QUALITATIVE CHEMICAL ANALYSIS BY THE SAME AUTHOR PRACTICAL METHODS OF ELECTRO-CHEMISTRY With Frontispiece (Portrait of FARADAY) and 64 Illustrations in the Text Svo. 6s. net LONGMANS, GREEN, AND CO. LONDON, NEW YORK, BOMBAY, AND CALCUTTA Perkins Qualitative Analysis. QUALITATIVE CHEMICAL ANALYSIS ORGANIC AND INORGANIC BY F. MOLLWO PERKIN, PH.D. !\ LATE HEAD OF THE CHEMISTRY DBl'ARTMENT, BOROUGH POLYTECHNIC INSTITUTE LONDON WITH SIXTEEN ILLUSTRATIONS AND SPECTRUM PLATE > ; ; ' . >, THIRD EDITION LONGMANS, GREEN, AND CO. 39 PATERNOSTER ROW, LONDON NEW YORK, BOMBAY, AND CALCUTTA 1910 All rights reserved FIRST EDITION .... 1901 Second Impression . . . 1904 Third Impression, SECOND EDITION ...... 1905 THIRD EDITION .... 1910 ? * : : ** ".' * PREFACE TO FIRST EDITION PROBABLY all teachers of chemistry are familiar with two classes of student : (i) book students, i.e. students who have obtained their knowledge of chemistry entirely by reading or by hearing lectures ; (2) laboratory students, those who, by use of a merely outline book or chart, and by attention to details of experiment, have obtained the whole of their knowledge in the laboratory. The first class of student, if brought into the laboratory, is unable to carry out a single experiment without bungling. The second, although he may be able to carry out experiments with machine- like precision, from a sheet of instructions, is quite at sea when questioned upon the underlying theoretical principles. One of the great difficulties in teaching chemistry is to get students to apply their theoretical knowledge to aid them in their practical work, and, on the other hand, to bring their practical knowledge to bear in the elucidation of theoretical problems. The theoretical knowledge is generally kept rigidly apart from the facts practically gained, so that the student loses all the mutual help which the two branches of study afford each other. Recognising this difficulty, I have endeavoured to write a book in which theory and practice are more or less dovetailed. Perhaps the theoretical considerations are not quite so fully dealt with as some would desire; but it must be remembered that the book is a practical one, and is only intended to contain 216639 vi Preface to First Edition. sufficient theory to make practical chemical analysis clear, and, I trust, interesting. If, as I hope, the appetite of the student is whetted, and he " asks for more," then he can obtain it from theoretical text-books. In writing the theoretical portions of this book, I have been much aided by the works of Professor Ostwald. In the practical part I have consulted the latest literature, and among other works Fresenius's " Qualitative Analysis " and Allan's " Commercial Organic Analysis." No reaction has been included which has not been worked out by myself and assistants in the laboratory. In conclusion, my best thanks are due to Dr. W. Semple, M.A., B.Sc., and Dr. J. E. Mackenzie, B.Sc., for . their kind help in revising the sheets be'fore they went to press, and for many valuable suggestions. My thanks are also due to Messrs. E. E. Cornick and A. R. Warnes for much help in testing many of the reactions. I also desire to thank Messrs. Longmans for kindly allowing me a number of proof copies for the use of my students during the time the book was passing through the press. F. M. P. November, 1900. PREFACE TO SECOND EDITION THE book has been most carefully revised; considerable more theory has been added, but, with the exception of the short para- graph upon the important subject of " Mass Action," it has not been placed in a special chapter devoted to theoretical considera- tions, but has been interspersed throughout the practical parts of the book. In the first edition this arrangement was found satis- factory, and it has therefore been adhered to in the present edition. The portions dealing with the analysis of the acids and " The Treatment of the Substance to be analysed " have been completely recast; also amongst other additions, the reactions of pel-sulphuric acid and hydrogen peroxide have been added to the inorganic part. In the organic portion of the book consider- able additions have been made which it is hoped may be found useful especially by University and Pharmaceutical students, and also by students in general. No additions have been made which have not been carefully worked through in the laboratory, and I am much indebted to Mr. F. B. Hart, B.Sc., and to Mr. A. J. Hale for help in this part of the work. Mr. Hart has also assisted me in revising the proofs. F. M. P. August, 1905. PREFACE TO THIRD EDITION OWING to the request by several of the reviewers when the second edition was published, a short section dealing with some of the rarer elements has been added. One would like to have made this section larger, but the scope of the book does not permit of it. I trust, however, that what has been included will be found useful. A new chapter on Ethereal Salts has been added to the Organic Section, mainly because of enlargement in the Board of Education Syllabus, but also because it makes the book more complete. A few other additions and alterations have also been made. F. M. P. LONDON, May, 1910. CONTENTS PART I. INORGANIC ANALYSIS. CHAPTER PACR I. DRY REACTIONS 3 II. REACTIONS IN SOLUTION 12 III. DIVISION OF THE METALS INTO GROUPS 25 IV. THE COPPER GROUP 35 V. THE ARSENIC GROUP 44 VI. THE IRON GROUP 67 VII. THE BARIUM GROUP 89 VIII. THE SODIUM GROUP 94 IX. THE ACIDS 104 X. ANALYTICAL TABLES FOR THE DETECTION AND SEPARATION OF THE METALLIC RADICALS (CATIONS) AND ACID RADICALS (ANIONS) 153 RARER ELEMENTS 187 PART II. ORGANIC ANALYSIS. XI. QUALITATIVE "ELEMENTARY" ANALYSIS OF CARBON COM- POUNDS ' ... 201 XII. REACTIONS AND SEPARATION OF ORGANIC ACIDS AND PHENOLS * 210 XIII. ETHEREAL SALTS 239 xii Contents. CHAPTER PAGE XIV. HYDROCARBONS, HIGHER FATTY ACIDS, AND GLYCERIDES 253 XV. ALDEHYDES, ALCOHOLS, ACETONE, GLYCEROL .... 261 XVI. THE CARBOHYDRATES AND SACCHARIN 272 XVII. BASES, GLUCOSIDES, ETC 280 XVIII. ALKALOIDS 293 SUMMARY 313 APPENDIX. SOLUBILITIES, REAGENTS, STEAM DISTILLA- TION, WATER BATH 317 INDEX 333 PART I INORGANIC ANALYSIS CHAPTER I. DRY REACTIONS. IN qualitative analysis, two classes of tests are employed : (i.) dry reactions, tests applied to the solid material ; (ii.) wet reactions, or tests applied to the substance in solution. The dry reaction tests are usually applied first, and from data thus obtained very much valuable information is often given, which greatly facilitates the application of the tests in solution. In this chapter the methods employed in testing by means of dry reactions will be explained, and will be taken in the following order : 1. Action of heat alone on the substance. 2. Blow-pipe reactions. 3. Match tests. 4. Film tests. 5. Flame colorations and the spectroscope. 6. Borax beads. 7. Other dry reactions. i. Action of Heat on the Dry Substance. Much may often be learned by simply heating the dry substance in a glass tube ; e.g. the substance may sublime, or may be decomposed and give off coloured vapours, or the colour of the substance may undergo a change. The two following examples will serve as illustrations. (a) Sublimation. Place a small quantity of ammonium chloride in the bottom of a glass tube three to four inches long, about a quarter of an inch wide, and closed at one end. Heat B 2 4 Qualitative Chemical Analysis. the end of the tube in the flame of the Bunsen burner ; white vapours will be seen to be given off, which will condense, " sublime," on the cool parts of the tube. (b) Decomposition and Sublimation. In another tube heat a little red mercuric oxide. The red colour becomes darker and darker, and finally almost black, while on the cool portions of the tube a grey deposit of metallic mercury collects, forming into small globules when rubbed with a glass rod. If a glowing splint of wood is held in the mouth of the tube, it bursts into flame, showing that oxygen gas is being evolved owing to the decomposition of the mercuric oxide. 2 HgO = 2Hg + 2 On cooling again, the undecomposed mercuric oxide gradually becomes lighter and lighter in colour until, when quite cold, it assumes its original appearance. This change in colour, due to heating, is a physical change. 2. Blowpipe Reactions. The use of the blowpipe is very important where gas is not available or the Bunsen burner is not at hand. The flame of an oil or spirit lamp, or of a Bunsen burner with blow- pipe tube, is used as follows : Hold the nozzle of the blowpipe just outside the flame (Fig. i), and blow gently and steadily from the cheeks. The jet is partially luminous, owing to FlG j the presence of unburnt carbon, and is called the reducing flame. To obtain the oxidising flame, hold the nozzle of the blowpipe in the centre of the flame (Fig. 2). The jet is now non-luminous, like the Bunsen flame, and contains no unburnt carbon. The use of the reducing and oxidising flames is illustrated by the two following examples : (a) Place a little oxide of lead (litharge) in a small hollow on a piece of charcoal, and direct the reducing flame on to it. The oxide becomes reduced, and small bright beads of metallic Dry Reactions. 5 lead are obtained. The reducing gas and unburnt carbon in the flame, together with the red-hot charcoal, combine with the oxygen of the lead oxide, with formation of carbon mon- oxide. PbO + C = Pb + CO (b) Place a small piece of lead in a small hole scooped out in the charcoal, and direct the extreme tip of the oxi- dising flame upon it ; the lead ' FIG becomes oxidised, and the oxide is deposited on the cooler portions of the charcoal, forming a yellow incrustation or film. 2Pb + O a = 2PbO Since the introduction of the Bunsen burner, it is practically unnecessary to employ the blowpipe in ordinary qualitative analysis. Much practice is required before the results obtained can be depended upon. Indeed, many students are never able to successfully use the blowpipe. Since the following reactions with a little practice are easier of interpretation, and moreover do not take so long in the carrying out, the student is recommended to employ these reactions instead of those of the blowpipe. As, how- ever, the blowpipe is still employed by many chemists, the blow- pipe reactions are included among the other dry reactions. The Bunsen Burner. Before describing the manner in which the dry reactions due to Bunsen are carried out, it will be necessary to explain the structure of the flame of a Bunsen burner. The flame of the burner (Fig. 3) may be divided into three chief divisions : (i) the dark central zone, a, a' t d\ which is a mixture of unburnt gas and atmospheric air; (2) the flame mantle, , or zone of complete combustion ; (3) the luminous point, B, which is produced by partially closing the air-holes at Qualitative Chemical Analysis. the bottom of the burner. It should not be visible when the holes are entirely open. The bottom of the flame, A, has comparatively a very low temperature. The zone of fusion, or the hottest portion of the flame, is at E, where the flame mantle is thickest. D is called the lower oxi- dising flame; here there is an excess of oxygen. G is the higher oxidising flame : it contains an excess of oxygen, but is not so hot as D. The reducing flame is at K, in the middle of the luminous tip; it contains finely divided incandescent carbon and partially burnt gas, but no free oxygen. H, H, is a metal chimney standing on the star support S. It is employed to keep the flame from flickering with draughts ; it should always be used when carrying out .A the film tests. 3. Match Tests. Cut the head off a stout wooden match, or obtain a splint of wood about the same size as a match. 1 Take a lump of crystallised sodium car- FIG. 3. bonate (washing soda), hold it in the flame so that it partially fuses, and rub the fused salt over about three-quarters of the length of the match. Now heat the match in the flame, at the same time rotating it. As soon as the match is covered with dry salt, repeat the first operation, in order that the wood may be thoroughly covered with the sodium carbonate, and again heat, with continual rotation, until the end of the match is thoroughly charred and the sodium carbonate fuses on it. 2 Now mix a small portion 1 Very thin matches are liable to break in the carrying out of the experi- ment. Matches about 6 cm. long and 3 mm. thick, or pieces of wood about the same thickness, should be employed. 2 These tests are more readily carried out and the charred wood is less likely to break off, if the splints are first impregnated with a mixture of sodium Dry Reactions. 7 of copper sulphate with a little melted sodium carbonate on a watch glass, and with the hot end of the match pick up a portion about the size of a pin's head. Hold it in the luminous tip of the flame. The copper sulphate becomes reduced to metallic copper. Hold it for about half a minute in the cooler non- luminous portion of the flame. Gently crush the carbonised end with a pestle in a mortar containing a little water, and wash away the light portions of the charcoal, when metallic copper will be left behind. Repeat this experiment, using silver nitrate, lead oxide, etc., etc. 4. Film Tests. Take a porcelain basin, glazed outside, and about half full of cold water. Hold this immediately over the luminous point B, of the Bunsen flame. The point should be made just visible by partially closing the air-holes. If any carbon is deposited upon the porcelain, air must be admitted until a deposit is no longer produced. Having arranged the flame correctly, take a thread of asbestos, moisten the end with water, pick up with the moistened end a trace of arsenious oxide, and heat it in the luminous tip, at the same time holding the basin immediately over the luminous tip of the flame. A black metallic film will be deposited on the porcelain. The film will be found to be difficultly soluble in 20 per cent. nitric acid, but will dissolve at once if touched with a drop of a solution of bleaching powder. Now take a fresh portion of the arsenious oxide upon the asbestos thread, and again hold it in the same portion of the flame, but this time hold the dish just outside the upper oxidising flame G. A white deposit of arsenious oxide will be produced on the porcelain. By looking sideways at the bottom of the dish, the portion where the oxide film is deposited will be seen to have a dull appearance. The first film is the metallic film, the second carbonate and alum. This may be done by boiling them for about half an hour in a nearly saturated solution of 2 parts sodium carbonate and I part alum. After drying they are ready for use. It is a good thing to keep a stock of splints prepared in this manner. These splints must be treated with the fused sodium carbonate as above described. 8 Qualitative Chemical Analysis. the oxide film. On p. 157 a table giving various tests for the metallic and oxide films will be found. The iodide film test (p. 157) is most readily carried out as follows : Dissolve some iodine in alcohol, and dip into the solution a small bundle of asbestos wired on to a glass rod and reserved for this purpose. Ignite the moistened asbestos, and, when the flame begins to go out, hold it under the oxide film (the basin should contain water, because some of the iodide films are readily volatile). Or, better still, hold the basin over a 2-oz. wide-mouthed bottle containing fuming hydriodic acid. This may be prepared by placing a few small pieces of yellow phosphorus in the bottle, just covering with water, and then cautiously adding small quantities of powdered iodine, until the whole of the phosphorus has entered into reaction. The iodine should only be added a little at a time or the reaction may be too vigorous. The bottle must be kept well stoppered. The sulphide film (p. 157) can be produced by adding a drop of ammonium sulphide to the oxide film by means of a glass rod or a capillary tube, or by fitting a small flask up like a wash bottle, both tubes being bent at right angles. A little ammonium sulphide is poured into the flask, and on blowing down the long tube which passes below the surface of the liquid, the vapour is directed upon the film held in front of the opposite tube. The first method gives very satisfactory results if only very small quantities of the sulphide are added. The iodide and sulphide film are, in the case of mercury, which gives no oxide film, applied to the metallic film. The student should repeat the above exercise, employing the metals mentioned in the table, p. 157. 5. Flame Tests. Take a fine platinum wire, about three inches long, and fuse one end into a piece of glass rod or tube. Clean the platinum wire by holding it in the flame till it no longer colours it. Moisten the wire with a little concentrated hydrochloric acid contained in a watch glass, dip it into a little powdered potassium chloride, a small portion of which will Dry Reactions. 9 adhere, and when the wire with the potassium chloride is in- troduced into the lower part of the flame mantle, the potassium chloride volatilises and colours it a violet blue. Thoroughly clean the wire, by alternately boiling it in a little concentrated hydrochloric acid, and heating it in the flame until the flame is no more coloured. Again moisten with concentrated hydrochloric acid, as already described, and take up a little strontium chloride. When introduced into the hottest portion of the flame mantle at E, strontium chloride colours the flame a brilliant crimson. As potassium volatilises at a lower temperature than the salts of most other metals which give flame colorations, its presence may often be shown, even when mixed with other substances, by introducing the platinum wire into the cooler portions of the flame mantle near the base. When a little potassium and sodium chlorides are mixed together, and brought into the flame of the Bunsen burner, the golden yellow imparted by the sodium completely masks the violet of the potassium. If, however, the flame so coloured is viewed through a thick piece of blue glass or a hollow glass prism filled with a solution of indigo, the yellow rays are cut off, and only those due to the potassium are visible, the flame appearing of a violet-red colour. 6. The Spectroscope. By means of the spectroscope the flame reactions may be rendered much more delicate, and the metals more readily detected, even when several are present together. If a metallic salt is volatilised in the flame, as just described, and viewed through a spectroscope, certain lines which are distinctive for each metal will be seen. Introduce separately small portions of the salts of sodium, potassium, calcium barium, strontium, and lithium into the Burden flame by means of a piece of platinum wire, examine the coloured flame with a spectroscope, and compare the results thus obtained with the coloured diagram at the beginning of the book. In using the spectroscope some little practice is necessary, and it will be found advisable to clamp the glass end of the io Qualitative Chemical Analysis. platinum wire in a stand, so that the wire remains steady. The spectroscope should also be clamped. A direct vision spectro- scope is the most convenient for laboratory use. It should not, however, be too small, otherwise the field obtained is too short. 7. Borax Bead Tests. Take a clean platinum wire which has been fastened into a piece of glass tube, and make a small loop at the end. Heat the wire in the Bunsen flame, and dip it while hot into powdered borax; some borax will adhere to the wire. Now heat in the hottest part of the Bunsen flame. The borax will swell up, and then become fluid, finally fusing to a clear bead. With the hot clear bead touch a small crystal of a cobalt salt, and again fuse in the hottest 'part of the flame. The bead becomes coloured a brilliant sapphire blue, the colour being the same whether the bead be held in the oxidising or reducing flame. Manganese salts produce an amethyst violet bead in the oxidising, but a colourless one in the reducing flame. Other metallic salts cause characteristic colorations, which are described under the reactions of the particular metal. Microcosmic salt (sodium-ammonium - hydrogen-phosphate), Na(NH 4 )HPO 4 , is also used for forming beads. Owing, however, to its being more readily fusible, it is not so easily held in the platinum loop as is the borax bead. The reactions underlying these tests may be explained in the following manner. The borax when fused is resolved into sodium metaborate and boric anhydride. Na 2 B 4 O 7 = 2 NaBO 2 + B 2 O 3 The metallic oxide then unites with the metaborate and with the boric anhydride, forming an orthoborate and a metaborate, e.g. NaBO 2 -f CuO = CuNaBOa B/) 3 + CuO = Cu(BO a ), When microcosmic salt is fused, sodium metaphosphate, ammonia and water are the products. Na(NH 4 )HPO 4 = NaPO 3 + NH 3 + H 2 O Dry Reactions. II The metallic oxide combines with the sodium metaphosphate with production of an orthophosphate, thus NaPO 3 + CuO = CuNaPO 4 8. Other Dry Reactions. Some substances, when heated on charcoal before the blowpipe, then moistened with a solution of cobalt nitrate, and again heated, give characteristic coloured masses e.g. zinc salts give a green mass, while magnesium salts produce a pink. These reactions may also be carried out as follows : Moisten a piece of filter paper with a solution of zinc sulphate and then with a drop of cobalt nitrate. Dry over the Bunsen flame and ignite. The ashes of the paper will be coloured green, especially at the edges. The Draught Tube. Take a glass tube about four inches long and a quarter of an inch wide, place in the middle of it a small quantity of mercury sulphide, and heat the portion of the tube where the mercury sulphide is with the Bunsen flame. The tube should be slightly inclined. Mercury will condense on the cool upper portion of the tube, and a smell of sulphur dioxide will be perceptible. Sulphides, when thus heated or " roasted " in a stream of air, are decomposed into the metal or its oxide and sulphur dioxide, e.g. HgS + 2 = Hg + S0 2 2PbS -f 3<3 2 = 2PbO + 2SO 2 The student is urged to make a very careful study of the dry reactions, the importance of which, as an aid to analysis, cannot well be overestimated. A low power microscope or a magnifying lense is fre- quently of great help in the laboratory. It is often possible to distinguish the different ingredients in a mixture by their use, and this is of very material help in the subsequent analysis. CHAPTER II. REACTIONS IN SOLUTION. THE application of dry reactions is necessarily limited. The difficulty of recognising substances in a mixture by means of dry-tests alone, which usually take place at high temperatures, renders it necessary to apply so-called " wet-reactions," or reactions in solution, by means of which not only may the elements present be detected, but also, in many cases, the state of combination in which they are present may be determined. But even with reac- tions in solution it is often a matter of great difficulty, sometimes of impossibility, to decide in what form or combination the ele- ments occur in the original mixture. Thus, when a solution of common^salt is added to a solution of potassium nitrate, no sign of chemical reaction is observable. Yet this solution is similar in every respect to one obtained by mixing together solutions of sodium nitrate and potassium chloride. Indeed, if equivalent pro- portions of the two pairs of salts in question be dissolved in equal volumes of water, the resulting solutions are absolutely identical in their reactions. Many such instances might be given. It is therefore evident that, even by means of reactions in solution, we cannot say what the components of a mixture originally were whether, for example, the above-mentioned mixture contained, in the first place, sodium chloride and potassium nitrate, or sodium nitrate and potassium chloride. It must, however, be noted that a physical examination of the original solid, and an intelligent combination of dry-way tests with tests in solution, often supply this information. As the chief reactions and tests in analytical chemistry are pro- duced in solution, a short account of the theoretical considerations Reactions in Solution. 13 involved will make it easier for the student to follow out and understand many of the reactions which may at first sight appear very complicated. Theory of Solution. In solution, salts, acids, and bases do not behave as complete molecules, but are resolved into simple factors. In analysis it is only necessary to recognise these factors instead of the many compounds which the combinations of these simple factors may give rise to. Thus the reactions of any soluble salt of a particular metal with a particular reagent are the same, no matter what salt of the metal is employed ; e.g. the chloride nitrate, bromide, or any other soluble salt of barium, all give a white precipitate with sulphuric acid, or a yellow one with potassium chromate. Likewise all the soluble salts derived from a given acid react similarly with the same reagent, and indepen- dently of the metal contained in the salt. Thus the sulphates of potassium, magnesium, zinc, etc., all give the same white precipitate on addition of barium chloride. The observation of the facts already alluded to, and of the formation of salts by the interaction of bases and acids, also of the decomposition of compounds by the electric current (electro- lysis) led Berzelius to formulate his theory of the constitution of salts. According to this theory, a salt is composed of a positive or basic portion, and a negative or acid portion, both of which retain to a modified extent their individual existence in the mole- cule ; the basic portion being a basic oxide, the acid portion an acid anhydride. The nomenclature associated with this view still persists, more especially in treatises on chemical analysis and in analytical reports. Thus, potassium sulphate is still called sulphate of potash, and sodium nitrate, nitrate of soda. The Berzelius formula for these salts, according to the present atomic weights, would be written for sulphate of potash K 2 O . SO 3 , and for nitrate of soda Na 2 O . NaC^. 1 1 The author has, in the course of this book, thought it advisable in general to employ the terms in common use, such as "acid" and "base," instead of the more correct "anion" and " cation," Reactions in solution are also repre- sented by ordinary chemical equations. 14 Qualitative Chemical Analysis. The theory of the constitution of salts now generally accepted has been arrived at from a closer study of electrolytic reactions. This theory also assumes salts to consist of two parts : the one a metal or metallic radical, the other an acid radical. These parts exist independently of each other in dilute solutions, the metallic radical being electrified positively, while the acid radical has a corresponding negative charge. The difference between the new and the old views is best shown by considering how they represent the electrolysis of a salt solution. According to the old theory the decomposi- tion of a salt was effected by the expenditure of electric energy. The modern theory says the salt is already dissociated by the water. The electric current merely neutralises the charges on the electrified radicals, and thus sets them free to form new whole molecules. The radicals which are positively charged move towards a negatively charged body, while the negatively charged radicals migrate towards a positively charged conductor. The nomenclature suggested by Faraday for the old theory expresses the modern interpretation so fitly that it is retained. Faraday called the radicals ions (travellers), and, seeing that the positively charged ions move with the positive current, they are called cations, while the negatively charged ions, having to travel against the positive stream, are called anions. The cations give up their positive charge to the negatively charged cathode, and the anions give up their negative charge to the positively charged anode. Thus, e.g., the molecule of cupric chloride, CuCl 2 , is supposed in solution to be more or less dissociated or ionised 1 (according to the concentration) into a positively charged cation, Cu, coloured blue, and into two odour- less and colourless anions, Cl, the two together having a charge of negative electricity equivalent to the positive charge on the one Cu cation. When electrodes are placed in a solution con- taining these ions, the blue Cu cations are attracted to the cathode, 1 " Electrolytic dissociation " is rather an unfortunate name, as it seems to suggest that the dissociation is due to electrolysis. "lonisation" seems preferable. Reactions in Solution. 15 and, on having their positive charges neutralised, appear as red copper molecules. Similarly the Ci anions are attracted and discharged by the anode. These radicals unite to form chlorine molecules recognisable by their colour and odour. 1 The electro- lysis of other salts may be interpreted in a similar manner, though they are often complicated by so-called secondary reactions. The current of electricity which passes through a solution is, in fact, conveyed by the ions. Substances which in solution are ionised, and therefore capable of carrying electric currents, are called electrolytes. The more a substance is ionised the greater the conductivity of its solution. Electrolytes are more completely ionised in dilute solutions than in concentrated solutions. Upon the degree of ionisation of an acid (or base) depends the electric conductivity and its chemical activity. In strong acids such as hydrochloric acid and sulphuric acid, the degree of ionisation is great, whereas such weak acids as hydro- cyanic and silicic acid are hardly dissociated to a measurable extent, consequently they are very poor conductors of the electric current. Again, sodium and potassium hydroxides are powerful bases, and exist in solution largely as ions, while ammo- nium hydroxide is only feebly dissociated. In acids the charac- teristic ion is the hydrogen cation H, in bases it is the hydroxyl anion OH. Hydrolysis. Even water itself is very feebly dissociated into the cation H, and the anion OH. 2 But although the disso- ciation is very slight, yet the fact that water is dissociated plays a very important part in the hydrolytic dissociation of the salts of weak acids and bases, 3 i.e. salts of acids and bases which when produced tend to revert to the non-ionised 1 Atoms and molecules must not be confused with ions, which are part- molecules or radicals having electric charges. 2 Some authorities consider that if it were possible to obtain water abso- lutely pure, it would not contain the ions H' and OH', and would be an absolute nonconductor of electricity. 3 Hydrolytic dissociation or hydrolysis is not ionisation, but is a secondary change due to ionisation. 1 6 Qualitative Chemical Analysis. condition. This may either be due to the base being weak or to the acid being weak. In the first case, the salts will have an acid reaction. In the second case, they will show an alkaline reaction, e.g. acid reaction Fe . 3d + sH . 3 OH = Fe(OH) 3 + sH . sCl not ionised ionised alkaline reaction + - + - "V -^ K . CN + H . OH = HCN + K . OH not ionised ionised From the foregoing statement, it is evident that " salts do not exist, as such, in aqueous solution, but are dissociated more or less completely into their constituents, or ions ; " 1 and it therefore follows that in analysis most reactions in solution are reactions of the ions. And that in so-called double decomposition it is the ions which react, and not the molecules. Hydrate Theory of Solution. The ionic theory of solution is an exceedingly useful working hypothesis, and it certainly clears up and elucidates many reactions which, without its help, are difficult to explain. There are, however, those who do not accept the theory, and prefer to consider that when a salt is added to water, a series of hydrates is produced, the com- plexity and amount of hydration of which increase with dilution. There is probably truth in both theories, but whereas in strong solutions we may have hydrated molecules thus Na 2 SO 4 , #H 2 O, there are also ions present which may likewise be hydrated. But as the dilution increases the number of hydrated molecules becomes fewer, and finally the solution contains only hydrated ions. The assumption of the ions being hydrated, does not interfere with or modify the above statement "that in analysis most reactions in solution are reactions of the ions . . ." 1 Arrhenius. Reactions in Solution. 17 Reactions in solution will now be considered under the follow- ing heads Formation of Precipitates, Evolution of Gases, Colour-changes. Precipitation. If two solutions contain the one an anion, the other a cation, which by their union may give rise to an insoluble salt, then this insoluble substance will be precipitated (thrown down) by the union of these two ions when the solutions are mixed. After carefully studying the solubility of various salts, and the mutual reactions of ions under the heading " Reactions of the Metals " and " Reactions of the Acids," the student will be able to judge whether a given ion or group of ions is present in a solution by adding to that solution another containing an ion which is capable of forming an insoluble compound with the ion or ions in question. Thus silver chloride is practically insoluble in neutral and acid solutions, but readily soluble in ammonium hydroxide. More- over, it is the only white salt that acts in this way. It is composed of the cation Ag, 1 and the anion Cl'. If, then, the addition of a solution containing the anion Cl' to a certain solution produces a white precipitate readily soluble in ammonium hydroxide, and reprecipitated by nitric acid, the ion Ag is present in that solution. Again, if a solution containing the cation Ag, e.g. silver nitrate, be added to an unknown solution with production of the same white precipitate, the presence of the anion Cl' is demonstrated. A solution of silver nitrate is a reagent for the detection of the anion Cl' ; and a solution containing the anion Cl', e.g. hydrochloric acid, is a reagent for the detection of the cation Ag. But silver nitrate is not a reagent for the element chlorine ; thus silver nitrate gives no precipitate with a solution of potassium chlorate, because, in solution, potassium chlorate is dissociated into the cation K and the anion ClOg. Similarly, on adding sodium hydroxide to a solution of ferric chloride a reddish-brown precipitate of ferric 1 The valency of the cation is represented by a (') : thus, in ferrous salts the cation is Fe , in ferric salts Fe 1 ". The valency of the anion is represented thus ('), e.g. the anion of the ferrocyanides is Fe(CN)o", that of ferricyanides Fe(CN)'. C 1 8 Qtialitative Chemical Analysis. hydroxide is produced. But on adding a solution of sodium hydroxide to one of potassium ferrocyanide a precipitate is not formed. The ferric chloride exists in solution as the cation Fe* and the anions 3d', but the molecule of potassium ferrocyanide is dissociated into the cations 4-K, and the complex anion Fe(CN)" 6 ". Sodium hydroxide is therefore a reagent for the trivalent ion Fe'", but not for the element Iron. It has already been stated that reactions are produced by interaction of the ions. From this it follows, therefore, that in writing equations it is only necessary to specify the ions. Thus, as has already been pointed out (p. 13), all the soluble salts of a given metal behave as if the metallic ion alone were present. For example : copper chloride, nitrate, or sulphate might equally well be employed for demonstrating the reactions of copper with various reagents (see p. 38), therefore the equations can be expressed in terms of the cation Cu" and of the anion of the reacting substance. E.g. the reactions 2, 3, and 4, on p. 40, might be more generally expressed as follows : (1) Cu".+ 20H' = Cu(OH) a (2) Cu" + S" = CuS (3) 2Cu + Fe (CN) 6 "" = Cu 2 Fe(CN) 6 Written as above, the equations make it clear that the ions react together to form un-ionised products, and, as these un-ionised substances are insoluble in water, a precipitate is produced. Evolution of Gases. The evolution of a* gas often results when two solutions are mixed and an exchange of ions takes place. Thus, when sulphuric acid is added to a solution of common salt, the ions H and Cl' exist together in the same solution. Their union will produce hydrochloric acid. But in dilute solution, such union does not take place. When, however, the solution is concentrated by evaporation, the hydrochloric acid is given off 1 owing to the combination of the ions H and Cl'. 1 It must not be supposed that because sulphuric acid will liberate gaseous hydrochloric acid from its salts, that it is a stronger acid than hydrochloric acid. In fact, the contrary is the case, the hydrochloric acid being expelled because it is more volatile than the sulphuric acid. Reactions in Solution. 19 In cases of feebly dissociated acids such as hydrogen sulphide, the evolution of gas is much more marked, taking place even in extremely dilute solutions, also in the case of an acid such as carbonic acid, which is readily decomposed into carbon dioxide and water. The evolution of ammonia from ammonium salts on addition of sodium hydroxide is a case similar to the latter. The feebly dissociated ammonium hydroxide (p. 15) being decomposed into ammonia and water. Colour-changes. The colours of precipitates are often characteristic, and are thus of great importance in the recognition of the ions which form the precipitates. The colour of solutions is also of great use, some methods of testing in qualitative and quantitative analysis being entirely based on change of colour of solutions. Changes in colour may either be due to ionisation, or to reversion to a non-ionised condition. The importance of litmus as an indicator to show whether a liquid is alkaline, acid, or neutral probably depends upon the fact that red litmus is a very feebly ionised acid, while blue is the colour of the litmus acid anion in the dissociated salt. When an acid neutralises an alkali, the H* cations of the acid unite with the OH' anions of the base to form undissociated water. The ions which remain in solution are the anions of the acid and the cations of the base, e.g. : H* . Cl f + Na . OH' = HOH + Na . Cl' not ionised ionised. It follows, then, that as long as any OH* anions remain unannexed, the cation H' of the litmus acid can unite with them to form water, and thus the blue litmus anion exists in the dissociated state. But the moment the least excess of free H" cations appears, they unite with the blue litmus anion to form red un- dissociated litmus acid. The red coloration produced by the addition of potassium thiocyanate to a solution of a ferric salt (p. 73) is attributed to the formation of non-ionised ferric thiocyanate, because the CNS' ion is colourless, while the ferric ion Fe*" is pale yellow. 1 1 The brown colour of the solution of ferric chloride in pure water is due to hydrolytic production of non-ionised ferric hydroxide. See p. 16. 2O Qualitative Chemical Analysis. Many colour changes are due to the conversion of one ion into another. Thus the monovalent permanganate anion is a deep purple, while that of the divalent Mn" cation is very light pink. Hence, when the permanganate anion MnOi is reduced to the divalent Mn" cation by the action of reducing agents, a striking loss of colour follows. Again the green chromium salts are converted by oxidising agents to the yellow chromates, i.e. the green trivalent Cr'" cation becomes changed to the yellow CrO^' anion. Many such changes will be noticed in working through the reactions mentioned in this book. For fuller information on the subject, the student should study Ostwald's " Foundations of Chemical Analysis," Walker's " Intro- duction to Physical Chemistry," or " Solutions " by Ostwald. Mass Action. Many chemical reactions are reversible; that is, under certain conditions they will go in one direction and under other conditions in the opposite direction. For example, when calcium carbonate is heated, carbon dioxide and calcium oxide are produced, but if the heating is carried out in such a way that the carbon dioxide gas is not removed, a portion of it unites with an equivalent proportion of calcium oxide to re-form calcium carbonate. Finally a point is reached at which the decomposition and reformation of calcium carbonate take place at equal rates, and a condition of equilibrium is said to be produced. Such a condition is usually expressed as follows : C0 If the carbon dioxide be removed the reaction goes from left to right only, but if the pressure of the carbon dioxide be increased, then the reaction proceeds more rapidly from right to left, and the amount of calcium carbonate remaining undecomposed is increased. The law of mass action states that the velocity of the reaction at any instant is proportional to the concentration of the reacting substances. Barium sulphate is insoluble in most substances, yet it can be Reactions in Solution. 21 partially decomposed by boiling with sodium carbonate solution, soluble sodium sulphate and insoluble barium carbonate being formed. The reaction is reversible, and can be represented by the following equation : BaS0 4 + Na 2 CO 3 ^BaCO 3 + Na, 2 SO 4 Further, let the concentration or number of molecules of barium sulphate per unit volume of the reacting mixture at the beginning of the action be a, and that of the sodium carbonate be /?. If at the end of any instant x molecules each of barium carbonate, and sodium sulphate be formed, x molecules each of barium sulphate and sodium carbonate will have been decom- posed, and the concentrations of the barium sulphate and sodium carbonate will be a x and ft x respectively. The velocity of the reaction between the barium sulphate and sodium carbonate at any instant will be k(a. x)(fi x), where k is a constant, and the velocity of the reaction between the barium carbonate and sodium sulphate will be k^x 1 . When equilibrium is produced these velocities are equal, therefore k(a - x)(0 - x) = k lX * (a - x)(P - x) h or f- = -T- = constant X K Now, if J3 be made very large, compared with a, then a x will be very small, and a will become approximately equal to x. That is, if the concentration of the sodium carbonate be very great, then the whole of the barium sulphate will be converted into barium carbonate. The greatest concentration of ft can be obtained by fusing barium sulphate with excess of sodium carbonate, and then the reaction from left to right is quantitative. A similar process of reasoning shows that to remove the sodium sulphate formed when barium sulphate is fused with sodium carbonate, without any of the barium carbonate being reconverted into the sulphate, the fused mass must first be washed with very small quantities of water, and when most of the excess 22 Qualitative Chemical Analysis. of the sodium carbonate has been removed, a solution of sodium carbonate must be employed, till the washings no longer contain SO 4 " anions (see p. 128). The residue then contains all the barium, as barium carbonate free from sodium sulphate. The solution is a mixture of sodium sulphate and carbonate. Filtration and Washing of Precipitates. For purposes of filtration, the larger and more granular the particles of the precipitate are, the more rapid will the filtration be, and the more readily is the precipitate washed. If the particles are very small, they block up the pores of the paper, and thus render the process of filtration very tedious, and often very imperfect. It is therefore important that the precipitation be conducted in such a manner that the grains of solid matter may be as coarse as possible. When other considerations allow, precipitation is best conducted in hot solution ; the solution in which the precipitate is suspended should then be allowed to stand in a warm place for some little time, and should again be boiled before filtering. 1 By digestion, especially in hot solution, the granular structure of the precipitate becomes more marked, the reason being that the smaller grains dissolve, while the larger grains become coarser, the reduction in size and the consequent solubility of the smaller grains being traceable to the surface tension exerted between liquids and solids. This explanation presupposes that no subsfance is absolutely insoluble, a fact which has been proved by recent refinements in physical chemistry. When the precipitate is coarse grained, filter papers containing fairly large pores can be employed, and so, of course, filtration is much expedited. The filter paper should always be moistened before being used for filtering, otherwise the first portion of the filtrate is liable to be turbid. It is the force of gravity which causes pressure to be exerted on the filter paper, and thus for the solution to pass through. The force can be increased by decreasing the pressure below the 1 Water at 100 will filter about six times as rapidly as water at o. Whenever possible, solutions should therefore be filtered hot. Reactions in Solution. 23 funnel ; this may be done by means of a vacuum pump, but it is not satisfactory for ordinary analytical purposes. The best method is to join a long, narrow glass tube on to the end of the funnel, as shown in Fig. 4. The length of the column of liquid exerts hydrostatic pressure, but in order that the tube may be full of liquid, it must be of narrow bore, otherwise the liquid will simply run down the sides, and no pressure will be produced. On the other hand, the bore of the tube must not be too narrow, or else the surface tension will more than counterbalance the advantages gained by the column of liquid. It is, further, most important that the filter paper should fit quite closely to the funnel, otherwise air will be drawn down between the paper and the walls of the funnel. Washing the Precipitate. Having transferred the precipitate to the filter paper, it requires washing to free it from adhering foreign matter which is present in the solution. Before commencing to wash, the whole of the solution must be allowed to run through. It then is ** G * 4* washed with successive small quantities of water, allowing each portion to drain through before the next quantity is added. Where admissible, hot water should be employed, and it should be directed by means of a wash bottle upon the upper portion of the precipitate, in order to wash it down to the foot of the cone. Much time may often be saved, and the washing be more thoroughly effected, by a combination of decantation and filtration. The precipitate is allowed to settle, and the supernatant liquid poured on to the filter paper. Hot distilled water is added, and the operation repeated several times ; finally the whole of the precipitate is poured on to the filter, where it may be further washed, if necessary. 24 Qualitative Chemical Analysis. Colloidal State. It sometimes happens that the precipitate assumes the colloidal state to a greater or less extent. That is, under certain circumstances it is soluble and under others insoluble. The soluble form is called hydrosol, and the insoluble hydrogel. When in the hydrosol condition it passes through the filter paper; e.g., when sulphuretted hydrogen is added to or passed through a solution of an arsenate, the solution becomes yellow, but no precipitate is formed, and, on filtering this solution, all the arsenic passes through in the solution. Boiling will often cause precipitation of colloidal substances, or addition of salts, such as ammonium acetate, sodium sulphate, etc., will effect the same purpose. Some substances, again, though they may have been precipitated in a granular form, become more or less colloidal when brought into contact with pure water as, for example, when being washed on the filter. When this happens, the filtrate becomes turbid towards the end of the operation, owing to the colloidal substance passing through the pores of the paper. The pores finally become blocked, and render further washing almost an impossibility. When a precipitated substance shows a tendency to assume the colloidal or hydrosol state, it should first be allowed to stand for some time in contact with the precipitant, and may, with advantage, be placed on a water bath. It should then be filtered as far as possible, by decantation, and, when permissible, washed with a strong solution of ammonium acetate, or nitrate, or sodium sulphate. In the arsenic group (p. 64), where both tin and arsenic sulphide have a tendency to become colloidal, these pre- cautions should invariably be adopted. CHAPTER III. DIVISION OF THE METALS INTO GROUPS. IN analytical chemistry the metals are divided into groups, accord- ing to their behaviour with certain reagents. For convenience of arrangement, it is usual to number these groups i., ii., iii., etc. ; but this arrangement has the disadvantage of loss of individuality. The student is apt to talk in a vague manner of group i., group ii., etc., often forgetting the principles which underlie such an arrange- ment. In this book, therefore, the groups are not numbered, but designated by the name of a characteristic element. The order of arrangement is as follows : Silver Group (Group reagent: hydrochloric acid). This group consists of silver, lead, and mercurous mercury, the chlorides of which are insoluble in water (lead chloride is soluble in hot water). The chlorides are precipitated by the addition of the group reagent, hydrochloric acid, to solutions of their salts. Copper Group (Group reagent : hydrochloric acid and sulphuretted hydrogen). This group contains mercuric mercury, lead, copper, bismuth, and cadmium, the sulphides of which are all insoluble in water and in dilute hydrochloric acid. They are, therefore, precipitated in acid solution by the addition of a solu- tion of sulphuretted hydrogen, or when a stream of the gas is passed through solutions of the salts of these metals. They are insoluble in alkali sulphides and caustic alkalis. Arsenic Group. The metals of this group, arsenic, anti- mony, tin, gold, and platinum, are also precipitated as sul- phides by sulphuretted hydrogen in acid solution. Their sulphides 26 Qualitative Chemical Analysis. differ, however, from those of the copper group in being soluble in alkali sulphides and in caustic alkalis. Iron Group (Group reagents : ammonium choride^ then ammo- nium hydroxide, and sulphuretted hydrogen \ammonium sulphide^). The metals iron, nickel, cobalt, zinc, manganese, chro- mium, aluminium, and cerium are either precipitated by sul- phuretted hydrogen in ammoniacal solution, or are, on the addition of ammonium hydroxide thrown out as hydroxides. For example, when their solutions are made alkaline with ammonium hydroxide in presence of ammonium chloride, iron^ aluminium, chro- mium, and cerium are precipitated as hydroxides. This fact is made use of in separating these metals from the other metals of the group. The addition of ammonium chloride before adding ammo- nium hydroxide is to prevent precipitation of manganese, cobalt, nickel, zinc, and magnesium hydroxides, as these hydroxides are not precipitated in presence of ammonium salts. (See p. 1 01.) Barium Group (Group reagent : ammonium carbonate). The metals barium, strontium, and calcium all form carbo- nates which are insoluble in water, and are precipitated from their alkaline solutions by the addition of ammonium carbonate. Sodium Group. This group includes magnesium, potas- sium, sodium, lithium, and ammonium. They are not pre- cipitated by any of the group reagents already mentioned. There is, in fact, no reagent known which will precipitate them all. Furthermore, although ammonium is included in this group, it is never tested for at this stage, but in the original substance. Reactions of the Metals. i. Only small quantities of the solution of the metallic salt should be taken, and the solution should not be a strong one. Most of the reactions, being very delicate, are better shown in dilute solutions. 2. Strength of Reagents. It is recommended that all Division of the Metals into Groups. 27 solutions employed be of known strength, because then, if a given volume of an alkali is added, it can be neutralised by the addition of a known volume of an acid solution. Four times normal (4N.) is a very convenient strength to employ for acids and alkalis. For further particulars, see p. 320. 3. In testing the solubility of a precipitate, filter off from the solution in which it is suspended. The method of obtaining a precipitate, and then adding a solvent without first filtering, is slovenly, and often leads to error. 4. The reactions of the metals should not be rushed through as if they were of no importance. The more carefully the student has worked through the reactions, the better will he be able to understand the theoretical and practical importance of the ana- lytical separations. 5. Careful notes should be taken, and an experiment should never be attempted without first carefully reading through the directions given. THE SILVER GROUP. Silver. Silver is readily soluble in moderately strong nitric acid, with evolution of nitric oxide. 3 Ag + 4 HNO 3 = 3AgN0 3 + NO + 2 H 2 O It also dissolves in strong sulphuric acid on heating, sulphur dioxide being evolved. 2 Ag + 2H 2 SO 4 = Ag 2 SO 4 + SO 2 + 2H 2 O Dry Reactions. Blowpipe Test.- When heated on charcoal with fusion mixture, silver compounds yteld a bright metallic bead of silver. Match Test. Beads of silver obtained. Reactions in Solution. Use a solution of silver nitrate. * i. 1 Sodium or potassium hydroxide give a dark brown, 1 The most important reactions are marked thus (*). Dry reactions, although not marked with an asterisk, should never be neglected. 28 Qualitative Chemical Analysis. amorphous precipitate of silver monoxide. When freshly pre- cipitated, this substance acts as if it were silver hydroxide. AgNO 3 + KOH = AgOH + KNO 3 2 AgOH = Ag 2 + H 2 It is readily soluble in ammonia, with formation of silver ammonium hydroxide, the silver replacing one of the hydrogen atoms of the NH 4 group, and thus forming a complex cation. The dry oxide is completely decomposed into metallic silver and oxygen when heated to about 300. Ag 2 O +2NH 4 OH = 2AgNH 8 OH + H 2 O 2. Ammonium hydroxide produces the same precipitate, which immediately dissolves in excess. Therefore if the ammo- nium hydroxide is incautiously added, no precipitate is produced. * 3. Hydrochloric acid, or soluble chlorides, form a white curdy precipitate of silyer chloride, which darkens on exposure to light. AgNO 3 + HC1 = AgCl + HNO 8 It is readily soluble in ammonium hydroxide and in potassium cyanide. It is also partially soluble in excess of strong hydro- chloric acid or of alkali chlorides, and in concentrated solutions of magnesium chloride. Nitric acid reprecipitates it from these solutions. AgCl + NH 3 = AgNH 3 Cl AgCl 4- 2KCN = KAg(CN) 2 + KG *4. Potassium chromate in neutral solutions produces a brick-red precipitate of silver chromate insoluble in cold acetic acid, but readily soluble in mineral acids ; so that no precipitation takes place in presence of mineral acids. 2AgNO 3 4- K 2 CrO 4 = Ag 2 CrO 4 4- 2KNO 3 *5. Sulphuretted hydrogen gives a black precipitate of silver sulphide, insoluble in dilute acids, soluble in hot nitric acid. 2AgNO 3 + H 2 S = Ag 2 S 4- 2HNO, The Silver Group. 29 6. Metallic zinc, precipitates metallic silver from its solu- tions. Even silver chloride is decomposed if it is suspended in dilute sulphuric acid, and zinc added. The zinc and the silver chloride must be in intimate contact. 2AgCl + Zn = Ag + ZnCl 2 Lead. Lead is insoluble in dilute sulphuric and hydrochloric acids. It dissolves in nitric acid with evolution of nitric oxide. 3Pb + 8HNO 3 = 3Pb(NO 3 ) 2 + 2NO +4H 2 O With concentrated nitric acid a white crystalline residue of lead nitrate is obtained, which dissolves on addition of water. Dry Reactions. Blowpipe Test. When heated on charcoal lead compounds are reduced to the metallic condition, the reduction being more complete if the lead compound is mixed with fusion mixture. The bead so obtained is soft, and can be easily cut with a penknife. When drawn across a sheet of white paper, it leaves a black mark. A yellow incrustation of PbO is, at the same time, formed on the charcoal. Match Test. Malleable beads of metallic lead are obtained, having the properties already described. Film Test. See table, p. 157. Flame Test Lead compounds impart a lambent blue appear- ance to the flame of a Bunsen burner. Reactions in Solution. Use a solution of lead acetate or nitrate. * i . Hydrochloric acid produces in cold solutions a white pre- cipitate of lead chloride, which is soluble in boiling water, and separates out again, on cooling, in brilliant plates. It is insoluble in ammonium hydroxide. Pb(N0 3 ) 2 + 2HC1 = PbCl 2 + 2 HN0 3 *2. Sulphuretted hydrogen gives a black precipitate of 3O Qualitative Chemical Analysis. lead sulphide, soluble in dilute nitric acid. On boiling with strong nitric acid it is converted into lead sulphate. Pb(N0 3 ) a +H 2 S = PbS + 2 HN0 3 3 PbS + 8HN0 3 = -3PbS0 4 + 8NO + 4 H 3 O When sulphuretted hydrogen is passed into lead solutions con- taining much hydrochloric acid the precipitate is first brownish- red, and consists of PbCl 2 . PbS. 3. Sulphuric acid throws down a white precipitate of lead sulphate, soluble in ammonium acetate, ammonium tartrate, and concentrated caustic soda or potash (distinction from barium sulphate). Pb(NO 3 ) 2 + H 2 SO 4 = PbSO 4 + 2 HNO 3 Lead sulphate is slightly soluble in water, but is quite insoluble in water containing an equal bulk of alcohol. The solubility in ammonium acetate is probably due to the formation of a molecule of lead acetate and one of ammonium plumbi-sulphate thus : ,O.SO 2 .ONH 4 2PbSO 4 +2CH 3 COONH 4 =Pb<; +(CH 3 .COO) 2 Pb. X O . S0 2 . ONH 4 Lead sulphate is again precipitated from this solution by addition of sulphuric acid, or on dilution with water. Sodium and potassium hydroxide produce a white pre- cipitate of lead hydroxide. Pb(N0 3 ) 2 + 2KOH = Pb(OH) 2 -f 2 KNO 3 It is soluble in excess of caustic alkali, with formation of a complex anion, lead plumbite, thus Pb(OH) 2 + 2KQH = Pb(OK) 2 + 2 H 2 O 4. Potassium iodide gives a yellow precipitate of lead iodide, soluble in hot water. On cooling, the lead iodide separates out in beautiful golden yellow plates. Pb(N0 3 ) 2 -f 2KI = PbI 2 + 2KN0 3 *5. Potassium chromate produces a yellow precipitate of lead chromate (chrome yellow) soluble in nitric acid. Pb(N0 3 ) 2 + K a Cr0 4 = PbCr0 4 + 2 KNO 3 The Silver Grotip. 