LIBRARY OF THE UNIVERSITY OF CALIFORNIA GIFT OF Class A MANUAL QUALITATIVE ANALYSIS. V The following new work, by the same autJtor, will shortly be published: THE SECOND STEP IN CHEMISTRY. The subjects treated of in this work will be taught in a series of progres- sive and practical exercises. The following are a few of the subjects: The specific gravity of gases. The correction of gases for temperature, pressure, and moisture. Combination by volume. Atomic volumes. The specific gravity of vapours. Application of the specific gravity of vapours to control the chemical analyses of substances. Unitary Notation. A MANUAL OF QUALITATIVE ANALYSIS. BY EGBERT GALLOWAY, F.O.S., PROFBSSOB OF PRACTICAL CHEMISTRY IN THE MUSEUM OF IRISH INI AUTHOB OF "THE FIRST STEP IN CHEMISTRY," ETC. THIRD EDITION. i llustrates an LONDON: JOHN CHURCHILL, NEW BURLINGTON STREET. MDCCCLXI, PRINTED BY J. E. ADLARD, BARTHOLOMEW CLOSE. PREFACE TO THE THIRD EDITION. IN this Edition I have given, in addition to other new processes, the photo-chemical methods of Cartmell and Bunsen. I have given Bunsen's paper on his blowpipe experiments in the appendix. I have also given various methods for the separation of the phos- phates and oxalates precipitated by ammonia. I trust the additions and improvements I have made in this Edition will render my work still more acceptable to the student. EGBERT GALLOWAY. DUBLIN; February, 1861. 117581 PREFACE TO THE SECOND EDITION. IN issuing a New Edition of this Manual, I will here briefly describe the scheme or plan of analysis developed in the Work, and the way in which the book ought to be used. In all other works on Qualitative Analysis with which I am acquainted, the properties of the bases and acids, and the application of these properties to the analysis of substances, are treated separately. As a consequence, the student, when he goes through the experiments on each base and acid, performs these illustrations of the properties without perceiving their use or application. In the part of the Work devoted to the analytical course, he is told what to do either by tables (as in the c Giessen Outlines/ and some other works), or, as in Fresenius, by a more tedious and, in my opinion, as defective a method. The principles upon which these instructions are based are not given with the instruc- tions, but in a separate chapter of the Work; and unless the student is able himself to unite the two the principles with the practical instruction he becomes a mere analytical machine. Students who can give their whole time and attention to the study of the science can, if they will, accomplish this ; but I have found by experience, that those who can only devote some five or PREFACE. Vll six hours in the week to the acquirement of the science fail to become intelligent analysts by this system. The system is very difficult, as well as defective ; it is so difficult, that those who employ it generally teach one thing, useless in itself, in order that they may teach another : they teach the student first to look for one acid arid one base a limitation which is not adopted in actual practice solely for the purpose of rendering the course in which they have to look for all the bases and acids less difficult. In the plan I have adopted, the properties of the different members of each group are contrasted by placing them in parallel columns; the advantage of this is, that the student, after he has performed the experiments, is able himself to devise methods for the detection and separation of the different membersT^it places him, in fact, in the position of a judge who has to decide some cause after having heard all the pleadings. It enables him also to judge for himself how many different methods might be adopted in the sepa- ration of substances; it therefore enlarges his views, and enables him to reason on the methods he adopts. This Manual is intended to be used in the following way: The student commences with the first group; and after he has performed all the experiments given in the table of that group, several analyses are given him, each of which he examines for the members of this group. When he can perform these practical exercises correctly, he commences the second group first performing the experiments in the group, and then analysing several solutions for the members of this group. When he can perform these correctly, he ex- Vlll PREFACE. amines several solutions for the members of the first and second groups. In this progressive way he passes through the groups ; so that by the time he has com- pleted them, he will have become an accurate analyst. In the former Edition I proposed, and partially car- ried out, the division of the third group of bases, by employing ammonia as a group reagent ; this alteration not only simplifies the subject, but it makes the plan of analysis taught in the laboratory more consonant with the methods adopted in actual practice. This alteration is fully carried out in this Edition, and a more complete description of the properties of the basic groups is given. I have also given, in this Edition, an outline of the special tests to be adopted in the detection of the acids, and considerable additions have been made in the Chapter on the Preliminary Exami- nation of Solids. I have also introduced a new feature at the very commencement of the book ; a series of experimental exercises are given, illustrating the prin- ciples upon which analytical operations are based, which it is intended the student should perform before he commences the groups. My aim in writing the book has been to furnish a suitable guide to the beginner ; and I confidently hope that this Edition will be found superior to the former in this respect, and that it is what I wish it to be a Student's Book. R. G. DUBLIN; Nov. 1357. PREFACE TO THE FIRST EDITION. THE increased attention which has of late years been given to Chemistry in this country has caused the production of several excellent works on Qualitative Analysis. The majority of these works have, however, been found better adapted for the advanced student than for the beginner. To supply the latter with a suitable Elementary Work is the object aimed at in the present Treatise. The Author having had ample opportunities, for some years past, of ascertaining the difficulties which oppose the student's progress in the study of Analysis, has endeavoured in the present little Work to obviate these, as much as possible, by simplifying the course of study. The peculiar arrangement adopted, whilst simplifying the study of this particular branch of Chemical Science, will afford the student the means of increasing his knowledge of General Chemistry. Although the Work professes to be a mere introduc- tion to the study of Analysis, several new processes have been described, when they appeared to be an improve- ment on those usually employed : thus, a new method is given for the detection of magnesia, and its separation X PREFACE. from the fixed alkalies. The separation of phosphoric and oxalic acids from the alkaline earths is rendered easier or more secure to the unpractised student, by the new process here recommended; and the deter- mination of tin and antimony is facilitated by a modi- fication of the process usually adopted. But, in im- proving processes which appeared to be defective, the Author has not forgotten that the main object of the Work is to present to the student a simple Introduc- tion to Qualitative Analysis. QUEENWOOD COLLEGE; October, 1850. CONTENTS. CHAPTEE I. PAGE Introduction ....... 1 Operations ....... 9 Reagents . . .... 18 Apparatus . . .27 Principles upon which Analytical Operations are founded . 27 How the Work ought to be Studied . . . .33 Sources of Error ....... 35 Systematic Course of Qualitative Analysis . . .36 Arrangement of the Results of the Analysis . . .38 CHAPTEE II. FIEST GEOtTP. Potash, Soda, Ammonia . . . .41 TABLE I. Behaviour of the Members of the First Group with the Special Reagents . . . . .44 The Precautions to be attended to in the Analysis of this Group . 45 Special Remarks ....... 46 APPENDIX TO THE FIEST GBOTJP. Lithia . . .50 SECOND GEOTJP. Baryta, Strontia, Lime, Magnesia . .. 52 TABLE II. Behaviour of the Members of the Second Group with the Special Reagents . . . . .55 The Precautions to be attended to in the Analysis of this Group . 58 Special Remarks . . . . . .59 Xii CONTENTS. PAGE THIED GBOUP. Oxide of Zinc, Oxide of Manganese, Oxide of Nickel, Oxide of Cobalt .... .66 TABLE III. Behaviour of the Members of the Third Group with the Special Reagents. .... .70 The Precautions to be attended to in the Analysis of this Group . 69 Special Remarks ....... 71 FOTTETH GEOUP. Alumina, Sesquioxide of Chromium, Sesqui- oxide of Iron, Protoxide of Iron . . .76 TABLE IV. Behaviour of the Fourth Group with the Special Reagents ....... 80 The Precautions to be attended to in the Analysis of this Group . 79 Special Remarks ....... 79 SECTION OF THE GEOUP. Phosphates of Alumina, Iron, and the Alkaline Earths, the Oxalates of Baryta, Strontia, and Lime ....... 84 TABLE V. Method for separating these Phosphates and Oxalates ....... 89 Precautions to be attended to in the Analysis of this Section . 88 APPENDIX TO THE FOUETH GEOUP. Sesquioxide of Uranium, Titanic Acid 93 FIFTH GEOUP. Protoxide of Tin, Binoxide of Tin, Oxide of Antimony, Arsenious Acid, Arsenic Acid, Teroxide of Gold, Binoxide of Platinum ..... 97 Precautions to be attended to in the Analysis of this Group . 98 Special Remarks ....... 99 .,"- SIXTH GEOUP. Oxide of Silver, Suboxide of Mercury, Oxide of Lead, Protoxide of Mercury, Oxide of Bismuth, Oxide of Copper, Oxide of Cadmium ..... 116 TABLE VI. Behaviour of the Sixth Group with the Special Reagents . . . . ... . 118 The Precautions to be attended to in the Analysis of this Group . 121 Special Remarks ...... 123 CONTENTS. Xlll CHAPTEE III. THE GENEEAL PEOPEETIES OE THE BASIC GEOUPS. PA.GE TABLE VII. Behaviour of the Basic Groups with, the General Eeagents ....... 134 Particular Observations regarding the Precipitates produced by the General Reagents, and the Precautions to be attended to in examining the Solutions .... 140 CHAPTER IV. PEOPEETTES OF THE ACIDS. General Properties of the Inorganic Acids . . . 149 TABLE VIII. Behaviour of the Inorganic Acids with the Gene- ral Reagents ...... 156 Special Tests for the Inorganic Acids . . . .155 Special Properties of the Inorganic Acids . . 159 Carbonic Acid ....... 159 Hydrosulphuric Acid ...... 161 Chromic Acid ....... 163 Sulphuric Acid ....... 164 Boracic Acid . . . . . . . . 165 Phosphoric Acid ....... 166 Oxalic Acid 171 Hydrofluoric Acid ...... 172 Silicic Acid ....... 175 Hydrochloric Acid . ... . . .178 Hydrocyanic Acid ...... 178 Hydrobromic Acid ...... 180 Hydriodic Acid ....... 182 Nitric Acid . 184 Chloric Acid . . . . . . .185 General Properties of the Organic Acids .... 187 Special Tests for the Organic Acids .... 189 Tartaric Acid 192 XIV CONTENTS. PAGE TABLE IX. Behaviour of the Organic Acids with the General Reagents ....... 190 Citric Acid ....... 192 Malic Acid 193 Benzoic Acid ....... 194 Succinic Acid ....... 195 TannicAcid ....... 195 Gallic Acid 196 Acetic Acid ....... 196 Formic Acid ....... 196 Uric Acid 197 CHAPTER V. EXAMINATION OF LIQUIDS AND SOLIDS. Preliminary Examination of a Liquid .... 198 Preliminary Examination of Solid Substances . . . 201 TABLE X. Course of Blowpipe Operations to which Substances must be submitted before commencing their Analysis in the humid way . . . . . . 212 The Divisions into which Solid Substances are arranged . 216 APPENDIX . . . . . . . 224 Detection of Arsenic and Antimony in the Presence of Tin . 224 Separation of Cadmium from Copper .... 225 Supports for Fusions and Reductions by the Blowpipe . . 226 Fusibility of Minerals . . . . . .230 Bunsen's Blowpipe Experiments ..... 232 QUALITATIVE ANALYSIS. CHAPTEE I. INTRODUCTION OPERATIONS REAGENTS APPARATUS THE PRIN- CIPLES UPON WHICH ANALYTICAL OPERATIONS ARE FOUNDED How THE WORK OUGHT TO BE STUDIED SOURCES OF ERROR SYSTEMATIC COURSE OP QUALITATIVE ANALYSIS ARRANGEMENT OP THE RESULTS OF THE ANALYSIS. 1. QUALITATIVE ANALYSIS enables one to discover the composition and properties of any unknown substance ; and it teaches one the mode of separating substances from each other. 2. Only those substances, which are commonly met with in nature, or which have some useful application, are treated of in this work ; the following is a list of them : 3. BASES. Potash, soda, ammonia, baryta, strontia, lime, magnesia, oxide of manganese, oxide of zinc, oxide of nickel, oxide of cobalt, the oxides of iron, sesquioxide of chromium, alumina, oxide of uranium, oxide of lead, oxide of silver, the oxides of mercury, oxide of bismuth, oxide of copper, oxide of cadmium, oxide of gold, oxide of platinum, oxide of anti- mony, the oxides of tin. 4. IWOBGANIC ACIDS. Arsenious acid, arsenic acid, chromic acid, carbonic acid, hydrosulphuric acid, hydro- 1 Z INTRODUCTION. cyanic acid, sulphuric acid, boracic acid, phosphoric acid, oxalic acid, hydrofluoric acid, silicic acid, hydrochloric acid, hydrobromic acid, hydriodic acid, nitric acid, chloric acid. 5. OKGANIC ACIDS. Tartaric acid, citric acid, malic acid, benzoic acid, succinic acid, tannic acid, gallic acid, uric acid, acetic acid, formic acid. 6. Each of these bases and acids is A SOLID, A LIQUID, or A GAS ; in whichever state the base or acid exists, it must be soluble or insoluble in water. If the base or acid is A SOLID, and insoluble, it will, on being sepa- rated from any of its soluble compounds, float in or upon the water or else fall to the bottom ; in either case it is called a precipitate; if it is soluble, it will remain dissolved when separated from any of its soluble com- pounds. If it is a LIQUID, and insoluble, it will float upon the water if lighter than that liquid, and if heavier, the water will float upon it ; if it is soluble, it will mix with the water. If it is A GAS and insoluble, it will, on being separated from any of its soluble or insoluble compounds, escape into the air ; if it is soluble, it will remain dissolved in the water, if there is sufficient for its solution if there is not sufficient, the excess will escape into the air ; if it is dissolved by the water, it will most probably escape when the liquid is warmed, being expelled by the heat. 7. The bases, with the exception of ammonia, are all solid and non-volatile bodies. Potash, soda, ammonia, baryta, strontia, and lime, are soluble in water ; the rest of the bases are insoluble in that liquid. The compound pro- duced by the union of a base with an acid is called a salt. Many of the salts of the insoluble bases are soluble in water. The salts of the gaseous base, ammonia, and the salts of the gaseous acids, are solids ; some of these solid salts are soluble, some are insoluble, in water. EXERCISES. 3 8. If to a solution of any of the soluble salts of the insoluble bases a soluble base is added, the soluble base will take away the acid from the insoluble base ; the latter viz., the insoluble base being set free, will con- sequently precipitate, on account of its insolubility in the liquid. We may here observe, that many of the bases, when they are set free in this manner, combine with water ; this compound of the base and water is termed the hydrate of the base, whichever base it may be. The three following experiments are given to teach the student the principle just stated ; he must, therefore, carefully perform the expe- riments according to the directions : EXEECISES. 9. Dissolve, by the aid of heat, two or three grains of alum, which is a compound containing sulphate of alumina, in a test-tube half filled with water ; add ammonia to the solution after the alum is dissolved, and, after the addition, close the mouth of the test-tube with the thumb, and then shake the liquid in it very violently. If the liquid smells of ammonia after the agitation, a sufficient quantity has been added ; but if it does not, a further quantity of ammonia must be added, and the liquid again shaken ; and this must be repeated until the liquid smells of ammonia, after it has l)een well shaken. The ammonia deprives the alumina of its acid ; the alumina, on being set free, combines with water this compound of alumina and water appears under the form of a white, gelatinous solid, insoluble in water. 10. Dissolve two or three grains of sulphate of cop- per in a test-tube half filled with water; boil the so- lution, by means of a spirit or gas lamp, and add to the boiling liquid a solution of caustic soda, until it 4 INTRODUCTION. turns red litmus paper blue. After tlie caustic soda has been thoroughly mixed with it by agitation, in the way described in the first exercise (par. 9), oxide of copper, which is of a black colour, will precipitate, owing to its being deprived of the sulphuric acid by the soda. If the oxide of copper is precipitated under the boiling point, it combines with water, forming hydrate of the oxide, which is of a blue colour. 11. Dissolve two or three grains of sulphate of zinc in a test-tube half filled with water ; add ammonia, drop by drop, until a white precipitate, which is hydrate of zinc, is formed ; then continue to add the ammonia until the precipi- tate disappears. The precipitate disappears, because the hydrate of zinc is soluble in ammonia ; it is also soluble in the other alkalies, soda and potash ; therefore, if caustic soda had been added, a precipitate would have formed, as in the case of the ammonia, which, on a further addition of soda, would have disappeared. 12. When substances are employed in analysis in the way ammonia and caustic soda have been employed in the above experiments, they are called tests, or reagents , and the phe- nomena produced by them are termed reactions. The re- agents are either acids, bases, or salts ; and the reaction consists sometimes in a change of colour, sometimes in the production of effervescence, but most frequently by the formation of a precipitate, which, in many cases, possesses a characteristic colour. Reagents may be divided into two classes general and special. The general reagents are employed to divide substances into families or groups, and the special reagents to detect the individual members of a group. A special reagent is said to be characteristic, when it produces a reaction so decisive that it admits of no mis- take. A reagent is called sensitive, or delicate, if its EXERCISES. 5 action is clearly perceptible with a very minute quantity of the substance tested for. The student must be very par- ticular in always mixing thoroughly the reagent with the solution to which he has added it, and not simply content himself by adding it (as is generally the case with begin- ners), without attempting, by agitation, to incorporate the two fluids. The way for incorporating them has been fully described in the first experiment (par. 9) ; it only remains for us to guard the student against the accident of losing the liquid, which is likely to occur, when the liquid is hot, unless the operator keeps his thumb firmly fixed upon the mouth of the test-tube ; because the air in the upper part of the test-tube, in passing over the heated liquid, becomes expanded, and would therefore expel the liquid, unless the mouth of the tube was kept firmly closed. 