 5. NITRATES. It has been seen in the last experiment (p. 130) that ammonia can be made to combine with oxygen to form a substance (a nitrite) which may be represented as containing a compound of nitrogen and oxygen. This oxidation of nitrogen goes on in nature on a large scale, during the decay or putrefaction of organic substances. The ammonia first formed is slowly oxidised to a nitrate ; and thus soil is found to yield such salts as potassium nitrate (' nitre ' or ' saltpetre '), and sodium nitrate. From either of these hydrogen nitrate (' nitric acid ' or ' aqua fortis ') can be prepared by heating it with hydrogen sulphate in the manner next to be described. 1 Preparation of Hydrogen Nitrate. Apparatus required 1 Stoppered (or plain) retort, about 2co c.c. in capa- city ; retort-stand ; sand-bath with sand ; argand, or spirit lamp ; thistle funnel (Fig. 12, a); small flask; porcelain mortar; Bunsen's holder; funnel, 10 cm. in diameter ; beaker ; test-tube-stand ; test-tubes in basket; watch-glass ; washing bottle with distilled water ; wooden blocks ; blot- ting paper; lamp cotton, or tow; cloth; solutions of barium chloride, silver nitrate, litmus, indigo sulphate, ammonium hydrate, iron proto- sulphate ; crystallised potassium nitrate ; common hydrogen sulphate ; bit of worsted or flannel ; quill pen ; piece of thin sheet lead ; copper filings ; charcoal. 1 In future, lists of apparatus required will only be given where a more or less elaborate apparatus has to be set up, as for distillation, or prepara- tion and collection of a gas. K 2 132 HYDROGEN NITRATE. Measure 20 c.c. of water into a beaker placed on a plate and add to it by degrees 20 c.c. of strong common hydrogen sulphate. This should be done carefully, as great heat is evolved by the union of the acid with the water (compare the action of quicklime on water, p. 58) and the beaker may be broken. Add only about i or 2 c.c. at a time, and stir with a glass rod. While the mixture is cooling, weigh out 20 grms. of potassium nitrate, powder the salt roughly in a mortar, and transfer it to the retort, in the manner shown in Fig. 54. Fig. 54- Arrange the retort on the sand-bath, precisely as for the distillation of water, p. 63, putting a large test-tube temporarily in place of the flask as receiver, to collect the first portions of the distillate. Pour the diluted acid through the tubulure by means of a funnel, taking particular care that none of the liquid passes down the neck of the retort ; then replace the glass stopper and proceed to heat the mixture. Meanwhile, the condensing arrangement may be set up, in the way described at p. 64. Hydrogen nitrate will soon begin to distil over, not in the most concentrated form (since the hydrogen sulphate was slightly diluted) but sufficiently strong for experiments. [The action which goes on in the retort is a ' double decompo- HYDROGEN NITRATE. 133 sition f (see p. 74), the potassium and part of the hydrogen changing places, as shown in the diagram below *, Potassium ( /Nitrogen, 14 parts \ nitrate, < \ Oxygen, 48 parts/ 101 parts. ( Potassium, 39 parts Hydrogen \ Hydrogen, 2 parts sulphate, J /Sulphur, 32 parts \ 98 parts. ^ \ Oxygen, 64 parts/ Hydrogen nitrate, 63 parts. Potassium and hydrogen sulphate, 136 parts. Thus only half the hydrogen in the hydrogen sulphate is replaced by potassium, in the process as ordinarily conducted ; but at a higher temperature the whole of the hydrogen may be replaced and potassium sulphate formed.] When 2 or 3 c.c. of acid have distilled over remove the test- tube to the test-tube stand and substitute for it a flask as a receiver. The heat should be regulated so as to keep the liquid in the retort gently boiling. It will be advisable to provide some means for cooling the receiver as well as the neck of the retort, to ensure the efficient condensation of the corrosive vapours of the acid. For this purpose lay over the flask as it rests in the mortar one or two folds of blotting- paper, and pour over it from time to time some cold water. While the distillation is going on, you may examine the purity of the acid which came over first, and was collected in the tube. Add to it about 10 c.c. of water, and pour one half of the solution into another test-tube. (a) Test the first half of the solution with a drop of solution of barium chloride ; shake the mixture and hold it up to the light. If a turbidity is perceptible, hydrogen sulphate is present as an impurity 2 . (b] To the other half of the solution add a drop of solution 1 Or by the equation, KNO 3 + H 2 SO 4 = KHSO 4 + HNO 3 . 2 It must be borne in mind that barium nitrate is insoluble in strong hydrogen nitrate ; and hence if the solution of hydrogen nitrate is not very dilute, a crystalline precipitate may be formed. This, however, is easily distinguishable in appearance from barium sulphate, and'will readily dis- solve when more water is added, and the liquid warn\e. hypoch i orite . 2KHO + C1 2 = H 2 O + KC1 + KC1O. 2 2HI + KC1O = KC1 + H 2 O + I 2 . O 2 196 HYPOCHLORITES. *2. They yield chlorine when acted on by hydrogen chloride. 2. Place a little ordinary bleaching powder at the bottom of a large test-tube, and pour on it a few drops of strong hydrogen chloride. A violent action will take place, and a greenish yellow gas will fill the tube, which may be proved to be chlorine by its odour and bleaching action on litmus-paper *. In the case of ordinary bleaching powder, any acid will produce the same effect as hydrogen chloride ; since the substance contains the elements of calcium chloride as well as calcium hypochlorite ; and the calcium chloride yields hydrogen chloride when decomposed by an acid. 3. They bleach organic colouring matters, but only when a free acid is present. (a) Dip a piece of blue litmus-paper into the solution of potassium hypochlorite. Its colour will not be altered. Lay it on a plate and pour on it a drop or two of dilute hydrogen chloride ; it will be immediately bleached. The reason is that hydrogen hypochlorite is formed by the action of the acid, and this is much less stable than the potassium hypochlorite, and gives up its oxygen to the colouring matter forming a colourless compound. (b} Shake up a little bleaching powder with 10 c.c. of water, filter it into a small beaker, and add to the liquid a drop or two of solution of blue litmus. The colour of the litmus will remain unchanged. Now blow air from the mouth into the solution through an elbow tube. The blue colour will soon disappear; the carbon dioxide of the breath having decom- posed the calcium hypochlorite in the same way as the hydrogen sulphate in the previous experiment. (c) Add a few drops of solution of potassium hypochlorite to a dilute solution of indigo (which always contains free acid). The blue colour will be at once discharged. 1 The reaction is a remarkable one. Hydrogen hypochlorite is first formed by double decomposition; and then a molecule of chlorine is formed by the union of I atom derived from the hydrogen hypochlorite and i atom from the molecule of hydrogen chloride. Thus, HC10 + HC1= H 2 + C1 2 . CHLORATES. 197 [(*/) It is clear from the above experiments that white patterns may be formed on coloured cloth by putting an acid on certain parts of it, and then dipping it into a solution of a hypochlorite, which will only discharge the colour where it meets with the acid. This is the principle of the ' discharge ' process of dyeing, and may be illustrated as follows. Powder about a gramme of hydrogen tartrate (tartaric acid 1 ), add to it in the mortar about i c.c. of ordinary thick solution of gum arabic (this prevents the solution from spreading over the cloth), and grind the whole together. Take a small piece of coloured cloth or calico (the thin cotton cloth dyed with madder answers well), lay it flat on a double fold of blotting paper, and draw on it letters with a glass rod dipped in the acid solution. Dry this partially before a fire or by hanging it at some distance above a lamp-flame, and meanwhile make a strong solution of bleaching powder by grinding about 20 grms. of it with enough water to make a thin cream, then rinsing it into a flask, adding about 80 c.c. of water, and shaking it up thoroughly. Lastly, it must be filtered from the residue, mainly of calcium hydrate, which is sure to remain. Warm the filtered solution gently, and pour it upon the piece of coloured cloth laid flat on a plate, taking care to soak the whole of the cloth in the liquid, and seeing that it is kept flat and that no folds overlie each other. The acid will at once decompose the calcium hypochlorite : chlorine will be liberated, as above explained, and will discharge the colour in those parts where the acid was placed. As soon as the design appears in white, remove the cloth and rinse it well in plain water.] 23. CHLORATES. [Typical example, Potassium chlorate, (KC1O 8 ).] These are formed when solutions of hypochlorites are heated to boiling ; a part of the salt giving up oxygen to the rest, and being itself reduced to a chloride. To illustrate this, take the solution of potassium hypochlorite which was obtained in Ex. 20 by saturating potassium hydrate with chlorine, and evaporate it down in a dish until a drop 1 Hydrogen oxalate will do if hydrogen tartrate is not at hand. 198 CHLORA TES. placed on a watch glass deposits crystals on cooling; then leave it to crystallise. In this reaction two molecules of the potassium hypochlorite give up all their oxygen to a third molecule which is thus converted into potassium chlorate \ Thus the liquid contains a mixture of potassium chlorate and potassium chloride; and the former being much less soluble in water than the latter, crystallises out in the form of flat rhombic plates as the solution cools. These may be drained from the liquid, washed with a little water, and left to dry in a funnel. The liquid drained from the crystals will contain much potassium chloride, as may be proved by testing it with silver nitrate. The crystals should be proved to be a chlorate by tests 2 and 4. Meanwhile the properties of the chlorates may be examined, another sample of potassium chlorate being used. [For some of the following experiments a solution of potassium chlorate will be required, containing i grm. of the salt dissolved in 40 c.c. of water.] *1. They give up oxygen readily. This has been already proved in the first experiment made in the preparation of oxygen, p. 96. Put a small crystal of potassium chlorate into an ignition- tube, add a splinter of charcoal, and heat nearly to redness. The same deflagration will be observed as took place in the similar experiment with nitrates, p. 137, the potassium chlorate giving up all its oxygen to the carbon, with formation of potas- sium chloride and carbon dioxide. *2. They give off chlorine tetroxide when acted on by hydrogen sulphate. This experiment requires caution, but is quite safe if made with quantities not larger than those mentioned below. Put 2 c.c. of strong hydrogen sulphate into a test-tube, add half a gramme (not more) of potassium chlorate, coarsely powdered, and place the tube in a beaker containing warm water (not hotter than 40 C., i.e. not too hot to be borne by the hand). The mixture will become deep orange and a 1 3KC1O = 2KC1 + KC1O 3 . CHLORATES. 199 greenish yellow gas (chlorine tetroxide) will gradually fill the tube, having a very characteristic smell, somewhat resembling (but easily distinguishable from) that of chlorine l . Take a piece of wire bent at right angles (the wire to which the taper is affixed, fig. 8, p. 9, the taper being removed, will do very well), heat one end of it in a lamp-flame, and plunge it while hot into the gas in the test-tube. The gas will decom- pose with slight explosion, and its greenish yellow colour will almost instantly disappear, owing to the formation of chlorine, the colour of which is less intense, and oxygen. When the experiment is over, pour the mixture in the tube into a jug of water at once, and throw it away : the tube may then be safely washed out with water. [The instability of chlorine tetroxide may also be shown by its violent action on phosphorus. Nearly fill a large wine-glass or beaker with water, and drop into it a few crystals of potassium chlorate, which will sink to the bottom without much loss, as the salt is not very soluble in water. Drop upon the crystals a bit of phosphorus about as large as a pea, and support a tube funnel in the glass in such a position that the ex- tremity of the tube may just touch the crystals at the bottom of the glass. Now pour down the funnel 2 or 3 c.c. of strong hydrogen sulphate ; chlorine tetroxide will be evolved when the acid comes in contact with the potassium chlorate, and the phosphorus will take fire, as in chlorine gas, and burn underneath the water.] *3. They bleach indigo when heated with it. Add one drop of solution of indigo sulphate to some solution of potassium chlorate, and boil the mixture. The blue colour of the indigo will be destroyed; as in the case of nitrates, P- 137- 1 The following equations express the action. (i) Potassium Hydrogen Hydrogen Hyd. and potassium chlorate. sulphate. chlorate. sulphate. SKC10 3 + 3 H 2 S0 4 = 3HC10 3 + 3 KHSO 4 . (ii) Hydrogen Hydrogen Chlorine -^ , chlorate. perchlorate. tetroxide. 3 HC10 3 = HC10 4 + C1 2 4 + H 2 0. It will be seen that the chlorate is split up into a higher and a lower oxidised compound of chlorine. 200 CHLORATES. *4. They bleach indigo, even in the cold, when hydrogen sulphite is added. This action depends upon the reduction of chlorates by hydrogen sulphite, which has a great tendency to absorb oxygen (as will be explained under SULPHITES) ; lower and less stable compounds of chlorine are formed, which readily give up chlorine, decomposing the indigo. Add a drop of solution of indigo sulphate to some solution of potassium chlorate. Put into another test-tube some solution of hydrogen sulphite (or, if this is not at hand, sodium sulphite to which a few drops of hydrogen sulphate have been added ; hydrogen sulphite is thus formed by double decomposition) and add to it also a drop of indigo sulphate. In neither case will the blue colour be discharged. Now mix the contents of the two tubes ; the blue colour of both the solutions will disap- pear, for the reason above explained. This reaction serves to distinguish a chlorate from a nitrate, since the latter will not under the same conditions bleach indigo at once. The experiment should be repeated, using a solution of potassium nitrate instead of potassium chlorate, to prove this fact. 5. They give no precipitate when tested with silver nitrate. Add a drop of solution of silver nitrate to some of the solu- tion of potassium chlorate. No precipitate will be produced if the chlorate is pure, since silver chlorate (as indeed every other chlorate) is soluble in water 1 . Observe that although chlorine is present in the chlorate, it is present in such a condition as to be unable to combine per se with silver to form a chloride. 3 Commercial potassium chlorate generally contains a trace of chloride, sufficient to give a turbidity with silver nitrate, but it may be readily purified by dissolving in as little hot water as possible (about 20 grms. in 60 c.c.) and re- crystallising. BROMINE. 201 24. BROMINE. [Formula of molecule, Br 2 . Weight of molecule, 80 hydrogen -atoms.] / This element is obtained from sodium bromide or potassium bromide by a reaction precisely analogous to that by which chlorine was obtained from sodium chloride (p. 184). Its vapour is even more offensive in smell and poisonous than that of chlorine, and all possible precautions should be taken not to inhale any of it : all experiments being done in a draught- cupboard. Mix intimately in a mortar about half a gramme of potas- sium bromide with twice as much manganese dioxide. Put the mixture into a dry test-tube, add about 3 c.c. of strong hydrogen sulphate, and heat the tube very gently on a sand- bath, supporting it upright by passing over it the smallest retort ring, and placing behind it a sheet of white paper. Deep red vapours of bromine will soon fill the tube, and will condense near the top into an intensely-coloured liquid. Some of its properties may be examined as follows. 1. Its bleaching action on organic colours. Dip a wetted piece of blue litmus paper into the vapour. It will be at once bleached. 2. Its weight, and solubility in water. Put about 5 or 6 c.c. of water into a test-tube, and pour on it some bromine by inclining the tube containing the vapour (taking care that none of the mixture in the tube is poured out as well). The vapour will readily be transferred in this way, owing to its weight. Now shake up the water with the bromine vapour, closing the mouth of the tube with the finger. An orange-coloured solution of bromine will be readily formed. Pour one or two drops of this into a dilute solution of indigo sulphate ; the blue colour will be discharged, as in the case of chlorine. 3. Its action on potassium hydrate. Add a few drops of solution of potassium hydrate to the 2O2 BROMIDES. solution of bromine just obtained. The orange colour will disappear, the bromine uniting with the potassium and oxygen to form a mixture of potassium bromide and potassium bro- mate 1 . This result is analogous to that which takes place when potassium hypochlorite is heated (p. 198), but in the case of bromine the potassium hypobromite, if formed at all, is decomposed even in the cold. 25. BROMIDES. [Typical example,- Potassium bromide (K Br.). A solution of this salt containing i grm. of it dissolved in 40 c.c. of water may be used.] *1. They are decomposed by hydrogen sulphate, yielding hydrogen bromide mixed with vapours of bromine. Place a few crystals of potassium bromide in a test-tube and add a few drops of hydrogen sulphate. A strong action takes place, and a gas giving white fumes in moist air is given off which is hydrogen bromide ; but this is itself partly decom- posed by hydrogen sulphate, orange vapours of bromine being set free. Hence hydrogen bromide cannot be obtained pure by the same method as hydrogen chloride : it is usually prepared by a process of which the principle will be explained under IODIDES. *2. They give a yellowish-white precipitate, difficultly soluble in ammonia, when tested with silver nitrate. Add a drop of solution of silver nitrate to solution of potassium bromide. A yellowish white precipitate of silver bromide will be formed. Divide the liquid in which the pre- cipitate is suspended into two parts; add to the one some hydrogen nitrate; the precipitate will not dissolve. To the other portion add some ammonia, and warm ; the precipitate will dissolve by degrees, but not so readily as silver chloride. The fact of its solubility may be proved, without waiting until all the precipitate has disappeared, by pouring off a little of the clear liquid into another tube and adding to it some dilute 3 H 2 O. IODINE. 203 hydrogen nitrate : the portion of silver bromide which had dis- solved will be again precipitated. *3. They are decomposed by chlorine, with liberation of bromine. Add a few drops of solution of chlorine to some solution of potassium bromide in a test-tube. The bromine will be dis- placed by the chlorine from its combination with potassium, and will dissolve in the excess of potassium bromide, colouring the solution yellow. Now add a small quantity of carbon disulphide J , shake the mixture thoroughly, and allow it to stand for a few moments in order that the scattered particles of the carbon disulphide may collect at the bottom of the tube in one globule, which will be found to have acquired an orange tint, while the fluid above it will be colourless. The bromine has been withdrawn entirely from the solution by the carbon disulphide, in which it is very soluble. Pour off the upper stratum of fluid, fill up the test-tube with water, and again pour it off; then add some solution of potassium hydrate, shake it up, and allow it to stand as before. The globule of carbon disulphide will have lost its colour, the bromine having acted upon the potassium hydrate, to form potassium bromide and bromate, as just now explained. 26. IODINE. [Formula of molecule, I 2 . Weight of molecule, 254 hydrogen-atoms.] Iodine has many striking analogies to chlorme and bromine, but it is a solid at ordinary temperatures, and its vapour when formed is not so injurious and unpleasant as the other two elements. Hence it will be unnecessary to take the same pre- cautions in experimenting upon it. It is obtained from potassium iodide by a reaction similar to that by which chlorine and bromine are prepared. 1 If carbon disulphide is not at hand, ether will serve the purpose, as it will form a coloured stratum on the top of the aqueous solution. 204 IODINE. Weigh out 3 grms. of potassium iodide and the same quan- tity of manganese dioxide, mix them intimately in a mortar and put the mixture into a porcelain dish about 8 or 9 cm. in diameter ; then add 5 c.c. of strong hydrogen sulphate, stir the whole thoroughly together, and cover the dish with an inverted funnel just large enough to fit within the rim. On warming the dish on a sandbath, deep violet vapours of iodine will be formed, and will condense in the upper part of the funnel in glittering rhombic plates, the crystalline form of which may easily be made out with a magnifying glass 1 . In a few minutes sufficient iodine will be obtained for use in the following expe- riments on its properties. [It should be borne in mind that iodine stains the skin yellow, and therefore it should be handled as little as possible. A glass rod or platinum (not aluminium or bone) spatula should be used. Stains may be removed by dilute solution of potassium hydrate.] *1. It melts and volatilises readily, forming a violet vapour, much heavier than air. Put a few crystals of iodine into a large dry test-tube, and heat them gently. They melt into an almost black liquid, and on further heating turn into a splendid violet vapour. Warm the upper part of the tube, to prevent the condensation of the vapour, and when the tube is full of it pour some out on a white plate. The heavy vapour will pour out almost like a liquid, and will condense into a cloud of small flakes of iodine which will fall in a shower on the plate. 2. It is scarcely soluble in water. Place a crystal or two of iodine in a test-tube, pour on them about 5 or 6 c.c. of water, and shake the mixture. Hardly any of the substance will dissolve; only sufficient to colour the liquid a pale yellow. 3. It readily dissolves in alcohol. Pour off the liquid from the crystals used in the last experi- ment, and add to them a little alcohol. A red solution will be at once formed, rapidly deepening in colour, when the tube is 1 Very fine crystals of iodine are often formed by spontaneous sublima- tion on the stopper of a bottle containing it. IODINE. 305 shaken, until it becomes almost opaque. Now fill up the tube with water ; most of the iodine will be reprecipitated as a black powder. 4. It also dissolves in solution of potassium iodide. Put about half a gramme of crystallised potassium iodide into a test-tube, add 5 or 6 c.c. of water and then a few crystals of iodine. The latter will dissolve even more readily than in alcohol ; but it will not be reprecipitated on filling up the tube with water. 5. It has little or no bleaching properties. This may be tried by dipping a piece of blue litmus paper into the solution of iodine just obtained. *6. It forms a deep blue compound with starch. This is the most characteristic and delicate test for iodine, when it is free and uncombined : mere traces of it being re- cognisable. Pour 5 or 6 drops only of the solution of iodine obtained in experiment 4 into a beaker, add 100 c.c. of water and then 8 or 10 c.c. of a freshly made solution of starch *. A deep blue colour will be produced, even in so highly dilute a solution of iodine. Pour a little of the liquid into a test-tube, add a few drops more of the solution of iodine, to deepen the colour, then heat it over a lamp. When it has nearly reached the boiling point the blue colour will quickly disappear, showing that the compound of iodine with starch is decomposed by heat. Cool the liquid by holding the tube in a stream of water (or in a jug of cold water) ; the blue colour will soon reappear and become as intense as at first 2 . Hence in testing for iodine by this method care must be taken that the liquid is quite cold. [Conversely, iodine may be used as a test for starch. If a few drops of a very dilute solution of iodine are put on a piece of writing paper, a blue colour will be produced on account of the starch present in the size used in making the paper. Similarly, a slice of raw potatoe may be shewn to contain starch.] 1 For the method of making this see Appendix B. 2 Notice that the blue colour reappears first in the lowest part of the liquid. It reappears, of course, where the liquid is coldest ; and the fact that it appears at the bottom is a proof that cold water is denser than hot water. 206 IODIDES. 27. IODIDES. [Typical examples, Hydrogen iodide (HI). Potassium iodide (KI). Phosphorus tri-iodide (PI 3 ).] The formation of one or two of these compounds of iodine with other radicles has been illustrated already. Thus iodine was shown to combine readily with phosphorus and with mer- cury in Exercise 8 (pp. 72, 73). Preparation of Hydrogen iodide. Apparatus required Large test tube ; corks ; cork borers ; elbow tubes as used in Ex. 1 1 ; Bunsen's holder ; wooden blocks ; two small gas bottles ; one large do. ; two cylindrical gas jars, 20 x 5 cm. ; glass disc ; taper on wire. Potassium iodide; strong hydrogen sulphate; red phosphorus ; iodine ; litmus paper ; bleaching powder ; strong hydrogen chloride. This substance cannot be obtained in a pure condilion by a reaction analogous to that by which hydrogen chloride was obtained, viz. by decomposing potassium iodide by strong hydrogen sulphate ; since part of the hydrogen iodide is itself decomposed by the hydrogen sulphate *, and iodine set free. To illustrate this place a few crystals of potassium iodide in a test-tube, pour on them some strong hydrogen sulphate, and heat gently. A gas will be given off which forms white fumes in the air, like hydrogen chloride, but it will be mixed with violet vapours of iodine. Hence to prepare the gas recourse is usually had to the action of water on phosphorus tri-iodide. This is of the fol- lowing nature, the iodine combines with half the hydrogen in 1 Thus: Hydrogen Hydrogen Hydrogen w Iodi iodide. sulphate. sulphite. 2 HI + H 2 SO 4 = H 2 SO 3 + H 2 O + I 2 Observe that this reaction is the reverse of what takes place when cold solutions of iodine and hydrogen sulphite are mixed together. IODIDES. 2O7 three molecules of water, while the phosphorus together with the rest of the hydrogen and the oxygen form hydrogen phos- phite (phosphorus acid) l . It has been already seen (p. 72) that phosphorus unites readily with iodine, but with a violence which is not easy to control. Hence it is best to use the modification of phosphorus called ' red ' or ' amorphous ' phosphorus, the affinities of which are much less strong than those of ordinary Fig- 58- phosphorus. In any case, however, the process requires care ; and strict attention must be paid to the directions given. Take a large test-tube, about 2*5 cm. in diameter and 16 or 1 8 cm. in length ; adapt to it a cork fitted with an elbow tube and right-angled delivery tube connected by a cork joint, such as was used in the preparation of carbon dioxide, p. 155, and support it in an inclined position in a Bunsen's holder thus, Fig. 58. H 3 P0 3 . 208 IODIDES. Weigh out half a gramme Of red phosphorus in powder 1 , and transfer it to the test-tube. Pour upon it i c.c. (not more) of water, and then (having previously placed a beaker of cold water within reach,) add 6 grms. of iodine, and mix the whole by shaking the tube, cooling it as soon as the action begins by dipping it into the beaker of water. The iodine acts on the phosphorus readily but not violently if the temperature is kept down, arid the water decomposes the phosphorus tri-iodide, as above explained. We thus obtain a very strong solution of hydrogen iodide, from which the gas will be given off abundantly when it is very gently heated. Replace the cork with delivery tube, and re-adjust the ap- paratus in the holder, placing under the end of the delivery tube a small gas bottle covered with a card. Now heat the mixture in the test-tube very carefully with a lamp ; the gas will soon begin to pass over into the bottle, and from its very high density (4^ times that of air) it may most readily be collected by downward displacement, its position in the bottle being tested, as in the case of hydrogen chloride, by a lighted taper. Two small bottles and one cylindrical gas jar should be filled with the gas, the flame of the lamp being just waved under the test- tube if the evolution of gas becomes slow. The unstable nature of the gas will be at once noticed ; a slight deposit of iodine will be found in the bottles, even if kept only for a short time ; and vapours of iodine will be seen whenever the lighted taper is immersed in the gas. In most other respects hydrogen iodide strongly resembles hydrogen chloride, and the following properties of the gas may be examined in exactly the same manner as the corresponding properties of hydrogen chloride described in Ex. 21. p. 191, which should be referred to for the details of the experiments. 1. Its pungent smell and the white fumes it produces in moist air. 1 It is usually sold in a state of powder. If however you have obtained it in lumps, it must be ground with care to a coarse powder in a mortar, covering it with water while crushing it with the pestle, in case any small particles of ordinary phosphorus may be present which might inflame by the friction and set the whole mass on fire ; then pour off" the water and transfer the moist powder to the test-tube. IODIDES. 209 2. Its extremely high density. 3. Its acid reaction on litmus 1 . 4. Its relation to combustion. 5. Its solubility in water. *6. Its decomposition by chlorine. This reaction serves to distinguish it from hydrogen chloride, and also illustrates well the relative affinities of chlorine and iodine for hydrogen. Place a large wide-mouthed gas bottle on a sheet of white paper before you. Pour into the bottle a little hydrogen iodide from one of the small bottles, then make 'a little chlorine by pouring a few drops of strong hydrogen chloride upon a little bleaching powder in a test-tube, and pour some of the gas (by inclining the tube) into the large bottle containing the hydrogen iodide. Violet clouds of iodine will be formed when the gases mix ; the chlorine, from its stronger affinity, combining with the hydrogen and liberating iodine 2 . [After the experiment, wash out the test-tube containing the chlorine with plenty of water, that the gas may not escape un- necessarily into the room.] Tests for iodides. [A solution of potassium iodide containing i grm. of the pure colourless salt 3 dissolved in 30 c.c. of water may be used.] 1. They are, with few exceptions, decomposed by hydrogen sulphate. This has been already shown in a previous expt., p. 206. *2. They give a pale yellow precipitate, insoluble in am- monia, when tested with silver nitrate. 1 It will be noticed that a brown deposit of iodine is formed on the litmus and that the colour of the latter is eventually destroyed, although iodine has by no means the same strong bleaching powers as chlorine and bromine. 2 2HI + C1 2 = 2HC1 + I 2 . 3 Potassium iodide is very apt to decompose on keeping, especially if exposed to the light, or if it contains any potassium iodate, becoming yellow owing to liberation of iodine. 210 IODIDES. Pour a few drops of the' solution of potassium iodide into a test-tube, dilute with water, and add one or two drops of solution of silver nitrate. A yellow precipitate of silver iodide will form, which should be divided into two portions. To the one add some dilute hydrogen nitrate, which will fail to dissolve it; to the other add excess of ammonia, which will also fail to dissolve it ; as may be proved by pouring off some of the clear liquid and adding to this some dilute hydrogen nitrate which will produce no precipitate. *3. They are decomposed by many oxidising agents, with liberation of iodine. (a) Add one drop of solution of chlorine to a very dilute solution of potassium iodide (about 3 drops of the solution to 10 c.c. of water). Iodine will be liberated and will colour the solution yellow. On addition of 2 or 3 c.c. of solution of starch, the characteristic deep blue compound will be formed. Now add some stronger chlorine water, and notice that the starch reaction will entirely disappear, owing to the formation of a colourless iodine chloride which does not act upon starch. Hence in applying this test it is important not to use an excess of chlorine. It is, in fact, best not to use chlorine at all for the purpose of liberating iodine, but hydrogen nitrite, as de- scribed in the next experiment. () Add a few drops of dilute hydrogen sulphate to a very dilute (see last experiment) solution of potassium iodide, and then a drop of a recently-made solution of potassium nitrite. This will decompose the hydrogen iodide formed by the action of the hydrogen sulphate, and liberate iodine (see p. 141). Shake up the yellow solution with a little carbon disulphide, and allow it to stand for a minute. The carbon disulphide will be found to have withdrawn the iodine from the solution, collect- ing into a deep purple globule at the bottom of the tube. [It will be well to repeat the similar experiment with potassium bromide, given at p. 203, and compare the colours of the two globules, the bromine imparting a bright orange, the iodine a fine purple colour to the carbon disulphide. Notice also that potassium nitrite will not decompose hydrogen bromide, but that chlorine water must be used for the purpose. If an excess of strong solution of chlorine is FLUORIDES. 211 added to the contents of both tubes, and the mixture shaken and again allowed to settle, the globule containing iodine will be found to have lost its colour, while the globule containing bromine remains unchanged.] 28. FLUORIDES. [Typical examples, Hydrogen fluoride (HF). Calcium fluoride (GaF 2 ).] We have in this case to deal with the compounds of an element which has itself never been isolated ; its affinities being so strong that chemists have only succeeded in transferring it from one combination to another. Its most important compound is hydrogen fluoride, a sub- stance having many analogies to hydrogen chloride, and obtained, like the latter, by the action of a strong acid on other fluorides such as calcium fluoride (fluor spar). *Formation of Hydrogen fluoride, and its action upon glass. * Take a small cup of lead or platinum (a leaden ink-well answers perfectly) 1 and put into it as much powdered fluor spar as will lie on the end of a spatula. Obtain a piece of sheet glass about 6 cm. square, warm it gradually before the fire or over a lamp, and when it is thoroughly hot, rub over it a piece of bees'-wax (or the end of a wax-candle) and incline the plate in different directions, so that the melted wax may run over it and form an even coating. Set it up edgeways to cool, on a piece of rjaper, and then place it with the coated side upwards on the table, and trace on it with a pointed piece of wood (a match cut like a pencil answers very well) any letters or device which may occur to you, taking cafe that the lines are drawn quite through the wax so as to expose the bare 1 A cup of lead may be made by turning up the edges of a circular piece of thin sheet lead about 7 or 8 cm. in diameter. It should be placed in a mortar just large enough to hold it, and moulded into shape by strong pres- sure with the pestle. P 2 212 FLUORIDES. glass. Pour a little strong hydrogen sulphate upon the fluor spar in the leaden dish, mix the two thoroughly by stirring with a glass rod (which should be washed immediately afterwards) and cover the dish with the piece of glass, the coated side being downwards. Heat the dish very gently by placing it on some warm sand, and leave it for a short time undisturbed, taking especial care not to use so much heat as to melt the wax. The hydrogen sulphate will decompose the fluor spar, forming calcium sulphate, while gaseous hydrogen fluoride will be evolved 1 , which will act upon the glass where it is unprotected by the wax. In about ten minutes the glass may be removed from the dish ; the pungency and the acid reaction on litmus paper of the fumes of hydrogen fluoride should be noticed, and the contents of the dish washed away at once, in order that the glass bottles in the room may not be damaged. The wax may be removed from the glass by warming the glass and rubbing it with a cloth, and the device will be found deeply and per- manently etched into the glass. In the above reaction one of the chief products formed is silicon tetrafluoride, resulting from the union of the silicon of the glass with fluorine. This gas is very readily decom- posed by water, with formation of silicon hydrate (silica), which appears as a white crust on the glass if the action is carried very far. The preparation and properties of this substance will be more fully described under SILICATES, but its formation may be illustrated on a small scale by placing a finely powdered mixture of equal parts of fluor spar and glass or fine sand in a leaden dish, adding some strong hydrogen sulphate, heating gently, and covering the dish with a bit of glass on the centre of which a drop of water has been deposited. The drop will soon become coated with a film of silica, owing to the de- composition of the silicon fluoride by moisture. Before proceeding further it will be advisable to gain some more experience in analysis; taking, as before, single salts 1 CaF 2 + H 2 S0 4 = CaS0 4+2 HF. SULPHUR. of an alkali-metal (such as sodium) united with one of the radicles already treated of, and examining each of them for the latter constituent. A short course, including all the radicles hitherto examined, is given in Appendix C. 29. SULPHUB. [Formula of molecule, S 2 Weight of molecule, 64 hydrogen atoms.] Sulphur is usually obtained from volcanic districts where it is found ' native ' or uncombined ; but large quantities of it are also procured from iron pyrites, a very common mineral, which consists of iron united with sulphur. When this is heated (air being excluded) it gives off one-third of the sulphur it con- tains, as the following experiment will show. Powder a small fragment of iron pyrites in a porcelain mortar and place it in an ignition tube. Heat it to redness in the lamp-flame, and notice that a sublimate of sulphur is formed in yellowish-brown drops in the cool part of the tube. It may be proved to be sulphur by cutting off the sealed end of the tube (which may be effected by touching it while still hot with a drop of water) and heating the sublimate gently while the tube is held obliquely so that a current of air may rise through it. The sulphur will be oxidised to sulphur dioxide, (the gas formed by burning sulphur in oxygen, p. 102) which may be recognised by its odour and by its acid reaction on a piece of moist blue litmus-paper held at the upper end of the tube. Allotropic forms of Sulphur. An account of these will be found in any text-book on chemistry ; the following experiments will illustrate the modes of preparing them. 1. S a (octahedral sulphur). This is the most stable form, and the one in which sulphur nearly always crystallises from solutions of it. 214 SULPHUR. Fig. 59- Place about a gramme of ' flowers of sulphur ' in a dry test-tube, and pour over them about 5 c.c. of carbon disul- phide. Leave the tube, loosely corked, in a beaker of water for a few minutes, shaking it occasionally. Care must be taken that there is no lighted lamp or fire near at hand, on account of the inflammability of the carbon disulphide. There will be a residue left, not necessarily because there is not sufficient disul- phide to dissolve the substance, but because the flowers of sulphur consist of two varieties of the element, of which one only is soluble in carbon disulphide. Filter the fluid quickly into another tube, through an ordinary paper filter (which must be perfectly dry). Pour about 2 c.c. of the solution into a watch-glass, and leave it on the table to evaporate. The carbon disulphide, from its great volatility, will quickly pass off, and small transparent crystals of sulphur will be formed and rapidly increase in size. They may be easily recognised, especially if a magnifier is used, to be right rhombic octohedra, Fig. 59. 2. Sp (prismatic sulphur). This is the form in which sulphur is obtained by crystallisation from a melted state. Place some pieces of roll sulphur or flowers of sulphur in an evaporating dish 1 , and heat it gently on a sandbath over a lamp until the sulphur is just melted. Allow it to cool until a crust has just begun to form on its surface ; then, taking up the dish, pour out the portion which is still fluid into a large dry test-tube (for use in the next ex- periment). The interior of the dish will be found lined with needle-shaped transparent crystals, Fig. 60, which are referred to the oblique prismatic system, a system totally distinct from that to which the crystals obtained Fig. 60. 1 The experiment is best made on a rather larger scale, a common clay crucible about 10 cm. in height being used instead of the dish. SULPHUR. 215 from solution in experiment i belong, viz. the right prismatic, Fig. 59. In a few days the prismatic crystals lose their trans- parency, and are spontaneously converted into aggregations of minute octohedra. 3. S y (plastic sulphur). This is the most remarkable form of the three, and is obtained by the action of heat upon ordinary sulphur. Take the large test-tube containing the sulphur poured off from the crystals in the last experiment, add a little more sulphur and support it on a piece of wire gauze in the retort stand, resting it in the smallest retort ring. Lay a cork loosely on its mouth (to prevent entrance of air) and heat it, gently at first, by an Argand burner. While it is being gently heated, fill a jug with cold water, and place in it mouth downwards a large funnel. The sulphur will first melt to a clear pale- yellow fluid, almost as mobile as water. Pour a few drops of it into some water in a dish : it will solidify into the usual yellow, brittle mass. Heat the remainder more strongly ; as the tem- perature rises higher it will darken in colour and become thicker and thicker, until it has so far lost its fluidity that the test-tube may be inverted for a moment without spilling any of it. When the heat is further raised it becomes again fluid, but not so much so as at first. When it has reached this point, take hold of the test-tube with a cloth, or paper holder (p. 60, note), and pour its contents in a thin stream into the cold water, round the stem of the funnel. By being thus suddenly cooled, the sulphur will be preserved in the allotropic condition into which it has been converted by heat, and on lifting the funnel out of the water, the threads of sulphur which surround it will be found to be semi-transparent, soft, almost as elastic as india-rubber, and scarcely soluble in carbon disul- phide. If the residue in the test-tube be watched as it cools, it will be seen to undergo the same changes as when it was being heated, but in a reverse order, becoming thick, then losing its dark colour and becoming fluid again, and finally solidifying to a yellow, crystalline, brittle mass. It is only when the tem- perature has been raised nearly to its boiling-point that the SULPHIDES. above modification, called ' plastic sulphur,' is obtained. The elastic threads should be dried with a cloth, and put aside in a bottle. In a few days they will be found to have lost both their transparency and their plasticity, (being, in fact, recon- verted into the ordinary form,) but will still be in a great mea- sure insoluble in carbon disulphide. Combination of sulphur with metals. An experiment showing that sulphur will when heated com- bine with copper has already been tried, p. 73. It will also combine with iron, but a higher temperature is required. Mix about 2 grms. of iron filings with an equal weight of sulphur, and heat it strongly in a small test-tube. The sulphur will melt again and finally boil, filling the lower part of the tube with its dark yellow vapour. When the bottom of the tube becomes redhot, a bright glow will spread through the iron filings as the metal combines with the sulphur (just as it did with oxygen, p. 103,) to form iron protosulphide. Allow the tube to cool, and keep the bronze-coloured residue for use in the next exercise (p. 217), 30. SULPHIDES. [Typical examples, Hydrogen sulphide (H 2 S). Iron protosulphide (FeS).] Preparation of Hydrogen sulphide. This gas is so extremely poisonous and offensive in smell that all experiments with it must be made in a draught cup- board, or in the open air. The best method of getting rid of any of the gas which escapes into the room is to place a little bleaching powder on a plate and add a few drops of dilute hydrogen chloride. This will liberate chlorine, as already explained, which will diffuse into the air and decompose the hydrogen sulphide. Do not, however, add too much acid SULPHIDES. 