31 If the lead chromate is warmed with a little sodium hydroxide, it is converted into basic lead chromate (chrome red) PbCrO 4 , PbO, soluble in excess to a yellow solution. Mercury. This metal differs from all others in being liquid at ordinary temperatures (m.p. 39*4) ; it boils at 357. It is insoluble in hydrochloric acid, but soluble in hot sulphuric and nitric acids. Mercury forms two series of salts : mereurous compounds such as Hg-jCL, Hg 2 (NO 3 )2, which are derived from mercurous oxide, Hg 2 O, and mercuric compounds such as HgCl. 2) Hg(NO 3 ) 2 derived from mercuric oxide, HgO. In preparing mercur02y compounds, it is necessary to have an excess of the metal present, and when kept in solution there should always be a little metallic mercury placed in the bottle. If the acid is in excess, mecur/V compounds are formed. (a.) 6Hg + 8HN0 3 = 3Hg 2 (NO 3 ) 3 + 2NO + 4 H 2 O (b.) 3 Hg + 8HN0 3 = 3 Hg(N0 3 ) 2 + 2NO + 4 H 2 O General Reactions for Mercury Compounds. i. When heated in a dry tube most mercury compounds sublime, condensing unchanged on the cool portions of the tube. Some few compounds, however, such as the oxide, nitrate and chromate, are decomposed ; e.g. Hg(N0 3 ) 2 = 2HgO + N0 2 + O HgO = Hg + O 2. Mixed with fusion mixture or, better, with soda lime, and heated in a dry tube, mercury compounds are reduced to metallic mercury, which is deposited as a grey mirror on the cool part of the tube. 3. Film Test See table, p. 157. 4. A clean piece of copper placed in neutral or slightly acid solutions becomes coated with a film of mercury; on gently rubbing with a piece of filter paper, the surface assumes the appearance of polished silver. When the piece of " silvered " 32 Qualitative Chemical Analysis. copper after being dried, first by filter paper, then by gentle warming in the Bunsen flame is heated in a dry test tube the mercury sublimes, condensing on the upper portions of the tube. Mercurous Compounds. Use a solution of mercurous nitrate. *i. Hydrochloric acid gives a heavy white precipitate of mercurous chloride (calomel), insoluble in hot water and in acids, but soluble in aqua regia; and, in bromine and chlorine water, these substances cause solution by converting it into a soluble mercuric salt. Hg 2 (N0 3 ) 2 + 2HC1 = Hg. 2 Cl 2 + 2 HNO 8 It is turned black by addition of ammonium hydroxide, amino- mercurous chloride being produced. 2 HgCl + 2NH 3 = Hg 2 NH 2 Cl + NH 4 C1 All mercurous compounds are turned black by alkaline hydroxides. Sodium and potassium hydroxide precipitate black mereurous oxide. 2Hg 2 (NO 3 ) 2 + 2NaOH = Hg 2 O + 2NaNO 3 + H 2 O. *2. Sulphuretted hydrogen produces a black precipitate of mercuric sulphide, not of mcrcurous sulphide. The precipitate also contains finely divided metallic mercury. Hg 2 (N0 8 ) 2 + H 2 S = HgS + Hg + 2HN0 3 On warming with nitric acid the mercury alone is dissolved, mercuric sulphide being soluble only in aqua regia. See p. 35. *3. Stannous chloride gives a white precipitate of mercurous chloride, which on warming with excess of stannous chloride turns grey, owing to separation of mercury. On pouring off the supernatant liquid and warming with a little strong hydro- chloric acid, the mercury aggregates into a globule. When an excess of the stannous chloride is added in the first place, an immediate grey precipitate is produced, the reaction passing directly to the second stage. The Silver Group. 33 Hg 2 (N0 3 ) 2 + SnCl 2 = Hg 2 Cl 2 + Sn(NO 3 ) 2 Hg 2 Cl 2 -f SnCl 2 = 2Hg + SnCl 4 4. Potassium iodide precipitates from solutions which are not too strongly acid a bright yellow or yellowish green precipitate of mercurous iodide. Hg 2 (N0 3 ) 2 + 2KI = Hg 2 T 2 + 2KN0 3 With an excess of potassium iodide, in which mercurous iodide is soluble, a slight grey precipitate of mercury is produced on boiling. Analysis of the Metals of the Silver Group. The separation of the metals of the silver group depends upon the behaviour of the chlorides with boiling water and with ammonium hydroxide. Lead chloride is soluble in boiling water, silver and mercurous chlorides are insoluble. Silver chloride is soluble in ammonium hydroxide, lead chloride is insoluble, and mercurous chloride is turned into a black insoluble compound (see p. 32). In order to analyse the solution, add dilute hydrochloric acid until no further precipitate is produced, allow to settle, pour off the excess of solution, and add water. I. Boil the mixture and filter hot, washing the residue on the filter paper several times with hot water. The solution contains lead chloride which crystallises out on cooling. The presence of lead may be further confirmed by adding potassium dichromate to the hot solution, when a yellow precipitate of lead chromate will be produced. The residue on the filter paper is treated with ammonium hydroxide, which, dissolves out the silver chloride, the mercurous chloride being turned black. The presence of silver chloride in the filtrate is demonstrated by acidifying the ammoniacal solution with nitric acid, when it is reprecipitated. The black residue of mercurous-ammonium- chloride may be dissolved in aqua regia, the solution evaporated to small bulk, diluted with excess of water, and a piece of copper D 34 Qualitative Chemical Analysis. foil placed in it, when the copper will be coated with a grey film of mercury, which becomes bright when gently rubbed. II. When there are very small quantities of silver present with considerable amounts of a mercurous salt, it is often difficult, if not impossible to separate the silver by solution in ammonia as described above. Therefore the following method of separation is a better one to employ. Separate the lead chloride by boiling with water in exactly the same way as above described. Now transfer the filtered and washed residue to a test tube cover with water and add small quantities of bromine water, warming between each addition, until upon allowing the precipitate to settle, the solution has a permanent light brown colour. The residue is a mixture of silver chloride and bromide, which after filtering off and washing, may be dissolved in a little strong warm ammonia, from which it can again be precipitated by addition of nitric acid. The solution contains mercunV chloride and bromide. Boil off the excess of bromine, add a few drops of nitric acid and a small piece of clean copper foil, which will become coated with a film of mercury, the metal being thus confirmed. CHAPTER IV. THE COPPER GROUP. Mercuric Compounds. USE a solution of mercuric chloride. *i. Sulphuretted hydrogen, when added in very small quantities to a solution of a mercuric salt, throws down a white precipitate which is a double compound of the mercuric salt taken, and of mercuric sulphide (e.g. HgCl a . 2HgS) : on adding further quantities of sulphuretted hydrogen, the precipitate becomes yellow, then reddish-brown, and finally black, the black precipitate consisting entirely of mercuric sulphide. (a.) 3HgCl a + 2H 2 S = HgCl 2 . 2 HgS + 4 HC1 (b.) HgQ 2 . 2HgS + H 2 S = 3 HgS -f 2HC1 Mercuric sulphide is insoluble in nitric and hydrochloric acids, but jt is readily soluble in aqua regia. On boiling for some time with nitric acid, it is converted into the white salt Hg(NO 3 ) 2 . HgS. It is also readily soluble in a strong solution of sodium sulphide, especially if this contains polysulphides or free alkali. *2. Sodium or potassium hydroxide give a yellow precipitate of mercuric oxide. 2 NaOH + HgCl 2 = HgO + 2NaCl + H 2 O When added in very small quantities a brownish-red basic salt is at first produced. This last reaction is shown best when barium or calcium hydroxide are taken. 3. Ammonium hydroxide produces a white precipitate of a ammo-mercuric chloride. HgCl 2 + 2NH 4 OH = NH 2 HgCl + NH 4 C1 + 2H 2 O 36 Qualitative Chemical Analysis. *4. Potassium iodide gives a beautiful red precipitate of mercuric iodide. HgCl 2 + 2KI = HgI 2 + 2KC1 The precipitate, when first formed, comes down yellow, but rapidly changes to red. It is soluble in excess of either potassium iodide or mercuric chloride to a colourless solution. When dis- solved in potassium iodide it forms a complex salt the cation of which is potassium, the mercury being in the anion; therefore from this solution mercury is not precipitated by most of the ordinary reagents. It is, however, precipitated by sulphuretted hydrogen. Nessler's reagent is an alkaline solution of this salt (p. 328). HgI 2 + 2KI = K 2 HgI 4 *5. Stannous chloride precipitates mercurous chloride, which, if an excess of the reagent has been added, rapidly becomes reduced to grey metallic mercury. On boiling this with a little concentrated hydrochloric acid, the mercury separates as a globule. (a) 2HgCl 2 + SnCl 2 =Hg. 2 Cl 2 + SnCl 4 (b) Hg 2 Cl 2 + SnCl 2 = 2Hg + SnCl 4 6. Hypophosphorous acid precipitates metallic mercury from its salts on warming. This is used as a quantitative method for estimating mercury. 2HgCl 2 + H 3 PO 2 + 2H 2 O = H 3 PO 4 + 2Hg + 4 HC1 Bismuth. Bismuth is readily soluble in nitric acid, nitric oxide being evolved. 2Bi -f 8HNO 3 = 2Bi(NO 3 ) 3 + 2NO It is insoluble in dilute sulphuric acid, and only slightly soluble in hydrochloric acid. Bismuth forms many alloys, most of which can be analysed by dissolving in nitric acid. The trivalent bismuth ion is very weakly basic, therefore its salts are hydrolytically decomposed by water with formation of almost insoluble oxy-salts. The Copper Group. 37 Dry Reactions. i. Flame Test. Bismuth compounds im- part a lambent blue colour to the flame of the Bunsen burner. 2. Dry Tube Test. When heated in a dry test tube, bismuth salts are decomposed into the oxide, which is orange-red while hot, yellow on cooling. 3. Blowpipe Test. When heated on charcoal with fusion mixture, a brittle metallic bead is obtained, an orange-red in- crustation, which becomes light yellow on cooling, being formed on the charcoal at the same time. 4. Match Test. A brittle bead of metallic bismuth is obtained. 5. Film Test. See table, p. 157. Reactions in Solution. Use a solution of bismuth nitrate or chloride. *i. Sulphuretted hydrogen gives a dark brown, almost black, precipitate of bismuth sulphide, really soluble in warm nitric acid. 2 Bi(NO 3 ) 3 + 3H 3 S = Bi 2 S 3 + 6HNO, *2. Alkali hydroxides and ammonium hydroxide pro- duce a white precipitate of bismuth hydroxide, BiO(OH) or Bi(OH) 3 , insoluble in excess of the reagent (distinction from cad- mium, the hydroxide of which is soluble in ammonium hydroxide). *3. Water, added to a moderately acid solution of a bismuth salt, forms a white precipitate of an oxy-salt. If the solution of the bismuth salt is very dilute, only a cloudy appearance is produced. BiCl 3 -f H 2 O = BiOCl + 2HC1 In order to show this reaction to advantage, it is best to pour the bismuth solution into about 500 c.c. of water, to which some ammonium chloride has been added. The oxy-salts of bismuth are insoluble in tartaric acid (dis- tinction from antimony). They are also insoluble in alkali hydroxides (distinction from tin). The formation of oxy-salts is due to hydrolysis, the bismuth ion being very weakly basic. The formation of the oxy-salts may be expressed as a reversible 38 Qualitative Chemical Analysis, reaction, because excess of acid causes the formation of the normal salt. Bi(N0 8 ), 4- H 2 O ^ 2HNO 3 4- BiO(NO 3 ) It should be noted that in the case of Bismuth nitrate, a further quantity of water results in the formation of crystalline bismuth subnitrate of the Pharmacopoeia. /OfT 2BiO(NO 3 ) 4- H 2 O ^ HN0 8 4- O : BiO . Bi owing to formation of metallic mercury. (Cf. Mercury, p. 32, 3.) (a.) SnCl a 4- 2HgCl 2 = Hg 2 Cl 2 + SnCl 4 (b.) SnCl 2 + Hg 2 Cl 2 = 2Hg + SnQ 4 4. On placing a piece of zinc in a solution of either a stann0#j or a stann/V salt, the tin is deposited on the zinc as a soft crystalline mass. 5. Hydrogen aurichloride in acid solutions is reduced by stanni&r salts to metallic gold. 2HAuQ 4 = 3SnQ 4 + 2Au + 2HC1 In neutral solutions the precipitate is purple ; in very dilute solu- tions only a purple coloration is produced "purple of Cassius." The Arsenic Group 59 The reaction is more delicate in presence of a small quantity of stann/V chloride. 6. Potassium permanganate, in acid solution, or other oxidising agents oxidise stann^wj salts to stanmV salts. The permanganate is decolourised and this reaction can be employed for estimating tin. 5SnCl 2 + 2KMnO 4 + i6HCl = 5SnCl 4 + 2MnCl 2 + 2KC1 + 8H 2 O *y. If ferric chloride is added to potassium ferricyanide the solution darkens without formation of a precipitate (p. 118). The addition of a little stannous chloride produces an immediate blue precipitate of ferrous ferricyanide (Turnbull's Blue), the ferric chloride having been reduced to ferr^/j chloride (p. 73, 4). (a.) SnCl a + 2FeCl 3 = SnCl 4 + 2FeCL, (b.) 3FeCl 2 + 2K 3 Fe(CN) 6 = Fe 3 [Fe(CN) 6 ] 2 + 6KC1 Stannic Compound. II. Use a solution of stannic chloride in hydrochloric acid, or in water. *i. Sulphuretted hydrogen gives a yellow to yellowish- brown precipitate of stannic sulphide. SnCl 4 + 2H 2 S = SnSa -f 4 HC1 This is soluble in hot hydrochloric acid, in sodium and potassium hydroxides, in colourless or yellow ammonium sulphide, and in alkali sulphides. 2SnS a + iNaOH/= SnS(ONa) 2 + NaaSnSa + 2H 2 O Sodium Sodium . oxythiostannate. thiostannate. SnS 2 +\NHJ]=l(NH.) g SnS.\ Ammonium thiostannate. 2. Sodium or potassium hydroxide produces a white precipitate of stannic hydroxide SnCl 4 + 4NaOH = Sn(OH) 4 + 4 NaCl which is soluble in excess of the precipitant and in acids. When 60 Qualitative Chemical Analysis. dried over sulphuric acid it is converted into SnO(OH) a ; it is then almost insoluble in dilute acids. On ignition, it is converted into SnO 2 , and is quite insoluble in acids. 3. Ammonium hydroxide behaves in the same manner. If tartaric acid is present only metastannic acid is precipitated. *4. Sodium sulphate or ammonium nitrate, when added to hot neutral solutions of stannates precipitate stann/V or metastannzV acid. SnCl 4 + 4Na.SO 4 + 2H 2 O = SnO 2 + 4NaCl + 4NaHSO 4 Stann/f sulphate is first formed, and then hydrolysed by the action of the water. *5. Stannic salts are reduced to stannous salts when boiled with hydrochloric acid and copper turnings or zinc, and will then give the tests for stannous compounds. Gold. Gold is not oxidised when heated in the air. It is insoluble in acids, but is soluble in aqua regia, being converted into auric chloride. 2 Au + 2HNO 3 + 8HC1 = 2HAuCl 4 + 4H 2 O + 2NO It also dissolves in bromine water and in potassium cyanide in pre- sence of oxidising agents, such as hydrogen peroxide. All gold com- pounds on ignition are decomposed with separation of the metal. Dry Reactions. i. Blowpipe Test. Heated on charcoal with fusion mixture and borax, a yellow malleable bead of metallic gold is obtained. 2. Match Test. The charred end becomes covered with a thin coating of metallic gold. Reactions in Solution. Use a solution of gold chloride (hydrogen aurichloride). *i. Suphuretted hydrogen gives in cold solutions a black precipitate of auric sulphide. -f 8HC1 The Arsenic Group. 61 If the solution is boiling, a reddish-brown precipitate of amcous sulphide mixed with metallic gold is obtained, which on con- tinued boiling is entirely converted into metallic gold. 8HAuCl 4 + 3H 2 S + i2H 2 = 8Au + sH 2 SO 4 + 32 HC1 Both aurous and auric sulphides are insoluble in single acids, but soluble in aqua regia*; and also in ammonium sulphide and in sodium sulphide. From the latter they are reprecipitated on addition of acids, the colour of the reprecipitated sulphide varying from yellow to dark brown. *2. Ammonium hydroxide produces a yellowish-orange precipitate of fulminate of gold (AuNH.NH 2 ), soluble in ex- cess. On drying and heating this substance it explodes violently. *3. Potassium and sodium hydroxide produce a reddish-brown precipitate of auric hydroxide, which is soluble in excess with formation of aurate (a.) HAuQ 4 + 4KOH = Au (OH), + 4 KC1 + H 2 O /O (b.) Au(OH) 3 + KOH = Au^ + 2H 8 O X OK 4. Reducing substances, such as oxalic acid, precipitate metallic gold on warming, as a brownish powder, which on rubbing becomes burnished, and shows the yellow colour of gold. The gold sometimes forms a mirror on the sides of the tube. COOH 2HAuG 4 + 3 | = 2 Au + 8HC1 + 6CO a COOH Ferrous sulphate also reduces solutions of gold in the cold. HAuCl 4 + 3FeS0 4 = Au + Fe 2 (SO 4 ) 3 + FeCl 3 + HC1 *5. Stannous chloride gives (especially in presence of a little stann/V chloride) a brownish to purple-coloured precipitate (see Stannous Reactions, 5, p. 58). *6. An alkaline solution of hydrogen'peroxide produces a precipitate of metallic gold 2HAuCl 4 -f 3H 2 O 3 + SNaOH = 2Au + SNaCl -f 8H 2 O + 30, 62 Qualitative Chemical Analysis. The colour of the solution varies from a brownish-black to greenish-purple ; the reaction is one of extraordinary delicacy. Platinum. Platinum does not oxidise when heated in the air, and it is insoluble in all single acids, but is soluble in aqua regia. On ignition of its salts, metallic platinum is obtained. Dry Reactions. i. Blowpipe Test. When ignited on char- coal with fusion mixture and potassium cyanide, compounds of platinum are reduced to a dark grey powder of the metal, which is insoluble in ordinary acids, but soluble in aqua regia. 2. Match Test. A. dark-grey powder of metallic platinum is produced. Reactions in Solution. Use a solution of platinum chloride f (hydrogen platini- chloride). *i. Sulphuretted hydrogen produces from cold solutions a dark chocolate-coloured precipitate of platinum sulphide. The precipitation only takes place after some time. H 2 PtCl 6 -f 2H 2 S = PtS 2 + 6HC1 It is insoluble in simple acids, but dissolves in aqua regia. It is also soluble in ammonium sulphide. *2. Potassium and ammonium hydroxide, in presence of hydrochloric acid, give a yellow crystalline precipitate of potassium or ammonium platinichloride. The precipita- tion is more complete if an equal bulk of absolute alcohol be added. H 2 PtCl 6 + 2NH 4 C1 = (NH 4 ) 2 PtCl 6 4- 2HC1 t Platinic chloride is really hydrogen platinichloride and should be written II 2 PtCl 6 . In solution it is dissociated into the ions 2H and PtCl 6 ; it is there- fore incorrect to write it as PiCl 4 , the ions of which would be Pt and 4 C1'. The Arsenic Group. 63 It is best to carry out this test on a watch glass, two or three drops of hydrogen platinichloride being added to a drop or two of ammonium or potassium chloride to which has been added one drop of hydrochloric acid, and finally an excess of alcohol The platinichloride then separates out in form of golden spangles. 3. Stannous chloride gives no precipitate, but the colour changes from yellow to brownish-red, the platinic salt being reduced to a platinous salt. H 2 PtCl 6 + SnCl 2 = H 2 PtCl< + SnCl 4 4. Metallic zinc or iron precipitate finely divided platinum, H 2 PtCl 6 + sZn = Pt + 2ZnCl 2 + 2HC1 *5. Formic acid gives from boiling neutral solutions a precipitate of black metallic platinum. H 2 PtCl 6 + 2H.COOH = Pt + 2 C0 2 + 6HC1 Summary. Arsenic, antimony, and tin lie on the border-line between metals and non-metals. They all possess the distinctive feature of metals, viz. the capacity of forming at least one elementary cation. Arsenic and antimony just satisfy that condition and no more, since the trichlorides of arsenic and antimony are dissociated in acid solutions, though hardly to a measurable extent; in aqueous solutions they are more or less completely hydrolysed. The existence of at least the tendency to form elementary cations is shown by the precipitation of the sulphides of these metals by sulphuretted hydrogen. On the other hand, these three elements have a much more marked tendency to enter into the formation of complex anions a characteristic, though not an exclusive characteristic, of the non-metals : indeed, all of their oxides dissolve readily in caustic alkalis (many of them even in ammonia), owing to the formation of soluble salts in which these elements occur in the anion. Similarly their sulphides dissolve in alkali hydroxides and sulphides, forming soluble thio-salts, whose anions contain these elements (in the thio salts sulphur takes the place occupied by oxygen in the anion of 64 Qualitative Chemical Analysis. the oxygen salt). The analytical separation of the arsenic group from the copper group is founded on the formation of these soluble thio-salts, and as the sulphides of gold and platinum likewise dissolve in caustic alkalis and ammonium sulphide, they are for analytical purposes also included in this group. As the 'acids which contain these anions are but feebly ionised, extensive hydrolysis of the salts takes place in aqueous solution ; hence the alkaline reaction of the arsenites and arsenates. The sulphides of these three elements, especially those of arsenic and tin, have a great tendency to form " colloid " solutions ; hence arsenious sulphide is not readily precipitated from a neutral solution, but the presence of excess of hot hydrochloric acid accelerates its precipitation : on the other hand, stannic sulphide is not precipitated in strongly acid solutions ; hence complete precipitation of both sulphides requires intelligent manipulation. Owing to the tendency of stannic sulphide to assume the hydrosol condition, the filtration of this sulphide is often tedious. The addition of sodium sulphate or other electrolyte to the solution pro- motes coagulation of the precipitate, and so facilitates nitration. Sulphide of arsenic is insoluble in hydrochloric acid, while the sulphides of antimony and tin readily dissolve in the concentrated acid when warmed. Stannic and stannous sulphides are not precipitated in presence of oxalic acid, while antimony sulphide is precipitated under these conditions. This property may be employed in the separation of these elements. Separation of Arsenic, Antimony, and Tin. The separation of the metals of the arsenic group is one which requires considerable care. The precipitate obtained by passing sulphuretted hydrogen through" the solution from the silver group, is filtered and washed with hot water. It is then removed from the filter paper, and boiled for several minutes with yellow ammonium sulphide (stannous sulphide is insoluble in colourless ammonium sulphide) ; a little water is then added, and the liquid is again filtered. The filtrate contains the metals of The Arsenic Group. 65 the arsenic group as thio-salts. The residue consists of the metals of the copper group as sulphides. The solution containing the thio-salts is acidified with dilute hydrochloric acid. This precipitates arsenic, antimony, and tin as sulphides, together with a considerable quantity of sulphur from the yellow ammonium sulphide. The precipitate is filtered off and boiled with concentrated hydrochloric acid till no more sulphuretted hydrogen is given off. The sulphides of antimony and tin dissolve, but arsenious sulphide is unacted upon. After the arsenious sulphide has been filtered off, the antimony and tin are separated by taking advantage of the insolubility of antimony sulphide and the solubility of tin sulphide in a solution of oxalic acid. In order to carry out this separation the strong acid solution is made just alkaline with ammonia (an excess should on no account be used), then about 4 grams of solid oxalic acid added, and the solution boiled.t Sulphuretted hydrogen is now rapidly passed through the hot solution until no further precipitate is produced. The precipitate, which consists of antimony sulphide, is filtered off and well washed with hot water. (The first wash water which is added to the solution containing the tin should be of dilute oxalic acid.) The solution is made slightly alkaline with ammonium hydroxide (a slight precipitate will be produced), and then ammonium sulphide added until a perfectly clear solution is obtained. On now adding a slight excess of acetic acid \ the tin is precipitated as sulphide, and some sulphur will be precipi- tated along with it. Instead of adding ammonium sulphide, the solution after the addition of ammonia may be made slightly acid with acetic acid, and sulphuretted hydrogen passed through it. The antimony may be confirmed by the film reaction, the f When the amount of tin exceeds 0-5 gram, correspondingly large quantities of oxalic acid must be employed. \ Highly ionised acids, such as hydrochloric acid, must not be employed, because they would liberate the oxalic acid, and thus prevent the precipitation of the tin as sulphide. F 66 Qualitative Chemical Analysis. sulphide being taken up upon an asbestos thread and moistened with strong hydrochloric acid. The tin may be confirmed by dissolving the sulphide in a little moderately strong hot hydrochloric acid, and adding a small crystal of potassium chlorate. If there is much sulphur left, filter. Now add a piece of zinc to the clear solution, and boil until both the zinc and any precipitated tin have dissolved : it may be necessary to add a little more strong hydrochloric acid. Filter from any undissolved substance, add two or three drops of a solution of ferric chloride, and then a few drops of a freshly prepared solution of potassium ferricyanide : a blue precipitate or coloration confirms tin. (See 7, p. 59.) Arsenic can best be confirmed by dissolving the precipitate in a little nitric acid, and then neutralising with ammonia. A few drops of the solution are then tested by the modified Gutzeit test ( 5, p. 46). As, however, this test is extremely delicate, and as it is very difficult to obtain reagents quite free from arsenic, it is best to first do a blank experiment with the reagents to be employed, and then a second experiment with the solution under examination. If in the second experiment there is a very distinct coloration, whereas there was none or only a slight coloration in the blank, then the presence of arsenic is confirmed. When considerable quantities of arsenic are present it may be confirmed by converting it into magnesium ammonium arsenate Mg(NH 4 )AsO 4 . In order to do this, dissolve the precipitate in a few c.c. of fuming nitric acid and boil until no more fumes are given off. Evaporate to about one- third its bulk, dilute with a little water, add excess of strong ammonia, and then a few c.c. of a solution of magnesium chloride. Stir well with a glass rod, a white crystalline precipitate shows the presence of arsenic. When only very small quantities of arsenic are present the precipitate will take some time to form, but if no precipitate is produced within 10 hours arsenic is not present. CHAPTER VI. THE IRON GROUP. Aluminium. ALUMINIUM is readily soluble in hydrochloric acid, with evolu- tion of hydrogen. Cold sulphuric acid has practically no action on it, and even on boiling the action is very slow. Nitric acid, also, has very little action. It dissolves readily in sodium and in potassium hydroxide, with formation of an aluminate. 2A1 + 6KOH = 2A1(OK) 3 + 3 H a Dry Reactions. On ignition, compounds of aluminium are converted into the oxide, which becomes incandescent when strongly heated. On adding to the alumina so produced a drop of a solution of cobalt nitrate, and again igniting, a brilliant blue coloration is produced. This test can be carried out by heating on charcoal ; or a piece of filter paper may be moistened with a solution of an aluminium salt and a drop of cobalt nitrate. If the paper is dried over the Bunsen flame and then ignited, the ash is coloured blue (p. n). The test is not conclusive in presence of other oxides or of phosphates or borates. Reactions in Solution. Use a solution of potash alum. *i. Ammonium hydroxide gives a white gelatinous pre- cipitate of aluminium hydroxide, slightly soluble in excess, but insoluble in presence of ammonium chloride, and on boiling. A1 2 (S0 4 ) 3 + 6NH 4 OH = 2A1(OH) 3 + 3 (NH 4 ) 2 SO 4 *2. Potassium and Sodium hydroxide produce the same 68 Qualitative Chemical Analysis. precipitate, readily soluble in excess forming an aluminate. No precipitation of the hydroxide occurs on boiling. Al(OH), + sNaOH = Na 3 AlO 3 + 3H 2 O The aluminium hydroxide is reprecipitated from this solution by addition of excess of ammonium chloride, the precipitation taking place from strong solutions, partially in the cold, and completely on boiling even from dilute solutions. Na 3 A10 3 + 3NH 4 C1 = Al(OH), + aNaCl + 3 NH 3 The cause of this precipitation is attributable to the formation of ammonium aluminate (NH 4 ) 3 A1O 3 , which is then completely hydrolysed. Aluminium hydroxide is not precipitated in the presence of fixed organic acids such as tartaric or citric acid ; excess of sugar or glycerol likewise prevent precipitation. - 3. Ammonium sulphide also precipitates aluminium hydroxide, the precipitation being more complete in presence of ammonium chloride. Aluminium sulphide is probably first pro- duced, but is hydrolytically decomposed with formation of the hydroxide. (a.) A1 2 (S0 4 ) 3 + 3 (NH 4 ) 2 S = A1 2 S 3 + 3(NH 4 ) 2 SO 4 (.) A1 2 S 3 + 6HOH = 2A1(OH) 3 + 3 H 2 S 4. Sodium phosphate gives a white precipitate of alu- minium phosphate. A1 2 (S0 4 ) 3 + 2Na 2 HPO 4 = 2A1PO 4 + 2Na 2 SO 4 + H 2 SO< It is soluble in potassium and ammonium hydroxide, but not in warm acetic acid. (Distinction from aluminium hydroxide). Chromium. Metallic chromium is very hard, and has much the appearance of cast iron. It is only fusible at very high temperatures, and oxi- dises slowly on heating in the air. It is readily soluble in sulphuric and hydrochloric acids, but practically insoluble in nitric acid. There are two series of chromium compounds ; those derived The Iron Group. 69 from chromium sesquioxide, Cr 2 O 3 , the chromic ; and those derived from chromic anhydride, CrO 3 , the dire-mates. There are also chronuw; salts, such as CrCl 2 . It is only, however, necessary to consider the reactions of the chromic compounds, and of the chromates, because the chromous compounds are very unstable, readily changing into the chromic condition. The dry reactions are the same for both. In the chromic salts Cr'" is the cation. The solutions are violet or green (depending upon their concentration and the temperature), and from them chromium hydroxide, etc., are precipitated by reagents that precipitate the corresponding alu- minium compounds. In chromates, however, the chromium forms merely part of a complex anion, hence the reagents above referred to do not produce precipitates unless, as in the case of ammonium sulphide, they first reduce the chromate to a chromic salt. Chromates and dichromates form solutions which are yellow and orange respectively. Their reactions are discussed under the head of acids (p. 144). Dry Reactions. i. Borax Bead Compounds of chromium colour the borax bead an emerald green, the colour is more intense when the bead is heated in the reducing flame. 2. On mixing a small quantity of a compound of chromium with potassium nitrate and fusion mixture, and heating in a loop of platinum wire, a yellow mass of sodium and potassium chromate is obtained. If this is dissolved in a little water, the yellow solution so obtained acidified with acetic acid, and then a little silver nitrate added, a red precipitate of silver chromate is produced. (a.) Cr 2 O 3 + 3KNO 3 -f 2Na 2 CO 3 = 2Na 2 CrO 4 + sKNO 3 + 2 CO 2 (b.) Na.CrO 4 + 2AgNO 3 = Ag 2 CrO 4 -f 2NaNO, Chromic Compounds. Use a solution of chrome alum, or any soluble chromic salt. *i. Ammonium hydroxide gives a bluish or whitish-green 7o Qualitative Chemical Analysis. gelatinous precipitate of chromic hydroxide, slightly soluble in excess of the reagent, the solution becoming a bluish pink. From this solution the hydrate is completely precipitated by boiling. CrCl 3 + sNH 4 OH = Cr(OH) 3 + 3 NH 4 C1 *2. Sodium or potassium hydroxide produce the same precipitate, soluble in excess to a bright green solution of sodium chromite. The hydrate is reprecipitated by a large excess of water, the precipitation being complete on boiling. The reaction is therefore reversible. (a.) Cr 2 (SO 4 ) 3 + 6NaOH = 2Cr(OH) 3 + 3Na 2 SO 4 (b.) Cr(OH) 3 + 3 NaOH^Cr(ONa) 3 + 3H 2 O Presence of non-volatile organic compounds interferes with or entirely prevents the precipitation of chromic hydroxide. 3. Ammonium sulphide gives the same precipitate as (i and 2), insoluble in excess. (Cf. 3,. p. 68.) Cr 2 (S0 4 ) 3 + 3(NH 4 ) 2 S + 6H 2 O = 2 Cr(OH) 3 + 3 (NH 4 ) 2 SO 4 + 3 H 2 S 4. On adding sodium peroxide to a cold solution of a chromic salt, and boiling till effervescence ceases, the chromic salt is oxidised, sodium chromate being produced. The colour of the solution changes from green or purple to yellow. 2Cr(OH) 3 + 3Na 2 O 2 = 2Na 2 CrO 4 + 2NaOH + 2H 2 O 5. Chlorine or bromine water, added to a cold solution of a chromic salt which has previously been rendered strongly alka- line with -sodium or potassium hydroxide, also oxidises it to a chromate on boiling. In this case the chlorine or bromine is first converted into an alkali hypochlorite, or hypobromite, which then oxidises the chromic salt. (Hypochlorites and hypo- bromites are not produced in hot solutions.) (a.) Br 2 + 2NaOH = NaOBr + NaBr + H 2 O (b.) 2Cr(OH) 3 + 3 NaOBr+4NaOH = 2 Na 2 CrO + 3NaBr + 5 H 2 O If this solution is acidified with sulphuric acid, and boiled till no The Iron Group. 71 more bromine is evolved, it may be tested for a chromate with hydrogen peroxide ( 7, p. 145). When analysing a substance containing a chromate, it becomes reduced to a chromic salt by the action of sulphuretted hydrogen, the chromium is therefore precipitated in the iron group. Iron. Metallic iron dissolves readily in "acids, with hydrochloric and sulphuric acid passing into the fenous state, but with nitric acid into the ferr/V condition. Fern?7/.r salts are readily converted into ferr/V salts by oxidation with nitric acid. When ferrous oxide is dissolved in hydrochloric acid, ferrous chloride is produced. FeO -f aHCl = Fed, + H 2 O Whereas when ferric oxide is dissolved, ferric chloride is produced. ,Fe = O 0<" + 6HC1 = 2 FeCl 3 + 3H 2 O X Fe = Dry Reactions. i. Blowpipe Test. When heated on char- coal before the blowpipe, iron compounds yield a black magnetic residue, v 2. Match Test. A black magnetic powder is obtained. If this powder is placed on a filter paper and moistened with dilute hydrochloric acid it dissolves, leaving a yellow stain, which, upon being moistened with a drop of potassium ferrocyanide, turns dark blue. 3. Borax Bead. In the reducing flame a bottle-green bead is produced. In the oxidising flame the bead is dark yellow while hot, light yellow when cold. Ferrous Iron. Reactions in Solution. Use a solution of ferrous sulphate or ferrous ammonium sulphate. *i. Ammonium sulphide gives a black precipitate of 72 Qualitative Chemical Analysis. ferrous sulphide, soluble in dilute mineral acids. Moist ferrous sulphide when in contact with air gradually becomes reddish- brown, owing to oxidation. FeS0 4 + (NH 4 ) 2 S = FeS + (NH 4 ) 2 SO 4 *2. Caustic alkalis and ammonium hydroxide produce a voluminous greenish-white precipitate of ferrous hydroxide, which quickly absorbs oxygen from the air, turning first green and finally brown, owing to conversion into ferric hydroxide. FeS0 4 + 2 NH 4 OH = Fe(OH) 2 + (NH 4 \SO 4 *3. Potassium ferrocyanide gives a white precipitate of potassium ferrous-ferrocyanide, which rapidly turns blue owing to oxidation. Ferrous salts usually contain traces of ferric salts, therefore the precipitate is very rarely white, but generally light blue. FeS0 4 + K 4 Fe(CN) 6 = K 2 Fe[Fe(CN) 6 ] + K,SO 4 *4. Potassium ferricyanide forms a deep blue precipitate of ferr^-ferricyanide (Turnbull's blue). In very dilute solutions only a blue coloration is produced. 3 FeS0 4 + 2 K 3 Fe(CN) 6 = Fe 3 [Fe(CN) 6 ] 2 -f 3 K 2 SO 4 Turnbull's blue is decomposed by caustic alkalis, ferrous hydroxide and an alkali ferricyanide being produced. Only the iron which is present as the cation is precipitated as ferrous- hydrate ; that in the complex anion Fe(CN) 6 is unacted upon. Fe 3 [Fe(CN) 6 ] 2 + 6KOH = 2 K 3 Fe(CN) 6 + 3 Fe(OH) a Ferric Iron. Use a solution of ferric chloride. *i. Ammonium sulphide precipitates black ferrous sul- phide, along with sulphur. 2 FeCl 3 + 3(NH 4 ),S = 2 FeS + 6NH 4 C1 + S The Iron Group. 73 *2. Caustic alkalis and ammonium hydroxide give a reddish-brown gelatinous precipitate of ferric hydroxide, soluble in dilute acids (the presence of many organic compounds, such as tartrates and citrates, hinders or prevents precipitation). FeQ 3 + 3 NH 4 OH = Fe(OH) s + 3 NH 4 C1 *3. Potassium ferrocyanide produces a deep-blue pre- cipitate of ferric-ferrocyanide (Prussian blue), Fe 4 [Fe(CN) 6 ] 3 . It is insoluble in hydrochloric acid, but is soluble in oxalic acid, forming a blue solution (blue ink), but is decomposed by caustic alkalis, with separation of ferric hydroxide. The iron in the cation alone is precipitated as ferric hydrate, that in the complex anion not being acted upon. Fe 4 [Fe(CN)J 3 + I2KOH = 4 Fe(OH) 3 + 3 K 4 Fe(CN) 6 4. Potassium ferricyanide gives no precipitate, but the colour of the solution becomes brown, because the ferric ferri- cyanide produced is soluble in water, and is only slightly ionised. Fe(CN);' + Fe"'^ Fe[Fe(CN) 6 ] *5. Potassium thiocyanate gives a most intense blood-red coloration of ferric thiocyanate. The coloration is shown even in excessively dilute solutions, especially if excess of the thiocya- nate is added. FeCl 3 + 3 KCNS = Fe(CNS) 3 + 3 KC1 Ferric thiocyanate dissolves in ether, and is not decolourised by dilute hydrochloric acid (distinction from red coloration produced with ferrous salts by acetates and formates). Mercuric chloride, however, destroys the colour, as does rochelle salt (potassium sodium tartrate). This is due to the formation of undis- sociated ferric tartrate and the production of strongly dissociated alkali thiocyanate. 2 Fe(CNS) 3 + 3 C 4 H 4 6 NaK = Fe 2 (C 4 H 4 O 6 ) 3 + 3 NaCNS + 3 KCNS Although, as already stated (p. 19), ferric thiocyanate is only very 74 Qualitative Chemical Analysis. slightly ionised in solution hence its red coloration ferric tartrate is still less ionised j therefore, when the two solutions are brought together the Fe" 1 ions unite with the tartrate C 4 H 4 O 6 " ions to form undissociated ferric tartrate.f Equilibrium is thus disturbed, and a further quantity of the ferric thiocyanate becomes ionised. This process goes on until the whole of the ferric thiocyanate has become converted into ferric tartrate. The same reasoning applies to the action of the mercuric chloride, mercuric thiocyanate being less ionised than ferric thiocyanate. The colour reaction is more intense in presence of excess of potassium thiocyanate, as it tends to prevent ionisation of the ferric thiocyanate. 6. Alkali acetates produce a red to reddish-brown colora- tion from neutral salts ; on boiling, the iron is completely preci- pitated as a basic acetate. (The precipitation does not take place in presence of many organic acids and of poly-alcohols.) (a.) FeQ 3 + 3CH 3 COOK = (CH 3 COO) 3 Fe + 3 NaCl Dark brown colour. (b.) (CH 3 COO) 3 Fe-f 2H-OH = CH 3 COO. Fe(OH) 2 -f 2CH 3 COOH Reduction of Ferric Compounds to the Ferrous State. If a solution of a ferric salt is warmed with zinc and hydrochloric acid, the nascent hydrogen evolved reduces it to a ferrous salt. 2FeCl 3 + 2H = 2FeCL + 2HC1 The same effect is produced on warming with sulphurous acid. 2FeQ 3 + 2H,O +SO 2 = 2FeCl 2 -f 2HC1 -f H,SO 4 Reduction is also effected by H a S, with accompanying precipita- tion of sulphur. 2FeCl 3 -f H 2 S = 2FeCl 2 -f S -f- 2HC1 If the reduction is complete, the iron salt no longer gives the reactions of the ferric ion, but will answer to those for the ferrous ion. Detection of Ferrous Iron in Presence of Ferric Iron. t This is probably a basic compound, and very likely consists of colloidal ferric hydroxide and basic ferric tartrate. The Iron Group. 75 Add to the solution of the mixed salts a solution of potassium thiocyanate an intense red coloration, showing the presence of ferric iron, is produced. Now add a few crystals of rochelle salt and warm gently, the colour changes to a light brown. On addition of a solution of potassium ferricyanide a deep blue coloration or precipitate is produced, indicating the presence of a ferrous salt. Manganese. Metallic manganese resembles iron very much in appearance, and is soluble in dilute mineral acids. It forms several series of compounds. Thus there are two in which the cation is divalent and trivalent Mn respectively ; viz. stable manganous salts, derived from basic manganous oxide, MnO ; and unstable manganic salts, from basic manganese sesquioxide, Mn 2 O 3 . There are also the manganates and permanganates, in which Mn is merely one part of the anion, which in each case is MnO 4 , being divalent in the manganates, but monovalent in the permanganates. Dry Reactions. i. If a small quantity of a manganese compound is mixed with fusion mixture, and is then taken up upon a small loop of platinum wire, and held in the oxidising flame of the Bunsen burner till completely fused, the resulting mass will be of a deep green colour, owing to the formation of an alkali manganate. MnO 3 -f Na,CO 3 + O = Na 2 MnO 4 + CO 3 It is sometimes recommended to add a little nitre as well as fusion mixture in this case. However, owing to the formation of potassium nitrite, the following reaction does not show to advan- tage, because of its reducing action. If the fused mass is dissolved in about i c.c. of water, and acidified with dilute sulphuric acid, a rose-red coloration will be imparted to the solution, owing to the oxidation of the sodium manganate to permanganate. The oxidation takes place 76 Qualitative Chemical Analysis. without the addition of acid on allowing the solution to stand in contact with air for a short time. In the latter case, however, a brown precipitate of MnO(OH) 2 is produced at the same time. 3Na 2 MnO 4 + 3H.O = 2NaMnO 4 + MnO(OH) 2 + 4NaOH 2. Borax Bead. Manganese compounds, when heated in the oxidising flame, colour the borax or microcosmic bead an amethyst purple. The bead is colourless in the reducing flame. Reactions in Solution. Use a solution of manganese chloride or sulphate. *i. Ammonium sulphide gives a flesh-coloured precipitate of manganese sulphide. In very dilute solutions the precipi- tate has a yellowish-white appearance. It is readily soluble in mineral acids, and in acetic acid (distinction from zinc). MnCl 2 + (NH 4 ) 2 S = MnS -f 2 NH 4 C1 *2. Sodium or potassium hydroxide produce a white pre- cipitate of manganous hydroxide, which rapidly turns brown in the air, owing to formation of manganic hydroxide, MnO(OH) 3 , by oxidation. (i.) MnCl 2 + 2KOH = Mn(OH). + 2KC1 /OH /OHf (2.) Mn< +O = Mn<=O X OH \ OH *3. Ammonium hydroxide forms the same precipitate. In presence of ammonium chloride no precipitation takes place, because ammonium hydroxide, although ordinarily sufficiently dis- sociated to precipitate manganese hydroxide, is in the presence of a strongly dissociated ammonium salt so slightly ionised that there are not enough OH' ions present to cause precipitation of Mn(OH) 2 . On exposure to air, a brown precipitate of manganic hydroxide gradually separates out. *4. Permanganate Reaction. If one or two grams of red t This is acidic in character, and reacts with the basic manganous hydroxide to form salts. manganites. The Iron Group. 77 lead be warmed with about 3 c.c. of concentrated nitric acid, and a solution of a manganese salt free from hydrochloric acid be added, on again warming, the manganese compound becomes oxidised to permanganate ; and the solution, after the brown precipitate of lead peroxide has settled, is seen to be coloured a rose pink. 2MnSO 4 + sPbO, + 6HNO 3 = 2HMnO 4 + 2PbSO 4 + 3Pb(NO 3 ) 2 The solution must not be filtered, because the permanganic acid becomes reduced by the fibre of the filter paper. The manganese salt should be very dilute, an excess making the reaction less delicate. NOTE. As permanganates are reduced by H 2 S, SO 2 , etc., they will, after treatment with such reducing agents, give the same reactions as manganous salts. For reactions of permanganic acid, see p. 146. Zinc, Perfectly pure zinc is not readily soluble in acids ; but as usually obtained it is readily soluble. The pure metal may be caused to dissolve by the action of dilute acids and the addition of a drop or two of copper sulphate or of cadmium sulphate solu- tion. It dissolves in boiling alkalis, with evolution of hydrogen and formation of an alkali zincate. Zn + 2 KOH = K 2 ZnO 2 + H 2 Dry Reactions. i. Blowpipe Test. Heated on charcoal with fusion mixture, compounds of zinc are reduced to the metallic state. Owing, however, to the volatility of the metal, no bead is obtained; but on the charcoal an incrustation of the oxide is formed, which is yellow while hot, and white on cooling. If the oxide is moistened with a drop of cobalt nitrate, and again heated, a green-coloured compound is produced. 2. Filter Ash Test (p. n). The ash is tinged green. 3. Borax Bead. This is yellowish while hot, but colourless 78 Qualitative Chemical Analysis. on cooling; if a large quantity of zinc salt has been employed the bead is often opaque. Reactions in Solution. Use a solution of zinc sulphate. *i. Ammonium sulphide gives a white precipitate of zinc sulphide, soluble in mineral acids, insoluble in acetic acid and sodium acetate (distinction from manganese). ZnS0 4 + (NH 4 ) 2 S = ZnS + (NH 4 ) 2 SO 4 *2. Sodium or potassium hydroxide produce a white gelatinous precipitate of zinc hydroxide, soluble in excess with formation of an alkali zincate, from which ammonium sulphide precipitates zinc sulphide. (a.) ZnSO 4 + 2NaOH = Zn(OH) 2 + Na,S0 4 (b.) Zn(OH) 2 + 2NaOH = Na 2 ZnO 2 + 2H 2 O 3. Ammonium hydroxide gives the same precipitate soluble in excess, but no precipitation takes place in presence of salts of ammonium. *4. Potassium ferrocyanide forms a white gelatinous precipitate of zinc ferrocyanide, insoluble in acetic acid. (See 3, P- 7 2 -) 2 ZnS0 4 + K 4 Fe(CN) 6 = Zn 2 Fe(CN) 6 + 2 K 2 SO 5. Sodium carbonate produces a bulky white precipitate of a basic zinc carbonate. 5ZnS0 4 + sNa^COs + 3 H 2 O = 2 ZnCO 8 , 3Zn(OH) 2 Nickel. Nickel is a very hard metal, which takes on a bright polish when burnished. It is readily soluble in nitric acid, less soluble in sulphuric and hydrochloric acids. The salts of nickel are green in solution or when crystalline, usually yellow when anhydrous. Nickel forms many alloys, most of which are soluble in nitric acid. The Iron Group. 79 Dry Reactions. i. Blowpipe Test. When heated on charcoal before the blowpipe nickel compounds are reduced to a black powder of metallic nickel, which is magnetic. 2. Match Test. Black magnetic powder obtained. 3. Borax Bead. In the oxidising flame compounds of nickel give a yellowish-brown bead ; in the reducing flame it is opaque apd grey, owing to particles of metallic nickel being distributed throughout the bead. Reactions in Solution. Use a solution of nickel chloride or sulphate. *i. Ammonium sulphide gives a black precipitate of nickel sulphide which is slightly soluble in ammonia ; therefore, on filtering a strong ammoniacal solution, the filtrate is often coloured brown. If this solution is acidified with acetic acid and gently warmed, the nickel sulphide is completely precipitated. NiCl 2 + (NH 4 ) 2 S = NiS + 2NH 4 C1 Nickel sulphide is practically insoluble in dilute hydrochloric acid, but is readily dissolved on warming with hydrochloric acid containing a crystal of potassium chlorate, or in aqua regia. *2. Sodium or potassium hydroxide produces a light green gelatinous precipitate of nickel hydroxide, insoluble in excess, but readily soluble in acids. NiCl 2 = 2 KOH = Ni(OH) 2 + 2KC1 On addition of oxidising agents such as hypochlorites, hydrogen peroxide, etc., the nickel hydroxide is oxidised tonickelic hydroxide. 2 Ni(OH) 2 + NaOBr + H 2 O = 2Ni(OH) 3 + NaBr 3. Ammonium hydroxide gives a voluminous greenish basic precipitate which is readily soluble in excess, a deep blue solution of a complex nickel ammonium salt [Ni(NH 3 ) 6 SOJ being formed. Ni\ OH 2NiSO 4 + 2NH 4 OH = >SO 4 + (NH^C^ Ni/_OH Consequently in presence of ammonium salts no precipitation takes place. 8o Qualitative Chemical Analysis. *4. Potassium cyanide produces a green precipitate of nickel cyanide. NiQ 2 + 2KCN = Ni(CN) 2 + 2 KCI It is soluble in excess of potassium cyanide, forming a so-called double cyanide of potassium and nickel. Ni(CN) 2 + 2KCN = K 2 Ni(CN) 4 From this solution nickel cyanide is precipitated by addition of acids. Sulphuretted hydrogen produces no precipitate from this solution, because the nickel is in the stable complex anion Ni(CN); It is, however, readily decomposed by chlorine or bromine and by hypochlorites. K 2 Ni(CN) 4 -f 4Br 2 = NiBr 2 + 2KBr + 4CNBr This decomposition is one of great importance, because it is made use of in separating nickel from cobalt (see p. 83). The potassium cobalticyanide is much more stable than the potassium nickelocyanide, and is not decomposed under similar conditions. The above reaction is carried out in alkaline solution, so that nickel hydroxide is precipitated, and is then oxidised by the excess of bromine or chlorine to the higher hydroxide. (Cf. 2, p. 79.) 5. Add to a solution of a nickel salt just sufficient potassium cyanide to dissolve the precipitate at first produced. Now add a slight excess of caustic soda and then sufficient bromine water to give a permanent colo'ur to the solution. On gently warming, a black precipitate of nickelic hydroxide will be thrown down. The nickelic hydroxide is precipitated owing to the complete decomposition of the molecule K 2 Ni(CN) 4 (distinction from cobalt). 2 K 2 Ni(CN) 4 + NaOBr + 5H 2 O = 2Ni(OH) 3 + NaBr + 4KCN + 4HCN Jf a large excess of potassium cyanide or caustic soda is present the reaction does not take place very readily. The Iron Group. 81 Cobalt. Metallic cobalt is very similar to nickel. Nitric acid is the best solvent. The solutions of cobalt salts are red ; the anhydrous salts, however, are usually blue. But anhydrous cobalt sulphate is red, as is its aqueous solution. Dry Reactions. i. Blowpipe Test. When heated on char- coal, cobalt compounds are reduced to a black metallic powder, which is attracted by the magnet. 2. Match Test. A black magnetic powder obtained. 3. Borax Bead. In both the oxidising and reducing flame the bead is coloured a beautiful sapphire blue. Reactions in Solution. Use a solution of cobalt chloride or nitrate. i. Ammonium sulphide produces a black precipitate of cobalt sulphide, which is insoluble in excess of ammonium sulphide, and in dilute acids. It is readily soluble in aqua regia, or in hydrochloric acid, to which a little potassium chlorate has been added, or in aqua regia. Co(N0 3 ) 2 + (NH 4 ) 2 S = CoS + 2 NH 4 N0 3 *2. Potassium or sodium hydroxide gives a bluish precipitate of basic chloride. (a.) CoCl 2 + NaOH = Co(OH)Cl + NaCl (b.) Co(OH)Cl + NaOH = Co(OH) 2 + NaCl This on boiling turns light red, being converted into cobaltous hydroxide Co(OH) 2 , which, owing to further oxidation, rapidly turns brown. 2 Co(OH) 2 + O -f- H . OH = 2 Co(OH) 3 *3- Ammonium hydroxide produces the same precipitate which dissolves readily in excess of the reagent, forming a brown solution which turns purple on boiling, but owing to oxidation it rapidly becomes a permanent brown. G 82 Qualitative Chemical Analysis. *4. Potassium cyanide forms a buff-coloured precipitate of cobaltous cyanide. Co(N0 3 ) 2 + 2KCN = Co(CN) 2 + 2KNO 3 It dissolves readily in excess of the precipitant, being converted into potassium cobaltocyanide. Co(CN) 2 + 4 KCN = K 4 Co(CN) 6 This salt is very readily oxidised to potassium cobalticyanide, the conversion taking place even on boiling with water alone, but more rapidly if a trace of acid is present, or by the addition of oxidising agents. 2 K 4 Co(CN) 6 + O + H 2 = 2 K 3 Co(CN) 6 + 2KOH It should be noticed that potassium cobaltocyanide corre- sponds to potassium ferrocyanide, and the cobalticyanide to ferricyanide. Caustic alkalis and bromine water do not precipitate the hydrate from this solution (cf. Nickel), because the potassium cobalticyanide is a very stable substance, and so long as it is undecomposed and the cobalt remains in the complex anion Co(CN)7j it will not be precipitated by the ordinary reagents for the ion Co". *5. Potassium nitrite, when added to neutral solutions of cobalt salts which have been strongly acidified with acetic acid, produces a brilliant yellow precipitate of potassium cobalti- nitrite. Probably the first course of the reaction consists in the formation of potassium cobaltonitrite, which then becomes oxidised by the nitrous acid, set free on the addition of the acetic acid, to potassium cobaltinitrite. (i.) CoC! 2 + 6KNO 2 = K 4 Co(NO 2 ) 6 + 2KC1 (ii.) K 4 Co(N0 2 ) 6 -f HN0 2 -f CH 3 . COOH = K 3 Co(N0 2 ) 6 + CH 3 . COOK + H 2 O + NO *6. Ammonium Thiocyanate. When a concentrated solution of ammonium thiocyanate is added to a cobaltous The Iron Group. 83 solution a brilliant blue coloration due to the formation of ammonium cobaltous thiocyanate is produced. (i.) Co(N0 3 ) 2 + 2NH 4 CNS = Co(CNS) 2 + 2 NH 4 NO 3 (ii.) Co(CNS) s -h 2NH 4 CNS ^ (NH 4 ) 2 Co(CNS) 4 If the solution is diluted the blue colour vanishes, the re- action is therefore reversible. The test can be made extremely^ delicate by adding a mixture of equal volumes of amyl alcohol and ether. On shaking up the blue coloration is imparted to the alcohol-ether layer, which floats upon the surface of the aqueous solution. The amyl alcohol and ether should be added before the ammonium thiocyanate. The reaction can be employed in presence of nickel, which gives no coloration. The merest trace of cobalt can be detected in this manner. Separation of Nickel and Cobalt. Owing to the similarity of the reactions of these two metals their separation is attended with considerable difficulty. They may, however, be separated (i.) by taking advantage of their different behaviour with potassium cyanide, and (ii.) by the behaviour of cobalt with potassium nitrite. (i.) To a neutral solution containing nickel and cobalt, add potassium cyanide till the precipitate first formed is just redis- solved. Now add two or three drops of acetic acid, and boil in the draught cupboard for three or four minutes (any precipitate which forms should be filtered off and neglected). Cool the solution ; make slightly alkaline with caustic soda, and add bromine water till a permanent brown coloration is produced. Warm ; a black precipitate of nickel hydroxide will be formed : filter this off, and, after washing, confirm nickel by means of the borax bead. The cobalt is obtained by evaporating the solution to dryness and testing with the borax bead, a sapphire-blue colour showing the presence of cobalt. (ii.) Render the neutral solution strongly acid with acetic acid, and add a solution of potassium nitrite. Add to the mixture about one-third its volume of alcohol, and shake well. Potassium 84 Qualitative Chemical Analysis. cobaltinitrite will separate out as a golden yellow powder. Allow to stand about a quarter of an hour, or, if the solution is dilute, for an hour or two, and filter off. The nickel may be precipitated from the solution by means of sodium hydroxide, and confirmed by means of the borax bead. Cerium. Cerium forms two classes of compounds the cerous, derived from the sesquioxide Ce 2 O 3 ; and the eerie, derived from the dioxide CeO 2 . The eerie salts as a rule are not very stable. Dry Reactions. i. Blowpipe Test. When strongly heated on charcoal an orange or reddish-brown mass of cerium dioxide is obtained. 2. Borax Bead. In the oxidising flame the bead is brownish- green while hot, bluish-green on cooling. In the reducing flame the bead is colourless. Reactions in Solutions. Use a solution of cerium nitrate. * i. Ammonium sulphide or hydroxide give a white precipitate of eerous hydroxide. CeCl 3 + 3NH 4 OH = Ce(OH) 3 + 3NH 4 Cl 2. Potassium or sodium hydroxide produce the same precipitate. Addition of oxidising agents, such as chlorine water or hydrogen peroxide, convert cerous hydroxide into yellow eerie hydroxide. *3. Sodium peroxide added to a solution of the cerous salt produces a yellow gelatinous precipitate of eerie hydroxide, which rather resembles ferric hydrate in appearance. 2Ce(NO 3 ) 3 + 6NaOH + H 2 O 2 = 2Ce(OH) 4 + 6NaNO 3 *4. Ammonium oxalate or oxalic acid give a white precipitate of cerium oxalate, which is insoluble in excess of oxalic acid. 2CeCl 3 + 3H 2 C 2 O 4 = Ce 2 (C 2 O 4 ) 3 -f 6HC1 The Iron Group. 85 Separation of the Metals of the Iron Group. Several methods of procedure may be adopted for separating the metals of the iron group. The method most generally appli- cable will be found on p. 174. But in presence of large quantities of manganese or cobalt or both, the following method will be found more satisfactory. In this case advantage is taken of the insolubility of the sulphides of nickel and cobalt in dilute 2N . hydrochloric acid. The method of procedure, in the absence of phosphoric acid,f is as follows : The solution from the copper group is evaporated to small bulk, then about one quarter of its volume of ammonium chloride is added to the hot solution, and a slight excess of ammonium hydroxide. This precipitates the hydroxides of iron, chro- mium, aluminium, and cerium. Sulphuretted hydrogen is now added or passed through the mixture without previous nitration. This precipitates the sulphides of zinc, man- ganese, cobalt, and nickel, the iron at the same time being converted into ferrous sulphide. The mixed hydrates and sulphides are filtered off and washed with hot water; then they are transferred to a small flask or test tube, and mixed with excess of cold dilute hydrochloric acid of the above-mentioned strength. The flask is closed with a cork, and shaken vigorously for two or three minutes. By this treatment the hydrates of chromium, aluminium, and cerium, together with the sulphides of iron, manganese, and zinc, are dissolved. The sulphides of cobalt and nickel are filtered off, and dissolved in 4N . hydrochloric acid with a crystal of potassium chlorate. From this solution cobalt and nickel are separated as described on p. 83. To the cold solution, which should be transferred to an evapo- rating dish, sodium peroxide is added in small quantities at a time, until the solution is strongly alkaline, when it is boiled till f If a phosphate is present, the phosphoric acid must be removed before proceeding to analyse for the metals of this group (see p. 87). 86 Qualitative Chemical Analysis. effervescence cases.j Sodium aluminate, zineate, and chro- mate are produced, and go into solution. The iron and cerium are precipitated as ferric and eerie hydroxides, and the manganese as hydrated manganese dioxide. For the further separation of these metals, see table on p. 176. Separation of Phosphoric Acid from Mixtures. See- ing that all phosphates are soluble in mineral acids, the presence of the phosphoric acid anion does not interfere with the course of testing for the cations of the silver and copper groups, because, till these are removed as insoluble chlorides and sulphides, the solution is kept acid. So soon, however, as the solution is rendered alkaline by ammonium hydroxide, the insoluble phosphates of the iron group, of the barium group, and of magnesium are precipitated ; e.g. FeCl 2 + H 3 P0 4 + 3 NH 4 OH = FeP0 4 + 3 NH 4 C1 + sH 2 CaCl 2 + H 3 PO 4 + 2NH 4 OH = CaHPO 4 + 2NH 4 C1 + 2H 2 O { The metals thus precipitated need not have been originally present as phosphates ; the presence in the solution of phosphoric acid, liberated by hydrochloric acid and sulphuretted hydrogen from phosphates belonging to the cations of the silver and copper groups or soluble alkali phosphates, would at this stage cause precipitation of the insoluble phosphate ; thus (NH 4 ) 2 HP0 4 + CaCla = CaHPO 4 + 2NH 4 C1 It is apparent, then, that, unless the phosphoric acid be re- moved before the addition of ammonium hydroxide, very serious complications may ensue. Therefore, after having got rid of the metals of the silver, copper, and arsenic groups, phosphates should always be tested for. f Instead of sodium peroxide, sodium hydroxide may be added until strongly alkaline, and then hydrogen peroxide; after which, it is treated as already described. \ With excess of ammonium hydroxide tricalcium phosphate is produced. The Iron Group. 