13. If to any salt of ammonia one of the soluble bases is added, the latter will deprive the ammonia of its acid ; consequently, the ammonia will be set free, which will be perceived by the smell. The soluble bases set the ammonia free from its salts in the solid, state, as well as in solution ; heat assists the liberation in each ease. If, to any salt of the volatile acids, an acid having a stronger affinity for the base of the salt is added, the volatile acid will be set free ; the decomposition takes place as well when the salt of the volatile acid is insoluble as when it is soluble, in water. The following experiments illustrate the principles here stated. EXEBCISES. 14. Dissolve two or three grains of chloride of ammo- nium in a test-tube containing water ; add to it some caustic soda solution, and then warm the liquid in the tube; ammonia will be set free in the gaseous state. It will be known, when it is in the free state, by the smell. INTRODUCTION. 15. Mix two or three grains of dry, powdered chloride of ammonium very intimately with a like quantity of slaked lime; place the mixture in a crucible, and warm it by means of a spirit or gas lamp ; ammonia will be set free as in the previous experiment. 16. Dissolve a few grains of carbonate of soda in water ; add to the solution sulphuric, hydrochloric, or nitric acid each of these acids deprives the carbonic acid of its base : it is consequently set free ; and, by its escaping through the water into the atmosphere, causes an effervescence. 17. Place a few grains of chalk or marble at the bottom of a test-tube ; cover it with water, and then add to it hydrochloric or nitric acid either of these acids deprives carbonic acid of its base, consequently it is set free ; and by its evolution, produces effervescence, as in the previous experiment. Hydrochloric and nitric acids are to be pre- ferred to sulphuric acid in this experiment, because the former give with lime, salts soluble in water ; but the latter produces with that base, a ait, sulphate of lime, sparingly soluble in water ; the greater part of the sulphate of lime therefore falls down, and thus shields the undecomposed chalk or marble from the acid. 18. The student will see by these two courses of experi- ments, that salts are decomposed by adding to them either acids or bases, provided the acids or bases added have stronger affinities than the acids or bases in the existing compound ; and that, according as acids or bases are added, so acids or bases are set free. Thus, ammonia and alumina are liberated from their salts on the addition of a stronger base, and carbonic acid is liberated from its combinations on the addition of a stronger acid. 19. All the salts of ammonia containing volatile acids, on being heated volatilize completely, either with or without EXERCISES. 7 decomposition ; but the ammonia salts of the non-volatile acids viz., phosphoric, boracic, and silicic acids are de- composed by heat ; the ammonia escapes, but the non-vola- tile acid remains behind. The salts of the volatile acids do not volatilize, on being heated, unless ammonia is the base ; the acid may be expelled by the heat, but the base with which it was combined remains behind, with the exception of ammonia. The following experiments are given to illus- trate the principles here stated : 20. Place two or three grains of powdered chloride of ammonium in a crucible ; heat the crucible, by means of a Berzelius spirit or gas lamp, until all fuming ceases. The ignition must be continued so long, because the fumes are the volatilizing salt ; and therefore, until they cease, all the ammoniacal salt is not expelled. If the chloride of ammo- nium employed is perfectly pure, there ought to be no residue after the fuming ceases. 21. Place two or three grains of powdered chalk in a crucible ; heat the crucible for some time by means of a Berzelius spirit or gas lamp. After the lamp is removed, and the crucible has become cold, add some water to the ignited chalk, and then test the water with red litmus paper it will change the colour of the paper from red to blue, showing that some of the carbonic acid has been expelled by the heat. 22. If, to the solution of any salt, an acid, or a salt con- taining an acid, is added, which acid would produce, by combining with the base of the salt in solution, an insoluble salt, it will always take away that base from all other acids which form with that base soluble salts, and unite with it, producing the insoluble salt ; also, if to the solution of any salt, a base, or a salt containing a base, is added, which base would produce by combining with the acid of the salt in 8 INTRODUCTION. solution an insoluble salt, it will always take away that acid from all other bases which form with that acid soluble salts, and unite with it, producing the insoluble salt; for in whatever ivay the most insoluble substances can be gene- rated, decomposition occurs. The following experiments are given to illustrate the principles here stated : EXEECISES. 23. Dissolve two or three grains of nitrate of baryta in a test-tube half filled with water ; add to the solution a few drops of dilute sulphuric acid; the sulphuric acid will deprive the nitric acid of the baryta, by combining with that base, and forming with it an insoluble salt, sulphate of baryta. 24. Dissolve two or three grains of nitrate of baryta, as before ; add to the solution a solution of sulphate of potash sulphate of baryta and nitrate of potash will be produced. The former, being insoluble in water, will be precipitated ; the latter, being soluble, will remain in solution. 25. Dissolve two or three grains of common salt, chloride of sodium, in water ; add to the solution a few drops of nitrate of silver chloride of silver and nitrate of soda will be produced. The former, being insoluble in water, will be precipitated ; the latter, being soluble, will remain in solution. 26. Dissolve two or three grains of sulphate of potash in water ; add to the solution some baryta water sulphate of baryta will be formed, and potash set free. The former, being insoluble in water, will be precipitated ; the latter, being soluble, will remain in solution. 27. Before attempting to show how these different prin- ciples are employed in analysis, we must describe the prin- OPERATIONS. 9 cipal operations employed in analysis, and give a list of the reagents and apparatus required. OPEKATIONS, SOLUTION. 28. Many solid bodies, when placed in contact with a liquid, possess the property of becoming thoroughly incor- porated with it, by passing into the fluid state. This change is expressed by the term solution, and the liquid in which the solid dissolves is called the solvent. 29. Solutions are of two kinds, simple and chemical. A simple or mechanical solution is the mere dissolving of a solid in a liquid, no chemical change occurring in either ; on the removal, therefore, of the liquid by evaporation, the solid is obtained in its original condition. Common salt dissolved in water affords an illustration of a simple solution. 30. In a chemical solution the solid and fluid combine together, forming an entirely new substance, from which the original solid and fluid can no longer be extracted by mere mechanical operations. Chalk dissolved in hydro- chloric acid affords an example of a chemical solution. 31. The solvent in a simple solution cannot dissolve un. limited quantities of the substance to be dissolved ; it can only dissolve certain fixed quantities of the solid, the amount varying with the kind of solid, and the amount of any par- ticular solid varying with the solvent. When the solution contains as great a quantity of the solid matter as it is capable of dissolving, it is said to be saturated. A solution is known to be saturated when fresh solid matter of the same sort, on being put into it, remains undissolved. " But M 10 OPERATIONS. as fluids dissolve generally larger quantities of a substance the higher their temperature, the term saturated, as applied to simple solutions, is only relative, and refers invariably to a certain temperature." From the tendency of heat to diminish the force of cohesion, it naturally results that the solubility of most bodies is increased by heat j this, however, is not always the case ; some bodies, as common salt, are equally soluble in water at all temperatures, whilst, in other cases, the solubility is greater at particular temperatures than either above or below them. The liquids employed as solvents in simple solutions are water, alcohol, ether, oils, &c. The most important solvent is water ; the others are only resorted to when the substance to be dissolved is in- soluble in that liquid. 32. "A chemical solution may be accelerated by eleva- tion of temperature ; and this is, indeed, usually the case, since heat generally promotes tlje action of bodies upon each other. Eut the quantity of the dissolved body remains always the same in proportion to a given quantity of the solvent, whatever may be the difference in temperature the combining proportions of substances being invariable, and altogether independent of the gradations of tempera- ture.' 7 The liquids which produce chemical solutions are, in most cases, either acids or alkalies. 33. The process of solution is conducted either in evapo- rating dishes or test-tubes. The latter are generally em- ployed when the quantity of the solid operated upon is small. The more minutely any substance is powdered, the more its solution is facilitated. Solid substances are gene- rally reduced to powder in mortars. PBECIPITATIOF. 34. It is frequently necessary to remove a constituent OPERATIONS. 11 it may be either the metal or metalloid of some binary compound, or the acid or base of some ternary one from the liquid in which the compound is dissolved. This is effected by making it a constituent of some new compound, which is insoluble in the liquid in which the original com- pound was dissolved. This operation, which is called pre- cipitation, is owing, therefore, to the formation of a new solid substance, which is insoluble in the liquid in which its elements were dissolved, and which falls, or is precipi- tated to the bottom, owing to the solid being specifically heavier than the liquid. Occasionally, however, it is lighter, and floats upon the surface. In both cases, the insoluble substance is called the precipitate, and the substance pro- ducing the precipitation is termed the precipitant. 35. Precipitation is an operation which is constantly practised in the preparation of substances in the manufac- tory as well as in the laboratory. We also resort to it in the laboratory, for the purpose of detecting and separating substances from one another. Thus, if we had a solution which might contain some compound of baryta and lime : to ascertain whether baryta was present, and, if it was, to separate it from the solution, before ascertaining whether lime was likewise present, we might add a soluble chromate if baryta was present, the chromic acid would combine with it ; and as chromate of baryta is insoluble in water, it would precipitate, whilst chromate of lime, being soluble, would remain in solution. If we were now to add to the clear filtered solution some soluble oxalate, oxalate of lime, being insoluble in water, would precipitate. If the chro- mate produced no precipitate, there could be no baryta ; if the oxalate produced no precipitate, after having separated the baryta (if present), lime must be absent. 36. Precipitates are classified, according to their appear- 12 OPERATIONS. ances, into crystalline, pulverulent, flocculent, curdy, and gelatinous. The terms turbid and turbidity are applied when the precipitate is so small that it cannot be distin- guished, except by impairing the transparency of the fluid. 37. The separation of precipitates from liquids is, with some few exceptional cases, much assisted by the applica- tion of heat and agitation. The operation, when performed as an analytical operation, is conducted in test-tubes, which, from their transparency, admit of an inspection of the process. FILTBATION AND DE CAPTATION. 38. These terms are applied to a modification of the same operation viz., the mechanical separation of fluids from solid matter mixed with them. riLTEATIOB". 39. In filtration, the separation of the fluid from the solid matter is accomplished by passing it through filtering paper of a proper size and shape, supported in a funnel. The pores of the paper permit the fluid to pass through ; whilst the solid matter, being prevented, remains behind. 40. To prepare a filter, take a small piece of filtering paper (the best white blotting paper), and fold it twice, from side to side ; then round off with scissors the project- ing corners, so that the paper may fall wholly within the funnel ; moisten the paper when placed within the funnel, and then carefully pour the liquid to be filtered upon it. The funnel, when large quantities have to be filtered, is supported in one of the rings of the retort stand ; but in the ordinary nitrations required in qualitative analysis, it may rest on the. mouth of a test-tube. The filter should OPERATIONS. 13 not project over the edge of the funnel, especially if the substance in the filter requires to be washed. Should the first portions of the liquid which pass through the filter not be perfectly bright, which is frequently the case, they must be returned to the filter, and this must be repeated until it is perfectly bright. The liquid which passes through the filter is called the filtrate. DECANTATION. 41. "When the solid particles are very heavy, the" super- natant liquid can be perfectly separated, without passing it through a filter, by simply inclining the vessel, so as to allow the fluid to pass away unattended by the precipitate? or by removing the fluid by a syphon. 42. The separation in this way of a solid from a fluid is called decantation. 43. Too great attention cannot be paid to the washing of precipitates when they are required for further examination. After the precipitate has been thrown upon the filter, a stream of water must be projected from the wash-bottle upon it, from time to time, until it is perfectly freed from soluble matter ; this is sooner accomplished if hot water be employed. Hot water may therefore be used in all cases unless the contrary be expressly stated. EYAPOEATION. 44. This process is used for the purpose of obtaining matter in a solid state from solutions. By the aid of heat, the volatile fluid passes off" in the gaseous form, whilst the non-volatile matter remains behind. 45. If the evaporation be conducted slowly, the solid matter will frequently, on being deposited, assume a crys- 14 OPERATIONS. talline form. The operation is then termed crystalliza- tion. 46. This operation is frequently conducted for the pur- pose of obtaining a liquid in a more concentrated form, by volatilizing a portion only of the fluid. Vessels are con- structed expressly for the purpose, called evaporating dishes. DISTILLATION. 47. This operation, like the former one, consists in the separation of a volatile from a less volatile fluid, or in the separation of a liquid from a solid. But in evaporation no attention is paid to the volatilized fluid, whilst in distillation it is frequently the only substance required. A distilling apparatus is therefore so constructed as to allow the evapo- rated fluid to be collected, which is called the distillate. It consists of three parts : 1. A vessel in which the liquid to be distilled is heated. 2. An apparatus in which the vapour is cooled and condensed. 3. A vessel for receiving the dis- tillate. 48. On a small scale, glass retorts are employed ; but in the distillation of large quantities, copper stills are usually substituted for them. IGNITION. 49. By this operation volatile is separated from non- volatile solid matter ; it requires the application of a high temperature, and must be conducted in crucibles. This process is therefore an evaporation of solid bodies. SUBLIMATION. 50. By sublimation we effect not only the separation of volatile from less volatile solid matter, but by cooling we OPERATIONS. ] 5 bring the volatile matter back to the solid state, and in this state it is called the sublimate. 51. This process is therefore a distillation of solid bodies. FUSION. 52. This term is applied to the liquefaction of a solid, by the mere application of heat. It is also used for the decom- position of solids in the " dry way." 53. By this operation we are able to resolve insoluble substances into forms which admit of solution. This is accomplished by causing their proximate elements to unite with bodies the compounds of which will be capable of solu- tion. Thus sulphate of baryta, which, from its insolubility both in water and acids, resists the action of reagents in the fluid state, is decomposed in this way. It is mixed with three or four times its own weight of dry carbonate of soda, and the mixed mass exposed in a crucible for some time to a high temperature. The two salts mutually suffer decom- position when placed in these conditions, the sulphuric acid passing over to the soda whilst the carbonic acid unites with the baryta. If the fused mass be treated with water, the sulphate of soda dissolves in that liquid, whilst the carbonate of baryta, being insoluble, remains behind. This substance, after being well washed, may be dissolved in hydrochloric or nitric acid. The decomposition of substances in the dry way requires, in most cases, a higher temperature than that which a small spirit lamp affords. "When a limited amount of heat can only be obtained, it is better to employ a mixture of equal parts of carbonate of soda and carbonate of potash, instead of the former salt alone. DEFLAGBATIO1S". 54. This term is applied to all decompositions attended 16 OPERATIONS. with noise. It also includes tlie oxidation of a substance by a reagent, in the dry way, on account of the slight explo- sions which frequently attend this kind of oxidation. THE BLOWPIPE. 55. The mouth blowpipe is a small instrument which is employed for directing a fine and continuous stream of air into the flame of a wax candle or oil lamp. By the flame thus produced two reverse chemical operations may be per- formed, viz., oxidation and reduction. The flame is there- fore distinguished by these properties into the outer or oxidizing flame and the inner or reducing flame. 