217 to the bleaching powder, lest the remedy should prove less endurable than the evil it is intended to cure. Hydrogen sulphide is obtained by the action of acids on many sulphides ; the hydrogen of the acid uniting with the sulphur at the moment of its liberation. Iron protosulphide (the substance you lately obtained by the union of iron with sulphur) is, on the whole the most convenient for the purpose. Take the test-tube containing the iron protosulphide made in the last experiment (p. 216) and detach the substance from it by an iron wire (this will probably result in breaking the tube, since the substance becomes fused into the glass by the heat evolved in its formation). Powder the lump of iron sulphide and put it into a moderate-sized test-tube, to which should be fitted by a cork a short bit of glass tubing about 4 or 5 mm. in diameter (which answers better than a smaller jet). Pour 4 or 5 c.c. of dilute hydrogen chloride upon the iron sul- phide, and immediately fit the cork into its place and support the test-tube upright resting in the smallest ring of the retort stand in a draught cupboard. Hydrogen sulphide will be at once given off with effervescence : the action being an ordinary double decomposition, iron sulphide and hydrogen chloride giving iron chloride and hydrogen sulphide 1 . The following properties of the gas may be examined : *1. Its extremely fetid smeU, like that of rotten eggs. These, in fact, give off the gas ; since they contain sulphur which unites with hydrogen during the process of decay. 2. Its acid reaction on litmus paper. Hold a bit of wetted litmus paper close to the tube from which the gas is issuing. It will be reddened, but not very strongly. 3. Its inflammability. Apply a light to the end of the tube. The gas will catch fire and burn with a blue flame, uniting with the oxygen of the air to form water and sulphur dioxide 2 . To prove this, hold a small dry gas bottle over the flame: moisture will be de- 1 FeS+2HCL = FeCl,+ H 2 S. 2 2H a S + 3O 2 = 2H a O+2SO a . 2l8 SULPHIDES. posited on it, and the presence of sulphur dioxide in it will be proved by its characteristic odour, and the strong acid reaction shown when a piece of blue litmus paper is put into the bottle. *4. Its action on compounds of lead, turning them black. Pour a drop of solution of lead acetate upon a bit of white blotting paper and hold it in the stream of gas issuing from the tube. It will immediately turn black, owing to the formation of lead sulphide. This is the most delicate test for the presence of hydrogen sulphide, and will serve, for instance, to detect the presence of traces of it in ordinary coal gas. 5. Its solubility in water. The method of making the solution of hydrogen sulphide for use in the laboratory is given below ; and in the following experiments a solution of the gas, and not the gas itself, may be conveniently used. 6. Its action upon other radicles forming sulphides. The chief use of it in the laboratory depends on this pro- perty, since the sulphides thus formed are often of very characteristic colours. To illustrate this, take dilute solutions of the following metal- salts (3 or 4 drops of the ordinary laboratory solution to 5 c.c. of water), and add to each several drops of solution of hydrogen sulphide. (a) Copper sulphate. A black precipitate will be formed, of copper sulphide. (V) Arsenic chloride 1 . A yellow precipitate will be formed. (c] Zinc sulphate. A white precipitate will be formed. 7. Its decomposition by chlorine, and other oxidising agents. (a) Add a few drops of solution of chlorine to some solution of hydrogen sulphide and heat it. A white milky precipitate of sulphur will be formed, the chlorine having united with the hydrogen and liberated the sulphur. A solution of bleaching powder will act in a similar way, and 1 This may be made by dissolving a very small quantity of arsenic tri- oxide (white arsenic) .in a few drops of hydrogen chloride. SULPHIDES. this illustrates its action as a 'disinfectant* in destroying the hydrogen sulphide which is evolved from putrefying organic substances. () Add to another portion of the solution of hydrogen sulphide a few drops of strong hydrogen nitrate, and warm it gently. A precipitate of sulphur will be formed in this case also, since the oxygen of the acid unites with the hydrogen of the gas. Hence we learn that in the course of an analysis hydrogen sulphide should never be added to solutions which contain much free hydrogen nitrate. Similarly, the solution of the gas is decomposed by the oxygen of air; and hence it is best to keep it in a closely- corked bottle, inverted in a glass of water. Tests for Sulphides. *1. They are, in general, decomposed by acids, giving off hydrogen sulphide. (a) Add a few drops of dilute hydrogen sulphate to a little solution of ammonium sulphide, and warm the mixture. Hy- drogen sulphide will be given off, and may be recognised by its odour and its action on a strip of blotting paper moistened with a drop of solution of lead acetate. Moreover, if the solution of ammonium sulphide has been made some time and has become yellow, a white, milky precipitate of sulphur will be produced \ We learn from this that ammonium sulphide (a test very com- monly employed in the laboratory) should never be added to a solution containing a free acid. (b} Add 2 or 3 c.c. of strong hydrogen chloride to a small quantity of antimony sulphide. No decomposition will in this case take place until the liquid is boiled, when hydrogen sulphide will be given off, and may be recognised in the usual 1 The reason is, that ammonium protosulphide slowly absorbs oxygen from the air, forming ammonia, water, and sulphur, 2(H 4 N) 2 S = 4 H 3 N + 2H 2 O + S 2 ; and the latter combines with another portion of the sulphide to form ammonium disulphide, from which it is separated when an acid is added. 220 SULPHIDES. way. This is a process which is sometimes used with ad- vantage for obtaining the gas. *2. They are decomposed by fusion with potassium hydrate. Powder in a porcelain mortar a small bit (about the size of a pea) of iron protosulphide or iron pyrites ; add a bit of potassium hydrate 1 about the same size, and grind the whole together. Fill the bulb of an ignition tube with the mixture, and heat it to redness for half a minute. The potassium hydrate will decompose the iron sulphide, with formation of potassium sulphide. Before it cools dip the bulb into a little water in an evaporating dish, when it will crack to pieces and the potassium sulphide will dissolve in the water. The presence of a sulphide in the solution may be proved by the blackening which takes place when a drop of the liquid is put upon a clean silver coin, or a piece of blotting paper moistened with lead acetate. This is the best way of detecting the presence of a sulphide in minerals such as galena (lead sulphide), blende (zinc sul- phide), or the golden yellow scales which often occur in coal, and which are iron persulphide ; and the experiment should be tried with at least one of the above. 3. Their solutions give a black precipitate when tested with silver nitrate. Dilute 2 or 3 drops of solution of ammonium sulphide with 5 c.c. of water and add a drop of solution of silver nitrate. A black precipitate of silver sulphide will be formed, which will not dissolve on addition of dilute hydrogen nitrate. Additional Experiment. Preparation of solution of Hydrogen sulphide. Adapt sound corks to two bottles with moderately wide mouths, holding about 200 c.c. Prepare (if not already at hand) four elbow tubes of glass tubing about 5 mm. in diameter : two of them with branches of equal length, about 6 cm. ; the other two with unequal branches, the shorter about 6 cm., the longer about 18 cm. in length, 1 Sodium carbonate will also answer the purpose, but the temperature required for the decomposition is higher. SULPHIDES. 221 or of sufficient length to reach, when fitted into the cork, nearly to the bottom of the bottle. Bore two holes in each cork and fit into it one long and one short elbow tube. Fit up a flask with funnel and elbow tube, similar to that used in Ex. 13. Place in it about 20 grms. of iron protosulphide, previously broken up with a hammer into lumps about as large as peas. Pour into the flask enough water to cover the iron sulphide, and fill the bottles about three-fourths full of distilled water ; replace the corks L.J.F. Fig. 61. and connect the tubes, as shown in Fig. 61, with short pieces of india-rubber tubing, so that the gas may bubble through the water in each bottle successively. [The above apparatus will serve for general use when a liquid is to be saturated with a gas. It will be necessary in some cases, and indeed not inexpedient in all, to interpose a small wash-bottle con- taining a little water between the generating flask and the first bottle, for the purpose of retaining any acid or other impurities which may come over with the gas. This bottle may be supported 222 SULPHIDES. upon a glass (or wooden) disc placed on one of the rings of the retort-stand, as shown in the figure. It will also be usually necessary to provide some means of getting rid of any 'excess of gas which may escape absorption by the water. This may be done best by putting the whole apparatus in a draught cupboard or by attaching to the elbow tube proceeding from the last bottle a long tube passing through the window or, better, into a chimney or stove-flue ; or, the gas may be led to the bottom of a tall jar filled with lumps of pumice or charcoal, moistened with a solution of caustic soda. One or other of these methods should always be employed when dealing with such injurious gases as hydrogen sulphide or chlorine.] Having ascertained that the joints are tight, pour into the flask a little strong hydrogen chloride. The evolution of hydrogen sul- phide commences without the application of heat (although some little time may elapse before the action begins), and, if the stream is not too rapid, the greater part of the gas is absorbed by the water in the bottles. You will observe, however, that some gas passes through the water unabsorbed. This consists mainly of hydrogen, the evolution of which is due to the presence of uncombined iron in the sample of iron sulphide. When a steady stream of hydrogen sulphide has passed through the bottles for five or six minutes, disconnect the first bottle, and connect the other directly with the flask. Ascertain whether the water is saturated with the gas, in the following way. Take out the cork and tubes, close the bottle tightly with the thumb or palm of the hand, and shake it briskly for a few seconds in order to bring the water thoroughly in contact with the gas. Hold the bottle in a slanting position with its mouth downwards, and relax the pressure of the hand, noticing whether any bubbles of air enter the bottle, or whether on the contrary the liquid is forced outwards. In the latter case the water is fully saturated with the gas ; in the former case the bottle must be again connected with the flask as at first, and more gas passed through it. When no more gas is absorbed by the water in the first bottle, it may be withdrawn, and a little more gas passed through the water in the second bottle, which is already partially saturated by the excess of gas which has passed through the first bottle. The whole of the solution should then be poured into a larger bottle, which should be kept, well corked, in an inverted position, resting in the angle at the corner of a shelf, or in a tumbler or test-glass half full of water. SULPHUR DIOXIDE. Finally, take the apparatus to pieces, at once, in the open air, and throw away the contents of the flask, washing it out thoroughly with water. COMPOUNDS OF SULPHUR AND OXYGEN. 31. SULPHUR DIOXIDE. [Formula of molecule, SO 2 . Weight of molecule, 64 hydrogen-atoms.] Apparatus required Flask, elbow-tubes, &c., used in Ex. n. p. 155; one large and three small gas bottles ; taper on wire ; glass disc ; deflagrating jar and cup ; basin of water ; small strips of sheet copper ; strong hydrogen sulphate ; blue litmus-paper ; solution of logwood ; a few flowers, such as violets or pansies. Sulphur dioxide is the product invariably formed by synthesis when sulphur is burnt in oxygen or air, as seen already, p. 102. It is, however, usually prepared by a process of analysis ; viz. by the action of mercury or copper upon hydrogen sulphate. The chemical change is analogous to that which occurs when copper acts upon hydrogen nitrate (p. 142), hydrogen being first displaced from the acid by the metal, and this 'nascent' hydrogen acting upon another molecule of the acid taking away some of its oxygen with formation of sulphur dioxide and water 1 . The gas is very soluble in water, and should therefore be collected by displacement, which, from its great density, may be readily accomplished. It is very corrosive and poisonous, and hence it should be prepared and all experiments made with it in a draught cupboard. Arrange an apparatus similar to that used in preparing carbon dioxide 2 . Place in the flask about 10 or 12 small strips of sheet copper 3 , add 60 c.c. of strong common hydrogen sul- 1 Cu + 2 H 2 SO 4 = Cu SO 4 + 2 H 2 O + SO 2 . 8 It is advisable, though not necessary, to interpose a small wash-bottle containing a little water, to retain any spray of acid which may come over. 3 It is slightly preferable to use about 20 grms. of mercury instead of the copper, as the action is more regular ; but the expense is greater. 224 SULPHUR DIOXIDE phate, and heat cautiously. 'The action scarcely commences until the boiling point of the acid is reached (about 320 C.) and the gas is rendered cloudy at first by particles of the acid which are thrown up as spray ; these, however, soon subside, and their presence will not interfere with the experiments. Collect one large and three small bottles of the gas, using a lighted taper, as in the case of hydrogen chloride, to ascertain when the bottles are full. [Reserve the large bottle for use in Exercise 34.] The following properties of sulphur dioxide may now be examined ; *1. Its suffocating odour will have been already sufficiently noticed. 2. Its high density, more than twice that of air. 3. Its relation to combustion. These two properties may be illustrated as in the case of hydrogen chloride, by placing a lighted taper in an empty gas jar, and pouring sulphur dioxide upon it. *4. Its solubility in water, forming an acid. Replace the stopper of a bottle of the gas by a glass plate, invert it, and withdraw the plate under water in the supple- mentary pan of the pneumatic trough (or a basin). On shaking the bottle so as to wet the sides, the gas will be readily, though not suddenly, absorbed. In this case, as already noticed, p. 103, an acid, hydrogen sulphite, is formed \ as may be proved by dipping a piece of blue litmus paper into the solution. 5. Its combination with metallic oxides or hydrates to form sulphites. Pour 10 c.c. of solution of potassium hydrate into a bottle of the gas, inserting a strip of paper between the neck and the stopper, and shake up the solution with the gas. Combination will readily take place, and the odour of the gas will entirely disappear, potassium sulphite being formed 2 . *6. Its bleaching action on organic colours. (a) Take 20 c.c. of a rather dilute solution of logwood or 1 S0 2 +H 2 = H 2 S0 3 . 2 SO 2 +2KHO = K 2 SO 3 + H 2 O. SULPHITES. 225 cochineal, or of the dye known as ' magenta ' (made by boiling a little of the substance in water for a few minutes) ; pour about half of it into a bottle of sulphur dioxide, reserving the other half in the tube for comparison, put a strip of paper between the neck and the stopper, and shake the bottle for half a minute : then pour out the liquid into a test tube. It will have nearly or quite lost its colour. (ti) Put a deflagrating jar on a plate containing a little water, and place in it some flowers, such as roses, violets and pansies. Heat a little sulphur in a deflagrating cup, until it begins to burn in air, then place it in the jar. The sulphur dioxide pro- duced will more or less quickly take away the colours from the flowers; the reds and the blues being soon bleached while the greens resist a prolonged action of the gas. It does not, however, discharge the colour so completely as chlorine, and if the flowers are dipped in very dilute hydrogen sulphate, and left for some hours, their colour will be in most cases restored. 32. SULPHITES. [Typical examples, Hydrogen sulphite (H 2 SO 3 .) Sodium sulphite (Na 2 SO 3 ). A solution of sodium sulphite (freshly made) containing i grm. of the salt in 40 c.c. of water may be used.] *1. They give off sulphur dioxide when acted on by acids. Add a few drops of strong hydrogen sulphate to a little of the solution of sodium sulphite placed in a test-tube, and warm the mixture. Sulphur dioxide will be given off, and may be recognised by its smell. If a slip of paper moistened with solution of lead acetate is held within the tube it will not be altered in colour. 2. They give up oxygen when acted on by nascent hydro- gen, forming hydrogen sulphide. Pour 5 or 6 c.c. of dilute hydrogen sulphate upon a bit of granulated zinc in a test-tube; hydrogen will, of course, be given off. Now add a drop (not more) of solution of sodium Q 226" HYPOSULPHITES. sulphite, and test the escaping gas with moist lead acetate paper, which will be blackened. The hydrogen has decomposed the hydrogen sulphite (formed by double decomposition when the sodium sulphite was added to the acid), with formation of water and hydrogen sulphide l . *3. Their solutions readily absorb more oxygen, with forma- tion of sulphates. This property renders hydrogen sulphite one of the most useful reducing agents for laboratory use: but solutions of sulphites cannot be kept long unchanged since they absorb oxygen from the air. (a) To some of the solution of sodium sulphite add a drop or two of solution of silver nitrate. A white precipitate of silver sulphite will be formed, which will on being warmed turn gray owing to reduction of the silver to the metallic state : part of it being deposited as a bright mirror on the sides of the tube. (Z>) Acidify a little of a very dilute solution of potassium iodide with hydrogen chloride, and add one drop of chlorine water, or of solution of potassium nitrite in order to liberate iodine, which, on addition of some solution of starch, will give a deep blue solution (p. 205). Add to this a few drops of solution of sodium sulphite; the solution will immediately become colourless, showing that the iodine has entered into combination. The change really consists in the decomposition of water ; its oxygen uniting with the hydrogen sulphite, while its hydrogen unites with the iodine to form hydrogen iodide 2 . 33. HYPOSULPHITES. [Typical example, Sodium hyposulphite (Na 3 S 2 O 8 ). A solution of sodium hyposulphite containing i grm. of the salt in 20 c.c. of water may be used.] These are of importance, both in volumetric analysis and in photography. A reference to the formula will show that the 2 I 2 + H 2 + H 2 S0 3 = 2 HI + H 3 S0 4 . HYPOS ULPHITES. 227 molecule of a hyposulphite only differs from that of a sulphite in containing one atom more of sulphur. This addition is easily effected by digesting sulphur for some time with a solu- tion of a sulphite. *1. They are decomposed by heat, giving off sulphur. Heat a small quantity of crystallised sodium hyposulphite in an ignition tube. It will fuse and give off water of crystallisa- tion (which should be absorbed by a twisted strip of blotting- paper) ; and finally a yellow sublimate of sulphur will form in the tube. *2. They are decomposed by acids, giving off sulphur dioxide and depositing sulphur. Add to a portion of the solution of sodium hyposulphite a few drops of strong hydrogen sulphate, and warm gently. Sulphur dioxide will be given off (recognisable by its smell, &c.) and a milky deposit of sulphur will be formed. (Compare the reaction of sulphites, Expt. i, in the last exercise, in which no deposit of sulphur was formed.) - . *3. Their solutions readily absorb more oxygen. This property (which renders them of great use in volumetric analysis, especially as their solutions are much more stable than those of sulphites) may be illustrated by adding a few drops of a solution of sodium hyposulphite to a solution containing free iodine made as in Expt. 3 b of the last exercise. The colour will disappear, as in the case of sulphites, and for a similar reason. *4. They give a white precipitate, quickly turning black, when tested, with silver nitrate. To another portion of the solution add some solution of silver nitrate. A precipitate is produced (soluble in excess of the hyposulphite), which is at the first moment white, but rapidly becomes yellow, brown, and finally black. These changes are due to the instability of the silver hyposulphite which is first precipitated; in presence of water it is rapidly converted into silver sulphide 1 . 5. Their solutions dissolve many compounds of silver. This is due to their tendency to form double salts of silver 1 Ag 2 S 2 3 + H 2 = Ag 2 S+H 2 S0 3 . Q 2 228 SULPHATES. which are soluble in water. IFor instance, Form a little silver chloride by mixing a few drops of solutions of silver nitrate and ammonium chloride, wash it twice by decantation, then pour upon it some solution of sodium hyposulphite. This will form silver hyposulphite, which will unite with more of the sodium hyposulphite to form a double salt, sodium-and-silver hypo- sulphite, which dissolves readily in water. (The use of the hyposulphites in photography will be illustrated under SILVER.) 34. SULPHATES. [Typical examples, Hydrogen sulphate (H 2 SO 4 ). Sodium sulphate (Na 2 SO 4 ). Calcium sulphate (CaSO 4 ).] 1. Hydrogen sulphate. The details of the English process for making hydrogen sulphate will be found in the text-books on general chemistry. The principle of the process may be illustrated on a small scale as follows : Take the bottle of sulphur dioxide reserved in Ex. 31, pour into it 2 or 3 drops of strong hydrogen nitrate, and shake it so as to wet the sides. Orange vapours will be formed, consisting of nitrogen tetroxide ; the sulphur dioxide taking away oxygen from the hydrogen nitrate to form hydrogen sulphate and the lower nitrogen oxide 1 . If the sulphur dioxide is moderately free from moisture, part of it unites with hydrogen nitrate to form a white crystalline substance, and this when shaken up with 2 or 3 c.c. of water is decomposed into hydrogen sulphate and nitrogen tetroxide, as above. [In actual practice a large excess of sulphur dioxide is used and this reduces the nitrogen tetroxide still further, viz. to nitrogen dioxide, which latter (as has been proved, p. 144) combines readily with the oxygen of the air to form the tetroxide. And it is easy to see that, if more sulphur dioxide and water are supplied, the 1 2 HNO 8 + SO 2 = H 2 SO, + N 2 O 4 . SULPHATES. 229 nitrogen tetroxide would be again reduced to the dioxide, more hydrogen sulphate being formed. Thus by continually supplying sulphur dioxide water and air to a small quantity of hydrogen nitrate, an indefinitely large quantity of hydrogen sulphate may be produced.] The solution in the bottle should be examined by adding to it a drop of solution of barium chloride to prove that a sul- phate has really been formed ; if so, a white precipitate will be obtained (see Expt. i, p. 230). Properties of Hydrogen sulphate. 1. Its high density (1.84). This has been already examined, p. 49. 2. Its strong acid reaction. Put a single drop of hydrogen sulphate into 100 c.c. of water, and observe that even this extremely dilute solution reddens litmus paper. 3. Its intense affinity for water. This is shown by the heat evolved when the acid is diluted with water, which will have been sufficiently observed already (see pp. 132, 185). Owing to this property it decomposes many organic sub- stances which contain the elements of water, combining with the latter and separating carbon, as the following experiments will show. (a) Dissolve sufficient white sugar (about 3 ordinary lumps) in 20 c.c. of water to form a syrup, place it in a beaker stand- ing on a plate, add to it an equal volume of strong common hydrogen sulphate, and stir the mixture. It will become hot and blacken, and will finally swell up into a porous pasty mass of charcoal. Sugar is a combination of carbon with hydrogen and oxygen, the two latter being present in the proportions in which they form water, and hydrogen sulphate combines with these latter, leaving the carbon. (b) Dip the end of a glass rod into dilute hydrogen sulphate (the ordinary laboratory solution), and draw letters with it upon 230 SULPHATES. a piece of writing paper ; then dry the paper by holding it before a fire, or at a little distance above a lamp. The acid, as it becomes concentrated, will act upon the paper (which is of nearly the same chemical constitution as sugar) in the manner above explained, and the letters will appear in black, owing to the separation of carbon. 4. Its action on substances, forming sulphates. Several illustrations of this will have been noticed already in the course of work; for instance, its action on zinc (p. 104), on potassium nitrate (p. 133), on sodium chloride (p. 184). One other example of its action may be noticed, viz. its action on metal-oxides, which is applied to the preparation of numerous salts. Put a little copper oxide into a test tube, add 2 or 3 c.c. of water, and then the same volume of hydrogen sulphate, and heat it to boiling over a lamp. The copper oxide will dissolve, copper sulphate and water being formed 1 . If the blue solu- tion is concentrated by evaporation in the usual way (p. 55), crystals of copper sulphate (blue vitriol) will be obtained. Tests for sulphates. [A solution of calcium sulphate (the ordinary laboratory solution), although it is scarcely stronger than lime water, will answer for the following tests.] *1. They give a white precipitate, insoluble in acids, when tested with barium chloride. Add to a portion of the solution of calcium sulphate a drop or two of solution of barium chloride. A white precipitate of barium sulphate will be formed (even in this weak solution) which will not dissolve on the addition of a little strong hydrogen chloride, even on boiling the mixture. This is the most delicate and characteristic test for sulphates. *2. They give a white precipitate when tested with lead acetate. 2 SO 4 PHOSPHORUS. 23 1 Test another portion of the solution with a drop or two of solution of lead acetate. A white precipitate of lead sulphate will be formed, nearly insoluble in cold dilute hydrogen chloride, but decomposed and dissolved by it on boiling. *3. They are decomposed when heated with carbon, forming sulphides. Mix together a very little calcium sulphate (plaster of Paris) with about twice as much sodium carbonate in a mortar ; place some of the finely-powdered mixture in a cavity made in a piece of charcoal (see p. 90), and heat it strongly in the reducing blowpipe- flame for about a minute. The calcium sulphate will thus be reduced to sulphide \ and this is decomposed by the sodium carbonate, forming sodium sulphide. When it is cool, detach the ignited mass from the charcoal, place it in a test- tube, and pour on it a little dilute hydrogen chloride. The presence of a sulphide will be shown by the evolution of hydrogen sulphide, recognisable by its smell and the blacken- ing of a piece of blotting-paper moistened with solution of lead acetate. 35. PHOSPHORUS. [Formula of molecule, P 4 . Weight of molecule, 124 hydrogen-atoms.] [It is hardly necessary to repeat that whenever phosphorus is to be used for an experiment, it must be handled with the greatest care, owing to the low temperature at which it catches fire. It should be cut under water and should never be touched by the fingers when dry ; a pair of crucible tongs being used to transfer it from one place to another. In cutting it, not even the smallest piece should be allowed to get under the nails or to remain upon the table or floor. All residues, after the experiments are over, should be covered with water until they can be thrown away in a safe place. A jug of water should always be at hand, in case the phosphorus should, in spite of precautions, catch fire 2 .] 1 CaSO 4 + C 2 = CaS+aCO 2 . 2 As the burns produced by phosphorus are usually severe and slow to heal, it may be worth mentioning that lint soaked in water containing a 232 PHOSPHORUS. The properties of phosphorus which can be safely tried are the following : 1. It readily dissolves in carbon disulphide. Place about 2 c.c. of carbon disulphide in a test-tube, add a small fragment of dry phosphorus about half the size of a pea, and cork the tube. Leave it to digest for a few minutes, until wanted for use in Expt. 3, shaking it occasionally to pro- mote the solution of the phosphorus. 2. It melts easily (at 44) and catches fire when heated slightly above its melting point. Place a very small fragment of phosphorus (not larger than a grain of wheat), carefully dried by blotting-paper, on a watch- glass, and float it on hot water in a basin. The phosphorus will melt and inflame spontaneously, giving off white fumes of phosphorus pentoxide, and leaving a small residue consisting of ' red' phosphorus, an allotropic form of the element. 3. It inflames spontaneously in air -when in a finely divided condition. Pour the clear solution obtained in Expt. i upon a piece of blotting-paper placed in a plate (best in a draught cupboard). The phosphorus will, as the carbon disulphide evaporates, be left in a state of fine division upon the paper; it will emit white fumes, and appear faintly luminous in the dark, and will shortly catch fire and burn away. The paper itself will be found to be only superficially charred, owing to the protective action of the phosphorus pentoxide formed. 4. It reduces many metals from their salts. Place a small bit of phosphorus in a test-tube, pour on it about i c.c. of solution of silver nitrate, and leave it undis- turbed for a few hours. A bright crystalline coating of metallic silver will be formed on the phosphorus, the latter having de- composed the nitrate owing to its affinity for oxygen, while the metal is separated. ' Red ' or ' amorphous ' phosphorus, the allotropic form ob- little common washing soda is the best application at first. After the hydrogen phosphate is by this means neutralised, nothing is better than lint soaked in a mixture of equal volumes of glycerine and water, the whole being covered with oilskin to prevent evaporation. HYPOPHOSPHITES. 233 tained by the long-continued action of heat on ordinary phos- phorus, differs remarkably from the latter, especially in having much less strong chemical affinities. Thus, Put a little red phosphorus on a watch-glass floating on nearly boiling water, as. in Expt. 2. It will not melt or catch fire, or show any alteration. If, however, it is touched with a red-hot wire, it will inflame, burning with the same bright light, and emitting the same white fumes of the pentoxide as ordinary phosphorus. It is, in fact, reconverted into the ordinary transparent form by a high temperature, as may be proved in the following way : Place a little red phosphorus in an ignition-tube, connect the outer end of the tube by an india-rubber connector with a glass jet (the object being to check admission of air), and heat the phosphorus very carefully over a lamp. It will sub- lime without previously melting, and will condense in the cooler part of the tube in amber-coloured transparent drops, which are easily recognised as being ordinary phosphorus. COMPOUNDS OF PHOSPHORUS WITH HYDROGEN AND OXYGEN. 36. HYDROGEN PHOSPHIDE. [Formula of molecule, H 3 P. Weight of molecule, 34 hydrogen-atoms.] 37. HYPOPHOSPHITES. [Typical example, Potassium hypophosphite (KH 2 PO 2 ).] Both hydrogen phosphide and potassium hypophosphite are formed by heating phosphorus with a solution of potassium hydrate. In this case the water is decomposed; part of its 234 HYPOPHOSPHITES. hydrogen unites with some 1 phosphorus to form hydrogen phosphide, while the rest of the hydrogen together with the oxygen unites with potassium and phosphorus to form potas- sium hypophosphite l . The following experiment in illustration of this must be made in a draught-cupboard or in the open air, since hydrogen phos- phide is not only an extremely poisonous and offensive-smelling gas, but also spontaneously inflammable. Put some solution of potassium hydrate (5 grms. dissolved in 20 c.c. of water) into a small beaker, add a piece of phosphorus about as large as a pea, and heat the solution nearly, but not quite, to boiling on a sand bath. Hydrogen phosphide will be given off, as above explained, and each bubble as it reaches the surface of the liquid will catch fire spontaneously, combining with the oxygen of the air, and forming a white smoke-wreath of hydrogen phosphate 2 . After allowing the action to go on for about half an hour, set the beaker aside (in the draught- cupboard) to cool. When it is quite cool, decant the contents into a test-tube, and imme- diately fill up the beaker with water, to prevent the remaining phosphorus catching fire before it can be thrown away. Add to the solution of potassium hypophosphite enough dilute hydro- gen sulphate to render it slightly acid to test paper (this will cause a white precipitate of potassium sulphate which should be filtered off), and use it for the following experiment, which illustrates one of the chief characteristics of hypophosphites, viz. * Their reducing action on copper salts. Add to a portion of the solution a few drops of solution of copper sulphate, and heat the mixture gradually to boiling. A greenish-yellow turbidity will soon appear, rapidly changing to a dull red precipitate of metallic copper. This reaction serves to distinguish hypophosphites from phosphites and phosphates, neither of which latter reduce copper salts. The yellow substance formed at first is copper PHOSPHATES. 235 hydride, and is one of the few examples of the combination of a metal with hydrogen 1 . 38. PHOSPHORUS PEBTTOXIDE. [Formula of molecule, P 2 O 5 . Weight of molecule, 142 hydrogen-atoms.] 39. PHOSPHATES. [Typical examples, Hydrogen phosphate (H 3 PO 4 ). Sodium, phosphate (Na 3 PO 4 ). Sodium and hydrogen phosphate (Na 2 HPO 4 ). Sodium-ammonium-and- ) /vr /TT X 7\ TJTJ^ \ > (i>a (nuM i njrw4.i hydrogen phosphate ) Phosphorus pentoxide is always produced when phosphorus is burnt in a full supply of oxygen or air. It has an extremely strong affinity for water ; so much so that it cannot be exposed for even a few minutes to ordinary air without combining with the moisture present and becoming liquid. The substance thus formed is hydrogen phosphate (ordinary 'phosphoric acid'), and from it other phosphates can be obtained in the usual ways. For instance, by addition of just sufficient sodium carbonate to neutralise it, part of the hydrogen is replaced by sodium, and thus sodium and hydrogen phosphate (com- mon ' phosphate of soda ') is obtained. In illustration of these facts, Place a small piece (about twice as large as a pea) of carefully dried phosphorus upon a plate : set fire to it with a match, and cover it with a deflagrating jar, slightly tilted by a short bit of glass rod or tube placed under its lower edge? so as to allow free access of air. The stopper should be laid across the mouth in order to check the upward draught, which would carry off a portion of the product. Dense white fumes of phosphorus pentoxide will be formed, and will be deposited partly on the sides of the jar, partly on the plate. Remove the a SO 4 + 2Cu a H a . 336 PHOSPHA TES. jar and scrape together, with a spatula, the snow-white powder on the plate. Pour a few drops of water upon it; it will hiss like a red-hot iron from the intensity of the combination, and a solution of hydrogen phosphate will be formed. A piece of blue litmus-paper dipped into the solution will be at once reddened. Notice also that the phosphorus pentoxide depo- sited on the sides of the jar will, after a few minutes exposure to the air, deliquesce into an oily liquid. From its affinity for water, which has been thus illustrated, phosphorus pentoxide is one of the most efficient substances for drying gases. Rinse the contents of the jar and the plate into a porcelain dish, and evaporate it until the liquid becomes syrupy, then add a little more water, and boil the solution again for a short time ; finally filter it, heat the greater portion of the nitrate again in the dish (reserving a little, to be added in case too much sodium car- bonate may be inadvertently mixed with the rest) and add solution of sodium carbonate to the hot liquid, until the ad- dition of it no longer produces effervescence and the liquid is neutral to test-paper. You have thus obtained a solution of sodium-and-hydrogen orthophosphate, which may be examined by tests 2 and 3. Properties of Orthophosphates. [A solution of sodium-and-hydrogen phosphate, containing 3.5 grms. of the salt dissolved in 50 c.c. of water, may be used.] *1. They give a white precipitate, soluble in hydrogen acetate, when tested with calcium sulphate. Add to a little of the solution of sodium-and-hydrogen phos- phate about half its volume of solution of calcium sulphate. A white precipitate of calcium phosphate will be formed, which will readily dissolve on addition of a little hydrogen acetate (this distinguishes it from calcium oxalate, p. 176). *2. They give a yellow precipitate when warmed with excess of a strongly acid solution of ammonium molybdate. Pour some solution of ammonium molybdate, acidified with hydrogen nitrate, into a test-tube, and add a drop or two of the PHOSPHATES. 237 solution of sodium phosphate. The solution will become yel- low, and on warming it (it should not be boiled) a yellow precipitate will fall. This is an extremely delicate and characteristic test for phosphates, if properly used. The precautions necessary in applying it are, (a) the solution of ammonium molybdate must be used in excess, (<5) it must be strongly acid, (c) it should not be heated to boiling, otherwise a precipitate of hydrogen molyb- date is liable to form. *3. They give a white crystalline precipitate when tested with magnesium sulphate, in presence of ammonium salts. To another portion of the solution of sodium phosphate add one-fourth its volume of solution of ammonium chloride, then a little ammonia, and test it with a drop of solution of magnesium sulphate. A white crystalline precipitate of magnesium and ammonium phosphate will be formed, which will readily dissolve in dilute hydrogen nitrate. 4. They give a yellow precipitate, soluble in hydrogen nitrate, when tested with silver nitrate. To another portion add a drop of solution of silver nitrate. A canary-yellow precipitate of silver phosphate will be formed. Pour off one half of the fluid in which the precipitate is suspended into another test-tube, and add a few drops of dilute hydrogen nitrate; to the remaining half add the same quantity of ammonia; in both cases the precipitate will be redissolved. *5. They give a yellowish white precipitate, insoluble in acetates, when tested with iron perchloride. Add to another portion of the solution about one-third its volume of solution of sodium acetate J and then one drop (not more) of solution of iron perchloride. A dull white precipitate of iron phosphate will be produced, which will dissolve when excess of iron perchloride is added (hence the reason for only adding a little at first). This reaction is important, since it enables us to decompose, 1 If this is not at hand, a little potassium acetate (made by adding a slight excess of hydrogen acetate to about 2 c.c. of solution of potassium hydrate) will do quite as well. 238 PHOSPHATES. in the course of an analysis, Certain phosphates (such as those of barium, strontium, and calcium) which are soluble in an acid, but are reprecipitated unchanged when the solution is neu- tralised. Additional experiments. The action of phosphorus pentoxide on water is not very simple. A molecule of it may combine with i, 2, or 3 molecules of water forming three distinct acids, hydrogen metaphosphate, hydrogen pyrophosphate, and hydrogen orthophosphate *, from each of which series of salts are derivable, having very different properties. For a full account of these a general text-book must be consulted ; it will be sufficient to observe here that the salts examined above belong to the series of orthophosphates, and that from them pyro- phosphates and metaphosphates can be obtained by selecting a salt from which it is possible to drive off just the requisite quantity of the elements of water by heat. Pyrophosphates. [Typical example, Sodium pyrophosphate (Na 4 P 2 O 7 ).] Sodium pyrophosphate is obtained by heating the ordinary sodium- and-hydrogen orthophosphate, with which experiments were made just now. When strongly heated, two molecules of this latter salt give off one molecule of water, leaving a residue of the pyro- phosphate. Place a few crystals of the salt in a platinum capsule, or in a cup of platinum foil made as directed, p. 8, and heat it gently at first, afterwards to redness. The salt will melt and give off its water of crystallisation, and at a higher temperature two molecules of it will give off one molecule of water, leaving a white earthy-looking residue consisting of sodium pyrophosphate 2 . This should be powdered, dissolved in about 40 c.c. of cold water, and examined by tests 3 and 4 in exactly the same way as directed in the case of the orthophosphate. The following results should be obtained : 3. No precipitate will be obtained (if enough solution of ammonium chloride has been added) : but on warming the liquid a white precipitate of magnesium pyrophosphate will fall. 1 P 2 O S + H 2 O = 2HPO 3 , Hydrogen metaphosphate. P 2 O B + 2 H 2 O = H 4 P 2 O 7 , Hydrogen pyrophosphate. P 2 O 6 +3H 2 O = 2H 3 PO 4 , Hydrogen orthophosphate. 2 2Na 2 HP0 4 = H 2 + Na 4 P 2 7 . PHOSPHATES. 239 4. A perfectly white granular precipitate of silver pyro- phosphate will be obtained, soluble in hydrogen nitrate and ammonia. Metaphosphates. [Typical example, Sodium metaphosphate (NaPO 3 ).] To obtain this it is necessary to drive off a larger amount of the elements of water from an orthophosphate, and hence a salt must be selected which contains more hydrogen as a basic radicle, and less of a non-volatile radicle, such as sodium. Such a salt is sodium-ammonium-and-hydrogen phosphate, or microcosmic salt, the formula of which has been given already, p. 235. Heat a little of this salt in a platinum cup, exactly as directed in the preparation of the pyrophosphate. The substance froths up very much, and gives off ammonia and water J ; finally a transparent, glassy residue of sodium metaphosphate will be left. This should be powdered, dissolved in 50 c.c. of cold water, and examined by tests 3 and 4 as above. 3. No precipitate ; if enough ammonium chloride has been added. 4. A white precipitate, soluble in hydrogen nitrate and ammonia. It will be seen that these results scarcely distinguish meta- phosphates from pyrophosphates, but the following test is highly characteristic of the metaphosphates ; viz. their property of co- agulating albumen (white of egg). Add to some of the solution of sodium metaphosphate 6 or 8 drops of hydrogen acetate, and then a few drops of a clear solution of albumen. A white precipitate of coagulated albumen will form at once. Conversion of hydrogen metaphosphate and pyrophosphate into the orthophosphate. This change is easily effected by boiling either of them with water; the additional amount of water being quickly taken up. To illustrate this, Add a few drops of hydrogen nitrate to some of the solution either of sodium pyrophosphate or of sodium metaphosphate (this 1 Na(H 4 N)HP0 4 = 240 -B ORATES. will liberate the corresponding 1 acid), and boil for ten minutes in a beaker. Hydrogen orthophosphate will be reproduced, as may be proved by neutralising the solution with sodium carbonate and examining it by tests 3 and 4. 40. EQUATES. [Typical examples, Hydrogen borate (H 3 BO,). Sodium diborate (Na a B 4 O T ).] These are almost the only compounds of boron which are commonly met with. They are related to boron trioxide, which may be obtained from them, as the following experiment will show. Make a concentrated solution of sodium diborate (borax) by boiling about 8 grms. of the crystals with 10 c.c. of water in a test-tube until no more is dissolved. Pour off the warm solution from the crystals, add about half its volume of strong hydrogen chloride, and cool the mixture by holding it in a stream of water. Shining scales of hydrogen borate will be precipitated, which may be separated by nitration from the solution of sodium chloride, and left to drain on a porous tile 1 . Meanwhile the other experiments may be proceeded with. When the hydrogen borate is moderately dry, place a little of it on a piece of platinum foil formed into a cup (p. 8) and heat it over a lamp. It will fuse, give off water, and leave a clear, glassy residue of boron trioxide. Tests for borates. [A solution of sodium diborate, containing 1.5 grm. of the salt in 20 c.c. of water, may be used.] *1. They give a white precipitate, soluble in ammonium chloride, when tested with calcium sulphate. 1 This is often a useful method of drying substances, the solution being quickly drawn by capillary action into the pores of the tile. After use, the tile should be soaked for some time in several changes of water, and then dried in an'oven. SILICON DIOXIDE. 