87 Test for Phosphoric Acid. A small portion of the solution is strongly acidified with concentrated nitric acid, an excess of ammonium molybdate is added, and the mixture gently warmed (not boiled) ; if a canary-yellow precipitate is formed, this shows the presence of a phosphate. It may be necessary and is always advisable to allow the mixture to stand for a few minutes. Removal of the Phosphoric Acid. The presence of a phosphate having been ascertained, the rest of the solution is neutralised with ammonium hydroxide until a slight turbidity is produced. About 2-3 c.c. of a strong solution of ammonium acetate is now added, and then ferric chloride, drop by drop, till the solution acquires a permanent red coloration, f On first adding the ferric chloride a yellowish-white precipitate is formed : this is the ferric phosphate precipitate. The appearance of the red coloration shows when the phosphate has been entirely pre- cipitated and ferric acetate (see p. 174) is being formed. As soon as the red colour is permanent, no more ferric chloride should be added, because ferric phosphate is slightly soluble in this reagent.J The mixture is now boiled, when the excess of iron is precipi- tated as basic ferric acetate. The precipitate is filtered off, and the solution analysed as usual for the metals of the f The ammonium acetate is added in order to neutralise the hydro- chloric acid set free, when ferric chloride reacts with a phosphate, because ferric phosphate is soluble in hydrochloric acid. (Sr + 2NH 4 C1 COONH, COO/ Calcium. Dry Reactions. Compounds of calcium colour the flame a dull red ; the colour, however, is not so intense as that produced by strontium. When viewed through the spectroscope, a bright bluish-green line, ft, and a sharp line, a, in the orange are seen ; there are also several lines between these. Both the chloride and nitrate are soluble in absolute alcohol, they are also soluble in a mixture of equal volumes of alcohol and ether. Reactions in Solution. Use a solution of calcium chloride. *i. Ammonium carbonate forms a dense white precipitate 92 Qualitative Chemical Analysis. of calcium carbonate, soluble in dilute acids. Precipitation is not complete if a large excess of an ammonium salt is present. CaCl 2 + (NH 4 ) 2 CO 3 ^CaCO 3 + 2NH 4 C1 2. Sulphuric acid produces from strong solutions an imme- diate precipitate of calcium sulphate. In dilute solutions either no precipitation takes place, or only after standing some time. *3. Ammonium oxalate produces a heavy white powdery precipitate of calcium oxalate, which is insoluble in acetic acid, but soluble in hydrochloric acid. COONH 4 COO. CaQ 2 +1 =| ;Ca + 2 NH 4 C1 COONH 4 COO 7 Separation of Barium, Strontium, and Calcium. There are various ways of separating the metals of the barium group. Two methods are here given, the one being based on the different solubility of the nitrates in strong nitric acid, the other upon the solubility of calcium nitrate in absolute alcohol. I. Ammonium carbonate is added to the hot solution obtained from the iron group. Carbonates of barium, strontium, and calcium are precipitated. They are filtered off, dissolved in dilute nitric acid, and the solution is evaporated nearly to dryness. The pasty mass is taken up with a little concentrated nitric acid, and filtered cold. The residue on the filter paper,! which consists of the nitrates of barium and strontium, is washed with a little strong nitric acid. The solution contains the soluble calcium nitrate. The barium and strontium nitrates are dissolved in water, and separated by precipitating the barium as chromate. For complete table of separation, see p. 178. NOTE. After the ammonium carbonate has been added, the mixture should not be boiled, because, as there is excess of ammonium chloride in the solution from the previous group, the t Instead of filter paper it is better to use a wad of asbestos. The Barium Group. 93 calcium carbonate will be partially decomposed, owing to the reaction being reversible. (NH 4 ) 2 CO 3 + CaCl 2 ^CaCO 3 -f 2NH 4 C1 On the other hand, it is better to have the solution hot before adding the ammonium carbonate, because the solution of ammo- nium carbonate in the laboratory generally contains bicarbonate, which gives rise to the soluble bicarbonates of the metals of this group. Warming decomposes these bicarbonates into normal carbonates, water, and carbon dioxide. S r ci 2 + 2 NH 4 HC0 3 ->Sr(HC0 3 ) 2 + 2 NH 4 Cl->SrCO 3 + H 2 O On warming. +C0 2 +2NH 4 C1 II. To the hot ammoniacal solution of the three metals, add a slight excess of ammonium carbonate and allow to stand for ten minutes. Filter off the carbonates and wash with a little water. Now dissolve the carbonates off the filter paper with the least possible quantity of acetic acid. Add excess of K 2 CrO 4 to the solution, a yellow precipitate of barium ehromate is produced. Filter off, and make the solution just alkaline with ammonium hydroxide and add ammonium carbonate, allow to stand a few minutes and filter. Dissolve the carbonates in a little dilute nitric acid. Evaporate to complete dryness on the water bath. Treat the residue with a little absolute alcohol, stir for a minute or two, and filter. Wash the residue on the filter paper with a little alcohol. The residue is strontium nitrate, the solution contains calcium nitrate. The complete table of separations will be found on p. 179. It is interesting to note that the salts of the metals of this group which are deliquescent are soluble in absolute alcohol, those which are not are insoluble. CHAPTER VIIT. THE SODIUM GROUP. THIS group includes, besides the metals potassium, sodium, lithium, and magnesium, the compound cation ammonium NH 4 . The hydroxides of the first three metals are very largely dissociated in solution into the ions R and OH ; they are, there- fore, extremely strong bases. They are not precipitated by ordi- nary reagents, because they form soluble salts; for this reason, the group of the alkali metals remains in solution to the last. Magnesium does not really belong to the alkali group it should, strictly speaking, be classed with the alkaline earths ; but, for con- venience of analysis, it is placed in this group. Ammonia, when dissolved in water, exists partly as NH 4 OH ; and, as this is only slightly ionised, ammonium hydroxide is a much weaker base than potassium, sodium, or lithium hydroxides, Potassium. The majority of potassium salts are readily soluble in water, and many of them have a strong alkaline reaction, owing to hydrolysis, as, for example, cyanide, borate, and silicate. Dry Reaction. Flame Test. Potassium compounds impart a violet coloration to the Bunsen flame. The presence of sodium masks the colour reaction, but on looking at the flame through a piece of blue glass or an indigo prism, the yellow rays emitted by the sodium are cut off, and only those due to the potassium, appearing now as a violet-red, are discernible. The Sodium Group. 95 Wheri viewed through the spectroscope, a characteristic red line and an indigo-blue line are seen. Reactions in Solution. Use a solution of potassium chloride or nitrate. *i. Hydrogen platinichloride gives, from neutral or acid solutions, a golden-yellow crystalline precipitate of potassium platinichloride, insoluble in alcohol, but soluble in caustic potash. 2 KC1 + HoPtCle = K 2 PtCI 6 + 2HC1 This test should be done on a watch glass. A few drops of hydrogen platinichloride are added to a solution of the potassium salt which has been made slightly acid with hydrochloric acid. If the solution is very dilute, the precipitation will be hastened by adding a little alcohol and scratching with a glass rod. *2. Sodium hydrogen tartrate or tartaric acid produces, in solutions which are not too dilute, a white crystalline precipitate of potassium hydrogen tartrate. CH(OH)COONa CH(OH)COOK KC1 + | =| + NaCl CH(OH)COOH CH(OH)COOH The precipitation is accelerated by rubbing the sides of the tube with a glass rod, and by the addition of alcohol. If any mineral acid is present, addition of sodium acetate facilitates precipitation. *3. Sodium cobaltini trite gives, from solutions which have been strongly acidified with acetic acid, a brilliant yellow precipitate of potassium cobaltinitrite. The reaction may be carried out as follows : Add to the solution to be tested about 2 c.c. of a 5 per cent, solution of cobalt nitrate, and about an equal volume of a fairly strong solution of sodium nitrite, then excess of glacial acetic acid, and about one-third its volume of alcohol. Either at once, or on shaking, a bright yellow precipi- tate is produced. The reaction is more readily carried out, and is more delicate, by dissolving about \ gram of the solid sodium g6 Qualitative Chemical Analysis. cobaltinitrite (p. 298) in about 2 c.c. of water, and adding the solution to be tested, and about an equal volume of alcohol. 3 KN0 3 + Na 3 Co(N0 2 ) 6 = K 3 Co(NO 2 ) 6 + 3 NaNO 3 4. Hydrofluosilicic acid produces a white gelatinous preci- pitate of potassium silicofluoride. H 2 SiF 6 + 2KC1 = K 2 SiF 6 + 2 HC1 5. Sodium thiosulphate and bismuth (Carnot's reaction). Add a drop or two of a dilute solution of bismuth nitrate to i to 2 c.c. of a solution of sodium thiosulphate, and then about four times the volume of absolute alcohol (if the solution is not clear a few drops of water may be added). On now adding a few drops of potassium salt a yellow precipitate of potassium bismuth thiosulphate is produced. (i.) Bi(N0 3 ) 3 + 3 Na 2 S 2 3 = Na 3 Bi(S 2 O 3 ) 3 + 3NaNO 3 (2.) Na,Bi(S a O,), + 3KN0 3 = K 3 Bi(S 2 O 3 ) 3 In presence of ammonium chloride this reaction does not take place. Sodium. Dry Reaction. Flame Reaction. Sodium compounds, even in extremely minute quantities, colour the flame of the Bunsen burner a brilliant golden yellow. On viewing the flame through an indigo prism or a piece of blue glass, it appears colourless. When seen through the spectroscope, a single yellow line is visible. Reactions in Solution. Use a solution of sodium chloride. Owing to the fact that all sodium salts are soluble in water, it is usual to prove the presence of sodium by the flame reaction, having first shown that all other elements are absent. i. Hydrogen platinichloride gives no precipitate with sodium salts even on addition of alcohol, because the sodium The Sodium Group. 97 platinichloride is soluble both in alcohol and water. On carefully evaporating almost to dryness, however, small triclinic prisms are obtained, whereas those of potassium platinichloride are octahedra. By means of a low power microscope the two salts can readily be distinguished when they are obtained together. *2. Potassium pyroantimonate gives from neutral solutions a white crystalline precipitate of sodium pyroantimonate. Precipitation is facilitated by shaking and rubbing the sides of the test tube. K 2 H 2 Sb 2 7 + 2NaCl = Na a H 2 Sb 2 O 7 + 2KC1 It is decomposed by acids, with formation of metantimonic acid, HSbO 3 Na 2 H 2 Sb 2 O 7 + 2HC1 = 2HSbO 3 + 2NaCl +H 2 O There is considerable contradiction in the literature about the soluble salt usually called potassium pyroantimonate. It would appear, at any rate when the salt is freshly prepared, that it is really potassium metantimonate. The fact that when freshly precipitated the sodium salt is of a rather gelatinous character, only gradually becoming granular, points to the precipitation of sodium metantimonate which gradually passes into the granular pyroantimonate. (i.) KSbO 3 + NaCl = NaSbO 3 + KC1 (ii.) 2NaSbO 3 + H 2 O = Ammonium. Nearly all the salts of ammonium are soluble in water. Dry Reaction. Many compounds of ammonium are volatile when heated, condensing again unchanged on the cool portions of the tube. Some compounds, such as the phosphate, lose H 98 Qualitative Chemical Analysis. ammonia when they are heated ; the presence of the ammonia is readily detected by the smell. (NH 4 ) 2 HPO 4 = 2NH 3 + HPO 3 + H 2 O Metaphosphoric acid. Reactions in Solution. Use a solution of ammonium chloride. *i. Hydrogen Platinichloride gives a golden yellow crystalline precipitate of ammonium platinichloride. 2 NH 4 C1 + H 2 PtCl 6 = (NH 4 ) 2 PtCl 6 + 2HC1 On igniting this salt it is decomposed, ammonium chloride being volatilised, and a grey residue of platinum remaining behind. When the similar compound of potassium is ignited, a residue of platinum mixed with potassium chloride is obtained. *2. All ammonium compounds when boiled with a solution of caustic alkali evolve ammonia which may be recognised by its smell, and by colouring red litmus paper blue, or turmeric paper brown. It also turns a piece of filter paper soaked in a solution of mercurous nitrate black. NH 4 N0 3 + KOH = NH 3 + KNO 3 + H 2 O 3. Nessler's reagent (p. 328) gives a brown precipitate; even with excessively dilute solutions a yellowish-brown coloration is produced. The precipitate or coloration is due to formation of oxydimercuric ammonium iodide. This test is too delicate for ordinary analysis, but is employed in water analysis. The precipitate is soluble in excess of ammonium salts. *4. Sodium cobaltinitrite gives a yellow precipitate of ammonium cobaltinitrite (NH 4 ) 3 Co(NO 2 ) 6 . (Cf. 3, P- 95-) The Sodium Group. 99 Lithium. Most lithium compounds are soluble in water. Lithium chloride is soluble in amyl alcohol and in a mixture of alcohol and ether. Dry Reactions. Flame Reaction. Compounds of lithium colour the flame of the Bunsen burner a carmine red. On viewing through a thick piece of blue glass or an indigo prism, the flame appears colourless. Seen through the spectroscope, a bright crimson red line and a more feeble orange are visible. Reactions in Solution. Use a solution of lithium chloride. *i. Sodium phosphate gives on warming a white crystalline precipitate of lithium phosphate. The precipitation is more complete if the solution is first made strongly alkaline with sodium hydroxide. 3 LiCl + Na 2 HP0 4 = Li 8 P0 4 + 2NaCl + HC1 In presence of ammonium salts no precipitate is formed. *2. Alkali carbonates produce from concentrated solution a white precipitate of lithium carbonate. 2LiCl + Na 2 CO 3 = Li 2 CO 3 + 2NaCl Magnesium. Metallic magnesium is very readily soluble in dilute mineral acids. When exposed to the air it gradually becomes coated with a thin film of oxide. The metal is insoluble in caustic alkalis, but dissolves readily in solutions of ammonium salts with evolution of hydrogen. Mg + (NH 4 ) 2 S0 4 = MgS0 4 + 2NH 3 + H 2 Dry Reactions. Blowpipe Test. Heated on charcoal before the blowpipe compounds of magnesium become incandescent. Filter Ash Test. If a piece of filter paper is moistened with ioo Qualitative Chemical Analysis. a salt of magnesium and a drop or two of cobalt nitrate, then dried and ignited, the ash assumes a pink tinge. Reactions in Solution. Use a solution of magnesium sulphate. 1. Sodium or potassium carbonate gives a white pre- cipitate of basic magnesium carbonate. 4MgCl 2 + 4Na 2 CO 3 + H 2 O = 3MgCO 3 ,Mg(OH) 2 + CO 2 + SNaCl The precipitation is more complete on boiling. No precipitate is formed in presence of ammonium salts. 3 M g C0 8 ,Mg(OH) 2 + 8NH 4 C1 = 4 MgCl 2 + 3 (NH 4 ) 2 C0 3 + 2NH 3 + 2H 2 O 2. Ammonium carbonate produces no immediate precipita- tion, but after some time separation of crystalline ammonium magnesium carbonate takes place. In presence of ammo- nium salts this separation does not take place. MgS0 4 + 2(NH 4 ) 2 C0 3 = Mg(NH 4 ) 2 (C0 3 ) 2 + (NH 4 ) 2 SO 4 *3- Ammonium hydroxide forms a white gelatinous precipitate of magnesium hydroxide. The well-washed precipitate is slightly soluble in pure water, and turns red litmus blue. Presence of ammonium salts prevent precipitation, hence the use of ammonium chloride before adding ammonium hydroxide in precipitation of metals of the iron group. MgS0 4 + 2NH 4 OH = Mg(OH) 2 + (NH 4 ) 2 S0 4 *4. Sodium phosphate produces a white amorphous preci- pitate of magnesium hydrogen phosphate. MgCl a + Na 2 HP0 4 = MgHP0 4 + 2 NaCl In presence of ammonium chloride and hydroxide (the ammonium chloride being added to prevent precipitation of mag- nesium hydroxide by the ammonium hydroxide) a crystalline precipitate of magnesium ammonium phosphate is produced. MgS0 4 + Na 2 HP0 4 + NH 4 OH = Mg(NH 4 )PO 4 + Na 2 SO 4 + H 2 O The Sodium Group. 101 This precipitate is almost insoluble in water containing am- monium hydroxide. From very dilute solutions the preci- pitate only comes down slowly ; its precipitation is facilitated by scratching the sides of the test tube with a glass rod. The explanation of the prevention of precipitation by ammo- nium salts is as follows : The magnesium hydroxide is slightly soluble in water and is partially dissociated into Mg" and 2OH' ions. On addition of ammonium chloride, which is strongly ionised into NH 4 and Cl' ions, the OH' ions are taken up by the NH 4 ions to produce un-ionised or very feebly ionised NH 4 OH (or NH 3 + H 2 O). Hydroxyl ions therefore disappear, and equili- brium is destroyed. Therefore more Mg(OH) 2 goes into solution in order to supply more OH' ions, which in turn are taken up by the NH 4 , and if sufficient ammonium salt is present this will go on until the whole of the magnesium hydroxide has gone into solution. Addition of an excess of hydroxyl ions by adding a highly ionised base such as KOH, causes a reprecipitation of magnesium hydroxide. In analysis the ammonium salt is added first, because, as already stated, ammonium hydroxide is very slightly dissociated in solution, but still sufficiently to cause partial precipitation (see 3, p. 100). It is, however, very much less ionised in presence of its salts. Therefore, if a salt of ammonium is first added, the concentration of the hydroxyl ions of the now very feebly dissociated ammonium hydroxide is not sufficient to cause precipitation of magnesium hydroxide. Separation of the Metals Potassium, Sodium, and I' Magnesium. In testing qualitatively for these metals, it is not usual to separate magnesium from potassium and sodium, but to divide the solution obtained from the previous groups into two portions. To the first and smaller portion a solution of sodium phos- phate or of microcosmic salt along with excess of ammonium hydroxide is added, the mixture is thoroughly agitated, and the sides of the test tube are scratched with a glass rod. The magnesium IO2 Qualitative Chemical Analysis. is precipitated as crystalline magnesium ammonium phos- phate, Mg(NH 4 )PO 4 . The second and larger portion is evaporated to dryness, and ignited strongly, until no more fumes of ammonium salts are given off. It is then cooled and dissolved in a small quantity of water, and acidified with two or three drops of hydrochloric acid. To the acid solution excess of hydrogen platinichloride is added, and it is evaporated on a water bath to a very small bulk (nearly to dryness). A few drops of this solution may be tested for potassium, by Carnot's reaction ( 5, p. 96). Alcohol is now added (about 5-6 c.c.) ; this dissolves the sodium platini- chloride, also that of lithium, should this metal be present. The potassium salt is insoluble in alcohol, and may be filtered off and washed with a little alcohol. The potassium may be recog- nised by means of the flame test or spectroscope. The solution is evaporated to dryness, and the residue tested for sodium by means of the flame test or examined under the microscope. Fuller methods of separation will be found on p. 179. NOTE. It is a matter of the utmost importance that the whole of the ammonium salts should be volatilised, because ammonium salts also give an insoluble platinichloride. It is not unusual for students to imagine that they have discovered potassium in the substance they are examining, whereas the supposed potassium platinichloride is ammonium platinichloride, and is simply a result of careless working. Again, students, through careless manipulation, often do not find potassium when it really is present. This is traceable to imperfect washing of precipitates and non-reser- vation of the washings, and also to the fact that, on evaporating to dryness previous to the elimination of the ammonium salts, the evaporation is conducted in such a manner that most of the salts are lost by spirting out of the dish. This is easily prevented if, as soon as the concentration of the solution has become so great that further heating on the sand bath causes spirting, the evaporating basin is placed on a water bath until quite dry. It may then be ignited without danger of loss by spirting. Let the student bear in mind that a little extra time spent over an The Sodium Group. 103 operation in order to insure accuracy is not lost. Much more time is lost by having to go through the whole analysis again. If it is desired to remove the magnesium, this may be done by evaporating the whole of the solution from the barium group to dryness, and igniting to get rid of the ammonium salts. The residue is then dissolved in water, and barium hydroxide solution added till an alkaline reaction is obtained. The mixture is then boiled, and the magnesium hydroxide filtered off. The excess of barium hydroxide is got rid of by adding ammonium hydroxide and carbonate, boiling and filtering. The solution is examined for potassium and sodium as above, after evaporating and igniting to get rid of the ammonium salts. Test for the Ammonium Radical. As, during the course of analysis, ammonium salts have been repeatedly added, ammonium cannot be here tested for ; but a small portion of the original substance is boiled with caustic soda, the ammonia is liberated, and can be recognised by its smell and by its turning moist red litmus paper blue, or turmeric paper brown, or by blackening filter paper moistened with mercurous nitrate. CHAPTER IX. THE ACIDS. THE acids are electrolytes which contain the cation H', which is replaceable by metals with formation of salts. Acids are strong or weak according to whether they are dissociated to a large or small extent. The strong acids are sulphuric and nitric acids, the halogen acids (with the exception of hydrofluoric acid), chloric acid, and a few others. Among those which are only ionised to a medium extent, and are therefore only moderately strong, are phosphoric, sulphurous, etc., and many of the organic acids such as formic and acetic acids. The acids which are only very slightly ionised are hydrogen sul- phide, hydrocyanic, carbonic, silicic and boric acids. These are weak acids, and are incapable of forming neutral salts with the strong bases, their salts with the strong bases all having an alkaline reaction owing to hydrolytic dissociation. Acids which are weak or only moderately strong have a much feebler action in the presence of neutral salts containing the same anion. Thus, e.g. acetic acid, which is classed with the moderately strong acids, is a very weak acid in presence of sodium acetate, because the ionisation of the acetic acid is lowered. Grouping of the Acids. To arrange a separation for the acid radicals (anions) which will be as thorough and reliable as the methods employed in separating the metallic or basic radicals (cations) is not prac- ticable. Nevertheless, it is possible to place the anions into groups, according to their behaviour with such reagents as silver The Acids. 105 nitrate and barium chloride, and by this means an approxi- mate separation can be made. According to this arrangement the acids fall into five groups. Group I. Silver nitrate produces a white precipitate, insoluble in nitric acid. Barium chloride produces no precipitate. This group includes HC1, HBr, HI (light yellow),t HCN, H 4 Fe(CN) 6 , H 3 Fe(CN) 6 (orange yellow), HC1O, HCNS. Group. II. Silver nitrate produces a precipitate, soluble in nitric acid. Barium chloride produces no precipitate. This group includes HNO 2 , H 2 S (black), H 3 PO 2 , H 2 SO 3) H 2 S 2 O 8 (black). Group III. Silver nitrate produces a precipitate soluble in nitric acid. Barium chloride produces a white precipitate, soluble in nitric acid. This group includes H 3 PO 4 (yellow), HPO 3 , H 3 PO 3 , H 4 P 2 O 7 , H 2 S 2 O 3 (brown), H 3 BO 3 , H 3 AsO 3 (yellow), H 3 AsO 4 (chocolate), H 2 CrO 4 (red), H 2 SiO 3 (orange), HIO 3 (difficultly soluble in HNO 3 ), H 2 C0 3 . Group IV. Barium chloride produces a white pre- cipitate, insoluble in acids. Silver nitrate produces no precipitate. This group includes H 2 SO 4 , HF. V Group V. Barium chloride produces no precipitate. Silver nitrate produces no precipitate. This group includes HNO 3 , HC1O 3 , HC1O 4 , HMnO 4 . NOTE. It must be remembered that silver nitrate gives a brown precipitate of silver oxide from alkaline solutions of hydroxides. As far as possible the acids in the succeeding pages have been f Colours refer to the silver precipitates which are white unless otherwise stated. io6 Qualitative Chemical Analysis. arranged according to the above grouping. But in certain cases for studying the reactions of the acids it is more convenient to slightly vary this arrangement. Thus, for example, in the grouping of the acids, sulphuric acid occurs in Group IV., and sulphurous acid in Group II. But for studying the reactions, sulphuric and sulphurous acid have been placed together. Hydrochloric Acid. HCl All chlorides, except silver, mercurous, and lead chlorides, are soluble in water. Chlorides of bismuth, tin, and antimony are only soluble in water containing free hydrochloric acid. i. Most chlorides, when warmed with concentrated sulphuric acid, give off fumes of hydrochloric acid. (a.) 2KC1 + H 2 S0 4 = K 2 S0 4 + (b.) MnCl 2 + H 2 SO 4 = MnSO 4 + 2HC1 *2. Silver nitrate forms a white curdy precipitate of silver chloride. NaCl + AgNO 3 = AgCl + NaNO 3 When exposed to light it gradually turns violet, and, finally, black. It is insoluble in nitric acid, but readily soluble in ammo- nium hydroxide, potassium cyanide, and in sodium thiosulphate. (Cf. Silver, p. 28.) *3. Lead acetate gives a white crystalline precipitate of lead chloride, soluble in boiling water, from which it crystallises again on cooling. 2 KC1 + (CH 3 COO) 2 Pb = PbCl 2 + 2 CH 3 COOK 4. On mixing a chloride with manganese dioxide, adding concentrated sulphuric acid, and gently warming, chlorine gas is liberated, which may be recognised by its yellow colour, by its The Acids. 107 smell, and by its bleaching a strip of moist litmus paper held in the mouth of the tube. 2 NaCl + MnO 3 + 2H 2 SO 4 = Na. 2 SO 4 + MnSO 4 + 2H 2 O + C1 2 *5. When a dry chloride is mixed with an excess of potassium dichromate and a few cubic centimetres of concentrated sulphuric acid, and then distilled from a small distilling flask, chromyl chloride is formed, which condenses in the receiver as a heavy brownish-red fuming liquid. 4NaCl + K,Cr,O, = 2CrO 3 Cl 3 + aNaaSO* + K^SO, + 3H 2 O The chromyl chloride dissolves in water, forming a yellow solu- tion of chromic acid, which, on addition of ammonium hydroxide or caustic soda, is converted into ammonium or sodium chromate. Cr0 2 Cl 2 + 4NH 4 OH = 2 NH 4 C1 + (NH 4 ) 2 CrO 4 + 2 H 2 O On now acidifying with acetic acid, and adding lead acetate, a yellow precipitate of lead chromate is produced. Bromine, if it were present, would dissolve in the ammonium hydroxide, form- ing a colourless solution, and on the addition of lead acetate no yellow precipitate would be produced. If, however, the bromine was there in considerable quantity, a white precipitate of PbBr 2 might be produced, soluble in boiling water. Hydrobromic Acid. HBr Bromides, with the exception of those of silver, mercury, lead, bismuth, antimony, and tin, are soluble in water. *i. Silver nitrate gives a very pale yellow precipitate of silver bromide, which is insoluble in nitric acid, and soluble, with difficulty, in ammonia; it is, however, readily soluble in potassium cyanide. NaBr + AgNO, = AgBr + NaNO 3 io8 Qualitative Chemical Analysis. 2. Lead acetate precipitates white crystalline lead bromide, almost insoluble in cold water, but fairly readily soluble on boiling. 2 KBr + (CH 3 COO) 2 Pb = PbBr a + 2 CH 3 COOK *3. Concentrated sulphuric acid liberates a portion of the bromine from a bromide, a portion escapes as hydrobromic acid. (a.) 2KBr + H 2 SO 4 = 2HBr + K 2 SO 4 (J.) 2 HBr + H 2 SO 4 = 2H 2 O + SO 2 + Br 2 *4. When a mixture of a bromide and manganese dioxide is heated with concentrated sulphuric acid, free bromine is obtained, recognised by its heavy brown vapour and unpleasant odour. In this case the whole of the bromine is liberated. 2KBr + MnO a + 2H 2 SO 4 = Br a + K 2 SO 4 + MnSO 4 + 2H 2 O *5 Chlorine water, when added drop by drop to a solution of a bromide, liberates bromine, which colours the liquid brown. 2 KBr + C1 2 = 2KC1 + Br 2 On shaking the solution with chloroform or carbon disulphide, the bromine dissolves, forming a coloured layer. On addition of a further quantity of chlorine water, the brown colour gradually disappears, owing to the formation of colourless bromic acid. Br + 5C1 + 3H 2 = HBrO 3 + 5HC1 Hydriodic Acid. HI Nearly all the iodides are soluble in water, but many of them only with difficulty. With the exception of silver iodide, they are all soluble in acids. *i. Silver nitrate gives a heavy, curdy light yellow precipi- tate of silver iodide. KI + AgN0 8 = Agl + KN0 8 The Adds. 109 It is insoluble in nitric acid and in ammonium hydroxide, but soluble in potassium cyanide and in sodium thiosulphate. 2. Lead acetate produces a yellow crystalline precipitate of lead iodide, soluble in boiling water, from which it recrystallises in shiny glistening leaflets. 2 KI + (CH 8 COO) 2 Pb = PbI 2 + 2 CH 3 COOK *3. Mercuric chloride forms a yellow precipitate of mer- curic iodide, which immediately changes to deep red. (Cf. Mer- cury, p. 36.) The precipitate is soluble in excess of mercuric chloride, and also in excess of potassium iodide. 2KI + HgQ 2 = Hgl a + 2 KC1 4. Concentrated sulphuric acid decomposes iodides, a portion being liberated as free iodine. (a.) 2KI + H 2 SO 4 = K 2 SO 4 + 2HI (b.) 2HI + H 2 S0 4 = I 2 + SO 2 + 2H 2 The reaction appears to take place partially in the following manner, the sulphuric acid being still further reduced. SHI + H 2 SO 4 = H^ + 4H 2 O + 4X2 5. Concentrated sulphuric acid and manganese dioxide liberate iodine, 2KI + MnO 2 + 2H 2 SO 4 = MnSO 4 + I 2 + K 2 SO 4 + 2H 2 O The iodine may be distilled, when it passes over as violet vapours, crystallising on the cool portions of the receiver in small shining crystals. *6. Chlorine water, or a solution of bleaching powder, when added drop by drop to a solution of an iodide, liberates iodine. The presence of the liberated iodine can be made manifest, even if the quantity is extremely small, by adding a few drops of starch paste, when the deep blue coloration of iodide of starch is produced. Iodine is more soluble in chloroform and carbon disulphide no Qualitative Chemical Analysis. than in water. If 2 c.c. of either of these solvents be added to the solution containing free iodine, and the mixture be shaken up, the solvent dissolves the iodine, forming a violet layer at the bottom of the test tube. Excess of chlorine water causes the coloration to disappear, owing to the iodine being converted into iodic acid. I + 3H 2 + 5d= HI0 3 + 5HC1 *7. A very delicate test for iodine may be carried out as follows : Acidify the solution with dilute sulphuric acid, and add a few drops of starch paste, then a small scrap of zinc, and one drop of nitric acid. Iodine will be liberated and cause a deep blue coloration of the starch. When sulphuric acid is added to an iodide, hydriodic acid is produced, which of itself does not colour starch. But on addition of zinc and nitric acid, the hydrogen evolved by the action of the zinc on the sulphuric acid reduces the nitric acid to nitrous acid (p. 127), and this, acting on the hydriodic acid, liberates iodine, which with the starch forms blue " iodide of starch." HNO 3 -I- 2H = HNO 2 + H a O Detection of Chloride, Bromide, and Iodide. Owing to these three substances forming insoluble silver salts, they are all precipitated on adding silver nitrate to a solution which has been acidified with nitric acid. a. Silver iodide may be separated from silver chloride and bromide, owing to its insolubility in ammonia ; whereas the others readily dissolve in warm ammonium hydroxide. b. A bromide and iodide may readily be detected when they occur together by carefully adding chlorine water to the dilute neutral solution, and shaking up with about 2 c.c. of carbon disulphide or chloroform. The chlorine first liberates the iodine, which dissolves in the lower layer of chloroform or carbon disulphide, forming a violet solution. The upper aqueous solution may now be decanted or removed with a pipette into another test tube, containing a little chloroform, and chlorine again added. If The Acids. in the whole of the iodine has already been liberated, the further addition of chlorine water will now liberate bromine, and the chloroform will become brown. In the event of the iodine not having been entirely liberated in the first instance, the chloroform will become coloured violet, but on adding more chlorine water the violet colour will gradually fade away ( 6, p. 109), and the brown due to the bromine will take its place. Further addition of chlorine water will finally cause the brown colour of the bromine to vanish. Instead of using chlorine water, add to the neutral solution a solution of bleaching powder : \ this liberates the iodine from the iodide, but has no action on the bromide. Extract the iodine from the solution with chloroform or carbon disulphide ; add a little more bleaching powder, and, if a further quantity of iodine is liberated, again extract. As soon as all the iodine has been got rid of, pour off the colourless aqueous solution, and add a drop of acetic acid. The acid liberates chlorine from the calcium hypo- chlorite, which then reacts with the bromide, liberating bromine. On now shaking with chloroform, the bromine dissolves in this solvent with formation of a brown solution at the bottom of the aqueous layer. If no bromine is present, the liquid will be coloured yellow, owing to liberation of chlorine, but, when shaken up with chloroform or carbon disulphide, both the lower layer and the upper aqueous layer take on nearly the same yellow tint; whereas, when bromine is present, the lower layer becomes a more or less intense brown, the upper one being either light yellow or colourless. It is, of course, necessary to test a separate portion of the mixture for chlorine. This is best done by taking a little of the solid substance and distilling it with potassium diehromate and concentrated sulphuric acid, when chromyl chloride will distil over. (Cf. 5, p. 107.) The distillate maybe made alkaline with ammonia, acidified with dilute sulphuric acid, and tested for t Only a very small quantity of bleaching powder should be added in the first place, because, if there is very little iodine, the excess of bleaching powder almost immediately oxidises it to iodic acid. 112 Qualitative Chemical Analysis. a chromate with hydrogen peroxide, or acidified with acetic acid and lead acetate added. c. Separation of Iodine as Cuprous Iodide. Saturate the solution with sulphur dioxide, or add 2 or 3 c.c. of a strong solution of sulphurous acid. Now add excess of copper sulphate, when the iodine will be precipitated as cuprous iodide. After filtering, boil the solution till free from sulphurous acid, and divide into two portions. Test one portion for bromine, by the addition of chlorine water in presence of carbon disulphide. Evaporate the second portion to dryness, and apply the chromyl chloride test. As a matter of fact, cuprous iodide is actually precipitated by the addition of copper sulphate to a solution of potassium iodide, thus 2CuSO 4 + 4KI = CujLj +2K 2 SO 4 + I 2 Probably, in the first place, cupric iodide is formed, which is almost immediately converted into cuprous iodide with liberation of iodine-t 2Cu" + 4l'~iCu 2 I 2 -f I 2 The reaction, however, is never complete, a certain quantity of copper always remaining in solution, a balanced condition being produced, as shown in the equation. The addition of SO 2 removes one of the reaction products the liberated iodine. The equilibrium balance thus being destroyed, the reaction is enabled to complete itself. Detection of Chloride, Bromide, and Iodide in Pre- sence of Cyanides. Cyanides give a white curdy precipitate with silver nitrate, which is almost identical in appearance, solubility, and general chemical reactions with silver chloride. If, in the preliminary tests, the presence of a cyanide has been dis- covered, it is better to remove it before testing for the halogens. t The reduction may be supposed to take place by the cupric ions losing one of their + charges, the charge becoming neutralised with the charge of an iodine ion. Insoluble cuprous iodide is then produced from the union of the partially discharged copper ions with other iodine ions. The Acids. 113 This may be done by boiling the solution with dilute (i.) nitric acid ; by passing (ii.) carbonic acid gas through the solution, and then boiling; or (iil) by boiling with excess of sodium bicarbonate. The operation must be conducted in a draught cupboard. If it has been precipitated along with the halogens, it may be removed by (a) boiling with strong nitric acid, (b) fusing the mixed silver salts, when silver cyanide will be decomposed, cyanogen being evolved and silver remaining. Hypochlorous Acid. HC1O This acid is only known in aqueous solution, and in the form of its salts. When a solution of an alkali hypochlorite is boiled it is converted into a chloride and a chlorate ; e.g. 3NaClO = 2NaCl + NaClO 3 *i. On treating a hypochlorite with dilute sulphuric or hydrochloric acid, chlorine gas is evolved. NaCIO + 2HC1 = C1 2 + H 2 + NaCl 4NaClO + 2H 2 SO 4 = 2C1 2 + 2Na.,SO 4 + 2H 2 O + O 2 2. Silver nitrate, when added to a solution of a hypochlorite which has been neutralised with dilute nitric acid, gives a white precipitate of silver chloride. The silver hypochlorite which is first produced being converted into silver chloride and chlorate. This change is more rapid and complete on boiling. (a.) NaCIO + AgNO 3 = AgCIO + NaNO 3 (b.) sAgCIO = 2 AgQ + AgC10 3 *3. Lead acetate produces a white crystalline precipitate of lead chloride, which, in the cold, gradually becomes orange yellow, and finally brown, owing to its being converted into lead peroxide. These changes take place rapidly on boiling. *4. When shaken up with mercury, hypochlorous acid or a i H4 Qualitative Chemical Analysis. slightly acidified solution of a hypochlorite covers the surface of the mercury with a yellow or brown scum of oxide of mercury or mercuric oxychloride. The scum or precipitate, when separated from the mercury, dissolves in warm dilute hydrochloric acid, the solution giving the reactions for mercury. 2HC10 + 2Hg = HgO,HgQ 2 + H 2 This reaction serves to distinguish hypochlorous acid from chlorine. A solution of chlorine when shaken up with mercury forms an insoluble precipitate of white mercurous chloride, which is also insoluble in warm dilute hydrochloric acid. If, there- fore, the precipitate formed by shaking hypochlorous acid and chlorine with mercury be warmed with dilute hydrochloric acid, the brownish part of it will dissolve, leaving unchanged the white mercurous chloride : the presence of hypochlorous acid is confirmed by finding mercury in the solution. Hydrocyanic Acid (Prussic Acid). HCN Hydrocyanic acid is an exceedingly weak acid, being very feebly dissociated in solution ; therefore, owing to hydrolysis, the alkali salts have a strongly alkaline reaction. The salts and solutions of the alkali cyanides possess a strong smell of hydro- cyanic acid, because in solution they are hydrolysed thus K' CN' K* OH' H' OH' HCN (not dissociated) The hydrocyanic acid not being to any extent dissociated, is there as such, hence the smell this also explains the alkalinity because as the H" ions are taken up by the CN' to form un- dissociated HCN, hydroxyl ions become free. The solution, therefore, contains undissociated HCN and K* and OH' ions. The cyanides of the alkali metals and alkaline earths are The Acids. 115 soluble in water ; the cyanides of the metals other than these are insoluble, but are decomposed by dilute acids with evolution of hydrocyanic acid. Most of the insoluble cyanides dissolve in a solution of potassium cyanide, forming soluble salts, e.g. KAg(CN) 2 , from which the metal cannot be precipitated by ordinary reagents, because it is in the anion Ag(CN)/. Dry Reactions. The alkali cyanides are not decomposed on heating, but silver and mercury cyanide yield cyanogen, which can be recognised by its burning with a pink flame, and by its unpleasant smell. (Caution, the gas is very poisonous.) Hg(CN) a = (CN) 2 + Hg Ferrous cyanide, on ignition, gives iron carbide and nitrogen. Fe(CN) 2 = FeC a + N Wet Reactions. Use a solution of potassium cyanide. *i. Hydrochloric acid decomposes most soluble cyanides in the cold with evolution of hydrocyanic acid, but those of the heavy metals are only decomposed on heating. KCN + HC1 = HCN + KC1 Hydrocyanic acid is extremely poisonous^ and the greatest care must be taken when working with it. *2. Silver nitrate produces a white, curdy precipitate of silver cyanide. KCN + AgN0 3 =AgCN + KNO 8 On adding small quantities of silver nitrate to a solution of potassium cyanide, the precipitate dissolves as soon as it is formed, owing to the solubility of silver cyanide in potassium cyanide. The precipitation, therefore, is only complete when the silver nitrate is added in excess. AgCN + KCN = KAg(CN) 2 Silver cyanide is also readily soluble in ammonium hydroxide. It is decomposed on ignition with evolution of cyanogen, a residue Ii6 Qualitative Chemical Analysis. of silver remaining. When boiled with concentrated nitric acid it also suffers decomposition (distinction from silver chloride). *3. Add a few drops of yellow ammonium sulphide to a few drops of a solution of a cyanide, and evaporate to dryness on the water bath ; then moisten the residue with dilute hydrochloric acid and a few drops of water, and again evaporate, nearly to dryness. On now adding ferric chloride, a blood-red coloration will be produced, owing to the formation of ferric thiocyanate. Ammonium thiocyanate is, in the first place, produced by the action of the ammonium sulphide on the cyanide. (1) NH 4 CN + (NH 4 ) 2 S 2 = NH 4 CNS + (NH 4 ) 2 S (2) 3 NH 4 CNS + FeCl 3 = Fe(CNS) 3 + 3NH 4 C1 *4. When a mixture of a cyanide with caustic alkali and ferrous sulphate, to which a few drops of ferric chloride have been added, is boiled, and then acidified with hydrochloric acid, a deep blue precipitate of " Prussian blue " is obtained. If the quantity of cyanide is very small a blue coloration only is produced. (1) Fe(OH) 2 + 6KCN = K 4 Fe(CN) 6 + 2 KOH (2) 4 FeCl 3 + 3 K 4 Fe(CN) 6 = Fe 4 [Fe(CN)J 3 + 1 2KC1 *5. To a mixture of a cyanide with ten to fifteen drops of a mixture of sodium nitrate and ferric chloride solutions dilute sulphuric acid is added until a yellow coloration is pro- duced. The mixture is gently warmed, then cooled, and the excess of ferric salt removed by the addition of ammonium hydroxide and filtration. On adding a drop of ammonium sulphide to the filtrate, a violet coloration is produced. The reaction is due to the formation of sodium nitroprusside. (Cf. 3, p. 132.) Hydroferrocyanic Acid. H 4 Fe(CN) 6 The ferrocyanides of the alkali metals are soluble in water, those of the alkaline earths difficultly soluble ; most of the other ferrocyanides are insoluble in water and dilute acids. The Acids. 117 i. When a ferrocyanide is heated with concentrated sul- phuric acid, carbon monoxide is evolved. K 4 Fe(CN) 6 + 6H2SO 4 + 6H 2 O = 6CO + 2K 2 SO 4 + FeSO 4 + 3(NH 4 ) 2 S0 4 2. On heating with dilute sulphuric acid, hydrocyanic acid is produced. 4 = K 2 Fe[Fe(CN)J + 3 K 2 SO 4 + 6HCN 3. Silver nitrate produces from freshly prepared solutions a white precipitate of silver ferrocyanide, which is insoluble in ammonium hydrate, but soluble in potassium cyanide. K 4 Fe(CN) a + 4AgNO, = Ag 4 Fe(CN) 6 + 4 KNO 3 From solutions which have been prepared for some time the precipitate may be flesh coloured. 4. Ferrous salts precipitate white potassium ferrous ferrocyanide, which rapidly turns blue, owing to oxidation. K 4 Fe(CN) 6 + FeSO 4 = K 2 Fe[Fe(CN) 6 ] + KO< Usually the precipitate, owing to oxidation of the ferrous sul- phate, is light blue, even when freshly precipitated. *5 Ferric chloride produces an intense blue precipitate of ferric ferrocyanide, " Prussian blue." 3 K 4 Fe(CN) 6 + 4 FeCl 3 = Fe 4 [Fe(CN) 6 ] 3 + "KCl It is insoluble in dilute acids, but soluble in oxalic acid, with formation of a deep blue solution. Potassium and sodium hydroxides decompose Prussian blue, ferric hydroxide and potassium ferrocyanide being formed. Fe 4 [Fe(CN) 6 ] 3 + i 2 KOH = 3 K 4 Fe(CN) 6 +4Fe(OH) 3 It is interesting to notice that only the iron which is present in the cation is precipitated as ferric hydroxide on the addition of caustic alkali. That which occurs in the anion, being present as a compound anion, is not acted upon. n8 Qualitative Chemical Analysis. *6. Copper sulphate gives a purplish-brown precipitate of cupric ferrocyanide. In very dilute solutions a purplish- brown coloration and no precipitate is produced. The precipitate is insoluble in acetic acid. K 4 Fe(CN) 6 + 2 CuSO 4 = Cu 2 Fe(CN) 6 + 2K 2 SO 4 Hydroferricyanic Acid. H 3 Fe(CN) 6 The ferricyanides of the alkali metals and alkaline earths are soluble in water: those of the other metals are insoluble, both in water and in dilute acids. 1. Concentrated and dilute sulphuric acid behave with ferricyanides in the same manner as with ferrocyanides. 2. Silver nitrate produces a reddish-brown precipitate of silver ferrieyanide, which has the appearance of ferric hydrate. It is only partially soluble in ammonium hydroxide, a white residue being left behind. K 3 Fe(CN) 6 -f 3AgNO 3 = Ag 3 Fe(CN) 6 + sKNO 3 *3. Ferrous sulphate produces an intense blue precipitate of ferrous ferricyanide, " Turnbull's blue." It is insoluble in oxalic acid. 2 K 3 Fe(CN) 6 + 3FeS0 4 = Fe 3 [Fe(CN) 6 ] 2 Caustic soda decomposes " Turnbull's blue " with formation of sodium ferricyanide and ferrous hydroxide, only the iron which is present at the cation being converted into ferrous hydroxide. Fe 8 [Fe(CN)J 2 + 6NaOH = 2 Na 3 Fe(CN) 6 + 3Fe(OH) 2 4. Ferric chloride forms no precipitate, but the colour changes to olive-brown. (See 4, p. 73.) The iron contained in the ferro- and ferricyanides cannot be precipitated by the usual reagents, because it is in the anion. In The Acids. 119 solution we have the ions 4.K* and Fe(CN)'e, and 3K' and Fe(CN)e', the potassium, of course, being the cation. In ferrocyanides the anion is tetravalent, but in the ferricyanides it is trivalent. ThiocyaniC Acid (Sulphocyanic Acid)< HCNS The thiocyanates, with the exception of those of lead, silver, mercury, and copper, are soluble in water. *i. Silver nitrate gives a white curdy precipitate of silver thiocyanate, soluble in a large excess of ammonia. KCNS + AgNO 3 = AgCNS + KNO S *2. On adding copper sulphate to a thiocyanate, no pre- cipitate is produced, but the colour becomes greenish. If the thiocyanate is in excess, a black precipitate is gradually formed. On adding a mixture of copper sulphate and sulphurous acid, a white or grey precipitate of cuprous thiocyanate is produced, owing to the reduction of the cupric thiocyanate first produced. 2KCNS + 2CuSO 4 +SO 2 + 2H 2 O = Cu 2 (CNS) 2 + K^ + 2H 8 SO 4 *3. Ferric chloride produces an intense blood-red coloration of ferric thiocyanate. 3 KCNS + FeCl 3 = Fe(CNS) 3 + 3KC1 The coloration is destroyed by addition of mercuric chloride and by rochelle salt. It is soluble in ether. (Cf. 5, P. 73-) 4. Mercuric nitrate gives a white precipitate of mercuric thiocyanate. 2KCNS + Hg(N0 3 ) 2 = Hg(CNS) a + 2 KNO Detection of Ferrocyanides, Ferricyanides, and Thio- cyanates in a Mixture. To the solution which has been I2O Qualitative Chemical Analysts. acidified with hydrochloric acid, add ferric chloride in excess. A deep blue precipitate of " Prussian blue " shows the presence of a ferrocyanide. Filter off this precipitate. If the solution has a blood-red colour, this shows that a thiocyanate is present. The red colour may, however, be masked by the brown colour produced by the action of the excess of ferric chloride upon the ferricyanide. It is therefore better to shake up with a little ether : the red ferric thiocyanate will colour the ethereal layer red. Now, in order to test for the ferricyanide, add a few drops of hydrogen peroxide or stannous chloride, either of which will reduce the excess of ferric chloride to ferrous chloride, which will then react with any ferricyanide which may be present, and give a blue precipitate of Turnbull's blue. When cyanides are present with ferro- and ferricyanides, and it is desired to get rid of, or to test the mixture for cyanide before testing for the double cyanides, the mixture should be distilled with sodium or potassium bicarbonate, which only decom- poses the cyanide, the double cyanides being unacted upon. The distillate must be tested for the cyanide, the residue being tested for the double cyanides. In all cases in which hydrocyanic acid is evolved, great caution must be used, owing to the extremely poisonous nature of the substance, and all operations must be conducted in the draught cupboard. Insoluble Double Cyanides. Before testing, insoluble cyanides must be converted into soluble salts. The substance is boiled with caustic soda, and, after diluting, the solution is filtered from any insoluble residue. The insoluble double cyanides are by this treatment converted into sodium ferro- or ferricyanides and a hydroxide of the metal ; e.g. Cu 2 Fe(CN) 6 + 4NaOH = Na 4 Fe(CN) 6 + 2Cu(OH) 2 The filtrate, after acidifying with dilute hydrochloric acid, is tested as already described. Treatment of a Mixture containing Cyanogen Com- pounds before proceeding to analyse for the Bases The Acids. 121 (Cations). The presence of ferro- or ferricyanides will have been indicated when examining the substance in the dry way; (i) by the odour of cyanogen produced when the mixture was heated in a dry tube ; (2) on treating the substance with hydro- chloric acid, when a blue or green solution is obtained, or, if insoluble, a blue or green coloration of the residue. Before pro- ceeding to the separation of the metals, it is necessary that cyanogen compounds should be removed. This may be done in several ways. m (i.) If the double cyanide is ignited with from three to four times its bulk of a mixture of equal parts of ammonium nitrate and sulphate, the bases unite with SO 4 to form sulphates, and the cyanide anions are destroyed. The ignition should be performed in a draught cupboard, and be carried on until all the ammonium salts have been volatilised. The residue should then be dissolved in water or dilute hydrochloric acid, and examined for bases as usual. If an insoluble residue remains, it will consist of insoluble sulphates, and must be fused with fusion mixture. The acids must be tested for in a solution prepared as in (ii.). (ii.) Boil the mixture with a considerable quantity of a strong solution of caustic alkali ; then add a little solid sodium carbonate, and boil again for about five minutes. Dilute with water, and filter. The solution contains all the acids, beside the alkali salts of such metals as aluminium, zinc, lead, etc. The residue contains all the other metals, and should be dissolved in hydro- chloric acid and examined for these as usual (p. 169). Carbonic Acid, H 2 CO, This acid is formed when carbon dioxide dissolves in water, but owing to its instability, it has not been isolated. The acid is very slightly dissociated : this explains its feeble acid reaction, and the fact that its normal salts, which are soluble in water, have an alkaline reaction. This is due to hydrolysis. Potassium carbonate 122 Qualitative Chemical Analysis. is ionised into 2K' and CO!,, but in water there are H' and OH ions, although only in minute quantities. The tendency is for H" and COl ions to unite to form undissociated H 2 CO 3 , and this uses up the H ' ions, leaving the hydroxy lions. More water molecules become ionised, with the formation of more un-ionised H 2 CO 3 , and the alkalinity of a solution of potassium carbonate is thus due to the presence of OH' ions (as alkalinity is in all cases) thus 20H' The normal carbonates, with the exception of those of the alkali metals, are insoluble in pure water, though many of them are soluble in water containing carbonic acid, owing to formation of bicarbonates. They are precipitated from such a solution on boiling. in the cold CaC0 3 + H 2 + CO 2< _ ->Ca(HCQ 3 ) a on boiling i. When strongly heated, all the carbonates, with the exception of those of the alkali metals and barium carbonate, are decomposed with evolution of carbon dioxide, e.g. CuCO 3 = CuO + CO 2 *2. All carbonates, when acted upon by dilute acids, effervesce with evolution of carbon dioxide. BaC0 3 + 2HC1 = BaCl 2 + CO 2 + H 2 O NaaCOg + H 2 SO 4 == Na 2 SO 4 + CO 2 + H S O If the evolved gas is passed into lime-water, or a solution of barium hydroxide, the liquid becomes turbid owing to precipita- tion of calcium or barium carbonate, which is insoluble in water, but soluble in water containing excess of carbonic acid. Ca(OH) 2 + CO 2 = CaCO 8 + H 2 O The best way of applying this test is to place the carbonate in a test tube, add some acid, and then to bring the end of a glass rod The Acids. 123 which has been dipped in lime-water into the mouth of the tube. The evolved carbon dioxide causes the lime-water to become turbid. Care must be taken that the glass rod does not come in contact with the mineral acid on the inside of the tube. *3 Barium chloride when added to a solution of a car- bonate produces a white precipitate of the carbonate of the metal. The precipitate dissolves readily in dilute hydrochloric or nitric acid, distinction from sulphates. BaCl a + Na 2 C0 3 = BaCO 3 + 2NaCl *4. Silver nitrate gives a white precipitate of silver carbonate soluble in nitric acid (distinction from chlorides) ammonium hydrate, and in ammonium carbonate. KaCO, + 2AgNO 3 = Ag 2 C0 3 + 2KNO 3 Bicarbonates; Bicarbonates are readily converted into normal carbonates on heating. The bicarbonates of the alkali metals are, compared with those of other metals, relatively stable ; but they, too, are readily converted into normal carbonates when heated. 2 NaHCO 3 = Na 2 C0 3 + H 2 O + CO a Some normal carbonates give off carbon dioxide when heated at comparatively low temperatures; but if they have been pre- viously dried at 100, they will not give off water, as a bicarbonate, however, would. Hence the presence of a bicarbonate in a mixture containing only alkali metals may be demonstrated by heating some of the substance in a dry test tube, the sides of which will become coated with moisture, and testing the gas evolved with lime-water. Further, the normal carbonates of the alkali metals are very much more soluble in water than the acid or bicarbonates, therefore they may be roughly separated by washing. In general, bicarbonates show the same reactions as the normal carbonates. Bromide Test. To a solution of bleaching powder add 124 Qualitative Chemical Analysis. about i c.c. of a solution of potassium bromide and 2 c.c. of chloroform or carbon disulphide. On the addition of a solution of a bicarbonate bromine is liberated, which, upon shaking up, dissolves in the chloroform, which becomes brown. The reaction is due to liberation of hypochlorous acid by the bicarbonate thus ; NaHC0 3 + NaOQ = HOC1 + N^CO, 2HOC1 + 2KBr = Br 2 + 2KC1 + H 2 O +O Nitric Acid. HN0 3 Nitric acid when pure is colourless, but it has usually a yellow appearance owing to dissolved oxides of nitrogen. All nitrates, with the exception of basic mercury and bismuth nitrates, are soluble in water. Dry Reactions. i. All nitrates deflagrate when heated with charcoal. 2. The nitrates of the alkali metals are decomposed, when strongly heated, into a nitrite and oxygen. NaNO 3 = NaNO 2 + O The nitrates of the heavy metals are converted into an oxide or metal with evolution of oxygen and of brown fumes of nitrogen peroxide. Pb(NO 3 ) 2 = PbO + 2NO 2 + (a.) Hg(N0 3 ) 2 - HgO + 2N0 2 + O (b.) HgO - Hg + O The nitrates of the alkali metals when heated with copper sulphate also yield nitrogen peroxide. 2NaNO 3 + CuSO 4 = Na 2 SO 4 + CuO + 2NO 2 + O Wet Reactions. Use a solution of potassium nitrate. i. Concentrated sulphuric acid when added to a nitrate The Acids. 125 liberates nitric acid, the vapours of which have a slight brownish- yellow colour. NaNO 3 4- H 2 SO 4 = NaHSO 4 + HNO 3 If, however, a small piece of copper is added to this mixture, deep brown fumes are produced, owing to the formation of nitric oxide by the action of the liberated nitric acid on the copper. The oxygen from the air causes the nitric oxide to be converted into brown nitrogen peroxide. (1) 8HNO 3 + 3Cu = 3Cu(NO 3 ) 2 + 2NO + 4H 2 O (2) 2 NO -f O 2 = 2NO 2 (brown vapours) *2. Brucine. To a few drops of a nitrate solution in the bottom of a porcelain basin add 3 to 4 c.c. of concentrated sulphuric acid, and i c.c. of a solution of brucine in sulphuric acid (see Reagents, p. 329). A rose-red coloration gradually deepening in intensity is produced, which slowly changes to yellow. This very delicate test is not reliable in presence of bromides or iodides. When carried out in this manner it serves to distinguish nitrates in presence of nitrites. *3. When concentrated sulphuric acid is poured cautiously down the side of a test tube containing a cold mixture of solutions of ferrous sulphate and of a nitrate, a brown coloration is obtained, where the specifically heavier sulphuric acid mixes with the supernatant liquid. This brown coloration is due to an unstable compound of ferrous sulphate and nitric oxide (2FeSO 4 . NO), the formation of which may be thus explained sulphuric acid liberates nitric acid from the nitrate ; nitric acid oxidises ferrous sulphate to ferric sulphate, and is itself reduced to nitric oxide ; the nitric oxide unites with the still unoxidised portion of the ferrous sulphate. 2 KNO 8 + 4H 2 S0 4 + 6FeS0 4 = K 2 S0 4 + 2NO + 3Fe 2 (S0 4 ) 3 + 4H 2 O This test is not reliable in presence of iodides, bromides, or nitrites. 