56. In the oxidizing flame, the inflammable vapour is in a state of complete combustion, being supplied and mixed with an excess of atmospheric air. From the high tempe- rature resulting from the perfect combustion of the inflam- mable vapour, and likewise from the excess of oxygen, all the requisite conditions are present for causing substances with an affinity for that element to enter into union with it. 57. In the reducing or deoxidizing flame the inflammable vapour is in an incomplete state of combustion, due to a deficiency of atmospheric air; hence any metallic oxide placed in this portion of the flame is robbed of its oxygen by the inflammable vapour, which requires that element for its combustion. 58. A reducing flame is obtained by keeping the nozzle of the blowpipe in an inclined direction, parallel to the surface of the wick, and just touching the exterior surface of the flame. An oxidizing flame is obtained by keeping the nozzle of the blowpipe at the same inclination as in the former case, and introducing it into the flame to about one third the breadth of the wick, at such a distance only from the OPERATIONS. 17 surface of the latter as to obtain a clear, unbroken flame. A weak blast of air is only required for the reducing flame, but a strong blast is required for the oxidizing flame. 59. The colour of the reducing flame is bright yellow if an oil lamp or candle is used ; but if gas is used, it should be of the same blue colour as the centre of the oxidizing flame. The colour of the oxidizing flame in all cases is a pale-blue colour, almost invisible by daylight. 60. " "When any substance is submitted to the action of the reducing flame, it should be so held as to be entirely surrounded by the reducing flame, and protected from the oxidizing action of the surrounding atmosphere ; but this condition being fulfilled, it should be held as near as possible to the point of the flame, in order to gain the greatest amount of heat, and prevent any deposition of soot, which would shield the substance from the action of the flame, and would be occasionally attended with other disadvantages." 61. When a substance is submitted to the action of the oxidizing flame, it should be held just beyond the point of this flame if a candle or oil lamp is used ; but if gas is used, it should be held at a considerable distance (viz., one half to three quarters of an inch) beyond the point of the visible flame.* 62. " As the current of air which is supplied ought to be continuous, its production requires some attention and address. The air is not blown directly from the lungs, but is forced from the mouth by means of the cheeks. The difficulty consists in inspiring and expiring through the nose, while a continued stream escapes from the mouth. This may be attained by attention to the following direc- * In order to exercise himself in the manipulation of the blowpipe flame, the student will do well to practise the reactions afforded by the oxides of manganese and copper, as described in the par. " On the Treatment with Borax," and the corresponding part of the table on blowpipe operations. 18 REAGENTS. tions : Inflate the mouth fully, and then, with the lips firmly closed, and the back of the mouth closed by the tongue, breathe freely through the nostrils. While the respiration proceeds, and the mouth is inflated, allow a little air to escape through a very minute opening between the lips, renewing the supply in the mouth by occasionally admitting air from the lungs without interfering with the process of respiration through the nose." Parnell. In attempting this the student will not, probably, be immediately suc- cessful, but a few days' persevering practice will enable him entirely to master this primary difficulty. EEAGENTS. 63. LIST OF THE BEAGENTS EMPLOYED IN THE FLUID STATE. 1. Hydrochloric acid (muriatic acid), if perfectly pure, leaves no residue when evaporated. The substances with which it is generally contaminated are iron, arsenic, and sulphuric acid. Dilute one part of the concentrated acid with four parts of water. 2. Nitric acid (aqua fortis), when free from non- volatile matter, leaves no residue on evaporation. The impurities often found in it are hydrochloric and sulphuric acids. Dilute one part of the concentrated acid with five of water. 3. Nitro-liydrochloric acid (aqua regia) is prepared by adding four parts of concentrated hydrochloric acid to one of concentrated nitric acid. This test is employed in an undiluted state. 4. Sulphuric acid (oil of vitriol) frequently contains both arsenic and lead, and not unfrequently nitrous acid. The REAGENTS. 19 lead is deposited to a great extent when the acid is diluted, sulphate of lead being less soluble in dilute than in con- centrated sulphuric acid. The dilute acid is prepared by adding four parts of water to every one of the concentrated acid. 5. Tartaric acid is generally sufficiently pure for analytical purposes. As it undergoes decomposition in solu- tion, a small quantity only should be prepared at a time. For use, dissolve one part, by weight, of acid, in two parts, by measure, of water. 6. J3itartrate of soda is prepared by dissolving a quantity of tartaric acid in water, dividing the solution into two equal parts, and neutralizing one exactly with carbonate of soda, and then adding the neutralized portion, and after- wards evaporating the whole solution until the bitartrate crystallizes. For use, make a saturated solution. 7. Acetic acid, when employed in analysis, ought to be free from non-volatile matter and sulphuric acid. Dilute one part of the acid with four parts of water. 8. Hydrosulphuric acid (sulphuretted hydrogen) is pre- pared by adding to sulphide of iron, in an appropriate apparatus, dilute sulphuric or hydrochloric acid. The sul- phuretted hydrogen is liberated in its gaseous state, and may be passed through any solution under examination ; or a solution of the gas may be obtained by passing it through pure water. As this solution very soon decomposes by contact with the atmosphere, it ought to be prepared very frequently, and kept in well-stoppered bottles. Sulphide of iron, from which hydrosulphuric acid is ob- tained, is prepared by projecting a mixture of thirty parts of iron filings with twenty-one of flowers of sulphur, in small portions at a time, into a red-hot crucible, replacing 20 REAGENTS. the cover after each addition. When the whole has been added, the ignition must be continued for a short time, until the excess of sulphur has been dissipated. 9. Sulphurous acid is prepared by acting upon copper or charcoal with sulphuric acid. For this purpose small pieces of charcoal are introduced into a flask, with from six to eight times their weight of sulphuric acid, and a mo- derate heat applied. The evolved gas must be conducted into cold water until it is no longer absorbed. On account of the great tendency which this reagent has to absorb more oxygen, and become converted into sulphuric acid, it must be preserved in well-stoppered bottles. 10. Chlorine gas is prepared by introducing into a flask bne part of peroxide of manganese along with four parts of hydrochloric acid ; the liberation of the chlorine is assisted by a gentle heat. A solution of the gas may be prepared by passing it into cold water. Chlorine water must be kept in well-stoppered bottles, and excluded from the light. 11. Oxalic acid. Dissolve one part, by weight, of the acid, in twenty parts, by measure, of water. 12. Oxalate of ammonia must be free from sulphuric acid. Dissolve one part, by weight, of the salt, in twenty parts, by measure, of water. 13. Ammonia ought to be free from non-volatile matter, and also from carbonic, sulphuric, and hydrochloric acid. Dilute one part of the strong ammonia with four of water. 14. Chloride of ammonium is frequently contaminated with iron, from which it ought to be entirely free. Dissolve one part, by weight, of the salt, in ten parts, by measure, of water. 15. Sulphide of ammonium (hydrosulphuret of ammonia) is prepared by passing hydrosulphuric acid through liquid REAGENTS. 21 ammonia until it no longer produces a precipitate in a solu- tion of magnesia. Dilute one part with three of water. 16. Carbonate of ammonia must be free from non-volatile matter, and likewise from sulphuric acid. Dissolve one part, by weight, of the salt, in four parts, by measure, of water, and add one measure of ammonia. 17. Arscniate of ammonia is prepared by neutralizing arsenic acid with carbonate of ammonia, and evaporating to dryness.. Dissolve one part, by weight, of the salt, in ten parts, by measure, of water. Arsenic acid is prepared by dissolving arsenious acid in nitric acid, mixed with a little hydrochloric acid, evapo- rating the solution to dryness, and igniting somewhat below a low red heat, until all nitric acid is expelled. 18. Molybdate of ammonia. Digest molybdic acid in ammonia until complete solution is effected; filter the colourless fluid. Solution of molybdate of ammonia, mixed with nitric acid or hydrochloric acid until the precipitate which forms at first is redissolved, must remain colourless upon boiling. If it acquires a yellow tint, the reagent con- tains phosphoric acid, and is unfit for use (supposing always, of course, that the hydrochloric or nitric acid was perfectly pure). 19. Sulphate of potash. Dissolve one part, by weight, of the salt, in two hundred parts, by measure, of water. 20. Nitrite of potash is prepared by fusing one part of nitrate of potash in an iron pan, then adding two parts of lead, and keep stirring the mixture with an iron rod. The lead oxidizes in a great measure, even at a dull-red heat, changing to a yellow powder. To oxidize the last remaining particles of the metal, increase the heat to visible redness. 22 REAGENTS. The mixture generally takes fire ; there is, however, no dan- ger, at least when no more than a quarter of a pound of ni- trate of potash has been used. Let the mass cool, and then treat it with cold water to dissolve out the soluble part ; filter this solution, and conduct carbonic acid into the filtrate. This serves to precipitate nearly the whole of the oxide of lead that has passed into the solution ; a little sulphide of hydrogen will remove the remainder. Filter again, and evaporate the filtrate to dryness, stirring the mass towards the end of the operation ; heat the dry residue to fusion, to destroy any hyposulphite of potash that may have been formed. Dissolve one part of the fused mass in two parts of water. 21. Ferrocyanide of potassium (yellow prussiate of potash) . Dissolve one part, by weight, in twelve, by mea- sure, of water. 22. Ferricyanide of potassium (red prussiate of potash). Dissolve one part, by weight, of the salt, in twelve parts, by measure, of water. 23. Sulphocyanide of potassium. Dissolve one part of the salt in ten parts of water. 24. Chromate of potash must be free from sulphuric acid. Dissolve one part, by weight, in eight parts, by measure, of water. 25. Caustic soda is prepared by dissolving one part, by weight, of carbonate of soda, in twelve parts, by measure, of water, and boiling the solution in a clean iron pan. Hy- drate of lime must be added in small portions to the boiling liquid, until hydrochloric acid causes no effervescence in a portion of the liquid. "WTien this point has been attained, the pan must be removed from the fire, and the precipitate REAGENTS. 23 allowed to subside. The supernatant liquid must then be drawn off by means of a syphon, or passed through a filter of bleached linen, and the filtrate evaporated rapidly over a quick fire until it has been reduced to half its original bulk. On supersaturating a portion of the liquid with hydro- chloric acid, no, or only a slight, effervescence should take place. The solution must be kept in well-stoppered bottles. 26. Carbonate of soda must contain no sulphuric or hydrochloric acid. Dissolve one part, by weight, of the salt, in ten parts, by measure, of water. 27. Phosphate of soda must form no precipitate with ammonia. Dissolve one part, by weight, of the salt, in ten parts, by measure, of water. 28. Acetate of soda is made by adding acetic acid to a concentrated solution of carbonate of soda until all effer- vescence ceases. This solution must be free from sulphuric acid. Dilute one part of the concentrated solution with four parts of water. 29. Chloride of larium. Dissolve one part of this salt in ten parts of water. 30. Nitrate of baryta. Dissolve one part of this salt in ten parts of water. 31. Lime water is made by digesting recently prepared hydrate of lime for some time with cold distilled water, with frequent agitation of the mixture ; allow the undis- solved portion of the lime to subside, decant subsequently, and keep the clear fluid in well-stoppered bottles. 32. Chloride of calcium is made by dissolving pure carbo- nate of lime in dilute hydrochloric acid ; the solution thus obtained must be neutral to test-paper. 24 REAGENTS. Dilute one part of the concentrated solution with five parts of water. 33. Sulphate of lime (gypsum). Dissolve as much of the salt as the water will take up. 34. Sulphate of magnesia (Epsom salts). Dissolve one part in eight of water. 35. Per chloride (sesquichloride) of iron is prepared by dissolving recently precipitated and well-washed peroxide of iron in hydrochloric acid. It must not contain any free acid. 36. Acetate of lead. Dissolve one part, by weight, of the salt, in ten parts, by measure, of water. 37. Subnitrate of mercury is made by heating gently in a small flask nine parts of nitric acid in conjunction with ten parts of mercury, until the disengagement of nitrous fumes ceases ; the solution is then boiled for some time with the undissolved portion of the mercury, care being taken to replace the water lost by evaporation. The crystals, which separate on the cooling of the liquid, are dissolved in twenty parts of cold water, slightly acidulated with nitric acid. The fluid is then filtered, if necessary, and the filtrate kept in a glass bottle, the bottom of which is covered with mercury. 38. Chloride of mercury. Dissolve one part of the salt in sixteen parts of water. 39. Sulphate of copper. Dissolve one part of the pure crystallized sulphate in ten parts of water. 40. Nitrate of silver. Dissolve one part, by weight, of the salt, in twenty parts, by measure, of water. 41. Nitrate of cobalt. Dissolve one part in ten parts of water. 42. Solution of indigo. Heat one part of indigo, in powder, with six parts of fuming sulphuric acid. Eor use, REAGENTS. 25 dilute the solution obtained with just sufficient water to make the fluid appear of a light-blue colour. 43. Distilled water ought always to be employed in all the above solutions and in all analytical operations. It should leave no residue on evaporation, and should give no precipitate or even turbidity with chloride of barium, nitrate of silver, oxalate of ammonia, or lime water. 44. Reagent papers. Blue litmus paper serves to detect the presence of free acids or of acid salts in fluids, since they change the blue colour to red. Reddened litmus paper serves to detect the presence of free alkalies,* and of earths and salts possessing an alkaline reaction, by changing the red colour to blue. Turmeric paper aids, like reddened litmus paper, in the detection of free alkalies, &c., by changing its yellow colour to brown. Preparation of Hue litmus paper. " Digest one part of litmus of commerce with six parts of water, and filter the solution ; divide the intensely blue filtrate into two equal parts ; saturate the free alkali in the one part, by repeatedly stirring with a glass rod dipped in very dilute sulphuric acid, until the colour of the fluid just appears red ; add now the other part of the blue filtrate, pour the whole fluid into a dish, and draw strips of fine, unsized paper through it ; suspend these strips over threads, and leave them to dry. The colour of litmus paper must be perfectly uniform, and neither too light nor too dark." Preparation of reddened litmus paper. " Stir blue solu- tion of litmus with a glass rod dipped in dilute sulphuric acid, and repeat this process until the fluid has just turned distinctly red. Steep slips of paper in the solution, and * Dr. Taylor states that a very delicate test-paper for detecting alkalies may be prepared by steeping slips of paper in an acid infusion of rose petals. 2 26 APPARATUS. dry them as directed in the preceding paragraph. The dried slips must look distinctly red." Preparation of turmeric paper. " Digest and heat one part of bruised turmeric root with six parts of weak spirit of wine, filter the tincture obtained, and steep slips of fine paper in the filtrate. The dried slips must exhibit a fine, yellow tint." 64. LlST OF THE BEAGENTS EMPLOYED HIS THE DRY STATE. 45. Nitrate of ammonia is made by neutralizing nitric acid with carbonate of ammonia. The solution is evaporated until crystals begin to be deposited, and is then allowed to cool. The crystals are collected and placed in well-stop- pered bottles. 46. Cyanide of potassium must be of a milk-white colour, and perfectly free from any admixture of iron. 47. Sulphate of iron is principally employed for the de- tection of nitric acid. 48. Copper turnings are likewise employed for the detec- tion of nitric acid. 49. Carbonate of soda must not contain any sulphuric or hydrochloric acid. 50. Biborate of soda (borax) is employed in blowpipe analysis. It should be heated below the fusing point to drive off its water of crystallization, and then powdered. 51. Phosphate of soda and ammonia (microcosmic salt) is likewise employed as a reagent in blowpipe analysis. APPABATT7S. 65. The processes employed in qualitative analysis are exceedingly simple, and do not require much apparatus for PRINCIPLES OF ANALYSIS. 27 their execution. The small amount actually requisite is described in the following list, and may be procured in the shops of operative chemists. 1^ dozen test-tubes. Small retort stand. Test-tube stand. 3 small glass funnels. 2 small evaporating dishes. 2 porcelain crucibles. Washing bottle. -| Ib. glass tubing Spirit lamp. ^ Ib. glass rod. 2 watch-glasses. Small mortar and pestle. Eat- tail and triangular file. 1 quire filtering paper. Platinum wire and foil. Crucible tongs. Sulphuretted hydrogen ap- Black's blowpipe. paratus. Tube cleaner. A number of best corks. Small gernian beakers. A few lengths of small vul- Litmus paper, blue and red. canized tubing. Turmeric paper. 