241 Add to a portion of the solution of sodium diborate about half its volume of solution of calcium sulphate. A white preci- pitate of calcium borate will be formed, which will readily dissolve on addition of a little solution of ammonium chloride (resembling calcium tartrate, p. 174, in this respect). *2. They impart a green colour to flame. This cannot well be observed in the presence of volatile substances, such as sodium, which themselves impart a colour to flame. Hence in applying the test, hydrogen sulphate must be first added, to retain such substances in a less volatile con- dition than the hydrogen borate produced by double decom- position. Place about i c.c. of the solution of sodium diborate in a porcelain dish, mix it with a few drops of strong hydrogen sulphate, then add about three times the volume of common alcohol, stir the mixture with a glass rod and set fire to it. The edges of the flame will be tinged yellowish green, owing to the presence of hydrogen borate, liberated by the action of the hydrogen sulphate, and volatilised in the alcohol vapour. *3. Their solutions, when rendered acid, tinge turmeric paper red. Place a little solution of sodium diborate in a watch-glass, and add enough hydrogen chloride to make the solution give an acid reaction to test-paper. Dip into the solution one-half of a slip of turmeric-paper, and dry it at a gentle heat, by holding it before the fire; the dipped portion will be coloured red. If a drop of solution of sodium carbonate be placed on the reddened portion of the turmeric-paper, the -colour will be changed to bluish-black. [For experiments illustrating the use of borax in blowpipe work, see pp. 92, 93.] Li 1 ^. 243 SILICATES ' 41. SILICON DIOXIDE. [Formula of molecule, Si O 2 . Weight of molecule, 60 hydrogen-atoms.] 42. SILICATES. [Typical examples, Hydrogen silicate (H 2 SiO 3 ). Sodium silicate (Na 2 SiO 3 ). Aluminium silicate (Al 2 Si 2 O 7 ).] A very large number of minerals consist of or contain these compounds of silicon, and they are often difficult to decompose and identify. A few are acted on by strong hydrogen chloride, which separates hydrogen silicate as a gelatinous precipitate and combines with the basic radicle to form a chloride. But the great majority of silicates are best decomposed by fusion with excess of sodium carbonate, which forms sodium silicate by double decomposition, while the basic radicle is converted into a carbonate or oxide. Preparation of Sodium silicate. To prepare this, any one of the numerous forms of silicon dioxide, such as flint 1 or white sand, may be strongly heated with sodium carbonate. In this action, the silicon dioxide simply takes the place of carbon dioxide, which latter gas escapes with effervescence 2 . (a) Make a ring, as described in p. 92, at the end of a piece of platinum wire ; moisten it with water, dip it into some powdered sodium carbonate, and fuse the adhering salt in the hottest part of the blowpipe flame. It will give a bead which 1 If flint or quartz is to be used, it should be previously heated to full redness in a fire and quickly dropped into water. It will then form an opaque white mass, which can be more easily pulverised 2 Na a CO 3 + SiO 2 = Na 2 SiO 3 SILICATES. 243 is clear while hot, but opaque when cold. Now add to this bead some finely powdered white sand or flint (silica), and again heat it to fusion; an effervescence will take place, owing to the liberation of carbon dioxide, as above explained. You will, when enough silica has been added, obtain a bead which re- tains its transparency when cold. A sodium silicate, such as you have here obtained, is the basis of ordinary glass ; and if the bead is dipped into solution of cobalt nitrate and again strongly heated, it will be coloured blue, illustrating the mode in which various colours are im- parted to glass by fusion with the oxides of certain metals. (b) Although ordinary glass is practically insoluble in water, yet if excess of an alkali is used in preparing it, the resulting silicate dissolves without difficulty in water; forming, in fact, the ' soluble glass ' which is now much used in varnishes and paints. Grind about i grm. of flint (previously ignited, see note, p. 242) or of white sand to an extremely fine powder in a porcelain mortar, add to it about 4 grms. of sodium carbonate 1 , and grind the whole thoroughly together. Put some of the mixture (about enough to half fill it) into a platinum capsule or a piece of platinum foil formed into a cup, and heat it to full redness over a gas blowpipe. It is an advantage to lay over the capsule a bit of platinum foil as a cover, in order to check loss of heat by radiation. When the mass ceases to swell up (owing to evolution of carbon dioxide as above explained) add some more of the mixture, and heat again until all action is over, and a fused glassy residue remains in the capsule. This should, when cool, be detached from the capsule (which may generally be done by pouring a little water into the capsule and boiling it rather quickly over a lamp), and ground with a little water in a mortar, then transferred to a beaker and boiled for some time with about 20 c.c. of water. It should almost entirely dissolve, if the fusion has been properly effected ; and 1 It is preferable to use a mixture of potassium and sodium carbonates (2.6 grms. of potassium carbonate with 2 grms. of sodium carbonate) if it is at hand ; since this mixture fuses at a much lower temperature than sodium carbonate. R 2 244 SILICA TES. the solution of sodium silicate may be used for some of the following experiments. Tests for Silicates. *1. They are, in some cases, decomposed by strong acids, giving a gelatinous precipitate of hydrogen silicate. (a) Add a few drops of hydrogen chloride to a portion of the solution of sodium silicate, obtained in the last experiment. A dense gelatinous precipitate will be formed, and if the solu- tion of sodium silicate is strong the whole will appear to solidify. (i) Repeat the last experiment, using a much less strong solution of sodium silicate (about 5 or 6 drops of the original solution mixed with 5 c. c. of water). In this case no precipi- tate will be formed. Now add a little of the clear liquid to some solution of ammonium chloride mixed with one-fourth its volume of solution of ammonia, and apply heat. A gelatinous precipitate will now be formed ; since hydrogen silicate, though soluble in water under certain conditions, is quite insoluble in solution of ammonium chloride. Hence in testing for silicates, the acidified solution should always be added to a mixture of ammonium chloride and ammonia, and heated, before deciding that no silicate is present. . *2. They are decomposed by fusion with sodium carbonate. This will usually be found the best way of dealing with in- soluble silicates, even though they may be slowly decomposed by acids. Grind a small bit of slate or earthenware to very fine powder in a mortar, mix it intimately with about 4 times its weight of sodium carbonate, and fuse the mixture in a platinum cup precisely as directed above, in the preparation of sodium sili- cate. After detaching the fused mass from the crucible, and grinding it with a little water in a mortar, transfer it to a porce- lain dish, add about 10 c.c. of dilute hydrogen chloride, and evaporate the whole to perfect dryness on the sandbath. The hydrogen silicate which is separated by the action of the hydro- SILICA TES. 245 gen chloride, gives off water when heated above 100, with formation of silicon dioxide which is quite insoluble in water and acids. Continue the heat, stirring the residue until it loses all gelatinous appearance; then add 10 or 12 drops of strong hydrogen chloride and incorporate it with the residue by gentle rubbing with a pestle. By this treatment all the basic radicles (such as aluminium, iron, &c.) are converted into chlorides, while the silicon dioxide remains unaltered. Lastly, warm the residue with a little water, and pour the whole on a filter. The filtrate will contain .aluminium, &c. as chlorides, and need not now be regarded. The white residue on the filter consists of silicon dioxide, and should, after being washed (until the filtrate is no longer acid), be tested as follows ; (a) Boil a portion of it with a little solution of potassium hydrate. It will dissolve pretty readily. (K) Test another portion in a bead of microcosmic salt, as directed in the next experiment. It will float in the bead undissolved. *3. They are decomposed when heated in a bead of micro- cosmic salt, silicon dioxide being formed which floats un- dissolved. Make a bead of microcosmic salt (sodium-ammonium-and- hydrogen phosphate) in the same way as a borax bead, p. 92 \ When a perfectly clear bead (of sodium metaphosphate, p. 239) is obtained, add to it a very minute quantity of powdered porcelain, slate, or brick, and heat it for half a minute as strongly as possible. The substance will be decomposed, and a white, semitransparent residue of silicon dioxide will be seen floating in the clear globule. It will be best to examine this with a magnifier while the bead is hot, since in many cases it becomes turbid when cold. 1 This requires rather more care than in making a borax bead, since microcosmic salt becomes so liquid during its decomposition that it is apt to drop off the ring. It should be heated gently at first, until the white fumes of ammonia have gone off, and the ring should be held so that its plane is horizontal, not vertical, in the flame. 246 SILICA TES. Additional experiment. Preparation of Hydrogen silicofluoride. [Formula of molecule, H 2 SiF.] The reaction by which this substance (also known as 'hydro- fluosilicic acid ') is formed, viz. the decomposition of silicon fluoride by water, has been tried on a small scale already, p. 212. A solution of it may now be made on a larger scale, since it is occasionally used as a test for barium, and moreover the process illustrates a good method of acting upon difficultly decomposable silicates, and of obtaining pure silica. Apparatus required Florence flask ; glass tubing, 7 or 8 mm. in dia- meter ; corks ; cork-borers ; fish-tail burner ; argand burner ; retort- stand ; wire-gauze ; gas jar, 20 x 5 cm. ; tube-funnel ; funnel, 10 cm. in diameter; filter, or circular piece of linen, about 20 cm. in diameter; bottle, holding 200 c.c.; test-tube; fluorspar; sand; hydrogen sulphate; mercury ; strontium nitrate ; barium chloride ; distilled water, Take a piece of glass tubing about 60 cm. long, and of rather larger internal diameter than the ordinary gas delivery tube. Having slightly rounded the ends in the gas-flame, bend it twice to a right angle in the same direction, making the first bend about 10 cm. from one end, and the second about 30 cm. from the other end, so as to give the tube the following shape, n . The end of the longer branch should be bevelled off, or notched with a file, to enable the bubbles of gas to escape more freely. Select a Florence flask of stout glass (since it is liable to be corroded by the hydrogen fluoride, and will soon give way if the bottom is thin), fit the shorter branch of the delivery tube to it, by a perforated cork, and support it in the retort-stand with a piece of wire-gauze under it. Place under the outer extremity of the delivery tube a cylindrical gas jar containing a stratum of mercury about 1 2 mm. deep, into which the end of the delivery tube must dip. This stratum of mercury is quite essential, since it acts as a valve and prevents the entry of water into the tube, which would then soon be obstructed by the silica which is one of the products of the decomposition of the silicon fluoride. SILICATES. 247 Reduce 10 grms. of fluor spar to a coarse powder in the mortar, mix it intimately with twice its weight of powdered glass or fine sand (that which is called ' silver sand ' is the best), and transfer the mixture to the flask. Pour on it through a funnel 60 c,c. of strong hydrogen sulphate, and shake the whole with a circular motion until it is thoroughly incorporated. Replace the cork and delivery tube, and after seeing that the end of the latter is completely covered by the mercury, fill up the jar or test-glass with distilled water, pouring it gently down the sides of the vessel so that none may enter the delivery tube through a disturbance of the surface of the mercury. Heat the flask very slowly with an argand burner or spirit lamp. The reaction between the fluor spar and the acid requires only a moderate temperature, and if too much heat be applied, the mixture froths up inconveniently, and may pass over into the water *. When the gas begins to come over, each bubble as it emerges from the mercury becomes coated with a film of silica, which is left behind when the bubble reaches the surface of the water, as a shrunken, collapsed bag 2 . Increase the heat slightly if the stream of silicon fluoride becomes slow, and continue it until no more gas comes over 8 : then loosen the cork and take the delivery tube quickly out of the solution by raising the retort-stand, and filter the liquid from the gelatinous silica through a paper, or more conveniently, a fine linen filter; care being taken that none of the mercury falls on the filter. [The silica thus obtained is very pure, and hence may be worth the trouble of washing, an operation which takes some time, and must be done very thoroughly. After a final rinse with warm water, the filter containing the silica may be left to dry, either spontaneously or in a hot-air cupboard.] It is best to keep the solution of the acid, not in glass, but in a gutta-percha bottle, since the former is always acted upon to a certain extent. Before using it as a test for barium, examine it by the two following tests, to make sure that it contains no hydrogen sulphate, which may have been carried over mechanically, if the action has proceeded too rapidly. SiO 2 +2H 2 SO 4 = 2 CaSO 4 + 2 H 2 O + SiF 4 . 3 Do not, however, apply a strong heat, or hydrogen sulphate may distil over, and render the solution useless for analytical purposes. If a strong solution of hydrogen silicofluoride be wanted, it is a good plan to set up another similar apparatus, with a delivery tube leading into the same jar of water. The time necessary to obtain the required solution is thus dimi- nished by one half. 248 SILICA TES. (a) Dissolve a few small crystals of strontium nitrate in 10 c.c. of water, and add to the clear solution about 5 c.c. of the acid which you have prepared. If a precipitate or turbidity is produced immediately, or within a few minutes, hydrogen sulphate is present. (b) If the result of the above test is satisfactory, add a few drops of the acid to a little solution of barium chloride in a test tube. An immediate crystalline precipitate should be produced; otherwise the solution of the acid is not sufficiently strong, and should have more silicon fluoride passed through it, in the manner above described. [The student is recommended, before passing on to the study of the different metals, to refer to the account of the course of analysis given at the commencement of Part II, and to practise himself in the analysis of single salts containing some one of the foregoing non -metallic radicles associated with an alkali-metal.] SECTION III. PREPARATION AND EXAMINATION OF THE PROPERTIES OF THE PRINCIPAL METALLIC RADICLES AND THEIR COMPOUNDS. Group 1. Metals which are separated from solutions by Hydrogen chloride 1 . SILVER, MERCURY, LEAD 2 . 1. SILVER. [Symbol of atom, Ag (argentum). Weight of atom, 108 hydrogen-atoms.] [Liquids containing silver, such as the mother liquor from the crystals of silver nitrate and the residues from the following experi- ments, should on no account be thrown away, but reserved in a bottle labelled ' Silver Residues V It must be borne in mind that solutions of silver salts, if allowed to touch the skin or clothes, stain it black. The quickest way of removing these stains is to moisten them first with a solution of potassium iodide, and then with strong solution of potassium cyanide. Great care must, however, be taken in using the latter, as it is very poisonous : all traces of it should be washed away as soon as it has removed the stains.] Preparation of silver nitrate from an alloy such as silver coin. The English silver coinage consists of silver alloyed with about one-thirteenth its weight of copper. This alloy dissolves 1 For an account of the principle on which the metals are classified into groups, see Part II. Sect. i. 2 Mercury is only thus separated when in the monatomic condition. Lead is only partially separated, since lead chloride is not quite insoluble in water. 3 For the method of recovering the silver from these residues, see Ap- pendix B. 250 SILVER. readily in hydrogen nitrate, but the silver alone is precipitated as chloride when hydrogen chloride is added to the solution. Place a small silver coin in a large test-tube, pour on it 8 or 10 c.c. of concentrated hydrogen nitrate, and warm the tube very gently on a sand-bath. A strong action will commence, and nitrogen oxides will be evolved, the fumes of which should not be allowed to escape into the room 1 . In a short time a clear bluish green solution will be formed, containing silver nitrate and copper nitrate. Dilute the solution with four or five times its volume of water, and add about 10 c.c. of com- mon hydrogen chloride. The silver will be completely pre- cipitated as chloride, while the copper chloride, being soluble in water, remains in the liquid. Close the mouth of the tube and shake it for a few seconds : the suspended silver chloride will then separate in curdy masses, and after adding a few more drops of hydrogen chloride to make sure that the precipitation is complete, the liquid may be poured off. The precipitate should next be thoroughly washed on a filter with several changes of water, until the liquid which runs through the filter ceases to redden blue litmus-paper. While the last portions of water are draining off, take a strip of sheet zinc about i cm. broad and 12 or 14 cm. long, cover its surface with a thin film of mercury 2 by immersing it for a minute in an acid solution of mercury perchloride (2 c.c. of the ordinary laboratory solution with 20 c.c. of water and 5 c.c. of dilute hydrogen sulphate), and then wash it with clean water. Transfer the silver chloride to a large test-tube, rinsing it through a hole made in the filter : then fill the tube half full of water, add about 5 c.c. of dilute hydrogen sulphate, and put in the strip of zinc, taking care that it comes closely into contact with the mass of silver chloride at the bottom of the tube. A galvanic action will be set up, and 1 The action is similar to that of hydrogen nitrate on copper in the pre- paration of nitrogen dioxide (see p. 142). 3 Ag 2 + 8 H NO 3 = 6 AgNO 3 + 4 H 2 O + N 2 O 2 . 2 This is advisable, though not absolutely necessary, since it prevents ' local action ' (see under ZINC) and avoids the separation of the particles of carbon, lead, &c. which always occur in ordinary zinc, and are rather difficult to separate from the reduced silver. SILVER. 251 the hydrogen liberated in contact with the silver chloride will combine with the chlorine and thus the silver will be separated in the metallic state as a fine black powder, which, as the mole- cules aggregate together into larger masses, will become of a light brown, or gray. In about half an hour the reduction will be complete, and the zinc may then be taken out, and the liquid (which contains hydrogen chloride, as may be proved by testing a small portion of it with silver nitrate) poured off from the spongy mass of reduced silver. Wash the latter thoroughly by decantation, (breaking up the lumps by stirring with a glass rod,) boiling it with several successive changes of water, until the washings are no longer acid to test-paper. Lastly, after pouring off the water, add a little strong hydrogen nitrate, a few drops at a time, and warm the mixture ; the metal will readily dissolve, forming silver nitrate. The solution should be filtered (if necessary) after addition of a little water to prevent action on the filter-paper, and then evaporated to the crystallising- point, and left to cool. Flat rhombic crystals of silver nitrate will be formed, which should be placed in a funnel (the neck being partially obstructed by a bit of broken glass or porcelain to prevent the crystals falling through), slightly washed by pouring a little water over them to remove adhering acid, and left to drain and dry. Tests for Silver salts. [A solution of silver nitrate containing i grm. of the salt in 30 c.c. of water may be used.] ^ *1. With hydrogen chloride they give a white precipitate, soluble in ammonia. Put 2 or 3 drops (not more, in order that the delicacy of the test may be observed) of the solution of silver nitrate into a test-tube, dilute with 5 or 6 c.c. of water, and add a drop or two of dilute hydrogen chloride. A white, curdy precipitate of silver chloride will be produced, quickly subsiding if shaken, and turning gray (owing to its reduction) when exposed to daylight. 352 SILVER. (a) Pour Off half the liquid containing the precipitate in suspension into another tube, add a little strong hydrogen chloride and a drop or two of hydrogen nitrate (so as to form aqua regia) and boil the mixture. The precipitate will not dis- solve or be altered in any way (being thus distinguished from the precipitate of mercury protochloride, p. 263). (d) To the remaining portion add solution of ammonium hydrate, which will readily dissolve it. If excess of dilute hydrogen nitrate is added to the clear solution, silver chloride will be re-precipitated. *2. With potassium chr ornate they give a crimson preci- pitate. Add to another portion of the solution a drop or two of solution of potassium chromate. A dark crimson precipitate of silver chromate will be formed, readily soluble in dilute hydrogen nitrate. *3. Reduced on charcoal before the blowpipe, they yield a brilliant metallic globule, but no incrustation. Powder a small crystal (no larger than a grain of wheat) of silver nitrate, mix it intimately in the mortar with about twice as much sodium carbonate ; then place some of the mixture in a cavity cut in a piece of charcoal (see p. 90), and heat it strongly in the blowpipe flame, as directed, p. 92. Bright globules of metallic silver will be formed, which may with a little care be fused together into one mass. This will remain untarnished in the oxidising flame, and no incrustation will be formed on the cooler parts of the charcoal, since silver has but little tendency to unite with oxygen \ Reduction of Silver salts. Some methods of effecting this have been already described ; e. g. by nascent hydrogen, p. 251, and by sodium carbonate in the experiment last made. The following processes are also of great practical importance. 1 The slight white ash which charcoal leaves when burnt, must not be mistaken for an incrustation of a metal-oxide. SILVER. 253 1. By organic substances. (a) Draw letters on a piece of paper with a glass rod dipped in a solution of silver nitrate, and heat the paper in front of a fire, or at some distance above the flame of an argand burner, until it is nearly hot enough to become scorched. The letters will appear in an indelible black ; the hydrogen and carbon having decomposed the salt, combining with its oxygen, while metallic silver is separated, and adheres closely to the fibre of the paper. This illustrates the use of marking ink, which is simply a solution of silver nitrate thickened with gum. It also explains why silver salts stain the skin black. (<$) Tartrates (as seen already, p. 174) and some other or- ganic salts, readily reduce silver from its combinations; the action being in general similar to that of the paper in the ex- periment just made. Mirrors for telescopes are thus covered with a firm deposit of silver which will even bear careful polishing. Place some very dilute solution of ammonium hydrate (2 drops of the ordinary laboratory solution in 5 c.c. of water) in a test-tube, and add solution of silver nitrate, a few drops at a time, shaking the mixture after each addition. A brown precipitate of silver oxide will be formed, which will at first redissolve readily ; but finally a point will be reached when the addition of a drop of silver nitrate will cause a permanent turbidity. Now add to this slightly turbid liquid a drop of solution of sodium-and-hydrogen tartrate, mix thoroughly, and warm it by placing the tube in a jug or beaker of hot water. The liquid will turn black, and a brilliant film of metallic silver will be deposited on the sides of the tube. A watch-glass may be silvered in a similar way by first cleaning it thoroughly with a few drops of solution of potas- sium hydrate, and rinsing it with several portions of distilled water; then embedding it in sand, filling it with the solution made as above directed (or, better, of twice the strength) and heating the sand very slowly. A fairly good convex mirror may be thus obtained; and a concave one may be made by 254 SILVER. floating a watch-glass upon the surface of the solution, warmed in a porcelain dish. 2. By the action of light. It has been already noticed that silver chloride becomes dark in colour when exposed to light. This is due to the separa- tion of the silver and chlorine, first a subchloride and then metallic silver being produced. The reduction takes place much more readily when organic matter and a large excess of silver nitrate are present: the liberated chlorine then forms more silver chloride from the nitrate, which is reduced in its turn, and thus a black of considerable intensity is produced. This is the principle of the process for obtaining photographic prints which is still very largely employed. [Solutions required, Ammonium chloride, i grm. in 50 c.c. of water. Silver nitrate, 4 grms. in 50 c.c. of water. Sodium hyposulphite, 20 grms. in 100 c.c. of water.] Pour the solution of ammonium chloride into a flat plate or dish. Take a piece of fine drawing-paper about 10 or 12 cm. square, make a small pencil-mark in one corner, then taking it up by the two opposite corners lower it gently upon the solution in the plate, keeping the marked side downwards, so that the centre touches the liquid first, the two corners being lowered afterwards, in order that no air-bubbles may be re- tained between the solution and the paper. Allow the paper to float upon the solution for five or six minutes, then take it up quickly by one corner, and pin it to a shelf or the back of a chair, to drain and dry. The next stage of the prepara- tion of the paper, since it involves the formation of a com- pound sensitive to light, must be performed by candle-light, and therefore in a cellar, or a room with closed shutters, or in the evening. Pour the solution of silver nitrate into a perfectly clean plate, carry it into a room lighted only by a candle, and float upon it the piece of salted paper (with the marked side downwards), taking particular care to avoid air-bubbles. The SILVER. 255 silver nitrate in the solution will act upon the ammonium chlo- ride in the paper, and ammonium nitrate and silver chloride will be formed at the surface of the paper. After the lapse of three minutes, raise the paper by one corner and pin it up, as before, to dry in a dark cupboard or drawer. Obtain two pieces of flat window-glass, rather larger than the piece of pre- pared paper; lay one of them flat on the table in a room lighted by a candle only, or at any rate in the darkest corner of a room in which the blinds are drawn down. Place upon the glass a piece of black velvet or thick brown paper ; lay upon the latter the piece of prepared paper, having the marked side upwards ; place upon the paper a piece of black lace or a fern leaf, or a small engraving (which should be on thin paper), and on the top of all lay the other plate of glass. Bind the whole together by two letter clips or india-rubber bands, one on each side, and bring the extempore printing- frame into full daylight. You will observe the portions of the prepared paper, which are not protected by the lace or the engraving, to pass through shades of red and purple, finally becoming black and bronzed, if looked at obliquely by reflected light. When this is the case, remove the apparatus again to the dark room, and take out the prepared paper. The lace, or other opaque object, will be found to have protected the paper from the action of the light, and an image of it will be formed, white on a black ground. Of course, if the paper be now brought out to the daylight, it will blacken all over, and the image will be obliterated. If it be thought worth preserving, it must be soaked in common water to remove all excess of silver nitrate, and then placed in the solution f sodium hypo- sulphite. This solution will dissolve away all the unaltered silver chloride (see p. 228), leaving the reduced silver untouched. After the print has remained about ten minutes in the solution it should be removed, and washed in several changes of water ; after which it may be brought out to the light without damage. The black portions will have become reddish brown, and will be reduced in intensity, since no toning process has been em- ployed ; but the experiment will serve the purpose of illustrat- 25 6 MERCURY. ing the action of light on silver chloride, and the principles of the art of photography. 2. MERCURY. [Symbol of atom, Hg (hydrargyrus). Weight of atom, 200 hydrogen-atoms. It must be borne in mind that mercury and most of its compounds are very poisonous, whether taken internally or absorbed by the skin. Moreover, the metal should not be spilled about on the table or floor, or thrown down the sink, since it combines with lead and soon destroys the pipes.] Mercury is chiefly obtained from its sulphide, the mineral cinnabar, which is chemically the same as vermilion. This yields the metal when heated with quicklime, the calcium and oxygen of which combine with the sulphur \ Powder a small bit of cinnabar or vermilion (the ordinary red paint), and mix it intimately with an equal quantity of quick- lime : then put some of the mixture into an ignition-tube and heat it strongly. Bright globules of a liquid metal will condense on the tube, running together into one drop when scraped off the glass with a splinter of wood, such as a match. These must be mercury, since it is the only metal which is liquid at ordinary temperatures. Properties of Mercury. 1. Its liquidity and cohesion. Pour a few drops of mercury on a clean plate ; if the metal is pure the drops will preserve their roundness as they roll about, since their cohesion to each other is much greater than their adhesion to the surface on which they rest 2 . 2 If the metal contains lead or other impurity, its liquidity is impaired, and the drops will become elongated when the plate is inclined, and will move about sluggishly, leaving portions behind them. In order to purify it, pour it into a plate or shallow dish in sufficient quantity to form a thin MERCURY. 257 2. Its high density, 13.6 times that of water. This may be ascertained in the manner described in pp. 48, 49 ; 5 c.c. of mercury being carefully measured and then weighed. Owing to the strong cohesion of mercury compared with its adhesion to the glass, the curve of its surface in the tube will be convex, thus -^, instead of concave, - -, as in the case of water ; and hence, in order to obtain an approximately correct measure, the 5 c.c. mark should coincide with the line where the liquid touches the glass (and not from a tangent to the curve, as usual). 3. Its volatility (boiling point, 360). Place a small drop of mercury in a dry test-tube (using a pipette to transfer it), and heat it over a lamp, holding the tube nearly horizontal. The metal will boil below a red heat, and, if pure, will wholly volatilise, its vapour condensing in the cooler parts of the tube, and forming a bright metallic ring, which, when looked at through a magnifier, will be seen to consist of minute liquid globules like dew. These, if touched with a glass rod, may be made to run together into one large drop. Preparation of Compounds of Mercury. Mercury forms two distinct series of compounds, in one of which a given weight of it is combined with twice as much of the electro-negative radicle as is present in the other. It is found, in fact, that one atom of mercury [Hg] will saturate and form a definite crystallisable compound with either (i) one atom of the nitrate radicle [NO 3 ], to form a molecule of mercury stratum at the bottom, and pour over it enough dilute hydrogen nitrate (i vol. of the strong acid to 20 vols. of water) to cover it. Leave it in contact with the metal for three or four hours, stirring it occasionally with a gla'ss rod to expose a fresh surface of the metal to the acid ; then pour off the acid, wash the mercury with a stream of water poured from a jug, and finally, after pouring off as much water as possible, absorb the remainder with a clean cloth or blotting-paper. Pit a filter in a funnel, and make a fine hole with a pin at the point, support the funnel over a beaker or bottle, and pour into it the dry mercury. The metal which runs through will be found very nearly pure ; it may be further purified by distillation, but, except for special purposes, the gain in purity will scarcely compensate for the trouble and risk. 258 MERCURY. protonitrate [HgNO s ], or (ii) with two atoms of the same radicle to form a molecule of mercury pernitrate [Hg(NO 3 )J. Either one of these can be formed, to the exclusion of the other, by varying the conditions under which hydrogen nitrate acts on mercury. 1. Preparation of mercury protosalts. [Typical examples, Mercury protonitrate (Hg 2 (NO 3 ) 2 ). Mercury protochloride Mercury protonitrate is prepared by taking hydrogen nitrate slightly diluted and allowing it to act on excess of the metal, the temperature being kept low. Place a globule of mercury about as large as a pea in an evaporating dish, and pour upon it a mixture of 5 c.c. of strong hydrogen nitrate with 3 c.c. of water. Allow the action to go on for ten minutes or so (while other experiments are proceeded with) stirring the liquid frequently, but applying no heat ; then pour the solution together with the remaining mercury into a test-tube, dilute it with water to 50 c.c., and reserve it (labelled 'mercury protonitrate') for experiments, p. 262. 2. Preparation of mercury persalts. [Typical examples, Mercury pernitrate (Hg(NO,) 2 . perchloride (HgCl 2 ). periodide (Hg I 2 ). persulphide (Hg S).] The conditions necessary for preparing mercury pernitrate are, strong acid taken in excess, and a high temperature. Put a small globule of mercury (about half as large as was taken in the last experiment) into an evaporating dish, pour on it 4 or 5 c.c. of strong hydrogen nitrate, and heat the whole on a sand-bath, in a draught cupboard if possible. Allow the action to go on until all the metal is dissolved, then add a drop of strong hydrogen chloride (to convert any remaining protosalt 1 The above formulae for the molecules are used instead of the simpler ones, HgNO 3 , and HgCl, because the protosalts show a tendency to se- parate into metallic mercury and a persalt ; indicating that there may be more than one atom of mercury in the molecule. MERCURY. into persalt 1 ) and drive off most of the excess of acid by eva- poration 2 . Pour the concentrated solution into a test-tube, dilute it with water to 50 c.c., and reserve it (labelled ' Mercury pernitrate') for experiments, p. 263. 3. Formation of mercury periodide. This substance has been prepared already (p. 74), but not in a manner in which the remarkable change of colour which it undergoes could be noticed. (a) Dilute 2 drops of a solution of mercury perchloride with 5 or 6 c.c. of water, and add i drop of solution of potas- sium iodide. The precipitate of mercury iodide which forms is, in this dilute solution, bright yellow at first, but changes in the course of a minute or more into pink and finally scarlet. The reason of the change of colour appears to be this ; Mercury periodide exists in two different allotropic conditions, which differ in crystalline form : the one occurring in oblique rhombic prisms which are yellow, the other in square octohedra which are scarlet. Of these the most stable is the latter, and hence the yellow precipitate, which consists of the prismatic modification, changes to scarlet, the conversion being quicker in strong solutions. If a few more drops of solution of potassium iodide are added to the precipitate it will readily dissolve, a double salt, mercury-and-potassium iodide, being formed 3 . () Put a little of the scarlet mercury iodide obtained in exercise 8, p. 74, into a small dry test-tube, and heat it slowly over a lamp. It will melt and volatilise, condensing in yellow prismatic crystals in the cool part of the tube. The yellow sublimate, however, is not permanent; on rubbing it with a 1 It does this, owing to the chlorine which is liberated, and which from its strong affinities determines the change in the saturating power or ' atomicity ' of the metal more readily than hydrogen nitrate. 2 If the evaporation has been unintentionally carried to dryness, a little dilute hydrogen nitrate must be used to dissolve the residue ; otherwise a basic salt insoluble in water will be formed. 3 The use of this as a test for ammonium salts will be described under AMMONIUM. By dissolving a large quantity of mercury iodide in a saturated solution of potassium iodide, a liquid may be obtained which is of so high a density that glass will float in it. S 2 260 MERCURY. glass rod scarlet lines will appear and the whole will soon pass again into the more stable modification. [If you possess a moderately good microscope, you will find it interesting to watch the progress of the change by subliming a little of the scarlet mercury iodide from a watch-glass to one of the ordi- nary microscope slides, placing it on the stage of the instrument, examining the crystals with a one-inch power, and lightly touching one of them with a needle. The change will begin in the crystal which was touched and gradually spread through the whole, while its progress may readily be watched; the yellow rhombic prisms becoming aggregations of red octohedra with a square base, belong- ing to a different crystallographic system 1 .] 4. Formation of mercury persulphide. This substance, which is identical with vermilion, affords another example of the change of colour due to difference of allotropic form which is often observable in the compounds of mercury. Weigh out half a gramme of sulphur and 3 grms. of mercury, place them in a small test-tube and apply heat. As the tempe- rature approaches the boiling point of mercury, a strong action will commence, the sulphur and mercury combining to form a black mass of mercury sulphide. Continue heating this for half a minute, observing its volatility, on account of which it can be driven about from one part of the tube to another : then, after allowing it to cool, detach some of it from the tube and grind it to powder in a mortar. Lastly, shake the powder out on a sheet of writing paper, and rub it strongly with the pestle. Observe that it changes during the grinding and rub- bing from black to a dull red, leaving a streak of that colour upon the paper. The same change, which is due to the black, amorphous sulphide becoming crystalline, is effected by a very 1 To obtain good crystals for the microscope, it is generally necessary to resublime the crystals first obtained. To do this, place over the slip of glass on which the crystals have been deposited, another similar slip of glass, separating the two by strips of card placed between them at each end. Hold the plates in this position between the finger and thumb, and heat both of them over a spirit lamp. When they are pretty hot, apply a higher temperature to the one on which the mercury iodide is deposited, waving the lamp-flame to and fro under it. The sublimation thus takes place slowly, and large crystals are formed. MERCURY. 26l slow process of sublimation, as in the Chinese method of making vermilion. If, however, a little vermilion or cinnabar is heated in an ignition-tube it forms a black sublimate of the amorphous sulphide. General properties of Mercury salts. *1. They are volatile at a temperature below redness. (a) Place a small crystal of mercury perchloride (' corrosive sublimate') in an ignition tube, and heat it gently over the lamp. The salt will fuse, and at a rather higher temperature volatilise entirely, forming a white crystalline ring in the cool part of the tube. (b] Heat a little mercury protochloride ('calomel') in a similar way. It will be found to volatilise without previous fusion. *2. Heated with sodium carbonate in an ignition tube, they yield a sublimate of liquid metallic globules. Mix a little mercury protochloride, or perchloride, with an equal quantity of anhydrous sodium carbonate in a mortar, introduce it into an ignition tube in quantity just sufficient to half fill the bulb, and cover it with a layer of the dry sodium carbonate. Wipe the tube clean with a twisted strip of blotting- paper, and heat it very gently over the lamp. At first, if the substances are not carefully dried, some moisture will be given off, which must be absorbed by strips of blotting-paper, before a stronger heat is applied; otherwise it will be difficult to obtain a well-defined sublimate. When no more water con- denses in the tube, increase the heat, until tbfe bulb is nearly red-hot. A metallic sublimate will form in the tube which, when examined with a magnifying glass, will be seen to consist of small round globules of metal, very different in appearance from the crystalline crust of arsenic, p. 280. To remove any doubt as to the character of the deposit, introduce a thin slip of wood (such as the end of a match) into the tube, and em- ploy it to scrape the sublimate from the sides of the tube. The small globules will run together into one large glo- 263 MERCURY. bule, which from its metallic 1 lustre and fluidity can only be mercury *. *3. They are reduced by copper. Place a drop of solution of mercury perchloride on a clean strip of copper. Allow it to remain for half a minute, and then wash it off. A dull white stain will be left on the copper, which when rubbed with a cloth will become bright and silvery. The mercury salt has been decomposed, copper nitrate being formed, while the mercury is deposited on the more electro- negative metal, the copper, with which it forms an alloy or amalgam. If the copper is heated, but not to redness, the bright deposit will disappear. Distinctive properties of the protosalts and persalts of Mercury. [For the following experiments the solutions of mercury proto- nitrate and mercury pernitrate, which have been already prepared (p. 258), may be used. It will be convenient to apply each test successively to the proto- salt and the persalt, and to record the results in parallel columns in the note-book.] A. Mercury protosalts. *1. With hydrogen chloride they give a white precipitate. Pour a little of the solution of mercury protonitrate into a test tube, and add a few drops of dilute hydrogen chloride. A white precipitate of mercury protochloride will be formed. (a) Pour off a portion of the liquid, in which the precipitate is suspended, into another tube ; add a little more hydrogen chloride, and then a drop or two of strong hydrogen nitrate, and boil. The chlorine evolved from the aqua regia thus 1 Mercury iodide is the only commonly occurring mercury compound which under the above conditions volatilises unreduced, in spite of the superposed layer of sodium carbonate. It may, of course, be easily identi- fied by its colour and its behaviour when heated alone, p. 259. MERCURY. 263 formed (see p. 193) will convert the mercury protochloride into perchloride J , and the latter will dissolve. (b) Add to the remainder of the precipitate some ammonia. It will turn black, owing to the formation of mercury prot- oxide. *2. With hydrogen sulphide they give a black precipitate, Test another portion with solution of hydrogen sulphide. A black precipitate of mercury protosulphide will be formed. Pour off a little into another tube; render it alkaline with ammonia, add some ammonium sulphide, and warm the mix- ture ; the precipitate will remain undissolved. 3. With potassium hydrate they give a black precipitate. Add to a third portion some solution of potassium hydrate. A black precipitate of mercury protoxide will be formed, in- soluble in excess. *4. With tin protochloride they give a dark gray precipitate. Add to another portion some solution of tin protochloride. A dark gray precipitate of finely divided metallic mercury will be at once formed 2 . B. Mercury per salts. [The corresponding tests should be applied in precisely the same way as directed for the protosalts.] 1. With hydrogen chloride they give no precipitate. *2. With hydrogen sulphide they give at first a white pre- cipitate, changing to yellow and finally black. If the hydrogen sulphide is added drop by drop, and the liquid shaken, a precipitate will be produced which is at first white, but on further addition of hydrogen sulphide becomes yellow, brown, and finally black. The cause of this charac- teristic reaction is, that a combination of mercury persulphide and nitrate is first thrown down, which is converted entirely 1 Hg 2 Cl 2 + Cl 2 = 2 HgCl 2 . 2 This may, but not without trouble, be made to aggregate into larger globules by allowing it to subside, washing it by decantation from traces of nitrate, and then boiling it with a little solution of tin protochloride, to which a few drops of hydrogen chloride should be added. 364 LEAD. into mercury persulphide by 'excess of the precipitant. The mercury persulphide, like the protosulphide, will be found in- soluble in ammonium sulphide, and also in hydrogen nitrate, but decomposable by aqua regia. 3. With potassium hydrate they give a yellow precipitate. It is noticeable that this precipitate which consists of mer- cury peroxide, has precisely the same composition as the ' red oxide' of mercury already used for experiments, p. 69. *4. With tin protochloride they give a white precipitate, turning gray when more of the test is added. The white precipitate formed by the addition of one drop of solution of tin protochloride is mercury protochloride. This turns gray on addition of more of the reagent, owing to its reduction to metallic mercury. 