126 Qualitative Chemical Analysis. *4. A very delicate test, and one which can be carried out in presence of iodides and bromides, depends upon the formation of a nitrite by nascent hydrogen. Dissolve in the solution of the nitrate a small crystal of potassium iodide, then add a little starch paste, 2 c.c. of dilute sulphuric acid and a small piece of zinc. A blue coloration, which first begins to show round the zinc, indicates the presence of a nitrate. (a.) HN0 3 + 2 H = HN0 2 + H 2 O (b.) 2HNO 2 + 2HI = I, + 2NO + 2H 2 O Nitrous Acid. HN0 2 Nitrous acid is only known in the form of its salts, which are mostly soluble in water. Dry Reaction. All nitrites on being heated with charcoal, deflagrate. Wet Reaction. Use a solution of sodium or potassium nitrite. *i. Mineral acids and acetic acid decompose nitrites. Nitric oxide is liberated, and this combining with the oxygen of the air produces brown fumes of nitrogen peroxide, part of the nitrous acid is converted to nitric acid. (1) 2 KN0 2 + H 2 S0 4 = 2 HN0 2 + K 2 SO 4 (2) 3HNO 2 = HNO 3 + H 2 O +2NO 2. A crystal of ferrous sulphate when added to a solution of a nitrite is turned deep brown at once, even in the absence of acid. 3. With sulphuric acid and ferrous sulphate a brown coloration is produced, as with nitrates. 4. Silver nitrate gives from solutions which are not too dilute, a white precipitate of silver nitrite, soluble in boiling water. AgNO 3 + NaNO 2 = AgNO 2 + NaNO, The Acids. 127 5. Meta-phenylenediamine hydrochloride gives a very intense yellow coloration when added to a very dilute solution of a nitrite slightly acidified with acetic acid. This test is extremely delicate, and is used in water analysis. Nitrates do not give it. It depends upon the formation of triamidoazobenzene (Bismarck brown). In strong solutions a brown precipitate is produced. 2 C 6 H 4 (NH 2 ) 2 + HN0 2 = C 6 H 4 ( + 2 H a O \N = N.C 6 H 3 (NH 2 ) 2 6. On adding a small crystal of potassium iodide and some starch paste to a solution of a nitrite, and acidifying with a few drops of dilute sulphuric acid, a deep blue coloration is produced (distinction from nitrates). (Compare also 7, p. no.) Detection of Nitrates in Presence of Nitrites. (i.) Add to the solution to be tested one or two grams of urea, then carefully add dilute sulphuric acid. The nitrous acid is decomposed, and nitrogen and carbon dioxide are evolved. CO(NH 2 ) 2 + 2 HO . NO = 2 N 8 + CO 2 + 3 H 2 O As soon as evolution of gas ceases, a little more urea is added, and the mixture is gently warmed to insure complete decomposi- tion of the .nitrite. Cool the solution, and add a small crystal of potassium iodide and a few drops of starch paste. If the nitrite has been completely destroyed, no coloration will be obtained; but on addition of a small scrap of zinc a blue colour is produced, owing to the nitric acid being reduced to nitrous acid, which then liberates iodine from the potassium iodide. (Cf. 4, p. 126.) HN0 3 + 2 H = HNO 2 + H 2 (ii.) Instead of using urea, the substance containing the nitrate and nitrite may be boiled for some minutes with ammonium chloride, which decomposes the nitrite thus NaNO 2 + NH 4 C1 = NaCl + 2H 2 O + N a It is then tested as already described above. (iii.) By means of the brucine test, 2, p. 125. 128 Qualitative Chemical Analysis. Sulphuric Acid. H 2 SO 4 The neutral sulphates, with the exception of those of barium, strontium, and lead (slightly soluble), are soluble in water. Many basic sulphates, however, are insoluble. Dry Reaction. All sulphates, when heated on charcoal with fusion mixture, are converted into alkali sulphides. BaS0 4 + 2C + Na 2 C0 3 = Na 2 S + BaCO 3 On dissolving the fused mass in water, filtering and adding a drop of the solution to a drop of sodium nitroprusside on a watch glass, an intense violet coloration is produced (p. 132); or if a drop of the solution is placed on a silver coin, a black stain is obtained. Wet Reactions. Use a solution of sodium or magnesium sulphate. *i. Barium chloride gives, with sulphuric acid or soluble sulphates, a heavy white precipitate of barium sulphate, which is insoluble in mineral acids. Na 2 SO 4 + BaCl 2 = BaSO 4 + 2NaCl *2. Lead acetate produces a white precipitate of lead sulphate, which is soluble in ammonium acetate, am- monium tartrate, or caustic potash. Lead sulphate is also slightly soluble in water, but its complete precipitation may be secured by the addition of alcohol. K 2 SO 4 + (CH 3 COO) 2 Pb = PbSO 4 + 2CH 3 COOK Persulphuric Acid. H 2 S 2 8 Persulphuric acid is only known in solution it is obtained by the electrolysis of strong sulphuric acid. The alkali persulphates, however, are fairly stable. The Acids. 129 Dry Reaction. When persulphates are heated, they are decomposed with evolution of oxygen and sulphuric anhydride. NajSA = Na 2 SO 4 + SO 3 + O Wet Reactions. Use a solution of ammonium or potassium persulphate. *i. Potassium iodide when added to a solution of a per- sulphate is slowly decomposed in the cold, rapidly on heating, iodine being deposited. K&Oa + 2 KI = 2 K 2 S0 4 + I, *2. Barium chloride produces no immediate precipitate, but, on warming, a precipitate of barium sulphate is formed, the barium persulphate at first produced being decomposed. BaS 2 O 8 + H a O = BaSO 4 + H 2 SO 4 -f O *3. Silver Nitrate : On adding silver nitrate to a solution of a persulphate, a black precipitate of silver peroxide is produced. 2AgNO 3 -f K 2 S 2 O 8 + 2H 2 O = 2KHSO 4 -f 2HNO 3 + Ag 2 O 2 An interesting example of catalysis is shown when a concen- trated solution of ammonium persulphate and ammonia is treated with a very small quantity of silver nitrate, a vigorous evolution of nitrogen takes place, and the solution becomes very hot. This is due to the oxidising action of the silver peroxide formed in the first instance. Sulphurous Acid. Sulphurous acid is formed when sulphur dioxide dissolves in water ; but, because of its instability, it has not been isolated. Owing to its being only slightly dissociated in aqueous solution, it is not a strong acid, and its normal salts with the alkali metals have an alkaline reaction. Being a dibasic acid, it forms normal salts and acid salts or bisulphites. K 130 Qualitative Chemical Analysis. Dry Reaction. When a sulphite is heated on charcoal with fusion mixture, an alkali sulphide is formed. (Cf. Sulphates.) Wet Reactions, Use a solution of sodium sulphite. i. Sulphuric and hydrochloric acids liberate gaseous sulphur dioxide, the presence of which can be detected by its smell that of burning sulphur. No precipitation of sulphur is produced (distinction from thiosulphates). Na 2 SO 3 + H 2 SO 4 = Na 2 SO 4 -f SO 2 + H 2 *2. In solutions which are not too dilute, barium chloride gives a white precipitate of barium sulphite soluble in hydro- chloric acid. (Cf. sulphates, r, p. 128.) K 2 SO 3 + BaCl 2 = BaSO 3 + 2KC1 3. Silver nitrate precipitates white silver sulphite soluble in hot dilute nitric acid and in ammonium hydroxide. K 2 SO 3 + 2AgNO 3 = Ag 2 SO 3 + 2KN0 3 Silver sulphite is decomposed on boiling, turning grey owing to deposition of silver and formation of silver sulphate. 2 Ag 2 S0 3 = Ag 2 S0 4 + 2 Ag + S0 2 *4. Ferric chloride produces a red coloration, which under- goes no change on standing ; but, on boiling, a brown basic iron salt is precipitated (distinction from thiosulphates). *5. On adding a few drops of a neutral solution of a sulphite to a mixture of dilute solutions of zinc sulphate and sodium nitroprusside, a red coloration is either at once produced, or immediately becomes visible on adding a small quantity of potassium ferrocyanide (distinctive test in presence of thio- sulphates). *6. Owing to the readiness with which sulphurous acid is converted into sulphuric acid by oxidation, it acts as a strong reducing agent. A solution of potassium permanganate is The Acids. 131 decolourised, and solutions of chromates are turned green owing to their conversion into chromic salts. (a.) 5H 2 S0 3 + 2KMn0 4 + 3H 2 SO 4 = 5H 2 SO 4 + K 2 SO 4 -f 2MnSO 4 -f (b.) 3H3S03 + KaCrA + H 2 SO 4 = Cr 2 (S0 4 ) 3 + KaSO, -f- 4 H 2 O Detection of Sulphates and Sulphites. Acidify the solution with hydrochloric acid and add excess of barium chloride. From an acid solution only barium sulphate will be precipitated ; filter this off. The filtrate contains sulphurous acid with excess of barium chloride ; add bromine water, which will oxidise the sulphurous acid to sulphuric acid, when a further precipitate of barium sulphate will in consequence be produced. H 3 SO 3 + Br 2 4- H 2 O = H 2 SO 4 + 2HBr Hydrogen Sulphide (Sulphuretted Hydrogen). H 2 S Sulphuretted hydrogen is only a weak acid, as it is only slightly dissociated in solution, and for this reason the normal alkali salts have a strong alkaline reaction ; they are very readily soluble in water. The sulphides of most of the other metals are insoluble in water, but dissolve with decomposition in acids. Aqua regia is the only acid which dissolves the sulphides of mercury, arsenic, platinum, and gold. Dry Reaction. When heated on charcoal with fusion mix- ture, soluble alkali sulphides are formed. (Cf. Sulphates, p. 128.) Wet Reactions. Use a solution of ammonium sulphide. *i. Silver nitrate when added to a solution containing a sulphide gives a black precipitate of silver sulphide, soluble in nitric acid, and in aqua regia. 4- 2AgN0 3 = Ag 2 S + 2NaNO, 132 Qualitative Chemical Analysis, *2. All sulphides (except those of mercury, silver, arsenic, platinum, and gold), when heated with concentrated hydrochloric acid, give off sulphuretted hydrogen. The presence of this may be shown by the blackening of a piece of filter paper, moistened with lead acetate and held over the test tube ; or by the violet colour imparted by the gas to a piece of paper moistened with sodium nitroprusside and a drop of dilute ammonia. Sb 2 S 3 + 6HC1 = 2SbCl 3 + sH 2 S *3. Sodium nitroprusside, Na 2 Fe(NO)(CN) 5 , when added to a drop of a solution of a sulphide, which has been rendered alkaline with sodium hydroxide, and placed on a watch glass, produces a violet coloration. Thiosulphuric Acid. H 2 S 2 3 This acid is only known in the form of its salts, which are almost all readily soluble in water. The sodium salt Na 2 S 2 O 3 , 5H 2 O is the "hypo" of the photographer. Dry Reactions. i. When ignited with fusion mixture on charcoal, a soluble sulphide is produced. (Cf. Sulphates, p. 128.) 2. When ignited alone decomposition ensues and part of the sulphur burns. Wet Reactions. Use a solution of sodium thiosulphate. *i. Dilute mineral acids decompose thiosulphates with libera- tion of sulphur dioxide and precipitation of yellow sulphur. Na 2 S 2 3 + 2HC1 = S0 2 + S + H 2 O + 2NaCl 2. Barium chloride gives no precipitate in dilute solutions ; but, on addition of a few drops of bromine water, a white precipitate of barium sulphate is produced. (a.) Na 2 S 2 3 + Br 2 + H 2 O = Na 2 SO 4 + S + 2 HBr (b.) Na 2 SO 4 + BaCl 2 = BaSO 4 + 2NaCl 3. Silver nitrate, when added in excess, produces a white precipitate of silver thiosulphate. When added in small The Acids. 133 quantities the precipitate at first formed dissolves in the excess of the thiosulphate. 2AgNO 3 = Ag 2 S 2 O 3 + 2NaNO 3 On boiling, silver thiosulphate turns first yellow, then brown, and finally black. H a O = Ag 2 S + H 2 S0 4 *4. Ferric chloride produces a reddish-violet coloration with alkali thiosulphates. The colour disappears on warming. Even at ordinary temperatures it gradually fades away owing to the violet ferric thiosulphate, first formed, being converted into ferrous thiosulphate and ferrous tetrathionate. (a.) 3Na 2 S 2 3 + 2FeQ 3 = Fe 2 (S 2 O 3 ) 3 + 6NaCl (b.) Fe 2 (S 2 3 ) 3 = FeS 2 3 -f FeS 4 6 Detection of Sulphur Acids in a Mixture. It is necessary that the sulphide be first removed, and this must be done without decomposing the sulphites or thiosulphates, therefore the solution must not be acidified. To remove the sulphide shake up with lead carbonate,! which turns black, being converted into lead sulphide. Filter off the mixture of lead carbonate and sulphide. To the filtrate add excess of barium chloride to precipitate the sulphate and sulphite. Filter off the mixed barium salts, and treat the precipi- tate on the filter paper with dilute hydrochloric acid to decompose the sulphite. The barium sulphate remains on the filter paper, but the sulphite is decomposed, sulphurous acid being produced, which passes through in the filtrate, and may be tested for by adding bromine water, when a white precipitate of barium sulphate is produced. (See p. 128.) The thiosulphate is tested for in the solution left after filter- ing off the mixed barium salts. The solution is acidified with hydrochloric acid and warmed, when the thiosulphate is decom- posed, sulphur being precipitated and sulphur dioxide evolved. t Cadmium carbonate or zinc acetate may be employed instead of lead carbonate. 134 Qualitative Chemical Analysis. Hydrofluoric Acid. HF Hydrofluoric acid is a colourless mobile liquid, which fumes strongly in the air. It cannot be kept in glass vessels owing to its corrosive action, but is kept in vulcanite flasks, or platinum bottles. The fluorides of the alkali metals, and of silver, nickel, iron, tin and mercury, are readily soluble in water, the others being insoluble, or only soluble with great difficulty. * i. Fluorides, when heated with concentrated sulphuric acid in a leaden or platinum vessel, give off vapours of hydrofluoric acid; e.g. CaF 2 + H 2 S0 4 = 2 HF + CaSO 4 On holding over the vessel for a short time a clock glass, which has been covered with a thin coating of wax, and scratched at places with a pin so as to expose the surface of the glass, it is found, on removing it and cleaning off the wax, that the glass has been etched at the exposed portions. *2. When a mixture of a fluoride is heated with concentrated sulphuric acid in a test tube, the hydrofluoric acid which is liberated combines with the silica of the glass to form silicon tetrafluoride, which is partially evolved as a gas, but also forms oily globules beneath the surface of the acid. On holding a moistened glass rod in the vapour, the water decomposes the silicon tetrafluoride with formation of silicic acid, which is deposited on the rod as a white film. (a.) 4HF + SiO 2 = SiF 4 + 2H 2 O (.) 3SiF + 3H 2 O = H 2 SiO 3 + 2H 2 SiF 6 Hydrofluosilicic acid. Wet Reaction. Use a solution of sodium fluoride. *i. Barium choride produces a white precipitate of barium fluoride, which, on warming with a large excess of mineral acid dissolves. No precipitate is produced in presence of excess of ammonium salts. 2 NaF + BaQ 2 = BaF 2 The Acids. 135 Silicic Acid. H 2 Si0 3 Silicic acid is one of the weakest acids, being scarcely ionised at all in solution. The silicates of the alkali metals are soluble in water, to which they impart a strong alkaline reaction ; all other silicates are insoluble. A few of the insoluble silicates are decomposed by acids ; e.g. CaSiO 3 + H 2 SO 4 = H 2 SiO 3 + CaSO 4 The majority, however, are not decomposed in this manner. All the silicates of the alkali metals are decomposed by even dilute acids. Dry Reactions.*!. On fusing a little silica in a micro- cosmic bead, the silica usually does not dissolve, but floats about in the bead, producing on cooling an opaque bead or a bead with a more or less web-like structure. 2. When a piece of filter paper is moistened with a solution of a soluble silicate and a drop of cobalt nitrate, then dried over the Bunsen flame and ignited, the ash assumes a deep blue tint. *3. On mixing silica or a silicate with a powdered fluoride and concentrated sulphuric acid, and heating the mixture as described in 2, p. 134, for fluorides, silicon tetrafluoride is formed, and may be tested for as already described. This test must be made in a platinum or leaden dish. Wet Reactions. Use a solution of sodium silicate (water glass). i. When excess of a dilute mineral acid is added to the solution of a silicate, the silicic acid remains in solution in a colloidal state, but is thrown out in the form of a jelly on concentrating the solution on a water bath. a + 2HC1 = H.Si0 3 + 2NaCl 136 Qualitative Chemical Analysis. After evaporating to dry ness, it is no longer soluble in water. *2. Silver nitrate produces an orange-coloured precipitate of silver silicate, soluble in acids and in ammonium hydroxide. Na 2 SiO 3 + 2AgNO 3 = Ag 2 SiO 3 + 2NaNO 3 3.' Calcium chloride gives a white precipitate of calcium silicate which is soluble in acids. Na 2 SiO 3 + CaCl 2 = CaSiO 3 + 2NaCl Analysis of Silicates. In analysing a mixture containing insoluble silicates, it is necessary that they should be decomposed and the bases rendered insoluble. The substance should be finely powdered, first in an ordinary and finally in an agate mortar. It is then mixed with three or four times its weight of fusion mixture, and fused before the blowpipe until no more carbon dioxide is evolved, i.e. till effervescence ceases. A soluble silicate is by this means ob- tained; e.g. BaSiOs + NaKCO 3 = BaCO 8 + NaKSiO 8 On adding dilute hydrochloric acid till an acid reaction is ob- tained, the bases are converted into chlorides with evolution of carbon dioxide, and silicic acid is obtained, which, however, is in the colloidal state and remains in solution. NaKSiO 3 + BaCO 3 + 4HC1 = BaCl 2 + H 2 SiO 3 + NaCl + KC1 -f CO 2 + H 2 By evaporating this solution to dryness on the water bath, the silicic acid is converted into silica (SiO 2 ) or a polysilicic acid, e.g. H 2 Si 3 O 7 , which is insoluble in water. The bases can now be obtained in solution by washing several times with warm dilute hydrochloric acid, the silica remaining as an insoluble residue. TJie Acids. 137 Phosphoric Acid (Orthophosphoric Acid). H,P0 4 The phosphates of the alkali metals are soluble in water, those of the other metals in mineral acids. Dry Reaction. Phosphates, when burned on a piece of filter paper with cobalt nitrate, impart a blue coloration to the ash, or if the phosphate is heated on charcoal before the blow- pipe, moistened with cobalt nitrate, and again heated, a blue mass is obtained. Wet Reactions. Use a solution of disodium phosphate Na 2 HPO 4 . i. Calcium chloride gives a white precipitate of calcium phosphate, which is soluble in acetic acid and in mineral acids. Na 2 HP0 4 + CaCl 2 = CaHPO 4 + 2NaCl *2. Silver nitrate produces a canary-yellow precipitate of silver phosphate, soluble in nitric acid and in ammonium hydroxide. NagHPO, + 3AgN0 3 = Ag 3 PO 4 + 2NaNO 3 + HNO 3 *3. Ammonium molybdate, when added to a solution of a phosphate strongly acidified with concentrated nittric acid, produces at once, or on warming, a canary-yellow powdery precipi- tate of ammonium phosphomolybdate i2[MoO 3 ](NH 4 ) 3 PO 4 . It is soluble in excess of phosphoric acid and in ammonium hydroxide. Arsenates produce a similar precipitate of i 2 [Mo0 3 ](NH 4 ) 8 AsO 4 *4. Magnesia mixture gives a white crystalline precipitate of magnesium ammonium phosphate, which is insoluble in ammonia, but readily soluble in acids. Arsenates give an analogous reaction. (See 5, p. 51.) Na a HP0 4 + MgS0 4 + NH 4 OH = (NH 4 )MgPO 4 + Na.SO, + H 2 O 138 Qualitative Chemical Analysis. *5. Ferric chloride produces a yellowish-white precipitate of ferric phosphate. Na 2 HP0 4 + FeCl 3 ^ FeP0 4 + 2NaCl + HC1 The precipitate is soluble in excess of ferric chloride and in mineral acids, but is insoluble in acetic acid. In order that the above reaction may be quantitative, sodium acetate should be added to neutralise the free hydrochloric acid liberated in the reaction. The strong resemblance between phosphorus and arsenic is strikingly shown in the reactions of phosphoric and arsenic acids, both of which are tribasic and react with the same reagents. /OH /OH O = P<^-OH O = As<-OH NOH NOH For example, with a nitric acid solution of molybdic acid and with ammonium magnesium chloride. In a similar manner phos- phorous acid (H 3 PO 3 ) and arsenious acid (H 3 AsO 3 ) may also be compared, although the resemblance is not so striking as in the case of the higher acids. Separation of Phosphoric and Arsenic Acids. Both phosphoric and arsenic acid give a yellow precipitate with ammonium molybdate, and a white crystalline precipitate with magnesia mixture ; therefore they must be separated, in order to identify them. Of course, in analysing for the bases, phosphoric acid is always tested for after the arsenic has been precipitated by sulphuretted hydrogen, before proceeding to the analysis of the iron group ; but without separation in testing for the acids, it would be difficult to ascertain whether an arsenate or arsenite were being dealt with. Add excess of magnesia mixture to the solution, shake up, and allow to stand five to ten minutes. A white crystalline preci- pitate, consisting of a mixture of Mg(NH 4 )PO 4 and Mg(NH 4 )AsO*, is produced. Filter this off, wash, and dissolve in hydrochloric The Acids. 139 acid. Now boil the solution with a little sulphurous acid, to convert the arsenate into an arsenite. Having boiled off the sulphurous acid, pass sulphuretted hydrogen. The arsenic, if originally present as an arsenate, is precipitated as arsenic trisulphide. (a.) Mg(NH 4 )AsO 4 + sHCl = H 3 AsO 4 + MgCL 2 + NH 4 C1 (/;.) H 3 As0 4 + SO 2 + H 2 O = H 3 AsO 3 + H 2 SO 4 (c.) 2H 3 AsO 3 + sHsS = As 2 S 3 + 6H 2 O Filter off the arsenious sulphide, evaporate the solution to about half its bulk, and add excess of concentrated nitric acid and ammonium molybdate, when the phosphoric acid will be precipitated as yellow ammonium phosphomolybdate i2Mo0 3 (NH) 4 ) 3 P0 4 . Arsenites do not give a precipitate with magnesia mixture, so should be tested for in the solution after the arsenate and phosphate have been precipitated and filtered off. By acidifying with hydrochloric acid, and passing sulphuretted hydrogen, a yellow precipitate of arsenic sulphide is produced. Pyrophosphoric and Metaphosphoric Acids. When phosphoric acid is strongly heated pyrophosphoric acid is produced. When disodium phosphate is heated, a sodium salt of pyrophosphoric acid is obtained. (a.) 2 H 3 P0 4 = H 4 P 2 7 -f H 2 (b.) 2Na 2 HPO 4 = Na 4 P 2 O 7 + H 2 O On more strongly heating, the pyrophosphoric acid is con- verted into metaphosphoric acid, or better by heating it with phosphorus pentachloride. (a.) H 4 PA = 2HPO 3 + H 2 O (b.) H 4 P 2 7 + PC1 5 - 2 HP0 3 + POC1 3 + 2HC1 When boiled with water or dilute acids, both pyro- and meta- phosphoric acids are reconverted into orthophosphoric acid. 140 Qualitative Chemical Analysis. Metaphosphoric acid is generally called glacial phosphoric acid from its glass-like appearance ; pyrophosphoric acid has also a vitreous appearance. Metaphosphoric acid coagulates albumen when shaken up with it, whereas neither ortho- nor pyrophosphoric acid possess this property. Silver nitrate gives a white precipitate both with meta- and pyrophosphates. Mag- nesium sulphate in presence of ammonium chloride precipitates ortho- and pyrophosphates, but not metaphosphates. Hypophosphorous Acid. H 8 P0 2 = H(H 2 P0 2 ) Hypophosphorous acid has only one hydrogen atom which is replaceable by metals; it is, therefore, a monobasic acid. All hypophosphites, with the exception of that of silver, are soluble in water. Dry Reaction. Hypophosphorous acid and hypophosphites, when heated, are converted into phosphoric acid, with liberation of hydrogen phosphide. 2 H 3 PO 2 = H 3 PO 4 + PH 3 Wet Reactions. Usja^a solution of sodium hypophosphite. *i. Hypophosphorous acid and its salts are very powerful reducing agents. On adding a solution of copper sulphate to an acidified solution of a hypophosphite and gently warming, a yellow precipitate of cuprous hydride^ is produced, which rapidly becomes cht>colate-brown. 2 H 3 PO 2 + 2CuS0 4 +3H 2 O= 2H 3 P0 4 + H 2 SO 4 + H 2 SO 3 + Cu 2 H 2 When treated with concentrated hydrochloric acid, cuprous hydride evolves hydrogen. Cu 2 H 2 + 2HC1 = Cu 2 Cl 2 + 2H 2 *2. Salts of mercury are reduced to metallic mercury. This The Acids. 141 is sometimes employed for the quantitative determination of mercury compounds. In the case of mercuric chloride a white precipitate of calomel is first formed. H 3 P0 2 + 2HgCl 2 + 2H 2 = 2 Hg + 4HC1 + H 3 PO 4 3. Silver nitrate gives with neutral solutions a white precipi- tate of silver hypophosphite, which is reduced on boiling. NaH 2 PO 2 + AgNO 3 = AgH 2 PO 2 + NaNO 3 *4. Neutral ammonium molybdate gives, when added in excess, a beautiful blue coloration or precipitate. On boiling, the colour is destroyed. *5. When exposed to the action of nascent hydrogen, by adding a piece of zinc to a solution of a hypophosphite acidified with hydrochloric acid, hydrogen phosphide is produced. Detection of Free Phosphorus. If free phosphorus is present in a mixture, it may be detected by (i) the smell; (2) mixing with a little water, adding excess of tartarie acid, and boiling. During the boiling hold two strips of paper in the neck of the flask, the one moistened with silver nitrate, the other with lead acetate. If the silver nitrate paper becomes brown or black, while the other does not, then the presence of phosphorus is shown. Should, however, both pieces be blackened, then sul- phuretted hydrogen is present, and, of course, masks the reaction given by phosphorus with the silver nitrate. Take another portion of the acidified mixture, and boil in a dark room, the appearance of phosphorescence at the mouth of the flask proves the presence of phosphorus. (3) Mix the substance to be tested with sulphuric acid and zinc in a hydrogen-generating apparatus. As soon as all the air has been driven out of the apparatus ignite the issuing gas. If phosphorus is present, the flame assumes a lambent yellowish-green tinge. The green tinge is much more marked if a white plate is depressed over the flame. (4) Shake up the substance under examination with a little carbon disulphide and pour off the aqueous solution. Now pour a few drops of 142 Qualitative Chemical Analysis. the solution on a piece of filter paper ; as the carbon disulphide evaporates, the phosphorus will be left on the paper in a state of very fine division. Should the quantity of phosphorus present be considerable, it will spontaneously ignite ; or if the quantity is very small, it will merely show phosphorescence when examined in the dark. Red phosphorus may be detected by (i) its insolubility in solvents, i.e. water, alcohol, caustic alkali, acids, etc.; (2) its taking fire when heated, with formation of vapours of phosphorus pentoxide ; (3) on fusion with fusion mixture by the formation of a phosphate, which may be tested for with ammonium molybdate. Boric Acid (Boracic Acid). H 3 BO 8 Most of the salts of boric acid are derived from pyroborie acid, H 2 B 4 O 7 . The borates of the alkali metals dissolve in water, and have an alkaline reaction, this being due to the fact that boric acid is only very slightly dissociated in solution the disso- ciation is, in fact, hardly measurable. As none of the borates are quite insoluble in water, precipitation with reagents is never quite complete. 1. Most borates, when heated, swell up and fuse into a trans- parent glass. 2. Borates, when burnt on a filter paper moistened with cobalt nitrate, colour the ash blue. (Cf. aluminium, p. 67.) *3. When a borate is mixed to a thin paste with concentrated sulphuric acid, and a little alcohol is added, the alcohol on being ignited burns with a green-edged flame. The green tinge is more noticeable on stirring with a glass rod. The green flame is produced by the burning of the volatile compound ethyl borate B(OC2H 5 ) 3 produced in the reaction. B(OH) 3 + sC 2 H 5 OH ^ B(OC a H 6 ) 3 + sH.O The Acids. 143 Glycerol may be substituted for the sulphuric acid, in which case the mixture should be gently warmed before adding the alcohol and igniting. N.B. Metallic chlorides in presence of alcohol and sulphuric acid form ethyl chloride, which burns with a green flame. Again, copper salts on heating with concentrated sulphuric acid and alcohol may tinge the flame green. This is, however, not likely to occur if the mixture is not heated. Both these sources of error are minimised by using glycerol. *4. Grind up the dry substance with a little sodium hydroxide, or potassium hydrogen sulphate, and, by means of a platinum wire, heat in Bunsen flame. A transient green colour will be imparted to the flame. 5. Silver nitrate produces, in not too dilute solutions, a white precipitate of silver metaborate, soluble in acids and in ammonia. On boiling the precipitate with water, reduction takes place, the precipitate turning brown, and then black. Na 2 B 4 O 7 4- 2AgNO 3 -f sH 2 O = 2AgBO 2 + 2NaNO 3 + 2H 3 BO 3 *6. On moistening turmeric paper with a slightly acid solu- tion of a botate, it becomes reddish-brown. If the paper thus coloured be moistened with caustic soda the colour changes to a more or less greenish-brown shade. This reaction does not show so well in presence of ferric chloride, chromates, or chlorates. *y. All borates are decomposed by hydrofluoric acid with formation of volatile boric fluoride. Sulphuric acid and calcium fluoride may be employed instead of hydrofluoric acid. Na 2 B 4 O 7 + 6CaF 2 -f 7H 2 SO 4 = 6CaSO 4 + 4BF 3 + Na 2 SO 4 + 7H 2 O Boric acid is volatile with steam or hydrochloric acid, and may be removed from a mixture by evaporating several times to dry ness with hydrochloric acid. It may be more expeditiously got rid of by evaporating, in a platinum or lead dish, with hydrofluoric acid. 144 Qualitative Chemical Analysis, Chromic Acid. 1^004 The alkali chromates and dichromates are soluble in water, most of the other salts are insoluble. *i. Barium chloride gives, with chromates or dichromates, a light yellow precipitate of barium chromate, soluble in mineral acids, but insoluble in acetic acid (distinction between barium and calcium). K 2 CrO 4 + BaCl 2 = BaCrO 4 + 2KC1 K 2 Cr 2 O 7 + 2BaCl 2 -f H 2 O = 2BaCrO 4 + 2 KC1 + 2HC1 *2. Silver nitrate produces a brick-red precipitate of silver chromate, soluble both in nitric acid and in ammonia, but in- soluble in acetic acid. K 3 Cr0 4 + 2AgNO 3 = Ag 2 CrO 4 + 2 KNO 3 *3. Lead acetate forms a yellow precipitate of lead chro- mate. (CH 3 COO) a Pb = PbCrO 4 + 2 CH 3 COOK It is soluble in excess of caustic alkali, forming a yellow solution, PbCrO 4 + 4NaOH = Na 2 PbO 2 + Na 2 CrO 4 + 2H 2 O while on boiling with a small quantity of alkali, the precipitate changes from orange to chrome red. 4. Sulphuretted hydrogen and sulphurous acid turn the yellow or red solution green, owing to reduction to the green chromic salt. When sulphuretted hydrogen is employed, sulphur is precipitated. (a.) 2 H 2 Cr0 4 + sH 2 S + 3H 2 SO 4 = Cr 2 (SO 4 ) 3 + 8fl a O + 38 (b.) K 2 Cr 2 7 + 3 H 2 S0 3 +H 2 S0 4 = Cr 2 (SO 4 ) 3 + K 2 SO 4 + 4 H 2 O The chromium changes from the complex anion, in which it is present as CrO 4 ' or Cr-jOy, to the green cation, where it The Acids. 145 occurs simply as the ion Cr'~. In potassium chromate and potassium dichromate the ions are respectively 2H* and CrOij, and 2H* and Cr 2 0j, whereas in chromium sulphate they are 2Cr and 3SOI. This explains why it is that only in chromium salts, where we have the cation Cr", is chromium precipitated as hydrate on addition of caustic alkali. 5. On heating with concentrated hydrochloric acid, chlorine gas is given off. 2 K 2 CrO 4 + i6HCl = $C1* + 2CrCl 3 + 8H 2 O + 4KC1 *6. When chromates are heated with concentrated sulphuric acid and a chloride, deep red vapours of chromyl dichloride are produced, which condense to a heavy red liquid. K 2 Cr 2 O 7 +4NaCl+3H 2 SO 4 =2CrO 2 Cl 2 +2Na 2 SO 4 +K 2 SO 4 +3H 2 O Chromyl dichloride is decomposed, on mixing with water, into chromic and hydrochloric acids. CrO 2 Cl a + 2H 2 O = H 2 CrO 4 + 2HC1 On adding ammonia to this solution, or on passing the vapours into dilute ammonium hydrate, a solution of ammonium chro- mate is produced, which, on acidulation with acetic acid and addition of lead acetate, gives a yellow precipitate of lead chromate. This reaction may either be employed as a test for a chromate or indirectly as a test for a chloride, being of especial value when a chloride occurs in presence of a bromide. (Cf. Chlorides, p. 107.) *7. Hydrogen Peroxide. Acidify a very dilute solution of hydrogen peroxide with dilute sulphuric acid, add 3 to 4 c.c. of ether, and then a few drops of a dilute solution of a chromate or dichromate : a deep blue coloration is produced. On shaking up the mixture, the blue compound dissolves in the ether, forming a brilliant blue layer on the surface of the aqueous solution. This is the most delicate test for chromium. The coloration is pro- bably due to formation of perchromic acid 2H 2 CrO 4 + H 2 O 2 = 2HCrO 4 + 2H 2 O L 146 Qualitative Chemical Analysis. A large quantity of hydrogen peroxide should not be employed, neither should the chromic acid be in excess, becauses it decom- poses the perchromic acid. 2 HCr0 4 + 2H 2 Cr0 4 + 3 H 2 O = 4Cr(OH) 3 + 7O The amount of the chromate which it is required to add depends, therefore, upon the quantity of the hydrogen peroxide present, and it should be added drop by drop with continual shaking. It is also advisable to add the ether before the chromate, because, when dissolved in ether, the colour is more permanent. Permanganic Acid. HMnO 4 This acid is known only in its aqueous solutions, and in the form of its salts, the permanganates, all of which are soluble in water, forming purple solutions. *i. Solid permanganates when heated to about 250 give off oxygen with formation of a green manganate. 2KMnO 4 = K 2 MnO 4 + MnO 2 + O 2 *2. Solid permanganates dissolve in concentrated sulphuric acid, forming a deep green solution. On gently warming, violet vapours of manganese heptoxide, Mn 2 O 7 , are given off, and, at the same time, oxygen mixed with ozone is evolved. These gases are probably produced by the decomposition of the heptoxide. If this experiment is conducted in a test tube, it must be carried out with caution, because, when quickly heated, manganese heptoxide explodes. 2KMnO 4 + H 2 SO 4 = Mn 2 O 7 +K 2 SO 4 + H 2 O The best way to show the formation of manganese heptoxide is to place a few small crystals 01 a permanganate in a porcelain basin, and then to moisten with concentrated sulphuric acid, when a green solution is formed. On now placing the dish on a TJie Acids. 147 water bath, violet vapours are given off, which condense on the upper parts of the basin, forming a violet film. *3. Solutions of permanganates evolve chlorine when warmed with concentrated hydrochloric acid. 2 KMnO 4 -f i6HCl = sCl 2 + 2MnCl 2 + 2KC1 -f- 8H 2 O 4. Ammonium sulphide gives a flesh-coloured precipitate of manganese sulphide, which usually has a yellowish appear- ance, owing to admixture with sulphur. 2KMnO 4 -f 8(NH 4 ) 2 S = 2MnS + 58 + KoS-f- 8H 2 O -f i6NH 3 5. Hydrogen peroxide, when added to a solution of a per- manganate which has been acidified with sulphuric acid, causes evolution of oxygen (volumetric method for estimating strength of a solution of hydrogen peroxide). 2KMnO 4 4- 3H 2 SO 4 + sH 2 O 2 = sO 2 + K 2 SO 4 + 2MnSO 4 + 8H 2 O *6. All reducing agents decolourise solutions of permanganates, c.g. sulphuretted hydrogen, ferrous sulphate, oxalic acid, etc. If the solution is neutral or alkaline, a brown precipitate of hydrated manganese dioxide is produced. (a) 2KMnO 4 + = 2MnO 2 + 38 + 2KOH -f- 2H 2 O (b.) 2 KMnO 4 4- i oFeSO 4 -f- 8H 2 SO 4 = 5Fe 2 (S0 4 ) 3 + 2MnS0 4 -f- K 2 SO 4 4- 8H 2 O (c.) 2KMnO 4 4- 5C 2 H 2 O 4 + 3H 2 SO 4 = ioCO 2 + K 2 SO 4 -f 2MnSO 4 4- 8H 2 O Manganese is not precipitated from solutions of permanganates by the usual reagents, caustic alkalis, etc., because the man- ganese is present in the complex anion MnO 4 . Potassium permanganate, e.g., is dissociated in aqueous solution into the ions K" and MnO' 4 . As soon as reduction takes place, the manganese becomes the cation, and the colour of the solution changes from intense purple to colourless or light pink, e.g. MnSO 4 , which is dis- sociated into the ions Mn and SOJ. Manganese sulphide is 148 Qualitative Chemical Analysis. indeed precipitated from a permanganate on addition of ammonium sulphide, the explanation of this apparent anomaly being that the ammonium sulphide first reduces the permanganate to a manganese salt, the manganese then being precipitated as sulphide. The salts of H 2 MnO 4 are green, and contain the divalent anion MnO 4 . They are called manganates. The permanganates contain the monovalent anion MnO f 4, and are purple. Chloric Acid. HC10 3 Chloric acid is only known in aqueous solution and in form of its salts. The chlorates are all soluble in water. i. The chlorates are decomposed on heating, with evolution of oxygen gas ; e.g. 2 KC10 3 = 2KC1 + 30 2 *2. Concentrated sulphuric acid when added to a solid chlorate is coloured yellow, owing to the liberation of chlorine dioxide. If the mixture is warmed an explosion ensues, therefore only very small quantities should be taken. 3 KC10 3 + 2 H 2 S0 4 = 2dO 2 + 2KHS0 4 + KC1O 4 + H 2 O 3. On adding concentrated hydrochloric acid to a solution of a chlorate, the mixture becomes coloured yellow, and chlorine is evolved. KC10 3 + 6HC1 = 3 C1 2 + KC1 + 3 H 2 *4. Silver nitrate produces no precipitate with chlorates, because silver chlorate is readily soluble. If, however, the chlorate is first boiled with a little sulphurous acid, so as to reduce it to a chloride, a white precipitate of silver chloride is obtained. KC10 8 + 3 S0 2 + 3 H 2 = KC1 + 3 H 2 S0 4 Chlorates give no precipitate of silver chloride with silver The Acids. 149 nitrate, because the chlorine is present in the form of a complex anion : potassium chlorate, for example, when in aqueous solution being dissociated into the ions K' and C1O' 3 and silver chlorate Ag' and C1O' 3 . Bromic Acid. HBrO, This acid is only known in aqueous solution and in form of its salts. Most bromates are soluble in water. i. On strongly heating, the alkali bromates are converted into bromides, with evolution of oxygen. 2KBrO 3 = 2KBr -f 3O 2 Other bromates decompose with evolution of bromine and oxygen. Mg(Br0 3 ) 2 = MgO + Br 2 + 5 *2. Silver nitrate produces a white, beautifully crystalline precipitate of silver bromate, which is with difficulty soluble in nitric acid, but readily soluble in ammonia. KBrO 3 + AgNO 3 = AgBrO 3 + KNO 3 3. Mercurous nitrate produces a white precipitate of mercurous bromate. 2 KBr0 3 + 2HgN0 3 = Hg 2 (BrO 3 ) 2 + 2 KNO 8 4. Mineral acids decompose bromates with liberation of free bromine, bromic acid being first liberated, which then slowly decomposes into hydrobromic acid and oxygen. The hydrobromic acid then acts upon the bromic acid, thus HBr0 3 + 5 HBr = 3 Br 2 + 3 H 2 O *5. Sulphuretted hydrogen and sulphur dioxide reduce bromates to bromides. (a.) KBrO, + 3^ = KBr + 3 H 2 O + 3 S (b.) KBrO a + 3 SO a + 3 H 2 = KBr + 3 H a SO 4 IS 2 Qualitative Chemical Analysis. The addition of a small quantity of starch paste makes the reaction exceedingly delicate. *4. Hydrogen Auri-ehloride. In alkaline solution salts of gold are reduced, and finely divided gold is precipitated. The solution assumes a greenish or brownish-purple appearance. 2HAuQ 4 + sH 2 O 2 + SNaOH = 2 Au + SNaCl + 30 2 + 8H 2 O Hydroxyl Ion. OH' Solutions containing the hydroxyl ion are strongly alkaline, and will turn red litmus blue and yellow turmeric brown. *i. Phenol Phthalein. A deep purple solution is obtained when a solution of phenol phthalein is added to a solution containing free hydroxyl ions. *2. Ferric Chloride. On the addition of ferric chloride to a solution containing hydroxyl ions, a brown precipitate of ferric hydroxide is produced. Fe" + sOH' = Fe(OH) 3 Solutions of many other metallic salts behave in a similar manner, e.g. aluminum sulphate gives a white gelatinous precipitate; copper sulphate a greenish precipitate which turns black on boiling. (a.) AT + sOH' = Al(OH), (b.) Cu"+ 2OH' = Cu(OH) 2 It must be remembered that although the alkalinity of a solution is due to hydroxyl ions, it may not be due to the presence of an hydroxide. For example, a solution of sodium carbonate is strongly alkaline, the alkalinity being due to hydrolysis (see p. 121). A solution of potassium cyanide is likewise markedly alkaline (see p. 1 6), the alkalinity in this case also being due to hydrolysis. In both of these cases, besides giving the reactions for the hydroxyl ion, the solutions will give the reactions respectively for carbonates and cyanides. (For detection of hydroxyl in presence of carbonates, see p. 185.) CHAPTER X. ANALYTICAL TABLES FOR THE DETECTION AND SEPARATION OF THE METALLIC RADICALS (CATIONS) AND ACID RADICALS (ANIONS). Preliminary Examination of the Substance to be analysed. A. Heat a small portion of the dried and powdered substance in an ignition tube. (a.) The substance chars -> organic matter. (b.) melts -> fusible salts (e.g. alkali salts), some oxides, or salts containing much water of crystallisation. (c.) The substance swells up -> alums, berates, or Hg(CNS) 2 . (d.) changes in colour. These colour changes may be the result of complex double decomposition between substances occurring together, or they may be characteristic changes of the simple substance. Some examples of the common colour changes are noted below. i. Physical changes of oxides : Cold. Hot. Oxide. Light yellow White Yellowish-brown, does not fuse Yellow, does not fuse SnO, ZnO Yellow Dark brown, fuses PbO Lemon yellow Red Orange, fuses Black, on strong heating forms Bi 2 0, HgO globules of mercury Red Black, fuses on further heating, Pb 3 O 4 becoming yellow at the points of fusion Rusty red Black-red, does not fuse Fe 2 0, i5 2 Qualitative Chemical Analysis. The addition of a small quantity of starch paste makes the reaction exceedingly delicate. *4. Hydrogen Auri-chloride. In alkaline solution salts of gold are reduced, and finely divided gold is precipitated. The solution assumes a greenish or brownish-purple appearance. 2HAuCl 4 + sH 2 O 2 + SNaOH = 2Au + SNaCl + s0 2 + 8H 2 O Hydroxyl Ion. OH' Solutions containing the hydroxyl ion are strongly alkaline, and will turn red litmus blue and yellow turmeric brown. *i. Phenol Phthalein. A deep purple solution is obtained when a solution of phenol phthalein is added to a solution containing free hydroxyl ions. *2. Ferric Chloride. On the addition of ferric chloride to a solution containing hydroxyl ions, a brown precipitate of ferric hydroxide is produced. Fe" + sOH' = Fe(OH) 3 Solutions of many other metallic salts behave in a similar manner, e.g. aluminum sulphate gives a white gelatinous precipitate; copper sulphate a greenish precipitate which turns black on boiling. (a.) AT + sOH' = A1(OH), (b.) Cu"+ 2OH' = Cu(OH) 3 It must be remembered that although the alkalinity of a solution is due to hydroxyl ions, it may not be due to the presence of an hydroxide. For example, a solution of sodium carbonate is strongly alkaline, the alkalinity being due to hydrolysis (see p. 121). A solution of potassium cyanide is likewise markedly alkaline (see p. 1 6), the alkalinity in this case also being due to hydrolysis. In both of these cases, besides giving the reactions for the hydroxyl ion, the solutions will give the reactions respectively for carbonates and cyanides. (For detection of hydroxyl in presence of carbonates, see p. 185.) CHAPTER X. ANALYTICAL TABLES FOR THE DETECTION AND SEPARATION OF THE METALLIC RADICALS (CATIONS) AND ACID RADICALS (ANIONS). Preliminary Examination of the Substance to be analysed. A. Heat a small portion of the dried and powdered substance in an ignition tube. (a.) The substance chars -> organic matter. (b.) melts -> fusible salts (e.g. alkali salts), some oxides, or salts containing much water of crystallisation. (f.) The substance swells up -> alums, berates, or Hg(CNS)2. (d.) changes in colour. These colour changes may be the result of complex double decomposition between substances occurring together, or they may be characteristic changes of the simple substance. Some examples of the common colour changes are noted below. i. Physical changes of oxides : Cold. Hot. Oxide. Light yellow White Yellowish-brown, does not fuse Yellow, does not fuse SnO, ZnO Yellow Dark brown, fuses PbO Lemon yellow Red Orange, fuses Black, on strong heating forms Bi 2 3 HgO globules of mercury Red Black, fuses on further heating, Pb 3 4 becoming yellow at the points of fusion Rusty red Black-red, does not fuse Fe 2 0, 154 Qualitative Chemical Analysis. 2. Some sulphides undergo similar changes. 3. Dehydration of crystalline salts : Hydrated. Anhydrous. Substance. Blue or green Green Pink White or olive Dirty white or yellow Blue or violet Some cupric salts. Some nickel and iron salts. Some cobalt salts. 4. Changes of Colour due to Decomposition. The nitrates and carbonates of the heavy metals leave their oxides as residues; e.g. Original substance. Nitrates of mercury, colourless Cupric nitrate, blue Cupric carbonate, light green Cobalt nitrate, pink Nickel nitrate, green Ferrous sulphate, green Lead nitrate, colourless Lead carbonate, white Residue. Red HgO Black CuO Black CuO ! Black Co 2 O 3 Black Ni 2 O 3 Red Fe 2 O 3 Yellow PbO Yellow PbO 5, The substance evolves gas which is coloured Brown Greenish yellow Violet . . . White fumes . (a) Chromyl chloride from admixture of chloride and chromate. (b) Oxides of nitrogen from some nitrates and nitrites. (c) Bromine from some bromides and bromates. Chlorine from chlorides of gold, platinum, copper, etc. Iodine from some iodides and iodates. (a) Steam from water of crystallisation. (b) Hydrogen chloride from some chlorides. (c) Sulphur trioxide from certain sulphates. 50. The gas evolved is colourless and odourless : Oxygen . , . Nitrous oxide. Carbon dioxide . Carbon monoxide Rekindles a glowing chip of wood, from readily decom- posed oxides, peroxides, chlorates, and nitrates. Rekindles a glowing chip of wood, from ammonium nitrate. Steam will also be evolved. Turns lime-water turbid, from carbonates and oxa- lates, or admixture of carbon with oxidising agents. Burns with blue flame, from oxalates and other or- ganic salts. Analytical Tables. Gas is colourless with smell : 155 Sulphur dioxide . Cyanogen. . . Ammonia . Phosphoretted hy- drogen . Smells of burning sulphur, from thiosulphates, sul- phites, some sulphates, and from admixture of sul- phides with oxidising agents. Burns with purple flame, from cyanides of the heavy metals. Characteristic odour, and turns red litmus blue, from some ammonium salts and certain organic sub- stances ; e.g. urea, Odour of rotten fish, burns with a greenish flame, from hypophosphites. 6. A sublimate is formed : White. Coloured. Black. Ammonium, mercury, arse- Yellow : while hot, Arsenic, antimony, nic and antimony com- brownish drops of either in the free pounds, beside some or- liquid, sulphur state or from being ganic acids ; e.g. benzoic, set free by" action oxalic, etc. of reducing agents occurring in mixture. Examples, NH 4 C1, readily Yellow : becomes red Black, becoming red soluble in water on being rubbed, HgI 2 on rubbing, HgS. HgCl, HgBr, insoluble in Yellow: brownish-red Grey, cohering to glo- water while hot, As 3 S 3 bules on rubbing, HgCl 2 , HgBr 2 , soluble in Orange: almost black Black crystalline, sol- water while hot, Sb 2 S 5 uble in alcohol to As 4 O 6 octahedral crystals a brown solution. Sb 4 O g needle-shaped crys- Iodine. tals, not so readily vola- tile as As 4 O, When a white sublimate is obtained, a small quantity of the substance should be mixed with twice its bulk of soda lime, and heated in a test tube. If mercury is present, a mirror and globules of Hg will be produced on the cool part of the tube. A black mirror of arsenic is formed when arsenic compounds are present. A smell of ammonia points to the presence of ammonium salts. B. Heat some of the substance in a "draught tube" (a glass tube open at both ends) : I 5 6 Qualitative Chemical Analysis. (a) Sulphur and the sulphides of the heavy metals yield SO 2 , while more or less free sulphur may escape oxidation and appear as a sublimate. The sulphides yield residues or sublimates of metals, oxides, or oxysulphides. Examples : Metals. (1) Ag residue from Ag 2 S (2) Hg sublimate from HgS Oxides. (1) ZnO residue from ZnS (2) As 4 O 6 sublimate from As 2 S 3 (3) Sb 4 O 6 sublimate from Sb 2 S, () Carbon will be burnt off as CO 2 . (c) Some metals will be oxidised ; e.g. As, Sb, Mg, etc. Some of these yield sublimates. Other changes will go on as in the closed igni- tion tube. C. Heat a small portion of the substance in a tube with about three times its bulk of powdered soda-lime, or fusion mixture and potassium cyanide. Arsenic or antimony, if present, will form a black mirror on the sides of the tube ; mercury a grey mirror, which on rubbing with a match will cohere in globules. D. Heat a trace of the substance in the Bunsen flame on an asbestos thread, at the same time holding a porcelain basin over it as described under "Film Reactions," p. 7. If a film is produced, examine it according to the table on next page. E. Flame Test. Heat a little of the substance on a platinum wire in the Bunsen flame. First, however, moisten the wire with concentrated hydrochloric acid (p. 8) : Flame colour. Flame colour through blue glass. Element. i. Golden yellow 2. Violet I. 2. Violet-red I. Sodium. 2. Potassium. 3. Dull red 3. Greenish-grey 3. Calcium. 4. Crimson 4. Purple 4. Strontium. 5. Bluish-crimson 5. Purple 5. Lithium. 6. Yellowish-green 7. Green 6. Bluish-green 7- 6. Barium. 7. Boric acid, copper, phos- phates. 8. Lambent blue 8. 8. Copper, arsenic, antimony, bismuth, lead, cadmium, zinc. F. Examine the coloured flame through the spectroscope and Analytical Tables. 157 3 S 5 2 ng p tion hin soluti metalli II i:t M ~ .S 2 a ^ 2 K M 158 Qualitative Chemical Analysis. compare the spectra with the table at the commencement of the book. G. Apply the match test (see p. 6) : Appearance of metallic bead. Metal. 1. White, readily cut with a knife, marks paper 2. White and brittle 3. White, moderately soft 4. Red flakes, not usually a bead 5. Yellow flakes 6. Dark grey powder, which is magnetic Lead. Antimony, bismuth. Silver. Copper. Gold. Iron, nickel, cobalt. Separate the magnetic powder (Match Test, 6, above) from adhering carbon by means of a magnet or magnetised knife blade. Place any adhering particles upon a filter paper, and moisten with a drop each of dilute hydrochloric and nitric acids. Dry gently over the flame, faint pink turning blue cobalt ; greenish stain turning yellow nickel ; add a drop of potassium ferrocyanide to the stain, a deep blue coloration produced iron. The metallic bead should always be dissolved in nitric or hydrochloric acid, and wet tests applied, as much information can thus be obtained. H. Borax Bead Test: Reducing flame. Oxidising flame. I. Sapphire blue I. Sapphire blue Cobalt. 2. Red. (This may be more readily 2. Blue on cooling, green- Copper. obtained by adding a trace of ish while hot stannous chloride to the bead.) 3. Green 3. Green Chromium. 4. Yellowish-brown, often grey from 4. Yellowish-brown Nickel. specks of metallic nickel 5. Yellow while hot, bottle-green 5. Yellow while hot, Iron. on cooling 6. Colourless bottle-green on cooling 6. Amethyst violet Manganese. Element. I. Test for Ammonium Compounds. A little of the substance is boiled in a test tube with caustic soda. If a smell of ammonia is produced, and if a piece of moist red litmus paper held in the mouth of the tube be turned blue, presence of ammonium compounds is shown. K. Test for Manganese and Chromium. Mix a little of the substance with fusion mixture and a trace of nitre. Take up a portion of the mixture on a small loop at the end of a piece Analytical Tables. 159 of platinum wire and fuse in the oxidising flame of the Bunsen burner. A green mass shows manganese to be present. A yellow one shows the presence of chromium. If the two metals occur together, the green colour of themanganate obscures the yellow colour of the chromate. To test for chromium in the presence of manganese : dissolve the bead in water, add a few drops of alcohol, warm and filter. Acidulate the filtrate with acetic acid and add silver nitrate ; a red precipitate or colora- tion shows that chromium is present. Preliminary Examination for Acids. I. To a small portion of the substance add dilute sulphuric acid, and warm. Vapours are coloured. Vapours colourless and odourless. Vapours colourless and have an odour. I. Reddish - brown va- I. Effervescence takes I. Smell of burning sul- pours of NO 2 , nitrite. place. Hold a glass phur : sulphites. Confirm by i. or 6, rod which has been pp. 126, 127. moistened with lime- water in the mouth of the test tube. A white film of calcium car- bonate is formed on the rod : carbonate. 2. Reddish - brown va- pours of bromine. Pre- sence of bromide and 2. Hydrogen from ac- tion of certain metals on sulphuric acid. 2. Smell of burning sul- phur with precipitation of sulphur : thiosul- bromate together. phate. 3. Greenish-yellow, chlo- 3. Oxygen from perox- 3. Smell of rotten eggs. rine from hypochlo- ides or persulphates. Gas evolved turns lead rites. Confirm by paper black and nitro- adding lead acetate prusside paper violet : (3>P- 1 1 3) to the solu- sulphide. tion as prepared on p. 181. 4. Violet vapours of 4. Smell of bitter al- iodine. Presence of monds. Hold a glass both iodide and rod moistened with iodate. silver nitrate in mouth of test tube ; white coat- ing of silver cyanide : cyanide, ferrocya- nide, ferricyanide. 5. Vapours have a pun- gent acid smell. For- mate, acetate. i6o Qualitative Chemical Analysis. II. Add concentrated sulphuric acid to a small portion of the substance, and heat. Do not, however, heat to boiling, otherwise vapours of sulphuric acid will be given off which make it difficult to recognise the vapours of other acids. Vapours are coloured. Vapours colourless and odourless. Vapours colourless but have an odour. I. Brown vapours : bro- mine from bromides I. Oxygen gas evolved known by its ener- i. Sulphuretted hy- drogen, sulphur or bromates; chro- getically supporting dioxide (either from myl chloride from combustion : perox- a sulphite, or by action chromates in pre- ide, manganate, of reducing agents on sence of chlorides ; chromate, etc. sulphuric acid), and nitrogen peroxide from nitrites, and in cer- acetic acid may be obtained. (See I, 2, tain circumstances from and 4, p. 159.) nitrates. The bro- mine and chromyl chloride condense on the sides of the test tube to a brown liquid. 2. Very light brown va- 2. Carbon monoxide 2. White fumes: fluor- pours : nitrates. Con- which burns with a ide. Confirm by heat- firm by heating with blue flame: formate, ing with a little sand sulphuric acid and a oxalate, cyanide, and concentrated sul- piece of copper foil. Dark brown vapours ferrocyanide, and ferricyanide. phuric acid, and hold- ing a moist glass rod will be evolved if a in the mouth of the nitrate is present. test tube. The glass rod will, if a fluoride is present, become coated with a white film of silicic acid. 3. Violet vapours con- 3. Carbon dioxide from 3. White fumes : densing to shining cry- carbonates, oxa- hydrochloric acid, stals : iodide. lates, and other or- hydriodic acid, 4. Violet vapours of ganic acids. The hydrobromic acid. Mn 2 O T , which do not presence of organic Hy drobromic and hydri- form crystals : per- manganate. acids is usually ac- companied by char- odic acids are usually accompanied by fumes 5. Greenish yellow va- ring, and consequent of bromine or iodine. pours of chlorine evolution of sulphur dioxide, accompanied dioxide. by slight explosion : chlorate. 6. Chlorine from hypo- chlorites and from chlo- rides in presence of peroxides. Analytical Tables. 161 Treatment of the Substance to be analysed. I. The Substance is a Liquid. (a.) A few drops should be evaporated to dry ness on a piece of platinum foil. If no residue is left, and if the liquid is neutral to test-paper and has no odour, it is probably water. (.) If, on evaporating to dryness, a residue is left which, on further heating, chars, then organic matter is present, and must be eliminated before analysing for the metals (see p. 165). If there be no organic matter, proceed at once to test for bases and acids (cations and anions). The odour and colour of the solution will often give very useful information. (c.) Test the solution with litmus paper ; if it is alkaline, it may be due to the presence of hydroxides, alkali carbonates, peroxides, cyanides, borates or sodium salts of aluminium, or zinc. Test for peroxides (p. 151), carbonates (p. 121), hydroxides (p. 152). If the solution has an acid reaction, free acids or the acid salts may be present. II. The Substance is a Solid, The solid must be finely powdered, and a small portion, in no case the whole of the substance, should be treated with (a.) Water, first cold and then boiling. If it dissolves, proceed at once with analysis. If it appears to be insoluble, filter and evaporate a few drops of the filtrate to dryness on platinum foil or on a watch-glass. A residue indicates that a portion has dissolved. (b.) Treat the undissolved portion with dilute hydrochloric acid, and boil. If it does not dissolve, add strong hydrochloric acid, and again boil. It may be necessary to boil for some minutes, because such substances as FeaO 3 or MnO 2 only dissolve on continued boiling. In any case, should chlorine be evolved, M 1 62 Qualitative Chemical Analysis. the boiling must be continued till the gas is no longer given off, because the evolution of chlorine proves that action is taking place. If the substance appears not to dissolve, add about 3 volumes of water to the mixture, and boil ; solution may then take place. For example, when stannic oxide is boiled with hydrochloric acid, a chloride Sn 5 O 5 Cl 2 (OH) 8 is produced ; this is insoluble in strong hydrochloric acid, but dissolves on addition of water. Again, on treating potassium antimonate and potassium arsenate with hydrochloric acid, solution is not readily obtained, but on dilution and boiling, a clear solution is produced. The dry reactions are very useful guides as to how to treat in order to obtain solution. (c.) If it is insoluble in hydrochloric acid, boil another small portion with aqua regia (3 parts cone. HC1, i part cone. HNO 3 ). Treatment of Substance in Solution. A. The Aqueous Solution. Add dilute hydrochloric acid, and go through the group separations. B. The Hydrochloric Acid Sohition. Pass or add sulphu- retted hydrogen to the hot solution, and go through the group separations. C. A Portion of the Substance is soluble in Water, and another Portion in Hydrochloric Acid. If on adding a drop of hydro- chloric acid to the first solution no precipitate is produced, the two portions may be mixed. If a precipitate is produced, add hydrochloric acid until precipitation is complete. Filter oif, and examine the residue for metals of the silver group. These solutions may either be mixed or analysed separately. Generally speaking it saves trouble and often complications to analyse them separately, because each solution may only contain one substance, in which case it is merely a question of analysing two simple solutions. A precipitate may be produced on adding the aqueous solution to the hydrochloric acid, solution, even if the metals of the silver group are absent. This may be due to the formation of the oxy chlorides of bismuth, antimony, or tin. In such a case pass sulphuretted hydrogen without filtering, because Analytical Tables. 