66. Having explained the different operations employed in analysis, we will resume our previous subject. It has been stated already, that if, to a solution of any of the solu- ble salts of the insoluble bases, a soluble base is added, the soluble base will take away the acid from the insoluble base ; the latter (viz., the insoluble base) being set free, will consequently precipitate, on account of its insolubility in the liquid. If, then, we were to add the exact quantity, of the soluble base required for the complete decomposition of the salt, and no more, all the soluble base we added would be combined with the acid of the original salt, and all the acid of the original salt would be combined with the soluble base in other words, neither the acid of the salt nor the soluble base would either of them be in excess, but the entire amount of the one would be in combination with the entire amount of the other. It is impossible in 28 PRINCIPLES OF ANALYSIS. practice to add the reagents with such mathematical accu- racy ; we are therefore obliged to add, in order to ensure the complete decomposition of a salt of this kind, the soluble base in excess ; and in this excess, or in this uncom- bined portion, some of the insoluble bases dissolve, being soluble in the free soluble bases. One of the insoluble bases (oxide of zinc) is soluble both in the volatile and fixed alkalies ; some of the others are soluble in ammonia, but insoluble in the other two ; some are soluble in potash and soda, but insoluble in ammonia ; others are insoluble in each of the three alkalies. And there are some, although insoluble in ammonia, which are not precipitated by it, if salts of ammonia are present, and are only partly preci- pitated by the fixed alkalies under these circumstances. 67. The properties which the insoluble bases display, with regard to ammonia and the fixed alkalies, are exhi- bited in the table (page 29), which the student must study with the aid of the experiments. 68. To a solution of sesquichloride of iron add a solution of caustic soda in excess ; hydrate of the sesquioxide of iron will precipitate, and will not be redissolved by an ex- cess of the caustic soda. 69. To a solution of sesquichloride of chromium add a cold solution of caustic soda, until the precipitate which first appears is redissolved; then boil the solution until the hydrate of the sesquioxide of chromium once more pre- cipitates. 70. Add to a solution of sulphate of alumina caustic soda, until the precipitate which first forms is redissolved ; then add hydrochloric acid until the solution manifests an acid reaction ; and, finally, ammonia in excess, which will cause the precipitation of hydrate of alumina. 71. We will now attempt to show how the precipitation 29 TABLE SHOWING THE SOLUBILITY OF THE BASIC OXIDES AND THEIR HYDRATES. NAMES. SYMBOLS. NAMES. SYMBOLS. Hydrate of potash Hydrate of soda \white 5 Th Soluble KO,HO NaO, HO 3 rest are ins in water. Hydrate of baryta ^ Hydrate of strontia ( white Hydrate of lime ) oluble in water. BaO, HO SrO, HO CaO, HO Soluble in ammonia and the fixed alkalies. Hydrate of zinc (white) Insoluble in ammonia and the fixed alkalies. Hydrate of the sesquioxide of I Suboxide of mercury (forms no iron (reddish brown) Fe 2 3 , 3HO I hydrate) Hydrate of bismuth (white) Bi0 3 , HO I Hydrate of the protoxide of I mercury (yellow) Insoluble in ammonia, soluble in the fixed alkalies. A1 2 03, 3HO Hydrate of the sesquioxide of chromium (bluish green). SnO, HO (This oxide is insoluble in boiling solutions of the fixed Sn0 2 , HO alkalies) Sb0 3 Hydrate of lead (white), (This hydrate is only very slightly soluble in the fixed alkalies) Hydrate of alumina Hydrate of the pro- toxide of tin Hydrate of the perox- ide of tin Oxide of antimony white ZnO, HO H g2 HgO, HO Cr 2 3 , 3HO PbO, HO Soluble in ammonia, insoluble in the fixed alkalies. The presence of ammoni- acal salts prevents some of them from being completely precipitated by the fixed alkalies. Hydrate of cobalt (pale red) Hydrate of nickel (green) Oxide of silver (forms no hy- drate) Hydrate of cadmium (white) CoO, HO NiO, HO AgO CdO, HO Hydrate of copper (whitish green). (If the fixed alkalies are added to cold solutions of copper salts, the hydrate is precipitated; if added to boiling solutions, the anhy- drous oxide is precipitated) CuO, HO Insoluble in ammonia and the fixed alkalies ; but in the presence of salts of ammonia the volatile alkali cannot precipitate them, and the fixed alkalies only do so in part. Hydrate of magnesia (white) Hydrate of manganese (white), speedily becoming brown by absorbing oxygen from the air, and becoming converted into a higher oxide MgO, HO MnO, HO Hydrate of protoxide of iron is of a white colour, which, on exposure to the air, finally becomes red, owing to its being converted into the per- oxide. FeO, HO Ammonia does not precipitate the hydrate from solutions of protoxide of mercury, but a white precipitate having the following composition (Hg NH 2 + HgCl) ; the fixed alkalies likewise throw down the same precipitate, if salts of ammonia are present, but in the absence of these salts, they precipitate the hydrate. 30 PRINCIPLES OF ANALYSIS. or the volatilization of one substance and the non-precipi- tation or non-volatilization of another, under the same cir- cumstances, is applied in analysis in the separation and detection of substances. Limiting our observations to the bases, we must first inquire in what state they can be pre- cipitated. 72. The soluble "bases can only be precipitated from their solutions in the form of salts; therefore, if we wish to precipitate a soluble base from its solution, whether it exists in the solution uncombined or as a salt, we must add to the solution some acid, or some salt containing an acid, which acid will form with the soluble base a salt insoluble in the solution from which it has to be precipitated, whether the solution be acid, alkaline, or neutral. Now, if an insolu- ble salt, in the state the solution is in, cannot be formed, we must alter the properties of the solution to effect the precipitation ; for instance, if the solution is acid, and the salt of the base we wish to precipitate is soluble in acids, we must first neutralize the solution by some base, before attempting the precipitation, 73. The insoluble bases must, if in solution, be in the form of salts ; those of them, however, which are soluble in the volatile or fixed alkalies, can also be present in solution, by being dissolved in the alkalies in which they are soluble. The insoluble bases can be precipitated from the solution of their soluble salts, either as insoluble salts or in an un- combined state; therefore, to precipitate the insoluble bases from the solutions of their soluble salts, we must add some acid, or a salt containing an acid, which will form with them a salt perfectly insoluble in the solution ; or we must add some soluble base in an excess of which the insoluble base does not dissolve. We can precipitate them from their alkaline solutions by adding a free acid, which forms PRINCIPLES OF ANALYSIS. 31 with them an insoluble salt ; but, in the generality of cases, they cannot be precipitated from their alkaline solutions by a mlt, the acid of which forms with them a salt insolu- ble in a neutral or acid solution, or by a soluble base in which they are insoluble ; before they can be precipi- tated from alkaline solutions either by salts or buses, we must, in the generality of cases, neutralize the alkali, in which they are dissolved, by some acid. (Experiment, paragraph 70.) 74. The volatile base, ammonia, if in the free state, is at once distinguished by the smell; but when it is present in solution, in the form of a salt, the salt must be decomposed by the addition of some stronger base, before the ammonia can be detected. 75. We will now give a few examples* as illustrations. Suppose we had to examine a liquid for baryta and lime : they might be present in the solution either in the uncom- bined state or as salts ; and as chromate of baryta is insolu- ble, and ehromate of lime soluble, we might add to the solution a soluble chromate say, chromate of potash. If we obtained a precipitate by the soluble chromate, baryta must be present ; if we obtained no precipitate, it must be absent : to the nitrate from the chromate of baryta pre- cipitate, or to the solution which has failed to give a pre- cipitate with the soluble chromate, we must add some acid, or a salt containing an acid, which forms with lime an insoluble salt say we add oxalic acid or oxalate of am- monia ; if either of these reagents produces a precipitate, lime is present ; if it does not produce a precipitate, lime is * The teacher ought to give the student three or four solutions on each example ; some of the solutions containing one of the substances named in the example, some containing both of the substances named in the example. 32 PRINCIPLES OF ANALYSIS. absent. Suppose we had to examine a solution for sesqui- oxide of iron and alumina : now, if the sesquioxide of iron was present in the solution, the liquid could not have an alkaline reaction,* because sesquioxide of iron is insoluble -both in the volatile and fixed alkalies ; therefore, if the solution is alkaline, from one of the fixed alkalies, sesqui- oxide of iron must be absent ; if the alkalinity be due to the volatile alkali, alumina, as well as sesquioxide of iron, must be absent, because alumina, as well as sesquioxide of iron, is insoluble in ammonia. We will suppose that the solution is slightly acid, then both substances may be pre- sent ; we add to the solution one of the fixed alkalies in excess, the excess will keep the alumina in solution, but the sesquioxide-of-iron precipitate will remain undissolved. The solution must be filtered, if a precipitate is formed ; and to the filtrate, or to the solution which has failed to give a precipitate, must be added hydrochloric acid in excess : if ammonia is then added in excess, alumina, if present, will be precipitated. Suppose we had to examine a solution for ammonia and potash : as the same reagents which precipitate potash precipitate also ammonia, the latter, when present, must be got rid of before potash can be tested for ; we are therefore obliged to look for ammonia first ; to ascertain if it is present, we add to a part of the solution some soluble base, as potash or soda ; ^if present, it will be liberated from its combinations by either of these reagents, and can then be detected by the smell, ; I . * 4 d 'o 5 ffl 2 ^ C OS 1 EH , .2 O a- o to May be present : O,C0 2 , Sr O, C0 CaO, C0 2 ; olved in HO, A ivided into two portions. B is "o yj a? " O I's No precipitate Absent : CaO. S K & o o o o a a - o ^ N S5 O "2 a a => * nS f> -a ^ a to ja ._, -d H CL, g o o" d 5 o o" o o o <* S ^ 40 QUALITATIVE ANALYSIS. 88. PRELIMINAEY EXAMINATION OF A SOLID SUBSTANCE. 1st. It is a colourless, crystallized substance, probably a salt. 2d. Heated alone on charcoal, it deflagrates ; a white, infusible substance remaining behind, which becomes luminous, aud imparts a crimson colour to the flame, pro- bably strontia. 3d. Soluble in water; the solution is neutral to test-paper. As it is soluble in water, a large number of substances, all the insoluble salts, must be absent ; as it is neutral to test-paper, all the salts of the alkalies and alkaline earth having an alkaline reaction must be absent ; and the soluble salts of the other metals, with the exception of manganese and silver, must be absent, because their soluble neutral salts redden blue litmus paper. 89. The preliminary experiments indicate the presence of nitrate of strontia. EXAMINATION FOE ACIDS. 90. The following acids, viz., C0 2 , HS, As0 3 , As0 5 , and Cr0 3 , were proved to be absent on the examination for the 91. The remainder of the acids, which give precipitates with a salt of baryta, could not be present ; as they likewise form, with strontia, insoluble salts. 92. Added to a portion of the original solution AgO, N0 5 , no precipitate ; absent, Cl, Cy, Br, and I. 93. Added to another portion HO, S0 3 , and copper turnings, nitrous fumes were evolved, showing the presence of nitric acid. 94. The examination for chloric acid yielded a negative result. CHAPTER II. SPECIAL PBOPEKTIES OF THE BASIC GEOTJPS. PIEST GKOUP. POTASH. SODA. AMMONIA. (LITHIA.) 95. The members of this group are called alkalies. They are readily soluble in water in their pure (caustic) state. The solution restores the blue colour of reddened litmus paper, and imparts an intensely brown colour to turmeric paper ; the solution of their sulphides and carbonates acts in a similar manner upon vegetable colours. 96. Potash and soda are oxides of the metals potassium and sodium ; these metals are lighter than water, and decom- pose it at the ordinary temperature. Ammonia (NH 3 ), being a gas of a very pungent odour, is readily distinguished from all the other bases ; it dissolves freely in water, and may be again expelled on boiling the solution. Ammonia, when dissolved in an aqueous solution, unites with one atom of water, forming NH 4 O, the oxide of an hypothetical com- pound metal, ammonium (]S~H 4 ). 97. Potash cannot be detected in the presence of ammonia or any of its salts ; because the same reagents which preci- pitate potash from its solutions form also, with ammonia, a corresponding class of insoluble substances (A 3 and B 3); ammonia must therefore be expelled from the substance under examination, before proceeding to test forpotash and soda. The way for expelling the ammonia is described in paragraph 108- 42 THE SPECIAL PROPERTIES 98. HOW TO ASCERTAIN THE PRESENCE OR ABSENCE OF EACH OF THE THREE MEMBERS OF THIS GROUP IN A SOLU- TION WHICH CAN ONLY CONTAIN THESE THREE BASES. As the presence of ammonia interferes, as before stated, with the detection of potash, we are always obliged, on this ac- count, to look for ammonia before we look for potash. And as the reagent we add for the detection of ammonia would inter- fere (A 2) with the detection of the two other members of the group, we are obliged, on this account, to look for the ammonia in a portion only of the solution under examination. For these reasons, then, we divide the solution into two parts, which we shall call A and B. 99. In A we examine for AMMONIA according to the method described in A 2 and paragraph 1 06. The method there described is the characteristic test for ammonia ; in that way it can be distinguished from all other substances. As the absence or presence of ammonia regulates our mode of search for the two other members of the group, we must describe the mode of proceeding to be adopted when it is absent , as well as when it is present. 100. If it is absent, the B portion of the solution is examined for soda and potash in the following way : a clean (see Precautions, paragraph 103) platinum wire is dipped into the solution, and then exposed to the inner blowpipe flame: if the flame is coloured yellow, SODA is present ; if it is coloured violet, it proves the absence of soda (C 4) and the probable presence of POTASH (B 4). If soda is present, examine for potash by Cartmell's photo- chemical method (paragraph 112). The presence of potash may be confirmed by adding to the solution under exami- nation, which must be cold (B 3), a solution of tartaric acid or litartrate of soda (see paragraph 110) in excess, and shaking the mixed liquid very violently, and then allowing OF THE FIRST GROUP. 43 it to rest for some time ; if a crystalline precipitate appears after this, POTASH is present (B 3). The time required for the appearance of the crystalline precipitate depends upon the quantity of potash in the solution ; if the quantity of potash is small, the precipitate may not appear until several hours after the addition of the reagent. v 101. If ammonia is present, the B portion of the solution must be evaporated to dryness and ignited, in order to volatilize the ammonia or its salts (A 1, and paragraph 108) ; the ignition must be continued as long as any white fumes or smoke are evolved. If a residue remains after the am- monia or its salts are expelled, one or both of the other two members of the group are present ; this residue must be dissolved in the smallest possible quantity of water, and examined for POTASH and SODA, in the way described in the preceding paragraph. 102. WHEN THE EXAMINATION is NOT CONFINED TO THE ALKALIES, BUT ALL, OE, AT LEAST, SOME OF THE OTHER BASES HATE TO BE SOUGHT FOE IN THE SOLUTION, the Solu- tion, after being freed from all the other bases but those of the first group, must be evaporated to dryness, and ignited, to expel the ammoniacal salts, which have been added for their discovery. If a residue remain,* after the vapour of the ammoniacal salts has ceased to be evolved, it must be examined for potash and soda, in the way described in para- graph 100. In this case that is, when other bases besides those of the first group have to be sought for AMMONIA is to be tested for in a part of the original solution. * A fixed residue is not a certain proof of the presence of potash or soda, as it may arise from the presence of one of the non-volatile acids, viz., phosphoric, boracic, or silicic acid. (See paragraph 19.) THE SPECIAL PROPERTIES TABLE I. BEHAVIOUR OF THE FIRST GROUP WITH THE SPECIAL REAGENTS. AMMONIA (N H 4 0). POTASH (K 0). SODA (Na 0). A 1. Ammonia and its salts B 1. Potash and its C 1. Soda and its are volatile. (See par. 108.) salts are not volatile. salts are not volatile. A 2. All salts of ammonia are B 2. When salts of C 2. When soda decomposed with the liberation of potash are decomposed salts are decomposed by free ammonia, when any stronger base, such aslime*potash,orsoda, by a stronger base, the potash which is libe- a stronger base, the soda which is liberated, is added to their solutions. If the rated, not being volatile not being volatile like liquid be gently heated, the am- like ammonia, cannot ammonia, cannot be monia is volatilized, and its pre- be detected in a similar detected in a similar sence may then be recognised in way. manner. three distinct ways. a. By its pungent odour. (3. By turning red litmus paper blue. y. By forming white fumes, when any volatile acid, as hydrochloric acid, is brought into contact with it.f A 3. Tartaric acid (2 H 0, B 3. Tartaric acid, C 3. Tartaric acid, C 8 H 4 10 =2 H O, f), in solution, in solution, throws down in solution, produces no produces in neutral or alkaline from neutral or alkaline precipitate in solutions solutions of ammonia a white crys- solutions of potash a of soda, except in ex- talline precipitate of BITARTRATE white crystalline preci- tremely concentrated OF AMMONIA (N H 4 0, H 0, f), pitate of BITARTRATE solutions, bitartrate of which is rather more soluble in OF POTASH (KO, HO, soda being soluble. water than the corresponding f). This salt, and the potash salt. Vigorous shaking corresponding one of promotes the formation of this ammonia, are soluble in and the corresponding potash salt. free alkalies and free mineral acids. Slightly soluble in cold, much more so in hot, water. (Consult -pan. 110.) A 4. Ammonia and its salts B 4. Potash audits C 4. Soda and its impart to the blowpipe flame no characteristic colour. salts tinge the outer blowpipe flame VIOLET. salts impart to the ex- terior blowpipe flame an (Consult par. 112.) intense YELLOW colour. Small quantities of soda can by this means be detected in the presence of much potash, the yel- low flame overpowering the violet. * If lime is employed, it must be the solid hydrate, not a solution of lime (lime water). f This experiment is best performed "by inserting a glass rod moistened with hydrochloric acid into the mouth of the test-tube in which the decomposition of the ammonia salt has been effected. The hydrochloric acid employed should not be concentrated, but should be diluted with an equal volume of water. (Consult paragraph 106.) OF THE FIRST GROUP. 