3. LEAD. [Symbol of atom, Pb (plumbum). Weight of atom, 207 hydrogen-atoms.] 1. Density of lead ( = 11.45.) This, if not ascertained already, may be taken now by the method given in p. 51. 2. Action of water on lead. Fill two test-tubes, one half full of distilled water, the other half full of common hard spring water, and immerse in each a strip of lead, cleaned by scraping it with a knife. After the lapse of an hour or less, a slight white precipitate will be formed in the test-tube containing the distilled water, and in the course of a day some quantity of this precipitate will have been collected; while in the test-tube containing the common hard water there will be little or no perceptible action. The reason is this : The oxygen dissolved in the water attacks the lead, forming lead oxide, which dissolves in the water, but is to some extent precipitated as carbonate by its combination with the carbon dioxide present in air. If, how- ever, the water contains sulphates and carbonates (as common LEAD. hard water does, p. 66), these form a crust of insoluble lead sulphate and carbonate which protect the lead from corrosion. The presence of lead in solution in the test-tube containing the distilled water should be proved by applying to it test 2, p. 266. Preparation of compounds of lead. [Typical examples, Lead protoxide (Pb O). red oxide (Pb 3 O 4 ). dioxide (Pb O 2 ). nitrate (Pb (NO.),). acetate (Pb(C 2 H 3 O 2 ) 2 ).] 1. Lead nitrate. Cut off a small piece of sheet lead, weighing about 2 grms., with a strong knife, and hammer it thin on an anvil ; noticing its malleability, softness, and want of elasticity. Fold up the thin sheet thus obtained, place it in a porcelain dish, pour on it about 5 c.c. of strong hydrogen nitrate diluted with half its volume of water, and heat gently on the sand-bath. Orange vapours of nitrogen tetroxide will be given off, and lead nitrate will be formed and dissolve 1 . Evaporate the solution just to dryness, to drive off excess of acid; dissolve the residue by warming it with a little water, then add more water until the whole measures 50 c.c., and reserve it for future experiments, p. 266. 2. Lead red oxide ('red lead'). Mix 2 grms. of lead protoxide (litharge) with half a gramme of potassium chlorate, grinding the whole thoroughly together. Heat the mixture in an iron spoon or capsule until all effer- vescence due to escape of oxygen has ceased, and then allow it to cool. The lead protoxide will under these circumstances combine with more oxygen, and a bright red residue will be obtained, containing ' red lead/ 3. Lead dioxide. Pour some dilute hydrogen nitrate on a little red lead in a test-tube, and warm the mixture. A chocolate-coloured powder 266 LEAD. will remain undissolved, which is lead dioxide. The acid has separated the red lead into lead protoxide, which dissolves as nitrate, and lead dioxide, which is insoluble in the acid 1 . Properties of salts of Lead. [The solution of lead nitrate already made (p. 265) may be used.] *1. With hydrogen chloride they give a white precipitate, unaltered by ammonia. Add a few drops of dilute hydrogen chloride to some of the solution of lead nitrate. A white crystalline precipitate will be formed, insoluble in excess of the acid 2 . Divide the fluid containing the precipitate in suspension into three portions, and test them as follows : (a) Add to the first portion three or four times its volume of water. The precipitate will gradually redissolve. Owing to this solubility in water, it is not formed at all in weak solutions of lead salts. (b) Heat the second portion to boiling. It will in this case also redissolve, but will be reprecipitated as the solution cools, in snow-like flakes, which, when examined by a magnifier, will be seen to consist of groups of slender prisms. (c) To the last portion add ammonia. The precipitate will not dissolve or alter in colour. *2. With hydrogen sulphide they give a black precipitate. Test another portion of the solution of lead nitrate with solution of hydrogen sulphide. A black precipitate will be produced, insoluble in hydrogen chloride but decomposed on being boiled with excess of hydrogen nitrate. It will be re- membered that this property of lead, of forming a black com- pound with sulphur, furnished a very delicate test of the presence of a sulphide (p. 218). 1 Pb 3 4 = 2 A large excess of dilute hydrogen chloride will dissolve it, the effect being due, however, not to the action of the acid, but to the action of the water, as in (a). LEAD. 367 *3. With hydrogen sulphate they give a white precipitate. Test another portion of lead nitrate with dilute hydrogen sulphate. A white precipitate will be formed, insoluble in excess of the acid, but readily decomposed and dissolved if warmed with solution of ammonium acetate 1 . Since lead sulphate is slightly soluble in hydrogen chloride, the best method of applying this test is as follows : * Make a very dilute solution of lead nitrate by mixing 5 c.c. of water with 2 drops of the ordinary solution, and add 2 or 3 drops of ammonia. This will produce a white precipitate of lead hydrate. Now add to the liquid excess of dilute hydrogen sulphate; this will decompose the hydrate, forming lead sul- phate which will remain undissolved. It is always less easy to dissolve a precipitate than to prevent its formation. *4. With potassium chromate they give a yellow precipitate, soluble in potassium hydrate. Add to another portion of the solution of lead nitrate a drop of solution of potassium chromate. A yellow precipitate will be formed, consisting of lead chromate (the ' chrome yellow,' much used as a paint). Divide the liquid into two portions : to the first add some dilute hydrogen nitrate ; the precipitate will remain undissolved. To the second portion add some solu- tion of potassium hydrate, which will readily redissolve the precipitate. *5. Reduced before the blowpipe on charcoal they yield a malleable bead, and yellow incrustation. Mix a very little lead acetate with about twice as much potassium cyanide, and heat the mixture on charcoal as di- rected in Expt. 2, p. 94. A metallic bead will be obtained, the malleability of which should be tested as there directed ; and the surrounding parts of the charcoal will be covered with a light yellowish incrustation of lead oxide. 1 This may be made, if none is at hand, by putting about 3 c.c. of solu- tion of ammonia into a test tube, and adding hydrogen acetate until the liquid smells of it and is acid to test paper. 2,68 LEAD. Additional Experiment. Precipitation of Lead from its compounds by Zinc. This depends upon the superior affinity of zinc for the radicle combined with the lead; and the action, once begun, is aided by the galvanic current set up between the zinc and the portions of lead first thrown down (compare the reduction of silver by zinc, p. 251). Make a solution of lead acetate by dissolving 10 grms. of the salt in 200 c.c. of water, with addition of a few drops of hydrogen acetate. Place the filtered solution in a wide-mouthed bottle, and suspend in it a strip of thick sheet zinc, or, better, a rod of the metal the size of a pencil l . A short piece of glass tubing should be laid across the mouth of the bottle, from which the zinc may be suspended by a piece of string, so that it may not touch the bottom of the bottle. Leave the whole undisturbed for twelve or fourteen hours : the rod of zinc will soon be covered with thin brilliant plates of pure metallic lead (the so-called 'Lead Tree'), while a proportional quantity of zinc is dissolved. This is a good illustration of the replace- ment of one metal by another in a combination; and, if we ascertained the weight of zinc dissolved and the weight of lead deposited, we should find that the former weight was to the latter as 65 : 207, numbers which are the accepted atomic weights of zinc and lead respectively. In a day or two the whole of the lead will have been with- drawn from the solution, which may then be examined by test 3, p. 267, to prove the absence of lead. 1 As the shape of the rod is immaterial, it may be easily made by melting some zinc in a ladle, and casting it in a shallow trough formed by pressing a thick pencil or a piece of glass tube into a mass of fine slightly moistened sand, or clay. COPPER. 269 Group II. Metals which are separated from solutions containing hydrogen chloride by hydrogen sulphide. MERCURY (diatomic), LEAD, COPPER, CADMIUM, BISMUTH, ARSENIC, ANTIMONY, TIN, GOLD, PLATINUM. 1. COPPER. [Symbol of atom, Cu (cuprum). Weight of atom, 63.5 hydrogen-atoms.] Compounds of Copper. [Typical examples, Copper oxide (CuO). nitrate (Cu(NO a ) 2 ). sulphate (Cu SO 4 ).j 1. Combination of copper with oxygen, when heated. Clean a strip of sheet copper with emery paper, and hold it in the upper part of the flame of a Bunsen's burner. As it gets hot, brilliant-coloured films of copper oxide will form on it, where it is exposed to the current of hot air rising with the flame \ Finally, when it has been heated to redness for a minute, plunge it into a beaker of cold water, when the oxide will detach itself in scales (since it does not contract, as the temperature falls, in the same degree as the metal), and the surface of the metal will show the characteristic red colour of copper. 1 Observe that not only does the part of the copper which is actually immersed in the flame remain bright, but when the blackened part is brought into the middle of the flame the oxide is reduced and the bright red metal reappears. In fact, by holding the strip edgeways in the flame we get a good section of the oxidising and reducing parts. The iridescence of the films of copper oxide which are formed first, is due to the interference of the rays of light reflected from the upper and under surfaces of the film, respectively : due to the same cause, in fact, as the colours of a soap bubble. 2 70 COPPER. 2. Preparation of copper nitrate. Dissolve i grm. of fine copper wire in about 5 c.c. of strong hydrogen nitrate diluted with half its volume of water, heating the tube gently if the action becomes slow. Red vapours of nitrogen tetroxide will be seen above the liquid (the chemical action has been already explained, p. 142), and a blue solution of copper nitrate will be obtained. Evaporate this solution nearly to dryness in a dish, to drive off any excess of hydrogen nitrate, dilute it with water to 50 c.c., and use it in the following ex- periments. Tests for Salts of Copper. *1. With hydrogen 'sulphide they give a black precipitate. Acidify a portion of the solution with hydrogen chloride, and add solution of hydrogen sulphide. A black precipitate will be formed, consisting of copper sulphide. Allow this to subside (it will separate more readily if the solution is warmed), pour off the clear fluid, and wash the precipitate once or twice by decantation. Divide it into two portions : (a) To one of these add some ammonium sulphide, and warm it gently ', the precipitate will not dissolve. (b) Boil the other portion with strong hydrogen nitrate, which will readily decompose and dissolve it, with separation of sulphur. *2. With potassium ferrocyanide they give a reddish-brown precipitate. This should be tried with only one drop of the solution of copper nitrate, diluted with 5 c.c. of water, in order that the delicacy of the test may be observed. 3. With potassium hydrate they give a light blue precipi- tate, turning black on boiling. To another portion add a few drops of solution of potassium hydrate. A light blue precipitate of copper hydrate will be formed, which will not dissolve in excess of the precipitant, and will turn black when the solution is heated to the boiling-point, owing to its conversion into copper oxide. *4. With ammonia they give a light blue precipitate, solu- ble in excess, forming a blue solution. COPPER. 271 To another portion add one drop of solution of ammonia. A light blue precipitate will be formed, as in the last experi- ment, but will readily dissolve on addition of a few drops more of ammonia, and a deep blue solution will be obtained. This contains cuprammonium nitrate, a salt in which part of the hydrogen in the radicle ammonium is replaced by copper, as shown in its formula (H 6 CuN 2 ) 2 (NO 3 ) 2 . 5. They impart a green colour to flame. Put a drop or twt of strong hydrogen chloride into a watch- glass, dip into it the end of a piece of copper wire, and hold the latter in the flame of a Bunsen's burner. The copper chloride which has been formed will volatilise in the flame and give it a bright bluish green colour. *6. Heated with borax, they give a bead which is greenish- blue in the oxidising flame, red and opaque in the reducing flame. Make a borax bead, add to it a trace of copper sulphate, and heat it in the oxidising flame of the blow-pipe. The bead will be coloured green while hot, becoming blue as it cools. After being heated in the reducing flame, with addition of a little more copper sulphate, it will appear red by reflected light, owing to the presence of suspended particles of copper. 7. Heated on charcoal with sodium carbonate they give grains of metallic copper. Mix a minute quantity of copper sulphate with about twice as much sodium carbonate, and heat it on charcoal before the blowpipe-flame. You will obtain small grains of metallic copper, but the heat of the blowpipe-flame will be scarcely sufficient to fuse these into one globule. They will be better seen if the fused mass is placed in a mortar and washed with water until the soluble salts are dissolved; the red metallic particles may then be readily distinguished with a magnifier. Reduction of salts of Copper. 1. By grape sugar, with formation of copper suboxide. Dissolve a small lump (about the size of a pea) of grape sugar in 5 c.c. of water, filter the liquid if necessary, and add to 272 COPPER. it a drop or two of the solutidn of copper nitrate. If solution of potassium hydrate be now added, no precipitate of copper hydrate will be formed, or if formed (owing to the grape sugar not being present in sufficient quantity) it will be redissolved on addition of more potassium hydrate. But if the mixture is heated to the boiling-point, a yellow precipitate of copper subhydrate is obtained, which quickly changes to red copper suboxide. *2. By iron, with formation of metallic copper. () Pour a little of the solution of copper nitrate into a test- tube, and dip into it a strip of sheet iron cleaned with emery paper, or the blade of a knife. Metallic copper will be thrown down on the surface of the iron, while the latter is slowly dissolved, taking the place of the copper in the solution. Compare the action of zinc on lead acetate, p. 2 68. 3. By electricity. Copper is one of the metals most easily reduced by electri- city, and an experiment illustrating this has already been made, p. 70. Additional Experiment. Method of obtaining Electrotypes. When a current of electricity is sent through a solution of a salt of copper, the metal is deposited upon the negative electrode (i. e. upon that which is connected with the zinc plate of the battery), and since it is deposited molecule by molecule, the particles form a film which adheres very closely to, and is an exact copy of, the electrode itself. In order, therefore, to obtain a copy of a seal or medal, a * mould' or reversed impression must be first obtained, which is placed as the negative electrode in a solution of copper sulphate, and the current kept up until a sufficiently thick film of copper is deposited. To obtain the current it will not be necessary to employ a second battery. A * single-cell ' apparatus, arranged as directed below, will answer perfectly ; the mould itself forming the negative plate of the battery \ 1 For a fuller explanation of the principles of electrolysis a text-book on Electricity must be consulted. COPPER. 373 [Solutions required, Saturated solution of copper sulphate (350 grms. of the salt dis- solved in i litre of water; 20 c.c. of hydrogen sulphate added). Solution of ammonium chloride (60 grms. dissolved in 300 c.c. of water).] 1. Preparation of the mould. For seals nothing is better than good sealing-wax. Some of this should be melted on a card held at some height above a lamp-flame, and continually stirred with the end of the stick of wax until suffi- cient has been melted to form a thick circular lump rather smaller than the seal to be copied. After breathing upon the seal, bring it down with gentle pressure upon the wax, increasing the pressure as the wax gets cold and hard. It is best not to remove the seal until the wax is quite hard, otherwise the mould may lose its flat- ness. The card should next be cut away carefully close to the edges of the wax, and a copper wire (about No. 20 wire gauge) 30 cm. long should be attached to the margin of the mould by heat- ing it and pressing it into the wax near (but not touching) the edge of the impression. The wire must not be completely buried in the wax, and the exposed part should be scraped clean with a knife. For a medal, plaster of paris will answer very well, and the mould may be made according to the directions given under CALCIUM, being thoroughly saturated with wax in the manner there described. The end of a piece of copper wire, about 40 cm. long, should be passed round the rim and fastened by twisting to the main portion of the wire, so as to grasp the mould securely in a loop. Since wax is a non-conductor of electricity the surface of the mould must be rendered conductive by covering it with a thin film of graphite (the ordinary plumbago or black lead). For this pur- pose it should be laid face upwards on a sheet of paper (if of sealing- wax it should be held for a few seconds over the mouth of a beaker containing a little hot alcohol l ) and brushed over with some of the best plumbago 2 : being lightly breathed upon occasionally to promote the adhesion of the substance. The brush should be worked with quick circular strokes into all the crevices of the mould, until every part of it shows a metallic lustre when looked at obliquely. An 1 The vapour of this slightly softens the surface and gives the graphite a better hold. ' J Good stove black-lead will generally serve the purpose : but it is best to obtain a little pure plumbago from a chemist or optician. A shaving brush of badger's hair answers well for applying it. T 274 COPPER. extremely thin film is all that is required, but it must be continuous. A little plumbago must be brushed over the wire where it is attached to the mould, to make a good connection throughout. Lastly, the edges of the mould outside the wire, and about 10 or 12 cm. of the wire itself, must be varnished with 'black japan' or some other thick varnish 1 , to prevent the deposit of copper upon them when immersed in the solution. [If the mould is of fusible metal (see p. 278) a portion of its edge should be moistened with solution of ammonium chloride and a clean piece of copper wire heated and pressed against it until com- pletely imbedded. The back and edges of the mould must be thickly varnished to prevent deposit of metal upon them ; and it is advisable to brush a trace of black-lead over the impression to pre- vent too close adhesion of the deposit.] 2. Construction of the apparatus. Place a small jar of porous earthenware about 14 or 15 cm. high and 4 cm. in diameter in a wider jar of glass or china about 1 1 or 12 cm. in diameter and the same or rather more in height 2 . Put into the porous cell a rod of zinc about 1 8 or 20 cm. long, and at least as thick as a pencil. Hang the mould in the outer jar by bending the wire round the rim of the jar as shown in fig. 62, the bend being made thus : otherwise the solution 62. may creep up between the wire and the side by capillary action, and overflow. The other end of the wire should be twisted firmly round the zinc rod, so as to support it in the porous cell. Lastly, fill the porous cell about three-fourths full of the solution 1 Sealing-wax varnish may be made by powdering 10 grms. of black sealing-wax, and digesting it at a gentle heat (best applied by a pan of hot water) with 10 c.c. of methylated spirit, stirring occasionally. 2 For the porous cell, a common flower-pot, though unnecessarily wide, answers well, the hole at the bottom being stopped with a cork. For the wider jar nothing is better than the lower part of a large com- mon green glass bottle, the neck being cut off by the method given in p. 42. A preserve jar or gallipot will answer, but the solution is apt to pene- trate the glaze, unless the material is stonewares COPPER. 275 of ammonium chloride 1 , and the outer jar to the same level with the solution of copper sulphate. In the course of a minute a bright deposit of copper will be seen spreading over the mould. If it does not appear, there must be a break in the conducting surface, and the mould must at once be taken out, dried, and blackleaded with more care. When all is going on well, hang a small muslin bag containing crystals of copper sulphate just below the top of the solution in the outer jar, tying it to a glass rod laid across the jar : and leave the whole undisturbed for about a day, examining it occasionally to see that the deposit is forming regularly on the mould. The latter should not, however, remain out of the solution for more than half a minute, lest it should tarnish and the subsequent deposit fail to adhere to it 2 . [The defects which are most liable to occur are, 1. Gas given off at the surface of the mould and a sandy, dull-red, non- adherent deposit of metal. This is caused by the current being too strong in proportion to the strength of the copper sulphate solution. The remedy will be to pour off about two-thirds of the solution of ammonium chloride in the porous cell and add an equal volume of plain water to the remainder. The solution of copper sulphate must be kept fully saturated, fresh crystals being placed in the bag as the others dissolve. 2. The deposit forms 'very slowly; its surface being rough and bristling ^with crystals of copper. This is due to the current of electricity not being strong enough ; the action of the solution of ammonium chloride on the zinc having slackened. The spent solution must be poured away, and the porous cell filled up with fresh solution of the same salt. The same deficient action occurs in cold weather, and the apparatus should be kept in a warm room. When the conditions are right, the deposit appears of a bright pink colour, even in the surface, and tough in texture.] In about 24 hours a sufficiently thick film of metal will have been deposited, and the mould may be taken out and the copy detached from it by pulling the two apart very carefully. If there is much 1 If the mould is small, it will be advisable to use a much weaker solu- tion of ammonium chloride (the strong solution diluted with an equal volume of water), at any rate for the first half hour, or until the impression is completely covered with copper. 2 A black deposit forms upon the zinc, and should be occasionally brushed off. It consists of copper, and is due to the copper sulphate slowly diffus- ing into the porous cell, and being reduced by the zinc. T 2 276 CADMIUM. difficulty in separating them, the point of a knife may be inserted at the edges, and the copper film heated for a moment over a lamp. The thin, fragile deposit should next be strengthened by backing it up with tin. To do this, moisten the back of it with solution of ammonium chloride, lay it face downwards on a piece of wire gauze, and heat it over a lamp. When the ammonium chloride begins to volatilise in white fumes, press upon the surface a strip of metallic tin (or, better, soft solder). This will melt and spread all over the copper; enough should be applied to make a layer at least i mm. thick. Lastly, the edges should be trimmed by cutting away all super- fluous copper, and smoothing irregularities with a file. If the object is a medal, an electrotype of each side may be taken, and the two placed back to back and soldered together (or simply cemented by shellac) so as to reproduce the original. If a copy of a seal has been taken, it may be soldered to the head of a brass screw, and the latter inserted into a wooden handle such as those which are sold for bradawls. [A rather preferable method of depositing copper is to employ a separate battery, such as a single cell of Smee's battery ; the mould being connected with the zinc, and a thick strip of copper with the platinised silver of the battery. Both should then be im- mersed in a jar containing a solution of copper sulphate (150 grms.' dissolved in i litre of water ; 30 c.c. of hydrogen sulphate added). No addition of crystals of copper sulphate should be made : the copper being dissolved from the positive pole (the strip of copper) as fast as it is deposited on the negative pole (the mould).] 2. CADMIUM. [Symbol of atom, Gd. Weight of atom, 112 hydrogen-atoms.] Tests for compounds of Cadmium. [A solution of cadmium sulphate, containing i grm. of the salt in 25 c.c. of water, may be used.] *1. With hydrogen sulphide they give a bright yellow pre- cipitate insoluble in potassium hydrate. Add to a portion of the solution a few drops of dilute hy- drogen chloride, and then solution of hydrogen sulphide. A BISMUTH. 277 yellow precipitate of cadmium sulphide will be produced. Add to the solution in which the precipitate is suspended excess of solution of potassium hydrate, and warm the mixture. The precipitate will remain unaltered, differing in this respect from the two other yellow sulphides, those of arsenic and tin, which are dissolved under the same circumstances. *2. With ammonia they give a white precipitate, soluble in excess; this solution yields a yellow precipitate on ad- dition of hydrogen sulphide. Add a drop of ammonia to another portion. A white pre- cipitate of cadmium hydrate will be formed, which will readily dissolve on addition of more ammonia. Add to the clear solution some hydrogen sulphide. A yellow precipitate will be formed, of cadmium sulphide, since the latter is insoluble in ammonia and ammonium sulphide. *3. Reduced on charcoal they give a reddish-brown incrus- tation. Mix a small quantity of cadmium sulphate with an equal amount of sodium carbonate, and heat it on charcoal before the blowpipe. No metallic globule will be obtained, owing to the volatility of cadmium, but the surface of the charcoal will be covered with a characteristic reddish-brown coating of cadmium oxide. 3. BISMUTH. [Symbol of atom, Bi. Weight of atom, 210 hydrogen-atoms.] Compounds of Bismuth. [Typical examples, Bismuth nitrate (Bi(NO,),). chloride (Bi G1 8 ). oxychloride (Bi Gl O).] Preparation of Bismuth nitrate. Place a small fragment of bismuth in a strong porcelain mortar, and strike it with the pestle. It will not spread out, 378 BISMUTH. like lead, into a thin plate, but will be crushed into a crystalline powder. Dissolve about 0.5 grm. of the metal in 5 c.c. of hydrogen nitrate, as directed in the case of lead. It will be found to dissolve easily, and the solution of bismuth nitrate (after evaporation to half its bulk, in order to drive off excess of acid) may be reserved for testing, after dilution with about an equal volume (not more) of water. Preparation of * fusible metal.' Although bismuth itself only melts at a temperature of 260, yet an alloy of it with tin (melting-point 230) and lead (melting-point 330) fuses below the temperature of boiling water, viz. at 98. Weigh out 4 grms. of bismuth, 2 grms. of lead, and 2 grms. of tin. Melt the bismuth in a clean iron spoon, and add to it the lead and the tin, stirring the melted alloy with a glass rod or piece of iron wire. Pour it out on a clean iron plate or on a tile, and allow it to cool. Meanwhile, heat some water in a beaker, and when it is boiling put into it a piece of the alloy suspended in a loop of thread. It will readily melt, and drop off the thread. A still more fusible alloy is made by adding i grm. of cadmium to the above ingredients. This melts at a tem- perature of 80, or a little below. [Since the above alloy expands in solidifying, it is well adapted for taking casts of seals, medals, &c. for electrotyping. For this pur- pose, some of it should be melted and poured out on a clean plate. The edge of a card should be lightly drawn over its surface, to remove dross, and the moment it is observed to become pasty the seal should be brought down quickly upon it. A little practice will be required to hit the exact moment for applying the seal.] Tests for compounds of Bismuth. *1. They are, especially bismuth chloride, decomposed by water, forming insoluble basic salts. (a) Pour a few drops of the solution of bismuth nitrate into BISMUTH. 279 a test-tube, and add eight or ten times its volume of water. The solution will gradually become cloudy, and deposit a pre- cipitate of bismuth oxynitrate. (<5) To another small portion of the solution add a drop of dilute hydrogen chloride, and then a large quantity of water, as above. The liquid will at once turn milky, owing to the formation of bismuth oxychloride 1 . Divide the liquid into two parts, (a) To one portion add strong hydrogen chloride drop by drop. The precipitate will readily dissolve. [Reserve the solution for test 2.] () To the other add an equal volume of solution of sodium- and-hydrogen tartrate. The precipitate will remain undis- solved : a property which distinguishes it from the similar precipitate formed by antimony, p. 288. [The best method of applying this test is, to evaporate a few drops of the solution of bismuth salt to dryness in a watch-glass, to dissolve the residue in a drop of moderately dilute hydrogen chloride, and then, placing the watch-glass on a black surface, to fill it up with water from a wash-bottle. A very slight turbidity may thus be rendered evident.] *2. With hydrogen sulphide they give a black precipitate. Add solution of hydrogen sulphide to the clear solution containing bismuth chloride, obtained in the last experiment. A black precipitate of bismuth sulphide will be produced, in- soluble in potassium hydrate. *3. Reduced on charcoal they give a brittle globule of metal, with a light yellow incrustation. Evaporate the remainder of the solution of bismuth nitrate to dryness, mix the residue with about an equal quantity of potas- sium cyanide, and reduce it on charcoal in the usual way. Observe the yellow incrustation of bismuth trioxide formed round the cavity in the charcoal, and try the brittleness of the globule by crushing it with the pestle in the mortar. 1 BiCl s +H 2 O = BiClO + 2HCl. 280 ARSENIC. 4. AKSEWIC. [Symbol of atom, As. Weight of atom, 75 hydrogen-atoms, It should be remembered in dealing with arsenic that the sub- stance and its compounds are extremely poisonous. Very small quantities should be used for testing, and care must be taken not to inhale any of the vapours.] Compounds of Arsenic. [Typical examples, Arsenic trioxide (As 2 O 3 ). pentoxide (As 2 O 5 ). trichloride (As G1 8 ). Potassium arsenite (KAsO 2 ). arsenate (K 3 AsO 4 ).] Properties of Arsenic Trioxide. This is the common ' white arsenic ' of the shops, and is the source from which the other compounds of arsenic are usually derived. *1. It volatilises readily, condensing in brilliant octohedral crystals. Place a very small quantity of arsenic trioxide in a small dry test-tube, and heat it slowly over a lamp with a small flame. It will volatilise completely, forming a crystalline crust in the cool part of the tube. Now warm the part of the tube beyond the deposit, and when it is moderately hot carry the lamp -flame downwards, so as to volatilise the sublimate already formed. It will condense now more slowly, and form large F . , transparent glittering crystals, which, when examined with a magnifier, will be found to resemble Fig. 63, being more or less perfect octohedra belonging to the ' regular ' or ' cubic ' ARSENIC. 28l system. The triangular faces of these will be easily recog- nised. 2. Its solubility in water. Boil a very little of it in a test-tube with 8 or 10 c.c. of water ; notice the difficulty with which it is wetted by the water, the powder showing a tendency to float as a film upon the sur- face of the liquid, or remain at the bottom in lumps. It will, however, dissolve to a certain extent, as may be proved by setting the liquid aside to cool, when small brilliant crystals of the trioxide will be formed on the sides of the tube. The solution may be shown to contain arsenic by test i, p. 284. Preparation of Arsenic trichloride. Boil half a gramme of arsenic trioxide with 5 c.c. of strong hydrogen chloride in a test-tube. The substance will readily dissolve *, and the solution, which contains arsenic trichloride, may be kept for examination. Preparation of Potassium arsenite. In the last experiment we have seen that arsenic combines with the chlorine radicle like a metal. But in many respects it resembles more closely a non-metallic element; thus, arsenic trioxide combines with potassium hydrate just as nitrogen trioxide has been already proved to do (p. 140), forming a salt, potassium arsenite, analogous to a nitrite; in which arsenic, like nitrogen, forms part of the electronegative radicle. Boil i grm. of arsenic trioxide with 5 c.c. of solution of potassium hydrate. A solution, of potassium, arsenite will be formed 2 , which may be reserved for examination. Preparation of Arsenic pentoxide. This is obtained by oxidising the trioxide by means of hydrogen nitrate. Place half a gramme of arsenic trioxide in a small eva- As 2 O 3 + 6HCl= 2KAsO 2 --H 2 O. 282 ARSENIC. porating dish, pour over it about 5 c.c. of strong hydrogen nitrate, and heat the mixture (in a draught cupboard, if pos- sible). Orange vapours of nitrogen trioxide will be evolved, some of the oxygen of the acid being transferred to the arsenic trioxide *. When the liquid has nearly evaporated, add about 2 c.c. more acid and evaporate to complete dryness. Boil the residue of arsenic pentoxide with about 5 c.c. of solution of potassium hydrate, dilute the solution of potassium arsenate, thus obtained, with 20 c.c. of water, and reserve it for test- ing, p. 285. Tests for compounds of Arsenic. A. General Tests. *1. Heated with sodium carbonate, they are reduced, yield- ing a sublimate of metallic arsenic. Mix a very small quantity of arsenic trioxide with the same amount of potassium cyanide and about twice as much anhy- drous sodium carbonate. Half fill the bulb of an ignition-tube with the mixture, and wipe off any adhering particles from the sides of the tube with a twisted strip of blotting-paper. Heat the bulb, gently at first, over the lamp, and warm the whole of the tube (held in the crucible tongs) so as to drive out any moisture which would otherwise condense in it. When the whole is quite dry (the last portions of moisture may be absorbed by a strip of blotting-paper, so as to leave the whole of the tube quite clean), heat the mixture in the bulb more strongly. A black, shining ring of metallic arsenic will soon form in the tube. Allow the whole to cool and then cut off the bulb with a file, retaining the metallic sublimate in the tube; hold the latter in a slanting position (the part containing the arsenic being lowest), and heat the ring, beginning at the upper part, by a lamp with a very small flame. The arsenic will volatilise, 1 As a 3 + 2 HN0 3 = As 2 5 + H 2 -r N 2 8 . ARSENIC. 283 will be oxidised by the current of hot air ascending in the tube, and will condense near the top of the tube as arsenic trioxide, in small crystals. The heat should not be too strong, or a portion of the arsenic will volatilise unchanged and interfere with the distinctness of the crystalline ring. If this should occur, allow the tube to cool, and re- sublime the deposit as above directed. 2. Heated with hydrogen chloride, in contact with a strip of copper, they yield a deposit of metallic arsenic. [Reinsch's test.] Pour about 5 c.c. of dilute hydrogen chloride into a test-tube, and add 2 or 3 drops (not more) of the solution of arsenic trichloride lately made. Put into the liquid a piece, 4 or 5 cm. long, of fine copper wire, or a narrow strip of copper foil, cleaned with emery paper, and doubled up into a bundle. On boiling the solution, the arsenic will be thrown down on the more electropositive metal, the copper, in the form of a gray metallic film, which will, if the action be continued, separate in scales from the copper. Decant the solution, and pour some fresh water upon the coated copper, to wash away the last traces of the solution; then shake the copper out of the tube upon a piece of blotting-paper and dry it by gentle pressure, taking care not to disturb the film of arsenic ; com- plete the drying by warming the copper over a lamp-flame for a few seconds, then place it in an ignition-tube and draw out the middle of the latter in the blowpipe flame until it is contracted like the tube represented in fig. 20, p. 33. When it is cool, heat the bulb containing the copper, and notice that a ring of crystals is deposited at the contracted portion, which may with a magnifier be easily recognised as octohedra of arsenic trioxide. This test, which is usually called Reinsch's test, has the advantage that the presence of organic substances (e.g. milk, beer, in cases of poisoning) does not interfere with the de- position of arsenic on the copper. But other metals, such as antimony, bismuth, silver, are deposited on the copper under the same conditions as arsenic. Moreover, when the deposit of 284 ARSENIC. arsenic is heated, only a portion of the metal is volatilised, the rest forming a non-volatile alloy with the copper. The test, therefore, is by no means so reliable and characteristic as Marsh's test, which is described in p. 289. B. Tests for Arsenic protosalts and Arsenites. [The solutions of arsenic trichloride and potassium arsenite, already made, may be used.] *1. With hydrogen sulphide, in presence of hydrogen chlo- ride, they give a yellow precipitate, soluble in potassium hydrate. Add a few drops of the solution of arsenic trichloride to 5 c.c. of water, and test it with solution of hydrogen sulphide. A bright yellow precipitate of arsenic trisulphide (the common 1 orpiment ' used as a paint) will be formed. Divide the liquid into two portions. (a) To one portion add excess of solution of potassium hydrate and warm. The precipitate will readily dissolve, potas- sium sulpharsenite (KAsS 2 ) being formed. If a few drops of dilute hydrogen chloride are now added to the clear solution, arsenic trisulphide will be precipitated. (<5) Allow the precipitate in the other portion to subside, pour off the liquid, and boil the precipitate with a little strong hydro* gen chloride. It will remain almost unaltered, differing in this respect from antimony trisulphide, p. 288. This is given as being one of the methods for separating arsenic from antimony. *2. With silver nitrate, their solutions, when neutral, give a yellow precipitate. To a portion of the solution of potassium arsenite add enough dilute hydrogen nitrate to make the solution decidedly acid, and then add a drop of solution of silver nitrate. [If the hydrogen nitrate or potassium arsenite contained any chloride, a slight white precipitate will form on addition of the silver nitrate, which should be filtered off.] ARSENIC. 285 Mix in another test-tube some solution of ammonia with an equal volume of water, and pour the diluted ammonia from a pipette very slowly and carefully down the side of the test- tube containing the arsenic solution, so that the two fluids may not mix, but the lighter solution (the ammonia) may rest on the surface of the heavier. The tube containing the arsenic solu- tion should be held in an inclined position, in order that the ammonia may flow less rapidly down the side. A yellow film of silver arsenite will be formed at the surface of contact of the two fluids. We have in the test-tube three fluid strata : a lower one con- taining excess of hydrogen nitrate, an upper one containing excess of ammonia, and an intermediate one consisting of a neutral solution of ammonium nitrate. Silver arsenite is in- soluble in water, but soluble in excess both of acid and of alkali, and therefore appears only where the fluid is neutral. On shaking the fluid the yellow film will disappear altogether, unless just enough ammonia has been added to neutralise the acid. 3. With copper sulphate, their solutions, when neutral, give a bright green precipitate. Mix a little of the solution of potassium arsenite with about 5 c.c. of water and add a few drops of solution of copper sul- phate. A grass-green precipitate of copper arsenite will be formed. This is the brilliant but very poisonous paint called ' Scheele's green.' C. Tests for Ar senates. .. [The solution of potassium arsenate, already prepared, may be used.] 1. With hydrogen sulphide, they give hardly any precipi- tate, until reduced to protosalts. Acidify a portion of the solution of potassium arsenate with hydrogen chloride and divide it into two parts. (a) Add tp one portion some solution of hydrogen sulphide. 286 ANTIMONY. No precipitate will be produced, and even on heating only a slight yellow precipitate will fall. (3) Add to the remainder some solution of hydrogen sul- phite (or of sodium sulphite mixed with hydrogen sulphate), boil the liquid until it no longer smells of sulphur dioxide, and then test with hydrogen sulphide. A yellow precipitate of arsenic trisulphide will be formed, the hydrogen arsenate having been reduced to hydrogen arsenite by the action of the hydro- gen sulphite. *2. With, silver nitrate, their solutions, when neutral, give a red precipitate. Acidify another portion with hydrogen nitrate, add a few drops of solution of silver nitrate, and pour on the solution dilute ammonia, as directed, p. 284. A dull-red precipitate of silver arsenate will form at the point where the solution is neutral. *3. With magnesium sulphate, in presence of ammonium salts, they give a white crystalline precipitate. Add a few drops of ammonium chloride to another portion, and then a drop of solution of magnesium sulphate. A white crystalline precipitate will be formed, very similar in appearance, and analogous in composition, to magnesium-and-ammonium phosphate, the phosphorus being replaced by arsenic. Additional Experiment. Marsh's test for Arsenic. This is described in p. 289 & seq., and may be deferred until the reactions of antimony compounds have been examined. 5. ANTIMONY. [Symbol of atom, Sb (stibium). Weight of atom, 122 hydrogen-atoms,] ANTIMONY. 387 Preparation of compounds of Antimony. [Typical examples, Antimony trichloride (Sb C1 3 ). trisulphide (Sb a S 3 ). pentoxide (Sb 2 O 8 ). Antimony and potassium tartrate (K(SbO)C 4 H 4 O).] 1. Preparation of Antimony trichloride. Place a small fragment (about as large as a pea) of metallic antimony in a strong mortar, and strike it with the pestle. It will split to pieces and may readily be ground into a fine crystalline powder. Put a little of this powder into a test-tube, add 5 or 6 c.c. of strong hydrogen chloride and one or two drops (not more) of hydrogen nitrate, and apply heat. The metal will dissolve pretty readily, forming antimony trichloride. When the action has ceased, allow the liquid to cool, and decant the clear solution into another test-tube for use in experiments. 2. Formation of Antimony pentoxide. When strong hydrogen nitrate is poured upon antimony, the metal is not (like most others) dissolved as nitrate, but combines with some of the oxygen of the acid, forming antimony pentoxide. Put a little powdered antimony into ' a test-tube, pour over it a few drops of strong hydrogen nitrate, and heat gently. Orange vapours of nitrogen tetroxide will be given off abundantly, and the antimony will be converted into a white powder, the pentoxide, insoluble in the acid. Properties of compounds of Antimony. *1. They are, in some cases, decomposed by water, forming basic salts. Pour a few drops of the solution of antimony trichloride (prepared just now) into a test-tube and add 5 or 6 c.c. of water. A white precipitate, consisting of antimony oxychloride, will be produced. Divide the liquid into two portions ; (a) To one add a little strong hydrogen chloride. The precipitate will dissolve, and the solution may be reserved for use in experiment 2. 288 ANTIMONY. (b] To the other add some solution of sodium-and-hydrogen tartrate. The precipitate will in this case also be redissolved (differing in this respect from the corresponding bismuth oxy- chloride, p. 279). *2. With hydrogen sulphide they give an orange precipitate, soluble in potassium hydrate and ammonium sulphide, and in strong hydrogen chloride. Add to the acid solution of antimony trichloride, obtained in the last experiment, some solution of hydrogen sulphide. A characteristic orange precipitate of antimony trisulphide will be obtained. Allow this to subside (which it will do more quickly if gently warmed), pour off the fluid, and shake up the precipitate with a little water: then, before it has settled again, pour off half of it into another tube ; (a) To this portion add a little solution of potassium hydrate, and warm it. The precipitate will readily dissolve, potassium sulphantimonite being formed. (b] Pour off the clear liquid from the remainder, and boil the precipitate with a little strong hydrogen chloride. It will dissolve, differing in this respect from arsenic trisulphide, p. 284. *3. When placed in contact with zinc and platinum, they are reduced on the latter as a black powder. Place a piece of platinum foil in an evaporating dish ; put on it a small fragment of granulated zinc, and pour into the dish a little dilute hydrogen chloride. When the evolution of hydrogen has begun from the surface of the platinum, add a drop or two of the solution of antimony trichloride. The antimony will be thrown down on the platinum as a black coating, owing to galvanic action (p. 70). If the black de- posit is heated with a drop of ammonium sulphide it becomes orange 1 . *4. Reduced on charcoal, they give a brittle metallic globule, with a white incrustation. 