163 the finely divided oxychlorides will be converted into sulphides. The two solutions should not be mixed until the aqueous solution has been tested for metals of the silver group. D. The Solution in Aqua Regia. Evaporate nearly to dryness Add a little concentrated hydrochloric acid, and again evaporate to small bulk, in order to get rid of the last traces of nitric acid, which would cause precipitation of sulphur on passing sulphuretted hydrogen through the solution. Now dissolve the residue in hot water, adding a little hydro- chloric acid, if necessary, to re-dissolve bismuth, antimony, and tin oxychlorides. E. When a powder does not apparently dissolve in hydro- chloric acid, it is difficult sometimes to say whether the substance was originally insoluble in acid, or whether it has been converted into an insoluble chloride. Should this difficulty arise, treat a small portion of the original substance with nitric acid, and add a few drops of hydrochloric acid to the solution.f If the metals of the silver group are present, a white precipitate will be produced. In this case treat a fair quantity of the sub- stance in the same manner, and, after filtering off the precipitate, employ the solution for the analysis of the succeeding groups after the removal of nitric acid as described in the preceding paragraph. Analyse the residue for the silver group. Treatment of Substance insoluble in Acids. The chief substances insoluble in water and in hydrochloric acids are the halogen salts of silver and mercurous mercury, the sulphates of barium, strontium, and lead, mercuric sulphide, stannic oxide, calcium fluoride, ignited oxides such as Al a O 3 , SnO 2 , Sb 2 O 8 > Cr 2 O 8 , fused PbCrO 4 , and a few others. Aqua regia will not dissolve the halogen salts of silver (in fact, aqua regia converts silver salts into insoluble silver t It should not be forgotten that when soluble silver salts are present in a mixture, and also soluble halogen salts, that the addition of water will cause insoluble halogen silver salts to be formed ; these are, with the exception of the iodide, soluble in ammonia. 1 64 Qualitative Chemical Analysis. chloride), ignited Cr 2 O 3 , A1 2 O 3 , and fused PbCrO 4 ; neither will it attack the sulphates of barium and strontium ; SiO 2 is also insoluble. CaF 2} although insoluble in aqua regia, can be decom- posed with concentrated sulphuric acid. The dry reactions should indicate whether any of these sub- stances are present in a mixture, and should therefore act as a guide for the treatment of the insoluble portion. For example, all the silver salts are readily reduced, and small beads of the metal can be obtained by means of the match test. Lead and tin can also be obtained as metal. The beads may be dissolved in nitric acid and tested in the wet way. Sulphates, when heated on charcoal, are easily reduced to sulphides (see p. 128). I. The sulphates of barium and stiontium, and oxides such as A1 2 O 3 , Cr 2 O 3 , Sb 2 O 3 , and SnO 2 , are most conveniently brought into solution by fusing the solid substance with three times its weight of dry fusion mixture in a silver, platinum, or porcelain crucible.! The addition of a small quantity of sodium peroxide causes the reaction to take place at a lower temperature. When the fused mass forms a clear fluid, it is cooled and the fuse boiled with distilled water. The residue, if any, is filtered off. In the case of the metals barium and strontium, it consists of the carbonates of these metals. In the other cases cited, the metal is contained in the solution as sodium chromate, sodium aritimonate, etc. II. (a.) Insoluble silicates. Supposing it is required to analyse glass, porcelain, or other silicates, they can be brought into a condition for analysis by fusion as already described for the sulphates. Sodium silicate, which is soluble in water, is produced ; aluminium would also be converted into the soluble sodium aluminate, whereas iron would remain as a residue when the melt was treated with water. The solution, after acidifying with hydrochloric acid, is evaporated to dryness, when the silica is obtained as insoluble SiO 2 , and on extracting with dilute hydrochloric acid is left behind. (b.) Or the silicate may be heated with hydrofluoric acid, t Nickel may also be used, but in this case usually a small amount of nickel will be found in the fuse. Silver is really the most satisfactory. Analytical Tables. 165 when the silica is converted into silicon tetrafluoride, which is driven off on heating. III. Insoluble tin compounds, such as native tin stone, are best converted into the soluble condition by fusion with sulphur and sodium carbonate. Mix the dried substance with five or six times its weight of a mixture of equal parts of sulphur and dry sodium carbonate. Place in a crucible and put on the lid ; now heat over a small Bunsen flame until all the sulphur has burned off. On cooling, treat the fuse with hot water and filter. The insoluble portion may consist of the sulphides of other metals which do not form thio-compounds. The tin is obtained in the form of sodium thio-stannate Insoluble halogen salts, which can only be silver salts, may be decomposed by bringing them in contact with zinc in presence of dilute sulphuric acid. Zn + 2AgCl = 2Ag+ ZnCl 2 The metallic silver is filtered off and washed with a little water ; it can then be dissolved in nitric acid, and tested as usual. The solution is tested for the halogen acid. Elimination of Organic Matter. Organic matter need not, as a rule, be removed until after the precipitation of the metals of the copper group. Large quantities of tartaric or oxalic acids interfere, however, with the precipitation of tin. If this metal is present, these acids should be removed before passing H 2 S. To remove the organic matter the substance is evaporated to dryness and ignited, thus charring and destroying most organic materials. Oxalates do not char, but are converted into carbonates or oxides. When thoroughly charred the residue is dissolved in water or dilute hydrochloric acid. The solution is then filtered from charcoal and examined, as usual. 1 66 Qualitative Chemical Analysis. If it is necessary to remove the organic matter before com- mencing analysis for the metals of the silver and copper groups, the substance may be ignited as above. But should mercury, arsenic, or antimony be present such a proceeding is inadmis- sible, because salts of these metals are volatile. In presence of these metals the following method should be employed : Mix the finely powered substance into a thin paste with concentrated hydrochloric acid, heat on the water bath and stir in about \ gram of powdered potassium chlorate, repeating the addition every five minutes till about i gram of potassium chlorate has been added. Now add about 5 c.c. of concentrated hydrochloric acid, and evaporate to a pasty consistency. Dissolve in water, and analyse as usual. If the metals of the silver group are present, the chlorides formed will not dissolve in water. By this treatment any arsenic which may have been present will have been converted to the higher state of oxidation. The solution, therefore, must be reduced by boiling with sulphurous acid before passing or adding sulphuretted hydrogen. III. The Substance appears Metallic. (a.) Treat a small portion of the substance with dilute hydro- chloric acid, and boil. If it dissolves, analyse as usual. (b.) If it is insoluble in dilute hydrochloric acid, boil with a little strong hydrochloric acid. If soluble, dilute with water, and analyse as usual. (c.) If still insoluble, treat the original substance with nitric acid (one part acid to one part water). When nitric acid is used the solution must be evaporated nearly to dryness, and the residue taken up with water. On treatment of a metal with nitric acid a white residue may be left. If it dissolves on adding excess of water it is probably lead nitrate, which is insoluble in strong nitric acid. If the residue is insoluble in water it may be antimony pentoxide, Sb 2 O 5 , or metastannic acid, Sn 5 O 6 (OH) 10 .f These oxides will dissolve on boiling with hydro- chloric acid. t Metastannic acid appears not to be acted on by concentrated hydro- Analytical Tables. 167 (d.) The noble metals, such as platinum and gold, are only soluble in aqua regia. Gold and platinum may be separated from each other and from most other metals, by dissolving in aqua regia and evapo- rating several times to dryness to remove nitric acid. The residue is then dissolved in dilute hydrochloric acid, and the gold thrown out of solution in the metallic form by the action of reducing agents, such as oxalic acid, sulphurous acid, or ferrous sulphate (p. 61). The precipitated gold is filtered off, and the platinum precipitated as ammonium platiniehloride (p. 62). In alloys which contain a large proportion of silver or lead, gold may be separated by boiling with nitric acid in a platinum dish and extracting with water the residue, after decantation, consisting of metallic gold. When the proportion of gold is high, it will protect the alloy from the action of nitric acid. In such cases the alloy may be melted up with an excess of silver or lead, and then treated with nitric acid, when the silver or lead will go into solution and the gold will be left, as already described. The gold being in the form of a fine powder is very often black ; the yellow appearance may, however, be made manifest by rubbing or by melting it before the blowpipe. Cautions. i. Large quantities of substance should not be employed in analysis, because the precipitates produced will be so bulky that difficulty will be experienced in washing or dissolving them. 2. Precipitates, unless otherwise stated, must always be washed; and the first wash water must be mixed with the solution from which the precipitate has been filtered. If this precaution is omitted the student will in all probability fail to find metals which occur in the barium or sodium group. 3. If the precipitate is to be treated with a solvent, such as chloric acid. It is, however, converted into metastannic chloride, which is insoluble in concentrated hydrochloric acid. If the excess of acid is poured off and water added, it then goes into solution. It may also be dissolved in caustic alkalis. 1 68 Qualitative Chemical Analysis. ammonium sulphide in the copper group, a small portion of the precipitate should in the first place be subjected to the action of the solvent, because if it is quite insoluble there is no advantage in treating the whole precipitate. 4. If a solution is to be made acid, an excessive quantity of acid must not be employed. A neutral solution is one which neither turns blue litmus red nor red litmus blue. A solution is either neutral or it is not. When an acid solution is to be made alkaline, the mixture must be shaken up and tested with litmus paper after the alkaline solution has been added. Mistakes often occur through the student supposing he has made his solution alkaline (or acid) when the surface of the liquid alone is alkaline (or acid). 5. The use of excessive quantities of "reagents" should be avoided. It is only necessary to employ a sufficient quantity of the reagent to cause the particular reaction to take place, further additions causing an unnecessary increase in bulk, and even at times leading to errors. 6. Should the bulk of solution at any stage of analysis become too great, it must be evaporated to small volume. Instead of this being time lost, it more often results in a saving of time. As a general rule, the solution should be evaporated down considerably before proceeding to the next group. 7. It is a good rule to always take the same quantity of substance for analysis, say from i to i'5 grm. When this is done it is possible with a little experience to judge approximately the relative quantities of the various substances present in the mixture. 8. All the apparatus employed in chemical analysis must be kept strictly clean. The use of a dirty stirring rod or test tube may be sufficient to cause the introduction of some foreign substance in the material which is under examination. Analytical Tables. 169 bfl c -5 < 3 u hydrochlori ce, and filter. :1 -o 08 'o o aSS d evaporate to 4 OH until dis- anent. Before phosphates, acids. In the ed. Filter. c.S S - 1 *H 3 '-u O . an H m 8 xc S u Solution and filter Is rt s 3 I 5 cd Boi ution excess of filter. Sol y e a th K Ex m tion : ntain tals Mg, , and Li. ineby sch p. 179 (So- m Group). et a, Sol co m N am m n iu o d Cg CX, & rt^ 3^S^ ^;- s nd F vo eci n ^ e s s ^ 0^ x-s e o s "i o 2 -T w ' w Cj c O, w rQ r ,^ 2 -a rt O*!g g S ! Sg ll "S3 ,3 4J 4> H ^ *ii .& 1 11 c/3 .^i o 176 Qualitative Chemical Analysis. *rrt k" 1 G G N'S 12 o ,2 < o 'ill I-M O KH , , . ^wift-oS c^ 2 ^^-^3 &l!! a .5 SSJIffl 52sai ^s ^ ^<^2 O 8-S ft^ o^^! >h^^ * I (*~S H ? " ^5 ious s H eS, acid IVE SEPAR e from the prev ut filtering, pas NiS, CoS, F . hydrochloric hot filtrat nd, witho L y contain ' cold 2N vaporate ,ke stron y J| 95s l^a ell as-! sS>^ sis fes-s d t3 TJ a'ss rrt v n 9" I g" ^ . 1.1 2 - II be Fe(OH) 3 , MnO 2 , fash with warm water, L minute with dilute ter. . >FM jJ o >-. CU ** 11 Is 1 15=3 1 Ig s Analytical Tables. 177 ^ Barium Group. To the hot solution from the iron group add a slight excess of (NH 4 ) 2 CO a , allow to stand five minutes, and filter. (Cf. p. 93.) Precipitate may be the carbonates of barium, strontium, and calcium. Should there be a large quantity of solution from the iron group, it must be evaporated to small bulk before adding (NH 4 ). 2 CO 3 . Wash the precipitate with hot water. Pierce a hole through the bottom of the filter paper, and wash the precipitate into an evaporating dish with a little dilute HNO 3 . Evaporate to dryness. As the nitrates may on no account be ignited, it is best to complete the evaporation on the water bath. Dissolve a small portion of the residue in water, and add CaSO 4 solution. NOTES TO PAGE 176. t If the solution has a brown colour, this is owing to too much ammonium hydrate having been added, and is due to the slight solubility of nickel sulphide in excess of ammonium hydrate. Add a little acetic acid to the brown solution, boil, and filter ; the nickel sulphide will be thus precipitated, and may be mixed with the rest of the precipitate, or separately tested with the borax bead. \ The sodium peroxide should be added in small quantities at a time, the amount required depending upon the quantity of the substances in solution. The advantage of using sodium peroxide is that it contains no alumina, while caustic soda usually contains considerable quantities, and may thus be a source of error in analysis. Bromine water is sometimes used as an oxidising agent, but when it is employed, some part of the manganese is often converted into manganate or permanganate, and thus interferes with the detection of the chromium. In order to test for cerium in presence of iron, the solution is divided into two portions, the smaller of which is tested for iron by diluting with water and adding KCNS. The second and larger portion has excess of citric acid added to it, and is then made just alkaline with NH 4 OH. The citric acid prevents the precipitation of ferric and eerie hydrates. Excess of oxalic acid is now added, when a white precipitate of cerium oxalate is obtained. || Traces of nickel and cobalt may be found here, owing to their sulphides not being quite insoluble in dilute hydrochloric acid ; they cannot, however, be confounded with iron. N 178 Qualitative Chemical Analysis. (i.) An immediate precipitation is produced barium is present. (ii.) A precipitate is slowly formed, bSrium is absent strontium is present. (iu\) No precipitate produced, barium and strontium are absent calcium may be present. Dissolve the rest of the residue in water, add one or two drops of ammonia and then ammonium oxalate : a white precipitate confirms calcium. If a precipitate was produced with CaSO 4 , proceed by one of the following methods : I. Treat the dry residue with 2 c.c. of strong nitric acid, stir the mixture for a minute or two, and filter through asbestos.t Solution: May contain Ca(NO 3 ) 2 , this salt being soluble in strong nitric acid. Ren- der the solution just alkaline with NH 4 OH, and add ammonium oxalate. A white precipitate indi- cates Calcium. Confirm with flame t e s t + and spectroscope, P- 91- Residue : May contain Ba(NO 3 ) 2 and Sr(NO 3 ) 2 , both these nitrates being insoluble in concentrated nitric acid. Wash with a little strong HNO 3 to remove traces of calcium. Then wash off the filter with a little hot water. (Sufficient water must be used to dissolve the residue.) Make just alkaline with am- monium hydroxide, add a slight excess of acetic acid, then K 2 CrO 4 , and filter. Residue: Is barium clir ornate. Confirm by flame test. The flame is coloured green, and shows the characteristic bands for barium when viewed through the spec- troscope. Confirmation of Barium. Solution : Add 2-3 drops of concentrated sulphuric acid, and about 3 c.c. of (NH 4 ) 2 SO 4 . A white precipitate of strontium sulphate indicates Strontium. Confirm by flame test and spectroscope. II. Add 2 to 3 c.c. of a mixture of equal volumes of absolute alcohol and ether to the dry nitrates, and, after stirring, filter (the filter paper should be first moistened with absolute alcohol). t As the asbestos causes filtration to be rather slow, it is best to use a funnel with a long tube, as described on p. 23. \ The precipitates should always be moistened with strong hydrochloric acid before applying the flame or spectroscopic test. Potassium chromate should only be added to a small portion of the solution. If a precipitate is produced, then it must be added to the whole of the solution. In the event of no precipitate being formed, the bulk of the solution is used to test for strontium. Analytical Tables. 179 Wash the residue twice with small quantities of a mixture of alcohol and ether. Residue : Dissolve the nitrates in a little warm Solution : May water, add 2 or 3 c.c. of strong HC1, and evaporate to dryness. Stir the residue with a little absolute contain Ca(NO 3 ) 2 . Evaporate to dry- alcohol and ether. Filter. ness on the water bath, dissolve in a little water and Solution: Contains SrCl 2 Residue : Wash two or add a few drops Evaporate to dryness, three times with a little of ammonium hy- and confirm by flame alcohol. Test by means droxide, and then test and spectroscope. of flame coloration for ammonium oxa- Dissolve remainder of barium. Dissolve the late. A white pre- residue in a very little remainder of the residue cipitate confirms water and add 2 drops in a little water, and add Calcium. of cone. H 2 SO 4 and 3 c.c. (NH 4 ) 2 SO 4 . Allow to stand. A white precipitate confirms K 2 CrO 4 . A yellow pre- cipitate confirms Barium. Further confirm by flame test and spectroscope. Strontium. Sodium Group. Evaporate the solution from the barium group to dryness f and ignite until no more fumes are given off. Dissolve in a little dilute HC1, and filter from any residue. Divide the solution into two unequal portions. \ I. Smaller Portion. Add i c.c. ammonium chloride, then 2 c.c. Na 2 HPO 4 and 3 or 4 c.c. strong NH 4 OH. Shake up, and rub the sides of the test tube with a glass rod ; allow to stand a few minutes. A white crystalline precipitate of Mg(NH 4 )PO 4 shows the presence of magnesium. II. Larger Portion, if magnesium is present. { Add a slight excess of Ba(OH) 2 , boil, and filter. The residue is magnesium hydroxide, and may be discarded. Now pass carbon dioxide f The solution should be evaporated on the sand bath till it begins to spirt. The final evaporation should then be carried out on a water bath, and the ignition should only be commenced when the residue is quite dry. .(Seep. 102.) \ If magnesium is not present, do not treat with Ba(OH) 2 , but test at once for sodium and potassium. i i8o Qualitative Chemical Analysis. gas through the solution,! and boil for a minute or two, filter. Evaporate the solution to dryness. Test for potassium by means of flame coloration. J 1. The flame is coloured violet presence of potassium, absence of sodium. 2. The flame is yellow presence of sodium, potassium may also be present. Examine through blue glass, the flame has a lilac colour, potassium is also present. A. Confirm potassium by dissolving a portion of the residue in a very small quantity of water, (a) add i drop HC1 and a small quantity of H 2 PtCl 6 and an equal volume of alcohol. Golden yellow crystals confirm potassium, (b) or to the solution add a few drops of a strong solution of sodium hydrogen tartrate and a few drops of sodium acetate, rub with a glass rod a white crystalline precipitate confirms potassium, (c) confirm with Na 3 Co(NO 2 ) 6 . B. To another portion dissolved in a little water add K 2 H 2 Sb 2 O 7 , a white precipitate confirms sodium. Systematic Examination for Acids. By the study of the behaviour of the substance towards solvents, and by the absence or presence of certain metals, an idea of what acids may be present can be formed. Thus, if the substance is soluble an water, and bases of the barium group f On passing CO 2 through the solution the barium hydroxide is converted into barium carbonate ; as, however, part of it will probably be converted into the bicarbonate, it is necessary to boil the solution in order to decompose it. Ammonium carbonate may be used instead of CO 2 , but in this case the solution must be evaporated to dryness and ignited to drive off the ammonium salts before hydrogen platinichloride is added. J If the presence of lithium is suspected, a few drops of hydrochloric acid should be added to the residue before testing for potassium and sodium ; the solution must then be evaporated quite to dryness, and the residue extracted with a mixture of equal volumes of ether and absolute alcohol. The solution will contain the lithium chloride, which on evaporating off the solvent may be confirmed by the flame test, or the reactions on p. 99. The residue of sodium and potassium chlorides is dissolved in a little water and treated as described above. Analytical Tables, 181 have been found, then sulphuric, carbonic, or phosphoric acids are not present. Should silver be present, and the substance is soluble in water, evidently chlorides, bromides, or iodides are not present. Similar considerations will indicate whether it be necessary to remove the bases. In all probability, moreover, a fair idea of what acids are present will have been obtained from the preliminary examination. NOTE. The student is cautioned against wildly applying tests for acids which cannot possibly be present. Analysis must be systematic, but the students who allow any carefully worked out scientific system to cause them to become mere machines, going through operation after operation without taking the trouble to think whether it is necessary or not, need never expect to excel, neither will their work be trustworthy. Preparation of a Solution in which to test for Acids (Anions). I. The substance is soluble in water or dilute acids, and does not contain metals of the copper, arsenic, or iron groups. The solution may be employed to test for the acids without further preparation. II. If it is soluble but contains heavy metals, it is advisable to remove them by adding to the solution sufficient sodium carbonate to precipitate the metals as carbonates, which are filtered off, and the solution, after neutralising with acetic acid, tested for the acids,t e.g. 5ZnS0 4 + 5Na 2 CO 3 + sH 2 O = 2ZnCO 3 , 3 Zn(OH) 2 + 5NaO 4 + sCO a III. If arsenic or antimony are present, they should be removed by acidifying the solution (after it has been treated with sodium carbonate), with acetic acid and passing sulphuretted f It s sometimes difficult to remove copper by simply boiling with sodium carbonate. If the solution after boiling with sodium carbonate is blue, acidify with acetic, and pass sulphuretted hydrogen. 1 82 Qualitative Chemical Analysis. hydrogen. Before testing for the acids, the sulphuretted hydrogen must be boiled off. IV. The substance is insoluble in water and acids. In this case fusion may be necessary or treatment with a large excess of sodium carbonate (see p. 21). Add to the substance about three times its bulk of solid sodium carbonate and just sufficient water to bring the sodium carbonate into solution. Boil for 5 or 10 minutes, filter, and then wash with several small quantities of hot water. The solution may then be tested for acids. If halogen silver salts are present, it is best to add zinc and sulphuric acid, and proceed as directed on p. 165. In testing for the acids only, use small quantities of the solution, and always reserve a considerable portion for confirmatory tests. If arsenic or chromium have been found when analysing for the metals, ascertain, by taking a small portion of the original mixture whether they were there as anions or cations, and then remove them before testing for the other acids. Preparation of a Neutral Solution. The best way to prepare a neutral solution is, if the solution is alkaline, to make it slightly acid with acetic acid, then add a slight excess of ammonia, and boil until the excess of ammonia is driven off. If it is originally acid, add a slight excess of ammonia and proceed as above. For acid grouping, see p. 184. NOTES TO ACID TABLE I. (See next page.) f If a precipitate is produced which is soluble in hot water, it points to the presence of nitrites, sulphates, or borates, the silver salts of which are only precipitated from fairly concentrated solutions, and are soluble on boiling. J Even if the precipitate is reduced on boiling, the whole of it should be treated with nitric acid. It must be remembered that silver nitrate gives a brown precipitate with ammonia, but with a little care and experience there is very little chance of mistaking this brown colour for that of the acids mentioned. If arsenic and chromium have been removed, as recommended, from the original solution, arsenates, arsenites, or chromates will not be found here. || If cyanides are not present, the silver nitrate is added to a portion of the original solution, acidified with nitric acid. Analytical Tables. 183 -* II :a a s'S 3 *j K S is ""1 ** ill ~ M d O 11^ PI a H _Z ^ 4- M C/J i!t:-i s S2g 8 S .& g* g| V i-U O p >-i "T? UJ s^lltsill^lal |ft|^|li|| rt .ti &1S s rt rt I; 3 ^ g guffi'i igJ?^ 5 ^ ' . o-2^U rt -g H d ^|.2,,^ 2^ S^rt 2 3-sc-t x-^ lis^is-i*-! a?l|liil-ili H si fin 1 III *!iilML 8 j* ^g a rt T3 fl'S 5 e %f 32 .Si rt O h-t w ^- w w MMt>4 4-1 Owit^^M *O * |H IH HH IM I ( i^iPM^il^; d2p4" i i isrs^aiiy K i>: L^^t IS^a 5 a|? 8 f tlt<^ i s/~ tfl-w^^js^a ""SrS I 2 P^ >,-;ggjj5 w- n = ) 'w)2 ( "'^o I i-^-ifE 1 84 Qualitative Chemical Analysis. As already stated (p. 105) the acids may be divided into five groups, according to their behaviour with silver nitrate and with barium chloride. For convenience of reference the groups are reproduced here : Group L HC1, HBr, HI, HCN, H 4 Fe(CN),, H 3 Fe(CN) 6 , HC1O, HCNS. Group //. H 2 S, H 3 PO 2) H 2 SO 3 , H 2 S 2 O 8 , HNO 2 . Group ///. H 3 P0 4 , HP0 3 , H 3 PO 3j H 4 P 2 O 7J H 2 S 2 O 35 H 3 BO 3 (in strong solution), H 3 AsO 3 , H 3 AsO 4 , H 2 Cr0 4) H 2 SiO 3j HIO 3 , H 2 C0 3 . Group /K H 2 SO 4 , HF. Group KHNO* HC10 3 , HC1O 4J HMnO 4 . ACID TABLE II. To a portion of the original hot neutral solution, add an excess of barium chloride. No precipitate is produced: absence of Groups III. and IV. A precipitate is formed. Treat with a little dilute hydro- chloric acid, and warm. The precipitate dis- solves : absence of Group IV., HF and H 2 SO 4 . Precipitate does not dissolve. Group IV. is present. HF, if present, will have been found in the preliminary reactions. Boil the precipitate with an excess of strong HC1 ; if it is still insoluble, then sulphuric acid is present, f Observe. Group /. Hypochlorites will have been indicated in the preliminary tests : confirm by 4, p. 113. Group II. Persulphates : confirm by 3, p. 129. Sulphites. Test for sulphites by adding a few c.c. of bromine water, A white precipitate confirms H 2 SO 3 . Group III. is present : all these acids should have been found in the preliminary tests or when testing for the metals. Borates may be tested for by taking a small portion of the original mixture and treating it according to 3, p. 142. Thiosulphites : on warming a little of the original solution t CaF 2 is soluble in hot strong HC1. Analytical Tables. 185 with dilute sulphuric acid, sulphur is precipitated, sulphur dioxide evolved. Phosphates are tested for after removing the metals of the copper and arsenic groups. Silicates will either have been found in preparing a solution of the substance, or before testing for the metals of the iron group. lodic Acid : confirm by 7, p. 151. Group IV. Nitrites will have been indicated in the pre- liminary tests : confirm by 2, p. 126. Chlorates and Perchlorates will have been found in the preliminary examination on warming with strong sulphuric acid. Nitric Acid. Test a portion of the original solution which has been acidified with dilute sulphuric acid for nitric acid, by adding an equal volume of a freshly prepared solution of ferrous sulphate, and cautiously pouring concentrated sulphuric acid down the side of the test tube. A brown ring will be formed where the two liquids meet if a nitrate is present. If nitrites, bromides, or iodides are present, test for nitric acid, as described on p. 127. The presence of permanganate will have been recognised by the intense violet-red colour of the solution, the colour dis- appearing when the solution is warmed with dilute sulphuric and oxalic acids. Hydroxyl Ion in presence of soluble carbonates. To the solution add an excess of barium chloride. This precipitates the CO," as barium carbonate. On now adding phenolphthalein a red coloration is produced if OH' is present. The barium chloride is added in excess in order to entirely prevent the BaCO 3 from being ionised. Other Tests. I. Add ferric choride to solution acidified with hydrochloric acid. 1 86 Qualitative Chemical Analysis. 1. Blood-red coloration disappearing on addition of mercuric chloride : thio sulphuric acid. 2. Olive brown : hydroferricyanic acid. 3. Deep blue precipitate, turning brown on addition of excess of caustic alkali : hydroferrocyanic acid. For separation of ferro- and ferricyanides, see p. 119. 4. Iodine may be liberated from iodides; it dissolves in carbon disulphide, forming a violet solution. II. On adding ferric chloride to a neutral solution, beside the above colorations the following will also be shown : 1. Red coloration, which disappears on boiling, a brown basic iron salt being precipitated: sulphurous acid, acetic acid, formic acid. 2. Reddish-violet coloration, colour vanishes on warming : thiosulphuric acid. Organic Acids. If the substance chars when heated in a dry tube, organic acids must be looked for. For the analysis of organic acids, see Part II. In the grouping as above set out, certain organic acids might be found, e.g> tartaric acid, oxalic acid, in Group III. Analytical Tables. 187 Rarer Elements, It is not possible within the scope of this book to give com- plete analytical tables for the separations of the rarer metals, nor, indeed, to set out the reactions of all of them. In fact, owing to the similarity of the reactions of some of them, analytical separa- tions are often extremely difficult. Many of the elements are exceedingly rare, and are therefore much too expensive to pro- cure for ordinary analytical practice. The reactions of some of the more frequently used or occurring of these elements are, however, given, and the groups to which they belong. Silver Group. Thallium and Tungsten are precipitated with the metals of the silver group, the first as thallous chloride T1C1, and the second as Tungstie acid, H 2 WO 4 . Copper and Arsenic Groups. Ruthenium, Ru 2 S 3 ; Rhodium, Rh 2 S 3 ; Palladium, PdS ; Osmium, OsS ; Indium, IrgSg ; Molybdenum, MoS 3 ; and the Metalloids, Selenium (ppt. as Se) and Tellurium, TeSo. The sulphides of Ir 2 S 3 , TeS 2 , MoS 3 , and Selenium as metalloid are soluble in ammonium sulphide. Iron Group. Glucinium (Berylium), G1(OH) 2 ; Cerium, Ce(OH) 3 ; Scandium, Sc(OH) 3 ; Yttrium, Y(OH) 3 ; Ytterbium, Yt(OH) 3 ; Lanthanum, La(OH) 3 ; Thorium, Th(OH) 3 ; Zirconium, Zr(OH) 4 ; Titanium, H 2 TiO 3 ; Tantalum, H 3 TaO 4 ; Columbium, (Niobium), H 3 CbO 4 ; Uranium, (UO 2 )S; Indium, InS; Vanadium (not ppt. as sulphide, see reactions, p. 191). The elements to and including Zirconium form basic hydroxides. Titanium, Tantalum, and Columbium form acidic hydrated oxides, while Uranium and Indium form sulphides. Sodium Group. Rubidium and Caesium. Tungsten. Tungsten minerals are fairly widely distributed, but are by no means plentiful. The metal is very hard, and has somewhat the appearance of iron. 1 88 Qualitative Chemical Analysis. Tungsten forms two oxides, tungsten dioxide, WO 2 , a brown powder obtained by heating tungstic oxide in a stream of hydrogen WO 8 + H 2 = WO 2 + H 2 O Tungsten trioxide, WO 3 , is an acid anhydride which is pro- duced by ignition of tungstic acid H 2 W0 4 = W0 3 + H 2 It is a bright yellow powder insoluble in dilute acids, readily soluble in warm alkali hydroxides. Dry Reactions. i. Microcosmic Bead. Colourless in the oxiding flame, bright blue in reducing flame, the addition of ferrous sulphate causes it to become blood-red. Reactions in Solution. Use a solution of sodium tung- state. 1. Mineral Acids give in the cold a white more or less gelatinous precipitate of tungstic acid H 2 WO 4 , H 2 O. On boil- ing, or when precipitated from boiling solutions, the yellow anhydrous acid is produced. In presence of phosphates precipita- tion is not complete. Na 2 WO 4 -f 2HC1 = H 2 W0 4 + 2 NaCl When hydrochloric acid is added drop by drop to a boiling solution of a tungstate no precipitate is formed, but after long continued boiling the yellow tungstic acid is precipitated. 2. Ammonium Sulphide produces no precipitate, but if the solution is afterwards acidified a brown precipitate of WS 3 is produced, which can be redissolved in ammonium sulphide. 3. Mercurous Nitrate gives a white precipitate of mer- curous tungstate from neutral solutions, the precipitate rapidly turns yellow Na 2 WO 4 + Hg 2 (NO 3 ) 2 = Hg 2 WO 4 + 2NaNO 3 On ignition mercury is driven off and WO 3 remains, this is used to quantitatively estimate tungsten. 4. Stannous Chloride first produces a yellow coloration Analytical Tables. 189 or precipitate, which, on the addition of hydrochloric acid and warming, changes to a brilliant blue coloration or precipitate. This reaction is extremely delicate. W0 3 + SnCl 2 + 2HC1 = W0 2 + SnCl 4 + H 2 O Molybdenum. This metal is one of the rarer elements, being only found in comparatively small quantities. The most important oxide is MoO 3 , but it also forms MoO, Mo 2 O 3 , and MoO* Dry Reactions. i. Borax Bead, yellow while hot, in reduc- ing flame dark brown, may become opaque with large quantities of Molybdenum. 2. Blowpipe Test. When heated on charcoal a gray powder of the metal is produced, which is surrounded by a blue and white incrustation of oxides. 3. Film Test. Metal film : black with blue edges, soluble in 20 per cent HNO 3 and in NaOCl. 4. Oxide Film. Colourless (may be slightly blue), HI : blue which increases in depth when breathed on. Sulphide, add one or two drops of (NH 4 ) 2 S and gently evaporate off, brown film becomes colourless on moistening with NaOCl. Reactions in Solution. Use a solution of ammonium molybdate (NH 4 ) 6 Mo 7 O 24 , 4H 2 O. 1. Dilute Mineral Acids precipitate from solutions which are not too dilute, white molybdic acid, soluble in excess of the acid, distinction from tungstic acid which is insoluble (NH 4 ) 6 Mo 7 O24 + 6HC1 + 4H 2 O = 7H 2 MoO 4 + 6NH 4 C1 2. Concentrated Sulphuric Acid. When a trace of a molybdenum salt is moistened with concentrated sulphuric acid in a porcelain basin and heated until fumes of sulphuric acid are given off, and is then, after cooling, moistened with alcohol, an intense blue coloration is produced. The coloration is due to the formation of the sesquioxide, Mo 2 O 3 . 3. Hydrogen Sulphide first reduces the molybdic oxide to the dioxide which causes the solution to become blue. As, 190 Qualitative Chemical Analysis. however, an excess is added, a brown precipitate of the sulphide is gradually formed. The molybdenum sulphide, MoS 3 , is soluble in alkali sulphides, and is reprecipitated again on addition of acids. MoS 3 -f- (NH 4 ) 2 S = (NH 4 ) 2 MoS 4 It is rather a difficult matter to completely precipitate molybdenum as sulphide. This can only be done by boiling the solution after it has become brown, saturating again with gas, allowing to stand a short time, and again boiling. This usually requires repeating several times. The end of the operation can be seen by the supernatent liquor becoming colourless. 4. Mercurous Nitrate gives from neutral solutions a yellow precipitate of mercurous molybdate, which is soluble in nitric acid (cf. Tungsten). 5. Sodium Phosphate, when added to a molybdate strongly acidified with nitric acid, gives, on warming a yellow crystalline precipitate of ammonium, phosphomolybdate (cf. Phosphoric Acid, P- 137). 6. Ammonium Thiocyanate produces no coloration in acidified solutions of a molybdate, but, on adding a small piece of zinc, or a few drops of a solution of stannous chloride, an intense blood-red coloration of molybdenum thiocyanide is pro- duced. Phosphoric acid does not discharge the colour, distinc- tion from iron. On shaking the coloured solution up with ether, the thiocyanate dissolves in it, forming an orange red solution which becomes carmine red by the oxidising action of the air. Detection of Molybdenum in Presence of other Metals. In a systematic examination of the metals, molybdenum would be found in the arsenic group owing to its forming a thio- molybdenate with ammonium sulphide. It can be distinguished from As, Sb, Sn, Se, Te, and Ge, all of which occur in this group by (i) heating a small quantity of the dry precipitate with con- centrated sulphuric acid, 2, p. 189). Or by warming a small quantity of the precipitate with nitric acid, and then adding ammonium thiocyanate to the diluted solution and heating as 6, above. Analytical Tables. 191 Vanadium. Vanadium, columbium (niobium) and tantalum form com- pounds closely related to phosphorus. They also, however, show similarities to iron, chromium, and tungsten. Dry Reactions. Microsmic Bead> yellow in oxidising flame, beautiful green in the reducing flame. Reactions in Solution. Use a solution of sodium vanadate, Na 4 V 2 O 7 . 1. Hydrogen Sulphide gives no precipitate in acid solutions, but the solution becomes blue owing to reduction of the vanadic acid to a divanadyl compound. V 2 5 + H 2 S = 2VO 2 + H 2 O + S 2. Ammonium Sulphide causes the solution to turn brown, but no precipitate is produced owing to the formation of thiosalts on acidifying a brown precipitate of vanadic sulphide, V 2 S 5 , is produced. The sulphide is soluble in alkalis, alkali carbonates and alkali sulphides. (NH 4 ) 4 V 2 S 7 + 4 HC1 = 4 NH 4 C1 + V 2 S 6 + 2 H 2 S The precipitation of the sulphide is not quantitative as a portion of the vanadate is reduced, so that the solution always has a blue colour. 3. Ammonium Chloride. Solid ammonium chloride, when added to a solution of an alkali vanadate, produces a colourless crystalline precipitate of ammonium vanadate, very difficultly soluble in strong ammonium chloride. Na 4 VA + 4NH 4 C1= 2NH 4 VO 3 + 4NaCl + H 2 O + 2NH 3 4. Mercurous Nitrate gives, from neutral solutions, a yellowish precipitate of mercurous vanadate, soluble in nitric acid Na 4 V 2 7 + Hg 2 (N0 3 ) 2 = 2HgVO 3 + 2NaNO 8 5. Hydrogen Peroxide when added to an acid solution of a vanadate colours the solution reddish brown. This is a very 1 92 Qualitative Chemical Analysis. delicate test both for vanadium and conversely for hydrogen peroxide. The hydrogen peroxide must not be added in excess as then the reaction is less delicate. 6. Reducing Agents such as sulphur dioxide, oxalic acid, hydrobromic acid, etc., reduce vanadates to vanadyl salts, therefore the solutions become blue on addition of the reducing agent. With hydriodic acid the colour is first blue and then green because the vanadic oxide is reduced to the sesquioxide, but the presence of the iodine to a large extent masks the reaction. V 2 O 6 + 4HI = V 2 3 + 2l 2 + 2H 2 O The addition of Zn, Al, or Mg to acid solutions causes the reduction to be carried still further, and the solution becomes first blue, then green, and finally violet. Thallium. Forms Thallous and Thallic Compounds T1 2 O and T1 2 O 3 . Thallous Compounds. Colourless and generally soluble in water. The sulphide, bromide, chloride, iodide, and chromate are insoluble in water. Thallous oxide is soluble in water to which it imparts an alkaline reaction, the solution absorbs CO 2 from the air. Dry Reactions. Flame Test Thallium salts colour the flame of the Bunsen burner a brilliant green. The spectrum shows a brilliant green line. Film Test. Metal Film : Blackish brown, soluble in 20 per cent. HNO 3 . Oxide Film : colourless. Ammonium Sulphide : reddish-brown with black edges. Iodide : light yellow, intense yellow when breathed upon. i. Hydrogen Sulphide gives no precipitate in solutions containing mineral acid. The precipitate is also incomplete from neutral solutions. Analytical Tables. 193 2. Ammonium Sulphide gives a black precipitate of thallous sulphide, T1 2 S. Readily soluble in mineral acids, but insoluble in acetic acid. On standing in the air it readily oxidises to thallous sulphate. T1 2 S0 4 + (NH 4 ) 2 S = T1 2 S + (NH 4 ) 2 S0 4 3. Hydrochloric Acid produces a heavy white precipitate of thallous chloride, slightly soluble in water but much less so in water containing hydrochloric acid. T1 2 SO 4 + 2HC1 = 2T1C1 -f H 2 SO 4 4. Potassium Iodide forms a light yellow precipitate of the iodide the reaction is extremely delicate. T1 2 S0 4 + 2KI = 2T1I + K 2 S0 4 5. Potassium Chromate gives a yellow precipitate of thallous chromate insoluble in cold mineral acids. T1 2 SO 4 + K 2 CrO 4 = TI 2 CrO 4 + K 2 SO 4 5. Hydroplatinic Acid produces a light yellow precipitate of thallium chloroplatinate, which is extremely insoluble. T1 2 S0 4 + H 2 PtCl 6 = Tl 2 PtCl 6 + H 2 SO 4 7. Sodium Cobaltinitrite gives a scarlet precipitate of thallous cobaltinitrite. 3 T1 2 SO 4 + 2Na 3 Co(NO 2 ) 6 = 2Tl 8 Co(NO 2 ) 6 + 3Na 2 SO 4 Thallic Compounds. Thallic chloride can be prepared by the action of chlorine water upon thallous chloride. 1. Alkali Hydroxides give a brown precipitate of thallic hydroxide, insoluble in excess of alkali and difficultly soluble in acids. T1C1, + 3NaOH = Tl(OH), + 3 NaCl 2. Potassium Iodide produces a precipitate of thallous iodide, and at the same time iodine is liberated. T1C1, + 3KI = Til + I a + KC1 1 94 Qualitative Chemical Analysis. Titanium. Oxides, TiO, Ti 2 O 3 , TiO 2 , TiO 3 . TiO and Ti 2 O 3 form violet coloured salts which are easily converted into derivatives of TiO 2 by oxidising agents. The dioxide is most important, it has both acidic and basic properties. The best method to prepare a soluble salt is to fuse with potassium pyrosulphate. TiO 2 + 2K 2 S 2 O 7 = Ti(S0 4 ) 2 + 2K 2 SO 4 Dry Reaction. Borax Bead: No coloration in the oxidising flames, but on continued heating in the reducing flame the bead becomes yellow while hot and violet on cooling. The addition of a trace of stannous chloride causes the colour to appear much more rapidly. The addition of an iron salt produces a brownish or reddish-brown bead. Wet Reactions. Use a solution of titanium sulphate. 1. Potassium Hydroxide gives in the cold a gelatinous precipitate of orthotitanic acid. Ti(S0 4 ) 2 + 4 KOH = Ti(OH) 4 -f 2 K 2 S0 4 Almost insoluble in excess of the hydroxide but readily soluble in mineral acids. When precipitated from hot solutions meta-titanic acid is precipitated which is difficultly soluble in diluted mineral acids. Ti(S0 4 ) 2 + 4 KOH = Ti(OH) 2 + 2 K 2 SO 4 + H 2 O On long digestion with concentrated sulphuric or hydrochloric acid it slowly goes into solution. 2. Alkali Acetates upon boiling precipitate the whole of the titanium as meta-titanic acid. The acetate is first produced, but is hydrolytically decomposed. Ti(SO 4 ) 2 -f- 4CH 3 COONa + 3 H 2 O = TiO(OH) 2 + 2 Na 2 S0 4 -f 4CH 3 COOH 3. Water in excess hydrolytically decomposes all titanium Analytical Tables. 195 salts with precipitation of metatitanic acid, reaction is complete on boiling. TiCl 4 + 3 H 2 O^TiO(OH) 2 + 4 HC1 The separation of Titanium from the metals of the iron group depends upon this property. The mixed oxides are fused with potassium hydrosulphate, the fusion product dissolved in cold water and then boiled. Tartaric acid and many other organic substances prevent the precipitation, so that when organic substances are present they must first be removed by ignition. 4. Ammonium Hydroxide and Sulphide and also Barium Carbonate in the cold precipitate orthotitanic acid readily soluble in acids. From hot solutions the metatitanic acid which is difficultly soluble in acids is precipitated. Ti(SO 4 ) 2 + 4 NH 4 OH = Ti(OH) 4 + 2 (NH 4 ) 2 SO, Ti(S0 4 ) 2 + 2(NH 4 ). 2 S + 4 H 2 = Ti(OH) 4 + 4 H 2 S + 2(NH 4 ) 2 SO, Ti(S0 4 ) 2 + 2BaC0 3 + 2H 2 O = Ti(OH) 4 + 2BaSO 4 + 2 CO 2 5. Sodium Phosphate gives from boiling solutions a pre- cipitate of basic titanium phosphate. It is soluble in mineral acids /\ TiCl 4 + 2Na 2 HPO 4 + H 2 O = HOTi(-O-)P : O + 4 NaCl \O/ + 2NaH 2 PO 4 and in acetic acid. 6. Hydrogen Peroxide. On adding hydrogen peroxide to a slightly acid solution of titanium sulphate an orange-red colour is produced, with very diluted solutions the colour is yellow. The reaction, which is one of extreme delicacy, depends upon the formation of the trioxide. It is employed as a test for hydrogen peroxide and as a test for traces of titanium in rocks. Vanadic acid produces a similar coloration. 7. Zinc or Tin when added to acid solutions of titanium salts produce a violet coloration owing to reduction. TiCl 4 + H = TiCl 3 + HC1 Sulphur dioxide and Hydrogen Sulphide do not reduce titanium compounds. 196 Qualitative Chemical Analysis. Uranium. Uranium forms the dioxide UO 2 and the trioxide UO 2 O, called uranyl oxide. The dioxide (out of contact with air) dissolves in strong acids and forms uranous salts. These salts are very unstable, and on exposure to air rapidly change into uranyl salts. UC1 4 + H 2 O -f O = O 2 UC1 2 + 2HC1 Uranyl oxide dissolves in acids and forms uranyl salts. UO 2 O + H 2 SO 4 = O 2 USO 4 + H 2 O All uranyl salts are coloured either yellow or greenish yellow, and are mostly soluble in water. Dry Reactions. Borax Bead: Yellow in oxidising flame, green in reducing flame. Reactions in Solution. Use a solution of uranium nitrate, O 2 U(NO 3 ) 2 or the acetate O 2 U(CH 3 COO) 2 . Alkali Hydroxides give a yellow precipitate of potassium uranate. The reaction is rather complicated but probably takes place as follows : ,N0 2 KOH X)H U0 2 + =U0 2 +2KN0 3 ^NOg KOH ^OH The hydroxide splits off water and is converted into uranic acid by union of two molecules. yV-/J.J. yOH U0 2 UO NoH U0 2 U0 2 NDH ;>0 + H 2 / Analytical Tables. 197 The uranic acid then combines with the excess of alkali hydroxide and forms a salt. /OH KOH /OK U0 3 U0 2 \0 -f = \0 + 2H 2 O U0 2 U0 2 \)H KOH \)K 2. Ammonium Hydroxide gives a like precipitate of ammonium uranate. The alkali uranates dissolve in alkali carbonates, especially readily in ammonium carbonate, with formation of complex salts. U0 2 - ONH 4 >0 + 6(NH 4 ) 2 CO 3 + 3H 2 O U0 a - ONH 4 = 2[U0 2 (C0 3 ) 3 ](NH 4 ) 4 + 6NH 4 OH Therefore in presence of an alkali carbonate precipitation is either incomplete or fails to take place. Organic acids also prevent precipitation. 3. Ammonium Sulphide gives a brown precipitate of uranyl sulphide. UO a (NO 8 ) a + (NH 4 ) 2 S = UO*S + 2NH 4 NO, It is soluble in dilute acids and in ammonium carbonate. 170,8 -f 3 (NH 4 ) 2 CO, = [U0 2 (CO,) 3 ](NH 4 ) 4 + (NH 4 ) a S Consequently no precipitate is produced in presence of ammonium carbonate. 4. Sodium Phosphate gives a whitish-yellow precipitate of uranyl phosphate. /NO, Na^ U0 UO a -f Na-^PO 4 = yPO 4 -f 2NaNO, \NO, H/ H 198 Qualitative Chemical Analysis. When ammonium acetate is present, a precipitate of ammonium uranyl phosphate is obtained. Na 2 HP0 4 + U0 2 (N0 3 ) 2 + CH 3 . COONa = PO 4 \NH 4 -f-CH 3 .COOH + 2NaN0 3 The precipitates are soluble in mineral acids. 5. Potassium Ferrocyanide produces a brown precipitate of potassium uranyl ferrocyanide. K 4 Fe(CN) 6 + U0 2 (N0 3 ) 2 = [Fe(CN) 6 ]eK In very dilute solutions merely a brown coloration is pro- duced. The brown colour or precipitate can be distinguished from copper ferrocyanide by addition of potassium hydroxide which forms yellow potassium uranate, copper ferrocyanide under- goes no change. Potassium ferrocyanide is employed as an indicator in the volumetric estimation of phosphoric acid with uranyl salts. PART II ORGANIC ANALYSIS CHAPTER XL QUALITATIVE "ELEMENTARY* ANALYSIS OF CARBON COMPOUNDS. Detection of Carbon. i. Most organic substances char when strongly heated, with evolution of combustible gases. 2. When heated with concentrated sulphuric acid, many organic compounds blacken, owing to separation of carbon. 3. Some substances answer to neither of the above tests ; in this case the substance is dried at 100, finely powdered, mixed with seven or eight times its bulk of powdered dry copper oxide, and strongly heated. A glass rod which has been dipped in lime- water is held in the mouth of the tube, or the evolved gases are bubbled through lime water. If the latter is rendered turbid, the presence of carbon is proved. All organic substances, with the exception of some cyanides, yield carbon dioxide when treated in this manner. Detection of Hydrogen. Heat the substance as above with dry copper oxide. If hydrogen is present in the compound it will be converted into water, which will, as a rule, condense on the cool portions of the tube. If, however, the quantity of water produced is very small, its presence can be made apparent by dusting the upper portions of the tube with a little white anhy- drous copper sulphate, which will be turned blue by the water. Detection of Nitrogen. i. Many organic compounds which contain nitrogen evolve ammonia when strongly heated in a hard glass test tube with soda lime. As, however, all organic 2O2 Qualitative Chemical Analysis compounds which contain nitrogen do not yield it up as ammonia, the following is a better method. 2. Heat a small portion of the substance in a test tube, with a small piece of metallic sodium or potassium first gently, finally to redness ; dip the hot end of the test tube into a small basin containing a little water : f the tube will break, and the con- tents become mixed with water. Filter off from the carbonaceous residue ; add a small quantity of a solution of ferrous sulphate ; boil and acidify with hydrochloric acid ; if nitrogen be present, a blue precipitate or merely a bluish-green coloration will be produced. The reaction which takes place is as follows : The sodium combines with the nitrogen, forming sodium cyanide; and, since the solution is alkaline from the action of the excess of sodium on the water, when ferrous sulphate is added ferrous hydroxide is produced, which, when warmed with the sodium cyanide, is converted into sodium ferrocyanide. Fe(OH) 2 + 6NaCN = Na 4 Fe(CN) 6 + 2NaOH On acidifying the mixture, the ferric chloride which is produced in the solution owing to oxidation of the ferrous salt, acts upon the sodium ferrocyanide, with formation of " Prussian blue." 3Na 4 Fe,(CN) 6 + 4 FeQ 3 = Fe 4 [Fe(CN) 6 ] 3 + i2NaCl Sometimes the addition of a ferric salt is recommended, but usually sufficient is formed during the reaction. Detection of Chlorine, Bromine, and Iodine. i. Heat a piece of copper wire in the flame of the Bunsen burner, until it is black, and ceases to colour the flame green. Now dip the hot end of the wire in the substance to be tested (whether liquid or solid), and again introduce into the Bunsen flame. If a halogen is present a green or blue coloration is produced. This t The operation of dipping the hot test tube in water must be done with caution, because it often happens that some of the sodium has not been oxidised, and therefore, when it comes in contact with water, may cause a slight explosion. "Elementary" Analysis of Carbon Compounds. 203 test is not always certain ; further, it gives no information as to which of the halogens is present. 2. Mix a little of the* substance to be tested with two or three times its bulk of sodium carbonate, and about its own bulk of potassium nitrate or sodium peroxide, and fuse in a crucible or on a piece of platinum foil. Dissolve in water ; acidify with nitric acid, and apply the usual tests for the halogens. 3. The best method is as follows : Heat a little of the sub- stance with sodium, as already described in testing for nitrogen. If halogens are present, their sodium salts are produced ; and, on filtering the solution obtained after breaking the test tube in water, and acidifying with nitric acid, the usual tests for the halogens may be applied. Detection of Sulphur. i. Fuse a little of the substance with sodium carbonate and potassium nitrate or sodium peroxide as described above, in 2, for the halogens. Test the solution obtained, after dissolving in water and acidifying with hydrochloric acid, for a sulphate by means of barium chloride. 2. Ignite the substance with sodium, dissolve in a little water, filter, and place a drop or two of the solution on a watch glass, and add a drop of a solution of sodium nitro-pmsside ; if sulphur is present, a brilliant violet coloration will be produced, the sulphur having combined with the sodium to form sodium sulphide. The sulphide may also be tested for by acidifying with acetic acid, and adding a drop or two of a solution of a lead or silver salt, when a black precipitate will be produced. Sulphur and Nitrogen. If sulphur and nitrogen occur together, sodium thiocyanate will be produced when the organic substance is ignited with sodium. Acidify a portion of the solution, obtained after ignition with sodium, with hydrochloric acid, and add ferric chloride. A blood-red coloration indi- cates the presence of sulphur and nitrogen in the original substance.! t The tests for the halogens, nitrogen, and sulphur may be all carried out with one portion of the substance. It is ignited with sodium, and, after 2O4 Qualitative Chemical Analysis. Detection of Phosphorus. i. Fuse with sodium carbonate and sodium peroxide or potassium nitrate. Dissolve the fused mass in water, make strongly acid with con- centrated nitric acid, add ammonium molybdate, and warm : a yellow precipitate indicates the presence of phosphorus. N.B. When the substance to be tested is a liquid, saturate some fibres of recently ignited asbestos with it, and apply the tests as above. Liquids can, unless very volatile, be ignited directly with sodium. Determination of Boiling- and Melting- Points. As a test of the purity of an organic substance, the determination of the boiling or melting point is of great value. If a pure liquid is distilled, the boiling-point will remain constant from the beginning of the operation until the whole of the liquid has been distilled. If, on the other hand, the liquid is a mixture of two or more substances whose boiling-points lie some distance apart, then various fractions may be collected, each one of which will have a different boiling-point. For boiling-point of small quantities, see p. 244. A solid substance will usually melt sharply ', the moment the temperature at which it fuses is reached. If it be impure it will generally appear to shrink and soften before the correct melting- point is arrived at, and there may be a considerable number of degrees between the point at which it commences to melt and that at which it actually becomes fluid. The determination of the melting-point is, therefore, an important test of purity, and it is also of great value in identifying a compound. Determination of Boiling-Point. The determination may be carried out in a fractionating flask, A (Fig. 8), which should be connected with a condenser, B. The neck of the flask is closed addition of water and filtration, the solution is divided into four portions, which are separately tested. "Elementary" Analysis of Carbon Compounds. 205 with a cork, through which passes a thermometer, t, the bulb being placed immediately below the outlet tube C. A few pieces of broken glass or porcelain are put in the flask to prevent " bump- ing " or sudden boiling. In the case of liquids which boil at a temperature above 125 C., a glass tube without a water jacket is used instead of a Liebig's condenser, which is liable to crack. FIG. 8. To determine the boiling-point, the liquid is placed in the frac- tionating flask, which should be about one-third full. It is then heated, and as soon as it begins to distil the temperature is noted. If, after about one-third of the liquid has been distilled, the tem- perature is still the same, the liquid may be said to be pure. If the temperature is not constant, it is obvious that a mixture of substances is being dealt with. When the quantity of substance is very small, the determination of the boiling-point may be carried 206 Qualitative Chemical Analysis. out in a test tube, fitted with a cork through which two holes have been bored ; the thermometer passes through one hole, and is so arranged that the bulb is about an inch above the liquid. Through the other hole a piece of glass tube, bent at right angles, is fixed, and connected with a short, wide tube to act as condenser. Separation of Liquids by Fractionation. When the boiling-points of two liquids lie a long distance apart, it is often an easy matter to separate the liquids by fractionation, as just described. The liquid of the lower boiling-point distils over first, and, as soon as it is has all passed over, the boiling-point rapidly runs up and becomes constant again some degrees higher. When, however, the boiling-points lie fairly close to- gether, it is necessary, in order to get a separation, to employ a fractionating column. Fig. 9 represents such a column, " Young's Column," which con- sists of a series of pear-shaped bulbs. Exercises in Fractional Distil- lation. i. Make a mixture of 30 grams acetone and 15 grams aniline, and distil in the apparatus illustrated in Fig. 8. With care a complete separation should be obtained. 2. Another good exercise is to fractionate commercial benzene. Use apparatus shown in Fig. 9. Determination of Melting-Point. The apparatus em- ployed for determining the melting-point (Fig. 10) consists of a beaker, A, of about 40-60 c.c. capacity, containing sulphuric acid or glycerol, or, for substances with a low melting-point, water, and fitted with a glass stirrer, B. A very small quantity of the FIG. 9. "Elementary" Analysis of Carbon Compounds. 