45 103. The following precautions are to le attended to in ilie analysis of this group. In testing for ammonia, one error frequently committed is, that of allowing the glass rod to remain so long in the heated atmosphere of the test- tube, that on its removal a sensible evaporation takes place from its surface, which is mistaken for the white fumes which are formed when any volatile acid is brought in contact with ammonia. To avoid this error, the solution which is under examination should be heated until it approaches the boiling point, but should not actually be boiled, and the moistened glass rod should, immediately after its in- sertion into the test-tube, be withdrawn. If any fuming should then arise, it can only proceed from the presence of ammonia, which must be confirmed by the other appro- priate tests. Young students seldom continue the ignition for the expulsion of the ammoniacal salts sufficiently long ; consequently they find potash when it is not present, owing to the unexpelled ammonia giving precipitates with tartaric acid and bichloride of platinum. The attention of the student is therefore directed to paragraph 108. The detection of potash by tartaric acid requires, in the first place, that the solution be neutral or alkaline, not acid, and as concentrated as possible. The reagent must then be added in excess (if the fluid is alkaline the tartaric acid must be added until the solution is acid), and the fluid well agitated. The application of heat must be avoided, and time allowed for the appearance of the precipitate, as it becomes visible only after the lapse of some hours, when small quantities of potash are present. In testing for potash or soda by the blowpipe flame, it is necessary that the platinum wire should be perfectly clean. This can only be secured by directing the blowpipe flame upon it until it ceases to impart a colour ; care should then be 46 THE SPECIAL PROPERTIES taken not to touch, even with the fingers, that end of it on which the substance is to be placed. SPECIAL REMARKS. 104. AMMONIA. This substance is a gas, transparent and colourless, of a very pungent and peculiar smell and taste. It is instantly absorbed by water, forming the solution of the gas called aqua ammonice. If this liquid is boiled, the gas is expelled. When organic substances con- taining nitrogen decay and putrefy, carbonate of ammonia is constantly produced. The same salt is likewise formed when nitrogenized organic substances are submitted to de- structive distillation. 105. When any volatile acid is brought into an atmo- sphere of ammonia, they unite together, forming a solid salt; this is the white fumes observed in testing for ammonia. 106. Ammonia may be liberated from its combinations, and the most securely detected, in the following way : the substance supposed to contain the ammoniacal salt, either in the solid state or dissolved, is mixed with an excess of hydrate of lime in a small beaker, and, if necessary, a little water ; if the substance supposed to contain ammoniacal salt is in a state of solution, sufficient hydrate of lime must be added to the portion of the solution examined for ammonia to render it perfectly dry and solid. The beaker is covered, after the mixing, with a glass plate, on the lower side of which adheres a small piece of moist turmeric or moist red- dened litmus paper. 107. Bichloride of platinum (PtCLj) produces in neutral and acid solutions of ammonia a yellow crystalline pre- cipitate, which is a double salt of CHLORIDE or AMMONIUM and CHLORIDE or PLATINUM (NH 4 C1, OF THE FIRST GROUP. 47 108. Ammonia and its salts are distinguished from the fixed alkalies and their salts by being volatile (A 1) . "We have already noticed that ammonia is expelled from its aqueous solution on boiling the liquid; but salts of am- monia are not volatilized unless they are ignited in the dry state, for they are not expelled from their solutions by heat with one or two exceptions, and even these could not be volatilized with advantage in this way. Therefore, to volatilize an ammoniacal salt we must ignite the dry sub- stance in a crucible over a Berzelius spirit or a gas lamp, until all fuming ceases. We must continue the ignition so long because the fumes are the volatilizing salt, and therefore, until they cease, all the ammoniacal salt is not expelled. 109. POTASH. This alkali and its hydrate, when exposed to the air, absorb moisture and carbonic acid, the carbonate formed dissolves in the absorbed water. Almost all the salts of this base are readily soluble in water. They are colourless, provided the constituent acid be so. This alkali is an important constituent in many of our crystalline rocks ; it exists there, in combination with SILICIC ACID, and ALUMINA or IKON, as a double salt of SILICATE OF POTASH and SILICATE OF ALUMINA or IRON. The decay of these rocks is occasioned by the carbonic acid in the atmosphere decomposing the alkaline silicate. It is also found in the mineral kingdom as SULPHATE and NITRATE OF POTASH, the latter being saltpetre. 110. Bitartrate of soda* is a much more delicate test for potash than tartaric acid, because bitartrate of potash is soluble in acids, and an acid must be set free whenever tar- taric acid is added to a solution containing a salt of potash. * My friend, Mr. W. Plunkett, suggested the employment of bitar- trate of soda. See * Chemical Gazette/ vol. xvi, p. 217. 48 THE SPECIAL PROPERTIES If the solution is acid, the free acid must be expelled, if practicable, by evaporation or ignition ; or if not expelled, it must be neutralized with soda or carbonate of soda before testing for potash either with bitartrate of soda or tartaric acid. Bitartrate of soda cannot, of course, replace tartaric acid as a test for potash when the solution to be tested contains a free alkali, because bitartrate of potash is soluble in free alkalies ; but if the other bases are sought for, the solution cannot be alkaline when we arrive at the examination for potash, and it is not often that we have to deal with an alkaline solution, even when the alkalies are the only bases that are examined for. 111. Bichloride of platinum produces, in neutral and acid solutions of potash, a yellow, crystalline precipitate,* a double salt of CHLORIDE or POTASSIUM and CHLORIDE or PLATINUM (KC1, PtCl 2 ). The presence of free hydro- chloric acid promotes the formation of this precipitate. It is slightly soluble in water, but wholly insoluble in alcohol. This is a very delicate test for potash or any of its com- pounds : the best method of applying it is to mix the solution under examination for potash with bichloride of platinum, evaporate to dryness upon a water bath, and treat the residue with alcohol, the excess of bichloride of platinum dissolves in the alcohol, colouring the solution yellow; the double salt of bichloride of platinum and chloride of potassium is left undissolved as a yellow, crys- * Bichloride of platinum gives with iodine a dark-red colour ; and as this colour prevents the yellow precipitate of bichloride of platinum and chloride of potassium from being distinctly seen, iodine should be expelled, if present, before testing for potash by this reagent. To expel it, evaporate to dryness with concentrated nitric add / dissolve the residue in water, add hydrochloric acid and bichloride of platinum, and then proceed in the usual way. OF THE FIRST GROUP. 49 talline precipitate. The addition of bichloride of platinum should always be preceded by that of hydrochloric acid, to convert the potassium into chloride, if it should not exist already in that form. 112. Cartmell* has proposed a very beautiful photo- chemical method for the detection of potash in the presence of soda ; he views the blowpipe flame through deep blue cobalt glass ;f through this coloured glass no coloured rays from soda (or lithia) can pass, but it admits those peculiar to potash. Potash, viewed through this coloured glass, gives to the flame an intense violet colour ; and this is still visible when one part of potash is present with two hundred parts of soda. As all substances which make flame luminous, especially all organic substances which burn with separation of carbon, give the same violet colour, these substances must first be removed by heat, before the colour of the flame can be used as a test for potash. Cartmell recom- mends Bunsen's lamp as the blowpipe lamp to be used. 113. SODA. This alkali and its hydrate, on exposure to the air, attract moisture and become fluid ; but in absorbing carbonic acid from the air, which it does very rapidly, it again becomes solid. The salts of this base, with a few exceptions, are very soluble ; the means we have of detect- ing it are therefore limited. It exists in the mineral king- dom as CHLORIDE (kitchen salt), SULPHATE (Glauber's salt), BORATE (borax or tincal), NITRATE, and CARBONATE. It likewise forms a constituent of many SILICEOUS MINERALS. 114. The best test for soda is the blowpipe flame, to * 'Philosophical Magazine/ 1858. f The cobalt blue glass can be obtained at the operative chemists. Before using the glass, it must first, of course, be ascertained how small a quantity of potash mixed with soda (or lithia) it will clearly indicate. 3 50 THE SPECIAL PROPERTIES which it imparts a yellow colour, caused by the reduction of the soda and the subsequent reoxidation of the sodium. 115. Antimoniate of potash (KO, Sb0 5 ) produces, in neutral or alkaline solutions of salts of soda, a white crys- talline precipitate of ANTIMONIATE OP SODA (NaO, SbO 5 ). In concentrated solutions the precipitate is formed imme- diately ; but from dilute solutions it separates only after the lapse of some time. Violent agitation of the fluid pro- motes the separation of the precipitate. Acid solutions decompose antimoniate of potash, antimonic acid being precipitated ; free acids must therefore be first neutralized with potash before this test can be applied. Antimoniate of soda is soluble in carbonate of potash ; if this substance be present in the solution it must be nearly saturated with acetic acid. 116. The double chloride of bichloride of platinum and chloride of sodium is soluble in alcohol, and very solu- ble in water ; therefore this reagent (bichloride of platinum) produces no insoluble compound with soda or any of its salts, either in an aqueous or alcoholic solution. APPENDIX TO THE BIEST GBOUP. 117. LITHIA (LiO). The hydrate of this alkali is less soluble in water than the hydrates of potash and soda, and it does not deliquesce in the air. The salts of this base are colourless, provided the constituent acid be so. Most of its salts are soluble in water ; the carbonate is rather spa- ringly soluble in that liquid ; the solution of this salt has an alkaline reaction. Lithia occurs in certain minerals, particularly in spodumene, petalite, and lepidolite. 118. Phosphate of soda produces in not over-dilute solu- tions of lithia, upon boiling, a heavy white crystalline preci- pitate of basic phosphate of liiliia ; if the solution is then OF THE FIRST GROUP. 51 evaporated to dryness, and the residue treated witli cold water, the basic phosphate remains undissolved. AVe can therefore in this way distinguish lithia from, and in the presence of, potash and soda. 119. " If a salt of lithia (more particularly chloride of lithium) is exposed on a platinum, wire to the inner How- pipe flame, the outer flame shows a strong CARMINE tint. Presence of salts of soda (but not salts of potash) conceals this reaction." 120. Cartmell has found that when the coloured rays produced by burning soda, potash, and lithia, in the blow- pipe flame, are transmitted through a solution of indigo, the yellow- coloured rays from the soda are obliterated, whilst the red rays from lithia and potash pass freely through the solution. When potash is absent, the indigo solution* gives a means of rendering visible the red rays from lithia in the presence of soda, when the proportions do not exceed one part of the former to a thousand parts of the latter. The presence of lithia can be detected in that of potash, or of potash and soda, in the following way : Place side by side in the flame two platinum wires, one having on its point a little pure sulphate of potash, and the other the sample to be tested. If there be lithia in the sample to the extent of one part to two hundred parts of potash, a very marked difference will be seen between the colour of the two flames,f that containing lithia being of a much brighter red. * Cartmell prepares the indigo solution by adding water to the common indigotic acid of the laboratories, till the point is all but reached, when an intense flame of soda appears slightly pink, when observed through the bottle (of the size and shape of a common watch) filled with the solution. f Bunsen has found that the discrimination of these bodies in pre- sence of each other is more easily effected by observing the succession THE SPECIAL PROPERTIES 121. When soda, potash, and lithia occur together, one part of each can be detected in two hundred parts of the mixture. As soda in the minutest quantity is visible to the naked eye, we have now a perfect means of detecting the three alkalies in the presence of each other. 122. The following table will show how the detection is effected by Cartmell's method : Indigo solution. Comparative test with pure sulphate of potash. Brighter red than sulphate of potash alone : LITHIA. When the absence of potash has heen pre- viously proved by the cobalt glass, red rays visible through the indigo solution prove the presence of lithia. With the naked eye. Cobalt glass. Yellow : Violet-red : SODA. POTASH. SECOND GEOUP. BARYTA. STRONTIA. LIMB. MAGNESIA. 123. The members of this group are called alkaline earths. They are soluble in water in their pure (caustic) state, also of changes of colour, which the mixed flame produced by these sub- stances experiences when the rays reach the eye, after passing through gradually thicker layers of an indigo solution. For this purpose, Bunsen employs a hollow plate-glass prism, filled with indigo solution : it is 40 millimetres high, and its principal section is a triangle, with two sides of 150 millimetres, and the other of 35 millimetres. Bunsen pre- pares the indigo solution by dissolving 1 part of indigo in 8 parts of fuming sulphuric acid, diluting with 1500 to 2000 parts of water, and filtering. (Consult the account of Bunsen's blowpipe experiments in the Appendix.) OF THE SECOND GROUP. 53 as sulphides. Magnesia, however, is very sparingly soluble in water. Their solutions exhibit an alkaline reaction. 124. The metallic radicals of these oxides are larium, strontium, calcium, and magnesium, all of which decompose water at the ordinary temperature. 125. As magnesia differs so entirely from the other mem- bers of the group in its behaviour with reagents, it has not been included in the special table. 126. The group is subdivided; the first division com- prising BAKYTA, STKONTIA, and LIME ; the second containing MAGNESIA. The members of the first subdivision are pre- cipitated completely by CARBONATE OF AMMONIA, but mag- nesia is precipitated only in part by this reagent ; and if any salt of ammonia, the acid of which forms no insoluble com- pound with magnesia, is added to the solution containing the magnesia before adding the carbonate of ammonia, the carbonate of ammonia will not cause the least precipitate with the magnesia. If, therefore, we add to a solution which may contain the members of the second group chloride of am- monium and carbonate of ammonia baryta, strontia, and lime, if they are present, will be precipitated as carbonates, whilst the magnesia will not be precipitated in the least degree. "We generally add ammonia, after adding the chloride of ammonium, but before adding the carbonate of ammonia, to render the carbonate of ammonia we employ (if it is not) a neutral carbonate. FIBST DIVISION. 127. "When the student examines a solution even for the members of this group only, he must precipitate the baryta, strontia, and lime, by carbonate of ammonia, and precede the addition of this reagent by chloride of ammonium and ammonia. 54 THE SPECIAL PROPERTIES. 128. The precipitate produced by the general reagent, car- bonate of ammonia, must be dissolved in acetic acid, and the solution divided into two parts, which we shall call A and B. 129. Before we describe the way for separating the mem- bers of this division of the group, we shall propose six ques- tions, which the student ought to solve by the aid of the table before he attempts the detection of baryta, stroutia, and lime. 1st, Why are the precipitated carbonates directed to be dissolved in acetic acid ; why not dissolve them in hydrochloric acid or nitric acid ? 2nd, By what single re- agent can we discover, in one operation, the absence of baryta and strontia? 3rd, How can lime be detected in the absence of the other two members ? 4th, How can strontia be detected in the absence of baryta ? 5th, Can lime be detected when strontia is present? 6th, Can strontia and lime be detected when baryta is present. 130. SULPHATE OF LIME precipitates baryta immediately, strontia after the lapse of some time, and lime not at all (see D 1, E 1, and F 1). One of three cases will, therefore, occur on the addition of sulphate of lime to the A portion ; either there will be no precipitate, or there will be one after the lapse of some time, or there will be an immediate one. If there is no precipitate, examine according to par. 131 ; if there is one after the lapse of some time, examine according to par. 132 ; if there is one immediately, examine according to par. 133. 131. If, in the A portion, a solution of sulphate of lime causes no precipitate, even after the lapse of some time, BARYTA and STRONTIA are absent ; LIME must therefore be present* as one of the members of a group must, at least, * If the previous group or groups have been fully precipitated before adding the carbonate of ammonia, or else they might that is, the por- tion not precipitated cause a precipitate with carbonate of ammonia. 