1 The platinum may be cleaned from the deposit by warming it with a few drops of strong hydrogen chloride, to which one drop of hydrogen nitrate may be added. ANTIMONY. 289 Mix a little antimony trisulphide or antimony-and-potassium tartrate (tartar emetic) with potassium cyanide, and heat the mix- ture on charcoal before the blowpipe. Brilliant globules of metal will be produced, which lose their lustre at once on being removed from the reducing flame, and white fumes of antimony trioxide are produced and form an incrustation on the cool part of the charcoal. Owing to the volatility of the metal, these white fumes of oxide are emitted for some time after the globule is removed from the flame, especially if a stream of air from the blowpipe is directed upon it. When cold, the globule should be detached from the charcoal, placed in a mortar, and the pestle pressed forcibly down upon it. It will, as already observed, be crushed to powder instead of spreading out into a plate. Additional Experiment. Marsh's Test for Arsenic and Antimony. Apparatus required. Small flask ; thistle funnel ; two elbow tubes, one with long branch ; retort stand ; Bunsen's holder ; drying tube, filled with calcium chloride or quicklime ; hard glass tubing, 4 or 5 mm. external diameter ; Bunsen's burner ; Herapath's blow- pipe ; small por- celain dish, or broken pieces of one; three-square file; test tubes in basket ; small funnel ; filters. A. Detection of Arsenic. If a solution containing arsenic is brought into contact with nascent hydrogen, a volatile compound of arsenic and hydrogen is formed, corresponding in composition to the com- pound of nitrogen and hydrogen, or ammonia, and to one of the compounds of phosphorus and hydrogen. This reaction furnishes us with a most delicate test for arsenic, since the hydrogen arsenide is very readily decomposed, and thus the presence of arsenic in it may be demonstrated. The best method of applying the test, which is known as Marsh's test, is as follows: Place a few pieces of granulated zinc in a small flask, fitted u 290 ANTIMONY. with an acid funnel and right-angled elbow tube, and connect the latter with a drying tube filled with fragments of calcium chloride or quicklime, and supported in a horizontal position by a Bunsen's holder. Take a piece of difficultly fusible glass tubing about 4 mm. in diameter and 40 cm. in length ; soften it in the middle by means of the blowpipe-flame, and draw the two ends asunder, until the softened portion is contracted to a diameter of 2 mm. When it is cool, make a scratch with a file in the middle of the contracted portion, and break it at that point. You have now two tubes each about 18 cm. in length Fig. 64. and terminated by a jet J . Reserve one for an experiment with antimony, and connect the other with the drying tube, support- ing it horizontally on the largest ring of the retort- stand at such a height that a lamp may be placed underneath it. The whole apparatus will then be arranged thus, Fig. 64. Pour a little water on the zinc in the flask, and add a few 1 The jet shown in the figure is turned up. This, which is a slightly preferable form, may be obtained by moving the hands, in drawing out the glass, laterally (the one hand towards, the other from the body), so as to give the drawn-out tube the following form J^ . It should then be cut in two at a. ANTIMONY. 291 drops of strong pure hydrogen sulphate, so as to generate a moderately rapid current of hydrogen. Allow the gas to pass through the apparatus for about two minutes, in order to sweep out all traces of air. While this is going on, you may get ready a right-angled elbow tube with one long branch, a test-tube half filled with a dilute solution of silver nitrate (5 drops of the test-solution to 10 c.c. of water), and one or two pieces of clean porcelain, such as the lid of a crucible, or fragments of an evaporating dish. Now test the purity of the gas by collecting some in a test-tube held over the jet (see p. in). When you are quite sure that the gas is unmixed with air, you may light it at the jet and depress into the flame, for a few seconds, one of the pieces of porcelain. If any stain appears on the white surface (as may happen if the zinc or hydrogen sulphate is contaminated with arsenic) allow the stream of gas to pass a little longer, and do not proceed with the experiment until the porcelain depressed on the flame remains unstained. [If after several trials the stain still appears, the zinc is impure, and another sample must be used.] When this is the case, pour into the funnel about two drops (not more) of a solution of arsenic chloride, and wash it down into the flask with a little water. The first effect of this will be to increase the evolution of gas, and the flame of the jet will shortly become tinged with gray (not unlike the colour imparted to flame by the presence of potassium vapour). Hydrogen arsenide is now being formed, and you may proceed to decompose it in the three following ways : (a) By the heat produced by its own combustion. Place in the flame a clean cold surface of porcelain, such as the glazed interior of an evaporating dish, depressing it until it almost touches the jet from which the gas is issuing. A black spot, consisting of metallic arsenic or of a lower hydride, will be formed on the white surface. Two or three of these should be made on different parts of the porcelain, and reserved for future examination 1 . 1 They are formed for the same reason that soot is deposited on a plate held in a candle-flame. The gaseous compounds of carbon and hydrogen U 2 292 ANTIMONY. (b] By heat applied to the 'tube through which the gas is passing. Place a lamp underneath the tube near the end at which the gas enters, and heat that part of the tube to redness. A black, shining ring of arsenic will be deposited just beyond the heated portion of the tube, while the flame at the jet will lose its gray colour, showing that the arsenic has been arrested in its course to the jet. (c) By a solution of silver nitrate. Detach the drying tube (and the tube containing the arsenic deposit), and fit in its place the elbow tube, the longer branch of which should reach to the bottom of the test-tube containing the solution of silver nitrate : the latter may be sup- ported in an upright position by the smallest ring of the retort- stand. Pour, if necessary, a little more acid and solution of arsenic chloride into the flask. .The solution of silver nitrate will soon become turbid, and a black deposit of metallic silver will be formed, while silver arsenite will remain in solution in the hydrogen nitrate which is formed 1 . The evolution of gas should now be stopped, by taking the cork out of the flask and pouring the solution away from the zinc, which latter, after being thoroughly washed, may be retained in the flask for a similar experiment with antimony. You have now three results of the decomposition of the hydrogen arsenide, which are to be further examined. (a) The spots on the porcelain. Dip a glass rod in strong hydrogen nitrate, and moisten one of the spots with it. The metal will dissolve in the acid, especially if the porcelain be gently warmed, and on evapora- tion a white residue .of hydrogen arsenate will be left. Add another drop of acid, and again evaporate to dryness, to ensure are decomposed by the heat of combustion ; the hydrogen is completely oxidised to water, the carbon is only partially oxidised to carbon dioxide, the excess of carbon being suspended in the flame and deposited on any- cold surface brought in contact with it. Similarly in the present experi- ment the hydrogen of the hydrogen arsenide is oxidised into water, while an arsenic soot is deposited on the porcelain. = Ag 8 AsO i + 9 HNO i + 3 Ag 2 . ANTIMONY. 293 the complete oxidation of the arsenic. Do not raise the tem- perature beyond the point necessary to drive off the excess of hydrogen nitrate, lest the hydrogen arsenate should be itself decomposed. Moisten the residue with a drop of solution of silver nitrate and again evaporate to dryness. A red de- posit of silver arsenate will be left, readily seen on the white porcelain. 0) The deposit formed in the tube. Connect the tube with a drying tube (rilled with calcium chloride, not quicklime), and arrange them as before, when the deposit was to be formed (placing the whole in a draught cupboard, if possible). In place of the hydrogen gene- rating flask attach to the drying tube a test-tube fitted with a thistle funnel and elbow tube, and containing one or two lumps of iron sulphide and a little water. Pour down the funnel a few drops of strong hydrogen sulphate, just sufficient to liberate a slow stream of hydrogen sulphide gas. When the air has been expelled from the apparatus, light the gas at the jet (merely to prevent its escape into the room), and heat the metallic deposit by a spirit lamp with a very small flame, beginning at its outer border, or that farthest from the end at which the gas enters. The arsenic as it volatilises will decompose the hydrogen sulphide, combining with its sulphur and forming a yellow ring of arsenic trisulphide in the cool part of the tube, which is very volatile and may be driven about from one part of the tube to another by the heat of the lamp. (c) The solution containing silver arsenite. Filter this from the reduced silver, and pour gently upon its surface some very dilute solution of ammonia from a pipette (see experiment 2, p. 284). A yellow stratum of silver arsenite will be formed at the point where the solution is neutral. B. Detection of Antimony. Antimony, like arsenic, forms a volatile compound with hydrogen, which may be decomposed by heat and silver nitrate, but with results which enable us to distinguish it without diffi- culty from hydrogen arsenide. 294 ANTIMONF. Arrange an apparatus similar to that already described in the case of arsenic. After making sure that the hydrogen evolved is pure and leaves no stain upon the porcelain, pour into the funnel two drops of solution of antimony trichloride, and wash it down with a little dilute hydrogen sulphate. Then proceed with the experiments precisely as already directed for arsenic, and compare the results obtained in the two cases. (a) Decomposition of the gas by the heat of combustion. The dark spots formed on the porcelain are more like soot, and not so brown and lustrous as those of arsenic. They leave a white residue when treated with hydrogen nitrate, but yield no red deposit with silver nitrate 1 . (l>) Formation of a black deposit of antimony in the heated tube, and subsequent conversion of this into sulphide, by passing hydrogen sulphide over it. A dark orange-red film of antimony trisulphide will be formed, close to the deposit in the tube, which is only volatilised with difficulty, by the utmost heat of the lamp. (?) Decomposition of the gas when passed into solution of silver nitrate. The whole of the antimony is precipitated as silver anti- monide 2 . No yellow layer or precipitate, therefore, is seen when the filtrate is neutralised by ammonia. In order to prove the presence of antimony in the precipitate, wash it on the filter, then place the portion of the filter which contains the precipitate in a beaker and boil it with a little solution of sodium-and-hydrogen tartrate together with one or two drops of hydrogen chloride, when the antimony will dissolve while the silver will remain as insoluble chloride. Filter the solution and test it with hydrogen sulphide, which will give the charac- teristic orange precipitate of antimony trisulphide. It is obvious that in cases where we have both antimony and arsenic in the same solution this last test gives us a means of separating the two metals, the antimony being found in the 1 A black deposit of reduced silver is sometimes formed, if a sufficient excess of hydrogen nitrate has not been added. TIN. 295 precipitate produced when the gases are passed into the silver nitrate solution, while the arsenic remains in solution. The two metals may also be discriminated by the difference in volatility of their sulphides. When the mixed metallic deposit in the tube is heated in a current of hydrogen sulphide, the yellow ring of arsenic trisulphide is always deposited considerably in advance of the orange sublimate of antimony trisulphide. e. TIN. [Symbol of atom, Sn (stannum). Weight of atom, 1 1 8 hydrogen-atoms.] Crystalline character of tin. Take a strip of tin (the best tin is usually sold in strips or thin rods), bend it quickly backwards and forwards several times, holding it to the ear while doing so. A crackling sound will be heard, and the metal will become sensibly warm at the point of flexure. Cast tin although to a certain extent malle- able and ductile is crystalline in structure, and the crackling sound and heat is due to the motion of the crystals, over each other, and their mutual friction. The crystalline structure may also be shown by washing the surface of a strip of tin plate (which is sheet iron coated with tin) with a little alcohol to free it from grease, and then, after rinsing it with water, applying with a piece of sponge or tow a mixture of 5 c.c. dilute hydrogen chloride with 2 c.c. of dilute hydrogen nitrate (the ordinary laboratory solutions). The bright surface will soon show a variety of irregular patches, somewhat like ' watered ' silk, and should then be well washed with clean water, to stop further action of the acid. The reason is, that the film of tin upon the iron consists of numerous small crystals buried in a mass of less crystalline material. The acid attacks the latter more readily than the crystals, and lays bare the faces of the latter, showing their symmetrical arrangement, like masses of soldiers all facing the same way. 396 TIN. Preparation of compounds of Tin. [Typical examples, Tin protochloride (Sn C1 2 ). perchloride (Sn C\ t ). dioxide (Sn O 2 ),] Tin, like mercury, forms two well-defined series of salts, in one of which it is diatomic, in the other tetratomic. The conditions necessary for the formation of each series are, pre- sence of excess of the metal for the protosalts, and excess of the acid radicle for the persalts. 1. Tin protochloride. Place about 2 grms. of pure tinfoil (see note J ) in a large test-tube, add 10 c.c. of strong hydrogen chloride, and boil for a quarter of an hour. Hydrogen will be evolved, the metal taking its place and forming tin protochloride 2 . Pour off the solution while a little of the metal still remains undissolved, dilute it with water to 30 c.c., and reserve it in a corked tube or bottle for experiments, placing in it a small bit of metallic tin to prevent its passing into the state of persalt. 2. Tin perchloride. Put i grm. of tinfoil into a test-tube, pour on it 5 c.c. of strong hydrogen chloride, and two drops (not more 3 ) of strong hydrogen nitrate, and heat gently. The metal will readily dis- solve, and when the solution is complete the liquid should be poured into a porcelain dish and evaporated on the sand-bath, about i c.c. of strong hydrogen nitrate being added to convert any remaining protosalt into persalt (which it does, of course, by causing the liberation of chlorine, p. 193). To make sure that the conversion into perchloride is complete, take out a drop 1 Much of what is sold as tinfoil is an alloy of tin and lead. The pure tinfoil may be known by its comparatively rough surface and greater thick- ness. The sheets of the alloy are much thinner and more pliable, and have a bright polished surface. If tinfoil is not at hand, a little tin should be granulated as directed in the case of zinc (p. 28). = Sn Cl 2 + H 2 . 3 If much hydrogen nitrate is added at once, the tin may be precipitated as perhydrate. TIN. 297 or two of the liquid with a pipette, dilute it with water and test it with a drop of mercury perchloride. If any precipitate is produced, some tin protochloride still remains, and a few more drops of hydrogen nitrate must be added. Finally, evaporate the solution to half its original bulk (stopping the evaporation when white fumes of the perchloride appear), dilute it with water to 30 c.c., and reserve the solution for experiments. 3. Tin dioxide. This is formed by the action of strong hydrogen nitrate upon tin, which is quite analogous to its action upon antimony, p. 287. Place a bit of granulated tin, or of tinfoil, in a test-tube, and pour on it some strong hydrogen nitrate. Notice the violent action, the evolution of orange vapours of nitrogen tetroxide, and the formation of a white powder, tin dioxide, which is insoluble in excess of the acid. Properties of compounds of Tin. A. Protosalts (Stannous Salts). [The solution of tin protochloride already made, may be used.] *1. With hydrogen sulphide they give a dark brown pre- cipitate, soluble in potassium hydrate and ammonium sul- phide. Add excess of solution of hydrogen sulphide to a portion of the solution of tin protochloride. A dark brown, nearly black precipitate of tin protosulphide will be formed. Divide the liquid into two portions, (a) To one add some solution of potassium hydrate, and warm it. The precipitate will redissolve, a double sulphide of tin and potassium being formed. On addition of dilute hydrogen chloride to this, the brown protosulphide will be reprecipitated. (<5) To the other portion add a slight excess, of ammonia, then some solution of ammonium sulphide (which should be 298 TIN. yellow, owing to the presence of higher sulphides), and warm the mixture. The precipitate will redissolve, as in the last experiment, but in this case a higher sulphide of tin is formed, viz. tin disulphide, which forms a double salt, ammonium sulphostannate. On addition of excess of dilute hydrogen chloride to the clear solution, a light yellow precipitate of tin disulphide will be formed. *2. With mercury perchloride they give a white precipitate, quickly turning gray. To another portion add a drop of. solution of mercury perchloride. A white precipitate of mercury protochloride will be produced, the colour of which changes, however, im- mediately to gray (the tin salt being in excess) owing to its reduction to metallic mercury 1 . *3. Reduced in contact with zinc and platinum they yield a gray spongy deposit of metal. Put a piece of platinum foil in a porcelain dish, add a little dilute hydrogen chloride, and drop in a bit of granulated zinc. Hydrogen will of course be evolved. Now add one or two drops of solution of tin protochloride; metallic tin will be quickly reduced as a porous, moss-like mass (similar to the 'lead-tree/ p. 268) chiefly round the zinc, and readily washed away from both the zinc and the platinum by a stream of water. Compare the similar experiment with antimony, p. 288, in which the deposit obtained was formed on the platinum alone, black, and closely adherent. *4. Reduced on charcoal, they yield a malleable metallic globule, with a white incrustation. The mode of performing this experiment has been already given, p. 94. B. Persalts (Stannic Salts). [The solution of tin perchloride (p. 297) may be used.] *1. With hydrogen sulphide they give a yellow precipitate, soluble in potassium hydrate and ammonium sulphide. 1 (i) Sn C1 2 + 2 Hg Cl a = Sn C1 4 + Hg 2 C1 2 . (ii) Sn C1 2 + Hg 2 C1 2 = Sn C1 4 + 2 Hg. GOLD. 299 Add solution of hydrogen sulphide to a portion of the solution of tin perchloride, and apply heat. A light yellow precipitate of tin disulphide will be formed, increased in quan- tity and rendered flocculent, as the temperature rises. Divide the liquid into two portions and try its solubility in potassium hydrate and ammonium sulphide as directed in the case of the protosalts, p. 296. *3. With mercury perchloride they give no precipitate. *4. Reduced in contact with zinc and platinum. ) *5. Reduced on charcoal before the blow-pipe. \ The results with these two tests are the same as in the case of the protosalts. 7. GOLD. [Symbol of atom, Au (aurum). Weight of atom, 197 hydrogen-atoms.] [Solutions containing gold should not, of course, be thrown away, but put into a bottle labelled ' Gold Residues.' For the method of recovering gold from them, see Appendix B.] Preparation of Gold trichloride. [Formula of molecule, AuCl 3 .] Place a leaf of gold in a test-tube, by placing a slightly damp glass rod in contact with one edge of the leaf, rolling the latter round the rod, then transferring it to the tube and unrolling it within. Add about 2 c.c. of strong hydrogen chloride, and observe that the metal will not dissolve in the acid, even on boiling. Treat another leaf of gold with hydrogen nitrate in a similar way ; it will also be found to be unacted upon. Now mix the contents of the two tubes ; the metal will at once dissolve in the 'aqua regia' thus formed (see p. 193), and a yellow solution of gold perchloride will be obtained. Pour this into a porcelain dish, add two or three more leaves of gold, and 300 GOLD. a little more hydrogen chloride, and evaporate nearly, but not quite, to dryness on a sand-bath *. Dilute the solution with about 15 c.c. of water, and use it for the following experiments. Tests for compounds of Gold. *1. With hydrogen sulphide they give a black precipitate, soluble in potassium hydrate and ammonium sulphide. Add excess of hydrogen sulphide to a portion of the solution of gold trichloride, and warm the mixture. A black precipitate (or if the solution is dilute, a deep black liquid) will be obtained, which will slowly dissolve on addition of excess of potassium hydrate, forming a nearly colourless solution of potassium sulphaurate. *2. With iron protosulphate they yield a brown precipitate of metallic gold. Add to another portion some solution of iron protosulphate. The liquid will rapidly darken, and metallic gold will be preci- pitated as a brownish powder (the liquid in which the precipitate is suspended having a blue or green colour by transmitted light), or if the solution is strong, as a spongy mass. If the quantity of precipitate is sufficient, it may be washed by decantation and dried in a watch-glass ; if a portion of it be then burnished with the end of a glass rod or of a test-tube, it will acquire the metallic yellow lustre of gold. *3. With tin chloride they yield a purple precipitate. Test another portion of the solution of gold trichloride with solution of tin protochloride to which one drop of iron per- chloride has been added (in order to form a little perchloride in the liquid). A brownish purple precipitate will be formed, called from its discoverer, the 'purple of Cassius/ containing gold, tin, and oxygen, but not, apparently, of definite composi- 1 If you wish to drive off the whole of the excess of acid, the evaporation should be finished on the water-bath, since, if the temperature is raised much above 100, an insoluble protochloride is formed. For the following experiments a slight excess of acid is of no consequence. GOLD. 301 tion. When the solutions are very dilute, the colour of the liquid changes to brownish red, but no precipitate falls which can be separated by nitration. Additional Experiment. Transparency of Gold leaf. Gold is the only metal which has with certainty been reduced to sheets so thin that light will pass through them; their thickness being, in fact, no greater than Taboo mm. In order to examine this, it is best to spread out the leaf flat upon a glass plate, which may be done in the following way. Clean the glass plate, which should be about 15 cm. square, with a tuft of cotton- wool dipped in alcohol, dry it with a clean cloth, and lay it flat on the table. Slightly damp the edge of a paper-knife or a glass rod, an^ lay it on one edge of the leaf of gold, to which it will adhere ; you can then transfer the leaf to the plate and lay it approximately flat on the glass. Detach the paper-knife from the gold by slightly rubbing it against the glass, and then, still keeping the glass horizontal, direct a very gentle stream of water from a wash-bottle under the leaf of gold. The water will spread quickly over the glass, and the leaf will float on it, losing all inequalities and wrinkles. You have now only to raise very carefully and slowly one corner of the glass, holding a glass rod at the opposite corner to guide the water in flowing off, and to absorb the remaining water with blotting-paper, finally holding the plate over a lamp until it is perfectly dry. The leaf of gold is left as a perfectly smooth film on the glass. Hold it up to the light, and notice the deep green colour of the transmitted light. Examine it with a magnifier ; many holes will be seen, and much inequality of thickne'ss, but the greater portion of the leaf is a continuous film, even under high magnifying powers. 302 PLATINUM. 8. PLATINUM. [Symbol of atom, Pt. Weight of atom, 197 hydrogen-atoms.] [All waste solutions &c. containing platinum should be put into a bottle labelled * Platinum Residues.' To recover the metal from them they may be treated as directed in Appendix B.] Preparation of compounds of Platinum. [Typical examples, Platinum perchloride (PtCl 4 ). Platinum-and-ammonium chloride (Pt (H 4 N) C1 5 ).] 1. Platinum perchloride. For the experiments on platinum compounds the ordinary laboratory solution of platinum perchloride may be used ; but if you have any waste scraps of platinum foil or wire they may be converted into the tetrachloride in the following way. Measure 6 c.c. of strong hydrogen chloride into a large test- tube, add 2 c.c. of strong hydrogen nitrate, drop in about 0.2 grm. of thin platinum foil or wire, and heat the tube on the sand-bath. Platinum, like gold, is not soluble either in hydrogen chloride or in hydrogen nitrate, but is readily acted upon by the chlorine evolved during the mutual decomposition of these acids, and dissolves as perchloride. Evaporate the solution in a dish, in a draught cupboard or the open air, observing the same precautions as in the case of gold, since an insoluble platinum protochloride is formed if the temperature is high. Dilute the solution with about 10 c.c. of water for use in the following experiments. 2. Platinum-and-ammonium chloride. Put about 3 c.c. of the solution of platinum perchloride into a test-tube, add an equal volume of strong solution of am- monium chloride, and shake the mixture. A yellow, crystalline precipitate of platinum-and-ammonium chloride will be formed 1 , 1 The ordinary platinum foil &c. often contains iridium. If this is the case, the solution of the perchloride will be deep red, and the precipitate formed by ammonium chloride will be dull, brick-red, instead of yellow. The presence of iridium will not, however, interfere with the experiments. PLATINUM. 303 the separation of which will be hastened by the addition of 5 or 6 c.c. of common alcohol (in which the precipitate is less soluble than in water). Leave the precipitate to subside for a few minutes ; then pour the whole on a small filter, and wash it with water to which about one-fourth its volume of alcohol has been added, rinsing the precipitate as much as possible down to the point of the filter. Lastly, dry it on the filter at a gentle heat, while other experiments are proceeded with. 3. Spongy platinum. This is the condition in which the metal is obtained by gently igniting platinum-and-ammonium chloride. Take the dry (or partially dry) filter containing the preci- pitate of platinum-and-ammonium chloride, cut off the part of it which contains the precipitate, fold this up as closely as possible, and coil the end of a piece of platinum wire two or three times round it, so as to form a compact bundle. Heat this gradually to low redness over the flame of a Bunsen's burner, until all the paper has been burnt away and nothing remains but a gray mass of metallic platinum. During the ignition ammonia and chlorine are given off, and the skeleton of metal which remains is highly porous and has the property of absorbing large quantities of gases. It should be kept for use in the following experiments. [Platinum may be obtained in a state of division still finer than platinum sponge in particles so fine, in fact, that they almost cease to reflect light, and form a black impalpable powder. The readiest method of preparing 'platinum black' is to add excess of sodium carbonate to platinum perchloride, and then to boil the liquid with a little grape sugar. Carbon dioxide is evolved with strong effer- vescence, and a black powder is formed (gradually, if the solution is dilute) which should be washed by decantation successively with dilute alcohol, hydrogen chloride, potassium hydrate, and finally water, and then dried at a gentle heat. This powder is still more effective than spongy platinum in producing chemical combination.] Action of platinum in causing chemical combination. This is best shown when the metal is in a finely divided state, as in the form of spongy platinum and platinum black. 304 PLATINUM. But even platinum in the ordinary compact condition shows the same property to a certain extent, as has been already illustrated in the oxidation of ammonia, p. 130. The action is thought to be due to the power possessed by platinum of con- densing gases upon its surface, and thus bringing the molecules closely into contact. 1. Combination of oxygen and hydrogen. (a) Fit a glass jet by means of a cork to a moderate sized test-tube ; put into the latter a bit of granulated zinc and pour on it some dilute hydrogen sulphate ; then fit the cork again into its place. Allow the stream of hydrogen to escape for at least a minute, and test its purity by collecting some in a test- tube, as directed in p. in. When pure hydrogen is issuing from the jet, hold a little in front of it the spongy platinum already prepared, still held in the coil of wire. It will become red-hot, owing to the combination at its surface of the hydrogen with the oxygen of the air, and the gas will ignite at the jet \ () Hold the spongy platinum in a stream of coal gas and air (not ignited) issuing from the tube of a Bunsen's burner. The metal will become redrhot, but the gas will not ignite, since coal gas requires a higher temperature than hydrogen to kindle it. (c) Place a piece of fine wire gauze on the chimney of an Argand burner, and put upright upon it a small cylinder of platinum foil, made by rolling it loosely round a pencil or small test-tube. Turn on the gas partially, and light it above the wire gauze. When the platinum has become red-hot, extin- guish the flame by pinching the india-rubber connecting tube, and immediately (before the platinum has had time to cool entirely) allow the gas to flow again. The platinum will begin to glow afresh, and maintain a steady red heat. If a dry gas bottle is held close over it, moisture will be deposited, and the presence of carbon dioxide may be proved in the usual way. 2. Combination of ether with oxygen. Pour a few drops of ether into a beaker or wine-glass, and cover the glass partially with a card, to the centre of which is 1 If the spongy platinum has been exposed to the air for some time, it may be necessary to ignite it gently afresh, and let it cool before use. PLATINUM. 305 attached the wire carrying the spongy platinum (or a coil of platinum wire) previously heated to redness in a lamp, so that it may hang down within the glass nearly to the bottom. Pun- gent vapours of aldehyd are at once produced, and this com- pound is further oxidised to hydrogen acetate. The presence of the latter may be shown by holding in the beaker a strip of blue litmus paper which will be strongly reddened *. Tests for compounds of Platinum. [The solution of platinum perchloride may be used.] *1. With hydrogen sulphide they give a black precipitate, soluble in potassium hydrate and ammonium sulphide. Dilute a few drops of the solution with 5 or 6 c.c. of water, add solution of hydrogen sulphide, and warm it. A black pre- cipitate of platinum persulphide will be formed, which will dissolve, but only with difficulty, in excess of solution of potas- sium hydrate. *2. With potassium salts they give a yellow crystalline pre- cipitate. Add a few drops of dilute hydrogen chloride to a little of the solution of platinum perchloride (which shpuld not be diluted with water), and then a drop or two (not sufficient to neutralise the acid) of solution of potassium hydrate, and stir the mixture with a glass rod if the precipitate does not form at once. A yellow crystalline precipitate will be more or less quickly formed, especially along the lines where the sides of the tube were touched by the glass rod. This consists of platinum-and- potassium chloride, analogous to the platinum-and-ammonium chloride already prepared. 1 The successive stages of the oxidation may be expressed as follows : Ether. Aldehyd. (i) aC 4 H 10 O + O 2 = 4C 2 H 4 O+2H 3 O. Aldehyd. Hydrogen acetate, (ii) 4C a H 4 O+2O a = 4H(C 2 H 3 O)O. X 306 IRON. Group III. Metals which are separated from solutions by Ammonium sulphide. IRON, COBALT, NICKEL, MANGANESE, CHROMIUM, ALUMINIUM, ZINC. 1. IRON. [Symbol of atom, Fe (ferrum). Weight of atom, 56 hydrogen-atoms.] iiusiT Compounds of Iron. slA. J [Typical examples, Iron magnetic oxide (Fe 3 O 4 ). peroxide (Fe 2 O 3 ). protosulphate (Fe SO 4 ). persulphate (Fe 2 (S O 4 ) 3 ) .] [The combination of iron with sulphur has been illustrated already, p. 216.] 1. Formation of iron magnetic oxide. Clean a small strip of sheet iron with a file or with emery- paper, until it shows a bright metallic surface ; then hold it with a pair of pliers or crucible tongs in the flame of a Bunsen's burner or spirit lamp. The surface will soon lose its lustre, becoming in succession light yellow, orange, blue, and finally dark gray, owing to the formation of an extremely thin film of oxide. If the strip of iron be maintained at a red heat for a few minutes (in a blowpipe flame or in an ordinary fire), the film of oxide will increase in thickness, and will be detached in the form of black scales when the iron is quenched in cold water. These scales consist of the same iron oxide as that which was formed when the watch-spring was burnt in oxygen gas (p. 103). When a magnet is brought near them they will be attracted by it ; and this oxide, from this property and from IRON. 307 its identity in composition with the native loadstone, is called the magnetic oxide. 2. Formation of iron peroxide (ferric oxide). Fill the bulb of an ignition-tube with powdered iron proto- sulphate, and heat it strongly in the flame of a Bunsen's burner, holding it nearly horizontally in the crucible tongs. The salt will first melt in its water of crystallisation, then it will turn white, give off aqueous vapours, and lastly, as the temperature rises nearly to redness, it will decompose, giving off vapours of sulphur dioxide and trioxide, the latter of which will combine with the water to form an extremely strong kind of hydrogen sulphate which will redden litmus paper held at the mouth of the tube. A red residue will remain in the bulb, which consists of iron peroxide, or sesquioxide (the ordinary ' rouge ' used for polishing, &C.) 1 . [This illustrates the derivation of the term ' oil of vitriol ' applied to hydrogen sulphate, since the old name for iron protosulphate is ' green vitriol.' The acid thus obtained is called 'Nordhausen acid' from the place where it is made.] 3. Preparation of iron proto- and per-sulphates. Iron forms at least two well-defined series of salts, in one of which (the protosalts) i atom of the metal replaces 2 atoms of a monatomic radicle, such as hydrogen ; in the other (the per- salts) i atom replaces 3 atoms (or 2 atoms replace 6 atoms), of a similar radicle 2 . The conditions necessary to form them are, as usual, excess of the metal for the protosalts, and excess of the non-metallic radicle for the persalts. But the oxygen of the air, or that dis- solved in the water, so readily determines the .change of atom- icity that it must be excluded as far as possible in preparing the protosalts. A. Iron protosulphate (ferrous sulphate). Take about 2 grms. of fine iron wire (or of iron filings, if = 2Fe 2 3 +2S0 2 + 2 This will be seen by comparing the formula of each of the two iron sulphates with that of a quantity of hydrogen sulphate containing the same number of atoms of the sulphate radicle. Iron protosulphate, Fe SO 4 . Iron persulphate, Fe 2 (SO 4 \. Hydrogen sulphate, H 2 SO 4 . Hydrogen sulphate, H^SO 4 )s X 2 30 8 IRON. wire is not at hand), clean it from rust, if necessary, by drawing it between folds of emery paper, form it into a small close coil and place it in a moderate-sized test-tube, to which must be fitted a cork in the side of which a small nick has been cut to allow gas to escape. Pour on the iron about 10 or 12 c.c. of dilute hydrogen sulphate, and add a few drops of the strong acid and warm gently if the action appears slow. Hydrogen gas will be given off with effervescence 1 , the iron taking its place and forming iron protosulphate (compare the action of zinc on hydrogen sulphate, p. 106). Allow the action to go on for 10 or 12 minutes (keeping up a brisk action by warming the liquid and adding a little more strong acid when required) while other experiments, such as those in p. 313, are proceeded with. When nearly (but not quite) all the iron has dissolved, pour half the solution into a small porcelain dish, and reserve the rest (taking especial care that some metallic iron remains in it undissolved, and that the tube is kept corked, otherwise some persalt will be formed) for experiments on the proto- salts. B. Iron persulphate (ferric sulphate). To prepare this from the protosulphate we have in fact to cause two molecules of the salt [2 FeSO 4 ] to take up one atom of the sulphate radicle [SOJ and form a molecule of the per- sulphate [Fe 2 (SO 4 ) 3 ]. Excess of acid must therefore be present, and also some oxidising agent such as hydrogen nitrate ; the oxygen from which may combine with the hydrogen of a mole- cule of the acid, and leave the sulphate radicle free to unite with the iron protosulphate. Take the portion of the solution which was poured off just now into the dish, add a few drops of dilute hydrogen sulphate, and heat it gently on a sandbath. Add strong hydrogen nitrate, a drop at a time, as long as the addition of a drop causes a transient brown colour in the liquid 2 . Leave the dish exposed 1 Observe the strong peculiar smell of the gas (pure hydrogen having no perceptible smell), which is due to the presence of traces of compounds of hydrogen and carbon, the latter element being always present in ordinary iron. 2 The reason of this will be evident from the experiment already made IRON. 309 to a gentle heat for some minutes (in order to drive off any excess of hydrogen nitrate) while the following experiments are tried. Properties of iron protosalts (ferrous salts). [These are so very readily converted into persalts by mere expo- sure for a few moments to air or to water containing air, that it is rather difficult to observe their true reactions. In the following experiments a drop or two of the solution of iron protosulphate should be added to the tube already containing the test solution, and the cork must be replaced at once.] i 1. With hydrogen sulphide they give no precipitate or change of colour. Pour into a test-tube 2 or 3 c.c. of solution of hydrogen sulphide, and add about two drops of the solution of iron pro- tosulphate. This will produce no change, showing that iron differs from the group of metals last considered in not forming a sulphide in presence of acid. *2. With ammonium sulphide they give a black precipitate, soluble in hydrogen chloride. To the clear liquid obtained in the last experiment add solution of ammonium hydrate (which will combine with the hydrogen sulphide forming ammonium sulphide). A black precipitate of iron protosulphide will be formed, which will readily dissolve on addition of a few drops of dilute hydrogen chloride. *3. With potassium hydrate they give a white precipitate, quickly turning black and then reddish brown. Pour into a test-tube a few drops of solution of potassium hydrate, add a little water, and then a drop or two of the solu- tion of iron protosulphate. A grayish white flocculent preci- pitate of iron protohydrate will be formed, which, if the tube be shaken for half a minute, will rapidly become darker, and be with nitrogen dioxide (p. 146). The hydrogen nitrate, by the loss of oxygen, is reduced to nitrogen dioxide, which unites with the iron salt, forming a brown compound easily decomposed by heat. Compare the test for nitrates (p. 137). 310 IRON. finally converted into a reddish brown perhydrate, by absorbing oxygen from the air. *4. With potassium ferrocyanide they give a white preci- pitate quickly turning blue. Pour into another test-tube a little solution of potassium ferrocyanide, add water, and then a drop of the solution of iron protosulphate. A precipitate will be formed which is at the first moment nearly white, but rapidly changes to deeper and deeper shades of blue, when the test-tube is shaken, or when the solution is poured backwards and forwards several times from one test-tube to another. *5. With potassium ferricyanide they give a deep blue pre- cipitate at once. Repeat the last experiment, using potassium ferricyanide in- stead of ferrocyanide. A deep blue precipitate will be at once formed, and will undergo no further change in the air. This forms the paint called ' Turnbull's blue/ *6. With potassium sulphocyanate they give no change of colour or precipitate. To some solution of potassium sulphocyanate diluted with water add a drop or two of the solution of iron protosulphate. No change will take place at first in the solution, since iron proto-sulphocyanate is colourless ; but on shaking the test-tube the liquid will become light red, and eventually of the colour of dark sherry. The appearance of this red colour is an extremely delicate test for iron persalts, as will be seen, p. 312. *7. Heated in a borax bead they colour the bead yellow in the oxidising flame, dull green in the reducing flame. Form a borax bead in the usual way (p. 92) and add to it a minute quantity of powdered iron protosulphate. Heat the bead again, holding it near the tip of the blue flame until the iron salt is dissolved, then bring it into the oxidising flame and hold it there steadily for a few seconds. On withdrawing it from the flame, you will find that (if the right proportion of iron has been taken) it is orange-coloured while hot, becoming light yellow as it cools. In the next place, heat it in the reducing flame for half a minute ; its colour will now be found to have IRON. 311 changed to a dull green (like that of bottle-glass), which be- comes paler on cooling. Properties of iron persalts (ferric salts). Pour into a test-tube the solution of iron persulphate pre- pared already; notice that it has a yellow colour, while the original solution was nearly colourless ; add 30 c.c. of water, and examine portions of the solution with the tests given above, which may be applied in the usual way to portions of the solu- tion, since iron persalts are not altered in the air. *1. With hydrogen sulphide they give a white, milky pre- cipitate of sulphur. This is owing to their reduction to protosalts ; the hydrogen of the hydrogen sulphide combining with some of the non- metallic radicle (in this case the sulphate radicle), while its sulphur is separated 1 . *2. With ammonium sulphide they give a black precipitate. Add ammonium sulphide to another portion of the solution. A black precipitate of iron protosulphide will be formed, soluble (with the exception of a little sulphur which may separate) in dilute hydrogen chloride. *3. With potassium hydrate they give a reddish-brown precipitate. This consists of iron perhydrate, and is unaltered when shaken up with air. *4. With potassium ferrocyanide they give a deep blue precipitate. This consists of ' Prussian blue/ the formsrtion of which has been already mentioned, p. 181. 5. With potassium ferricyanide they give no precipitate, the liquid turning brown. (If the solution of potassium ferricyanide has been made for some time, it is liable to contain a trace of ferrocyanide, and then the solution becomes green instead of brown.) 1 2 Fe 2 (SO 4 ), + 2 H 2 S = 4 Fe SO 4 + 2 H z SO 4 + S a . 312 IRON. *6. With potassium sulphoeyanate they give a dark red liquid. This should be tried, with one (or at most two) drops of the solution of the iron persalt in order to prove the delicacy of the test. *7. Heated in a borax bead they give the same results as the protosalts. Conversion of salts of the one series into those of the other. A. Protosalts into persalts. The principle on which this may be done has already been explained, p. 308 : and one mode of effecting it, viz. by hydro- gen nitrate, has been employed. Besides oxygen, however, other substances which have an affinity for hydrogen may be employed to withdraw it, such as chlorine. In this case the change is, by analogy, still termed an ' oxidation/ Pour off the remainder of the solution of iron protosulphate into another test-tube (keeping back the undissolved iron), add a few drops of solution of chlorine, and warm the mixture 1 . The solution will now give the characteristic reactions of iron persalts, and portions of it should be examined by tests 4 and 6. B. Persalts into protosalts. In this case we have to withdraw a portion of the non- metallic radicle from the molecule of persalt. This may be done by various reducing agents (for instance hydrogen sul- phide, as in Expt. i, p. 311), but hydrogen in the nascent state is one of the best for the purpose. Add a few drops of dilute hydrogen sulphate to the re- mainder of the solution of iron persulphate, place a fragment of granulated zinc in the solution, and close the tube with a cork having a nick cut in its side. Hydrogen will be evolved by the action of the zinc on the acid, and the solution will 1 2 Fe SO 4 + H 2 SO 4 + C1 2 == Fe 2 (SO 4 ) 3 + 2 H Cl. IRON. 313 gradually lose its colour 1 , and will give the reactions of iron protosalts, viz. a deep blue precipitate with potassium fer- ricyanide, and a colourless solution with potassium sulpho- cyanate 2 . Additional Experiments. 