207 substance is placed in a capillary tube, C, closed at one end which is caused to adhere to the thermometer by simply moistening it with sulphuric acid, the surface tension of the FIG. 10. FIG. n. liquid keeping it from falling down. The acid is cautiously heated, being constantly stirred, and the temperature at which the substance becomes liquid noted. This is its melting-point (m.p.). Extraction with Ether. The cold solution to be extracted is transferred to a separating funnel, Fig. n. A layer of ether about i cm. deep is poured on to the solution, the stopper is replaced and the mixture gently shaken, so that the ether may thoroughly mix with the aqueous solution. One finger should be placed over the stopper while shaking, otherwise the pressure exerted by the volatile ether may cause it to fly out. As soon as the ethereal layer has completely separated, the lower aqueous 2O8 Qualitative Chemical Analysis. layer is run off by opening the tap of the funnel. The operation should be repeated with another small quantity of ether. The extraction is always more complete when successive small quanti- ties of ether are employed, than by adding a large quantity of ether at one time. In order to test the substance which has been extracted, the ethereal solution is transferred to a distillation flask and the ether distilled off. When chloroform is used as a solvent, being specifi- cally heavier than water, it forms the lower layer in the funnel. As an exercise take 2 grains of aniline, mix it with 50 c.c. of water, and extract with ether. After separation dry the ethereal extract with a few small pieces of anhydrous calcium chloride. After standing for 15 minutes decant from the calcium chloride into a weighed flask, washing the calcium chloride with 5 c.c. of ether, and distil off the ether. The resulting aniline should weigh 2 grams. Organic Acids. Organic acids all contain the monovalent carboxyl group, COOH, the hydrogen atom of which is replaceable by metals. They are, as a rule, only moderately dissociated in solution, and cannot, therefore, be classed among the strong acids. In solution they are dissociated into the cation H* and the anion R.COO', where R stands for any complex radical. For example, the ions of acetic acid (p. 212) are H* and CH 3 COO' } COO" whereas those of oxalic acid (p. 215) are 2H' and | . It is COO thus seen that the valency of the acid is determined by the number of * COOH groups which it contains. Almost all organic acids form soluble sodium and potassium salts, and are therefore soluble in solutions of sodium and potassium carbonates. Carbolic acid (phenol) and pyrogallic acid (pyrogallol) are not acids, but are phenols ; owing, however, to the negative character of phenyl, C 6 H 6 -, they have an acid character, carbolic acid dissolving in "Elementary" Analysis of Carbon Compounds. 209 caustic alkalis to form alkali salts. In pyrogallol the negative or acidic character is so strongly marked that it dissolves even in alkali carbonates. The addition of negative groups to phenol also increases its acidic character, thus picric acid (trinitrophenol) forms salts with alkali carbonates and with ammonia. Even nitro-phenols in which there is only one nitro-group present are able to decompose alkali carbonates. Organic acids may occur either free, as salts of the alkali metals, as salts of metals other than these, or mixed with various inorganic metallic salts. The usual tests may be applied at once to salts of the alkali metals, and, after neutralisation by sodium carbonate, to the free acids. In all other cases, however, the metals must be removed before the tests for the acids are applied. Usually the metals may be got rid of by boiling with a strong solu- tion of sodium carbonate, as recommended in testing for inorganic acids (Part I., p. 181); but certain metallic combinations are not decomposed under these conditions, e.g. antimony in tartar emetic. In such circumstances it is necessary to acidify with dilute hydro- chloric acid, and to pass sulphuretted hydrogen. The sulphides are then filtered off, the solution made alkaline with ammonia, and sulphuretted hydrogen again passed ; any further precipitate formed being again filtered off. This procedure will remove all the metals with the exception of those of the alkaline earths, which must be removed by boiling with sodium carbonate. Substances which do not form soluble salts with sodium carbonate, such as aniline, phenol, etc., should be extracted by means of ether before proceeding to analysis. The solution which has been treated by one or both of these methods should now be slightly acidified with dilute hydrochloric acid, and boiled for a few minutes to decompose any alkali sulphides which may have been formed. In all cases a neutral solution must be prepared before proceeding to analysis. If, during the above operations, the bulk of solution has become at all considerable, it should be concentrated before applying the tests. CHAPTER XII. REACTIONS AND SEPARATION OF ORGANIC ACIDS AND PHENOLS. THIS chapter is mainly devoted to the reactions of the acids, but, for convenience, the reactions of phenol have been placed after those of salicylic acid, and those of pyrogallol after tannic acid. Formic Acid; H.COOH Formic acid is a colourless liquid, with a pungent odour. When dropped upon the skin it causes painful blisters. It freezes to a transparent ice-like solid, which melts at 8*5; the liquid boils at ioo'6. It is soluble in water in all proportions. Its metallic salts, with the exception of those of lead and mercury, are also readily soluble in water ; the two latter are only slightly soluble. i. When formates are heated with soda lime hydrogen gas is evolved. H.COONa + NaOH =Na 2 CO 3 + H 3 *2. Cold concentrated sulphuric acid, when added to a formate or formic acid, liberates carbon monoxide, which burns on ignition with a blue flame. (Distinction from oxalic acid, which on heating, not in the cold, with concentrated sulphuric acid, evolves both carbon monoxide and dioxide, the evolved gases therefore turn lime water milky.) 2 H.COONa + H 2 SO 4 = 2CO -f Na 2 SO, -f Reactions and Separation of Organic A cids and Phenols. 2 1 1 3. Dilute sulphuric acid liberates formic acid, the presence of which is noticed on warming by its pungent acid odour. 2H.COONa + H 2 S0 4 = 2H.COOH + Na 2 SO 4 *4. When formic acid or a formate is warmed with a little concentrated sulphuric acid and ethyl alcohol, the pleasant characteristic odour of ethyl formate is noticed. 2H.COOK + H 2 S0 4 = 2H.COOH + K^ H.COOH -f C 2 H 5 OH = H.COOC 2 H 5 + H 8 O In this and similar reactions sulphuric acid first liberates the acid, and then the excess of the sulphuric acid acts as a dehy- drating agent. *5. Silver nitrate is reduced when added to a dilute solution of formic acid or a formate, the reduction taking place slowly in the cold, rapidly on heating ; a black precipitate of metallic silver being obtained. (a.) H.COOK -f- AgNO 3 = H.COOAg + KNO 3 (b.) 2H.COOAg = H.COOH -f 2Ag + CO 3 Ammoniacal solutions of silver salts are not reduced, even on warming. *6. Mercuric chloride gives, on warming either with formic acid or a formate, a white precipitate of mercurous chloride (distinction from acetic acid). If excess of formic acid or a formate is present, the mercurous chloride becomes reduced to metallic mercury. (a.) 2H.COONa+2HgCl 2 = Hg 2 Cl 2 -f CO + CO 2 + H 2 O + 2NaCl (b.) Hg 2 Cl 2 + 2H.COONa = 2Hg + CO 2 -f CO -f- H 2 O + 2NaCl *7. Ferric chloride produces a red coloration, which is destroyed on addition of hydrochloric acid. When the red solution is boiled a brown precipitate of a basic iron salt is produced. (a.) 3 H.COONa -f FeCl 3 = (H.COO) 3 Fe + sNaCl (b.) (H.COO) 3 Fe + 2H 2 O = (H.COO)Fe(OH) 2 + 2 H.COOH 212 Qualitative Chemical Analysis. *8. On acidifying a solution of formic acid or a formate with a little dilute sulphuric acid, shaking up with a small quantity ol mercuric oxide, and afterwards filtering, a solution of mercuric formate is obtained. 2H.COOH + HgO = (H.COO) 2 Hg + H 2 O When this solution is boiled a white precipitate of mercurous formate is produced, which rapidly changes to a grey deposit ol metallic mercury (distinction from acetic acid). (a.) 2 (H.COO) 2 Hg = (H.COO) 2 Hg 2 + H.COOH + CO 2 (b.) (H.COO) 2 H g2 = 2 Hg + H.COOH + CO a Acetic Acid. Acetic acid is a colourless pungent-smelling liquid, crystallising to an ice-like solid at 16-5, and boiling at 118; the boiling acid is inflammable, burning with a slightly bluish flame. It is readilj soluble in water, alcohol, and ether. The acetates, with the exception of mercurous and silver acetates and a few basic acetates, are soluble in water. 1. Dry acetates, when strongly ignited in a tube, give ofl inflammable vapours, consisting of acetone and other products. 2. When acetates are heated with either concentrated or dilute sulphuric acid, the characteristic " vinegar " smell of acetic acid is noticed. (Cf. 2, p. 210.) 2CH 3 .COOK + H 2 SO 4 = 2 CH 3 COOH + K 2 SO< *3 Acetates or acetic acid, when heated with concentrated sulphuric acid and alcohol, produce the pleasant and characteristic odour of ethyl acetate. CH 3 COOH + C 2 H 6 OH = CH 3 COOC 2 H B + H 2 O *4. Silver nitrate, when added to a strong neutral solution of an acetate, produces a white crystalline precipitate of silver Reactions and Separation of Organic A cids and Phenols. 2 1 3 acetate, which is not reduced on boiling. (Cf. Formates, 5, p. 211.) CH 3 COOK + AgNO 3 = CH 3 COOAg + KNO 8 *5. Ferric chloride gives in neutral solutions a deep red coloration, which is destroyed on addition of hydrochloric acid. On boiling the red solution, a brown precipitate of basic ferric acetate is produced. (a.) 3 CH 3 COONa + FeCl 3 = (CH 3 c66) 3 Fe + 3 NaCl (b.) (CH 3 COO) 3 Fe + 2 H 2 O = (CH 3 .COO)Fe(OH) a + 2 CH 3 COOH *6. Cacodyl Oxide Reaction. On mixing a dry acetate with a small quantity of arsenious oxide and heating in a test tube, an extremely nauseous odour of cacodyl oxide is produced. 8CH 3 . = 2 (CH 3 ) 2 As . O . As(CH 3 ) 2 + 4C0 2 This experiment should be conducted with great caution, and on a very small scale, as the fumes are extremely poisonous. If, during the heating, the finger is held over the mouth of the test tube, the smell is very noticeable on holding it to the nostril. Detection of Formic and Acetic Acids in Presence of each other. If the substance is a solution, part of it should be evaporated to dryness in order to apply the tests i, 4, and 5. It should be borne in mind that, if the solution is acid, it must first be neutralised with sodium carbonate before evaporating to dryness. 1. Formic Acid. x. Add to a small quantity of the solid substance a little cold concentrated sulphuric acid: carbon monoxide is evolved. (Presence of formate.) 2. Acidify part of the neutral solution slightly with dilute sulphuric acid, shake up with a little mercuric oxide, and filter. 2J4 Qualitative Chemical Analysis. On boiling the solution reduction takes place. (Presence of formate.) 3. Warm a portion of the neutral solution with silver nitrate : reduction takes place. (Presence of formate.) II. Acetic Acid. 4. Heat a small portion of the dry substance with arsenious oxide : a foetid odour of cacodyl oxide is produced. (Presence of acetate.) 5. Act on a little of the substance with concentrated sulphuric acid, and warm very gently ; as soon as no more carbon monoxide is evolved, add a little alcohol, and heat : a fruity odour of ethyl acetate produced. (Presence of acetate.) If formic and acetic acid or their salts occur mixed with other organic acids or compounds which are not readily volatile, the mixture should be acidified with dilute sulphuric acid and dis- tilled. The liquid in the receiver will contain the formic and acetic acids, and, after neutralising, may be tested for them. The non-volatile substances will remain in the retort. Lactic Acid ( a Oxy-propionic Acid). CH 3 .CH(OH)COOH There are three lactic acids, but the one most commonly occurring is the a or fermentation acid ; the other sarco-lactic acid and ethene lactic acid have, however, much the same properties, but whereas the a and sarco-lactic acids are optically active the ethene lactic acid is inactive. Lactic acid is a colourless, thick liquid, having rather the appearance of glycerol. It is odourless when pure, and has a strong acid taste. It cannot be distilled without decomposition. Lactic acid is soluble in water, alcohol, and ether in all pro- portions, but is insoluble in benzene, chloroform, and carbon disulphide. i. On being heated in a dry test tube irritating vapours are evolved. Reactions and Separation of Organic A cids and Phenols. 2 1 5 *2. Potassium permanganate is decolourised by solutions of lactic acid, effervescence taking place, and a smell of acetalde- hyde being produced. The reaction is very vigorous with hot solutions. 3. On adding an equal volume of cold concentrated sulphuric acid to lactic acid, the mixture gets hot and commences to effervesce. On warming, charring takes place, and carbon monoxide is evolved. *4. When a mixture of lactic acid and 4 parts of dilute sulphuric acid (i part concentrated acid and 2 parts water) is distilled, acetaldehyde and formic acid are produced, and may be tested for in the distillate. CH 3 . CH(OH)COOH = CH 3 . CHO + H . COOH 5. Silver nitrate but not Fehling's solution is reduced by lactic acid. 6. One of the best methods to identify lactic acid in dilute solutions is to form the calcium or zinc salt, and to examine the crystals under the microscope. The zinc salt (C^O^Zii, 3H.O, for example, may be prepared by digesting the warm acid solution with zinc carbonate, filtering, and concentrating on the water bath. Quadratic crystals are obtained, which usually cluster together. Oxalic Acid. COOH I COOH Colourless crystals, containing two molecules of water of crystallisation. Readily soluble in water, and in alcohol. When heated to 100, the crystalline acid melts in its own water of crystallisation ; and, on further heating, sublimes. Most oxalates are insoluble in water. i. When ignited, the oxalates of the alkaline metals and 216 Qualitative Chemical Analysis. earths are converted into carbonates, with evolution of carbon monoxide. COOK | = CO + K 2 CO, COOK Those of the heavy metals' produce an oxide, with evolution of carbon monoxide and dioxids. COO = CO + CO 2 + CuO Some few, such as silver oxalate, decompose into the metal and carbon dioxde. COOAg | = 2Ag + 2CO, COOAg Pure oxalic acid, on being heated, volatilises completely, without charring. It partly sublimes unchanged, but when rapidly heated it splits up into carbon dioxide and formic acid. COOH | = CO, + H. COOH COOH Part of the formic acid decomposes into carbon monoxide and water. H.COOH = CO + H a O *2. Concentrated sulphuric acid, on heating, decomposes oxalic acid or oxalates, carbon monoxide and carbon dioxide being evolved : the presence of this latter being shown by passing the evolved gases through lime water. (Distinction from formates which only give carbon monoxide.) COOH | = CO + C0 2 + H 2 O COOH 3. Silver nitrate produces, with neutral solutions, a white Reactions and Separation of Organic Acids and Phenols. 217 crystalline precipitate of silver oxalate, soluble in ammonium hydroxide and nitric acid. COONa COOAg | + 2 AgNO 3 = | + 2NaNO, COONa COOAg *4. Calcium chloride gives, with neutral or alkaline solutions of oxalates, a white crystalline precipitate of calcium oxalate, insoluble in acetic acid, soluble in hydrochloric or nitric acid. COONa COO I + CaCl 2 = | COONa COO *$. On adding a solution of potassium permanganate to a solution of oxalic acid or an oxalate acidified with dilute sulphuric acid, and warming, the colour of the permanganate is destroyed, carbon dioxide being evolved. 2 KMnO 4 = 6K 2 SO 4 -f 2MnSO 4 + 8H 8 O + ioCO a Tartaric Acid. CH(OH) . COOH CH(OH).COOH Tartaric acid forms large colourless crystals which are readily soluble in water, moderately so in alcohol. Being a dibasic acid, it forms acid and neutral salts. The normal salts with the alkalis, and most of the salts with metals of the iron group, are readily soluble in water. The acid salts of potassium and ammonium are difficultly soluble, the other acid salts readily soluble; while most other normal salts are insoluble, or only dissolve with difficulty. *i. Tartaric acid and tartrates char when heated, in the case of tartrates a carbonate or oxide of the metal being produced. 2i8 Qualitative Chemical Analysis. During the charring, a strong smell resembling that of burnt sugar is produced. *2. Warm concentrated sulphuric acid decomposes tartrates, almost immediate charring taking place, with evolution of carbon monoxide, carbon dioxide, and sulphur dioxide. *3. Silver nitrate produces with neutral solutions a white precipitate of silver tartrate, soluble in excess of the tartrate, also in nitric acid and ammonium hydroxide. CH(OH)COOK CH(OH)COOAg | + 2AgNO 3 = | + 2 KNO 3 CH(OH)COOK CH(OH)COOAg On heating the ammoniacal solution of silver tartrate, it is reduced to metallic silver. The silver may be obtained in the form of a beautiful mirror on the sides of the test tube, if the following directions be followed : Carefully clean a test tube with caustic soda and distilled water ; add ammonium hydroxide to the precipitated silver tartrate until it is almost (but not quite) dissolved ; drop in a crystal of silver nitrate to the bottom of the test tube and stand in a beaker of boiling water : in a short time, owing to the reduction of the silver salt, a beautiful mirror of metallic silver forms on the sides of the tube. *4. C alcium chloride gives, with neutral solutions of tartrates, a white crystalline precipitate of calcium tartrate. Scratching the sides of the test tube, and vigorous shaking, aid the precipi- tation, which, from dilute solutions, only takes place after some time. It is soluble in cold caustic potash, or soda, and in acetic acid. CH(OH)COOK CH(OH)COOv I + CaQ 2 = | >Ca + 2KC1 CH(OH)COOK CH(OH)COO/ *5. Potassium salts, when added to tartaric acid or a tartrate, give (especially if the solution is well shaken and a little acetic acid is present) a colourless crystalline precipitate of potassium-hydrogen tartrate. With neutral salts, to obtain Reactions and Separation of Organic Acids and Phenols. 219 complete precipitation, it is necessary to add acetic acid, other- wise the acid tartrate is not formed. (Cf. Potassium, p. 95.) CH(OH)COONa CH(OH)COOK + KC1 + CH 3 .COOH = | + NaCl + CH 3 .COONa CH(OH)COONa CH(OH)COOH When potassium salts are added to free tartaric acid a precipi- tate is not produced in dilute solutions, unless sodium acetate is added to neutralise the free mineral acid set free in the reaction. CH(OH)COOH ' CH(OH)COOK CH(OH)COOH "* ~ CH(OH)COOH "* From dilute solutions the precipitation only takes place after long standing. Presence of boric acid prevents precipitation. *6. If a minute quantity of solid tartaric acid or a tartrate is mixed with twice its bulk of resorcin, about 2 c.c. of concen- trated sulphuric acid added, and the mixture gently warmed, a bright red coloration is produced. (Distinction from citrate.) If pyrogallol is substituted for resorcin, a fine violet-blue coloration is obtained. (Distinction from citrate.) These reactions show best when extremely small quantities of tartaric acid or a tartrate are taken. Great care mast be taken not to heat too strongly, otherwise charring takes place. 7. On adding a few drops of a solution of ferrous sulphate to a solution of a tartrate, then a few drops of hydrogen peroxide, and finally excess of sodium or potassium hydroxide, a violet to blue coloration is produced. (Distinction from citrate.) Citric Acid. /CH 2 .COOH C(OH).COOH + 2 H 2 \CH 2 .COOH Citric acid forms colourless crystals, readily soluble in water and alcohol. The acid citrates are more soluble than the acid tartrates. i. Citric acid or citrates carbonise when heated, acrid-smelling vapours being evolved. *2. When heated with concentrated sulphuric acid, citric 22O Qualitative Chemical Analysis. acid and citrates evolve carbon monoxide and carbon dioxide. After some little time, the liquid becomes dark in colour, owing to charring, and sulphur dioxide is evolved. (Tartrates char almost immediately.) *3 Silver nitrate produces, with neutral solutions of citrates, a curdy white precipitate of silver citrate, soluble in ammonium hydroxide. On heating this solution no reduction takes place. (Distinction from tartrates.) But continued boiling causes slight reduction. C 3 H 4 (OH)(COOK) 3 + 3 AgNO,' = C 3 H 4 (OH)(COOAg) 3 + 3KNO 3 *4. Calcium chloride, when added to a neutral solution of a citrate, produces no precipitate in the cold (except after stand- ing some hours), but on boiling for several minutes a crystalline precipitate of calcium citrate is produced. The addition of caustic alkali causes an immediate precipitate of calcium citrate, soluble in ammonium chloride, but on boiling, the crystalline calcium citrate is precipitated, and is no longer soluble in ammonium chloride. 2 C 6 H 5 7 K 3 + 3 CaCl 2 = 3 Ca(C 6 H 6 7 ) 2 + 6KC1 *5. Cadmium chloride, when added to neutral solutions, produces a white gelatinous precipitate of cadmium citrate, insoluble in hot water, readily soluble in hot acetic acid. (Cad- mium salts give no precipitate with tartrates.) 2 C 6 H 5 7 K 3 + 3CdCl 2 = 3 Cd(C 6 H 5 7 ) 2 + 6KC1 Cadmium citrate sometimes forms a transparent jelly. *6. Denige's Test. Add to a solution of citric acid about i c.c. of mercuric sulphate solution (preparation, p. 329). Then add five to six drops of 2 per cent. KMnO 4 . Decolorisation will take place, and then a white turbidity will be produced. The amount of KMnO 4 to be added depends upon the concen- tration of the citric acid. Halogens should first be removed with AgNO 3 . In presence of other organic compounds larger quantities of permanganate are required, just sufficient being added to leave a permanent faint pink. Reactions and Separation of Organic A cids and Phenols. 2 2 1 Malic Acid. CH a . COOH CH(OH)COOH Malic acid is found in the juice of many unripe fruits, and can be prepared from unripe mountain-ash berries. It is a crystalline solid, m.p. 100. On being heated to 140-150 for some time, water is spilt off and fumaric acid produced. The fumaric acid then sublimes when the mixture is heated to 200, crystallising on the cool portions of the tube. When, however, the malic acid is rapidly heated to a high temperature malei'c anhydride distils over along with water. The reaction in either case is repre- sented by the following equation COQH.CH(OH).CH 2 .COOH - H 2 O = COOH.CH : CH.COOH The difference between fumaric and maleic acid is not shown in the equation, because they are steroisomers. For further informa- tion upon the subject, text-books on theoretical chemistry must be consulted. Malic acid is readily soluble both in water and alcohol. *i. Calcium Chloride, in presence of excess of ammonium chloride and ammonium hydroxide, produces no precipitate, even on continued boiling. (Distinction from citric acid.) The addition, however, of two volumes of alcohol causes a white precipitate of calcium malate to be produced. C 4 H 4 5 Na 2 -f- CaCl 2 + 3 H 2 O = C 4 H 4 O 6 Ca, 3 H 2 Calcium malate is soluble in boiling lime water. (Distinction from citric acid.) 2. Lead acetate produces a white precipitate of lead malate. C 4 H 4 O 5 Na 2 -f (CH 3 . COO) 2 Pb + 3 H a O = C 4 H 4 O c Pb, 3 H 2 O + aCHa.COONa The precipitate is more complete from neutral salts of the acid. If the precipitate is boiled with water a portion goes into 222 Qualitative Chemical Analysis. solution and a portion melts or becomes gummy. On cooling, the portion which had dissolved separates out again. Separation of Oxalic, Citric, and Tartaric Acids (and Malic Acid). Add excess of calcium chloride to a neutral solution, shake up, allow to stand for from twelve to fifteen minutes with occa- sional shaking, then filter and wash. Residue : This may be a mixture of calcium oxalate and tartrate. Boil with a little acetic acid, and filter. Solution : Add a little more calcium chloride, and boil for three or four minutes. If a white precipitate gradu- ally forms, the presence of Citric Acid is shown, which may be confirmed by filter- ing and warming with cone. H 2 SO 4 , when charring will slowly take place, f Besidue ; Is calcium oxalate. Confirm by suspending in dilute sulphuric acid, warm to 60-70, and add a dilute solution of potassium perman- ganate drop by drop. Decolorisation of the permanganate con- firms Oxalic Acid. Solution : Evaporate to dryness on a water bath, and test for tar- taric acid by warming a portion carefully with cone. H 2 SO 4 and pyro- gallol(6, p. 219). A violet coloration shows the presence of Tartaric Acid. It may be further con- firmed by 3, p. 218. Succinic Acid. CH 2 .COOH CH 2 .COOH Colourless inodorous crystals, m.p. 180, b.p. 235 with forma- tion of succinic anhydride. Readily soluble in hot water and alcohol. Only slightly soluble in ether and insoluble in chloro- form. t If malic acid is suspected, ammonium chloride and ammonia should be added before boiling : malic acid is not then precipitated. It can be detected after the calcium citrate has been precipitated by adding alcohol. Further, the precipitate of calcium malate is soluble in lime water. Reactions and Separation of Organic A cids and Phenols. 223 1, On strongly heating, succinic acid first melts and then boils the vapours which are given off being extremely irritating. 2. Concentrated sulphuric acid dissolves succinic acid on warming without charring. On strongly heating, the solution becomes brown and sulphur dioxide is evolved. *3. Silver nitrate produces a white precipitate of silver succinate from neutral solutions, readily soluble in ammonia. QH 4 (COONa) 2 + 2 AgNO 3 = C 2 H 4 (COOAg) 2 -f 2 NaNO 3 *4. Calcium chloride produces from neutral solutions a white precipitate of calcium snccinate. The precipitate is not usually produced at once, but comes down on standing a short time, especially upon shaking. *5. Ferric chloride gives with neutral solutions a light brown precipitate of basic ferric succinate. 3 C 2 H 4 (COONa) 2 - = 2C 2 H 4 (COO) 2 Fe . OH + 6NaCl + C 2 H 4 (COOH). 2 Benzoic Acid. C 6 H 6 . COOH. Benzoic acid forms colourless needles or small plates, possess- ing a slight but characteristic aromatic odour. It melts at 121, and sublimes, boiling at 250. Readily volatile with steam. Soluble in hot water, from which it crystallises on cooling, also in alcohol and ether. Benzoates are generally soluble in water. *i. On heating benzoic acid it first begins to sublime, then melts, and finally gives off dense white fumes, which cause sneezing or coughing. 2. Benzoic acid and benzoates dissolve in strong sulphuric acid on warming, without evolution of gas, and without charring. 3. Dilute mineral acids, when added to aqueous solutions of benzoates, decompose them, and a white crystalline precipitate of benzoic acid is produced. 224 Qualitative Chemical Analysis. 4. Silver nitrate produces from neutral solutions a white precipitate of silver benzoate, soluble in hot water, from which it recrystallises on cooling. The precipitate is readily soluble in ammonium hydroxide. C 6 H 6 COONa + AgNO 3 = C 6 H 5 COOAg -f NaNO s *5. Ferric chloride gives, with neutral solutions, a buff- coloured precipitate of basic ferric benzoate. 2 C 6 H 5 COONa + FeCl 3 + HJ3 = (CH 5 COO) 2 FeOH +.2 Nad + HC1 Citrates and tartrates hinder or prevent precipitation. Ferric benzoate is soluble in boiling water with difficulty, but if the solution is moderately dilute, it is not reprecipitated again on cooling. It is readily soluble in ammonium hydroxide. *6. Benzoic acid or benzoates, when heated with about i c.c. of concentrated sulphuric acid and about an equal bulk of alcohol, produce a pleasant and distinctive aromatic odour of ethyl benzoate. On diluting the mixture with water, oily drops of ethyl benzoate separate out C 6 H 5 COOH + C 2 H 6 OH = C 6 H 5 COOC 2 H 5 + H 2 O *7. On heating benzoic acid, or benzoates, with about four times their bulk of lime in a hard glass test tube, benzene is produced, which can be recognised by its odour, and by the inflammability of its vapour. C 6 H 6 COOH + Ca(OH) 2 = C 6 H a + CaCO 3 + H 2 O A delicate confirmatory test may be made as follows : The test tube in which the operation is carried out is fitted with a cork and delivery tube, and during the heating the end of the tube is made to dip below about \ c.c. of cone, nitric acid and i drop of cone, sulphuric acid contained in another test tube. The mixture is first gently, and then strongly heated, the cool sides of the tube being then warmed, in order to volatilise any condensed benzene vapour, Reactions and Separation of Organic A cids and Phenols. 22$ and cause it to pass into the nitric acid. The nitric acid is now largely diluted with water, when the characteristic odour of nitro- benzene is obtained. C,H. + HN0 3 = C 6 H 6 NO a + H a O Salicylic Acid (ortho-hydroxybenzoic acid.) OH (i) C 6 H 4 ( X COOH (2) Colourless needle-shaped crystals, possessing no smell. Very slightly soluble in cold water, rather more so in hot. Readily soluble in ether and alcohol. The acid melts at 155. Most salicylates are fairly soluble in water. The acid is soluble in sodium carbonate. 1. When heated in a dry tube salicylic acid first melts, and on further heating sublimes; when very rapidly heated it is decomposed into phenol and carbon dioxide. /OH C 6 H / = C 6 H 5 OH + COi X COOH 2. Concentrated sulphuric acid dissolves salicylic acid and salicylates. On heating for some little time, the solution darkens, and finally gas is evolved. 3. Dilute mineral acids, when added to aqueous solutions of salicylates, decompose them, liberating salicylic acid, which separates out as a white crystalline precipitate. *4. On being strongly heated with lime an odour of phenol is produced /OH Q,H 4 < + Ca(OH) 2 = C 6 H 5 OH + CaCO 3 + H 2 O X COOH A characteristic blue coloration may be obtained by conducting Q 226 Qualitative Chemical Analysis. the evolved phenol through a delivery tube into a little water, to which has been added one or two drops of ammonium hydroxide, then add a few drops of bromine water or a solution of bleaching powder, and gently warm. (Cf. 3, p. 229.) 5. Silver nitrate produces in neutral solutions a white precipitate of silver salicylate, soluble in boiling water. /OH OH C 6 H/ + AgNO 3 = C 6 H/ -f NaNO 3 x COONa x COOAg *6. Ferric chloride gives both with salicylic acid and salicylates an intense violet-red coloration, which vanishes on adding excess of mineral acids. Acetic acid, tartaric acid, citric acid, and most organic acids, when present in large excess, also prevent this coloration, but addition of a few drops of am- monia will cause it to appear. The coloration produced by phenol is destroyed by a small quantity of acetic acid. (See i, p. 229.) 7. Bromine water gives a white precipitate of dibrom- salieylic acid, or tribromsalicylic acid, depending upon the quantity added. 8. On heating with concentrated nitric acid, salicylic acid and salicylates are converted into picric acid, with formation of an intense yellow solution, and, on adding excess of caustic soda, the coloration is intensified. If the solution is now boiled with a little glucose, the colour changes to deep red, owing to the formation of picraminic acid. *9. When salicylic acid or salicylates are mixed with about i c.c. of concentrated sulphuric acid, and about an equal quantity of methyl alcohol, and the mixture heated, the characteristic smell of methyl salicylate, "Oil of Winter- green," is produced. /OH OH C 6 H 4 ( + CH 8 . OH = C 6 H 4 ( + H 2 COOH X COOCH 3 Reactions and Separation of Organic A cids and Phenols. 227 Cinnamic Acid (ft Phenyl Acrylic Acid). C 6 H 5 CH:CH.COOH Cinnamic acid forms colourless pearly crystals, m.p. 133. When rapidly heated it distils undecomposed at 300. On slow distillation it is converted into styrene and carbon dioxide. C 6 H 5 CH : CH . COOH = C 6 H 5 CH : CH 2 + CO 2 Cinnamic acid is only slightly soluble in cold water, but dissolves readily in hot water and also in alcohol, ether, and chloroform. Owing to its sparing solubility in water, it is precipitated by dilute acids from its alkali salts. i. On mixing cinnamic acid or its salts with lime, and strongly heating, benzene is evolved, which may be recognised by the tests described under benzoic acid, 7, p. 224. *2. Calcium chloride precipitates from neutral solutions, white calcium cinnamate. The precipitate is soluble in boiling water, and crystallises out again on cooling. 2 C 6 H 5 CH : CH . COOK + CaCl 2 = (C 6 H 5 CH : CH . COO). 2 Ca + 2 KC1 The precipitate shows a tendency to adhere to the sides of the test tube. (Benzoic acid gives no precipitate with calcium chloride, hence the two acids may be separated by means of calcium chloride.) *3. Ferric chloride gives a light yellow precipitate of basic ferric cinnamate. 4. Silver nitrate, when added to neutral solutions of cinnamates, produces a white precipitate of silver cinnamate. *5. Oxidising agents, such as potassium permanganate or persulphates, when warmed with an alkaline solution of cinnamic acid, oxidise it to benzaldehyde, which may be readily detected by the smell. 228 Qualitative Chemical Analysis. HippUfic Acid (Benzoyl-glycocoll). C 6 H 6 .CO.NH.CH 2 .COOH Hippuric acid is a good example of an acid occurring in animal life, since it is present in the urine of horses. It forms colourless and odourless rhombic prisms or needles, m.p. iS;^ , difficultly soluble in cold water (i : 600), more readily in hot water. It dissolves readily in alcohol, but only with difficulty in ether. It is insoluble in petroleum ether, and may thus be separated from benzole acid^ which is soluble in this solvent. 1. On heating in a dry tube the acid first melts, then becomes dark in colour, and a sublimate of benzoic acid is produced. The vapours have a smell reminiscent of benzaldehyde. 2. When ignited with soda lime, ammonia is evolved, which may be recognised by the smell and by turning moist red litmus paper blue. *3 Ferric chloride produces, from neutral solutions, a brownish-pink precipitate of ferric hippurate, which is soluble in alcohol. *4. Silver nitrate gives, from neutral solutions, a white curfly precipitate of silver hippurate, which is soluble in hot water, from which it crystallises on cooling in characteristic feathery tufts. It may be necessary to allow the solution to stand for a short time before it crystallises. C 6 H 6 . CO . NH . CH 2 . COONa + AgNO 3 = C 6 H 5 . CO . NH . CH 2 . COOAg + NaNO 3 5. When boiled with caustic potash (i : i) hippuric acid is hydrolysed into benzoic acid and glycocoll. The benzoic acid crystallises out on acidifying, and may be recognised by any of the tests on p. 223. C 6 H 6 . CO ! . NH . CH 2 . COOH = C 6 H B . COOH HO ! H + NH a . CH a . COOH Reactions and Separation of Organic A cids and Phenols. 229 Phenol (Carbolic Acid). C 6 H 5 OH Phenol forms colourless crystals; m.p. 43, b.p. 182. On adding 10 per cent of water the crystals form a syrupy fluid. Phenol, or its solution, has a strong, sweetish odour ; the smell is not characteristic, because other aromatic hydroxyl compounds, e.g. the cresols, have a very similar odour. It is soluble in caustic alkali, but not in alkali carbonates. *i. Ferric chloride produces a deep violet coloration, small quantities of hydrochloric acid or acetic acid destroy the colour, turning it yellow. *2. Bromine water, even in very dilute solutions, gives a white precipitate of tribromophenol, soluble in caustic alkalis. QH 5 OH -f 3Br 2 = C 6 H 2 Br 3 OH + 3 HBr *3. On adding to an aqueous solution of phenol a few drops of ammonium hydroxide, then a few drops of bromine water, and gently warming, a beautiful indigo blue coloration is produced. Hydrochloric acid, added to this solution, turns it red. In very dilute solutions the coloration is not immediate. *4. Liebermann's Reaction. If about i c.c. of cone, sulphuric acid, and a small piece of sodium or potassium nitrite about the size of a pin's head is added to a small quantity of phenol, and the mixture gently warmed, a deep green or blue coloration is produced ; when this solution is poured into water, it turns red, and on adding excess of caustic alkali, the blue or green colour returns. Separation of Benzoic and Salicylic Acids and Phenol. Make the solution to be tested alkaline f with sodium carbonate : the benzoic and salicylic acids will form sodium salts. t If the solution is already alkaline, it should be first acidified with hydro- chloric acid, in case the phenol may be present as a phenolate. 230 Qualitative Chemical Analysis. Phenol only forms a sodium salt with caustic soda (p. 229). Extract the phenol from the solution by means of ether. The ethereal solution is best separated by means of a small separating funnel. A pipette will answer the purpose when a funnel is not obtainable. Ethereal Solu- Aqueous Solution : Neutralise exactly with hydro- tion : Evaporate chloric acid, and add ferric chloride, f A buff- or distil off the coloured precipitate is produced. [The colour of the ether. The phenol precipitate will be more or less masked by the violet remains behind, colour produced by the salicylate, should this happen and may be con- to be present.] Filter and wash. firmed by A 1 \- 1 A. Dissolving a portion in water, Hesidue : Is ferric Solution is violet owing to and adding a few drops of ammonia benzoate : confirm benzoic acid by dry- the presence of salicylic acid. Make alkaline with and of bromine- ing the precipitate, ammonia, and filter off the water, and gently warming : an in- digo blue colora- tion, which turns and mixing with ex- cess of soda lime or lime, in a hard glass test tube fitted with a precipitated ferric hydroxide. Evaporate solution to dry- ness, and confirm salicylic acid by red on addition of hydrochloric acid (p. 227), con- delivery tube. Heat strongly, holding the end of the delivery A. Warming a small portion of the^residue with strong nitric acid: a yellow coloration, due firms tube under about \ to the formation of picric c.c. of strong nitric acid, which, on the addition Phenol. acid. Dilute with of a few drops of sodium B. It may be fur- ther confirmed by large bulk of water, when the character- hydrate (p. 226), become more intense. Liebermann's re- istic smell of nitroben- B. The other portion may be action ( 4, p. zene will be noticed heated with a little concen- 227). ( 7, p. 224). Confir- trated sulphuric acid and mation of methyl alcohol, when the characteristic odour of "oil Benzoic Acid. of winter-green " further con- firms Salicylic Acid. Uric Acid. C 5 H 4 N 4 3 Colourless crystalline powder, insoluble in cold, only slightly soluble in hot water. Insoluble in alcohol and ether. Soluble t The ferric chloride must not be strongly acid, but should be as nearly neutral as possible. Reactions and Separation of Organic Acids and Phenols. 231 in alkaline solutions, or in solutions containing salts which have an alkaline reaction, e.g. Na 3 P0 4 + C 5 H 4 N 4 O 3 = NaH 2 P0 4 + C 5 H 2 N 4 O 3 Na 2 1. On being heated, uric acid does not melt, but is decom- posed with charring; ammonia, cyanic acid, and hydro- cyanic acid being evolved. 2. Uric acid dissolves in cold concentrated sulphuric acid without charring; on heating, however, decomposition takes place, with evolution of carbon monoxide, carbon dioxide, and sulphur dioxide. *3. When heated in a dry tube with a little solid caustic soda, or potash, ammonia gas is evolved, and sodium cyanide is produced. On cooling and dissolving the fused mass in water the solution gives the reactions for hydrocyanic acid (p. 114). 4. When an alkaline solution of uric acid is added to Fehling's solution, a white precipitate of cuprous urate is formed on gently warming; on further heating, reduction with formation of cuprous oxide takes place. *5. On dissolving a little uric acid in sodium carbonate, and allowing a few drops to fall on a piece of filter paper, moistened with silver nitrate, a black stain is immediately produced, owing to reduction of the silver nitrate. This is a very delicate reaction, even very dilute solutions producing a light brown or yellow mark. *6. Murexide Reaction. Moisten a little uric acid with concentrated nitric acid, and evaporate in a porcelain dish to dryness on a water bath. A yellow, reddish-brown, or magenta residue is obtained, the colour varying according to the length of heating. Remove from the water bath and cool, then add a drop of ammonium hydroxide, when the colour changes to violet, and, on adding a drop of caustic soda, the violet becomes of a deep blue shade. The coloration disappears on warming. 232 Qualitative Chemical Analysis. Meconic Acid. C 5 H(OH)[COOH] 2 O 2 This acid is of interest because it occurs in opium in com- bination with morphine, as morphine meconate. Its detection is, therefore, important in cases of opium poisoning. Meconic acid crystallises in small plates, or in rhombic prisms containing 3 mols. H 2 O. It is sparingly soluble in cold, but readily soluble in hot water ; it is also readily soluble in alcohol. 1. When heated in a dry tube its gives up its water of crystal- lisation at 1 00, and at 120 splits up into comenic acid (C 6 H 4 O 6 ) and carbon dioxide, on further heating into pyromeconic acid. At higher temperatures it chars, and an odour rather resembling that produced by the charring of tartaric acid is produced. 2. Neither cold nor hot concentrated sulphuric acid pro- duce a visible change. *3. Silver nitrate produces a light yellow flocculent pre- cipitate of silver meconate, readily soluble in ammonia, with formation of a light yellow solution. C 6 H 2 O 3 (COONa) 2 + 2 AgNO 3 = C 5 H 2 O 3 (COOAg) 2 + 2 NaNO 3 *4. Calcium chloride slowly throws down a white silky crystalline precipitate of calcium meconate, which has a very characteristic appearance. C 5 H 2 3 (COONa) 2 + CaCl 2 = C 5 H 2 O 3 (COO) 2 Ca + 2 NaCl *5. Ferric chloride produces a characteristic purplish-brown coloration. On boiling, a basic precipitate is not nearly so readily produced, as is the case with ferric acetate or formate. 3QH 2 O 7 Na 2 + 2FeCl 3 = (C 7 HA) 3 Fe 2 + 6NaCl Reactions and Separation of Organic A cids and Phenols. 233 Gallic Acid.f C 6 H 2 (OH) 3 COOH Gallic acid forms light yellowish-brown crystals, containing i mol. H 2 O. It is slightly soluble in cold water, readily in hot water. It is also soluble in alcohol, glycerol, and acetone, but only slightly in ether. i. On heating with concentrated sulphuric acid, the solution first becomes green and then purple. *2. Ferric chloride produces a deep blue coloration or precipitate, which is soluble in excess of the reagent, forming a green solution. *3. Ferrous sulphate produces an azure blue coloration. *4. An ammoniacal solution of potassium ferricyanide gives a red coloration, changing to brown. *5. Potassium cyanide produces a pink coloration, which rapidly disappears; The colour reappears again on shaking with air. *6. Lime water or a solution of barium hydroxide pro- duces a blue precipitate ; small quantities give only a blue colora- tion. When the quantity is excessively small, a reddish colour is produced, which changes to a dirty brown. Gallotannic Acid (Tannin, Tannic Acid). C 14 H 10 O 9 Tannic acid, when pure, forms a colourless amorphous mass ; but it often occurs in commerce in the form of so-called needles. It is, however, generally of a yellowish appearance. It has a very astringent taste. It is readily soluble in water, especially on warming. Hydrochloric and sulphuric acids precipitate it from its t The reactions of gallic and tannic acids refer to solutions of the free acids, and not of their salts, as with the other acids. 234 Qualitative Chemical Analysis. solutions. Tannic acid is easily soluble in dilute alcohol, but almost insoluble in absolute alcohol and ether. i. Alkaline solutions of tannic acid rapidly oxidise in the air, becoming dark brown. *2. On adding a solution of gelatine to a solution of tannic acid, a white or buff-coloured flocculent precipitate is produced. (Distinction from gallic acid and pyrogallol.) *3. Ferric chloride gives a greenish-black precipitate of ferric-gallotannate (ink). *4. Lime water produces a grey precipitate. *5. Potassium cyanide forms a brownish-red coloration, which becomes brown, assuming the red tint again on being shaken with air. *6. Ferrous sulphate produces a blackish-violet coloration. *7. Lead nitrate precipitates white lead tannate. Neither gallic acid nor pyrogallol gives a precipitate with lead nitrate, although they give precipitates with lead acetate. 8. An ammoniacal solution of potassium ferricyanide produces a deep red colour, changing to brown. A large excess of the reagent should not be added. (Pyrogallic Acid). C 6 H 3 (OH) 3 Pyrogallol forms fine colourless needles, m.p. 131, b.p. 210. It is extremely soluble in water, alcohol, and ether, but not so readily in chloroform and benzene. It is an active poison, the symptoms being similar to those of phosphorus. *i. Alkaline solutions of pyrogallol rapidly become brown, owing to absorption of oxygen. For this reason alkaline solu- tions of pyrogallol are employed in gas analyses for estimating oxygen. *2. Lime water produces a purple coloration, which quickly becomes brown. Reactions and Separation of Organic A cids and Phenols. 235 *3. Fehling's solution is reduced on heating, while solutions of silver are immediately reduced in the cold : hence use of pyrogallol in photography. *4. Dissolve a little pyrogallol in about i c.c. of water, add one or two drops of formaldehyde (formalin), and then about 2 c.c. of concentrated hydrochloric acid. On standing a few minutes, a white precipitate, which rapidly turns red, and, finally, a deep purple, is produced. (Cf. Formaldehyde, 4, p. 262.) *5. Ferric chloride produces a reddish-brown coloration. *6. Potassium cyanide forms a brownish-red coloration ; the solution gradually turns brown, but the red tint appears on shaking with air. *y. Ferrous sulphate gives a brilliant purple-blue coloration. SYNOPTIC TABLE SHOWING BEHAVIOUR OF GALLIC AND TANNIC ACIDS AND PYROGALLOL WITH VARIOUS RE- AGENTS. Reagent. Gallic acid. Tannic acid. Pyrogallol. I. Concentrated i. First green, i. Darkens on I. Colourless solu- sulphuric acid, then bright) strongly heat- tion, darkening on warming purple ing, becoming on strongly heat- purple ing. 2. Lime water 2. Blue precipi- 2. Grey precipi- 2. Purple colora- tate or colora- tate tion, rapidly tion turning brown. 3. Ferric chloride 3. Blue precipi- 3. Bluish - black 3. Reddish -brown tate, soluble in precipitate (ink) coloration. excess to a green solution 4. Ferrous sul- 4. Azure blue 4. Blackish- violet 4. Azure blue phate coloration coloration coloration. 5. Potassium cy- 5. Pink colora- 5. Brownish -red 5. Brownish - red anide tion, quickly coloration, turn- coloration, turn- disappearing, ing brown. Red ing brown. Red returning on tint reappear- tint reappearing shaking with ing on shaking on shaking with air with air air. 6. Lead nitrate 6. 6. White precipi- 6. tate 7. Solution of 7- 7. White precipi- 7- gelatin. tate 236 Qualitative Chemical Analysis. General Method of Procedure in Testing for Acids. It is hardly possible to give a table for the separation of all the organic acids which may be met with in analysis, but, by the fol- lowing method of procedure, a fair idea of what acids are present may be obtained, and then special tests and separations may be applied. These reactions may be applied to the original substance, or the substance treated as described on p. 209, and evaporated to dryness. I. Tests in the Dry Way. Test. I. Heat a small portion of the substance in a dry tube 2. Heat a small portion with soda-lime 3. Heat the substances with a little dilute sul- phuric acid 4. Heat with concen- trated sulphuric acid Observation. (o) A sublimate is pro- duced (b) It chars, and an odour resembling that of burnt sugar is pro- duced (c) Chars, and acrid va- pours evolved (d) Ammonia and hy- drocyanic acid evolved (a) Inflammable vapours of benzene evolved (b) Vapours of phenol given off (c) Ammonia given off (so 4 Dimethyl sulphate S0 4 (OCH 3 ) 2 1 88 Ethyl mercaptan ... C 2 H 5 SH 36 ,, sulphide (C 2 H 8 ) 2 S 91 Propyl chloride C,H T C1 0-896 ,, bromide C 3 H 7 Br ^0 1-352 ,, iodide C 3 H T I 102 i'743 Isopropyl chloride ... ,, bromide ... (CH 3 ) 2 CHC1 (CH 3 ) 2 CHBr 36-5 59'5 0-859 1-31 ,, iodide (CH 3 ) 2 CHI 89-5 1-703 Amyl nitrite C 5 H U N0 2 97-99 0-88 On treating the nitrites with a reducing agent, e.g. tin and hydrochloric acid, they are reduced to the alcohol C 2 H 5 . NO + 6H = C 2 H 6 OH + NH 3 + H 2 O The nitrates, on the other hand, are not reduced by this treat- ment. Nitroparaffins. The nitroparaffins cannot be compared with the nitrates and nitrites. In the nitrites the nitrogen is attached to the alkyl radical through the oxygen atom Alk . O . NO, but in the nitro- paraffins the attachment is through the nitrogen atom Alk . In the first case the nitrogen is triad, and in the second pentad. The nitro-compounds, although they may dissolve in caustic alkalis, are not decomposed by them, as is the case with the nitrites, which are readily hydrolysed. On reduction with tin and hydrochloric acid the nitroparaffins are converted into amines C 2 H 5 NO 2 + 6H = C 2 H 5 NH 2 + 2H 2 O The amines form hydrochlorides, but upon rendering the reduced 242 Qualitative Chemical Analysis. solution alkaline, the characteristic amine smell is noticed, and they can be obtained from the solution by steam distillation. To test for the amine the distillate is exactly neutralised with hydro- chloric acid, and evaporated to dry ness on the water bath, when the hydrochloride of the amine is obtained in the solid condition. A portion of the residue can be used to show the carbylamine reaction (see p. 246). This reaction, however, can be shown with the crude mixture of the tin salt and amine, by making alkaline with alcoholic potash, and warming with a little chloroform. In order to find the alkyl radical which was present, pour off the reduced solution from any tin remaining, and add a little sodium nitrite to the acid solution. The amine will be converted to the alcohol, thus C 2 H 5 NH 2 + HO . NO = C 2 H 5 OH + H,O + N 3 Distil off a portion of the solution, and test the distillate for the alcohol. The reduction test is easily carried out, by taking three or four drops of the nitroparaffin in a test-tube, adding 2 or 3 c.c. of caustic alkali, and a small piece of zinc. On gently warming, the characteristic fishy smell of the amine thus produced is noticed. Further, a piece of moistened red litmus-paper held in the mouth of the test-tube is turned blue. Chloroform. CHC1 3 Chloroform is a colourless neutral fluid with a characteristic ethereal odour, almost insoluble in water, but readily soluble in alcohol or ether. It boils at 60-62, sp. gr. 1-49, and when the vapour is allowed to come into contact with the flame of a Bunsen burner, it colours the edges green. i. Carbylamine Reaction. When heated with a few drops of aniline and 2 or 3 c.c. of alcoholic potash, the characteristic and disgusting odour of phenyl isontrile (carbylamine) is pro- duced. CHC1 3 + 3(KOH) + C 6 H 6 NH 2 = C 6 H e N : .C + 3KC1 + 3 H 2 O Ethereal Salts. 243 2. Alcoholic Potash. On warming for a few minutes with a few c.c. of alcoholic potash the chloroform is decomposed, and if the solution so obtained is diluted with water, acidified with nitric acid, and a solution of silver nitrate added, a white pre- cipitate of silver chloride is produced CHC1 3 + 4 (KOH) = H . COOK + 3 KC1 + *H 2 O If the silver chloride is filtered off, and the solution neutralised and warmed, the formate will reduce the excess of silver salt. 3. Fehling's Solution. When chloroform is warmed with alkaline copper solutions, a precipitate of yellowish-red cuprous oxide is produced CHC1 3 + 2Cu(OH) 2 + 5KOH = CiigO + K 2 CO 3 + 3KC1 + 5H 2 O Chloral hydrate behaves in a similar manner, because when it is warmed with alkalis, chloroform is produced CC1 3 CH(OH) 2 + KOH = CHC1 3 + HCOOK + H 2 O 4. On covering a little powdered resorcinol with a few drops of chloroform, then with about o'5 c.c. of a strong solution of alkali hydroxide and warming, a brilliant reddish coloration is produced. Carbon Tetrachloride. CC1 4 Colourless, heavy, and pleasant-smelling liquid ; it boils at 76-77; sp. gr. i '608. 1. It is decomposed when heated with alcoholic potash : CC1 4 + 4 (KOH) = 4 KC1 + CO 2 + 2H 2 O On acidifying the solution with nitric acid, carbon dioxide is evolved, which may be tested for in the usual manner. Silver nitrate also gives a precipitate of silver chloride. 2. Distinction from Chloroform. With alcoholic potash and aniline it does not give the carbylamine reaction. 244 Qualitative Chemical Analysis. lodoform. CHI 3 Forms small yellow hexagonal tablets or yellowish leaflets, which have a peculiar and characteristic odour. It is almost insoluble in water, but is distinctly volatile in steam. It dissolves readily in alcohol, acetone, and ether, m.p. 119. 1. On heating with sodium, it gives the reactions for iodine (see p. 203). 2. Cover a little powdered iodoform with a few drops of phenol, and carefully warm with a small piece of sodium hydroxide. A red coloration is produced, and on dissolving in alcohol a very intense red solution is obtained. lodoform is such a characteristic substance that, if the melting point is taken and the substance proved to contain iodine, it is hardly necessary to try any further reactions. Determination of Boiling-point of Small Quantities of a Liquid. It is often necessary to determine the boiling-point of very small quan- tities of liquids. The apparatus em- ployed for this purpose is illustrated in Fig. 12. A flask A which holds about 100- 110 c.c. of fluid is placed upon a wire gauze fastened over an inverted cone, such as is used to prevent Bunsen burners from flickering. The flask has a very wide neck, about 4 cm. in diameter, and is fitted with a cork with three holes. Through the central hole a thermometer Ethereal Salts. 245 is passed, and through A a small thin-walled test-tube, about 7 to 8 cm. long, with a diameter of f cm. This tube, however, is not passed directly through the cork, but through a piece of glass tube which is fitted into a cork so that the test-tube may be inserted and withdrawn without any difficulty. It also serves to prevent charring of the cork with sulphuric acid when the test-tube is withdrawn. In order to prevent the test-tube from slipping through into the flask, the top of it is slightly widened out, so as to act as a collar. The thermometer also passes through a similar tube, and to prevent it dropping down too low a piece of rubber tube is placed round it to act as a support. The stirrer B of glass rod fits loosely through another tube, so that the air, as it expands upon heating, shall not set up a pressure. About J c.c. of liquid, the boiling-point of which is to be determined, is placed into the tube, and then a capillary tube, C, sealed at one end, and about i to i \ cm. long, is dropped into the liquid in such a way that the open end is to the bottom. The determination is then carried out as follows : The acid is heated by means of a Bunsen burner, the liquid being gently stirred. The temperature is raised fairly quickly at first until a continuous stream of bubbles is given off from the bottom of the capillary tube. The source of heat is then removed and the temperature allowed to drop, the heating liquid being thoroughly stirred while it cools. As the temperature drops the bubbles begin to be given off less rapidly, and finally stop altogether. At the moment the bubbles cease to be given off that is, when the pressure of the vapour within the tube is equal to the atmospheric pressure the thermometer is read off, and this is the boiling-point of the liquid. A second deter- mination can be made by at once again rapidly raising the temperature before the liquid is sucked back into the capillary tube. The stream of bubbles is again obtained, and on cooling down a second reading may be taken as before. It is found that by proceeding in this manner, and being careful to stir, absolutely accurate results may be obtained. 246 Qualitative Chemical Analysis. The Amines. The amines may be looked upon as ammonia in which one or more of the hydrogen atoms have been replaced by alkyl radicals. They are called Primary, Secondary, or Tertiary, according to whether one, two, or three hydrogen atoms have been replaced ; thus NH 3 CH 3 NH 2 (CH 3 ) 2 NH (CH 8 ) 3 N Ammonia Methylamine Dimethylamine Trimethylamine (Primary) (Secondary) (Tertiary) They also form salts corresponding to ammonium salts and to ammonium hydroxide /CH, NH 4 C1 (CH 3 ) 3 N . HC1 (CH 3 ) 3 N/ \OH Ammonium chloride. Trimethyl Tetramethylammonium ammonium chloride. hydroxide. By means of certain specific reactions one is able to determine whether the amine belongs to the primary, secondary, etc., class. Primary Amines. i. When warmed with a mixture of chloroform and alcoholic potassium hydroxide form isonitriles (isocyanides). The isonitrile, or carbylamine reaction, depends upon the offensive odour which the carbylamines possess. CH 3 NH 2 + CHC1 3 4- 3(KOH)* = CH 3 NC + 3KC1 + 3 H 2 O C 8 H 6 NH 2 + CHC1 3 + 3(KOH) = C 6 H 5 NC + 3 KC1 + 3H 2 O 2. On dissolving the amine in a little dilute hydrochloric acid and adding a small quantity of sodium nitrite, the amine is decomposed with formation of an alcohol (from which it may be identified) and liberation of nitrogen, thus C 2 H 6 NH 2 + HO . NO = C 2 H 6 OH + N 2 + H 2 O 3. Hydroplatinic acid and Hydroaurie acid produce yellow crystalline precipitates when added to solutions of primary amines acidified with hydrochloric acid. CH 3 NH 2 + H AuCl 4 = CH 3 . NH 2 , HAuCl 4 * KOH is placed in brackets to indicate that it is an alcoholic solution. Ethereal Salts. 247 Secondary Amines. These do not give the carbylamine reaction, neither are they converted into alcohols by nitrous acid, but form nitrosoamines. (QH-^NH + HO . NO = (C 2 H 5 ) 2 N . NO + H 2 O Dissolve the secondary amine in a little dilute hydrochloric acid, and slowly add an aqueous solution of potassium or sodium nitrite, taking care that the mixture does not become hot. An oily nitrosoamine gradually separates out; extract this with a little ether, wash with dilute sodium carbonate, and to a portion of the ethereal solution apply Liebermann's test (p. 229). Mix the solution with a few crystals of phenol and then cover with a few c.c. of concentrated sulphuric acid. A dark green solution will be obtained, which on diluting with water becomes red, and on addition after dilution with excess of caustic alkali, assumes an intense blue or green colour. 