55 TABLE II. BEHAVIOUR OF THE SECOND GROUP WITH THE SPECIAL REAGENTS. BA.RYTA (BaO). STRONTTA (Sr 0). LIME (CaO). D 1. Sulphate of lime, E 1. Sulphate of lime, F I. Sulphate of lime (CaO, S0 3 )in solution, pre- in solution, precipitates produces no precipitate cipitates baryta immedi- strontia after the lapse in solutions of lime. ately, from its solutions, of some time,* from its in the form of SULPHATE solutions, in the form (BaO, S0 3 ) insoluble in of SULPHATE (SrO, acids and alkalies. S0 3 ), almost absolutely insoluble ia acids and alkalies. ' D 2. Chromate of pot- E 2. Chromate of F 2. Chromate of ash (KO, Cr0 3 ), in solu- potash, in solution, potash, in solution, pro- tion, produces, in neutral causes, in concentrated duces no precipitate in and alkaline solutions of solutions of salts of solutions of !ime,CHRO- baryta, a pale yellow pre- strontia, a bright yel- MATE OF LIME being cipitate of CHROMATE OF low precipitate (Sr 0, soluble. BARYTA (BaO, Cr 8 ), Cr0 3 ), but not in dilute insoluble in the alkalies solutions, or such as and acetic acid, soluble in contains/Tee acetic acid. hydrochloric and nitric acids. D 3. Sulphuric acid E 3. Sulphuric acid F 3. Sulphuric acid and the soluble sulphates and the soluble sul- and the alkaline sul- behave in the same man- phates precipitate stron- phates cause only in ner in solutions of baryta tia completely from its concentrated solutions as sulphate of lime. solutions, in the form of lime a partial preci- of SULPHATE. The pre- pitate of SULPHATE OF cipitate will not appear LIME, which redissolves immediately, unless the completely in a large solution be very con- amount of water. centrated. D 4. Oxalic acid (H 0, E 4. Oxalic acid, in F 4. Oxalic acid, in C 2 3 = HO, O), in solu- solution, precipitates, solution, throws down tion, produces only in con- even from dilute solu- from neutral solutions centrated solutions of ba- tions of strontia,a white of lime, even if highly ryta a white precipitate of Oxalate of Baryta (BaO, precipitate of Oxalate of Strontia. The addi- diluted, a precipitate of Oxalate of Lime. The O), soluble in acids. The tion of ammonia pro- addition of ammonia addition of ammonia ren- motes the formation of renders this reaction ders this reaction there- the precipitate. more delicate. fore more susceptible. * The formation of the precipitate is much promoted by agitation. 56 THE SPECIAL PROPERTIES be present whenever a precipitate is obtained by the general reagent of that group.* As lime, in the form of sulphate, has been added to the A portion of the solution, we cannot in that portion discover whether it (lime) was originally present ; we therefore confirm its presence by adding to the B portion ammonia and a solution of oxalate of ammonia (F 4). 132. If, in the A portion, a solution of sulphate of lime produces a precipitate after the lapse of some time, BAEYTA is absent, STEOFTIA is, and LIME may be, present. The pre- sence or absence of lime cannot be determined, as long as any strontia remains in solution ; because the reagents, which precipitate lime, precipitate strontia also (E 3, F 3, E 4, F 4). "We add, therefore, to the B portion dilute sulphuric acid; this acid precipitates all the strontia (E 3), and only a small portion of lime in a concentrated and none at all from a dilute solution (F 3) ; in any case, sufficient lime remains in solution for detection. Filter off from the precipitate produced by the sulphuric acid, after sufficient time (one or two hours) has been allowed for the precipi- tation of the sulphate of strontia, and add to the filtrate ammonia and oxalate of ammonia, which will cause a pre- cipitate, if LIME is present. 133. If, in the A portion, a solution of sulphate of lime causes an immediate precipitate, BARYTA is, and STEONTIA and LIME may le, present. As sulphate of lime cannot be employed to detect strontia in the presence of baryta, and as baryta causes a precipitate with all the reagents which precipitate strontia and lime, the former must be got rid of before we can ascertain the absence or presence of the two latter substances. For this purpose, chromate of potash * This statement must be read in the light of the foot-note at page 54. OF THE SECOND GROUP. 57 must be added to the B portion, as this reagent precipi- tates baryta only (D 2, E 2, F 2). To the filtrate from this precipitate (the filtrate will be of a yellow colour, from the excess of chromate of potash, if the baryta has been completely precipitated) add ammonia and oxalate of am- monia, and warm the solution ; if a precipitate is produced, it may be due to the presence both of STEONTIA and LIME (E 4, E 4) ; if no precipitate is produced, STEOKTIA and LIME are absent. Ignite the oxalate precipitate,* if one has been produced, in a small porcelain crucible for a few minutes, in order to convert the oxalates into carbonates. Afterwards, when the crucible is sufficiently cold, dissolve the car- bonates in hydrochloric acid, and evaporate the solution to dryness, in order to expel all the free acid ; then dissolve the chlorides in as small a quantity of water as possible, filter the solution, if necessary, through a very small filter, and add to the solution (which must be quite cold before the reagent is added) not too small a quantity of the dilute solution of sulphate of potash,^ after which addition, the solution must be well agitated ; if the sulphate of potash produces a precipitate, after the lapse of some time, STEONTIA is present. If the sulphate of potash solution * If the precipitate is so small that it cannot be removed from the filter by means of the platinum knife, a hole must be made in the apex of the filter, and the precipitate must be washed into the crucible through the hole in the filter by means of the wash-bottle; the water must then be evaporated; and when it is expelled, the dry precipitate must be ignited for several minutes, in order to convert the oxalates into carbonates. t Care must be taken to make the solution of sulphate of potash of the strength directed in the list of reagents. Of that strength, it contains the same quantity of sulphuric acid as a saturated solution of sulphate of lime] contains in a like quantity of liquid ; it is, therefore, sufficiently strong to precipitate strontia, but not to precipitate lime. 3 58 THE SPECIAL PROPERTIES has produced a precipitate, add some dilute sulphuric acid to complete the precipitation, and allow sufficient time (one or two hours) for the complete separation of the sulphate of strontia before filtering ; add to the filtrate, or to the solution, without filtering, if sulphate of potash has pro- duced no precipitate, ammonia and oxalate of ammonia in excess ; if this last reagent produces a precipitate, LIME is present.* 134. The following precautions are to be attended to in the analysis of this group. The solution of sulphate of lirne must be added in not too small a quantity, and it must always be added in the cold, as this reagent is less soluble in hot than cold water. Time must be allowed for the formation of the precipitate produced by this reagent in solutions of strontia, the formation of which is much pro- moted by agitation. In separating strontia from a solution by sulphate of potash, the liquid ought not to be filtered immediately, but a due time allowed for the complete sepa- ration of the precipitate from the solution ; and the solu- tion ought not to be warmed, owing to the less solubility of sulphate of lime in hot than cold water. SPECIAL EEMAEKS. 135. BAEYTA. This oxide is of a grayish white colour ; it combines with water, forming a hydrate (BaO, HO). Both the oxide and its hydrate are soluble in water. The solu- tion reacts strongly alkaline, and when exposed to the air absorbs carbonic acid and becomes covered with a film, of * For another method for the separation and detection of these three substances, and for Cartmell's photo- chemical method, the student is referred to 149, 150, 151, 152, 153, and 154. OF THE SECOND GROUP. 59 carbonate of baryta, the absorption continuing until all the baryta has been precipitated as carbonate. 136. The salts of baryta are colourless, provided the con- stituent acid be so. Most of them are insoluble in water ; but they are all, with the exception of the sulphate, soluble in hydrochloric and nitric acid. The salts which are solu- ble in water do not affect vegetable colours, and are decom- posed upon ignition, with the exception of chloride of barium. The SULPHATE (heavy spar) and the CARBONATE (wifherite) are the principal minerals of this oxide. 137. Hydrofluosilicic acid (HF, SiF 2 ) throws down, both from neutral and alkaline solutions of baryta, a white pre- cipitate of SILICOELUORIDE OE BARIUM (Ba F, SiF 2 ), which appears only after much agitation and lapse of some time, in dilute solutions ; it is perceptibly soluble in hydro- chloric and in nitric acid. Addition of an equal volume of alcohol renders the precipitation rapid, and so complete that the nitrate remains clear upon addition of sulphuric acid. 138. Salts of lari/ta, strongly heated on a thin platinum wire in the inner blowpipe flame, impart a light green colour to the outer flame ; insoluble compounds should be moistened with a little dilute hydrochloric acid before applying the test. " The presence of strontia converts the colour-flame into an impure yellow colour, somewhat resembling that produced by soda. If a mixture of equal parts of carbonate of soda and chloride of barium is exposed before the blow- pipe on a loop of platinum wire, the yellow flame derived from the soda will only prevail for a few minutes, and will then give place to the pale green flame of baryta, the whole of the soda being volatilized under the form of chloride of sodium ." Chapman. 139. STBONTIA. This oxide and its salts resemble, in their colour, solubility, and other properties, the corre- 60 THE SPECIAL PROPERTIES spending compounds of baryta. The hydrate of this oxide is however less soluble in water than the hydrate of baryta. The STJLPHATE (celestine) and the CARBONATE (strontianite) are the principal minerals of strontia. 140. Hydrofluosilicic acid causes no precipitate in solu- tions of strontia ; even upon an addition of an equal volume of alcohol no precipitation takes place, except in very highly concentrated solutions. 141. The CHLORIDE and NITRATE of STRONTIA are solu- ble in alcohol ; the corresponding salts of baryta are in- soluble. If an alcoholic solution of either of these stron- tian salts be ignited, it will burn with a beautiful crimson flame, which becomes more apparent on stirring the solution. 142. Salts of strontia, when heated on the platinum wire in the inner blowpipe flame, impart a crimson colour to the outer flame. Insoluble compounds should be moistened with a little dilute hydrochloric acid before applying the test. The presence of baryta interferes with the test (par. 138). "A mixture of chloride of strontium and carbonate of soda will give, after a well- continued blast, the cha- racteristic crimson flame of the former." Chapman. 143. LIME. This oxide and its salts resemble in their general behaviour the corresponding compounds of baryta and strontia. The hydrate of lime is less soluble in water than the hydrates of strontia or baryta; it is also more sparingly soluble in hot than cold water. The solution absorbs carbonic acid from the air, the lime becoming converted into carbonate. The principal minerals of lime are the SULPHATE (gypsum, selenite CaO, S0 3 +2 aq) and (anhydrite CaO, S0 3 ),the CARBONATE (chalk, limestone, calcareous spar), the double CARBONATE OF LIME and MAGNESIA (dolomite) (CaO,CO 2 ) + 3(MgO, CO 2 ), and the FLUORIDE OF CALCIUM (fluor spar CaF). OF THE SECOND GEOUP. 61 144. Hydrofluosilicic does not precipitate lime from its solutions. 145. CHLORIDE OF CALCIUM and NITRATE OF LIME are soluble in alcohol. The alcoholic solution of these salts, when ignited, burns with a yellowish red-coloured flame. 146. Arsenite of ammonia produces, in aqueous solutions of chloride of calcium, an immediate precipitate of ARSENITE OF LIME. In solutions of chloride of barium or strontium a precipitate is produced by this reagent only after the lapse of some time. Should this test be resorted to for confirming the presence of lime, ammoniacal salts (if pre- sent) must first of all be removed from the solution, because all the salts of arsenious acid which are insoluble in water dissolve in it if ammoniacal salts are present. 147. Salts of lime, when heated on the platinum wire in the inner blowpipe flame, impart an orange-red colour to the outer flame; insoluble compounds of lime ought first to be moistened with dilute hydrochloric acid. 148. Before describing the special properties of mag- nesia, we will give Presenius's method for the separation and detection of baryta, strontia, and lime, and Cartmell's photo-chemical method. 149. " Dissolve the precipitate produced by the general reagent, carbonate of ammonia, after it has been well washed in the least possible amount of hydrochloric acid, and add to a small portion of the fluid some solution of sulphate of lime (not too little) ; a precipitate is formed immediately;* this indicates BARYTA. Besides this, strontia and lime may also be present. * If a precipitate is not formed immediately, but only after the lapse of some time, examine the other portion of the solution according to 132 ; if no precipitate is formed, examine the other portion of the solution according to 131. 62 THE SPECIAL PROPERTIES 150. " Evaporate the remainder of the hydrochloric solu- tion of the precipitate produced by carbonate of ammonia to dryness, digest the residue with strong alcohol, decant the fluid from the undissolved chloride of barium, dilute with an equal volume of water, mix with a few drops of hydrofluosilicic acid, which throws down the small portion of baryta that had dissolved in the form of chloride of barium. Allow the mixture to stand for some time ; filter, evaporate the alcoholic solution to dryness, dissolve the residue in water, and test a portion of the fluid with a dilute solution of sulphate of potash. If a precipitate forms immediately, or in the course of half an hour, the presence of STEONTIA is demonstrated. In that case, let the fluid, with the precipitate in it, stand at rest for some time, then filter, and add ammonia and oxalate of ammonia to the filtrate. The formation of a white pre- cipitate indicates LIME. If sulphate of potash has failed to produce a precipitate, the remainder of the solution of the residue left upon evaporation of the alcoholic fluid is tested at once with ammonia and oxalate of ammonia for lime." 151. The following, which is Cartmell's photo-chemical method, is particularly adapted to the discovery of small quantities of strontia ; and also for the detection of each of the three substances, baryta, strontia, and lime, in the presence of the other two, when they occur in so small quantities that they are no longer recognisable in the wet way ; they are still readily distinguishable by the re- actions of the flame and coloured medium. 152. The characteristic colours which baryta, strontia, and lime communicate to the flame are best observed when their sulphates are exposed on the point of a piece of the finest platinum wire to the outer part of OF THE SECOND GROUP. G3 the flame of a Buns en's lamp. The colours they com- municate to the flame can be , increased in intensity, by first putting them into the reducing flame, and then either moistening them with hydrochloric acid, or by holding some asbestos moistened with this acid in the flame directly under the point of the platinum wire on which the substances are supported. They always burn in the following order : First is seen the green of baryta, next the bright red of strontia, and lastly the dull and scarcely visible red of lime. When, however, a large quantity of strontia or lime is present in proportion to the baryta, the red colours of the two former are observed at the same time ; and, in this case, the green of the baryta can only be seen distinctly by passing the Avire on which the substance is supported in and out of the flame during the observation. When much lime is present, it modifies considerably the colours of baryta and strontia ; so much so, that these two last, when in small proportions, cannot be distinguished. By a solution of indigo more dilute than that used for the alkalies, strontia can be distinguished from lime, as through it lime appears olive-green, and strontia intense red, when they are first introduced into the flame, after being moistened with hydrochloric acid. As it is easy to separate the baryta and almost all the strontia from the lime by means of dilute sulphuric acid, and as when only baryta and strontia occur together, they are easily distinguished by the naked eye, when one part of baryta occurs with one hundred parts of strontia, and vice versa, it is best to separate baryta and strontia from lime. 153. The following method answers perfectly for their separation. The carbonates, as usually obtained, are dis- solved in hydrochloric acid, and to the solution, diluted with water, dilute sulphuric acid is added. The sulphates of 64 THE SPECIAL PROPERTIES baryta and strontia produced are to "be separated from the lime by filtration through as small a filter as possible, and which has been previously washed out with dilute nitric acid. When the precipitate is very small in quantity, it is necessary to burn the filter, and then to test the residue on platinum wire in the usual way. When strontia occurs in very small quantity, it will not be precipitated ; but, on adding ammonia and carbonate of ammonia, will go down with the lime, from which it can be separated and tested according to the manner described in the Table. 154. The carbonates as usually obtained are dissolved in hydrochloric acid, and to this solution diluted with water, dilute sulphuric acid is added. Precipitate. Sulphate of baryta and sulphate of stron- tia. Test on platinum wire in the air-flame : green (baryta), red (strontia). ' To the original solution add a solution of sulphate of strontia. A preci- pitate indicates the presence of BARYTA. Filtrate. Sulphate of strontia and sulphate of lime. Add ammonia and carbonate of ammonia. Precipitate. Carbonate of strontia and carbonate of lime. Collect on a filter and dissolve in a little nitric acid, evaporate to dryness on a water-bath, and treat with a little strong alcohol. Residue. Nitrate of strontia. Convert into sul- phate and test on pla- tinum wire in the flame, after having re- duced and subse- quently moistened with HCL Through dilute solution of indigo, Carmine-red : STRONTIA. Solution. Nitrate of lime. Add oxalate of am- monia. Precipitate. Oxalate of lime not soluble in acetic acid. Convert into sulphate and test on platinum wire in the flame, after having reduced and subsequently moisten- ed with HC1. Through dilute solution of in- digo, Olive-green : LIME. OF THE SECOND GEOUP. 65 155. The dilute solution of indigo, to distinguish between strontia and lime, is made by diluting the common indigotic acid till it gives with sulphate of lime an olive-green colour, on testing in the manner directed. Care must be taken not to make this solution too dilute, otherwise sulphate of lime appears slightly red through it. It is to be used in the same kind of vessel as the indigo solution for the alkalies. 