1. Formation of ink. Dissolve about half a gramme of iron protosulphate in 10 c.c. of water, and add a few drops of solution of iron perchloride (to ensure the presence of a persalt), and then a little infusion of nut galls or solution of hydrogen gallate (gallic acid). A bluish black precipitate of iron gallate will be formed, which will remain in suspension for a long time, owing to its finely divided state. Ordinary writing ink is thus made, a little gum being added to prevent the subsidence of the precipitate. 2. Passive state of iron. This is the name given to that condition of iron in which it is unacted on by strong hydrogen nitrate, probably owing to the presence of a thin film of oxide upon its surface (compare the protection of lead by a film of carbonate from the action of water, p. 264). Pour about 2 c.c. of strong hydrogen nitrate (see note 3 ) into a test-tube and put into it a strip of sheet iron or a piece of iron wire, thoroughly cleaned from rust with emery paper. There will be a momentary action only, a few bubbles of gas being given off, and the iron may then remain for any length of time quite unacted on, and with its surface apparently bright. But if a few drops of water are added, a violent action begins at once, and the iron dissolves, with evolution of quantities of nitrogen oxides. 1 Fe 2 (SO 4 ) 3 + H 2 = 2 Fe SO 4 + H 2 SO 4 . 2 The presence of the zinc salt will not interfere with these reactions, if the solution contains hydrogen sulphate. 3 The acid must not be of lower density than 1.35. The strong common acid, such as is used for Grove's battery, will do. If this is not at hand, , add to the ordinary laboratory acid about half its volume of strong hydjo- gen sulphate, which will concentrate it by withdrawing water. The mix- ture should be cooled before the iron is put in. 314 IRON. V Properties of Steel. 1. Annealing of steel. Take a piece of thick watch-spring, or clock-spring, about i cm. broad and 10 or 12 cm. long, heat the whole of it to redness in the flame of a Bunsen's burner and allow it to cool slowly, withdrawing it by degrees from the flame, in the same manner as glass, p. 30. It will be found, when cool, to have lost its elasticity almost entirely, being pliable enough to be bent into any shape, and soft enough to be pretty easily scratched with a file. 2. Hardening of steeL Straighten the piece of steel which was just now annealed, heat it again to a uniform redness in the lamp-flame, and plunge it quickly into a jug of cold water. This sudden cool- ing will be found to have had the effect of making it extremely hard and brittle, so that no file will scratch it, and a bit may be broken off the end almost as easily as if it was glass. It is even harder than glass, for its edge will make a scratch on a piece of glass. 3. Tempering of steel. It has been seen that steel, if heated to redness and cooled very slowly, becomes soft. If, however, it is only heated slightly it loses no more than a portion of its hardness; and the amount lost depends entirely upon the temperature to which it has been raised. This is the principle of the process of ' tempering ' steel ; the temperature being usually judged rather roughly by observing the colour of the film of iron oxide formed in consequence of the heat. A yellow colour implies a very thin film, and a blue colour denotes a thicker one ; and thus, by watching for the appearance of a particular colour and stopping the rise in temperature directly it appears, any desired degree of hardness may be obtained. To illustrate this, Take the strip of steel which has just been hardened, lay it flat upon a piece of board and rub it gently with a piece of moist- ened whetstone (or with a bit of wood dipped in fine emery made into a paste with water) until it becomes' quite bright. IRON. 315 Now lay it upon a strip of sheet iron and heat it again very carefully, holding it at some distance above the flame and moving it to and fro, so as to heat it uniformly. The surface of the steel will soon begin to show the same succession of tints as the iron in expt. i, p. 306, passing from yellow to orange and blue. When it has just reached this latter tint, plunge it into cold water, to stop any further action of the heat. You will now find that it has regained in a great measure the properties of the original watch-spring ; that it is stiff and elastic, and that its surface can be filed away, though with difficulty, and much to the damage of the file. If the application of heat had been stopped when the surface became straw-yellow, the hardness wjfuld have been less reduced, and the temper would have been such as is required for razors and tools for cutting steel. 4. Relation of iron and steel to magnetism. Iron is the most strongly magnetic of all bodies ; i. e. it is attracted strongly when a magnet is held near it. This is due, in fact, to its becoming a magnet itself, with poles opposite in kind to the magnet which causes or ' induces ' them. Support a strip of sheet iron, about 6 or 7 cm. long and i cm. broad, vertically in a Bunsen's holder, and bring close to it one pole (e. g. the N. or marked pole) of a small strong horse-shoe magnet. The lower end of the strip of iron will now shew mag- netic properties, and will attract a short bit of wire or a small iron nail held near it. This in its turn will become a magnet, and will attract another bit of wire, and thus several may be hung from the strip of iron. But as soon as the inducing magnet is withdrawn, all the magnetic properties of the iron cease to show themselves and the bits of wire drop off. Steel, on the contrary, is not only magnetic in the above^ sense, but is (especially when hardened) capable of being mag- netised permanently by several methods, of which the following is the simplest. Lay the strip of steel, which was tempered just now (or a similar piece of watch-spring), on the table, and hold it down by pressing the forefinger on its centre. Bring down the N. pole of the horse-shoe magnet vertically on the middle of the 316 IRON. strip, and move it to the extremity, rubbing it rather strongly upon the surface of the steel. Then bring it back through the air to the centre of the strip as before, and again pass it along to the extremity. Repeat this about six times, and then rub the other half of the strip with the other (i. e. the S.) pole in the same way and for the same number of times. Remember to move the pole along the strip always in the same direction, viz. from the centre to the end, and to bring back the magnet to the centre in a wide curve through the air, otherwise the magnetism already imparted will be weakened. The bit of steel will now be found to be a permanent mag- net, that end being the N. pole which was rubbed with the S. pole of the horse- shoe. \ (a) Touch some small nails with it : they will be strongly attracted. (b) Hang it in a small stirrup of paper, suspended by a fine bit of silk from a Bunsen's holder : it will range itself N. and S. like the compass needle, and its N. -seeking pole will be re- pelled by the N.-seeking pole of the horse-shoe magnet (the other pole of the horse-shoe being kept out of the way as much as possible); whereas if a strip of sheet iron is hung in the same way both ends will be attracted indifferently by the magnet. (c) Lay it flat on the table, place a sheet of paper upon it, and scatter some iron filings upon the paper; then tap the paper so as to allow the filings to arrange themselves in obe- dience to the magnet underneath. They will place themselves in regular curves marking the direction of the lines of magnetic force. 2. COBAJiT. [Symbol of atom, Co. Weight of atom, 59 hydrogen-atoms.] Properties of compounds of Cobalt. [Typical examples, Cobalt nitrate (Go(NO,) a ). chloride (Co C1 2 ). COBALT. 317 A solution of cobalt nitrate (1.5 grm. of the salt dissolved in 30 c.c. of water) may be used.] 1. With hydrogen sulphide, in acid solutions, they give no precipitate. Add to a portion of the solution of cobalt nitrate two or three drops of dilute hydrogen chloride and then some solution of hydrogen sulphide. No precipitate will be formed, showing that cobalt cannot, like the metals in Group II, be separated from acid solutions by hydrogen sulphide. *2. With ammonium sulphide, in neutral solutions, they give a black precipitate, scarcely soluble in dilute hydrogen chloride. Test another portion with a drop of solution of ammonium sulphide. A black precipitate of cobalt sulphide will be formed. Add to this i or 2 c.c. of dilute hydrogen chloride ; the preci- pitate will scarcely dissolve, even when heat is applied. If, however, two or three drops of strong hydrogen nitrate are added (so as to form aqua regia) the cobalt sulphide will be decomposed and dissolved (except, possibly, a slight white residue of sulphur). Observe that, though the addition of a very little hydrogen chloride was sufficient to prevent the for- mation of the sulphide (in Expt. i), yet a much larger quantity failed to dissolve it when once formed 1 . [This is the basis of a method of separating cobalt (and nickel) from the other metals of this group which form sulphides readily soluble in cold dilute hydrogen chloride.] *3. With potassium hydrate they give a light bluish precipi- tate, turning brown on boiling. Test another portion with solution of potassium hydrate. A light blue precipitate, consisting of a basic cobalt salt, will be formed ; which does not dissolve in excess of the precipitant, but becomes reddish brown when the solution is boiled for a minute or two, owing to its conversion into cobalt hydrate. This change is very slow unless an excess of potash is present. *4. Heated in a borax bead they give a deep blue transparent bead, both in the oxidising and reducing flames. This may be tried in the usual way, as directed in p. 93. 1 Compare what was noticed in the case of lead sulphate (p. 267). 31 8 COBALT. Additional Experiments. 1. Change of colour in cobalt chloride when heated. Cobalt chloride separates from its solutions in red crystals containing six molecules of water united with each molecule of the salt. These when slightly heated give up their water of crystallisation, leaving the anhydrous salt, which is blue. But this latter substance quickly absorbs water again, becoming once more the pink hydrated salt. Prepare a little cobalt chloride by evaporating 5 c.c. of the solution of cobalt nitrate with about 2 c.c. of strong hydrogen chloride nearly (but not quite) to dryness 1 . Dilute the con- centrated solution with 5 c.c. of water and trace letters with it on a sheet of writing paper with a camel's-hair brush or a glass rod : then allow them to dry in the air. The letters will now be only faintly visible from their pink colour (if pink paper is used they will be scarcely visible at all). Now warm the paper very gently by holding it before a fire or at some distance over a lamp. As it gradually gets warm, the letters will appear in deep blue, owing to the loss of water of crystallisation as above explained. Discontinue the heating as soon as the above re- sult is obtained (otherwise the salt may be decomposed entirely), and breathe upon the paper or hold it' in a current of steam from a kettle, or elbow-tube attached to a flask of boiling water. Water will be again absorbed by the cobalt chloride, and the original faint pink salt will be obtained, the letters almost disappearing. This illustrates what was formerly called a ' sympathetic ink/ in which secret messages could be written which only appear when warmed 2 . *2. Formation of cobalt-and-potassium nitrite. Add to about 2 or 3 c.c. of the solution of cobalt nitrate 1 Co(NO 3 ) 2 +8HCl = CoCl 2 + 4H 2 O+ 2NOC1+2C1 2 . 2 It may be interesting to notice that if three or four drops of a very concentrated solution of cobalt chloride are diluted with 4 or 5 c c. of alcohol, a liquid is obtained which is red when cold, but turns deep blue when the tube containing it is put into hot water. NICKEL. 319 five or six drops of hydrogen acetate and then a little solid potassium nitrite (about as much as will lie on the end of a spatula). Warm the liquid gently (but do not boil it), and set it aside in a warm place for a day. A bright yellow precipitate of cobalt-and-potassium nitrite (the paint known as ' cobalt yellow') will gradually form, and the whole of the cobalt -will eventually though slowly be separated from solution. This illustrates a method (probably the best) of separating cobalt from nickel, since nickel forms no similar insoluble double salt under the above conditions. 3. NICKEL. [Symbol of atom, Ni. Weight of atom, 59 hydrogen-atoms.] Properties of compounds of Nickel. [Typical example, Nickel sulphate (Ni SO 4 ). A solution of the salt containing i grm. dissolved in 30 c.c. of water may be used.] (These bear a very close analogy to the compounds of cobalt, and the experiments with them may be made in the same way as already directed in the case of the latter, the re- sults being put down in parallel columns in the note- book.) 1. With, hydrogen sulphide, in acid solutions, they give no precipitate. *2. With ammonium sulphide, in neutral solutions, they give a black precipitate scarcely soluble in dilute hydrogen chloride 1 . *3. With potassium hydrate they give a light green precipi- tate, unaltered on boiling. 1 This precipitate of nickel sulphide is very slightly soluble in ammo- nium sulphide, so that on filtering liquids containing nickel sulphide in presence of excess of ammonium sulphide the filtrate has a characteristic dark brown colour. The traces of nickel thus dissolved may be separated by evaporating the solution until the excess of ammonium sulphide has been decomposed and then filtering again. 320 MANGANESE. *4. Heated in a borax bead they colour the bead brownish red in the oxidising flame, gray and turbid in the reducing flame. This must be carefully distinguished from the results ob- tained with manganese compounds. The bead obtained with the latter is violet, and loses its colour but does not become turbid in the reducing flame. [Methods of separating cobalt and nickel will be given in vol. ii.] 4. MANGANESE. [Symbol of atom, Mn. Weight of atom, 55 hydrogen-atoms.] Compounds of Manganese. [Typical examples, Manganese dioxide (Mn O a ). protochloride (MnCl 2 ). Potassium manganate (K 2 MnO 4 ). permanganate (K Mn O 4 ).] Nearly all the compounds of manganese are obtained from the dioxide, which can be made both (a) to give up oxygen (and thus form salts related to lower oxides), and (&) to combine with more oxygen (and thus form compounds corresponding to higher oxides). 1. Decomposition of manganese dioxide by heat. Place a little dry manganese dioxide in a small test-tube and heat it in a Bunsen's burner as strongly as possible. It will, at a red heat, give off a portion (one-third) of the oxygen it con- tains, leaving a dull reddish residue consisting of a lower oxide of manganese 1 . The presence of oxygen in the tube may be proved by a glowing cedar match in the usual way. This reaction is of interest, as showing the method by which oxygen was formerly obtained on a large scale, before potas- sium chlorate could be cheaply obtained. 1 3MnO 3 = Mn 3 O 4 +O 2 . MANGANESE. 321 2. Preparation of manganese protochloride. Place 0.5 grm. of manganese dioxide in a porcelain dish, add 6 or 7 c.c. of strong hydrogen chloride, and heat the mixture gently on a sand-bath, taking great care that none of the chlorine evolved escapes into the room. The reaction has been already explained under CHLORINE, p. 186. The oxygen of the manganese dioxide is not, in this case, evolved as gas, but combines with the hydrogen of the hydrogen chlo- ride, forming water. Part of the chlorine unites with man- ganese to form manganese protochloride, while the rest is evolved as gas. When all the black oxide has disappeared, evaporate the liquid to complete dryness, and heat the light pink residue rather strongly (but not quite to redness), in order to decom- pose any iron chloride which has been formed, owing to the presence of iron as an impurity in the manganese dioxide. Warm the residue, when cool, with 20 c.c. of water, filter the solution and reserve it for experiments. 3. Preparation of potassium manganate. We have in this case an example of the way in which man- ganese dioxide combines with more oxygen to form an elec- tronegative radicle [MnOJ, somewhat analogous to the sulphate radicle [SOJ. This takes place when it is heated with an oxidising substance, such as a chlorate, in presence of a base, such as potassium hydrate, which can combine with the radicle formed. Make a mixture of 2 grms. of manganese dioxide with 1.5 grm. of potassium chlorate, and place it in an iron capsule, or spoon. Dissolve 3 grms. of potassium hydrate in 2 c.c. of water, and add the solution to the mixture in the spoon. Stir the whole together, and evaporate it to dryness over the lamp, stirring it, as it froths up, with an iron wire ; then heat the dish nearly to redness, and keep it at that temperature for two or three minutes. The dark green, semi-fused mass which is formed consists of potassium manganate 1 , and was formerly called 322 MANGANESE. ' mineral chameleon/ from the changes of colour which its solution undergoes, as will be presently observed. 4. Formation of potassium permanganate. This is obtained by the decomposition of the manganate, which shows a great tendency to split up into a compound containing more oxygen, viz. a permanganate, and a com- pound containing less oxygen, such as manganese dioxide or protoxide. Grind some of the potassium manganate, obtained in the last experiment, to fine powder, place a little of it (not more than will lie on the end of a pen-knife) in a test-tube and add about 10 c.c. of cold water. The salt will readily dissolve, forming a dark green liquid. (a) Pour about i c.c. of this solution into another test-tube, and add enough water to nearly fill the tube. The colour of the liquid will more or less quickly (according to the amount of free alkali present) change, first to a dusky neutral tint, and then to a fine purple, owing to formation of potassium per- manganate 1 . (l>) Pour 4 or 5 c.c. of the solution into another test-tube, and heat it to boiling. The change of colour will be much quicker in this case, and a flocculent brown precipitate of manganese dioxide, or rather, the corresponding hydrate, will be formed. (c) Add to the remainder of the solution a few drops of dilute hydrogen sulphate. The formation of the purple potas- sium permanganate will be immediate in this case; no pre- cipitate occurs, since manganese protosulphate is produced and remains in solution 2 . Dilute the liquid with 30 c.c. of water, observing how slightly the intensity of the rich purple colour is lessened by dilution, and keep it for use in the next experiments. 5. Properties of the permanganates. These salts are chiefly remarkable for the readiness with which they give up oxygen, passing (when an acid is present) 4H 2 O = 2 KMnO 4 + 4 K H O + MnH 4 O 4 . MANGANESE. 323 into the condition of colourless manganese protosalts. Hence they are much used as oxidising agents in the laboratory, and also on the large scale as disinfectants (' Condy's fluid ' being a solution of sodium permanganate). To illustrate this, (a) Add to a portion of the solution of potassium perman- ganate (containing free, hydrogen sulphate) a few drops of solution of hydrogen sulphite 1 . The purple colour will imme- diately disappear, the permanganate giving up oxygen to the hydrogen sulphite, to form a sulphate 2 . (d) Add to another portion about one-third its volume of dilute hydrogen sulphate, Ind 6 or 8 drops of solution of ammonium oxalate, and warm it. The liquid will gradually become brown and finally colourless; the oxalate being oxi- dised to carbon dioxide 3 (compare the reaction of oxalates with manganese dioxide, p. 176). (c) Add to another portion a few drops of a solution of iron protosulphate. The purple colour will disappear;, the iron protosalt being oxidised to a persulphate. This is the basis of a process for determining the value of iron ores. (d) Put about 200 c.c. of rain-water (or water from a stag- nant ditch 4 ) into a flask, add 5 c.c. of dilute hydrogen sulphate and about 3 drops of the solution of permanganate (not more than sufficient to colour the liquid decidedly pink) ; then leave it to stand for an hour or so. If the water contains organic matter (or nitrites formed by its oxidation), this will be oxidised (burnt, as it were) by the permanganate, and the pink colour will disappear. This illustrates the principle of a process for testing the wholesomeness of water to be used for drinking. 1 If this is not at hand, a freshly made solution of sodium sulphite, acidi- fied with hydrogen sulphate, may be used. 2 2 KMnO 4 +5H 2 SO 3 = K 2 SO 4 + 2 MnSO 4 + 2 H 2 3 2KMnO 4 + 3H 2 SO 4 +5H 2 C 2 O 4 = K 2 SO 4 +2MnS This reaction is used in volumetric analysis for determining the strength of a solution of potassium permanganate ; a known weight of hydrogen oxa- late being dissolved in water, hydrogen sulphate added, and the solution of permanganate dropped in carefully as long as the purple colour is destroyed. * If no such water is at hand, bruise a leaf in a mortar, and boil it with a little water for half a minute ; add 2 or 3 c.c. of the liquid to 200 c.c. of ordinary water. Y 2 324 MANGANESE. Tests for Manganese protosalts. [The solution of manganese protochloride, already prepared, may be used.] *1. With ammonium sulphide they give a dull pink coloured precipitate. Test a portion of the solution with a drop or two of solution of ammonium sulphide. This will produce a pink l precipitate of manganese sulphide, readily soluble on addition of a few drops of dilute hydrogen chloride. *2. With potassium hydrate they give a grayish precipitate, soon turning brown. Test another portion with a drop of solution of potassium hydrate. A nearly white precipitate of manganese protohydrate will be formed, which will soon become brown on agitation, passing into the perhydrate owing to absorption of oxygen from the air. *3. Heated in a borax bead they colour the bead violet in the oxidising flame, but it loses all colour in the reducing flame. Make a borax bead, add to it a minute quantity of manga- nese dioxide, and heat it in the oxidising flame of the blow- pipe. The bead will be coloured violet, but when heated for a short time in the reducing flame, it will become colourless. The reason of this has been already explained, p. 93. *4. Heated in a bead of sodium carbonate they colour it bluish green. Make a bead of sodium carbonate (p. 242), add to it a trace of manganese dioxide, and heat it in the oxidising flame. The opaque bead will, when cold, be of a bluish green colour. This is due to the formation of sodium manganate (analogous to potassium manganate, p. 321). 1 If any iron salt is present, the precipitate will be dark in colour. The solution of manganese protochloride must be evaporated to dryness and ignited again more strongly, to decompose the last traces of iron salts. CHROMIUM. 325 5. CHROMIUM. [Symbol of atom, Cr. Weight of atom, 52.5 hydrogen-atoms.] Compounds of Chromium. [Typical examples, Chromium sesquioxide (Gr 2 O 3 ). sesquichloride (Gr 2 Cl 6 ). sulphate and potassium (GrK(SO 4 ) 2 ). trioxide (CrO t ). Potassium chromate (K 2 CrO 4 ). dichromate (K 2 Cr 2 O 7 ).] Chromium, like manganese, forms several distinct series of compounds, in some of which (e. g. chromium sulphate) it is present as an electropositive radicle or metal, while in others (e. g. potassium chromate) it forms part of an electronegative radicle [Cr O 4 ], analogous to the sulphate radicle [SOJ. Tests for Chromium salts. [A solution of chromium and potassium sulphate (' chrome alum ') containing 0.5 grm. of the salt dissolved in 25 c.c. of water may be used.] *1. With ammonium sulphide they give a dull greenish pre- cipitate. Test a portion of the solution with a few drops of ammo- nium sulphide. A light bluish green gelatinous precipitate will be formed, which consists of chromium hydrate and not chro- mium sulphide, as might be expected ; since the latter is de- composed in presence of water, with evolution of hydrogen sulphide l . Warm the liquid, to promote the separation of the precipi- tate, adding another drop or two of ammonium sulphide to 1 Cr 2 S 3 + 6H 2 O 326 CHROMIUM. complete the precipitation : then pour the whole on a filter, wash the precipitate thoroughly, and put the filter containing it to dry in a porcelain dish on the sand-bath. Observe that it shrinks in .bulk considerably in drying, especially if the tempe- rature is pretty high, giving off water and becoming chromium sesquioxide, of an olive-green colour, sometimes used as a paint. Reserve it, when dry, for future experiments, p. 328. *2. With, potassium hydrate they give a dull greenish preci- pitate, soluble in excess. To another portion add, drop by drop, solution of potas- sium hydrate, shaking the mixture after each addition. The chromium hydrate, which is at first precipitated, will readily dissolve in excess of potassium hydrate to a clear green fluid. [Be careful to add no more potassium hydrate than is required to dissolve the precipitate.] Boil this fluid for two or three minutes ; it will become turbid, and eventually the whole of the chromium hydrate will be reprecipitated, in a form in which it is no longer soluble in potassium hydrate. *3. Heated in a borax bead they colour the bead bright green both in the oxidising and. reducing flames. This may be tried in the usual way, a very minute quantity (not so large as a pin's head) of chrome alum being used. Tests for Chromates. [A solution of potassium chromate, containing i grm. of the salt dissolved in 30 c.c. of water may be used.] *1. With hydrogen sulphide, in acid solutions, they give a white precipitate of sulphur, the colour of the liquid becom- ing green. Add a few drops of dilute hydrogen chloride to a portion of the solution of potassium chromate. Observe that the yellow colour of the solution changes to red, owing to the formation of potassium dichromate *. 1 A Thus, portion of the potassium is withdrawn by the hydrogen chloride. 2K 2 CrO 4 +2HCl = K 2 Cr 2 O 7 +2KCl + H 2 O. CHROMIUM. 327 Now add excess of solution of hydrogen sulphide and warm the mixture. A white, milky precipitate of sulphur will be formed, and the red colour of the solution will change to green. This is due to the reduction of the chromate to chromium sulphate, some of its oxygen having united with the hydrogen of the hydrogen sulphide (compare the somewhat analogous reaction of iron perchloride, p. 311). *2. With lead acetate they give a bright yellow precipitate. This, it will be remembered, has been already applied as a test for lead salts, p. 267. *3. With silver nitrate they give a purple-red precipitate. This has been already applied as a test for silver, p. 252. *4. Heated in a borax bead they colour the bead bright green in both flames. Reduction of chromates to chromium salts, and vice versa. These changes, which afford excellent instances of the pro- cesses of oxidation and reduction, are effected by means quite analogous to those described in the case of the compounds of manganese, pp. 321, 323; and the explanations there given will apply equally to the present case. A. Conversion of chromates into chromium salts. This is easily effected by boiling them, in presence of an acid, with alcohol; some of the hydrogen of the latter being withdrawn by the oxygen of the chromate, forming water, while a substance called 'aldehyde ' is given off 1 . Add to a little solution of potassium chromate about i c.c. of strong hydrogen chloride and 2 c.c. of alcohol, and warm the mixture. Vapours of aldehyde will be evolved,' easily re- cognised by their pungent oppressive smell, and the red colour of the solution will change to green, owing to the formation of chromium sesquichloride as explained above. After boiling 1 Potassium A1 , , Hydrogen Potassium Chromium A1J , j -, X r . chromate. Alcoho1 ' chloride, chloride, chloride. Aldeh y de - ater 2 K J Cr0 4 + 4 C 2 H 8 + loHCl = 4 KC1 + Cr 2 Cl 6 + 4 C 2 H 4 O + 8 H,O. CHROMIUM. it for half a minute, pour off half of the solution into another tube. (a) Add to one portion an equal volume of water (to prevent the precipitation of lead chloride), and test it with solution of lead acetate. No yellow precipitate will be formed ; this shows that no chromate is now present. () To the remainder add solution of potassium hydrate drop by drop, until it is in excess. The formation of a greenish precipitate soluble in excess shows that a chromium salt has been formed. [Other methods of effecting the same change are, 1. The action of hydrogen sulphite, which is analogous to its action upon permanganates, p. 323. 2. The action of strong hydrogen chloride at a high temperature upon a solid chromate. In this case chlorine is given off (as with manganese dioxide, p. 321); and this process is sometimes used for preparing chlorine.] B. Conversion of chromium salts into chromates. This is effected by heating them with an oxidising agent in presence of some basic radicle which will combine with the chromate when formed. Take the precipitate of chromium sesquioxide obtained in Expt. i, p. 325, mix it intimately with about the same quantity of potassium nitrate and of sodium carbonate (roughly mea- sured), and fuse the mixture in an ignition-tube. It will turn red, becoming yellow as it gets cooler ; the chromium sesqui- oxide having combined with oxygen and potassium from the potassium nitrate to form potassium chromate 1 . Dip the bulb while still hot into a little water placed in a porcelain dish, when it will crack and the chromates will readily dissolve in the water, forming a yellow solution. Pour this solution into a test-tube, warm it and add hydrogen acetate (to decompose the excess of sodium carbonate) as long as there is any effervescence. Then divide it into two parts. 1 Cr 2 O 3 + 4 KNO 3 = 2K 2 CrO 4 + N 2 O 4 -rN 2 O 3 . The above equation does not, of course, express fully what takes place. Some sodium chromate is also formed, and a variable mixture of various nitrogen oxides is given off. CHROMIUM. 329 (a) Test one portion with solution of potassium hydrate. No precipitate will be produced; hence no chromium salt is present. (b) Test the other portion with solution of lead acetate. A yellow precipitate will prove that a chromate has been formed. Additional Experiments. 1. Preparation of chromium trioxide. It has been seen already (Expt. i, p. 326) that when an acid is added to a chromate part of the base is withdrawn, and a dichromate is formed. If, however, a great excess of strong hydrogen sulphate is added, the whole of the base is withdrawn and chromium trioxide is separated. This latter, though soluble in strong as well as in very dilute hydrogen sulphate, is insoluble in slightly dilute acid (containing about 16 per cent, of water), and may thus be almost entirely precipitated. Dissolve 2 grms. of potassium dichromate in 15 c. c. of water heated in a small beaker. Allow it to cool until crystals just begin to appear, and then place it on a plate (lest it should crack), add 20 c. c. of strong common hydrogen sulphate, and stir with a glass rod. The liquid will, of course, get very hot, and the beaker should be covered with a glass plate or watch glass, and set aside to cool. Crimson crystals of chromium trioxide will be gradually deposited ; and when they have en- tirely subsided, the liquid may be poured off, and the mass of crystals may be scraped out with a glass rod upon a dry porous tile or clean brick. Cover them with an evaporating dish, and leave them until the liquid has been absorbed as far as possible by the brick. Ten minutes will generally be suffi- cient for this purpose, and as the chromium trioxide is very deliquescent it should be protected as far as possible from the air, and not left longer than is necessary on the brick. When it is dry the . following experiments may be tried with portions of it ; the remainder, if the crystals are good, may be kept as a specimen in a small stoppered bottle, or in a stout test-tube, 330 CHROMIUM. hermetically sealed by dra wing ' out the upper part of it in the blowpipe flame. 2. Properties of chromium trioxide. (a) It gives off oxygen when heated. Place a little of the chromium trioxide in a small test-tube, supported nearly horizontally, and heat it. The substance will melt, and on being further heated will decompose with incan- descence, leaving a green residue of chromium sesquioxide, while oxygen will be evolved, and may be tested for by a glow- ing match. (b] It oxidises alcohol. Pour a few drops of strong alcohol into a bottle, shake it up so as to diffuse the vapour ; then throw into the bottle some of the chromium trioxide. The latter will be reduced to sesquioxide, the action being occasionally so violent as to set the alcohol on fire. 3. Formation of a higher chromium oxide. Although chromium trioxide so readily gives up oxygen, yet it is possible to get it to combine with more oxygen. For this purpose a very powerful oxidising agent, hydrogen dioxide, must be used ; and the first step will be to prepare a solution of this by acting upon barium dioxide with hydrogen chloride (an action which will be more fully explained under BARIUM). Place a little barium dioxide 1 (as much as will lie on the end of a spatula) in a mortar, powder it, if necessary, pour upon it about 7 or 8 c. c. of dilute hydrogen chloride, and grind them together until the peroxide has entirely dissolved. A slight effervescence will probably be noticed, owing to the escape of oxygen, and a solution containing barium chloride and hydro- gen dioxide will be obtained. (a) Place about half of this solution in a test-tube, and add three or four drops of a solution of potassium chromate acidified with hydrogen chloride. The colour of the solution will change to a deep blue, but in a second or two this will disappear, while oxygen is given off with effervescence, and a pale green solu- tion will be obtained. These changes of colour are due to the 1 For the method of making this substance see p. 342. CHROMIUM. 331 formation of a higher chromium oxide, which is very unstable, and decomposes, when hydrogen chloride is present, into oxy- gen and chromium chloride. (b) This blue chromium oxide (of which the constitution is uncertain) is much more stable when dissolved in ether. To illustrate this, add to another portion of the solution of hydro- gen dioxide sufficient ether to form a stratum about i cm. in depth ; pour in one or two drops of the solution of potassium chromate, close the mouth of the test-tube with the thumb, and shake the mixture. If it is now allowed to remain undisturbed for a minute, the ether will rise to the surface, forming a magnificent blue stratum, while the liquid below is nearly colourless. Action of light upon Chromates. When a soluble chromate is exposed to light in presence of or- ganic matter, it is reduced to an insoluble chromium sesquioxide which adheres very closely to the substance, and, if the latter is gelatine, renders it quite insoluble also. This fact has lately found very extensive applications in the Autotype, Heliotype, and many other printing processes. Dissolve 4 grms. of potassium dichromate in 50 c.c. of water, and filter the solution into a plate. Float upon it a piece of drawing paper 10 or 12 cm. square (as directed, p. 254), covering the whole with a larger plate or inverted tray to protect it from the action of light. [It is best, in fact, to make the experiment in a darkened room or at night by candle-light, although the dichromate is not so sensitive to light as silver chloride.] When it has soaked for five minutes, remove the paper and pin it up to dry in a dark cupboard. When it is quite dry spread it out flat on a board, and lay upon it a piece of black lace, or a pattern cut out in thick brown or black paper : put over the whole a plate of glass to keep it flat, and expose it to full daylight. The unprotected portions of the paper will soon change in colour from bright yellow to dull brown, owing to the reduction of the dichromate, as above explained. In about half-an- hour's time the print may be taken into a dimly-lighted room, and washed with several changes of warm water. All the unchanged yellow salt will dissolve out, leaving a permanent brown picture on 33* ALUMINIUM. a white ground : the chromium sesquioxide attached to the paper being quite insoluble. In practice the dichromate is mixed with a warm solution of gelatine or glue, and lampblack is stirred up in the mixture, which is then spread upon paper. After exposure to light, the print is washed as above described, when all the unaltered dichromate, together with the gelatine and lampblack, is removed, leaving the picture in permanent black. [If it is desired to strengthen the print above obtained, it may, after washing, be soaked for 5 minutes in a solution of iron proto- sulphate (2 grins, in 50 c.c. water). Iron oxide is thus deposited where the chromium oxide exists ; and if the print, after another thorough washing, is placed in a solution of potassium ferrocyanide (5 c.c. of the laboratory solution with 20 c.c. of water, and one drop of dilute hydrogen chloride), a deep blue picture is obtained.] 6. ALUMINIUM. [Symbol of atom, Al. Weight of atom, 27.5 hydrogen-atoms.] Tests for compounds of Aluminium. [Typical examples, Aluminium sesquioxide ( A1 2 O 3 ). Aluminium-and-potassium sulphate (A1K(SO 4 ) 2 , 12 H 2 O). Aluminium-and-ammonium sulphate (A1(H 4 N)(S O 4 ) 2 , 12 H 2 O). A solution of either of the two latter (which are both sold under the name of 'alum'), containing 3 grms. of the salt in 30 c.c. of water, may be used (the presence of potassium or ammonium will not interfere with the tests).] *1. "With ammonium sulphide they give a white precipitate. Test a portion of the solution of alum with ammonium sulphide, warming the mixture. The grayish-white gelatinous precipitate thus produced consists of aluminium sesqui-hydrate, since the sulphide (like that of chromium) is not stable in pre- sence of water. ALUMINIUM. 333 *2. With potassium hydrate they give a white precipitate soluble in excess. To another portion of the solution add solution of potassium hydrate, drop by drop. A white gelatinous precipitate of aluminium hydrate will be formed at first, but on addition of more potassium hydrate it will readily dissolve. Divide the solution into two parts : (a) To one portion add one or two drops of solution of hydrogen sulphide. No precipitate will be produced, since aluminium sulphydrate is not formed in presence of water. (b) To the other add about half its volume of solution of ammonium chloride, and warm the mixture ; aluminium hydrate will be precipitated. [These two tests distinguish it from the somewhat similar precipi- tate formed by adding potassium hydrate to zinc salts, p. 336.] *3. Heated on charcoal they give a white infusible residue, turning blue when ignited with cobalt nitrate. Place a small crystal of alum in a cavity cut in a piece of charcoal, and heat it in the hottest part of the blowpipe-flame. The salt will at first swell up like borax, white fumes of ammo- nium sulphate (if ammonium alum is used) and hydrogen sulphate will then be given off, and finally a white infusible incandescent residue of aluminium oxide will be left on the charcoal. Allow this to cool, then moisten it with a drop of solution of cobalt nitrate (transferred from the bottle on a glass rod), and ignite it again for several seconds. The mass, when cool, will be found to have acquired a bright blue colour '. Additional Experiments. 1. Water of crystallisation of alum. Heat a small fragment of alum in an ignition-tube. It will melt, and at a temperature a little above 100 will give off a large quantity (nearly half its weight) of water, which was 1 This reaction, however, is not absolutely characteristic of aluminium, since some silicates, calcium phosphate, and one or two other substances behave in a similar way. 334 ALUMINIUM. chemically combined with the salt in its crystallised form. A white porous mass will be left, which is the common ' burnt alum/ 2. Formation of 'lakes.' These are combinations of aluminium hydrate with various colouring matters, for which it has a great affinity. Add some solution of cochineal to about 5 c.c. of the solu- tion of alum ; then add just enough ammonia to- precipitate all the aluminium' as hydrate, boil, and filter the liquid. The filtrate will be quite colourless, the colouring matter of the cochineal being retained on the filter in combination with the aluminium hydrate, forming the carmine lake used in painting. 3. Use of aluminium salts as ' mordants ' in dyeing. This depends upon the property possessed by aluminium hydrate of attaching itself firmly to the fibre of cloth and calico, as well as of combining with colouring matters, as already shown. Thus it may be employed to bind the two together, as it were ; the result being a ' fast ' colour, i. e. one which cannot be removed from the material by washing. In order to precipitate the aluminium hydrate on the cloth, the latter is soaked in some readily decomposable salt of alumi- nium, such as the sulphate or acetate, and left to dry in a warm place. By this means aluminium hydrate is deposited in close contact with the fibre. Put about 15 c.c. of a solution of alum into a test-tube, and add solution of sodium carbonate, drop by drop, shaking thoroughly after each addition. The precipitate of aluminium hydrate which is at first formed will redissolve, and the ad- dition of sodium carbonate should be continued until a slight permanent cloudiness shows itself; when about i c.c. of the solution of alum should be added to redissolve this. You have now a solution containing an aluminium sulphate which is readily decomposed on boiling, aluminium hydrate being precipitated. [Prove this by pouring off 2 or 3 c.c. of the liquid into another tube and heating it; a white precipitate will be formed.] Dip one half of a strip of white calico into the solution, and ZINC. 335 dry it before a fire, or at some distance above a lamp. During the process of drying, the aluminium sulphate is decomposed, aluminium hydrate being deposited in the fibres of the calico. Warm some moderately strong solution of cochineal or log- wood in an evaporating dish, immerse the strip of calico, and heat the liquid to boiling for about ten minutes ; then take out the calico, and wash it thoroughly in several changes of water. The part of it which was soaked in the ' mordant ' solution will be found to be permanently dyed, while all the colouring matter will be washed out of the other portion. [If a little powdered gum arabic is mixed in a mortar with 2 or 3 c.c. of the solution of aluminium sulphate, and patterns or letters are drawn upon a piece of calico with a brush or glass rod dipped in it, they will be permanently printed, when treated as above de- scribed.] 7. ZINC. [Symbol of atom, Zn. Weight of atom, 65 hydrogen-atoms.] Properties of the metal. 1. Its fusibility (at 330) and its oxidability when heated in air have been already noticed in the granulation of the metal (p. 27). 2. Action of heat in altering its tenacity. Take a strip of sheet zinc about 20 cm. in length, hold it by its extremities and bend it double; notice that it is stiff, and requires some little force to bend it. Now heat it in the middle gently over a lamp, and observe that its pliability is greatly increased. If, however, it is still further heated it be- comes quite brittle as the temperature approaches its melting- point. 336 ZINC. Compounds of Zinc. [Typical examples, Zinc oxide (Zn O). sulphate (Zn SO 4 ). chloride (Zn G1 2 ).] *1. Formation of zinc oxide. Heat a small fragment of zinc on charcoal in the hottest part of the blow-pipe flame. It will, when the heat rises to full redness, begin to burn with production of zinc oxide, light flakes of which will be swept away by the current of air, but the greater part will remain on the charcoal, as an incrustation which is yellow while hot, white when cold. Moisten this in- crustation with a drop of solution of cobalt nitrate on the end of a glass rod, and heat it again before the blowpipe. The mass will now acquire a fine green colour, a compound of zinc oxide and cobalt oxide being formed, which is used as a paint. 2. Zinc chloride. 3. Zinc sulphate. [These have both been prepared already, pp. 71, 106.] Tests for Salts of Zinc. [A solution of zinc sulphate, containing i grm. of the salt in 30 c.c. of water, may be used.] *1. With ammonium, sulphide they give a white precipitate. Test a portion of the solution of zinc sulphate with a drop of solution of ammonium sulphide. A white precipitate of zinc sulphide will be formed, which will readily dissolve on addition of a drop or two of dilute hydrogen chloride. *2. With potassium hydrate they give a white precipitate, soluble in excess. Add to another portion a drop of solution of potassium hydrate. A white precipitate of zinc hydrate will be formed, which will readily redissolve on addition of a few more drops ZINC. 337 of the solution of potassium hydrate. Divide the clear liquid into two parts : {a) To one portion add a drop or two of solution of hydrogen sulphide. A white precipitate of zinc sulphide will be formed. (/3) To the other portion add about half its volume of solution of ammonium chloride, and warm the mixture : no precipitate will be formed l . Com- pare the reactions of aluminium, p. 333. Additional Experiments. 