2. Hydroplatinic acid and Hydro-auric acid give orange- coloured precipitates when added to solutions of secondary amines acidified with hydrochloric acid. (QH^NH + H 2 PtCl 6 = [(C 2 H 5 ) 3 NH] 2 , H 2 PtCl 6 (C 2 H 5 ) 2 NH + HAuCl 4 = (C 2 H 5 ) 2 NH, HAuCl 4 Tertiary Amines do not give the carbylamine reaction, neither do they form nitrosamines. The tertiary amines, as also the secondary amines, are powerful bases and precipitate metallic hydroxides from salt solutions of the metals ; for example, ferric hydroxide from ferric chloride. To show this reaction it is best to make the solution of the amine alkaline with sodium hydroxide and to distil a few cubic centimetres ; the distillate will contain the amine, will have an alkaline reaction, and precipitate ferric hydroxide. The tertiary amines also unite directly with alkyl halogen compounds forming crystalline quaternary salts, e.g. (CH 3 ) 3 N + CH 3 I = (CH 3 ) 4 NI Extract a portion of the alkaline solution of a tertiary amine with ether, dry the ethereal solution with a little calcium chloride, 248 Qualitative Chemical Analysis. and add a few drops of ethyl iodide to it : a white crystalline pre- cipitate will show the presence of the quaternary compound. If the pure tertiary amine is to hand, the ethyl iodide may be directly added to it, when union will take place with great rise in temperature. Quarternary Salts. These are colourless and odourless. The iodide may, however, be brownish in colour, owing to slight decomposition. They are not decomposed by boiling with alkaline hydroxides, but when aqueous solutions are shaken with freshly precipitated silver hydroxide,* the free quaternary bases are obtained, a precipitate of the silver salt of the halogen being also produced. (CH 8 ) 4 NI + AgOH = (CH 3 ) 4 N . OH + Agl The solution will be strongly alkaline, and will liberate ammonia from a solution of ammonium chloride or other salt of ammonia. Halogen Acids of the Fatty Series. (Chloro-acetic acids.) In describing the halogen acids the compounds of acetic acid only will be dealt with, because the properties of all of the halogen acids are very similar. Acetic acid forms three chloro acids depending upon whether one, two, or three of the methane hydrogens are replaced by chlorine. Strange to say, the mono and trichloroacetic acids are crystalline solids, but the dichloroacetic acid is a liquid at ordinary temperatures. M.P. B.P. Monochloroacetic Acid, CH 2 C1COOH 63 185-187 Dichloroacetic CHC1 2 COOH 4 189-191 Trichloroacetic CC1 3 COOH 52 195 * To prepare silver hydroxide, add a slight excess of sodium hydroxide to a solution of silver nitrate. Filter off the hydroxide and wash until free from alkali with water. The hydroxide may now be used without being previously dried. Ethereal Salts. 249 In general properties these acids are very similar, forming neutral salts with alkalis. When the aqueous solutions are treated with a solution of silver nitrate, no precipitate of silver chloride is produced. Although from strong solutions of the salt the silver salt of the acid may separate out, e.g. CH 2 ClCOONa + AgNO 3 = CH 2 Cl 2 COOAg + NaNO, Monochloroacetic Acid. This acid melts at 63, but if the temperature of the bath is raised to 70 and then cooled until the acid solidifies in the capillary, on again raising the temperature it melts at 52. Monochloroacetic acid dissolves readily in water, a con- siderable lowering of temperature taking place. Alkali Hydroxides. On gently heating with sodium or potassium hydroxide, the acid is converted into glycollic acid. Addition of silver nitrate to a portion of the solution acidified CH 2 C1COOK + KOH = CH 2 (OH)COOK + KC1 with nitric acid gives a precipitate of silver chloride. Dichloroacetic Acid is a liquid at ordinary temperatures. When the silver salt is boiled in a small quantity of water for some little time with silver hydroxide, it is decomposed, silver chloride and glyoxalic acid being produced CHCla CHO | + AgOH = | + 2AgCl COOAg COOH The solution after separation by decantation from the silver chloride, gives SchifFs reaction and reduces Fehling's solution and ammoniacal silver nitrate. The silver salt of Dichloroacetic acid very rapidly darkens on exposure to light. Trichloroacetic Acid on warming with alkalis gives chloroform and carbon dioxide (carbonates). 250 Qualitative Chemical Analysis. CC1 3 COOK + KOH = CHC1 3 4- K 2 CO 3 If the solution is now warmed with aniline and alcoholic potash, the carbylamine reaction is given. It is, perhaps, better to carry out this reaction in one stage by heating the chloroacetic acid with alcoholic potash and aniline. Lead Acetate. Forms a lead salt which is readily soluble in water, but is precipitated out on addition of alcohol. Amides. Amides may be looked upon as being carboxylic acids in which the OH group of the carboxyl is replaced by the amide group NH 2 . Or they may be looked upon as derivatives of ammonia in which one of the hydrogen atoms is replaced by an acetyl, benzoyl, etc., radical, as the case may be. They are usually prepared by the interaction of an acid chloride or anhydride with ammonia, also by the action of alcoholic ammonia upon distillation of an acetate. As examples of this class of compound, we will take acetamide, oxamide, and benzamide. Acetamide. CH 3 CONH 2 Place about i c.c. of acetic anhydride or acetyl chloride in a test-tube, and cautiously add drop by drop, concentrated ammonia, until the vigorous reaction ceases. On cooling, acetamide will crystallise out. The acetamide may be melted and poured from the test-tube into an evaporating basin. When solid, spread upon a porous plate to drain. It melts at 80-82, and boils at 222. Has an unpleasant "mousy" odour, and is readily soluble in water and alcohol. i. On heating with dilute acids or alkalis, it is decomposed into acetic acid and ammonia. CH 3 CONH 2 + H 2 O = CH.COOH + NH 3 If acids are employed, ammonia can afterwards be detected by the addition of sodium hydroxide. If the hydrolysis is Ethereal Salts. 251 carried out by means of alkalis, the ammonia escapes during the hydrolysis. The acetic acid can be detected on distillation after acidification with dilute sulphuric acid. 2. On heating with phosphorus pentoxide, water is split off and methyl cyanide (acetonitrile) produced, b.p. 8i'6. CH 3 CONH 2 - H 2 O = CH 3 CN Oxamide. CO . NH 2 CO . NH 2 Dissolve a few c.c. of ethyl or methyl oxalate in alcohol, and add a slight excess of concentrated ammonia. Almost immediately a white precipitate of oxarmde is produced. COO . CH 3 CO . NH 2 + 2 NH 3 = | + 2CH 3 OH COO . CH 3 CO . NH 2 Oxamide is a white powder, almost insoluble in water, alcohol, and ether. It sublimes on heating without melting, but is partially decomposed during the operation. 1 . On heating with dilute acids or alkalis, oxamide is hydrolysed with formation of oxalic acid and ammonia. CO . NH 2 COOH + 2H.O = | + 2NH 3 CO . NH 2 COOH The ammonia can be detected as usual, and the hydrolysed solution after acidification with dilute sulphuric acid will at once decolorise permanganate. 2. On heating with phosphorus pentoxide, dehydration ensues with formation of cyanogen, which will burn at the mouth of the test-tube with a peach-coloured flame. CO . NH 2 - 2 H 2 = C 2 N 2 CO . NH 2 252 Qualitative Chemical Analysis. Benzamide. C 6 H 5 CONH 2 Place i c.c. of benzoyl chloride into a test-tube and cautiously add, drop by drop, excess of concentrated ammonia. Benzamide will crystallise out and can be re-crystallised by boiling with water. It melts at 139 and is a colourless solid, sparingly soluble in cold water but readily in hot. i. On hydrolysis with acids or alkalis, ammonia and benzoic acid are produced. C 6 H 6 CONH 2 + H 2 = C 6 H 5 COOH + NH 3 If hydrolysed with alkalis, ammonia is given off during hydrolysis, and benzoic acid is precipitated out on acidifying. Phosphorus Pentoxide produces phenyl cyanide, which has a smell resembling benzaldehyde. (Caution, it is very poisonous.) C 6 H 5 CONH 2 + H 2 = C 6 H 5 CN Methyl and Ethyl Oxalate. Methyl Oxalate is a colourless crystalline solid, m.p. 54, b.p. 163. It is readily soluble in water, alcohol, and ether. Ethyl Oxalate is a colourless liquid, boiling at 186; it is practically insoluble in water. 1. On hydrolysis with acids or alkalis, oxalic acid and the corresponding alcohol are produced. The alcohol can be dis- tilled off and tested for separately. The solution contains oxalic acid. COO . CH 8 COOH | + 2 H 2 O = | + 2CH 3 OH COO . CH 3 COOH 2. On dissolving in alcohol and adding concentrated ammonia, oxamide is produced. COOCH 3 CO . NH 2 | + 2NH 3 = | + 2 CH 3 OH COOCH, CO , NH a CHAPTER XIV. HYDROCARBONS, HIGHER FATTY ACIDS, AND GLYCERIDES. Hydrocarbons. IT is important to distinguish between hydrocarbons of the paraffin and hydrocarbons of the benzene series : Paraffins. The paraffins may either be liquids, solids, or semi-solids (greases), e.g. paraffin oil, paraffin wax, and vaselin. They are not very soluble in alcohol, but are readily soluble in ether, chloroform, and carbon disulphide ; they are insoluble in water. Use ligroin or kerosine for the reactions. 1. Concentrated sulphuric acid or a mixture of 2 parts sulphuric acid, and the i part strong nitric acid, has no action upon the paraffins in the cold. 2. On boiling with a strong aqueous solution of sodium hydroxide the oil does not dissolve, and on adding a strong solution of salt no precipitate of soap is produced, whereas with saponifiable oils, such as olive oil, or butter a soap is produced, and the oil dissolves. 3. Bromine water is not decolourised when shaken up with the paraffins. 4. Phenol is insoluble in the paraffins, but dissolves in aromatic hydrocarbons. 254 Qualitative Chemical Analysis. Benzene. C 6 H 6 Benzene is a colourless fluid which is insoluble in water, but readily soluble in the majority of organic solvents, such as alcohol, ether, etc. It freezes at 6 and boils at 8o'5. 1. Pure benzene does not impart any colour to concentrated sulphuric acid, but, generally speaking, owing to the presence of thiophen in commercial benzene, it is coloured brown, the addition of a trace of a nitrite changes the colour to violet. 2. To 5 c.c. of a mixture of 2 parts cone, sulphuric acid and i part cone, nitric acid, add drop by drop 2 c.c. of benzene with continual shaking. If the mixture gets hot, cool between each addition of benzene. Place the vessel containing the mixture into a hot water bath for about 5 minutes, and then pour into an excess of water. Oily yellow drops of nitrobenzene will sink to the bottom of the water. C 6 H 6 + HNO 3 = C 6 H 5 NO 2 + H 2 O. The nitrobenzene (oil of mirbane) has a smell rather resembling that of benzaldehyde ; the latter is therefore sometimes adulterated with nitrobenzene. Bromine, when added to benzene, colours it brown ; gradually the mixture becomes warm, and hydrobromic acid is evolved. The reaction is more rapid and energetic if the mixture is warmed, or if a piece of aluminium foil, coated with mercury, is placed in the mixture. Toluene. C 6 H 5 .CH 3 Colourless, rather pleasant-smelling fluid, b. p. 111. Insoluble in water, but readily soluble in ether, alcohol, acetone, chloroform, etc. Detection in presence of benzene. Heat the hydrocarbon Hydrocarbons, Higher Fatty Acids, and Glycerides. 255 with a mixture of part of a saturated solution of potassium dichromate and 4 parts cone, sulphuric acid. The toluene is oxidised to benzoic acid. Dilute the solution with water, arid extract three or four times with ether. On evaporating off the ether the benzoic acid is obtained, and may be proved by the tests on p. 223. A few drops of bromine, when added to a little toluene dissolved in chloroform, colour it brown, but the mixture gradually gets warm and vapours of hydrobromic acid are evolved. The greater the number of alkyl groups which the hydrocarbon of the benzene series contains, the more vigorous the reaction with bromine. Higher Fatty Acids. Palmitic acid C 15 H 31 COOH ; m.p. 62-6. Stearic acid QrH^COOH; m.p. 69-3. Oleic acid CnH^COOH ; m.p. 14-0. These acids all occur naturally, in the form of their glycerine esters, as fats. Hard fats (stearin) usually contain considerable quantities of the glycerides of stearic and palmitic acids (palmitin) ; "soft and liquid fats, the glyceride of oleic acid (olein). In order to obtain the acids for testing purposes, a small quantity of a fat may be saponified. Dissolve about 10 grams of fat in 40-50 c.c. of alcohol, and mix with a solution of 6-7 grams of caustic potash in 20 c.c. of water. Fit the flask which contains this mixture with an upright condenser, and boil until a few drops of the solution, on taking out, dissolve completely in distilled water. The solution now contains the alkali salt of the acid and glycerol. To obtain the free acid, pour into water, and acidify with dilute sulphuric acid. Stearic and palmitic acids separate as flocculent solids, oleic acid as an oil. Wash several times on a filter paper with warm water. The other acids can be separated from the oleic acid by pressing between filter paper and then crystallising from alcohol. 256 Qualitative Chemical Analysis. Reactions of Glycerol Esters (Fats). 1. Heat a few drops of the fat with i or 2 grams of solid sodium bisulphite. Characteristic acid odour of acrolein is produced. (See 3, p. 270.) 2. When dropped upon paper a greasy stain is left, which is not removed by heating on the water bath. *3. Make a mixture of 5 c.c. of alcohol and 10 c.c. of ether, and add one drop of phenolphthalein, then add two or three drops of a normal solution of caustic alkali. On now shaking up with the fat, the red colour caused by the alkali remains. Free fatty acids decolourise such a solution. Reactions of Free Acids. i. The melted acids, when dropped upon paper, leave a greasy stain, which is not removed by heating on the water bath. *2. When treated with phenolphthalein, as in 3 above, the acid discharges the red colour. *3- On warming with a concentrated solution of sodium carbonate, the acid dissolves. On cooling, the mixture sets to a solid or jelly-like mass. Fats do not dissolve when treated in this manner. *4. Warm i or 2 grams of the fatty acid with 100 c.c. of distilled water, and carefully add caustic alkali until most, but not quite all, the acid has dissolved. Filter off the undissolved portion. (a.) Shake up a few drops of this solution with distilled water : a soapy lather is produced. (b.) Lead acetate gives a white precipitate of the lead salt lead plaster which, on warming, becomes plastic. (c.) Phenol, and the higher phenols which are insoluble in water, readily dissolve in this solution. (d.) Acids reprecipitate the free fatty acid. The main difference in the reactions between oleic and palmitic and stearic acids is due to the fact that oleic acid Hydrocarbons, Higher Fatty Acids, and Glycerides. 257 is unsaturated, and therefore takes up bromine by addition. If a small quantity of these three acids are separately dissolved in chloroform, and then a few drops of a dilute solution of bromine in chloroform or carbon tetrachloride added to them, only the solution containing the oleic acid will decolourise the bromine. The alkali salts of oleic acid also reduce a solution of potassium permanganate, whereas the salts of stearic and palmitic acids have no action. Detection of Benzene Hydrocarbons in Presence of Paraffin Hydrocarbons. Unless the boiling-points of the hydrocarbons lie some distance apart, it is not possible to separate them by fractional distillation. A rough separation may be made by shaking the mixture up with 95 per cent, alcohol, which completely dissolves the benzene hydrocarbons but has very slight solvent action upon the paraffins. The mixture separates into two layers, the one being a solution of the benzene hydrocarbon in alcohol, the other mainly the paraffin. The layers are separated by means of a separating funnel, and then separately shaken up with an excess of water. On now applying tests, the one layer (generally the upper) will be found to consist mainly of the paraffin hydro- carbon, and the other of the benzene hydrocarbon. (a.) The most certain method of detection is to treat the mixture with fuming sulphuric acid. The benzene hydrocarbon is converted into a sulphonate, which is soluble in water, the paraffin being unacted upon. If it is desired to recover the aromatic hydrocarbon, the aqueous solution, after separation of the paraffin, is treated with excess of lime, the mixture evaporated to dryness, and the calcium salt subjected to dry distillation, when the hydrocarbon distils over. Or in some cases the sodium salt of the sulphuric acid can be obtained by pouring the strong acid solution into a saturated solution of sodium chloride. The sodium salt of the sulphonate 258 Qualitative Chemical Analysis. of the aromatic hydrocarbon separates out, and may be filtered off. The paraffin hydrocarbon floats upon the surface of the aqueous solution,! and may be separated in any appropriate manner. (b.) Another way is to treat the mixture of hydrocarbons with a mixture of equal volumes of concentrated nitric and sulphuric acids. Allow to stand for some time, cooling, if the reaction becomes too vigorous; and, finally, when reaction has ceased, heat on the water bath for a few minutes. Pour into cold water, and then separate the oily layer from the aqueous layer. The nitro compound is now reduced with tin and hydrochloric acid until its smell has vanished. The amido compound so produced remains dissolved in the acid solution. The paraffin can be extracted by means of ether. The amido compound can now be obtained by rendering the acid solution alkaline, and extracting with ether. When a fatty oil, such as olive or linseed, is mixed with paraffin or aromatic hydrocarbons, the method of separation becomes rather complicated. It is first necessary to saponify as described on p. 255. The mixture is then poured into an excess of a saturated salt solution, and steam distilled. The sodium salt of the fatty acid remains behind, and the unsaponifiable oils distil over with the steam, and may then be identified as above described. t A mixture of benzene and ligroin may be very readily separated by this means. Hydrocarbons^ HigJter Fatty Acids, and Glycerides. 259 Naphthalene. Naphthalene has a characteristic smell, and forms white pearly plates which melt at 80, and boil at 217; but it volatilises at all temperatures. It is readily soluble in alcohol, ether, benzene, and most organic solvents. It burns with a smoky, luminous flame. 1. Picric Acid. On dissolving naphthalene in alcohol and adding the solution to a strong alcoholic solution of picric acid, yellow needle-shaped crystals of naphthalene picrate separate out [C 10 H 8 ,C 6 H 2 (NO) 3 OH]. m.p. 149. 2. Naphthaquinone. Dissolve about i grm. of naphthalene in a few c.c. of hot glacial acetic acid, and, keeping hot, add, drop by drop, a strong solution of potassium permanganate, until the red colour of the permanganate is no longer destroyed. On pour- ing into water, naphthaquinone separates out and may be crystal- lised from alcohol or glacial acetic acid. Yellow crystals, m.p. 125, has the characteristic odour of quinones. C 10 H 8 + 3 = C 10 H 6 2 + H 2 3. Cover a trace of naphthalene with a drop of ferric chloride, and then drop on it concentrated sulphuric acid. A reddish colour changing to lilac is produced. Anthracene. Anthracene is odourless, and forms colourless lustrous plates which have a blue fluorescence, m.p. 213, b.p. 351, readily soluble in hot benzene, but only sparingly soluble in alcohol and ether, moderately soluble in hot acetone. i. Picric Acid. When anthracene is dissolved in hot 260 Qualitative Chemical Analysis. acetone, and a strong solution of picric acid in acetone added to. it, ruby-red needle-shaped crystals of anthracene picrate (C 14 H 10 ,C 6 H2(NO 2 )3OH) separate out, m.p. 138. An excess of alcohol decomposes the picrate. 2. Anthraquinone. Dissolve about i grm. of anthracene in a few c.c. of boiling glacial acetic acid, and add to it a con- centrated solution of chromic acid in glacial acetic acid, or a strong solution of potassium permanganate until the purple colour of the permanganate is no longer discharged. On pouring into water, anthraquinone separates out, and may be recrystallised from benzene, m.p. 286* CH CO C 6 H/ >C 6 H 4 + 30 = C 6 H/ >C 6 H 4 + H 2 X CH X \Xr When finely powdered anthraquinone is treated with zinc-dust and dilute sodium hydroxide and the mixture boiled, a deep red coloration is produced ; on shaking with air the solution is decolorised. The reaction depends upon the formation of Oxanthranol CH(OH) which dissolves in the sodium hydroxide producing the red coloration. On shaking up with air it is reconverted into anthraquinone. CHAPTER XV. ALDEHYDES, ALCOHOLS, ACETONE, GLYCEROL. THE aldehydes contain the monovalent group CHO, the hydrogen and oxygen of which are not present as hydroxyl, but are attached O separately to the carbon atoms thus C^ . The aldehydes are H powerful reducing agents, owing to the ease with which they take up an atom of oxygen, being oxidised to acids. They are obtained by the oxidation of primary alcohols ; therefore, as some of the tests for alcohols depend upon this property, the reactions of aldehydes are placed before those of the alcohols. Formaldehyde. H.CHO Formaldehyde is a gas which, at low temperatures, can be con- densed to a liquid. It has a peculiar sharp odour. If a solution of formaldehyde is evaporated on the water bath, it is converted into a white solid cake of paraformaldehyde. A 40 per cent, solution of formaldehyde comes into the market under the name of " formalin." *i. On adding formaldehyde to an ammoniacal solution of silver nitrate, and placing the test tube containing the mixture in a beaker of boiling water, a brilliant silver mirror is obtained. H . CHO + Ag 2 O = H . COOH -f 2 Ag 262 Qualitative Chemical Analysis. 2. Pehling's solution is reduced by formaldehyde on warm- ing, a red deposit of cuprous oxide being produced. H . CHO + 2 CuO = H . COOH + Cu 2 O *3. SehiflPs Reaction. To a dilute solution of " fuchsine " which has been rendered colourless by means of sulphurous acid, add a little formaldehyde ; in a few seconds the " fuehsine " solution becomes coloured pink, the coloration becoming very intense on standing. *4. If a freshly prepared solution of pyrogallol is added to a solution of formaldehyde, which is then strongly acidified with concentrated hydrochloric acid, in a few minutes (five or ten minutes if the solution is extremely dilute) a white precipitate is produced, which rapidly turns pink, and finally a deep magenta red. *5. When the solution of phenylhydrazine hydrochloride, which has been mixed with an equal volume of a freshly prepared solution of sodium nitroprusside, is added to a dilute solution of formaldehyde, and then an excess of sodium or potassium hydroxide is poured in, an intense indigo blue coloration is produced. The phenylhydrazine hydrochloride may be prepared as required by adding two or three drops of phenylhydrazine to about half a test-tubeful of water, and acidifying with dilute hydro- chloric acid. In carrying out the test, take about i c.c. of this solution and add an equal volume of the dilute solution of sodium nitro-prusside, then about 2 c.c. of the solution to be tested, and finally excess of caustic alkali. Acetaldehyde (Aldehyde). CH 3 .CHO Acetaldehyde is a colourless liquid, possessing a characteristic odour. It boils at 21, and is inflammable. It is soluble in water, alcohol, and ether in all proportions. Aldehydes, Alcohols, Acetone, GlyceroL 263 For the reactions of aldehyde, a solution may be prepared by oxidising alcohol with potassium diehromate and sulphuric acid, as described on p. 267 ; or by adding two or three drops (not more) of concentrated sulphuric acid to about 20 c.c. of paraldehyde, and cautiously distilling. *i. An ammoniacal solution of silver nitrate is re- duced by acetaldehyde on warming with formation of a silver mirror. The experiment is carried out as described under formaldehyde. *2. Fehling's solution is reduced on warming, red cuprous oxide being deposited. (Aromatic aldehydes do not reduce alkaline copper salts.) *3. SchifPs Reaction. With a decolourised solution of fuch- sine, acetaldehyde behaves like formaldehyde. (See 3, p. 262.) 4. If a freshly prepared, fairly strong solution of pyrogallol, containing excess of concentrated hydrochloric acid, is added to a solution of aldehyde, a white precipitate, which gradually turns slightly yellow, is produced on standing. In the case of very dilute solutions, the precipitate only appears after some time. (Cf. Formaldehyde, 4, p. 262.) 5. On warming with an equal volume of strong caustic alkali a yellowish-brown resinous mass (aldehyde resin) is produced. (Cf. 3, P. 264.) 6. On shaking with a concentrated solution of sodium bisulphite a colourless crystalline compound is produced, CH 3 . CH(OH)SO 3 Na. From dilute solutions the substance only separates out after standing for some time. Benzaldehyde. When freshly distilled, benzaldehyde is a colourless, highly refractive oily liquid, but on keeping it becomes light yellow. It is readily soluble in the usual organic solvents, but only slightly soluble in water, to which, however, it imparts its 264 Qualitative Chemical Analysis. characteristic smell of bitter almonds. B.p. 179. Bitter almond oil of the pharmacy contains the glucoside emulsin, and on warming with dilute alkalis, the aqueous solution gives the reactions for cyanides (p. 114) and for glucose (p. 273), after the benzaldehyde has been extracted with ether. *i. Ammoniacal silver nitrate is reduced by benzaldelyde, and, on warming, a brilliant silver mirror is produced. Alkaline copper solutions are not reduced by benzaldehyde. (Cf. Acetalde- hyde.) *2. A saturated solution of sodium hydrogen sulphite gives on shaking up with benzaldehyde a white crystalline compound. C 6 H 5 . CC + NaHSO 3 = C 6 H 5 CH X H \O.S0 2 Na The aldehyde is liberated again by warming with a solution of sodium carbonate. *3. When shaken up with an excess of a strong solution of caustic alkali (more rapidly on warming), benzaldehyde is converted into equal molecules of benzoic acid and benzyl alcohol. 2 C 6 H 5 CHO + KOH = C 6 H 5 . COOK + C 6 H 5 . CH 2 OH The alcohol can be removed by extraction with ether ; it boils at 206, and the benzoic acid may be recognised in the aqueous solution (p. 223). It should be noted that, when aldehydes of the aliphatic series are warmed with caustic alkali, a resinous substance (aldehyde resin) is produced. Detection of Nitrobenzene in Presence of Benzaldehyde. Shake the mixture up with sodium bisulphite. The benzalde- hyde unites with the bisulphite (cf. *2, above), forming a white crystalline mass. The nitrobenzene remains in solution, from Aldehydes, Alcohols > Acetone^ Glycerol. 265 which it can be extracted by means of ether. If the nitrobenzene is then mixed with dilute sulphuric acid, and reduced by adding a few small pieces of zinc, it is converted into aniline, which may be tested for, after making the solution alkaline and extracting with ether, by the reactions on p. 280. Chloral Hydrate. /OH CC1 3 .CH \OH Sharp-smelling colourless crystals, soluble in water, alcohol, ether, chloroform, and most organic solvents. It melts at 57, and boils at 97*5. *i. When about 2 c.c. of concentrated sulphuric acid is added to about 2 grams of chloral hydrate, water is absorbed, and fluid chloral floats upon the surface of the acid. *2. On gently warming with caustic alkali, chloral hydrate is decomposed into chloroform and formic acid. The solution CC1 3 .CH = CHC1 3 + H.COOH maybe tested for formates (p. 210). If the quantity of chloral hydrate taken was not too small, the chloroform separates out as an oily layer below the aqueous solution. *3. Ammoniac al silver nitrate is reduced by chloral hydrate, with formation of a silver mirror. *4. Silver nitrate gives no precipitate of silver chloride, but if the solution of chloral hydrate is acidified with dilute sulphuric acid, a small piece of zinc added, and the mixture allowed to stand a few minutes, the addition of silver nitrate now produces a white precipitate of silver chloride. 5. SchifFs reagent is not coloured when added to a solution of chloral hydrate. But phenylhydrazine and sodium hydrogen sulphite both react in the usual manner. 266 Qualitative Chemical Analysis. Methyl AlcohoU CH 3 OH Methyl alcohol is a colourless neutral liquid, boiling at 66. It is soluble in water in all proportions. When mixed with water, contraction of volume takes place, the mixture at the same time becoming warm. Commercial methyl alcohol often contains acetone, in which case it gives the iodoform reaction. (See Ace- tone, p. 269.) *i. On adding methyl alcohol to a small quantity of a formate, then about an equal volume of concentrated sulphuric acid, and warming, the distinctive odour of methyl formate is noticed. CH 3 OH + H . COOH = H . COOCH 3 + H 2 O *2. Formic Acid Test. Place about 3 or 4 grams of powdered potassium dichromate into a small flask fitted with a fairly long delivery tube, and cover the dichromate with water. Now add the alcohol, which has previously been mixed with an equal volume of 50 per cent, sulphuric acid. Allow to stand for three or four minutes, dilute with an equal bulk of water, and distil into a test tube. Neutralise the distillate with sodium carbonate, and boil vigorously for about one minute in order to drive off any formaldehyde or acetaldehyde (which may have been produced if ethyl alcohol were present). Divide the solution into two parts. To the first portion add ferric chloride, when a red coloration will be produced. To the second portion add silver nitrate, and warm : reduction will take place, a black or brown deposit being obtained. The following equations express the reactions which take place. The alcohol is first oxidised to formaldehyde, which is immediately further oxidised to formic acid. (a.) CH 3 . OH + O = H . CHO + H 2 O *. H. CHO +0 = H. COOH Aldehydes t Alcohols, Acetone, GlyceroL 267 Ethyl Alcohol; C 2 H 6 OH Ethyl alcohol is a colourless inflammable liquid, boiling at 7 8 '4. It is miscible with water in all proportions with contraction of bulk (48 volumes of water and 52 volumes of alcohol giving only 96 volumes, after being mixed). *i. On heating a little alcohol with an acetate and con- centrated sulphuric acid, the characteristic fruity odour of ethyl acetate is given off. CaH 6 OH + CH 3 . COOH = CH, . COOQHs + H 2 O *2. lodoform Reaction. To an aqueous solution of alcohol add a few small crystals of iodine, or a few drops of a solution of iodine in potassium iodide ; warm gently, and add drop by drop a solution of caustic soda or sodium carbonate, till the brown colour due to the iodine has disappeared. On cooling, a yellow crystalline precipitate of iodoform is produced. When the alcoholic solution is very dilute, no immediate precipitation takes place, but the peculiar and very characteristic smell of iodoform is noticeable. C 2 H 6 OH -h 5l 2 + 7KOH = CHI 3 + CO 2 + ;KI + 6H 2 O *3. Aldehyde Test. When heated with sulphuric acid and potassium dichromate, ethyl alcohol is not converted into acetic acid, but is merely oxidised to acetaldehyde. The reaction is carried out as already described in 2, under Methyl Alcohol ; and the aldehyde, which is best collected by distilling into a small quantity of water in a test tube, is tested for by means of Schiffs reaction (p. 263), and by reduction of an ammoniacal solution of silver nitrate with production of a silver mirror. QH 6 OH + O = CH 3 CHO + H 2 O 4. Oxidation with potassium permanganate. When ethyl alcohol is heated with a solution of potassium permanganate, the 268 Qualitative Chemical Analysis. colour of the permanganate disappears. On acidifying the mix- ture with dilute sulphuric acid and distilling, the distillate will be found to have an acid reaction, and will answer to the test for acetic acid. Detection of Methyl and Ethyl Alcohols when they occur together. 1. Methyl alcohol may be detected in presence of ethyl alcohol by the action of sulphuric acid and potassium dichromate, which oxidises it to formic acid ; 2. Ethyl alcohol, by the iodoform reaction, and by the for- mation of acetaldehyde, when warmed with potassium dichro- mate and sulphuric acid, and of acetic acid when warmed with potassium permanganate. Amyl Alcohol (Isobutyl Carbinol). Amyl alcohol is the chief constituent of fusei oil, and is a colourless, rather oily liquid, b.p. 132, with a characteristic odour. It is only slightly soluble in water. i. Concentrated sulphuric acid, added to amyl alcohol, causes it to turn red or reddish-brown, when the mixture is gently warmed. *2. On adding concentrated sulphuric acid, and a small quantity of acetic acid or of an acetate, to amyl alcohol, and then gently warming, an odour of essence of pears, amyl acetate, is produced. The smell is more marked on pouring the mixture into excess of water. C 6 H n OH + CH 3 COOH = CH 3 COOC 5 H n + H 2 O *3. When heated with potassium dichromate and sul- phuric acid, as already described under Methyl Alcohol, i, p. 266, a pleasant fruity odour of amyl valerianate is produced, Aldehydes, Alcohols, Acetone, Glycerol. 269 (C 4 H 9 COOC 5 H U ). The odour is better distinguished on pouring into water. 4. When amyl alcohol is heated with an equal volume of concentrated sulphuric acid until it just turns brown, then about half a volume of glacial acetic acid and i c.c. of ferric chloride added, and the mixture again heated, a brilliant violet coloration is produced. Acetone, CH S CH 3 >co Acetone is a colourless inflammable liquid, having a pleasant ethereal smell. It is miscible with water, alcohol, and ether in all proportions; b.p. 56-3. *i. lode-form Reaction. Add to a solution of acetone a few crystals of iodine, or a solution of iodine in potassium iodide ; then carefully add sodium hydrate or carbonate till the brown colour of the iodine disappears, and warm gently. On cooling, iodoform separates out in small golden yellow plates. (CH 3 ) 2 CO + 6I 2 + 8KOH = 2CHI 3 + KzCO 3 + 6H 2 O + 6KI This reaction is also given by ethyl alcohol. If, however, a solution of acetone is made alkaline with ammonia, which should not be added in large excess, and then a solution of iodine in potassium iodide added drop by drop, until a small quantity of a black precipitate of nitrogen iodide is formed, on gently warming the black precipitate disappears, and iodoform crystallises out. Under these conditions ethyl alcohol does not give the iodoform reaction. 2. On mixing a few drops of a freshly prepared solution of sodium nitroprusside with a solution of acetone, adding ammonia, and shaking, a violet or violet-red coloration is produced. The colour disappears on warming, but reappears on cooling. *3. Gunning's Reaction. If a solution of acetone is added to one of mercuric chloride, and caustic soda is then added 270 Qualitative Chemical Analysis. drop by drop, a yellow precipitate of mercuric oxide is formed, which immediately dissolves again. If the quantity of acetone is very small, so much precipitate may be formed that only partial solution will take place. In this case filter through a double filter paper; it may be necessary to filter more than once. Acidify the clear solution so obtained with hydrochloric acid, and add a little stannous chloride : a white or grey precipitate will be produced. This reaction depends upon the fact that mercuric oxide is soluble in acetone. *4, When shaken up with a concentrated solution of sodium bisulphite, a white crystalline addition product is produced. CH 3 \ CQ H \ go CH 3 \ C /OH CH3/ UU *~ Na/ bU3 CH,/ u \S0 8 Na Glycerol (Glycerine). CH 2 .OH CH.OH CH 2 .OH Glycerol is a colourless, odourless, viscid fluid, which has a sweet taste. It boils at 290 with more or less decomposition. Glycerol is readily soluble in water and alcohol, but insoluble in chloroform and ether. It is neutral to litmus. 1. Cold, concentrated sulphuric acid produces no change of colour with glycerol ; and even when they are heated together on a water bath, only a slight yellow coloration is produced. (Distinction from a solution of cane sugar.) 2. Potassium and sodium hydroxide' produce no change of colour, even on boiling. (Distinction from a solution of dextrose.) *3. Powdered potassium hydrogen sulphate, when heated with glycerol, produces acrid vapours of acrolein. = CH a : CH . CHO + 2 H a O If the reaction is carried out in a test tube fitted with a delivery tube, and the acrolein passed into water, a solution of acrolein is Aldehydes, Alcohols, Acetone, Glycerol. 271 obtained, which shows the usual tests for aldehydes, reducing ammoniacal silver with formation of a mirror, and colouring a decolourised solution of fuchsine. (Schift's reaction, p. 263.) *4. On adding to a i per cent, solution of borax a few drops of phenolphthalein, a pink coloration is produced ; the addition of glycerol causes the pink coloration to disappear, but reappears on warming, again vanishing on cooling. (Ammonium salts also cause this coloration to be destroyed, but it does not reappear on warming. Dextrose and other polyhydric alcohols also give this reaction, though not so markedly as glycerol.) Before testing a solution for glycerol, it should be evaporated to small bulk on the water bath. Should sugar be present, it must be removed. This is best done by evaporating to dryness on a water bath with lime and sand, then extracting the powdered mass with a mixture of equal volumes of absolute alcohol and ether. After distilling or evaporating off the alcohol and ether, the necessary tests may be applied. AHyl Alcohol. CH 2 : CH . CH 2 . OH Pungent, colourless liquid, b.p. 96. Miscible in water in all proportions, but can be salted out with potassium carbonate. 1 . Being an unsaturated compound, it shows reactions peculiar to such substances. It decolorises bromine water when this is added drop by drop to the alcohol or its aqueous solution. CH : CH . CH . OH + Br 2 = CHBrCHBrCHOH 2. A cold dilute solution of alkaline permanganate is reduced and thus decolorised. The permanganate solution should be sufficiently diluted with water to render it transparent and then rendered alkaline with sodium carbonate. 3. Acetyl chloride when added to the alcohol forms the ester. Shake up with dilute sodium carbonate to remove the excess of the acetyl chloride, when the characteristic odour of the ester is noticed. CH 2 : CH.CH 2 OH + CH 3 COC1=CH 2 : CHCH 2 O.CO.CH 3 +HC1 CHAPTER XVI. THE CARBOHYDRATES AND SACCHARIN. THE sugars belong to the class of organic compounds called the carbohydrates. They all contain carbon, oxygen, and hydrogen, the oxygen and hydrogen occurring in them in the proportion in which they are found in water, i.e. two parts of hydrogen to one part of oxygen. In the case of dextrose, for example, C 6 H 12 6 = C 6 + 6H 2 0. Saccharin, although not a sugar, has been placed in this chapter owing to its extremely powerful sweetening property. When sugars which contain an aldehyde or a ketone group are treated with i mol. 01 phenylhydrazine, they are converted into hydrazones ; thus glucose forms glucose-phenylhydrazone. CH 2 (OH)(CH . OH) 4 . CHO + C 6 H 5 NH . NH 2 = CH 2 (OH)(CH . OH) 4 CH : N . NHC 6 H 5 + H 2 O If, however, excess of phenylhydrazine is employed, the CH.OH group next to the end becomes oxidised to CO, part of the phenylhydrazine being reduced to aniline and ammonia. C 6 H 5 . NH . NH 2 + 2 H= C 6 H 5 NH 2 + NH 3 The oxidation product of the phenylhydrazone then combines with a second molecule of phenylhydrazine, with formation of an osazone. CH 2 (OH)(CH . OH) 3 CO . CH : N . NH . C 6 H 3 + C 6 H 5 . NH . NH 2 = CH 2 (OH)(CH.OH) 3 .C(N.NHC 6 H 5 ).CH : N.NH.C 6 H 5 + H 2 O As the preparation of the osazones has been of great value in The Carbohydrates and Saccharin. .273 identifying and isolating the sugars, the method of formation is here given. About half a gram of the sugar is dissolved in 5-6 c.c. of water, and 2 to 3 grams phenylhydrazine added, then about 3 c.c. of acetic acid, and the test tube containing the mixture placed in a beaker of boiling water. In about ten minutes the osazone separates out in shining yellow crystals. To identify the sugar, the osazone may be filtered off, washed with water, and, after drying, its melting-point taken, or its decomposition products studied. Grape Sugar (Glucose, Dextrose). CH 2 (OH)(CH.OH) 4 .CHO Glucose crystallises with one molecule of water in odour- less, colourless, warty masses. It is not so sweet as cane sugar. It is readily soluble in water and dilute alcohol, only with diffi- culty in strong alcohol, crystallising from it in the anhydrous state ; it is also insoluble in ether. Its solution turns the ray of polarised light to the right. [a] D = + 5 2 '5. i. When heated in a dry tube, ordinary glucose melts at 80-86, the anhydrous compound at 146, becoming brown when more strongly heated, and giving off a smell resembling burnt sugar. The brown mass so obtained is soluble in water. *2. Concentrated sulphuric acid does not char glucose in the cold (distinction from cane sugar) ; charring only takes place after heating for some little time. If the glucose is in solution the sulphuric acid must only be added a little at a time, and the mixture cooled between each addition, otherwise the heat generated by the mixing with the water may cause charring. *3. On heating with caustic potash or soda the solution becomes first yellow and then reddish-brown. If the mixture is now acidified with dilute nitric acid, the colour changes to pale yellow, and a smell resembling that of burnt sugar is noticed (Distinction from cane sugar.) 274 Qualitative Chemical Analysis. 4. On adding lead acetate to a solution of glucose, boiling the mixture for a few seconds and adding ammonium hy- droxide till a precipitate is just produced, and again boiling, the precipitate assumes a salmon-pink colour. (Distinction from cane and milk sugars.) Reactions depending upon the Reducing Action of Glucose. *5. Add a solution of glucose to Fehling's solution, and boil: a yellow precipitate of cuprous hydroxide will be pro- duced, which rapidly becomes converted into red cuprous oxide (Cu 2 O). *6. On adding silver nitrate to a solution of glucose, then ammonium hydroxide, and placing the test tube in a beaker of boiling water, reduction takes place, a silver mirror forming on the sides of the tube. 7. The osazone of dextrose melts when crystallised at 230-232 (P- 273). Cane Sugar. Cane sugar crystallises from water in hard four-sided prisms. It is readily soluble in water, sparingly so in alcohol. It melts at 160-161, and on cooling does not at once become crystalline again. Cane sugar loses water at 200-210, and becomes con- verted into a brown mass (caramel), which is soluble in water. It is dextro-rotatory. [a] D = + 66*5. *i. Concentrated sulphuric acid chars sugar or its solu- tions in the cold, the mixture becoming brown and rapidly black. A strong solution of sugar, to which sulphuric acid has been added, swells up j steam, carbon dioxide, and other gases being evolved. *2. When heated with caustic alkalis, solutions of cane sugar are not coloured brown, at the most a light straw colour is pro- duced. On acidifying the alkaline solution with nitric acid, no smell of burnt sugar is noticeable. (Cf. Dextrose, 3, p. 273.) The Carbohydrates and Saccharin. 275 3. On heating a solution of sugar with lead acetate, and adding ammonium hydroxide until a precipitate is produced, then again heating, no change of colour takes place. (Cf. Glucose and Milk Sugar.) *4. Cane sugar does not reduce an alkaline copper solution, or a solution of a silver salt. If, however, the sugar solution is first heated for some minutes with dilute sulphuric acid, it is converted into equimolecular amounts of dextrose and laevulose, and will then reduce Fehling's solution. C U H M 11 + H 2 = C 6 H 12 6 + C 6 H 12 6 Dextrose. Laevulose. The solution so obtained is called "invert sugar," and is laevo- rotatory. Cane sugar does not form an osazone. Cane sugar may be recognised in presence of dextrose, lactose, and maltose, owing to its not reducing Fehling's solution. In a mixture with these other sugars, its presence may be proved by heating the solution on a water bath with Fehling's solution until no more reduction takes place, i.e. till on further addition of a small quantity of Fehling's solution the blue colour remains. The precipitated cuprous oxide is then filtered off, the solution acidified with dilute sulphuric acid, and boiled for about five minutes. It is now rendered alkaline with caustic soda, and again heated with Fehling's solution : further reduction taking place shows that cane sugar was present, and has been inverted by boiling with sulphuric acid. Milk Sugar (Lactose). Milk sugar forms large hard warty crystals, containing i mol. of water of crystallisation. As usually obtained it is a white sandy powder. It is not very sweet to the taste. It is fairly soluble in water, but insoluble in ether and absolute alcohol. It is dextro- rotatory. [a] D = +52-53. 276 Qualitative Cliemical Analysis. 1. On heating milk sugar in a dry tube, it is converted into an amorphous brown mass, which is soluble in water. 2. Concentrated sulphuric acid has no action in the cold, but, on heating or on long standing in the cold, the mixture becomes yellow, then brown, and finally black, with evolution of carbon dioxide and sulphur dioxide. *3. When milk sugar is heated with caustic alkalis, the solution becomes yellow, and then brownish-red. On acidifying this solution with dilute nitric acid, it becomes colourless, and a smell resembling that of burnt sugar is produced. (Distinction from cane sugar.) *4. On boiling a solution of milk sugar with lead acetate for a few seconds, then adding ammonium hydroxide until a white precipitate is produced (it should not be added in excess) and again boiling, the precipitate becomes cream coloured, (Cf. Dextrose and Cane Sugar.) *5. Fehling's solution is reduced by milk sugar on warming. 6. The osazone of lactose melts at 200. Maltose. Maltose crystallises with one molecule of water in colourless needles, which are very soluble in water. It is almost insoluble in absolute alcohol. It is strongly dextro-rotatory. [a] D = -f- 140*6. i. When moistened with a drop of water, and gently warmed with concentrated sulphuric acid, maltose chars. In the cold, charring does not take place. *2. On boiling with caustic alkalis, the solution first turns yellow, then brown. If the brown solution is acidified with dilute nitric acid the colour is destroyed, and an odour of burnt sugar is produced. *3. Fehling's solution is reduced when boiled with maltose. *4. When maltose is boiled for a few seconds with a solution The Carbohydrates and Saccharin. 277 of lead acetate, then ammonium hydroxide added till a precipitate is just produced, and again boiled, the white precipi- tate first formed assumed a pinkish tinge. *5. The osazone of maltose melts at 196-198. Maltose can be detected in presence of glucose, by forming the osazones ; the mixed osazones are then boiled with a small quantity of water and rapidly filtered. On cooling the maltosazone crystallises out from the filtrate ; the glucosazone is insoluble in water. SYNOPTIC TABLE SHOWING BEHAVIOUR OF SUGARS WITH VARIOUS REAGENTS. Reagent. Glucose. Cane sugar. Lactose. Maltose. I. Concentrated No action in Chars in Chars on heat- Chars on heat- sulphuric acid. the cold, chars the cold. ing. ing. on heating. 2. Caustic soda Turns brown. No change. Turns brown. Turns brown. solution on On adding On adding On adding boiling. nitric acid, nitric acid, nitric acid, smell of burnt smell of burnt smell of burnt sugar. sugar. sugar. 3. Fehling's so- Reduction on No reduc- Reduction on Reduction on lution. boiling. tion. boiling. boiling. 4. Lead acetate Salmon - pink White pre- Very light yel- Very light yel- and ammo- precipitate. cipitate. lowish - pink lowish - pink nium hydrate. 5. Phenylhydra- Glucosazone, precipitate. Lactosazone, precipitate. Maltosazone, zine. yellow crys- yellow crys- yellow crys- tals, m.p. 230- tals,m.p. 200. tal s, m.p. 196- 232. 198. Starch (Amylum). (C 6 H 10 6 ) a Starch is a white powder, the structure of which, when ex- amined under the microscope, is seen to consist of peculiar con- centrically striated granules, which vary in size and appearance. It is insoluble in cold water; when heated, the granules burst, the cell wall remaining insoluble, but the granulose contained 278 Qualitative Chemical Analysis. within the cell dissolves, forming a gelatinous mucilage, called starch paste. 1. When heated in a dry tube, starch chars, water and com- bustible gases are given off, and an unpleasant odour resembling burnt leather is noticed. 2. On heating with concentrated sulphuric acid, starch quickly chars, sulphur dioxide and carbon dioxide being evolved. 3. When starch is boiled with dilute sulphuric acid it is converted into dextrine, and then into dextrose. (C 6 H 10 6 ) n + nH 2 = n(C 6 H 12 6 ) Dextrose. If the mixture has only been boiled for a short time, dextrine is sure to be present with the dextrose, and the addition of iodine will colour it red. *4. To a neutral solution of starch paste dissolved in a large quantity of water, add two or three drops of iodine solution : a deep blue coloration of iodide of starch is produced. The colour disappears on boiling, returning again on cooling. Starch may be separated from mixtures containing other substances, owing to its insolubility in cold water and other solvents. For example, water will dissolve out most acids, whereas, if caustic alkali is added, aniline and other bases may be extracted by means of ether. Saccharin (Glusidum, Qluside). CO C 6 H 4 NH S0 2 Saccharin, or benzoyl sulphonimide, is a white powder, possessing an intensely sweet taste. On heating, it fuses at 220, and then sublimes with partial decomposition. It is only slightly soluble in cold water, but more so in hot water, but is easily soluble in alcohol and ether. Saccharin dissolves readily in ammonia and in sodium bicarbonate. Soluble saccharin is The Carbohydrates and Saccharin. 279 prepared by dissolving saccharin in a solution of sodium bicarbonate, and evaporating to dry ness. *i. Place about i gram of caustic potash in a crucible, add 2 or 3 drops of water, and heat until fused. Now drop on to the fused mass about 0*2 of a gram of saccharin, and continue the fusion for a minute or two, taking care not to char the mixture. Cool, and dissolve in water, acidulate with dilute hydrochloric acid, and neutralise with ammonia. Now add a few drops of ferric chloride, when a violet-purple colour will be produced. This coloration is due to the presence of salicylic acid, which is produced when saccharin is fused with alkalis. / / = COOK QH 4 < >NK + 3 KOH = C 6 H + NH 3 + K 2 S0 3 OK *2. Saccharin dissolves in sodium carbonate with evolution of carbon dioxide. On acidifying the solution, and allowing to stand a few minutes, the saccharin crystallises out in lustrous plates. 3. Silver nitrate produces, from neutral solutions, a white precipitate of silver saccharate. CO CO C 6 H 4 / \NK + AgNOa = C 6 H 4 ( >NAg + KNQ 3 \30/ X SO/ *4. Place a little saccharin in a test tube, cover it with aniline, and boil for about half a minute. On cooling, and allowing to stand a short time, crystals of the anilide separate out. These can be obtained free from aniline by washing with a little dilute hydrochloric acid. After recrystallising from dilute alcohol, the m.p. will be found to be 189. C 7 H 6 S0 5 N + QH,NH 2 NH 2 , S0 3 . C 8 H 4 . CO . NHC 6 H 8 CHAPTER XVII. BASES, GLUCOSIDES, ETC. THIS chapter includes the important bases aniline, pyridine, and quinoline, the two latter substances being frequently pro- duced when the alkaloids (Chap. XVIII.) are fused with caustic alkalis, or strongly heated with zinc dust. The reactions of the glucosides salicin and digitalin, and of the artificial drugs acetanilide, phenacetin, and antipyrin, some of which are very similar to those of the alkaloids, are also given here. Urea, owing to its basic character, is also placed in this chapter. Aniline (Amidobenzene). C 6 H 5 NH 2 Aniline is a colourless liquid, b.p. 182, having a peculiar characteristic odour. It is readily volatile with steam, but very slightly soluble in water ; it is, however, readily soluble in alcohol and ether. Aniline rapidly turns brown on standing, but becomes colourless again on being redistilled. It forms crystalline salts with acids. They are decomposed with regeneration of aniline by caustic alkalis, but not by ammonia. (a.) C 6 H 5 NH 2 + HC1 = C 6 H 5 NH 2 . HC1 (b.) C 6 H 5 NH 2 . HC1 + KOH = C 6 H 6 NH 2 + KC1 + H 2 *i Bleaching powder solution, when added to a dilute solution of aniline or its salts, produces a purple-violet coloration, which becomes green on standing. If this solution is diluted with water till it is practically colourless, and then a drop or two Bases, Glucosides, etc. 281 of dilute ammonium sulphide added, an intense rose-red coloration is formed; the colour, however, rapidly disappears. This reaction is extremely delicate, often showing when the addition of bleaching powder solution gives no blue coloration. *2. Diazo Reaction. To a cold solution of aniline in dilute hydrochloric acid add 6 to 8 drops of a dilute solution of ^potas- sium or sodium nitrite, keeping the mixture cool by holding under the tap. Now add a few drops of a solution of a or ft naphthol dissolved in caustic soda, when a brilliant scarlet coloration will be produced (it may be necessary to add some caustic soda). This coloration is due to formation of benzene- azo-naphthol, and is shown by all primary aromatic amido compounds. The course of the reaction is as follows : The aniline hydrochloride is first converted into diazobenzene chloride, and this, on the addition of the a or /3 naphthol, forms benzene-azo-naphthol. (a.) C 6 H 5 NH 2 . HC1 + HO . NO = C 6 H 5 N : N . Cl + 2H 2 O (.) C 6 H 5 N : N.C1 + C 10 H 7 . OH = QE^N : N . Q H 6 .OH + HC1 *3- Carbylamine Reaction. When a drop or two of aniline is mixed with an alcoholic solution of caustic soda or potash, then a few drops of chloroform added and the mixture warmed, a most disagreeable smell of phenylisonitrile or carbylamine is produced. C 6 H 5 NH 2 + CHC1 3 + 3KOH = C 6 H 5 . N j C + sH 2 O + 3 KC1 In order to apply the tests for aniline, it should be separated from other substances with which it may be mixed. To do this, caustic soda is added till the solution is strongly alkaline, the alkaline solution is then extracted with ether, and, after evaporating off the ether, the various tests may be applied to the residue. The addition of caustic alkali liberates aniline from its salts, and at the same time converts acids and phenols into salts, which are insoluble in ether. If alkaloids are present, and it is desired to obtain a separation, the mixture after addition of caustic soda should be steam distilled. The aniline passes over with the steam, 282 Qualitative Chemical Analysis. and the alkaloids, etc., remain behind. A few alkaloids, such as nicotine and coniine, and such bases as pyridine and quinoline, are both soluble in ether and volatile with steam, but their presence would not materially interfere with the reactions of aniline. Pyridine. N Pyridine is obtained from bone oil, and, when pure, is a colour- less liquid, having a penetrating and characteristic smell ; it boils at 1 1 6. It is soluble in water, alcohol, and ether in all propor- tions. Pyridine is a powerful base, forming salts with acids, most of which are soluble in water, but the sulphate is rather sparingly soluble. It fumes in presence of volatile acids. Caustic alkali liberates pyridine from its salts. (a.) C 5 H 5 N + HC1 = C 5 H 5 N . HC1 (b ) C 5 H 5 N . HC1 + KOH = C 5 H 6 N + KC1 + H 2 O i. The aqueous solution of pyridine has an alkaline reaction, and precipitates the hydroxides of most metals from solutions of their salts, e.g. iron, cobalt. *2. Hydrogen-platinichloride gives with solutions of pyridine in hydrochloric acid an orange-yellow crystalline preci- pitate of pyridine platinichloride. 2 C 6 H 5 N + H 2 PtCl 6 = (C 6 H 6 N) 2 ,H 2 PtCl a It is soluble in hot water, but is reprecipitated on boiling as an almost insoluble light yellow salt, having the formula (C 6 H 5 N) 2 PtCl 4 . *3. On heating a few drops of pyridine in a test tube with an equal quantity of methyliodide, a vigorous reaction takes place. Bases, Glucosides, etc. 283 On now adding a small piece of solid caustic potash or soda, and again heating, a most offensive smell similar to that of highly rotten fish is produced. 4. The general reagents for alkaloids produce precipitates with pyridine (p. 294). Pyridine may be separated from most substances by rendering the solution strongly alkaline with caustic alkali and steam dis- tilling. From other volatile bases it may be separated by the action of fuming nitric or chromic acid, which decomposes them, while pyridine is not affected. Quinoline, CH H Quinoline is found in bone oil and in coal tar. It is a colour- less or slightly yellow mobile liquid, having a peculiar and cha- racteristic aromatic smell. It boils at 238, but even at ordinary temperatures it evaporates slowly. Quinoline is very slightly soluble in cold water, but is volatile with steam, and is readily soluble in most organic solvents. The basic properties of quino- line are strongly marked, its salts with acids are more or less deliquescent. 1. Concentrated sulphuric acid forms a white salt, which dissolves in excess of the acid, producing a colourless solution. 2 C 9 H 7 N + H2S04 = (C 9 H 7 N) 2 ,H 2 S0 4 2. When solutions of the salts of iron, aluminium, zinc, etc. are shaken with a little quinoline, the hydroxides of the metals are precipitated. *3. Hydrogen-platinichloride gives with a solution in 284 Qualitative Chemical Analysis. hydrochloric acid a yellow precipitate of quinoline platinichloride, which is soluble in hot water. 2C 9 H 7 N + H 2 PtCl 6 = (C 9 H 7 N) 2 H 2 PtCl 6 *4. Potassium dichromate, when added to an acid solution of quinoline, produces, especially on shaking, a fine yellow crystalline precipitate of the dichromate. 2 C 9 H 7 N . HC1 -f K 2 Cr 2 7 = (C 9 H 7 N) 2 ,H 2 Cr 2 O 7 + 2KC1 The dichromate is readily soluble in warm water, but crystallises out again on cooling. 