156. MAGNESIA. This oxide differs from the other mem- bers of this group, not only by its non-precipitation by carbonate of ammonia in the presence of ammonical salts, but likewise from the difficult solubility of its hydrate and the ready solubility of its sulphate. The oxalate and chro- mate, as well as some other salts of magnesia, are soluble in water. The soluble magnesian salts have a nauseous bitter taste ; they do not alter vegetable colours when in a neutral state, and, with the exception of sulphate of mag- nesia, they undergo decomposition when ignited. All the salts of magnesia which are insoluble in water dissolve readily in hydrochloric acid. Magnesia is found in the mineral kingdom principally in the state of SULPHATE (Epsom salts MgO, SO 3 +HO + 6aq), of CAEBONATE, and in combination with SILICIC ACID in various proportions, forming the meerschaum, serpentine, &c. 157. Ammonia precipitates from aqueous solutions of salts of magnesia a portion as HYDEATE (MgO, HO). The rest of the magnesia remains in solution, with the salt of ammonia formed, as a double salt. The presence of salts of ammonia prevents the precipitation altogether. 158. The fixed alkalies and the other alkaline earths precipitate magnesia from its solutions in the form of HYDEATE. This precipitate is soluble in salts of ammonia ; the addition therefore of these substances, either before or 66 THE SPECIAL PROPERTIES after the precipitation, prevents or redissolves the precipi- tate formed. 159. Arseniate of ammonia (3 NH 4 0, AsO 5 ) produces, in solutions of magnesia, a white precipitate of ARSENIATE OF MAGNESIA and AMMONIA (2 MgO, NH 4 O, As0 6 ), which is soluble in acetic and other weak acids. 160. Phosphate of soda (2 JS T aO, HO, P0 5 ) produces, in concentrated solutions of magnesia, a precipitate of PHOS- PHATE OF MAGNESIA (2 MgO, HO, P0 6 ). A niagnesian phosphate more insoluble in water may be produced by add- ing, along with the phosphate of soda, chloride of ammonium and ammonia ; the precipitate in this case being PHOSPHATE OF MAGNESIA AND AMMONIA (2 MgO, NH 4 0, P0 5 ) ; both phosphates are soluble in free acids. 161. Phosphate of magnesia and ammonia, and arseniate of magnesia and ammonia, are the only magnesian salts which are insoluble in aqueous solutions containing salts of ammonia. 162. If magnesia or any of its compounds, after being ignited strongly by the blowpipe name upon a charcoal support, be moistened with nitrate of cobalt, and again ignited, the mass assumes, on cooling, a pale flesh colour. THIED OXIDE OF ZINC. OXIDE OF MANGANESE. Oxios OF NICKEL. OXIDE OF COBALT. 163. The members of this group are insoluble in water ; but they dissolve readily in the dilute mineral acids, sul- phuric, nitric, and hydrochloric acids, the salts they form with these acids being soluble. They are not precipitated in the least degree from their solutions by hydrosulphuric OF THE THIRD GROUP. 67 acid, if a free mineral acid is present. They are not pre- cipitated completely frojn their neutral solutions_by hy_dro- sulphuric acid, but they are completely precipitated by that acid from their alkaline solutions in the state of sulphides. Their sulphides are insoluble in the alkalies and alkaline sulphides, with the exception of_^l^Me~^f^ceT,"wnich, under certain circumstances, dissolves to a slight "extent in the alkaline sulphides, imparting thereby to the solution a brownish colour. 164. The metallic radicals of these oxides possess the following properties : manganese decomposes water at 212 F., and zinc, nickel, and colalt decompose it at a red heat, and at common temperatures in contact with strong acids. 165. The precipitate produced by the general reagent, sulphide of ammonium, after being well washed with water containing a little sulphide of ammonium,* must be ex- amined in the following way : If it is of a liylit colour, NICKEL and COBALT must be absent (I 1, K 1). Examine the precipitate for MANGANESE by the blowpipe test (171) ; if manganese is absent, examine the precipitate for ZINC by the blowpipe test (174). When manganese is present, dissolve the precipitate in dilute 'hydrochloric acid ; boil to expel sulphuretted hydrogen, then add carbonate of ammonia in excess and boil for some time : the manganese will be precipitated as carbonate (Gr 3), whilst ZINC, if present, will remain in solution. Filter, and to the nitrate add sulphide of ammonium when zinc, if present, will be pre- cipitated as sulphide ; confirm its presence by examining the precipitate by the blowpipe test. 166. If the precipitate is Hack, all the members of the group must be sought for. Examine the precipitate for * Sulphide of ammonium is added in order to prevent the precipitate from oxidizing. 68 THE SPECIAL PROPERTIES MANGANESE by the blowpipe test. Treat the precipitate, whether manganese is present or not, with cold dilute hydro- chloric acid ; the sulphides of nickel and cobalt will remain undissolved, whilst the sulphides of manganese and zinc will dissolve ; boil the filtered hydrochloric acid solution, which may contain MANGANESE and ZINC, until all sulphide of hydrogen is expelled, then add a solution of one of the fixed alkalies in excess ; manganese * will be precipitated, whilst zinc will remain in solution ; filter if the alkali has produced any precipitate, and add to the filtrate or to the solution (when it does not require filtering) sulphide of hydrogen, when zinc, if present, will be precipitated. After having washed the black residue, examine it for nickel and cobalt in the following way : Expose a small portion of the pre- cipitate on a bead of borax to the outer blowpipe flame, in the way directed in par. 180. A blue bead denotes the presence of cobalt ; this is a safe and certain test for cobalt ; consequently, if a blue bead is not produced, cobalt is absent. If a yellow, and not a blue, bead has been formed, which becomes gray and dull in the inner flame, nickel is present. When cobalt is present, nickel is sought for in the following way: The remainder of the precipitate is dissolved in nitro-hydrochloric acid, and the acid solution evaporated almost to dryness ; a concentrated solution of cyanide of potassium is then added in excess, and the whole * It is almost impossible to prevent a minute quantity of the sul- phides of cobalt and nickel oxidizing, even if the precipitate is washed most carefully with water containing sulphide of ammonium; the oxidized portion of these two bodies will, therefore, be present in the hydrochloric acid solution, and consequently be precipitated by the fixed alkali ; a precipitate may, therefore, be produced by the alkali, when no manganese is present. It will not be necessary to examine the pre- cipitate for nickel and cobalt, as sufficient will remain undissolved, unless the student has allowed the precipitate to remain on the filter for a great length of time. OF THE THIRD GROUP. 69 solution must then be boiled for some time, adding a little water from time to time, to replace that which is evaporated. To the solution, which must not be filtered even if a preci- pitate has been formed, is added, when it is cold, sulphuric acid slightly in excess ; if in some hours after the acid has been added a precipitate appears, nickel is present ; if no precipitate appear, or at least only a crystalline one which redissolves in water, nickel is absent. 167. Nickel may also be detected in the presence of cobalt by the two following methods. 1st method: "The acid solution which contains cobalt and which may contain nickel, must be evaporated nearly to dryness, nitrite of potash must then be added in not too small a proportion, then acetic acid to strongly acid reaction, then let the mixture stand for at least several hours in a moderately warm place, when cobalt will separate as nitrite of sesquioxide of cobalt and potash; the nickel may then be readily precipitated from the filtrate by soda or sulphide of ammonium. 2d method: Saturate with chlorine the very dilute solution of the two metals in hydrochloric acid, having the acid slightly in excess ; add carbonate of baryta in excess, and let the fluid stand twenty-four hours. The cobalt is entirely pre- cipitated in this process as black sesquioxide, whilst the nickel remains in solution, and may, after the removal of the baryta by sulphuric acid, be thrown down with solution of soda."* 168. The following precautions are to be attended to in the analysis of this group : When manganese is present, care must be taken to expel all the sulphuretted hydrogen from the hydrochloric acid solution, before carbonate of ammonia is added to separate the manganese from the zinc. Before * The student ought to state all the different methods which could be adopted for the separation of the members of this group. 70 TABLE III. BEHAVIOUR o* THE THIRD GROUP WITH THE SPECIAL REAGENTS. OXIDE OF MAN- OXIDE OF ZINC OXIDE OF COBALT OXIDE OF NICKEL, GANESE CMnO). (ZnO). (CoO). (NiO). G 1. Sulphide of H 1. Sulphide I 1. Sulphide of K 1. Sulphide of Manganese (MnS) of Zinc (ZnS), Cobalt (Co S) is Nickel (NiS) is is flesh - coloured, like the oxide, is black. It is in- black. It is in- but becomes brown white. It is in- soluble in the di- soluble in the di- on exposure to the soluble in acetic lute mineral acids, lute mineral acids, air. It is soluble acid, but dissolves as well as in the as well as in the in the weak acids, in the dilute mine- weaker acids. It weaker acids. It as acetic, as well ral acids. is soluble in is soluble in as in the dilute Nitro-hydrochloric Nitro-hydrochloric mineral acids. acid. acid. G 2. The fixed H 2. The fixed I 2. The fixed K 2. The fixed alkalies precipitate alkalies precipitate alkalies produce in alkalies precipitate from solutions of from solutions of solutions of this from solutions of this Oxide (MnO) this oxide (ZnO) oxide (Co 0) blue this oxide (NiO; the HYDRATE, the HYDRATE, precipitates of the HYDRATE, in which is of a whit- which is white. basic salts of Co- the form of a light ish colour at &rst, The Hydrate of balt, which turn green precipitate, but speedily be- this oxide is com- green on exposure which is unalter- comes blackish pletely soluble in to the air ; and are able in the air, and brown on exposure an excess of either converted, upon insoluble in an ex- to the air. The of the fixed alka- boiling, into the cess of either of Hydrate is insolu- lies, if it (the al- PALE RED H Y- the fixed alkalits. ble in an excess of kali) is perfectly DRATE of this ox- either of the fixed free from carbonic ide, which is gene- alkalies. The pre- acid. rally discoloured, sence of ammo- owing to a little niacal salts pre- Co 2 3 beingformed. vents in a great Each of these pre- measure the preci- cipitates is insolu- pitation. ble in an excess of either of the fixed alkalies. G 3. Carbonate H 3. Carbonate 1 3. Carbonate of K 3. Carbonate of of Ammonia pro- of Ammonia pro- Ammonia pro- Ammonia pro- duces in solutions duces in solutions duces in solutions duces in solutions of this Oxi de a of this oxide a of this oxide a red of this oxide an precipitate of the precipitate of precipitate of CAR- apple-green preci- Carbonate (Mn 0, white BASIC CAR- BON ATE OF CO- pitate of Carbonate C0 2 ), which is BOXATE OF ZlNC, BALT, which is of Nickel, which ; s white, and insolu- which is easily readily soluble in readily soluble in ble in an excess of soluble in an ex- an excess of the an excess of the re- the reagent, espe- cess of the reagent. reagent, the solu- agent, the solution cially on boiling. tion having a red having a greenish colour. blue colour. The alkalies fail to precipitate the members of this group in the presence x of noil- volatile organic matter, such as starch, sugar, tartaric acid, &c. THE SPECIAL PROPERTIES. 71 adding sulphuric acid to the cyanide of potassium solution, it will be better to add a little water, in order to prevent any sulphate of potash from crystallizing out, which might mislead the student as regards nickel. On adding caustic soda to the hydrochloric acid solution, which may contain the oxides of zinc and manganese and small traces of the oxides of nickel and cobalt, from the partial oxidation of their sulphides, a small quantity of the zinc will frequently be precipitated. This is occasioned by the caustic alkali having absorbed some carbonic acid from the air, and become partially converted into carbonate, which causes a partial precipitation of the zinc. SPECIAL REMARKS. 169. PROTOXIDE or MANGANESE. Numerous oxides of manganese exist as natural productions, and a still larger number can be formed artificially. The only one treated of in this work is the first or lowest compound of oxygen with manganese. All the others are reduced to this state by adding to their solutions hydrosulphuric acid, or any other reducing agent. This oxide is of a greenish gray colour, and its hydrate is white. Both, however, turn brown when exposed to the air, being converted into higher oxides. Its salts are colourless or of a pale red ; the solutions of those soluble in water do not affect vegetable colours ; and the salts soluble in water are readily decomposed at a red heat, with the exception of the sulphate. The most abundant source of manganese is the PEROXIDE (Mn0 2 ), which exists in nature under a variety of forms. 170. Ammonia precipitates this oxide (MnO) in part from its solutions as hydrate, w r hich an excess of the reagent does not redissolve. But ammonia in the presence of chloride 72 THE SPECIAL PROPERTIES of ammonium, or in fact any salt of ammonia, the acid of which causes no insoluble compound with manganese, causes no precipitate in solutions of manganese. An ammoniacal solution of manganese attracts oxygen from the air, which converts the manganese oxide into a higher oxide ; and this latter oxide being insoluble in ammonia, is deposited, as it becomes formed, in brownish flocks. 171. The smallest quantity of manganese can be detected in any of its compounds, by fusing them, in conjunction with carbonate of soda and a small quantity of nitrate of potash, upon platinum foil or wire, in the outer blowpipe flame; manganate of soda (NaO, Mn0 3 ), which is of a bluish green colour, being produced. "This method fails to detect manganese in limestone rocks, on account of the in- solubility of the lime salt in carbonate of soda and nitrate of potash ; but if, along with the two reagents just mentioned, a little borax be added, so as to attack and dissolve a portion of the mass, the well-known greenish blue enamel is quickly produced." Chapman. 172. OXIDE OF ZINC. The colour of this oxide is wh e, but becomes yellow on being heated, regaining its original colour on cooling. The salts of zinc are colourless. The neutral ones, which are soluble in water, redden litmus paper and are decomposed by heat. The principal minerals of this metal are the anhydrous CARBONATE (calamine ZnO, CO 2 ) and the SULPHIDE (Zinc blende ZnS). 173. "When compounds of zinc, mixed with carbonate of soda, are subjected upon a charcoal support to the inner blowpipe flame, metallic zinc is produced, which volatilizes, and, on passing through the oxidizing flame, becomes again converted into oxide. The charcoal support becomes encrusted with this oxide, which is of a yellow colour while hot, and turns white on cooling. OF THE THIRD GROUP. 73 174. If a compound of zinc be moistened with protonitrate of cobalt and exposed on charcoal to the outer blowpipe flame, a mass of a beautiful green colour will be produced ; the colour is best seen when the mass has become cold. 175. OXIDE or COBALT. The colour of this oxide is greenish-gray, its hydrate being pale red. Salts of cobalt are red when they contain water of crystallization ; in the anhydrous state they are blue. Their solutions are red ; yet when concentrated, or when they contain a free acid, they are blue or green, but they become green simply by the addition of water. The solutions of the neutral salts that are soluble in water redden litmus paper, and are decomposed by heat. The principal mineral of this metal is the BRIGHT WHITE COBALT (Co As 2 +CoS 2 ). 176. Ammonia produces in solutions of this oxide the same precipitate as the fixed alkalies do ; but the precipitate is soluble in an excess of ammonia, the ammoniacal solution having a reddish-brown colour : the fixed alkalies produce no precipitate, or at least a very slight one, in an ammoni- acal solution of protoxide of cobalt. Ammonia fails to preci- pitate oxide of cobalt from its solutions, if chloride of ammo- nium is present. 177. Cyanide of potassium (K C 2 N=K Cy) precipi- tates from acid solutions of cobalt salts a brownish- white cyanide of cobalt, Co Cy, dissolving easily in an excess of the precipitant : from which solution the cyanide of cobalt cannot be again precipitated by acids, as it exists now in the form of cobalticyanide of potassium, K 3 Co 2 Cy 6 . 2 Co Cy + 3 KCy + H Cy = K 3 Co 2 Cy 6 + H. 178. "If the salt of cobalt contains nickel, the addition of hydrochloric acid to the solution of the cyanides pro- duces a greenish precipitate, which always contains the 1 74 THE SPECIAL PROPERTIES whole of the nickel, and under particular circumstances all the cobalt that is, when these two metals are in the proportion of three equivalents of nickel to two equivalents of cobalt. The precipitate consists then of cobalticyanide of nickel, JN"i 3 Co 2 Cy 6 . In case of a larger proportion of nickel, the precipitated cyanide of nickel is mixed with the former compound ; but if the proportion of nickel is smaller, a part of the cobalt remains in solution as cobalti- cyanide of potassium." Will. 179. " If nitrite of potash is added in not too small pro- portion to a solution of protoxide of cobalt, then acetic acid to strongly acid reaction, and the mixture put in a moderately warm place, all the cobalt separates, from con- centrated solutions immediately or very soon, from dilute solutions after some time, as NITRITE or SESQTJIOXIDE or COBALT AND POTASH (Co 2 3 , 3 KO, 5 N0 3 , 2 HO), in the form of a crystalline precipitate of a beautiful yellow colour. The precipitate is only sparingly soluble in pure water, and altogether insoluble in saline solutions and in alcohol. "When boiled with water it dissolves, though not copiously, to a red fluid, which remains clear upon cooling, and from which alkalies throw down hydrate of protoxide of cobalt. (Fischer, Aug. Stromeyer.) This excellent reaction enables us to distinguish nickel from cobalt. It is always neces- sary to concentrate the solution of protoxide of cobalt to a considerable extent before adding the nitrite of potash " (Fresenius) . 180. The compounds of cobalt fused with borax in the loop of a platinum wire, in either flame of the blowpipe, produce a beautiful blue glass, which is a very delicate and characteristic test for cobalt. The cobalt compound must be used in very small proportion. 181. OXIDE or NICKEL. The colour of this oxide is gray, OF THE THIRD GROUP, 75 its hydrate is green. Its salts likewise exhibit this latter colour, except when anhydrous ; in this state they are mostly yellow. The solutions of the neutral salts, which are soluble in water, redden litmus paper, and are decom- posed at a red heat. The principal minerals of this metal are the AESENICAL NICKEL (M As) and the NICKEL GLANCE (Ni S 2 +Ni As 2 ). 