1, Amalgamation of zinc. By this is meant the process of covering the metal with a film of mercury, which forms an alloy or ' amalgam ' with it. Ordinary zinc is readily acted on by dilute acids, as has been already noticed (p. 71), but this is chiefly due to the presence of particles of carbon, lead, &c., which promote the chemical action by the galvanic current set up between each of them and the zinc. This ' local action,' as it is called, is entirely prevented by covering the zinc with mercury; the latter buries the impurities, so that the acid does not reach them at all. Put about 20 c.c. of water into a test tube, add about i c.c. of common hydrogen sulphate, and dip into the acid a strip of zinc about 20 cm. long and i cm. broad. Bubbles of hydrogen will at once be given off at all parts of the surface of the zinc. Now add about i c.c. of solution of mercury perchloride, and mix it thoroughly with the acid by stirring with the strip of zinc. A bright film of mercury will be deposited on the zinc (compare the deposition of mercury on copper, p. 262), and form an amalgam with it; and the evolution of gas will cease entirely. The strip of zinc in this condition is said to be ' amalgamated,' and may be reserved for use in the next experiment 2 . 1 If the potassium hydrate contains aluminium hydrate, or silicon hydrate, a precipitate will, of course, be formed. . 2 Another and more usual mode of amalgamating zinc plates for batteries is, first to clean its surface with dilute acid, as above, and then to lay it in a flat plate and pour over it a drop or two of mercury, rubbing the latter all over the surface with a cork. The excess of mercury should then be drained off (and kept in a bottle for this purpose alone), and the zinc plate should be thoroughly rinsed with water. Z 338 ZINC. 2. Use of zinc in galvanic 1 batteries. This depends upon the readiness with which it is acted on by many substances; the conditions in the usual galvanic batteries being, two metals immersed in a liquid which acts more strongly upon one of them than upon the other. Put about 50 c.c. of water into a large test tube, and mix with it 5 or 6 c.c. of common hydrogen sulphate. Take the strip of zinc which you amalgamated just now, and a strip of copper of the same size ; put between them a flat bit of cork about i cm. thick, so as to keep them parallel but slightly separated, and bind them in this position by string or a couple of small india rubber bands. Twist tightly round the upper end of each a bit of fine copper wire 18 or 20 cm. long, taking care that these wires do not touch each other in any part. Immerse the strips in the dilute acid in the test tube, and observe that no action is perceptible on either metal. Now press together the ends of the wires attached to the copper and zinc respectively; bubbles of hydrogen gas will immediately appear on the surface of the copper, while an electric current flows along the wire 1 . The action may be explained as follows : The molecules of hydrogen sulphate between the zinc and the copper become ' polar- ised,' i.e. arranged in a definite direction (like a row of magnets), their electro-negative parts pointing towards the zinc ; thus, Zinc plate. 1 1 S O 4 H a , S O 4 H 2 , S O 4 H 2 1| Copper plate. When the metals are connected by a good conductor, such as the copper wire, the S O 4 radicle which is next to the zinc unites with it, while the H 2 unites with the SO 4 of the next molecule, and so on ; the H 2 of the last molecule being liberated on the surface of the copper. Thus a molecule of zinc sulphate (Zn S O 4 ) is formed, and a molecule of hydrogen is liberated. Then other molecules are polarise4 and decomposed in like manner, and thus the action con- tinues. It should be observed that, while the metallic connection between the two metals is maintained, the zinc alone is acted on, and not the copper, which remains bright. This illustrates the use of zinc in protecting iron from rust, as in the ordinary galvanised iron (which 1 The current from so small a battery is, of course, weak ; but if a part of the wire is straightened and placed in a north-and-south direction, and a small compass is held as close to it as possible, a distinct deflection of the needle will be noticed ; the tendency of an electric current being to set a magnet at right angles to its own direction. ZINC. 339 is iron coated with zinc). When a piece of this is exposed to air and moisture, the iron (though rapidly attacked when alone) remains unaltered so long as there is any zinc in contact with it. Preparation of a set of borax beads. Since so many of the metals hitherto studied give characteristic colours when added to a bead of borax, it will be interesting and useful to keep a set of characteristic borax beads, as a help to the memory, and as a standard of comparison. Such a set may be con- veniently made as follows. Seal one end of a glass tube about 6 cm. long and 2 mm. internal diameter. Place near the blowpipe a deep porcelain dish, about 10 cm. in diameter (a porcelain mortar, if glazed inside, or large tea-cup will serve the purpose), perfectly clean and dry. After making the bead in the usual way, and while it is still fluid, tap the platinum wire somewhat obliquely on the edge of the porcelain dish. The bead will detach itself and roll round the side of the dish, finally coming to rest at the bottom. It will be found to have preserved its spherical shape ; and if the colour is satisfactory, it should be placed at once in the glass tube, since its surface would soon effloresce in the air. Other beads may be formed in the same way, and dropped one by one into the tube, from which they should not much differ in diameter. When the set is complete, the tube should be heated about 5 or 6 mm. above the last bead, drawn out, and sealed, thus preserving the beads from further change. Two beads should be preserved in each case; the one showing the colour imparted by the substance in the oxidising, the other in the reducing flame. The following list includes nearly all the substances which impart characteristic colours to borax glass : Chromiunij manganese, nickel, cobalt, iron, copper. Z 2 340 BARIUM. Group IV. Metals which are separated from solutions by ammonium carbonate. BARIUM, STRONTIUM, CALCIUM. 1. BARIUM. [Symbol of atom, Ba. Weight of atom, 137 hydrogen-atoms.] ' Tests for compounds of Barium. [Typical examples, Barium chloride (Ba Gla). oxide (Ba O). hydrate (Ba H 2 O 3 ). dioxide (Ba O 2 ), A solution of barium chloride, containing i grm. of the salt in 25 c.c. of water, may be used.] 1. With ammonium sulphide they give no precipitate. To a portion of the solution add a drop of solution of am- monium sulphide. No precipitate will be formed, since barium sulphide is soluble in water, a property which distinguishes it from the sulphides of the metals included in the previous groups. *2. With ammonium carbonate they give a white precipi- tate. To another portion add a drop of solution of ammonium carbonate, and warm the liquid. A white precipitate of barium carbonate will be formed, which will readily dissolve, with evo- lution of carbon dioxide, on addition of a few drops of dilute hydrogen chloride. BARIUM. 341 *3. With calcium sulphate they give a white precipitate immediately. To another portion add about one-third its volume of solu- tion of calcium sulphate. A white precipitate of barium sul- phate will be immediately formed. The same reaction has already been employed to detect the presence of a sulphate (p. 230). *4. With hydrogen silicofluoride they give a white crystal- line precipitate. To another portion add a few drops of solution of hydrogen silicofluoride. A crystalline precipitate of barium silicofluoride will be produced. *5. Heated on platinum wire in the Bunsen's burner flame they tinge the flame green. Make a small loop (smaller than that intended for a borax bead, p. 92) at the end of a piece of platinum wire, dip it into strong hydrogen chloride (a few drops should be placed in a watch glass), and hold it just within the edge of the upper part of the flame of a Bunsen's burner (or, better, of a gas blow- pipe) until it does not itself impart any colour to the flame. Then moisten it again with hydrogen chloride, dip it into a little barium chloride, and hold it again in the flame. The barium chloride will, as it volatilises, impart to the flame a bright green colour. In applying this test, the substance under examination should always be moistened with strong hydrogen chloride before being brought into the flame, since the chlorides of the metals in this group are more volatile than their other salts. Preparation of compounds of Barium. 1. Preparation of barium hydrate. Place a small lump (as large as a pea) of barium oxide in a test-tube, and pour on it a few drops of water. If the barium oxide is pure, and has not been exposed to the air, it will swell up, evolving much heat as it combines with the elements of the water to form barium hydrate. (Compare the action of water 342 BARIUM. on calcium oxide, p. 58.) Pour about 8 or 10 c.c. of water upon the mass, heat it to boiling, and filter it while hot into a clean test-tube. Crystals of barium hydrate will be deposited as the liquid cools, since the salt is much more soluble in hot than in cold water (differing from calcium hydrate in this re- spect). Observe also the alkaline reaction of the solution on reddened litmus and turmeric-paper. This solution is often called ' baryta water/ and may be used in the laboratory for the same purposes as lime-water ; for in- stance as a test for carbon dioxide. Place a little of the solution in a test-tube ; dip the long branch of an elbow-tube into it and blow gently through it for a few seconds. A white cloudiness of barium carbonate will be formed. 2. Preparation of barium, dioxide. When barium oxide is heated, and oxygen gas passed over it, each molecule of the oxide unites with one atom of oxygen to form barium dioxide. For ordinary purposes it is most, convenient to evolve the oxygen in contact with the barium oxide, in the following way : Place about a gramme of barium oxide in a mortar, grind it to powder, then add rather more than an equal quantity of potassium chlorate, and mix the two substances intimately with the pestle. Place the mixture in an iron spoon or a small porcelain crucible, and heat it rather strongly over a Bunsen's burner. It will at first melt and effervesce, and finally a low incandescence will spread through the mass, the barium oxide burning in presence of the chlorate (precisely in the same way as carbon or any other combustible body) with formation of barium dioxide 1 . Allow the semi- fused mass to cool, then detach it from the spoon, grind it to fine powder, and keep it in a corked tube for use in experi- ments. 1 3 BaO+ KC10 3 = 3 Ba0 2 + KCl. BARIUM. 343 Additional Experiments. 1. Preparation of hydrogen dioxide. [Formula of molecule, H 2 O 2 .] This can be obtained by acting upon barium dioxide with an acid, the hydrogen of which unites with all the oxygen of the substance, while the other radicle unites with the barium. Place some powdered barium dioxide in a mortar, add a little water, and grind the whole till it forms a thin cream. Pour into the mortar about 6 or 8 c.c. of dilute hydrogen chloride, and mix it quickly with the semi-fluid mass, which ought to dissolve readily and completely ; if not, a little more hydrogen chloride must be added at once. A slight effervescence will take place, owing partly to the presence of carbonate as an impurity in the barium oxide, partly to the decomposition of the dioxide with evolution of oxygen gas. If, however, the hydrogen chloride is kept in excess, the amount of decomposition is small, and a solution is obtained con- taining barium chloride and hydrogen dioxide 1 . 2. Properties of Hydrogen dioxide. [The solution just made may be used, since the presence of barium chloride will not interfere with the experiments.] This substance shows a great tendency to give up one of the atoms of oxygen which its molecule contains, thus becoming ordi- nary water 2 . Hence it is a very powerful oxidising agent, and an experiment illustrating this property has been given already under CHROMIUM (p. 330). But it has scarcely less strongly marked reduc- ing powers ; the atom of oxygen which it gives up seeming to elicit a fellow-atom from other substances. Thus the two atoms from different sources combine to form a single molecule of oxygen gas, while both the hydrogen dioxide and the substance which it acts upon are simultaneously reduced. A. Its oxidising powers. Add a few drops of the solution of hydrogen dioxide to a dilute solution of potassium iodide (3 or 4 drops of the laboratory solution diluted with 5 c.c. of water). Iodine will be liberated by degrees, 1 BaO 2 +2HCl = BaCl 2 +H 2 O 2 . , . Potassium chloride is, of course, also present. 2 H 2 2 = H 2 0+0. 344 STRONTIUM. colouring the liquid yellow, and giving the characteristic blue com- pound if a little solution of starch is added. In this case hydrogen iodide (formed by the action of the excess of hydrogen chloride upon the potassium iodide) is decomposed, its hydrogen uniting with oxygen, while iodine is set free 1 . B. Its reducing powers. () Put a little manganese dioxide into a test-tube, and pour on it some of the solution of hydrogen dioxide. A strong effervescence will take place, owing to the formation of oxygen as above explained: half of it coming from the hydrogen dioxide, and half from the man- ganese dioxide. The latter is reduced to protoxide, which dissolves in the hydrogen chloride present, forming manganese protochloride 2 . () Add a little hydrogen dioxide to some rather dilute solution of potassium permanganate. The deep purple liquid will become colourless, manganese protochloride being formed, while oxygen is evolved with effervescence 3 . It is possible that this reaction may be strictly analogous to that of hydrogen dioxide on chromates, a higher and less stable manganese oxide being formed momentarily, which at once loses the greater part of its oxygen. 2. STRONTIUM. [Symbol of atom, Sr. Weight of atom, 87.5 hydrogen-atoms.] Tests for compounds of Strontium. [Typical examples, Strontium oxide (SrO). nitrate (Sr(NO 3 ) 2 ). chloride (Sr C1 2 ). A solution of strontium nitrate, containing i grm. of the salt dis- solved in 25 c.c. of water may be used, and the experiments should be tried in the same way as those with barium.] 1. "With ammonium sulphide they give no precipitate. *2. With ammonium carbonate they give a white precipi- tate. 2 MnO 2 +H 2 O 2 +2HCl = MnCl 2 + 2 H 2 O + O 2 . 3 2KMnO 4 +H 2 O 2 +6HCl - 2 MnCl 2 + 2 STRONTIUM. 345 *3. With calcium sulphate they give no immediate precipi- tate, but a white precipitate forms in four or five minutes. This is owing to strontium sulphate being decidedly more soluble in water than barium sulphate ; hence, when such a weak solution is used as that of calcium sulphate necessarily is, the precipitate only forms gradually. If dilute hydrogen sul- phate (the ordinary laboratory solution) is added to the solution of strontium nitrate, a precipitate forms at once. *4. With hydrogen silicofluoride they give no precipitate. *5. Heated on platinum wire in the Bunsen's burner flame they tinge the flame crimson. If the flame is looked at through a piece of deep blue glass, it still appears of a crimson colour, while the ordinary Bunsen's burner flame is almost invisible. Preparation and properties of Strontium oxide. This (and also barium oxide) is best obtained by strongly heating the nitrate, when it breaks up (like lead nitrate, p. 139) into strontium oxide, nitrogen tetroxide, and oxygen 1 . Place about 2 grms. of crystallised strontium nitrate in an iron spoon, or on a piece of a broken evaporating dish, and heat it to full redness before the gas blowpipe. The salt will fuse and effervesce, owing to the evblution of nitrogen oxides and oxygen, and, finally, a dark gray porous mass of strontium oxide will be left. When this is cool, pour a few drops of water upon it, and notice that it ' slakes ' like the correspond- ing barium and calcium salts, and that its solution in water has an alkaline reaction on test-paper. 1 2Sr(NO 3 ) 2 = 2SrO+ 2N 2 O 4 +O a . 346 CALCIUM. 3. CALCIUM. [Symbol of atom, Ga. Weight of atom, 40 hydrogen-atoms.] Tests for compounds of Calcium. [Typical .examples, Calcium oxide (Ga O). sulphate (Ga SO 4 ). carbonate (Ca CO 3 ). chloride (Ca G1 2 ). A solution of calcium chloride, containing i grm. of the salt dissolved in 50 c.c. of water may be used. The experiments should be made in the same way as in the case of the barium and strontium salts.] 1. With ammonium sulphide they give no precipitate. *2. With ammonium carbonate they give a white pre- cipitate. *3. With calcium sulphate they give no precipitate, even on standing for ten minutes. This result would be naturally expected, since no more calcium sulphate can be formed than exists already in the solution, and there is obviously more than enough water pre- sent to keep that amount dissolved. [Calcium sulphate is, however, not very soluble in water, and nearly insoluble in alcohol. To prove this, Add two or three drops of dilute hydrogen sulphate to some of the solution of calcium chloride, and divide the liquid into two portions. (a) Set one portion aside for a time, shaking it occasionally. A white crystalline precipitate will gradually form. *(b) Add to the other portion some alcohol. A white precipitate will appear at once.] 4. With hydrogen silicofluoride they give no precipitate. *5. Heated on platinum wire in the Bunsen's burner flame they tinge the flame orange red. If the flame is looked at through a piece of deep blue glass, it appears greenish gray. CALCIUM. 347 *6. With ammonium oxalate, in neutral solutions they give a white precipitate. This property, it will be remembered, was employed as a test for an oxalate, p. 176. Preparation and properties of Calcium oxide. This, which is the ordinary quicklime, is obtained by heating the carbonate to redness (as is done on a large scale in lime- kilns), when it breaks up into calcium oxide and carbon dioxide *. Place a piece of reddened litmus-paper in a porcelain dish ; lay on the paper a small fragment of marble or chalk, about as large as a pea, and pour a few drops of water from a washing bottle over the marble. The colour of the litmus-paper will not be altered, since calcium carbonate is quite insoluble in water. Place the fragment of marble on a piece of platinum foil, fold a corner of the foil over it to prevent loss of heat by radiation, and heat it to full redness before the blowpipe for a minute or two. Place it, when cool, upon the litmus-paper, and add a drop or two of water. The paper will now turn blue, since the marble has been decomposed and calcium oxide formed, as above explained, and the latter unites with the elements of water to form calcium hydrate, which has been already shown (p. 59) to be soluble in water and to give an alkaline reaction. Additional Experiments: 1. Hardness of water. Water is said to be 'hard' when it refuses to form a lather or permanent froth with soap. This hardness is mainly due to the presence of calcium salts in the water, especially calcium-and- hydrogen carbonate 2 and calcium sulphate. These decompose the CaO + CO 2 . 2 The formation of this has been already illustrated, p. 158. 348 CALCIVM. soap (which is chiefly sodium oleate and margarate) forming calcium oleate, &c. which are insoluble in water. Dissolve i grm. of common yellow soap in 20 c.c. of distilled water, warming it gently. (a) Put 100 c.c. of distilled water into a small gas bottle, add about 2 c.c. of the soap solution, and shake it up thoroughly. A thick, permanent layer of froth will be produced. (b) Put 100 c.c. of common hard water 1 into a small gas bottle, add about 2 c.c. of the soap solution, and shake it up. If the water is moderately hard, it will become milky (owing to the precipitation of calcium oleate, &c.), and no permanent layer of froth will be formed ; the bubbles bursting almost as soon as the shaking is dis- continued. Add 2 c.c. more of the soap solution and shake it up again. If the water is very hard no lather will even now be formed, and more soap solution should be added in successive small portions, the mixture being vigorously shaken after each addition. A point will finally be reached at which enough soap has been added to decompose all the calcium salts, and then any further addition will produce a lather lasting unbroken for five minutes or more. If we try different samples of hard water in the above way, and observe how much soap has to be added to each in order to get a permanent lather, we gain a knowledge of the comparative hard- ness of each sample. This is the basis of Clark's process for deter- mining the hardness of waters. 2. Preparation of plaster casts. The mineral gypsum (native calcium sulphate) contains two mole- cules of water of crystallisation attached to each molecule. This water is driven off by heating the powdered mineral to a tem- perature of 250, and the anhydrous calcium sulphate (the common ' plaster of Paris ') thus obtained combines with a considerable quan- tity of water, the whole solidifying by degrees into a hard porous mass. Moreover it expands in solidifying, and hence very sharp casts of medals can be obtained. Take a medal or large coin, and having slightly greased its sur- face by rubbing it with a cloth moistened with oil, roll a strip of paper (about i cm. broad) round its edge, so as to form a shallow circular trough ; then fasten down the end of the strip by sealing- wax or by a fold or two of string. Place 20 c.c. of water in a por- 1 If no hard water is at hand, add 10 c.c. of solution of calcium sulphate to 90 c.c. of rain water or distilled water, and use it for the above experi- ment. MAGNESIUM. 34$ celain dish, and shake into it gradually sufficient fresh plaster of Paris to form a thick cream, stirring the mixture continually with a glass rod. As soon as the whole is thoroughly mixed, pour over the coin sufficient of it to fill the trough, and stir it with a feather or splinter of wood, in order to detach any bubbles of air which may remain adhering to the surface of the coin. [Wash out the dish containing the residue of plaster at once, or it will be difficult to remove the hardened material.] Leave the whole at rest for about half an hour, in which time you will find that the paste has solidified, or ' set/ as it is termed, the calcium sulphate having (as above ex- plained) combined chemically with the water. Unroll the paper rim, and carefully detach the coin from the plaster by gently pulling them apart. You will thus obtain a copy of the coin in plaster, but reversed, the raised parts of the coin forming depressions in the plaster. The cast should be left for several hours in a drying cup- board, or in front of a fire, in order to dry it thoroughly. When dry, it may be used as a mould from which to obtain a facsimile of the original medal. For this purpose it should first be thoroughly saturated with wax by placing it, face upwards, in a porcelain dish containing some melted wax or paraffin (such as a portion of a candle) and heated on a sand-bath. The wax will rise by capillary action through the porous plaster, and when the upper surface appears thoroughly wet, it may be taken out and placed on a plate to cool. A paper rim should then be fastened round it, and a cast made in plaster as above directed. Or it may be covered with plumbago, and copper deposited on it by the electrotype process described already, p. 272. Group V. Metal which is separated from solutions by sodium phos- phate in presence of ammonium salts. MAGNESIUM. [Symbol of atom, Mg. Weight of atom, 24 hydrogen-atoms.] Properties of the metal. 1. It readily acts on acids, displacing their hydrogen. Place a bit of magnesium ribbon about 15 cm. in length in a test-tube, add 5 c.c. of water, and then one or two drops 350 MAGNESIUM. of dilute hydrogen sulphate Hydrogen gas will be evolved with effervescence, and the metal will readily dissolve l . [No more acid must be added than is absolutely required to dissolve it.] When the action has ceased, pour off the liquid into a small porcelain dish, and evaporate it down until it begins to crys- tallise. Long prismatic crystals of magnesium sulphate (Epsom salts) will be deposited as the solution cools : these, after the liquid has been poured off from them, should be rinsed once with a little water, to remove adhering acid, and then redissolved in about 20 c.c. of water, and the solution reserved for experi- ments. Observe the ready solubility of magnesium sulphate, as con- trasted with the slight solubility of barium-, strontium-, and calcium- sulphates. In fact magnesium, although its sulphide is soluble, has a greater analogy to zinc than to these latter metals. 2. It burns in air, forming an oxide. Place a piece of reddened litmus-paper in a porcelain dish, and moisten it with water. Cut off a piece of magnesium ribbon or wire about 10 cm. in length, hold it in the crucible tongs over the porcelain dish, and apply the lamp-flame to one extremity. The metal will take fire and burn with an intense white light, forming white flakes of magnesium oxide, which should be allowed to drop upon the test-paper, and spread over it with a glass rod. The blue colour of the paper will be restored, proving the alkaline character of magnesium oxide, and its solubility in water, which is, however, much less than even that of calcium oxide. Tests for compounds of Magnesium. [Typical examples, Magnesium sulphate, (Mg SO 4 ). Magnesium-and-ammonium phosphate (Mg(H0 4 in 50 c.c.). Pissolve 7.2 grms. of the salt in 50 c.c. of water, and dilute to 100 c.c. The salt is liable to contain a chloride and a carbonate. These impurities should be tested for in the manner described under the head of Potassium Hydrate, p. 447. 39. Sodium-and-Hydrogen Tartrate (NaHC t H t O 6 in 50 c.c.). Dissolve 3.8 grms. of the salt in 80 c.c., and dilute to 100 c.c. The ^ solution does not keep for any length of time, a growth of fungus soon appearing in it. When a Ijttle of it does not give an almost immediate crystalline precipitate on addition of one drop of solution of potassium hydrate (see p. 174), it should be thrown away. 40. Starch, solution of. Heat 100 c.c. of water to boiling in a flask or beaker. Weigh out i grm. of pure white starch, and mix it thoroughly with 4 or 5 c.c. of cold water in a test-tube. When the water in the flask boils, take away the lamp, and, as soon as the boiling has ceased, pour the starch little by little into the water, shaking after each addition. The starch granules swell and burst, their transparent contents being scattered through the liquid, giving the appearance of having dissolved in it. Replace the lamp, and boil the liquid again for half a minute, stirring or shaking it all the time : then allow it to cool slightly and filter it *, but do not use it for test- ing until it is quite cool. The solution does not keep well, the starch being gradually con- verted into dextrine, which gives a brownish violet colour with free iodine, instead of the characteristic deep blue formed by starch. The addition, however, of about one-twentieth of its volume of alcohol (or of a few drops of ammonia) seems to preserve it in good condition for at least six months. 41. Tin Protoehloride (Sn CI t in 50 c.c.). Boil 3 grms. of tin- foil with 10 c.c. of strong hydrogen chloride until the metal is nearly all dissolved; then dilute the solution with water to 50 c.c. and filter it into a bottle in which some pieces of granulated tin have been placed. An excess of the metal should always be kept in the bottle to pre- vent the formation of any perchloride, and if the solution becomes turbid, 2 or 3 c.c. of strong hydrogen chloride should be added. 1 This, although a rather tedious operation (since the pores of the filter soon get clogged) and not necessary for general work, results in a decided gain in the sensitiveness of the test. APPENDIX B. 449 II. RECOVERY OF SILVER, GOLD, AND PLATINUM FROM RESIDUES. 1. Treatment of Silver Residues. It has been already recommended (p. 249) that all waste solu- tions containing silver should be poured into a stock-bottle kept for the purpose, in order that when a sufficient quantity has accumu- lated the metal may be recovered from the mixture. The first step will be the conversion of any soluble silver salts which may be present into soluble silver chloride, by the addition of a con- siderable excess of common hydrogen chloride. This, if added in sufficient quantity, will even throw down any silver chloride whieh may have dissolved in sodium hyposulphite. The mixture, after being warmed in a flask and shaken, should be filtered, and the precipitate thoroughly washed, first with dilute acid and then with water, and finally dried by placing the filter containing it in a por- celain dish on the sand-bath. When it is thoroughly dry, it must be shaken out of the filter, and mixed in a mortar with twice its weight of dried sodium carbonate and one-tenth its weight of potassium nitrate, a little borax being also added to act as a flux. While the mixture is being made, a common Cornish clay crucible, about 12 or 13 cm. in height, should be gradually heated by being placed mouth downwards on the top of an ordinary fire, if there is no wind-furnace at hand. When it is thoroughly warmed, it may be turned up and surrounded with hot, coals. When it be- comes red-hot, the mixture should be thrown into it, little by little, with an iron spoon, the fire being urged by a pair of bellows, so as to keep the crucible at a full red heat. The mixture will at first effervesce considerably, and should be stirred with an iron rod to prevent its frothing over, but it will finally fuse into a clear fluid, under which the silver will collect in a button. When this takes place, the crucible must be kept at a bright yellow heat for about five minutes longer, the contents being occasionally stirred to hasten the aggregation of the small particles of reduced silver 450 APPENDIX B. disseminated through the mass. Finally, the crucible should be lifted from the fire by a pair of tongs, and the fluid mass poured out on a piece of slate or iron plate. When cold the silver may be separated from the flux by breaking off the latter with a hammer, and boiling the ingot with water to separate the last traces of slag. It is a good plan to re-melt the ingot of silver in a small clean crucible, sprinkling a little borax over it. When thoroughly melted the metal should be poured out as before on a piece of slate, and an approximate estimate of its purity may be formed by observing the degree of ' spirting ' which takes place as the silver solidifies, owing to the escape of absorbed oxygen. Unless the metal be very pure and especially free from copper and lead, this spirting will hardly take place at' all, and the surface of the ingot will remain unruffled. The lump of silver thus obtained may be either exchanged at a shop for the crystallised nitrate of silver, or it may be boiled for some time in a flask with hydrogen nitrate diluted with twice its volume of water, more of the acid being added when the action becomes slow 1 . The solution should be evaporated to complete dryness, in order to drive off the excess of acid, the residue should be redissolved in water, and the solution, after filtration, should be evaporated down and left to crystallise, the basin being covered with a glass plate or a sheet of paper to exclude dust. The crystals should be drained in a funnel and dried on filter-paper. The mother liquor, on further evaporation, will yield another crop of crystals, and the liquid drained from these may either be poured into the ' silver residues ' bottle, or reserved for purposes in which absolute purity is not required. This is decidedly the best method of reducing silver residues, since not only the chloride, but also the sulphide, iodide, &c., are reduced by fusion with sodium carbonate. If, however, the chloride only has to be dealt with, it may be reduced by hydrogen in the manner described, p. 250; the only disadvantages being that it is rather difficult to wash out the last traces of zinc salt from the spongy mass of silver, and also that organic impurities are liable to be carried down with the chloride, which form nitro-compounds when the metal is dissolved in hydrogen nitrate, and render the salt unfit for such delicate processes as photography. 1 If a perfectly pure salt is wanted, it will be necessary to precipitate the silver again as chloride from the hydrogen nitrate solution, and to reduce it with pure sodium carbonate in the manner above described. PLATINUM RESIDUES. 451 2, Treatment of Platinum Residues. These residues will usually contain the metal either as perchloride or as ammonium- or potassium-chloroplatinate. In the first place, add about one-tenth of the volume of strong solution of ammonium chloride (to separate any platinum which may be in the solution), and evaporate the whole to dryness. Heat the residue to redness in a porcelain dish or a clean clay crucible, to get rid of any organic impurities, and to decompose the chloroplatinates. The resulting porous mass, to which any waste scraps of platinum foil or wire may be added, should be thoroughly washed with warm water to remove all soluble salts, and then boiled for some time with a mix- ture of three parts of strong hydrogen chloride and one part of hydrogen nitrate, in a long-necked flask, having a test tube full of cold water placed in the neck, to prevent loss of acid by eva- poration. This will be best done in the open air, or at any rate the chlorous vapours must be led into a chimney or through a window, and not allowed to escape into the laboratory. When the mixture has boiled for half an hour, the solution should be poured off, fresh acids added, and the boiling repeated The solutions should then be mixed, and the whole evaporated at a gentle heat nearly, but not quite to dryness, a little hydrogen chloride being added at the last, to decompose any remaining hydrogen nitrate. The so- lution of crude platinum perchloride, obtained by warming the residue with ^ water, should be filtered and mixed with a saturated solution of ammonium chloride, which should be added until no further precipitate is thrown down. This precipitate, of ammonium chloroplatinate, should then be collected in a filter, and carefully washed with water to which about half its volume of common methylated spirit should be added, in order to prevent the loss of any considerable quantity of the salt, since ammonium chloro- platinate is not wholly insoluble in water. Lastly, it should be dried on the filter, and strongly heated in a porcelain dish, until the whole of the salt is decomposed (p. 303). The spongy platinum thus obtained should be dissolved in aqua regia, and evaporated down, at first over the lamp to a small bulk, and then on a water-bath ' 1 In default of a regular water-bath for the above evaporations, the porcelain dish may be placed on the mouth of a beaker or saucepan rather smaller in diameter ; the latter being previously half filled with water, which is kept gently boiling on a sand-bath. Gg 2 452 APPENDIX B. to complete dryness. The highly deliquescent residue should be transferred quickly to a well-stoppered bottle, or, better, dissolved at once in water for use. A solution of convenient strength is made by weighing the spongy platinum before dissolving it in the acids, 'multiplying the weight in grammes by 25, and making up the solution to this number of cubic centimetres. This will give a solution 50 c.c. of which contains 3.19 grms. of platinum perchloride (Pt C/ 4 in 50 c.c.). 3. Treatment of Gold Residues. These may be worked up in the same way as platinum residues, except that the solution in aqua regia must, after evaporation, be mixed with excess of a strong solution of hydrogen oxalate, and boiled for some time. The gold will thus be precipitated in the metallic state, and the yellow spongy mass obtained will readily dissolve in aqua regia. The solution should be carefully evaporated on the water-bath, and the residue dissolved in water. For each gramme of gold taken, 50 c.c. of solution should be made. The liquid will then contain 3.03 grms. of gold perchloride in 100 c.c. (Au C/ 3 in 100 c.c.). APPENDIX C SHORT COURSES OF ANALYSIS FOR BEGINNERS. I. ANALYSIS of a solution containing a salt which may be any one of the fol- lowing: NITRATE, CARBONATE, ACETATE, TARTRATE, OXALATE. (The other radicle being potassium, sodium, or hydrogen.) 1 Test the action of the solution on litmus paper. Take out a drop on a clean glass rod, and put it on a strip of blue litmus paper. If it does not change the colour of the litmus, put another drop on reddened litmus paper. A The liquid does not decidedly alter the colour of either paper. It is a solution of a neutral salt. Pass on to 2. B The liquid reddens blue litmus paper strongly (if only slightly, it may be considered as practically neutral). Then it is probably a hydro- gen salt, i.e. an acid. Pass on to 2. C The liquid turns reddened litmus paper strongly blue. Then it con- tains a CARBONATE. To test for this, pour about 5 c.c. of the solution into a test-tube, and add several drops of dilute hydrogen sulphate. If a CAR- BONATE is present there will be an effervescence, owing to liberation of carbon dioxide. To make sure that the gas is really carbon dioxide, dip the long branch of an elbow tube in lime water (calcium hydrate), and lower it into the test-tube containing the gas, but not so far as to reach the solution, then suck a very little air through the tube. If the lime-water becomes cloudy (seen by holding it up to the light) the gas is certainly carbon dioxide, and the solution contains a CARBONATE. 454 APPENDIX C. 2 Put about 5 c.c. of the original solution into a test-tube, add i c.c. of strong hydrogen sulphate, then one drop of solution of indigo sulphate, and boil the mixture. Observe if there is any change of colour. A The blue colour of the indigo remains unaltered. Pass on to 3. B The blue colour of the indigo disappears. Then the salt is a NITRATE. To confirm this inference, put about 2 or 3 c.c. of the solution originally given for analysis into a test-tube, add an equal volume of strong hydrogen sulphate, and cool the mixture by holding it in a stream of water. When cold, hold the tube slanting, and pour gently down the side (from a pipette) some solution of iron proto- sulphate, so that it may float upon the liquid in the tube : and let the tube remain in the stand undisturbed, for a minute. If a brown layer informed where the two liquids meet, the solution certainly con- tains a NITRATE. 3 Put about 6 or 8 drops of the original solution into a test-tube, add about 5 c.c. of water, and enough of solution of sodium car- bonate to make the liquid alkaline to test paper ; then add 2 or 3 drops of solution of silver nitrate, which will produce a white pre- cipitate, and boil the mixture. Observe whether the precipitate changes colour. A // is unaltered. Pass on to 4. B It turns black. Then the solution contains a TARTRATE. To confirm this, pour some of the original solution into a test- tube, add one drop (not more) of solution of potassium hydrate, stir the mixture with a glass rod, and shake it violently. If a crys- talline precipitate forms, especially along the lines where the glass rod touched the sides of the tube, a TARTRATE is certainly present. 4 Put a little manganese dioxide into a test-tube, add about i c.c. of strong hydrogen sulphate, and then 2 or 3 drops of the original solution. Observe whether any effervescence occurs (best heard by holding the open end of the tube close to the ear). A No gas is given off". Pass on to 5. B A gas is given off", with effervescence. The solution contains an OXALATE. To confirm this, add to some of the original solution sufficient ammonium hydrate to make it alkaline to test paper, and then add 2 or 3 c.c. of solution of calcium sulphate. If a white precipitate is produced, an OXALATE is certainly present. SHORT COURSES OF ANALYSIS. 455 5 If no other radicle has been found, the solution must contain an ACETATE. Test for this as follows, Put about 2 or 3 c.c. of the original solution into a test-tube, add about i c.c. of pure alcohol and i c.c. of strong hydrogen sul- phate, and warm the liquid gently. If vapours are given off which have the fragrant smell of acetic ether, an ACETATE is present. II. ANALYSIS of a Salt which may contain any one of the following radicles: CARBONATE, OXALATE, TARTRATE, FLUORIDE, CYANIDE, CHLO- RIDE, BROMIDE, IODIDE, ACETATE, NITRATE, CHLORATE. (The other radicle being potassium, sodium, ammonium, or hy- drogen.) A. The substance is a Solid. \ Examine and note down its appearance, e.g. colour, shape, crystal- line form (if any). Then powder a little of it (about as much as two peas) in a glass mortar, and put the powder in a test-tube ; add about 20 c.c. of water, and warm it until the salt is dissolved. While it is dissolving, heat a little of the solid salt in an ignition tube over a Bunsen's burner ; observe which of the following effects are produced : A The substance fuses, but gives off no gas, and is not otherwise altered. Then it is probably a FLUORIDE, CYANID.E, CHLORIDE, BROMIDE, or IODIDE. Pass on to 3. B The substance fuses, and gives off a colourless gas. Drop in a small splinter of charcoal (from the charred end of a match) and again heat. If the charcoal burns brightly, the gas is oxygen, and the substance is a CHLORATE or a NITRATE. Pass on to 6 B. C The substance becomes charred, i.e. turns black and gives off vapours (which have a strong smell like burnt paper. Then it is either an ACETATE or a TARTRATE. Pass on to 3. 456 APPENDIX C. D The substance 'volatilises entirely. Then it is either HYDROGEN OXALATE or an ammonium salt. Pass on to 3. B. The sttbstance is a Liquid. 2 See whether it has any colour or smell (a cyanide would smell like essence of almonds). Then take out a drop on a clean glass rod, and place it on a bit of blue litmus paper. If it does not change the colour of the litmus, put another drop on reddened litmus paper. A The liquid does, not alter (or only alters slightly) either litmus paper. Then it contains a neutral salt. Pass on to 3. B The substance reddens blue litmus paper strongly. Then it is probably a hydrogen salt, i. e. an acid. Pass on to 3. C The liquid turns reddened litmus paper strongly blue. Then it is a CARBONATE or a CYANIDE. Pour about 5 c.c. of the solution into a test-tube, and add several drops of dilute hydrogen sulphate. a. There is a strong effervescence. Then the salt is a CARBONATE. Dip the long branch of an elbow tube in lime water (calcium hydrate) and lower it into the test-tube, but not so far as to reach the solution, and suck a very little air through the tube. If the lime water becomes cloudy, the substance is certainly a CAR- BONATE, and no further tests are required. b. There is little or no effervescence. The salt is probably a CY- ANIDE. Pass on to 4. Put about 5 c.c. of the original solution into est " a test ' tu ^ e (if ^ * s ac ^> make it neutral by adding ammonia) and add i or 2 drops of solution of barium chloride. A No precipitate is formed. Pass on to 4. B A white precipitate is formed. The salt is a TARTRATE, OXALATE, or FLUORIDE. Put about 6 or 8 drops of the original solution into a test-tube, add about 5 c.c. of water and then enough solution of sodium car- bonate to make it alkaline to test paper: then add 2 or 3 drops of solution of silver nitrate (which will produce a white ppte.) and boil the liquid. (# .) The precipitate turns black on boiling. The substance is a TARTRATE. SHORT COURSES OF ANALYSIS. 457 (b.) No blackening of the precipitate is observed. The salt must be an OXALATE or a FLUORIDE. To decide which is present, put a little manganese dioxide into a test-tube, add about .1 c. c. of strong hydrogen sulphate, and then 2 or 3 drops of the original solution. (#.) Carbon dioxide is given off" with effervescence, (Prove that the gas is really carbon dioxide by the lime water test, 2 C .) The salt is an OXALATE. (b.) No gas is given off. The salt must be a FLUORIDE. Confirm this as follows : Pour a little of the original solution into a leaden cup and evaporate it to dryness. (If the original substance was a solid, some of this may be taken.) While the evaporation is going on, cover a glass plate with wax, and trace some letters on it with a pointed piece of wood. Pour a few drops of strong hydrogen sulphate on the residue in the cup : place over it the glass plate with the wax downwards, and warm gently for 5 minutes, taking care not to melt the wax. If the lines are etched in the glass the substance is a FLUORIDE. Put 3 or 4 drops of the solution into a test-tube, add 6 or 8 c> c ' of water and 2 dr ps f dilute hydrogen nitrate, then add 2 drops of solution of silver nitrate. A No precipitate is formed. Pass on to 6. B A ^white or light yellow precipitate is formed. The salt is an IODIDE, BROMIDE, CHLORIDE, or CYANIDE. 