5. The general reagents for alkaloids (p. 294) produce precipi- tates with quinoline. (Tannic acid, however, gives no precipitate.) Quinoline may be separated from pyridine by means of potassium dichromate in acid solution, pyridine not producing a precipitate under these circumstances. Quinoline is very sparingly soluble in water, whereas pyridine is readily soluble. Urea (Carbamide). /NH 2 C0( X NH 2 Urea forms colourless crystals; m.p. 132. It is readily soluble in water and alcohol, but almost insoluble in ether. *i. When urea is gently heated just above its melting-point for a few minutes, it is converted into biuret and ammonia, a white sublimate being formed at the same time. 2 NH 2 . CO . NH 2 = NH 2 . CO . NH . CO . NH 2 + NH 3 On dissolving the opaque residue in water, adding a few drops of caustic alkali, and then a drop or two of copper sulphate solution, a violet coloration is produced. (Biuret reaction.) When urea is more strongly heated it is converted chiefly into cyanuric acid, which remains as a white residue, 3NH a . CO . NH a = H 3 C 8 N 8 O 3 + Bases > Glucosides, etc. 285 If the cyanuric acid is boiled with water until it is partially dissolved (it is not readily soluble in water), and if to the solution one or two drops of dilute ammonia be added, then two or three drops of copper sulphate solution, an amethyst-coloured precipitate is produced. *2. Strong nitric acid produces from fairly strong solutions of urea a characteristic crystalline precipitate of urea nitrate, which is practically insoluble in nitric acid. *3. Oxalic acid gives with concentrated aqueous solutions of urea a crystalline precipitate of urea oxalate. Oxalate of urea may be produced from fairly small quantities of urea by dissolving it in amyl alcohol, instead of in water ; the oxalic acid also being dissolved in this solvent. On mixing the cold solutions, a white crystalline precipitate is almost immediately obtained. *4. When potassium or sodium nitrite is added to a solution of urea which has been acidified with dilute sulphuric acid, the urea is decomposed with evolution of nitrogen and carbon dioxide. NH a . CO. NH a + 2 HO . NO = CO a + 2N a + 3 H 3 O 5. On heating with dilute mineral acids, urea is decomposed into carbon dioxide and an ammonium salt. NH 2 . CO . NH. 2 + H 2 O + 2HC1 = CO a + 2NH 4 C1 Urea may be separated from mixtures of organic material by first extracting the solution (which has been made alkaline with caustic alkali) with ether. This will remove bases, most alkaloids, and oily or resinous products. Then evaporate to dryness, and extract with warm absolute alcohol or, better, amyl alcohol : this will dissolve the urea, but not salts of acids, and only to a very limited extent, sugars. The urea may be obtained from the alcoholic solution by evaporating to dryness, or, better, if amyl alcohol has been employed, by adding a cold solution of oxalic acid in the same solvent, when urea oxalate will be precipitated. 286 Qualitative Chemical Analysis. Acetanillde (Antifebrin). C 6 H 5 . NH . COCH 3 Acetanilide forms colourless, odourless shining plates; m.p 113. It is readily soluble in alcohol, ether, chloroform, and hot water. *i. To a little acetanilide, which has been placed in a porcelain basin, add a few drops of concentrated sulphuric acid, and sprinkle a small quantity of powdered potassium diehromate on it; a red coloration will be produced, which rapidly becomes dull green. Red streaks, however, reappear on rubbing the grains of diehromate with a glass rod. *2. When acetanilide is heated with caustic alkali, it decom- poses, forming an alkali acetate and aniline. C 6 H 5 NH . CO . CH 3 -f KOH = C 6 H 5 NH a + CH 3 COOK The aniline may be recognised by dissolving in a little alcohol and applying the carbylamine reaction. 3. On heating acetanilide with about i c.c. of concentrated hydrochloric acid for about one minute, aniline and acetic acid are produced. C 6 H 6 NHCOCH 3 + H 2 O = C 6 H 5 NH 2 + CH 3 COOH The solution may be tested for aniline and acetic acid. 4. When a little acetanilide is heated with concentrated sul- phuric acid arid alcohol, the characteristic fruity odour of ethyl acetate is produced. The sulphuric acid first decomposes the acetanilide into aniline and acetic acid; the alcohol then reacts with the acetic acid, producing ethyl acetate. *5. On boiling with ferric chloride, a turbidity is produced, but no red coloration, although the colour of the ferric chloride becomes darker. (Distinction from antipyrin and phenacetin.) 6. Place a mixture of acetanilide with about double its weight of sodium nitrite in an evaporating basin, and moisten with concentrated hydrochloric acid: a yellow coloration will be Bases > Glucosides, etc. 287 produced, which, when heated on a water bath, turns green, and, on evaporating to dryness, red. *7. To a little acetanilide, contained in an evaporating basin, add two or three drops of mercurous nitrate : on evaporating just to dryness a green mass will be obtained, which becomes a brilliant blood-red when moistened with concentrated sulphuric acid. 8. Mandolin's reagent (p. 329) produces an orange-red coloration, which changes to red, and finally to grey. Phenacetin (para-Acetamido-ethyoxybenzene). QH 6 O.C 6 H 4 .NH.COCH 3 Phenacetin forms colourless, odourless, crystalline leaflets ; m.p. 135. It is easily soluble in ether and chloroform, moderately soluble in hot, and almost insoluble in cold water. i. On heating with concentrated sulphuric acid and alcohol, an odour of ethyl acetate is produced. *2. When heated with equal volumes of concentrated nitric acid and water, a yellow or orange coloration is produced, and if the quantity taken be not too small, yellow crystals separate on cooling. If caustic alkali is added in excess to the mixture, a red coloration is produced, which is intensified on boiling. 3. Mandelin's reagent (p. 329) produces a very pale blue coloration. *4. Mix a small quantity of phenacetin with two or three times its bulk of zinc dust, and heat till it chars. Cool, and then boil with 2 or 3 c.c. of water ; filter, and add ferric chloride to the filtrate. A deep violet coloration will be produced, owing to the formation of salicylic acid by the action of the zinc dust on the phenacetin. *5. On grinding up equal quantities of phenacetin and a nitrite in an evaporating dish, adding a drop or two of concen- trated sulphuric acid, and then gently warming on a water bath, a green coloration, which changes to drab, is produced. (Cf. 6, p. 286.) 288 Qualitative Chemical Analysis. 6. On adding a few drops of concentrated sulphuric acid to phenacetin in a porcelain basin, and sprinkling a little powdered potassium dichromate on it, and allowing it to stand some time, a green coloration is produced. Antipyrin (Phenazone i, 2, 3, Phenyldimethyl- pyrazolon). C 6 H 5 . N - CO - CH I II CH 3 .N C.CH 3 Antipyrin forms colourless and odourless crystals, having a bitter taste; m.p. 114. It is soluble in water and alcohol, but sparingly soluble in ether. Antipyrin, although a base, forming salts with acids, has no alkaline reaction. Antipyrin is much used in medicine as an antipyretic. i. Antipyrin dissolves in warm concentrated sulphuric acid, forming a colourless solution. *2. When warmed with concentrated nitric acid, antipyrin colours it first yellow and then a deep red. *3. Mandelin's reagent (p. 329) produces a pale blue coloration, which gradually fades away. *4. Mercurous nitrate, when added in excess to a solution of antipyrin, produces a dirty green or yellow precipitate, which, on boiling, turns a deep red, and a red powdery precipitate gradually settles down. *5 To a solution of antipyrin add a small fragment of sodium or potassium nitrite, and then a few drops of dilute sulphuric acid, when a bright green coloration will be produced. The coloration is due to formation of isonitroso- antipyrin. If the solution is not too dilute, the isonitroso-compound crystallises out in small green needles. 6. Sulphuric acid and potassium dichromate produce a green coloration, as with Phenacetin. (See above, 2.) 7. Most of the general alkaloid reagents produce a precipitate with antipyrin (p. 294). Bases > Gluco sides, etc. 289 Stllphonal (Dimethyl-methane-diethylsulphone). .^ . Co 115 Sulphonal forms colourless prisms ; m.p. 1 2 6. It is slightly soluble in cold water, rather more so in hot water (i : 15). Difficultly soluble in cold alcohol, but readily in boiling alcohol, fairly soluble in chloroform and benzene. Sulphonal is used in medicine as a sedative. i. When heated upon a piece of porcelain or platinum foil, sulphonal burns with a luminous flame, and evolves sulphurous anhydride. It leaves no residue. *2. Place a small quantity of powdered sulphonal in a test tube, and cover it with powdered potassium cyanide. On now fusing, noxious-smelling vapours of mercaptan C 2 H 5 SH are evolved. (i.) A piece of filter paper soaked in lead acetate is stained brown or black when held in the mouth of the test tube. (ii.) Allow to cool, dissolve the fused mass in a little water, and acidify with hydrochloric acid. On now adding ferric chloride to this solution a blood-red coloration of ferric thio- cyanate is produced. *3. When a little powdered sulphonal is mixed with man- ganese dioxide, and the mixture gently fused, mercaptan is evolved, and on lixiviating the fuse with water, filtering from suspended manganese dioxide, then acidifying with hydrochloric acid, and adding barium chloride, a white precipitate of barium sulphate is produced. Glucosides. Glucosides are substances of vegetable origin which, upon being hydrolysed with acids or alkalis, yield a sugar (generally glucose), and one or more other substances, the other substances generally being phenols or aldehydes of the aromatic series. Thus on hydrolysis salicin yields saligenin (orthohydroxy-benzyl 290 Qiialitative Chemical Analysis. alcohol) and glucose, while amygdalin gives hydrocyanic acid, benzaldehyde, and glucose ; digitalin being split up into glucose, digitalose, and digitaligenin. Salicin. Salicin occurs in the bark of the willow. It forms silky needles, m.p. 196, has a bitter taste, and is not readily soluble in water and cold alcohol, but is more readily so on boiling. It is insoluble in ether, but readily soluble in caustic alkali and glacial acetic acid. i. When heated in a dry tube, salicin chars, and vapours are given off, which possess a smell rather resembling that of burnt sugar. *2. If a small quantity of the solid substance is placed upon a white porcelain basin, and moistened with a drop of concentrated sulphuric acid, a blood-red coloration is produced. 3. On warming a solution of salicin with a solution of silver nitrate to which excess of ammonium hydroxide and a little caustic alkali has been added, the silver is reduced with forma- tion of a mirror. *4. On heating with dilute sulphuric acid, salicin is hydro- lysed, glucose and saligenin (orthohydroxy-benzyl alcohol) being produced. CH 2 OH C 13 H 18 7 + H 2 = C 6 H / + C 6 H 12 6 X OH On making the hydrolysed solution alkaline, it reduces Fehling's solution on warming. Further, on addition of a few drops of potassium dichro- mate to the acid mixture, the suspended saligenin becomes coloured pink. Finally, if about i gram of powdered potassium dichromate is added to the hydrolysed mixture, and about a quarter of its volume of concentrated sulphuric acid, and the Bases, Glucosides, etc. 291 mixture then distilled from a small fractionating flask into a few cubic centimetres of water, salicylic aldehyde will be obtained, which may be recognised by its smell odour of meadow-sweet, and also by addition of a few drops of ferric chloride, which will produce a violet coloration. 5. Mandelin's reagent (p. 329) produces a purple-red coloration. 6. Froehde's reagent (p. 329), when added to a trace of salicin on a porcelain plate, gives a violet coloration. 7. Erdmann's reagent (p. 329) gives a bright red, the edges gradually becoming purple. Digitaliti. Digitalin occurs in the seeds of the purple foxglove. When pure, it forms a white amorphous powder, and melts at about 2 1 7. It is readily soluble in water, sparingly soluble in cold alcohol, but readily in hot absolute alcohol. It is very slightly soluble in chloroform and ether. On saponification, digitalin is converted into digitaligenin, digitalose, and glucose. CH0 U + H 2 O = QeHaO, + C 7 H 14 O 6 + C 6 H 12 O 6 Digitaligenin. Digitalose. Glucose. 1. Cold concentrated sulphuric acid turns digitalin, first golden-yellow, then brown, and, finally, after some time, red. 2. Cold concentrated sulphuric acid and a trace of powdered potassium dichromate produces a brown coloration, which gradually turns green. *3. On dissolving a small trace of digitalin in concentrated sulphuric acid, and stirring it with a glass rod moistened with bromine water, a mahogany brown coloration is produced. 4. On warming a solution of digitalin with a solution of silver nitrate, to which excess of ammonium hydroxide and a little caustic alkali has been added, the silver is reduced, and a mirror formed. 292 Qualitative Chemical Analysis. 5. Mandelin's reagent (p. 329) produces a mahogany- brown colour, which turns a deep cherry-red. 6. Froehde's reagent (p. 329) gives a brown colour, which changes to cherry-red, the edges gradually becoming grey. 7. Erdmann's reagent (p. 329) produces a brown colo- ration. CHAPTER XVIII. ALKALOIDS. THE vegetable alkaloids are obtained almost entirely from the family of the Dicotyledons ; colchicin, indeed, is found in a Mono- cotyledon. But no alkaloids have been found in the great families of the Composite or of the Labiate. They usually occur in the plants combined with organic acids, such as citric, malic, and tannic acids. Owing to the remarkable physiological action of many of the alkaloids, they are very much employed in medicine. The majority of the alkaloids are extremely poisonous, and have a very bitter taste. Most of the alkaloids are colourless, odourless, crystalline solids, which contain carbon, hydrogen, nitrogen, and oxygen. There are a few, however, containing no oxygen, which are liquids with unpleasant characteristic smells. Nicotine, coniine, and spartein are examples of the latter class. With very few exceptions, the alkaloids are practically in- soluble in water. They are, however, soluble in absolute alcohol, benzene, chloroform, and amyl alcohol, also with the exception of morphine and narceine in ether. The solubility of the alka- loids in various solvents is made use of in separating them. The alkaloids are bases, usually tertiary or secondary amines. They form, as a rule, well-defined crystalline salts with acids. In some cases, however, the basic character is only very feebly marked, the salts being decomposed by excess of water (hydro- lysed). The salts are usually readily soluble in water, but not in ether, benzene, chloroform, etc. Generally, the alkaloids, owing to their insolubility in water, are precipitated from the solutions 294 Qualitative Chemical Analysis. of their salts by addition of caustic alkali; occasionally, the alkaloid is redissolved by excess of the precipitant. This is the case with morphine, which is dissolved almost as quickly as it is precipitated. The following general reagents precipitate most alkaloids : 1. Tannic acid white or yellowish-white precipitate. 2. Picric acid yellow, generally crystalline, precipitate. 3. Mercuric chloride white to yellow precipitate. 4. Potassium-bismuth-iodide (Dragendorff's reagent) orange-red precipitate. 5. Iodine in potassium iodide brown precipitate. 6. Potassium mercury-iodide (Mayer's reagent) white to yellowish-white precipitate. 7. Phosphomolybdic acid light yellow to brownish- yellow precipitate. Special Reagents. Besides giving precipitates with the general reagents, most of the alkaloids give " characteristic " reactions with special reagents. As a rule, these reactions are well marked and exceed- ingly delicate. They are best carried out as follows : a trace of the alkaloid or its salt is placed on a white glazed tile or in a porcelain evaporating dish, a drop or two of the reagent is then added, when the reaction peculiar to the alkaloid under examina- tion will take place. In the reactions which follow, this method should always be adopted, unless other directions are given. Erdmann's reagent is prepared by mixing 6 drops of con- centrated nitric acid with 100 c.c. of water : 25 drops of this solution are then mixed with 50 c.c. of concentrated sulphuric acid. Froehde's reagent is composed of a i per cent, solution of ammonium molybdate in concentrated sulphuric acid. Mandelin's reagent is prepared by heating 0*5 gram, vanadium chloride or oxide with 100 c.c. concentrated sulphuric acid. Alkaloids. 295 OPIUM ALKALOIDS (MORPHINE, APOMORPH1NE, CODEINE, NARCOTINE). Morphine. C 17 H 19 N0 3 Morphine occurs in opium as morphine meconate (cf. Meconic Acid, p. 232). It crystallises in transparent, colourless prisms, containing i mol. H 2 O. It is nearly insoluble in cold water, slightly soluble in boiling water (i part in 160 parts); the solution has an alkaline reaction. Morphine is almost insoluble in ether, chloroform, benzene, and alcohol. Hot amyl alcohol is the best solvent (i part in 50 parts). The salts of morphine are readily soluble in water and alcohol. Morphine is precipitated from solutions of its salts by caustic alkali, but immediately dissolves in excess. Ammonium hydroxide only dissolves morphine slightly, therefore it is the best precipitant. i. Concentrated sulphuric acid produces a pale rose-red coloration, changing to reddish-yellow. On heating, it becomes violet, and, finally, brown. The addition of powdered potassium dichromate changes the colour to greenish-brown. *2. On intimately mixing in a mortar a little morphine with three or four times its bulk of cane sugar, placing the mixture on a white tile, and adding a drop of concentrated sulphuric acid, a deep-red coloration is produced (apomorphine produces no coloration). *3. When a little morphine is dissolved in a small quantity of concentrated sulphuric acid contained in an evaporating dish, and a trace of an arsenate added, a deep bluish-green coloration is produced on warming. *4. To a small quantity of morphine in an evaporating dish add a few drops of concentrated sulphuric acid and a small crystal of ferrous sulphate, heat on the water bath for one minute, and stir in the crystal. Cool, and add excess of ammo- nium hydroxide to the pink solution, when a rich red, rapidly becoming bright violet, is formed. (Distinction from codeine.) 296 Qualitative Chemical Analysis. 5. Concentrated nitric acid produces an orange-red colora- tion, which changes to yellow on heating. 6. Froehde's reagent gives a purple coloration, which becomes green, and finally, brownish-yellow. 7. Mandelin's reagent produces a brownish-purple colora- tion, which gradually becomes grey. *8. When a drop of ferric chloride is added to a small quantity of morphine, a bluish-green coloration is formed. On now adding a drop of potassium ferrieyanide, and stirring with a glass rod, a deep blue precipitate of Prussian blue is obtained. *9. On addition of a solution of morphine to iodic acid, iodine is liberated ; if the solution is very dilute, the presence of the liberated iodine can be readily detected by means of starch paste. *io. When morphine is moistened with formaldehyde, and then with 2 to 3 drops of concentrated sulphuric acid, an intense purple-red colour, changing to violet-blue, is obtained. Apomorphine, C 17 H 17 N0 2 Apomorphine is a snow-white amorphous substance, readily soluble in alcohol, ether, chloroform, and benzene. 1. Solutions of apomorphine rapidly acquire a green tinge, and finally become brown. With solutions of the salts of apomorphine these colour changes are shown after addition of alkali. 2. On adding a drop of concentrated sulphuric acid, and then sprinkling with potassium dichromate, an olive-green, changing to brown-green, is produced. *3- Nitric acid produces a purple-red coloration, becoming mahogany-brown. 4. Froehde's reagent gives a deep green coloration which gradually assumes a bluish tinge. Alkaloids. 297 5. Mandelin's reagent produces a greyish or greenish-blue coloration. *6. Ferric chloride gives a red or purple-red coloration, becoming brownish-black on heating. Codeine (Methyl Morphine). C 17 H 17 NO(OCH,)OH Codeine crystallises from water in well-defined orthorhombic prisms, containing i mol. H. 2 O. Anhydrous codeine melts at 150-155. It is readily soluble in alcohol, amyl alcohol, ether, chloroform, and benzene; fairly soluble in hot water. It is a strong base, with an alkaline reaction. Its salts are readily soluble in water. *i. Grind a little codeine in a mortar with about three times its bulk of sugar, and moisten the mixture with- concentrated sulphuric acid ; a light red colour, which slowly changes to violet-purple, will be formed. *2. When a drop of concentrated nitric acid is added to a solution of codeine in concentrated sulphuric acid, a deep red coloration is produced. 3. Froehde's reagent produces a dirty green coloration, which becomes bright green, then blue, and, after standing some time, yellow. 4. Mandelin's reagent gives a greenish-grey to greyish- blue coloration. *5. On moistening a trace of codeine with formaldehyde, and then with 2 to 3 drops of concentrated sulphuric acid, a bluish-violet coloration is produced. Narcotine, Narcotine crystallises from alcohol in colourless glittering prisms or groups of needles; m.p. 176. It is soluble in alcohol, ether, and chloroform ; almost insoluble in water. It is a feeble 298 Qualitative Chemical Analysis. base, its salts having an acid reaction, being more or less hydro - lysed in aqueous solutions. *i. Concentrated sulphuric acid, when added to a trace of narcotine in an evaporating basin, produces a greenish-yellow coloration, which on heating on the water bath, becomes a deep brownish-red, changing to a dirty violet. Potassium dichromate added to a solution of narcotine in concentrated sulphuric acid, produces a fine brown coloration. *2. If a little narcotine is warmed with concentrated sulphuric acid in an evaporating dish, and a drop of ferric chloride added, the brownish-red coloration at first produced becomes an intense crimson. *3. When a little narcotine is ground up with about four times its bulk of sugar, and the mixture moistened with concentrated sulphuric acid, a mahogany-brown coloration is produced. 4. Nitric acid gives a yellow to orange coloration. 5. On heating a solution of narcotine in dilute hydrochloric acid with bromine water, a yellow precipitate is produced, which dissolves on boiling. By carefully adding bromine water drop by drop to the hydrochloric acid solution, and boiling, a rose-red coloration is formed, which is destroyed by adding excess of bromine water. 6. Erdmann's reagent produces an orange-yellow colora- tion, which momentarily turns pink, then yellow again. 7. Proehde's reagent forms a deep grass-green coloration. 8. Mandelin's reagent gives an orange coloration, which gradually becomes pink. CINCHONA ALKALOIDS. The cinchona alkaloids all have well-marked basic properties, some of them displacing ammonia from its compounds. The free alkaloids are generally readily soluble in ether and chloroform. The solutions of the sulphates of some of the cinchona alkaloids show a strong blue fluorescence. The cinchona alkaloids here treated of are quinine, quinidine, and cinchonine. Alkaloids. 299 Quinine. Free quinine usually has the appearance of an amorphous or resinous mass. In commerce it is generally obtained as a coarse powder with a brownish-yellow tint. It may, however, be obtained crystalline from its solution in alcohol. On evaporating an ethereal solution, it separates as a gelatinous mass. Quinine is only sparingly soluble in water, but more readily in ammonium hydrate. It is readily soluble in petroleum spirit and benzene. It is strongly basic, its solution turning red litmus blue. i. Concentrated sulphuric acid, added to a little quinine, dissolves it, forming a colourless solution, which on addition of a crystal of potassium dichromate, becomes grass-green. *2. Solutions of quinine in dilute sulphuric acid exhibit a strong blue fluorescence. The fluorescence shows best in dilute solutions, to which has been added a large excess of dilute sulphuric acid, and may be best seen by looking down into a test tube held against a piece of black paper. *3. Ammonium oxalate, added to a solution of quinine sulphate, produces a white crystalline precipitate. Precipitation is accelerated by shaking. (Distinction from quinidine.) *4. Dissolve a little quinine sulphate in acetic acid, add an equal bulk of alcohol, and then an alcoholic solution of iodine. On now warming and allowing to stand a few minutes, a black crystalline powder of iodoquinine separates out, which possesses a very characteristic golden lustre. *5. Thalleoquinine Reaction. Make a dilute solution of bromine in water, f and add about i c.c. of this solution to about 10 c.c. of a solution of quinine sulphate, and then two or three drops of ammonia, when a bright green precipitate or coloration will be produced (thalleoquinine). On adding to this a few drops t A freshly prepared solution of chlorine water may be used instead of the bromine water. 3OO Qualitative Chemical Analysis. of a freshly prepared solution of potassium ferricyanide, the colour changes to a brilliant red (roseoquinine). 6. If a small quantity of quinine is placed in an evaporating dish, moistened with a few drops of concentrated hydrochloric acid, and evaporated to dryness over a naked flame, just before it chars it turns a violet colour, and if the heating is continued violet vapours, resembling those of iodine, are given off. This reaction is peculiar to the quinine alkaloids. *7. Mandelin's reagent gives no coloration, but, on addition of a drop of nitric acid, a violet coloration is obtained. Quinidine. Quinidine is deposited from alcohol in monoclinic efflorescent prisms or needles, with 2 mols. H./). The anhydrous substance melts at 168, first becoming brown. It is soluble in water, and fairly soluble in ether and alcohol. i. Concentrated sulphuric acid, when added to a trace of quinidine on a white plate, dissolves it without coloration, but on adding a crystal of potassium dichromate, it turns a grass- green. *2. A solution of potassium iodide gives a heavy sandy precipitate, with solutions of quinidine. *3. Quinidine gives the thalleoquinine reaction, (Cf. Quinine, 5.) 4. If a small quantity of quinidine is placed in an evaporating dish moistened with a few drops of concentrated hydrochloric acid, and evaporated to dryness over a naked flame, just before it chars it turns a violet colour, and, if the heating is continued, violet vapours resembling those of iodine are given off. *5. Mandelin's reagent produces no coloration, but on addition of a drop of nitric acid to the mixture, a violet colora- tion appears. Alkaloids. 301 Cinchonine. Cinchonine crystallises in white shining anhydrous prisms. It melts at 255, forming a colourless liquid, and at a higher tempera- ture partially sublimes. It is almost insoluble in cold water, and only very slightly in boiling water. It is fairly soluble in boiling alcohol, but much more readily in amyl alcohol, and dissolves most easily in a mixture of six parts chloroform and one part alcohol. Solutions of cinchonine have an alkaline reaction. Its salts are fairly soluble in water and alcohol. 1. When carefully heated in a dry tube, cinchonine first melts, then gives off white fumes, which condense on the cold sides of the test tube in small needles. 2. On adding a little powdered potassium dichromate to a solution of cinchonine in concentrated sulphuric acid, a grass- green coloration is produced. 3. On adding chlorine water to a solution of a salt of cinchonine, no change is produced, but on addition of ammonia, a yellowish-white precipitate is formed. (Cf. Quinine and Quinidine.) *4. Potassium ferrocyanide, when added to a solution of a salt of cinchonine, produces a light yellow flocculent precipitate of cinchonine ferrocyanide; if excess of the precipitant is added, and the mixture cautiously warmed, the precipitate dis- solves, separating out again, on cooling, in golden-yellow crystals. (Characteristic reaction.) 5. Cinchonine when evaporated to dry ness with a few drops of concentrated hydrochloric acid gives the same reaction as quinine and quinidine. *6. Mandelin's reagent gives no coloration with cinchonine, but on adding a drop of nitric acid to the mixture, a violet coloration is formed. 3NH CH 2 - OH, Coniine is the poisonous principle of hemlock (Conium maculatum}. It is an oily liquid possessing a very unpleasant odour, like that of a foul tobacco-pipe; it also has a peculiar 308 Qualitative Chemical Analysis. "mousy" smell, which is especially marked when coniine is dis- solved in water. Coniine is readily volatile with steam, and is easily soluble in water and practically all organic solvents. It is a very strong base, and forms neutral salts with acids. The chief interest of coniine lies in the fact that it was the first optically active plant alkaloid to be synthesised. *i. Concentrated sulphuric acid and potassium dichro- mate quickly produce a grass-green coloration. *2. If a few drops of alcohol are added to a trace of coniine contained in an evaporating dish, and then two or three drops of carbon disulphide ; on allowing to stand a minute or two, and then adding a drop of very dilute copper sulphate, a brown coloration is produced. (Distinction from nicotine.) *3. Dissolve a drop of coniine in about i c.c. of alcohol, and add an equal volume of water. On now adding a few drops of phenolphthalein a pink coloration is produced. Nicotine only shows this test when the alcoholic solution is very largely diluted with water. The test may be applied to a trace of coniine, contained in a watch glass, by adding two or three drops of alcohol, a little water, and about \ c.c. of a solution of phenolphthalein. 4. Mercuric chloride produces a white precipitate, which does not turn yellow, as does the corresponding precipitate produced with nicotine. 5. Froehde's reagent gradually produces a pinkish-yellow coloration. Detection of the Alkaloids. Having by means of the "general reactions" (p. 294) found that the subs'ance under examination is an alkaloid, or an alkaloid mixed with other substances, inorganic or organic, it is now necessary to determine which of the many alkaloids it may be. If it is mixed with other substances, it may be necessary, and is always advisable, to separate it first before applying special tests. In order to do this, the mixture is made alkaline with caustic alkali, evaporated to dryness, and extracted several times with Alkaloids. 309 small quantities of ether. On evaporating or distilling off the ether, the alkaloid will be obtained free from inorganic and most organic contaminations. Morphine, it must be remembered, is not soluble in ether, and must be extracted with hot amyl alcohol. If aniline, pyridine, or quinoline are present along with non- volatile alkaloids, it will be necessary first to subject the alkaline mixture to steam distillation. Having done this, evaporate the residue to dryness, and extract with ether as already explained. The tests enumerated in the table which follows (pp. 310, 311) should be applied, in the order given, to small portions of the alkaloids thus obtained, placed on a white porcelain tile, or, better, in an evaporating dish, because then heat may be more readily applied. One of the best methods for applying tests to the ethereal solution is, to place two or three drops in an evaporating basin and allow the ether to evaporate spontaneously, or by gentle warming, then to add the reagent to the residue. A fresh portion must be taken for each test. If the substance under examination is a solution of a salt of an alkaloid, the alkaloid may be pre- cipitated by addition of sodium carbonate or caustic alkali.f The test can then be applied to separate small portions of the pre- cipitated alkaloid. Or the solution may be rendered alkaline, and evaporated to dryness on a water bath, the residue being extracted with ether as already described. In many cases the tests in the table will be sufficient to prove which alkaloid is present, but in some cases it will be found necessary to apply confirmatory tests, e.g. in the case of quinine and cocaine, which give no very characteristic reactions with the reagents enumerated. Such confirmatory tests may be taken from the reactions found under the head of the particular alkaloid. At the end of the table the reactions of salicin, digitalin, acetanilide, phenaeetin, and antipyrin have been included, it being of interest to compare the reactions of these substances f Owing to the solubility of morphine in caustic alkali, if its presence is suspected ammonium hydrate should be employed as the precipitant, instead of caustic alkali. 310 Qualitative Chemical Analysis. Brownish-purpl becoming gre 1 M S o fl . n 1* S KriM Sl'SI & & t t/3 a 8 | a I I ys, * d Q rii |8 & C W> 1| o G i 2 r Si .g I 1 .3 -H 08 d II Alkaloids. 32 Ij ~< tfj 8 &* i? .1? , 8,-g'a ' 1 I 1 SJ5 5 sj 8 c t"l j.s ^w 1 1 1 1 3 111 s pq 0, . M i rt 3 2 J f 1 | 'S* 1 ' f 5 I cS ft So s ^M pq li I I I I i v6 o m g* P S d ^ sl eS 0" if if -I IS 1 1 1 Is- co O E c o d I w> I' 5 - X 2 < ev =5 S 3 S Q sS 1 ft Hi I. ^i^ c ^ | I !-a I ?o| I J3 w 2 iss .^s . , s - G ^ .., cq S 'd c o *J ^ S^~ ^ ' f '/ ^ J ^- ^. ^-^_^ ~f* J 7 --. ^^ - >~^ ' ^^ ^_ IJ / "S ^ . ' , . - i ^ - . 1 1 ^L- t . 50 75 100 125 150 175 200 225 FIG. 13. quantity of the given acid containing this amount of pure acid (obtained from the curve, Fig. 13) into about half a litre of water, and after cooling make up to the litre mark with distilled water. Suppose the density of the sulphuric acid is 1*2, then from Fig. 13 it will be seen that 151 c.c. of this acid diluted to I litre will make a litre of normal acid. Therefore to obtain a 4N. solution 604 c.c. would require to be diluted to i litre. Hydrochloric Acid (Dilute). Prepare a 4N. solution. A normal solution contains 36-45 grams of gaseous HC1 per litre, a4N. 145*8 V 322 Appendix. grams. Take the density of the acid, and from this find out how many cubic centimetres must be diluted to I litre in order to make a 4N. solution (Fig. 14). Nitric Acid (Dilute). Prepare a 4N. solution. A normal solu- tion contains 63 grams of pure acid per litre, a 4N. contains 252 grams. Acetic Acid (Dilute). Prepare a 4N. solution. A normal solution contains 60 grams of pure acid per litre, a 4N. solution 50 75 100 125 ISO 175 200 225 90 250 240 grams. The curve for acetic acid (Fig. 14) shows that for specific gravities above 1*055 two different quantities maybe read for the same specific gravity. To avoid this ambiguity it will therefore be necessary to dilute the acid with water till the specific gravity falls just below 1-055. Oxalic Acid (Solution). Prepare a 2N. solution of the acid containing 126 grams of oxalic acid crystals per litre. Sulphurous Acid. Prepared by saturating distilled water with Appendix. 323 the gas. Liquid sulphur dioxide can be obtained in siphons, from which the gas may be obtained as required. The saturated solution is about 37 N. Hydrofluoric Acid. This is best used as purchased ; the solution usually contains about 30 per cent, of HF, about 1*5 N. Hydrofluosilicic Acid is tiresome to prepare, and so is best purchased. Aqua Regia must always be prepared as required by mixing i volume concentrated nitric acid with 4 volumes concentrated hydro- chloric acid. Chlorine Water. Pass chlorine gas into distilled water until no more is absorbed. The bottle in which the chlorine water is kept should be painted black. A saturated solution is about f. Bromine Water. Add bromine to distilled water, and shake up till a portion remains undissolved. Keep in a cool place, in a well- stoppered bottle containing a little undissolved bromine. The solution is about f . Sulphuretted Hydrogen. Either the gas may be employed or a saturated solution of the gas in water. Fig. 15 shows an apparatus from which either the gas or a saturated aqueous solution can be obtained. The apparatus consists of a bottle A containing ferrous sulphide, which has a tubulus on either side, near the bottom, by means of which it is connected with the reservoir B (represented in the sketch by the dotted lines) and the flask C. D is a wash bottle containing a little water, the outlet tube of which is connected with a tube d passing nearly to the bottom of the bottle E (about 3 or 4 litres capacity) filled with distilled water. A second tube/, which does not dip below the surface of the water, passes into a small " catch " bottle F. This bottle has an outlet tube to which is attached, by means of a piece of rubber, a glass tube about 8 inches long ; g is a small brass clip which serves to close the rubber tube. Should an aqueous solution of sulphuretted hydrogen be required, it can be obtained by turning on the tap h, whereas one can get a supply of the gas by opening the clip g. When the apparatus is freshly charged, the clip g should be opened and a rapid current of the gas bubbled through the water in E for a few minutes. By this means the air on the surface of the water is driven out, and on closing the clip the gas will be absorbed until the water is saturated. As soon as the water is completely saturated, the pressure of the gas drives the acid up into C, and all action ceases. As there is no air present in E, no oxidisation can take place, and the solution, even if 324 Appendix. the apparatus is standing in strong light, deposits only a trace of sulphur. All the rubber connections of the apparatus should be carefully wired on, so that no leakage can take place, and it will usually be found best to keep the apparatus with the bottle C always in the position represented in the sketch. By so doing, the aqueous solution of sulphuretted hydrogen is always saturated. In order to prevent the solution in E from being driven back into the wash bottle D, should a back pressure be set up, owing to rise of FIG. 15. atmospheric temperature, and consequent decrease of solubility of the gas in water, a layer of mercury is placed in D below which the tube d just dips. The mercury acts as a seal, and prevents the solution from being driven back. For convenience the stand contains two holes in which test tubes may be placed whilst passing the gas. Hydrochloric acid (i part acid and 2 parts water) should be used to generate the gas, because when sulphuric acid is employed there is ten- dency for ferrous sulphate to crystallise out and to clog the apparatus. Appendix. 325 Bases, etc. Potassium or Sodium Hydroxide. 4N. solution. Normal solution of NaOH contains 40 grams to the litre and 4N. 160 grams per litre. Normal solution KOH contains 56 grams per litre, 4N. contains 224 grams per litre. Ammonium Hydroxide. 4N. solution. This solution can be made up by taking the density and then using the curve on Fig. 14. Normal solution contains 17 grams ammonia gas or 35 grams NH 4 OH. Calcium Hydroxide (Lime Water). Mix an excess of slaked lime with water, and allow to settle ; then siphon off the clear solu- tion, which must be kept in a well-stoppered bottle. The saturated solution is about -fa. Barium Hydroxide. The crystallised salt contains water of crystallisation Ba(OH),,8H a O, but it is also usually very much con- taminated with carbonate. The best way is to prepare a cold satu- rated solution by shaking up with cold water until no more is dissolved, and then filtering from the insoluble barium carbonate. This solution contains about 50 grams to the litre, it is therefore about f. Ammonium Sulphide. Saturate I volume of ammonium hydrate with sulphuretted hydrogen ; when saturated, mix with 2 volumes of ammonium hydrate of the same strength, and dilute with about 5 volumes of water. Yellow Ammonium Sulphide. Add to every litre of the colour- less ammonium sulphide 10 grams of flowers of sulphur. Salts, etc. Ammonium Chloride. 4N. solution ; dissolve 212 grams in I litre of water. Ammonium Oxalate. N. solution ; dissolve 78 grams of crystal- lised salt (COONH 4 ) 2 ,2H 2 O in I litre of water. Ammonium Sulphate. 2N. solution; 132 grams crystallised salt to i litre. Ammonium Acetate. 2N. solution ; 154 grams crystallised salt to I litre. Ammonium Carbonate. 80 grams solid ammonium carbonate and 32 c.c. ammonium hydrate (sp. gr. o'88) to i litre of water. Ammonium Molybdate. Dissolve 1 50 grams ammonium molyb- date in i litre of water, and then pour into I litre of nitric acid 3 26 Appendix. (sp. gr. i -2) ; now dissolve 100 grams of ammonium nitrate in this mixture, allow to stand over.night, and decant from any residue. Potassium Chromate. 2N. solution ; 194 grams per litre. Potassium Bichromate. f . solution ; 73-59 grams per litre. Potassium Cyanide. N. solution ; 65 grams per litre. This solution does not keep very well, so should only be prepared in small quantities at a time. Potassium Ferrocyanide.K 4 Fe(CN) 6 ,3H 2 O. N. solution; 105-5 grams per litre. Potassium Ferricyanide. N. solution ; 109-5 grams per litre. Solution should be prepared in small quantities as required. Potassium Nitrite. -Solution should be prepared as required. A normal solution contains 85 grams per litre. Potassium Thiocyanate. N. solution ; 97 grams per litre. Potassium Iodide. Should only be prepared in small quantities at a time. A normal solution contains 1 66 grams to the litre. Potassium Pyroantimonate. Boil 50 grams potassium anti- monate with concentrated nitric acid until no more red fumes are evolved. Allow to settle, and decant off the liquid, and wash the antimonic acid several times with water by decantation. Then boil the residue for 5 or 10 minutes with strong caustic potash (i part H 2 O and I part KOH). Cool the mixture, and filter off the excess of caustic potash on an asbestos filter. The acid potassium salt K 2 H 2 Sb 2 O 7 ,6H 2 O may now be dissolved in 500 c.c. warm water, and can then be used as a reagent for sodium. Potassium Carbonate. 4N. solution; 276 grams of K 2 CO 3 per litre ; the anhydrous salt to be used. Sodium Carbonate. N. solution ; dissolve 53 grams anhydrous sodium carbonate per litre. Sodium Cobaltinitrite may be prepared by dissolving 1 50 grams sodium nitrite in 150 c.c. of water with heating. The solution is then cooled to about 50 C., and 50 grams of crystallised cobalt nitrate added ; as soon as the cobalt nitrate has dissolved, 50 c.c. of 50 per cent, acetic acid is added. After shaking up, the brown solution is filtered, to separate any potassium cobaltinitrite which may have been formed, and a current of air is aspirated through it to remove oxides of nitrogen. 150 c.c of alcohol is now added, the mixture allowed to stand for about half an hour with occasional shaking, and then filtered. The sodium cobaltinitrite which is thus obtained as a more or less crystalline powder is washed with alcohol and dried. In employing Appendix. 327 it as a test for potassium or ammonium about \ gram is dissolved in about 2 c.c. of water. It decomposes when kept in solution. Sodium Phosphate. Na 2 HPO 4 , 1 2H 2 O. j. solution ; 59*6 grams per litre. Sodium Thiosulphate. Na. 2 S 2 O 3 ,5H 2 O. f. solution ; 62 grams per litre. As this solution readily decomposes, it is better to prepare it as required. Sodium Nitroprusside. This solution should be prepared as required by dissolving a few crystals in a little water. Barium Chloride. BaCl 2 ,2H 2 O. N. solution; 122 grams per litre. Bleaching Powder Solution. Shake up bleaching powder with water, allow to stand, and decant or filter off the clear fluid. Borax Solution (to test for Glycerine). Dissolve 5 grams of crystallised borax in I litre of water. Now add sufficient of an alcoholic solution of phenolphthalein to produce a rose-red coloration. Calcium Chloride. CaCl 2 , 6H 2 O. 2N. solution ; 219 grams per litre. Calcium Sulphate. Prepare a saturated solution by shaking up with water ; allow to stand until the excess of calcium sulphate has settled, and siphon off the clear solution. Cobalt Nitrate. f ; 72*5 grams per litre. Copper Sulphate. N ; 125 grams per litre. Ferrous Sulphate. Prepare a solution as required by shaking up the crystallised salt with cold water. It is better to use ferrous ammonium sulphate, because it is less easily oxidised. Ferric Chloride. N ; 54 grams of ferric chloride and 5 c.c. of concentrated hydrochloric acid per litre. Lead Acetate. (CH 3 COO) 2 Pb,3H 2 O. N. solution ; 190 grams per litre. Gold Chloride. f^ ; n '3 grams per litre. Magnesium Chloride. 2 N ; 203 grams per litre. Magnesium Sulphate. MgSO 4 ,7H 2 O. 2N ; 246 grams per litre. Magnesia Mixture. Dissolve 50 grams crystallised magnesium 328 Appendix. chloride or sulphate in water ; add 70 grams ammonium chloride dis- solved separately, and 300 c.c. strong ammonium hydrate ; make up to i litre with distilled water. Filter if necessary. Mercuric Chloride. f ; 68 grams per litre. Mercurous Nitrate. N. Dissolve 200 grams mercury in just sufficient moderately strong nitric acid, and dilute to i litre with water. Place a little metallic mercury into the bottle containing the solution. Silver Nitrate. T % ; 17 grams per litre. Stannous Chloride. SnCl 2 ,2H 2 O. 2N. Dissolve 225 grams stannous chloride in 500 c.c. 4N hydrochloric acid, and dilute to i litre. Place some fragments of metallic tin in the bottle containing the solution. Or dissolve 118 grams tin in concentrated hydrochloric acid, having a piece of platinum foil in contact with the tin, and make up to i litre, adding concentrated hydrochloric acid if the solution becomes opalescent. Preserve in a well-stoppered bottle in contact with granulated tin. The strength of this reagent does not remain constant. Stannic Chloride. 2N. Take the strong stannous chloride solution prepared as above, . containing 118 grams of tin, and add bromine water to it until it is just brown. Now heat on sand bath in draught cupboard until it becomes colourless. Make up to i litre. HydrogenPlatinichloride. ^. ; with respect to platinum ; io'66 grams per litre. Other Reagents. Fehlmg's Solution. Dissolve 69-28 grams of pure copper sulphate in 300 c.c. of water, with addition of 2 or 3 drops of sulphuric acid. Add to this a solution of 350 grams of Rochelle salt, and 100 grams of sodium hydrate in 500 c.c. of water. Now make the mixed solutions up to i litre. Indigo Solution. Gently warm a mixture of 4 grams indigo and 50 c.c. cone, sulphuric acid, then allow to stand for 24 hours, and make up to I litre with distilled water, and filter. Nessler's Reagent is prepared by first dissolving 32*5 grams of potassium iodide in 250 c.c. of distilled water. About 10 c.c. of this solution is reserved. Now gradually add the main portion to a cold saturated solution of mercuric chloride, with continual stirring. Sufficient mercuric chloride must be employed to cause a slight precipitate after the 240 c.c. of potassium iodide has been added. Appendix. 329 Then add the reserve portion till the precipitate is almost dissolved. Next dissolve 150 grams of caustic potash in 150 c.c. of water, cool, and add to above solution. Dilute to i litre, and allow to settle. Finally, decant clear liquid into a bottle, and keep in a dark place. Oxalic Acid (Test for Urea). Prepare a cold saturated solution. Starch Paste. Grind up from I to 2 grams of starch into a thin paste with cold water. Pour into 100 to 150 c.c. of boiling water, and continue to boil for a few minutes. Allow the liquid to stand till cold, and pour off the clear solution. Starch paste may be kept for some weeks if about I c.c. of chloroform be added to it. The blue coloration with iodine is, however, more intense when it is freshly prepared. Schiff *s Reagent. Make a dilute solution of fuchsine, and pass sulphurous acid into it till the colour is destroyed ; preserve in a well- stoppered bottle. Litmus Solution. Digest 100 grams of litmus with 500 c.c. hot water. Allow to stand over night, and filter. Now add 300 c.c. of methylated spirit to the solution, and dilute with water to I litre. Phenolphthalein. Dissolve 5 grams phenolphthalein in 100 c.c. of warm methylated spirit, and dilute to I litre with a mixture of equal volumes of methylated spirit and water. Methyl Orange. Dissolve 2 grams methyl orange in 200 c.c. methylated spirit, and dilute to I litre with water. Brucine (Test for Nitric Acid). Dissolve 0*5 gram brucine in 200 c.c. concentrated sulphuric acid. This solution does not keep very well. Denige's Citric Acid Test. Add 5 grams yellow mercuric oxide to 20 c.c. concentrated H 2 SO 4 and 100 c.c. water. Alkaloid Reagents. Erdmann's Reagent. Mix 6 drops of concentrated nitric acid with loo c.c. of water, then take 25 drops of this solution, and mix with 50 c.c. of concentrated sulphuric acid. Froehde's Reagent. Dissolve i gram of ammonium molybdate in ico c.c. of concentrated sulphuric acid. Iodine in Potassium Iodide. Dissolve i part iodine and 2 parts potassium iodide in 50 parts water. Mandolin's Reagent. Heat 0*5 gram of vanadium chloride or oxide with ico c.c. of concentrated sulphuric acid. Y 2 330 Appendix. Potassium-Bismuth-Iodide (Dragendorff 's Reagent f). Dis- solve 8 grams bismuth nitrate in 20 c.c. nitric acid (ri5 sp. gr.), and dissolve 27 grams potassium iodide in 40 c.c. water. Mix the bismuth solution with that of the potassium iodide with constant stirring. On standing, potassium nitrate crystallises out ; pour off from the crystals, and make up to 100 c.c. with distilled water, Potassium Mercury-Iodide (Mayer's Reagent). 13-5 parts mercuric chloride, and 50 parts potassium iodide dissolved in 940 parts of water. Tannic Acid. 10 per cent, solution. This solution does not keep well, so should be made up in small quantities at a time. Picric Acid. Shake up crystallised picric acid with cold water till no more is dissolved, and filter from the undissolved portion. STEAM DISTILLATION. Many substances, which can only be distilled with difficulty, are found to be much more easily volatile when distilled in a current of FIG. 16. steam. Again, some substances, which under ordinary circumstances are decomposed when subjected to distillation, may be readily distilled with the aid of steam. Steam distillation is also of great use in dis- tilling a mixture containing a volatile and a non-volatile substance, one or other of which might be decomposed by heating in the \ This reagent is sometimes called " Thresh's Reagent." Appendix. 331 ordinary way. For example, a mixture of aniline and sugar or of nicotine and cinchonine ; the aniline or nicotine would pass over with the steam, but the sugar and cinchonine would remain behind. In the course of this book the student has on several occasions been recommended to employ distillation by steam as a method of separa- tion, therefore it has been thought advisable to describe the apparatus which is generally used. The apparatus (Fig. 16) consists of a tin or, better, copper can, A, which is half full of water, and is connected by means of a rubber tube to a glass tube, c, which passes nearly to the bottom of a round- bottomed flask, B. The flask B contains the liquid which it is desired to distil, and is connected, by means of the tube d, with a Liebig's con- denser. The long upright tube, e, in the tin can is a safety tube ; it passes to within about I inch of the bottom of the can, so that should the water be below this level, steam will issue from the top of the tube ; or should the pressure in the flask become too great, it will act as a safety valve. WATER BATH. A very convenient form of water bath is a tin pint mug or measure. If a beaker is used as a water bath it is very liable to get broken. INDEX Where more than one reference is given^ that in heavy type refers to the reactions of the substance or to the tables. ACETALDEHYDE, 262 Acetamide, 250 Acetanilide, 286 Acetic acid, 212 I/ Acetone, 269 Acids, grouping of inorganic, 104 , organic, 186, 208, 236 , preliminary examination for, 159 , preparation of reagent, 320 , preparation of solution of, 181 , systematic examination for, 180 , Table I., 183 II., 184 , the, 104, 321 Alcohol, amyl, 268 , ethyl, 267 , methyl, 266, 268 Aldehyde resin, 263 Aldehydes, 261 Alkaloids, 293, 310 Allyl alcohol, 271 Aluminium, 67 Amides, 250 Amidobenzene, 280 Amines, primary, 246 , secondary, 246 , tertiary, 247 , quaternary, 248 Ammonium, 97 , test for, 103 Amyl acetate, 240 alcohol, 240 nitrite, 241 Amylum, 277 Analysis, general scheme of, 169 Aniline, 280 Anions, 14 Authracine, 259 Antifebrin, 286 Antimonic compounds, 55 Antimonious compounds, 54 Antimony, 51 Antipyrin, 288 Apomorphine, 296, 310 Aqua-Regia, 323 Arsenic, 44, 173 acid, separation from phosphoric, 138 compounds, 50 group, 25, 44, 63, 173 Arsenious compounds, 49 Atropine, 306, 310 BARIUM, 89, 178 from calcium and strontium, 92 group, 89, 177 Bases, 280, 325 Benzaldehyde, 263 Benzene, 254 Benzoic acid, 223, 230 Berylium, 187 Bicarbonates, 123 Bismuth, 36, 172 Biuret reaction, 284 Blowpipe reactions, 4 Boiling-point, 205, 244 Boracic acid, 142 Borax bead tests, 10, 158 Boric acid, 142 Bromic acid, 149 Bromine in organic compounds, 202 , separation of chlorine and iodine from, no Brucine, 275, 282 Bunsen burner, 5 334 Index. CADMIUM, 42, 172 Caesium, 187 Caffeine, 305, 310 Calcium, 91, 178 from barium and strontium, 92 Cane sugar, 274 Carbamide, 284 Carbohydrates, the, 272 Carbolic acid, 229 Carbon, detection of, 201 Carbonic acid, 121 Carbon tetrachloride, 243 Carbylamine reaction, 246 Cations, 14 Cautions, 167 Cerium, 84, 177, 187 Chloral hydrate, 265 Chloric acid, 148 Chlorine in organic compounds, 202 Chloroform, 242 Chromic acid, 144 compounds, 69 Chromium, 68, 175 Cinchona alkaloids, 298 Cinchonine, 301 Cinnamic acid, 227 Citric acid, 219, 222 Cobalt, 81, 175 , separation from nickel, 83 Cocaine, 302, 310 Codeine, 269, 297, 310 Colloidal state, 24 Colour changes, 19, 154 Columbium, 187 Coniine, 307, 310 Copper, 38, 172 group, 25, 43, 171 Cupric compounds, 40 Cuprous compounds, 39 Cyanogen compounds, I2O Cyanuric acid, 284 DEHYDRATION of crystalline salts, 154 Dextrose, 273, 277 Diazo-reaction, 253 Dichloroacetic acid, 240, 249 Digitalin, 291, 310 Digitalose, 291 Dimethyl sulphate, 241 Division of metals into groups, 25 Distillation, steam, 330 Double cyanides, 120 Dragendorff's reagent, 294, 329 Draught tube, II Dry reactions, 3, 153 ELIMINATION of organic matter, 165 Erdmann's reagent, 294, 329 Ether, extraction with, 207 Ethereal salts, 239 Ethyl acetate, 240 alcohol, 267 bromide, 241 benzoate, 240 butyrate, 240 formate, 240 hydrogen sulphate, 241 iodide, 241 mercaptan, 241 nitrate, 241 nitrite, 241 oxalate, 252 salicylate, 240 sulphide, 241 Evolution of gases, 18 FEH LING'S solution, 328 Ferric iron, 72 thiocyanate, colour of, 73 Ferrous iron, 71 Film reactions, 7, 257 Filtration, 22 Flame tests, 8, 156 Formaldehyde, 261 Formalin, 233, 261 Formic acid, 210, 236 Fractional distillation, 206 Froehde's reagent, 294, 329 GALLIC acid, 233, 235 Gallotannic acid, 223, 235 Glucose, 273, 277 Glucosides, 289 Gluside, 278 Index. 335 Glusidum, 278 Glycerine, 270 Glycerol esters, 255 Glucinium, 187 Gold, 60, 167 Grape sugar, 273 Gutzeit test, 46 HALOGEN acids, detection of, no, 183 (organic), 248 , in presence of cyanides, 112, 183 Higher fatty acids, 255 Hippuric acid, 228 Hydrate theory of solution, 16 Hydriodic acid, 108 Hydrobromic acid, 107 Hydrocarbons, 253 Hydrochloric acid, 106 Hydrocyanic acid, 114, 183 Hydroferricyanic acid, 118 Hydroferrocyanic acid, 116 Hydrofluoric acid, 134 Hydrogel, 24 Hydrogen, detection of, in organic compounds, 201 peroxide, 151 sulphide, 131 Hydroxyl ion, 152 Hypochlorous acid, 113 Hypophosphorous acid, 140 INDIGO solution, 328 Indium, 187 Insoluble substances, 163 Invert sugar, 275 lodic acid, 150 Iodide film, 8, 157 Iodine in organic compounds, 190 lodoform, 244, 267, 269 Ions, 14 Iridium, 187 Iron, 71, 175 group, 26, 175, 176 Isobutyl carbinol, 268 LACTIC acid, 214 Lactose, 275, 277 Laevulose, 275 Lanthanum, 187 Lead, 29, 170 Liebermann's reaction, 229 Lithium, 99, 180 (foot note) MAGNESIUM, 99, 179 Maleic acid, 221 Malic acid, 221 Maltose, 276, 277 Mandelin's reagent, 294 Manganese, 75, 175 Marsh's test, 46 Mass action, 20 Match tests, 6, 158 Mayer's reagent, 274 Meconic acid, 232, 237 Melting-points, 204 Mercuric chloride for alkaloids, 294 compounds, 35 Mercurous compounds, 32 Mercury, 31, 170 Metallic film, 7 Meta-phenylenediamine, 127 Metaphosphoric acid, 139 Metallic substances, treatment of, 1 66 Methyl acetate, 240 alcohol, 266 formate, 240 iodide, 241 morphine, 297 orange, 329 oxalate, 252 sal icy late, 240 Microsmic salt, 10 Milk sugar, 275, 277 Molybdenum, 187, 189 Monochloroacetic acid, 240, 249 Morphine, 295, 310 Murexide reaction, 231 NAPHTHALENE, 259 Narcotine, 297, 310 Nessler's reagent, 98, 328 Neutral solutions, preparation of, 182 336 Index. Nickel, 78, 175 from cobalt, 83 Nicotine, 307, 310 Niobium, 187 Nitric acid, 124 in presence of nitrites, 127 Nitrobenzene, 225 Nitrogen, detection of, in organic compounds, 201 Nitroparaffins, 241 Nitrous acid, 126 OLEIC acid, 255 Opium alkaloids, 295 Organic acids, 208, 236 matter, elimination of, 165 Orthophosphoric acid, 137 Osmium, 187 Oxalic acid, 215, 222 Oxamide, 251 Oxide film, 8, 157 Oxidising flame, 4 PALLADIUM, 187 Palmitic acid, 255 Paraffin hydrocarbons, detection of, 257 Paraffins, 253 Permanganic acid, 146 Persulphuric acid, 128, 183 Phenacetin, 287 Phenol, 229 Phenolphthalein, 152, 329 Phosphomolybdic acid, 190, 294 Phosphoric acid, 137 in mixtures, 86 , removal of, 87 , separation from arsenic acid, 138 Phosphorus, detection of, 141 in organic compounds, 204 Physical changes of oxides, 153 Picric acid, 294, 330 Platinum, 62, 167 Potassium, 94, 180 -bismuth iodide, 294 mercury iodide, 294 Precipitates, washing of, 22 Precipitation, 17 Primary amines, 246 Propyl bromide, 241 chloride, 241 iodide, 241 Purple of Cassius, 58 Pyridine, 282 Pyrogallol, 234 Pyrophosphoric acid, 139 QUINIDINE, 300, 310 Quinine, 299, 310 Quinoline, 283 RARER elements, 187 Reactions in solution, 12 of free fatty acids, 256 of the metals, 26 Reagents, 292 Reducing flame, 4, 158 Reinsch's test for arsenic, 48 Rhodium, 187 Rubidium, 187 SACCHARIN, 278 Salicin, 290, 310 Salicylic acid, 225, 230 Salts, 325 Scandium, 187 Schiff's reagent, 262, 329 Selenium, 187 Separation of nickel and cobalt, 83 Silicic acid, 135 Silver, 27, 170 group, 25, 33, 170 Sodium, 26, 94, 96, 101, 179 cobaltinitrite, 95, 326 Solubilities, 317, 319 Solution, theory of, 13 Spectroscope, 9 Stannic salts, 59 Stannous salts, 57 Starch, 277 paste, 329 Steam distillation, 330 Stearic acid, 255 Strength of reagents, 26 Index. 337 Strontium, 90, 178 from barium and calcium, 92, 178 Strychnine, 302, 310 Sublimates, 155 Sublimation, 3 Succinic acid, 222 Sulphide film, 8, 157 Sulphocyanic acid, 119 Sulphonal, 289 Sulphur acids, detection of, 133 Sulphur and nitrogen in organic com- pounds, 203 in organic compounds, 203 precipitation of, 171 Sulphuretted hydrogen, 131, 323 Sulphuric acid, 128, 184 Sulphurous acid, 129 Summary, 313 TABLE of alkaloid reactions, 310 of solubilities, 319 Tannic acid, 233 Tannin, 233 Tantalum, 187 Tartaric acid, 217, 222 Thalleoquinine, 299 Thallium, 187, 192 Theine, 305, 810 Theory of solution, 13 Thiocyanic acid, 119 Thiosulphuric acid, 132, 185 Thorium, 187 Tin, 56, 165, 173 Titanium, 187, 194 Toluene, 254 Treatment of substance insoluble in acids, 163 in solution, 162 to be analysed, 161 Trichloroacetic acid, 240, 249 Trimethyl xanthin, 305 Tungsten, 187 URANIUM, 187, 194 Urea, 284 Uric acid, 230 VANADIUM, 187, 191 Veratrine, 304, 310 WASHING of precipitates, 22 Water bath, 331 distilled, 320 YTTERBIUM, 187 Yttrium, 187 ZINC, 77, 175 Zirconium, 187 THE END. PRINTED BY WILLIAM CLOWES AND SONS, LIMITED, LONDON AND BECCLKS. THIS BOOK IS DUE ON THE LAST DATE STAMPED BELOW AN INITIAL FINE OF 25 CENTS WILL BE ASSESSED FOR FAILURE TO RETURN THIS BOOK ON THE DATE DUE. THE PENALTY WILL INCREASE TO SO CENTS ON THE FOURTH DAY AND TO $1.OO ON THE SEVENTH DAY OVERDUE. MAY 19 i943 LD if# LD 21-100m-7,'39(402s) YC 21857 THE UNIVERSITY OF CALIFORNIA LIBRARY