5 Add to a portion of the original solution one or two drops (not more) of solution of chlorine. A 'The liquid turns yellow. A BROMIDE or IODIDE is present. Pour off one half of the yellow liquid into another tube, and add some freshly made solution of starch. (a.) The solution turns deep blue. An IODIDE is present (no con- firmatory test is needed). (b.} The solution remains unaltered. A BROMIDE is present. Con- firm this by adding to the rest of the yellow liquid (containing chlorine) about i c. c. of carbon disulphide, and shaking it up. If the globule of carbon disulphide which settles to the bottom is orange-coloured, the presence of a BROMIDE is certain. B 'I he liquid does not turn yellow. The substance present must be a CHLORIDE or a CYANIDE. 458 APPENDIX C. To distinguish between them, put a little manganese dioxide into a test-tube, add about 2 c.c. of strong hydrogen sulphate, and then 6 or 8 drops of the original solution and warm gently (but do not boil the liquid). (a) A greenish gas is given off* which has the smell of chlorine, and bleaches a strip of moist litmus-paper held in the tube. The substance is a CHLORIDE. (b) A gas is given off" which has the smell of essence of almonds. The substance is a CYANIDE. To confirm this, add to some of the original solution, first 6 or 8 drops of solution of potassium hydrate, and then 2 or 3 drops of solution of iron protosulphate, when a greenish precipitate will form. Shake the whole thoroughly for a few seconds, and warm it gently; then add 2 or 3 c.c. of dilute hydrogen chloride. If a deep blue precipitate remains undissolved, the presence of a CYANIDE is certain. Put about 5 c. c. of the solution into a test-tube, add about * c * c - of stron S hydrogen sulphate, then one drop of solution of indigo sulphate, and boil the mixture. The blue colour of the indigo disappears. The salt is a CHLORATE, or a NITRATE. Put 5 or 6 drops of the original solution (or of the solid substance) into a test-tube, and add about 3 c.c. of strong hydrogen sulphate. (a) The liquid turns yellow, and gives off a yellow gas, when warmed, which smells like a chlorine oxide. The substance is a CHLORATE. (b) The liquid does not turn yellow. The substance is a NITRATE. Allow the liquid to become quite cold ; then holding the tube slanting, pour gently down the side from a pipette, some solu- tion of iron protosulphate, and let the liquid stand for a few minutes. If a brown ring is formed between the two liquids a NITRATE is present. The blue colour of the liquid is unaltered. The salt is an ACETATE. To confirm this, pour about 2 c. c. of the original solution into a test-tube, add about i c.c. of pure alcohol, and i c.c. of strong hydrogen sulphate and warm the mixture. If vapours are given off which have the fragrant smell of acetic ether, an ACETATE is present. APPENDIX D. LAWS OF CHEMICAL COMBINATION. It was only at the end of the last century that chemists, by accurate experiments and constant use of the balance, were enabled to establish certain laws which express the proportions by weight in which substances combine with, and act on, each other. They are the following, I. Law of Constant Proportion. A particular compound always consists of the same ele- ments united in the same proportion. Thus water, whether obtained from wells, or the clouds 2 or the sea, or formed in the laboratory in the course of experiments, in- variably consists of the two elements, oxygen and hydrogen, united in the proportions of 16 parts by weight of oxygen to 2 parts by weight of hydrogen. If we endeavour to form water by combining oxygen and hydrogen in any other proportions, we find that the excess of one or the other remains uncombined. Similarly, ammonia, whether formed in nature, or obtained by decomposing wool, silk, coal, ammonium chloride, &c., invariably contains nitrogen and hydrogen, united in^the proportions of 14 parts by weight of nitrogen to 3 of hydrogen. Two results follow from this law. 1. A few really well-made experiments are sufficient to settle once for all the composition of a substance. If a substance is brought to a chemist, which has all the pro- perties of water, he can feel sure what its composition is without taking the trouble actually to analyse it. 2. Any substance which is not quite constant in composition, is certainly not a chemical compound, but only a mixture. For 460 APPENDIX D. example, one reason for considering air to be a mixture is that the proportion of oxygen in it is slightly variable. II. Law of Multiple Proportion. When one body combines with another in more than one proportion, the higher proportions are multiples of the lowest. A good example of this law is afforded by the series of com- pounds of nitrogen and oxygen, of which a list is subjoined. COMPOUNDS OF NITROGEN AND OXYGEN. Name. Composition by weight. Nitrogen. Oxygen. Acid formed by its combination with water. Nitrogen Pentoxide 28 : 80 Hydrogen Nitrate. Tetroxide 28 : 64 Hydrogen Nitrate and Nitrite. Trioxide Dioxide 28 : 48 28 : 32 Hydrogen Nitrite. (None). Protoxide 28 : 16 (None). If we examine what quantity of oxygen is combined with the same quantity of nitrogen, say 28 parts, we find that in the compound which contains least oxygen it is 16 parts: in the next, 32 parts, or twice 16 ; in the next, 48 parts, or three times sixteen, and so on. Two results follow from this law. 1. We can predict the composition of compounds which have not yet been formed. Thus, if a nitrogen oxide is ever discovered which contains rather more oxygen than the pentoxide (nitrogen 28 : oxygen 80), we may say with certainty that it will be composed of 28 parts of nitrogen united with 96 parts of oxygen, 2. If any substance is found to contain nitrogen and oxygen not In the proportions of 28 to 1 6 or a multiple of 16, we can say with certainty that it is not a chemical compound but a mixture. Thus air contains nitrogen and oxygen, but the proportion of nitrogen to oxygen is as 28 : 8.36, which is not a simple multiple of 1 6. This is another reason for considering air to be a mixture. III. Law of Reciprocal Proportion. If two bodies, A, and B, each combine with a third body, C, they can only combine with each other in proportions which are measures or multiples of the proportions in which they each combine with C. Thus, nitrogen and hydrogen each combine with oxygen, in the proportions shewn below. Nitrogen. Oxygen. Nitrogen Protoxide 28 : 16 Hydrogen. Water .. 2 16 LAWS OF CHEMICAL COMBINATION. 461 Nitrogen and hydrogen also combine with each other in the propor- tions shown below Nitrogen. Hydrogen. Ammonia 28 : 6 in which we notice that 6 is a multiple of 2. IV. Law of Compound Proportion. The proportion in which a compound unites with any- thing else is the sum or a multiple of the sum of the pro- portions in which its elements are present in it. Thus, taking two compounds, ammonia and hydrogen nitrate, the proportions by weight in which their elements are present in them are the following : Ammonia. Hydrogen 3 parts Nitrogen 14 Hydrogen Nitrate. Hydrogen i part Nitrogen 14 Oxygen 48 Sum = 17 Sum = 63 Now it is found that ammonia only unites with hydrogen nitrate in the proportion of 17 parts of ammonia to 63 of hydrogen nitrate. If any other proportions are taken, there is found an excess of one or the other remaining uncombined. These laws are simply the expression of facts, proved by actual experiment ; but it was soon felt that there might be some simple underlying fact which would account for them all, and the hypothesis put forward by Dalton in 1801 has now been almost universally accepted as true and sufficient. The Atomic Theory 1 . According to Dalton, all kinds of matter are made up of distinct particles, respecting which the following assertions can be made. 1. They are incapable of being divided. 2. The particles of the same substance are similar to one another, and equal in weight. 3. The particles of different substances differ in weight. These small indivisible particles are called ' Atoms ' (aro/uop, that which cannot be divided). Dalton further said that the 'combining proportions' referred to in the above Laws simply express the relative weights of these atoms. 1 A fuller account of this is given in the next section, to which this should be considered as introductory. 463 APPENDIX D. Thus, the n 16, by which we .always can and generally must express the proportion in which oxygen combines with other things, is considered to be the weight of the atom of oxygen as compared with the weight of the atom of hydrogen, which is found to be the lightest of all atoms. In other words, the oxygen-atom is regarded as 16 times as heavy as the hydrogen-atom. Similarly, the nitrogen-atom is believed to be 14 times as heavy as the hydrogen-atom, and so on for other elements ; each having its own definite combining proportion, which indicates the weight of its atom. If it be asked how the relative proportions by weight in which things act on each other, as ascertained by our comparatively rough balances, can be taken to indicate the relative weights of their single atoms, which are far too small for us to weigh, the reply would be, that it is reasonable to suppose that in the large masses of atoms which we deal with in ordinary practice, each atom of the mass is acting and being acted on similarly to the rest : just as in a regiment, when marching, every individual moves similarly to and simultaneously with every other. We can hardly imagine, for example, when we mix a quantity of oxygen weighing 16 grms. with a. quantity of hydrogen weighing 2 grms. and make them com- bine, that some of the atoms in each are affected and not others. We have every ground for believing that any chemical action between masses represents accurately the action which is going on between the individual atoms of the masses. Now, if we allow that these atoms exist, and that all chemical changes consist in the shifting of them, like pieces on a chess-board, from one position to another, or from one group to another, all the observed facts of chemical combination can readily be explained. I. The ist law would be a necessary consequence, because if the atoms of each kind of matter have definite unalterable properties, different from those of the atoms of other kinds, then, whenever we find two or more specimens of matter having absolutely the same properties, they must be composed of the same number of atoms of the same kinds, united in the same way. II. The 2nd law follows because in forming compounds contain- ing larger proportions of a given element we must add a whole atom at a time, (and not half an atom or one-and-a-half atoms, since the atom is not divisible.) LAWS OF CHEMICAL COMBINATION. 463 Thus if the smallest quantity of nitrogen protoxide contains a single atom of oxygen weighing 16 hydrogen-atoms, we must add another whole atom, also weighing r6 hydrogen-atoms, to make the dioxide. Thus nitrogen dioxide will contain twice the weight of oxygen contained in the protoxide. Similarly nitrogen trioxide will contain three times the weight, and so on. III. The 3rd Law follows because the atom is unalterable in weight, whatever may be the compound it exists in ; and therefore when an element unites with any other substance it must do so in the proportion which the weight of its atom indicates or in some multiple of that proportion, if more than one atom of it combines. Thus if the weights of the atoms of hydrogen, nitrogen and oxygen are i, 14, and 16 respectively, all their compounds, nitrogen pro- toxide, water, ammonia, &c. &c. must contain them in these propor- tions, or multiples of these proportions. IV. The 4th Law also follows from the unalterability in weight of atoms. The weight of the particle of a compound which takes part in a chemical change is as certainly the sum of the weights of the atoms which compose it, as the weight of a bag of shot is the sum of the weights of the individual shot in it. CHEMICAL SYMBOLS. Chemists have agreed to represent the atoms of substances by symbols ; the first letter of the name of the element being generally taken to express its atom. Thus, the atom of Oxygen is .denoted by O. Hydrogen H. Nitrogen N. Carbon C. These symbols therefore represent definite weights of the respec- tive elements. Thus, H represents the unit of atomic weight, i.e. the weight of the hydrogen-atom, whatever that may be. O represents a weight of oxygen = 1 6 hydrogen -atoms. nitrogen =14 C carbon = 12 The group of atoms which form the smallest particle of a com- pound which can exist in a free state is called its ' molecule ' ; and we can express the molecule of a compound by simply putting together the symbols of the atoms which compose it, just as we form a word by putting letters together. This group of symbols is called a Formula. 464 APPENDIX D. Thus the molecule of water contains i atom of oxygen and 2 atoms of hydrogen, and may therefore be expresseH by the formula HHO. When however several similar atoms are present the symbol is only written once, and a small n is put on the right of it and a little below, to shew how many atoms are present. Thus the usual formula for the molecule of water is H 2 O. On the same principle the formulae of the molecules of some of the substances already examined should be written out from the follow- ing data as to their composition. Substance. Ammonia Composition. Formula. Hydrogen Nitrogen Hydrogen Nitrate ... Potassium Nitrate ... Ammonium Nitrate . Or (to show that it contains the AMMO- NIUM and NITRATE radicles) 3 atoms. i atom. Hydrogen Nitrogen Oxygen i atom. i atom. 3 atoms. Potassium Nitrogen Oxygen i atom. i atom. 3 atoms. Hydrogen Nitrogen Oxygen 4 atoms 2 atoms 3 atoms. /Hydrogen Nitrogen \ /Nitrogen Oxygen \ ^ 4 atoms i atom ) \ i atom 3 atomsA Nitrogen Pentoxide .. Tetroxide .. ,, Trioxide Dioxide Protoxide .. Nitrogen Oxygen 2 atoms. 5 atoms. 2 atoms. 4 atoms. 2 atoms. 3 atoms. 2 atoms. 2 atoms. 2 atoms. i atom. H. G. M. II. ON CHEMICAL SYMBOLS. The aim of these Exercises has been to present some of the facts of chemistry without entering upon questions of chemical theory. But symbols having been used to express the principal chemical changes which form the subject of the exercises, and the nature and strength of the various reagent solutions, a statement of the meaning of such symbols is subjoined, together with a Table of Atomic Weights. In the beginning of Part II is an explanation of the term ' single substance.' A chemical change consists in the conversion of any quantity of one or more single substances into an equal quantity, CHEMICAL SYMBOLS. by weight, of one or more different single substances. The remem- brance of some of the most important facts t elating to these changes is facilitated by the adoption of the following hypothesis. It may be the case that a portion, a gramme for instance, of any single substance is an aggregate of a vast but finite number of little particles, each of which has exactly the same properties as any other and as the whole mass. These little particles are, in almost all cases, themselves divisible; but when they are divided, it is not into smaller portions of the same substance, but into distinct parts which are called atoms, as being incapable of further division. These atoms unite into fresh groups which are the molecules of substances different from the original substance; and it is in this way, according to the hypothesis, that a chemical change takes place. A molecule may consist of any number of atoms, from one up to a very large number. The molecules of the elements are supposed to consist either of single atoms or of two or more similar atoms united together. Differences in the properties of different sub- stances may be due to the differences in the nature, or number, or arrangement, of the atoms of which their molecules consist. The weight of a molecule is the sum of the weights of its atoms ; and, since different atoms have very different weights, and different molecules consist of very different numbers of atoms, the weight of one molecule may be several hundred times as great as that of another. Chemists have agreed to represent the various atoms by letters, that assigned to each being generally the initial letter of the name of that element whose molecule is made up of such atoms. Thus H represents the hydrogen-atom and O the oxygen-atom. But as the names of several elements have the same initial letter, the requisite variety has been obtained by taking the Latin instead of the English name, or by using two letters. Thus K represents the potassium-atom (Kalium), Go the cobalt-atom, Sb the antimony- atom (Stibium). The union of two or more atoms to form a molecule or group of atoms is represented by placing their symbols together, thus Co O represents a molecule of cobalt oxide, which consists of a cobalt-atom united to an oxygen-atom. When similar atoms are united, a numeral is affixed to the symbol of the atom, to represent its repetition so many times ; thus, the molecule of water is expressed by H 2 O instead of H H O. It will be plain that, according to the hypothesis stated above, the atoms are not actual portions of any known substance except in H h 466 APPENDIX D. the case of those substances whose molecules consist of single atoms, where, consequently, the atom is also a molecule. The smallest particle, or molecule, of common salt is represented by the formula Na Cl : its atoms Na and Cl can be transferred to other molecules, but cannot be obtained as distinct substances ; we know them only as constituents of a number of different molecules. And in the same way the molecule of hydrogen is represented by H 2 , the letter H representing, not a minute portion of hydrogen, but a constituent of hydrogen, a hydrogen-atom, a portion of matter weighing half as much as the smallest particle of hydrogen which is transferable in chemical changes from one molecule to another. The determination of the relative weights of different atoms depends upon (i) the accurate quantitative analysis of a number of single substances, (2) a decision as to the constitution of the mole- cules of these substances. For example, analysis shows that nine weights of water can be decomposed into eight weights of oxygen and one weight of hydrogen. Choosing the weight of the hydrogen atom, as being the smallest relative weight we have to do with, as the unit of our system, if we decide that a molecule of water con- sists of one hydrogen-atom combined with one oxygen-atom, the weight of the oxygen-atom must be 8. If we decide that a mole- cule of water consists of one hydrogen-atom combined with two oxygen atoms, we must take 4 to be the atomic weight of oxygen ; or if we have reason, as in fact we have, to regard the molecule of water as consisting of two hydrogen-atoms and one oxygen-atom, we must call the weight of the oxygen-atom 16. The reasons which guide us in deciding what is the constitution of the molecule of a substance may be stated summarily under two heads: (i) that constitution is most probably true which affords the simplest account of the changes which the molecule is known to undergo, and which best exhibits the analogy between the substance in question and other substances which it resembles; (2} that con- stitution is most probably true which makes the molecular weight of the substance bear to the molecular weights of other substances the same ratio which its vapour-density bears to theirs. As this latter guide to the molecular constitution of substances is only available in the case of substances which can be volatilized without decomposition at a moderate heat, the weights of those atoms have been most definitely fixed which enter into the molecules of such substances. It has also been observed that the relative weights of the atoms are in most cases nearly in inverse proportion to the specific heats CHEMICAL SYMBOLS. 467 of the elements which they form. This observation furnishes us with another criterion of the true atomic weight. The following Table of Atomic Weights has been arrived at in the manner indicated. TABLE OF ATOMIC WEIGHTS. H represents Li a Hydrogen-atom weighing Lithium-atom i 7 B Boron-atom ii c Carbon-atom 12 N Nitrogen-atom 14 Oxygen-atom l6 F Fluorine-atom ig Na Sodium-atom 2 3 Mg Magnesium-atom 2 4 Al Aluminium-atom 27-5 Si Silicon-atom 28 P Phosphorus-atom Jl s Sulphur-atom 32 Cl Chlorine-atom 35-5 K Potassium-atom 39 Ca Calcium-atom 40 Ti Titanium-atom 50 V Vanadium-atom 51.2 Cr Chromium-atom 52.5 Mn Manganese-atom 55 Fe Iron-atom 5 6 Co Cobalt-atom 59 Ni Nickel-atom 59 Cu Copper-atom 63.5 Zn Zinc-atom 65 As Arsenic-atom 75 Se Selenium-atom 79 Br Bromine-atom 80 Sr Strontium-atom 87-5 Mo Molybdenum-atom 92 Pd Palladium-atom 106.5 Ag Silver-atom 108 Cd Cadmium-atom 112 Srt Tin-atom 118 u Uranium-atom 120 Sb Antimony-atom * 122 I Iodine-atom I2 7 Ba Barium-atom 137 W Au Tungsten-atom Gold-atom I8 4 196.7 Pt Platinum -atom I 9 7 Hg . Mercury-atom 200 Tl Thallium- atom 204 Pb Lead-atom 207 Bi Bismuth-atom 210 This Table, which includes all the atoms which are not of very rare occurrence, enables us to calculate the weight of any mole- H h 2 468 APPENDIX Z>. cule whose formula is known to usy relatively to the weight of a hydrogen-atom which is assumed as the unit. Thus, the formula of calcium carbonate being Ga G O 3 , the weight of its molecule is (40 + 12 + (3 x 16)=) TOO; that is to say, a molecule of calcium carbonate weighs a hundred times as much as a hydrogen-atom. A Table of Molecular Weights, which might be extended to all substances whose constitution has been determined, would have the following form. H 2 represents a molecule, or 2 parts by weight, or i volume of Hydrogen. N 2 28 Nitrogen. Hg 200 Mercury. P 4 >, 124 Phosphorus. NH 3 17 Ammonia. C 2 H 4 28 Ethylene. &c. &c. In the equations by which chemical changes are represented, the sign = has not simply its algebraic sense of ' equals/ but should rather be read ' is converted into.' That the substances formed in a chemical change weigh as much as the substances that went to form them, is a fact which renders the symbol appropriate, but is not all that it is understood to mean. The sign + , connecting the symbols of two molecules, denotes that these molecules disappear, or are formed, simultaneously ; it may be expressed in reading by the word ' and.' Thus the equation K 2 SO 4 + BaCl 2 = BaSO 4 + 2KC1 should be read thus, ' a molecule of potassium sulphate and a mole- cule of barium chloride are converted into a molecule of barium sulphate and two molecules of potassium chloride.' To obtain the relations by weight between the different substances we write down, K 2 -78 Ba - 137 Ba - 137 K - 39 S - 32 Cl a - 71 S - 32 Cl - 35-5 4 - 64 4 - 64 i74 BaCl 2 -2o8 BaSO 4 -233 KC1-74.5 whence we see that 174 weights of potassium sulphate and 208 weights of barium chloride are converted into 233 weights of barium sulphate and 149 weights of potassium chloride. Since equal volumes of all gases contain, under the same con- ditions, the same number of molecules, equations representing changes in which gases take part may be read off at once as ex- pressing changes of volume. The common volume occupied by an CHEMICAL SYMBOLS. 469 equal number of molecules of the different kinds of matter in the gaseous state should be called one volume. Thus, 2CO-fO 2 =2CO 2 may be read 'two volumes of carbon protoxide and one volume of oxygen are converted into two volumes of carbon dioxide.' If in comparing the molecular weights and volumes of different substances we take a gramme for unit instead of the weight of an atom of hydrogen, the common volume occu- pied by 28 grms. of carbon protoxide, 32 grms. of oxygen, 44 grms, of carbon dioxide, &c* is 22.3 litres, A. V. H. APPENDIX E. I. TABLES OF WEIGHTS AND MEASURES. The system of weights and measures used in this book is that which is known as the metric system. The unit of the system is the metre, the length of which is * O th part of the earth's circumference, .000 .000 as determined in 1796 by Delambre and others. 1. Length. From it the larger and smaller measures of length are all derived on the following simple principle. (a) The smaller measures are obtained by taking ^ of the length of the metre for the next smaller measure : yo of its length for the next smaller one ; and T^ of its length for the smallest. Their names are formed by adding to the word " metre " a prefix derived from a Latin numeral (decem, centum, mille], denoting what fraction of the metre the measure is. (6>) The larger measures of length are obtained by taking 10 times the length of the metre for the next larger measure; 100 times its length for the next larger one; and 1,000 times its length for the largest. Their names are formed by adding to the word "metre" a prefix derived from a Greek numeral (Se'/m, e/caror, ^1X101) denoting what multiple of the metre the measure is. A still larger measure, the myriametre (=10,000 metres) is sometimes, though rarely, used. The following Table shews the metric measures of length, and their value in English measure. WEIGHTS AND MEASURES. 471 Kilometre =1000 metres =1093.6 yards = 0.6214 of a mile. Hectometre = 100 = 3937.08 inches = 109.36 yards. Decametre = 10 = 393.71 = J o.93 Metre = i = 39.37 = 1.09 Decimetre = J^ = 3:94 Centimetre = jfa = 0.39 Millimetre = y^- = 0.039 It may be convenient to remember that a decimetre is very nearly four inches, and Fig. 82 shows a decimetre and its subdivisions, compared with a scale of English inches. 2. Volume. The unit of volume is a cube, each of the sides of which measures one decimetre. It is called a litre, and from it the other measures of volume are derived by taking ^, ^, and r^- of its size for the smaller ones, and 10 times, 100 times, and 1,000 times its size for the larger ones, precisely as those of length are derived from the metre. Their names also are formed on the same principle by adding to the word "litre 11 prefixes derived from the Latin for the smaller measures, and prefixes derived from the Greek for the larger ones. Kilolitre = 1000 litres = 220.01 gallons. Hectolitre = 100 = 22.00 Decalitre = 10 = 2.20 Litre = i = 1.76 pints. Decilitre = looc.c. = T ^ = 3.5 fluid oz. Centilitre = 10 c.c. jfa = 0.35 Millilitre = i c.c. = -^^ = 0.035 (or cubic centimetre) In scientific work, quantities smaller than the litre are almost always expressed in cubic centimetres instead of decilitres, &c. Thus, half a litre would be expressed (not as 5 decilitres but) as 500 c.c. 3. Weight. The unit of weight is the weight of i cubic centimetre of water at the temperature of 4 Centigrade. It is called a gramme, and the other weights are subdivisions and multiples of it, derived in the same way and named on the same principle as above explained. Kilogramme = 1000 grammes = 2.205 lbs - (avoird.) Hectogramme = 100 = 3-5 2 7 oz - Decagramme = 10 = 0.35 oz. Gramme = I =15-43 grains. Decigramme = ^ = i-54 Centigramme = ^ = 0.154 Milligramme = 1 - 1 tf6 = 0.015 473 APPENDIX E. A series of measures of surface -or area is sometimes used, of which the unit is the "are," which is a surface i decametre square. The hectare is very nearly 2^ acres.. Rules for Reduction. 1. To reduce the smaller measures to metres (litres, or grammes), and metres (litres, or grammes) to the larger measures, Divide by the no. expressed in the name of the measure. 2. To reduce the larger measures to metres (litres or grammes) and metres (litres, or grammes) to the smaller measures, Multiply by the no. expressed in the name of the measure* Examples : Reduce 1881 w/7/zinetres to metres. 1 88 1 -T- i ooo = i. 88 1 metre. Reduce 24 decagrammes to grammes and centigrammes 24 x 10 = 240 grammes. 240 x 100 = 24,000 centigrammes. Decimal fractions of the measures may always be read off into their equivalents without altering the figures, by simply attending to the value of each figure as fixed by the position of the decimal point. Thus I- 88 1 metre = i metre, ^ metre, ^ metre, j^^ metre. = i metre, 8 decimetres, 8 centimetres, i millimetre. TABLES OF ENGLISH MEASURES. 1. Length. I 12 3 r 4 4 8 inch inches, feet yards poles poles furlongs = foot yard pole chain furlong mile - 2.54 centimetres. 30-48 91.44 5.03 metres. 20.12 201.16 ,,. 1609.3 2. Volume. i cubic inch = 16.38 cubic centimetres. 1728 cubic inches = i cubic foot = 28.31 litres. 61.027 = i litre. WEIGHTS AND MEASURES. 473 1 drachm = 0.216 cubic inch = 3.55 cubic centimetres. 8 drachms = i ounce = 28.4 20 ounces = i pint = 567.9 2 pints = i quart = 1.136 litres. 4 quarts = i gallon = 4.543 ., = 277.274 cubic inches. i gallon = 70,000 grains (or 10 Ibs. avoird.) of distilled water at the temperature of 6oF (i5.5C). 3. Weight. (a) Apothecaries. i grain = 0.0648 gramme. 20 grains = I scruple = 1.296 3 scruples = i drachm = 3.888 8 drachms = i ounce = 31.104 12 ounces = i pound = 373.248 (b) Avoirdupois. i grain = 0.0648 gramme. 2 7-34 grains = i drachm = 1.772 1 6 drachms = i ounce = 28.35 > 1 6 ounces = i pound = 453.6 112 pounds = i cwt, = 50.8 kilogrammes, II. THERMOMETRIC SCALES. The temperatures mentioned in this book are all expressed on the Centigrade scale. According to this scale,., the space through which the column of mercury in a thermometer moves, when passing from the tem- perature at which water freezes to the temperature at which water boils, is divided into 100 equal parts or degrees, and the scale is extended below the freezing-point and above the boiling-point of water, in divisions of the same value. The point at which the mercury column stands when the thermo- meter is immersed in melting ice is marked o, and the degrees below this point are distinguished by a minus, sign, thus - i, - 2, &c. 474 APPENDIX E. The point at which the mercury column stands when the thermo- meter is immersed in the steam from boiling water (the barometric column being 760 mm.) is marked 100. In the Fahrenheit scale, which is not yet superseded in this country, the space between the freezing-point and the boiling- point of water is divided into 180 degrees, and, moreover, the freezing-point of water is marked 32 instead of o, the boiling- point of water being consequently marked 212 instead of 180. The points to be borne in mind, then, in converting temperatures expressed on the one scale to the corresponding temperatures on the other scale, are 1. The same space is divided on the Centigrade scale into 100 parts, on the Fahrenheit scale into 180 parts. Consequently, i degree on the Centigrade scale is equal in length to (-}=) of a degree on the Fahrenheit scale; and i degree on the Fahrenheit scale is equal in length to (-Hn^) s f a degree on the Centigrade scale. For since 100 C = 1 80 F 100 C : i8oF:: iC:$F and 1 80 F : 100 C : : i F : | C. 2. The point marked o on the Centigrade scale is marked 32 on the Fahrenheit scale. Consequently, in order to bring the two scales to the same level, we must subtract 3 2 from the number of Fahrenheit degrees before converting them into Centigrade degrees ; and, in the reverse pro- cess, after converting the Centigrade degrees into Fahrenheit degrees, we must add 32. If o C expressed the same temperature as o F, then, clearly iC would = i.8F. 5C 9F- 10 C i8F. &c. &c. But oC marks a point of temperature = 32 F. Hence all the above Nos. Fahr. have to be increased by 32 (lifted, as it were, in the row), so that iC = ( f + 32 =)33-8F. 5 C = ( 9 + 32 -)4iF. ioC = (18 + 32 =)5QF. Similarly in reducing Fahr. to Cent, we must take away 32 from the THERMOMETRIC SCALES. 475 no. of degrees (thus practically lowering it in the scale) before apply- ing the rule. Thus 59F- 3 2 = 27 || 27 x . 15 C. The rules, therefore, may be thus expressed : 1 . To convert Fahrenheit degrees into Centigrade degrees, Subtract 32 from the number of degrees, and multiply the re- mainder by f (or 0.5) ] . 2. To convert Centigrade degrees into Fahrenheit degrees, Multiply the number of degrees by (or 1.8) and add 32 to the product 2 . In applying the rule to degrees low in the scale, the character of the sign -f or - must be carefully attended to, and considered in its algebraic sense. Thus, 23 F - 32 = - 9 II - 9 * = - 5C. - 4 oF- 3 2 = -72 || -72 x $ = - 4 oC. III. TABLE OF THE SOLUBILITY OF SALTS. (See p. 481.) This Table is intended to indicate the solubility in water and acids of the single salts formed by the union of the different radicles treated of in the foregoing pages, and has been compiled mainly upon the authority of Storer's ' Dictionary of Solubilities.' The degrees of solubility are, however, so numerous that it is difficult or impossible to draw a sharp line between a soluble and an insoluble substance. The statements in the Table must there- fore be only regarded as approximations; as relatively rather than absolutely true. It is hardly necessary to remark that in cases where a sub- stance is said to dissolve in an acid, the phenomenon usually consists in the formation, by the action of the acid, of a salt soluble in water. 2 C-(fn+ 3 a)F. This rule may also stand as follows : Double the number of degrees, subtract r ^ of this product, and add 32 to the remainder. Thus, 25 C x 2 = 50 50 - 5 = 45 45 + 32 = 77 F. INDEX. Acetates, properties of, 172. Acids (see under Hydrogen salts). nature of, 103. Air, analysis of, 118, 144. composition of, no, 118. synthesis of, 119. Alcohol, density of, determined, 49. Alkaline reaction, meaning of, 59. Alum, crystals of, prepared, 53. Aluminium salts, properties of, 332. Ammonia, oxidation of, 130. preparation and properties of, 123. Ammonium amalgam, preparation of, 362. derivatives of, 364. Nessler's test for, 364. - radicle, composition of the, 1 29. radicle, nature of, 361. salts, formation of, 129, 135, 192. salts, properties of, 362. Analysis, course of, for an insoluble substance, 416. course of, for a metal, 398. course of, for a non-metallic radicle, 410. example of the mode of writing out results of; 419. grouping of metallic radicles in, 374- grouping of non-metallic ra- dicles in, 371. meaning of the term, 68. practical course of, 379. short courses of, for beginners, 453- Analytical course, explanation of the, 367. Annealing of glass, 30. Antimony compounds, properties of, 287. detection of, by Marsh's test, 2 95- Apparatus, list of, I. suggestions for the construc- tion of, 422. Aqua regia, formation of, 193. Archimedes' principle, statement of, 51. densities taken by, 51, 52. Argand burner, 6. Arsenates, tests for, 285. Arsenic, detection of, by Marsh's test, 289. salts, properties of, 282. white, properties of, 280. Arsenites, tests for, 284. Atom, definition of, 465. Atomic theory, account of, 461, 465. weights, table of, 466. Autotype process, principle of the, 331. Balance, i. examination of accuracy of, 46. Barium, properties of compounds of, 34- Bismuth salts, properties of, 278. Blower, india-rubber, 16, 432. Blowpipe burner, description of, 84, examination in analysis, 387. flame, structure of, 87, 88. Herapath's, description of, 15. mouth, exercise on the use of the, 83. simple form of, 428. Bone black, properties of, 151. Berates, properties of, 240. Borax beads, preparation of a set of, 339- Bottles, list of required, 20. method of pouring from, 66. INDEX. 477 Bromides, properties of, 202, Bromine, preparation and properties of, 201. Bunsen's burner, description of, 4. precautions in using, 5, 6. simple forms of, 427. Bunsen's holder, 3. Cadmium salts, properties of, 2 76. Calcium, properties of compounds of, 346. hydrate, solution of, prepared, 58. Carbon, properties of, 151. dioxide, preparation and pro- perties of, 154. dioxide, decomposition of by plants, 161. protoxide, Fownes' process for preparing, 166. protoxide, preparation and pro- perties of, 163. Carbonates, properties of, 162. Caustic soda, preparation of, 358. Centigrade thermometer scale, 473- Charcoal supports in blowpipe work, 90. Chemical action, exercise on, 68. Chemical affinity, action of, in ana- lysis, 71. combination, characteristics of, 72. combination, laws of, 459. equations, explanation of, 468. symbols, account of, 463, 465. Chemistry, definition of, 76. Chlorates, formation and properties of, 197. Chlorides, properties of, 193. Chlorine, preparation and properties of, 185. Chlorine, solution of, directions for preparing, 442. Chromates, action of light upon, 331. properties of, 326. Chromium salts, properties of, 325. Clark's retort and receiver, 18. Cobalt, properties of compounds of, 3i7- Collection by displacement, 122. Compound radicle, meaning of the term, 75. Compounds, action of, upon each other, 74. Condensation, arrangement for, 64. Condenser, Liebig's, description of, 433- Copper, electro-deposition of, 272. salts, properties of, 270. Cork borers, description of, 7. Corks, method of boring, 37. tubes fitted into, 38. Crystallisation, exercise on, 53. Cyanates, formation of, 181. Cyanides, properties of, 179. Cyanogen, preparation and proper- ties of, 177. Decantation of gases, 80. washing by, 77. Deflagrating cup, 9. Deflagrating jar, 9. mode of constructing, 429. Density, meaning of, 48. Density of alcohol, determined, 49, glass, determined, 50. hydrogen sulphate, deter- mined, 49. liquids, methods of ascertain- ing, 48. solids, methods of ascertaining, 49. Displacement, collection of gases by, 122. Distillation, exercise on, 62. of nitric acid, 132. Distilled water, tests for purity of, 67. Double decomposition, meaning of the term, 74. examples of, 74, 75. Drying tubes, 12. mode of constructing, 431. Dyeing, discharge process of, illus- trated, 197. use of aluminium salts in, 334. Efflorescence, meaning of, 57. Elbow-tubes, method of making, 28. Electricity, action of, in analysis, 70. Electrotypes, method of obtaining, 272. Element, meaning of the term, 68. Elements, combination of, 72, 73. Equations, chemical, explanation of, 468. Ethylene, preparation and proper- ties of, 1 68. 478 INDEX. Fahrenheit thermometer scale, Ferric salts (see Iron persalts). Ferrocyanides, formation of, 180. Ferrous salts (see Iron protosalts). Filters, method of folding, 53. . Swedish, 19. Filtration, method of, 76. Flasks, method of bordering the mouths of, 44. Fletcher's blower, description of, 43 2 - Fluorides, experiments with, 211. Fusible alloy, preparation of, 278. Fusion and granulation of zinc, 27. Gas generating apparatus, 437. Gas holder, simple form of, 437. Gas jars, 9, 10. Gases, changes in volume of, with pressure, 82. changes in volume of, with temperature, 81. decantation of, 80. Gay Lussac's law, 82. Glass, annealing of, 30. jet, method of making, 33. method of etching, 211. method of leading a crack along, 42. precautions necessary in heat- igi 3- soluble, mode of preparing, 243. tubes, bent, 31. tubes, cut, 29. Glass-blower's lamp, 1 7. Gold leaf, transparency of, 301. residues, treatment of, 452. salts, properties of, 300. Graduation of a test tube, 47. Granulation of zinc, 27. Group tests, application of, 371. Hardening and tempering of steel, 314. Hardness of water, 347. Heat, action of, in analysis, 68. Herapath's blowpipe, description of, 15. simple form of, 432. Hydrofluosilicic acid (see Hydro- gen silico fluoride). Hydrogen, diffusion of, through plaster of paris, 115. preparation and properties of, 104. Hydrogen chloride, preparation of, 190. dioxide, properties of, 343. fluoride, formation and pro- perties of, 211. iodide, preparation and pro- perties of, 206. nitrate, preparation of, 132. oxalate, preparation of, 175. phosphate, formation of, 236. phosphide, formation of, 234. silicon* uoride, preparation of, 246. sulphate, density of, deter- mined, 49. sulphate, formation and pro- perties of, 228. sulphide, preparation of, 216. sulphide, solution of, prepared, 220. salts, general properties of, 365. Hypochlorites, formation and pro- perties of, 195. Hypophosphites, formation and properties of, 234. Hyposulphites, properties of, 227. Ignition in blowpipe flame, ex- amples of, 92. Ignition tubes, method of making, 41. Insoluble substances, analysis of, 416. Iodides, properties of, 209. Iodine, preparation and properties of, 203. Iron, passive state of, 313. \ persalts, properties of, 311. preparation of salts of, 307. protosalts, properties of, 309. Lakes, formation of, 334. Laws of Chemical Combination, 459- Lead, action of water upon, 204. precipitation of, by zinc, 268. salts, properties of, 266. Liebig's Condenser, description of, 433- Liquids, method of pouring, from bottles, 66. Lime water, preparation of, 58. Magnesium and its salts, proper- ties of, 350. Magnet, method of making, 315. INDEX. 479 Manganese, preparation of com- pounds of, 320. Marriotte's law, 83. Marsh's test for arsenic, 289. Measure of cubic centimetres, construction of, 47. Mechanical mixture and chemi- cal compound, difference be- tween, 72. Mercury, properties of, 256. protosalts, tests for, 262. persalts, tests for, 263. Metals, table of groups of, 378. Metaphosphates, properties of, 2 39. Metric System, explanation of, 470. rules for reduction in, 472. Molecule, definition of, 465. Mordants, nature of, 334. Nessler's test for ammonium, 364- Nickel, properties of compounds of, 319. Nitrates, properties of, 137. Nitric acid, distillation of, 132. Nitrites, properties of, 140. Nitrogen, preparation and proper- ties of, 115. protoxide, preparation and pro- perties of, 146. dioxide, preparation and pro- perties of, 142. trioxide, preparation of, 140. tetroxide, preparation of, 139. Nitrogen oxides, list of, 460. Non-metallic radicles, table of, 377- Olefiant gas (see Ethylene). Orthophosphates, properties of, 236. Oxalates, properties of, 175. Oxalic acid, preparation of, 175. Oxidation and Reduction, in blow- pipe work, 93, 94. of ammonia and nitrates, 130, 138, of chromium salts, 327. of iron salts, 312. of manganese salts, 321, 323 264. of mercury salts, 258, 263, of nitrogen dioxide* 144, of sulphites, 225. of tin salts, 296, 298. Oxygen, preparation and properties of, 95- Permanganates, preparation and properties of, 322. Phosphorus, properties of, 232. amorphous, properties of, 233. pentoxide, formation of, 235. Phosphates (ortho-), properties of, 236. Photography, experiments in, 254, 331- Pinch-cock, Bunsen's, 19. Pipette, method of using, 18. method of making, 33. Plaster casts, mode of preparing, 348. Plastic sulphur, formation of, 215. Plants, action of, on carbon dioxide, 161, Platinum, action of, in causing com- bination, 113, 304. compounds of, tests for, 305. residues, treatment of, 451. spongy, mode of preparing, 303. supports in blowpipe work, 90. vessels, precautions in using, 8. method of cleaning, 8. Pneumatic trough, description of, 2. exercise on the use of, 79. simple forms of, 424.. Potassium, properties of, 353. Potassium salts, properties of, 355. Precipitates, filtration and washing of, 76. Preliminary examination in ana- lysis, 382. Pyrophosphates, properties of, 238. Radicle, meaning of the term, 75. Radicles,distributionof,into groups, 37. Reagent (see Test). Reagents, directions for preparing solutions of, 439. Reduction, meaning of the term, 87. examples of (see under Oxida- tion). Retort and receiver, Clark's, 18. Salt, meaning of the term, 75. Silicates, preparation of, 242. decomposition of, 244. Silicon dioxide, pure, mode of pre- paring, 247. 480 INDEX. Silver nitrate, preparation of, from silver coin, 249. Silver residues, treatment of, 449. - salts, properties of, 251. reduction of, by light, 254. reduction of, by organic substances, 253. Single substance, definition of a, 367. Soap test for hardness of water, principle of, 348. Sodium, yellow light emitted by, experiments on, 360. Sodium and its salts, properties of, 357- Solubilities, table of, 481. Solution of substances in analy- sis, 382. Solutions of reagents, directions for preparing, 439. Specific gravity, meaning of, 48. Spirit lamp, simple form of, 430. Spongy platinum, preparation of, SOS- Starch, solution of, directions for preparing, 448. use of, as test for iodine, 205. Steel, combustion of, in oxygen, 103. hardening and tempering of, 3i4- magnetisation of, 315. Stirring rod, method of making, 34- Stoppers, method of loosening, 20. Strontium, properties of com- pounds of, 344. Sublimation, example of, 192. Substances required for prac- tical work, 21. Sulphates, properties of, 230. Sulphides, properties of, 219. Sulphites, properties of, 225. Sulphocyanates, formation of, 182. Sulphur, experiments with, 213. Sulphur dioxide, preparation and properties of, 223. Sulphuretted hydrogen (see Hy- drogen sulphide). Sulphuric acid (see Hydrogen sul- phate). Supports for flasks, &c., construc- tion of, 425. Sympathetic ink, preparation of, 318. Synthesis, examples of, 72. Table of atomic weights, 466. groups of non-metallic ra- dicles, 377. groups of metallic radicles, 378. solubilities, 481. Tables of weights and measures, 470. Tartrates, properties of, 173. Test, meaning of the term, 61. Test papers, illustrations of use of, 14. Test tube, graduation of, as a mea- sure, 47. Test tubes, ends of, rounded, 41. mouths of, bordered, 44. precautions required in heating, 60. Thermometric scales, 473. Tin chlorides, preparation of, 296. Tin salts, properties of, 297. Tubes, drying, method of filling, 13. fitted into corks, 38. ignition, method of making, 41. method of sealing, 39. "Wash-bottles for gases, n. "Washing bottle, description of, 1 1. fitted with tubes, 35. "Water, common, method of testing, 65. . distillation of, 62. hardness of, 347. test for organic matter in, 323. Water bath, construction of, 428. Weighing, rules to be observed in, 45- Weighing and measuring, exer- cise on, 45. Weighing by subtraction, method of, 47. Weights, method of constructing, 423- set of, i. verification of, 46. Zinc, amalgamation of, 337. granulation of, 27. properties of compounds of, 336. use of, in galvanic batteries, 338. UNIVERSITY OF CALIFORNIA LIBRARY, BERKELEY THIS BOOK IS DUE ON THE LAST DATE STAMPED BELOW Books not returned on time are subject to a fine of 50c per volume after the third day overdue, increasing to $1.00 per volume after the sixth day. 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