182. Ammonia, added in small quantity to solutions of this oxide, produces in them a trifling greenish turbidity ; upon further addition of the reagent, this redissolves readily to a blue fluid, containing a compound of oxide of nickel and ammonia. 183. Cyanide of potassium throws down from solutions of nickel a yellowish green precipitate of cyanide of nickel (Ni Cy), which redissolves in an excess of the preci- pitant as a double salt of cyanide of nickel, and cyanide of potassium (M Cy-fK Cy) ; the solution is brownish- yellow. On the addition of hydrochloric or sulphuric acid to a solution of this double salt, the cyanide of nickel is reprecipitated, whilst the cyanide of potassium is decomposed, hydrocyanic acid being evolved ; the cyanide of nickel is very difficultly soluble in an excess of either of the acids in the cold, but more readily upon boiling. 184. "Nitrite of potasli, used in conjunction with acetic acid, fails to precipitate even concentrated solutions of nickel." 185. In the exterior flame of the blowpipe, oxide of nickel and its compounds impart to beads of borax a reddish- yellow tint ; the colour fades upon cooling, and finally dis- appears almost entirely. If exposed with borax to the inner flame, the bead becomes gray ; if a minute fragment of nitrate of potash be added to the bead after exposure to the inner flame, and it is then fused in the outer flame, it ac- quires a rich purple colour. 76 THE SPECIAL PROPERTIES FOUKTH GROUP. ALUMINA, SESQUIOXIDE or CHEOMIUM, SESQUIOXIDE OF IEON, PEOTOXIDE or IBON. The PHOSPHATES OF ALUMINA, CHEOMITJM AND IEON. The PHOSPHATES OF THE ALKALINE EAETHS. The OXALATES OF BAETTA, SlEONTIA AND LlME.* APPENDIX TO THE G-EOUP. TITANIC ACID. SESQUIOXIDE OF UEANITJM. 186. The members of this group are insoluble in water, but they dissolve readily in the dilute mineral acids ; after ignition, however, they dissolve with great difficulty, even in the concentrated mineral acids. 187. The metallic radicals of these oxides decompose water at a red heat, and at common temperatures in con- tact with strong acids. 188. Sulphide of ammonium precipitates the members of this group : it precipitates alumina and sesquioxide of chro- mium as oxides, for sulphide of aluminum and sulphide of chromium cannot be formed in the humid way ; they (the * The phosphates and oxalates do not engage the attention of the student as he passes through -the basic groups ; he has therefore only to deal with the substances given in Table IV. It is not until he has had some practice in examining both for acids and bases that the inso- luble salts which are precipitated along with the oxides of this group are included in the course ; the precipitate is then examined according to Table V. The substances in the different appendices do not form a part of the course ; they are, therefore, not included in the tables. OF THE FOURTH GROUP. 77 sulphides) are decomposed by water into the oxides of the metals and hydrosulphuric acid. It is, therefore, the am- monia in the sulphide of ammonium which determines the precipitation of these two substances ; consequently hydro- sulphuric acid is always evolved when sulphide of ammo- nium is added to a solution containing either or both these substances. Protosulphide of iron is always formed when sulphide of ammonium is added either to a solution of a per- or proto- salt of iron, as a persulphide of iron is not formed in the humid way. Protosulphide of iron is of a black colour; it oxidizes rapidly on exposure to the air, which causes its colour to change from black to brown. 189. The precipitate produced by the general reagent, ammonia, after being well washed to free it from all foreign substances, must be examined in the following way : 190. 1st. Manganese precipitates in small quantities along with the members of this group, owing to its becom- ing converted into a higher oxide, the cause of which is fully explained at (170). A small portion of the washed precipitate must be examined for MANGANESE by the Uow- pipe test (171). 191. 2d. Another portion of the washed precipitate must be dissolved in as small a quantity of dilute hydro- chloric acid as possible : to this acid solution a cold solution of soda or potash in excess must be added, which will pre- cipitate IRON as peroxide (N. 3.), if present ; the presence of iron must be confirmed by dissolving the precipitate produced by the fixed alkali in acetic acid, and adding to this acid solution ferrocyanide of potassium (see 205). On lotting the filtrate from the iron precipitate, or the solution which has failed to give a precipitate, SESQUIOXIDE or CHROMIUM is thrown down (M. 3.) ; this test for chromium must not be relied upon, and therefore the remaining part 78 THE SPECIAL PROPERTIES of the precipitate produced by the general reagent must be examined for chromium in the way described in the next paragraph. To the filtrate from the chromium precipitate,, or to the solution which has failed to give a precipitate, add hydrochloric acid until the solution is acid ; then add one grain of chlorate of potash, and warm the solution so as to destroy all organic matter (note 2, page 80) ; add, lastly, ammonia in excess. ALUMINA, if present,* will be thrown down (L. 2. & 3.) as a white fiocculent precipitate, on gently warming the solution; when a precipitate is pro- duced, it must be examined for alumina by the blowpipe test. When iron is present, the original solution must be examined to ascertain in what state of oxidation it exists j for this purpose a portion of the original solution must be examined for PROTOXIDE by means of ferrici/ani cle of potas- sium (202) ; another portion must be examined for the SESQUIOXIDE by means of the ferrocyanide of potassium (205). 192. 3d. Mix the rest of the washed precipitate with one part of carbonate of soda and three parts of nitrate of potash ; fuse the mixture in a porcelain crucible ; after the fusion, allow the mass to cool, and then boil it with water, and filter. If the filtrate has a yellow colour, SESQUIOXIDE or CHROMIUM is present ; confirm its presence by acidify- ing the filtrate with nitrie acid, if chromium be present the solution will change, when acidified, to an orange red. If chromium is present, and it was not precipitated on boiling the alkaline solution (see 191), and a precipitate * If chromium lias been found to be present in the way described in paragraph 192, and it was not precipitated from the alkaline solution (paragraph 191), it will, most probably, be precipitated by ammonia,, the alumina reagent; it is necessary, therefore, to look for alumina in the way described in paragraph 192, when chromium is present and is not precipitated on boiling the fixed alkaline solution. OF THE FOURTH GROUP. 79 was produced by ammonia, after acidifying with hydro- chloric acid, and adding chlorate of potash, it is necessary to look for alumina in the filtrate from the fused mass, for the reasons stated in the foot-note, page 78. Add, therefore, to the filtrate from the fused mass, after it has been acidi- fied with nitric acid, ammonia in excess, when, if ALUMINA is present, a precipitate will be produced.* 193. The following precautions are to le attended to in the analysis of this group : Before dissolving the precipi- tate produced by ammonia, it must be completely freed, by washing it with distilled water, from all traces of ammonia. Dissolve the precipitate in as little acid as possible; for this purpose, pour the acid, small quantities at a time, in a boiling state, upon the precipitate collected upon the filter. If the precipitate be very large, remove it from the filter into an evaporating dish, before adding the acid. The pre- cipitate produced by the soda solution in the cold, must be examined for iron, as it might be due to manganese, which was precipitated by ammonia, and which, like iron, is inso- luble in the fixed alkalies. SPECIAL REMARKS. 194. ALUMINA. This -substance is very abundant in nature. It forms not only the basis of common clay, but is likewise a principal ingredient in many of the precious stones. Along with slight traces of silica and peroxide of iron, it forms the CORUNDUM, SAPPHIRE, RUBY, DIAMANT SPAR, &c. As hydrate, it is known under the names of DIASPORE and GIBBSITE. Combined with silica and glucina, * By the fusion a portion of the alumina becomes converted into aluminate of soda, which dissolves in the water, whilst a portion of the alumina remains tmdissolved. 80 TABLE IY. BEHAVIOUR OF THE FOURTH GROUP WITH THE SPECIAL REAGENTS. OXIDE SEsauioxiDE PROTOXIDE ALUMINA OF CHROMIUM OF IRON OF IRON (A1 2 3 ). (Cr 2 3 ). (Fe 2 3 ). (FeO). L.I. This oxidf M. 1. This oxide N. 1. This oxide 0.1. This oxide and its hvdrate is green, and its hv- and its hydrate are is black, and its hy- (AL,0 3 , 3HO) are drate (Cr. 2 3 ,3HO) of a reddish-brown drate is white. white. a bluish-green pow- colour. der. L. 2. Ammonia, M. 2. Ammonia, N. 2. Ammonia, 0. 2. Ammonia, even in the pre- sence of its salts, evenin the presence of its salts, precipi- even \ n the presence of its salts, preci- but not in the pre- sence of its salts, precipitates Alu- mina in the form tates this oxide in the state of HY- pitates this oxide from its solutions precipitates the HYDRATED PROT- ofHYDRATE,which DRATE, which an in the form of HY- OXIDE (FeO, HO) an excess of the re- excess of the re- D R A T E (Fe 2 0,, from solutions of agent does not re- agent does not re- H 0), which an ex- the protosalts of dissolve. dissolve. cess of the reagent iron, which an ex- does not redissolve. cess of the reagent does not redissolve. L. 3. The fixed M. 3. Tine fixed N. 3. The fixed O. 3. The fixed Alkalies throw Alkalies throw Alkalies precipi- Alkalies precipi- downAlumitiafrom down from solu- tate from solutions tate from solutions its solutions in tions of this oxid^ of this oxi:ie the of this oxide the the form of HY- the HYDRATK, , HYDRATR, inxolu- HYDRATE, insolu- DRATE.which isso- which is soluble in ble in an excess 01 ble in an excess of lulle in an excess an excess of there- the reagent. the reagent. of reagent, from agent in the cold ; which solution it jut on boiling the may be again pre- solution, it is again cipitated on the ad- precipitated. dition of Chloride of Ammonium. L. 4. Carbonate M. 4. Carbonate N. 4. Carbonate 0. 4. Carbonate of Ammonia preci- pitates from solu- of Ammonia preci- pitates from solu- of Ammonia preci- pitates from solu- of Ammonia pre- cipitates from solu- tions of Alumina tions of this oxide tions of this oxide tions of this oxide the HYDRATE. the HYDRATE, car- the HYDRATE, car- the PROTOCARBO- This precipitation is attended with an bonic acid being given off. bonic acid being given off. NATE (FeO,C0 2 ), soluble in chloride evolution of carbo- of ammonium. nic acid. The fixed alkaline carbonates throw down from their solutions all the members of this group, some as oxides, the rest as carbonates. An 'excess of the reagent does not redissolve the precipitate. The alkalies fail to precipitate the members of this group in the pre- sence of non-volatile organic matter, such as starch, sugar, tartaric acid, &c. THE SPECIAL PROPERTIES. 81 it forms the EMERALD, BERYL, ETJCLASE, and CHRYSOBERYL. When pure, it is white ; but it frequently possesses a yel- lowish tint when obtained by drying the hydrate. Its salts are colourless ; the soluble ones redden litmus paper, and lose their acids upon ignition. " The insoluble salts are dissolved by hydrochloric acid, with the exception of certain native compounds of alumina; the compounds of alumina which are insoluble in hydrochloric acid are decomposed by ignition with carbonate of soda or bisulphate of potash'* (Fresenius) . The SULPHIDE OF ALUMINUM cannot exist in contact with water, being decomposed into alumina and hydrosulphuric acid. 195. If alumina or any of its compounds be ignited upon charcoal by the blowpipe flame, afterwards moistened with a few drops of protonitrate of colalt, and again strongly heated, the mass assumes a BLUE COLOUR on cooling. This can only be used as a confirmatory test, as other sub- stances, phosphates and readily fusible salts, exhibit the same reaction. 196. OXIDE OR SESQUIOXIDE or CHROMIUM. The colour of this oxide is green; its hydrate is bluish-gray. The salts of this oxide have a green or a violet colour ; their solutions possess a beautiful green colour by reflected, and reddish- violet by transmitted light. The salts of this oxide, which are soluble in water, redden litmus paper. Sulphide of chromium is decomposed in contact with water into oxide of chromium and hydrosulphuric acid. The principal mine- ral from which this oxide is extracted is the CHROME IRON (EeO, Cr 2 O 3 ), which is found principally in Sweden, in the TJralian Mountains, and in America. 197. When oxide of chromium, or any of its compounds, are fused with nitrate of potash, it becomes converted into a higher oxide, viz., CHROMIC ACID, which, combining with 82 THE SPECIAL PROPERTIES the potash, forms yellow chromate of potash. This potash salt must be dissolved in water and tested for chromic acid by adding acetic acid in excess, and then acetate of lead, when yellow chromate of lead will precipitate. This test distin- guishes it at once from all otber substances. 198. Borax dissolves oxides of chromium and its salts, both in the inner and outer blowpipe flame ; the bead, on cooling, assumes an EMERALD GREEN COLOUR. Microcosmic salt has the same effect. 199. In the fixed alkalies, a small quantity of oxide of chromium in the presence of a large quantity of peroxide of iron is totally insoluble ; but a small quantity of the latter dissolves readily when a large quantity of the former is present. Under these circumstances, the two oxides are best separated from each other by fusing the mixed sub- stances with nitre and carbonate of soda, and treating the fused mass with water ; the CHROMATE OF POTASH dissolves in the liquid, whilst the PEROXIDE OF IRON remains behind. 200. PROTOXIDE OR OXIDE OF IRON. The colour of this oxide is black ; its hydrate is white, which, in the moist state, absorbs oxygen from the air very rapidly, acquiring a grayish-green, and finally a brownish-red, colour. The salts of this oxide are white in their anhydrous, and green in their hydrated state ; their solutions appear coloured only when very concentrated. They turn blue litmus paper red, and are decomposed at a red heat. "When dissolved, they absorb oxygen from the air, the oxide being thereby con- verted into peroxide, which, in a neutral solution, is deposited as a yellow basic salt. Oxidizing agents, such as chlorine and nitric acid, effect this conversion more speedily. 201. Ferrocyanide of potassium (Cy 3 Fe, 2 K=Cfy, 2 K) produces, in solutions of protoxide of iron, a white precipi- tate Of FERRO CYANIDE OF IRON AND POTASSIUM (2 Cfy, K, OF THE FOURTH GROUP. 83 3 Fe), which speedily becomes Hue by absorbing oxygen from the air. Free alkalies prevent the formation of this precipitate. It is insoluble in the dilute acids. 202. Ferricyanide of potassium (2 Cfy, 3 K) produces a beautiful blue-coloured precipitate of FERRICYANIDE OP IRON (2 Cfy, 3 Fe), which is insoluble in hydrochloric acid, but is decomposed with precipitation of oxide of iron by the alkalies. In highly dilute solutions of protoxide of iron, ferricyanide of potassium produces only a bluish- green colouration. If the solution is alkaline, it must be acidified with acetic acid ; if it is acid, and the acidity is caused by one of the mineral acids, an alkaline acetate must be added, in sufficient quantity so that the base of the acetate may neutralize the free mineral acid (see 207). 203. PEROXIDE OR SESQTJIOXIDE OF IRON. This oxide, which is abundantly spread through nature, has received from mineralogists the name of HEMATITE. It is of a brownish-red colour, and is well known as rust of iron. Its salts usually possess a reddish-yellow colour. The soluble neutral salts of mineral acids redden litmus paper, and are decomposed by heat. 204. Soluble SULPHOCYANIDES give to neutral and acid solutions of persalts of iron an intense blood-red colour. 205. Ferrocyanide of potassium throws down, even from highly dilute solutions, a beautiful blue precipitate of FERRO- CYANIDE OF IRON (Prussian blue, Cfy 3 ,Fe 4 ), which is insoluble in acids, but is decomposed by the alkalies. In highly dilute solutions of this oxide of iron, only a blue tinge is produced at first ; after long standing a scanty precipitate is formed. The same precautions are required in this case as in testing for protoxide with the ferri- cyanide. 206. Ferricyanide of potassium deepens the colour of the 84 THE SPECIAL PROPERTIES solution of persalts of iron to a ruddy brown, but causes no precipitate ; if the ferricyanide contains a trace of ferro- cyanide,* it will impart to the iron solution a greenish tinge. 207. The ferro- and ferri- cyanide of potassium are de- composed by the mineral acids, green-coloured solutions being formed. In testing, therefore, for iron in add solu- tions, it is necessary to avoid this error by the previous ad- dition of an alkaline acetate. 208. Sulphocyanide of potassium (K, CyS 2 ) produces in neutral, and even in moderately acid, solutions of sesqui- oxide of iron a very intense blood-red colour, arising from the formation of a soluble STJLPHO CYANIDE or IRON ; it disappears on the addition of alkalies, or of a large quantity of strong acid. This is by far the most delicate test for sesquioxide of iron. The following SALTS, ~being insoluble in Neutral and Alkaline Solutions, are precipitated along with the members of the Fourth Group. ^ PHOSPHATE OF ALUMINA, PHOSPHATE OF CHROMIUM. THE PHOSPHATES OF IRON, AND THE PHOSPHATES AND OXALATES OF THE ALKALINE EARTHS, WITH THE EX- CEPTION OF OXALATE OF MAGNESIA. 209. PHOSPHATE OF ALUMINA behaves in the same way with reagents as pure alumina, with this exception, that it is insoluble in acetic acid, whilst pure alumina is soluble. * The solution of ferricyanide of potassium ought to be made as it is wanted, as the ferricyanide decomposes when in a state of solution, a trace of ferrocyanide being formed. f The student will do well to omit this section of the group until he has had some practice in detecting the more simple combinations of acid and base. OF THE FOURTH GROUP. 85 The presence of phosphoric acid, when combined with alu- mina, may be detected by the following method : After having dissolved the alumina compound in a small quantity of hydrochloric acid, tartaric acid must be added, and then ammonia in excess. If on the addition of sulphate of magnesia to this solution a precipitate be formed, PHOS- PHORIC ACID is present. When the quantity of acid pre- sent is small, the precipitate will not appear until after the lapse of some time ; in all cases the formation of the pre- cipitate is much promoted by agitation (consult paragraph 429). 210. The phosphoric acid in phosphate of alumina may also be detected in the following way : " Add carbonate of soda to the hydrochloric acid solution until the free acid is nearly neutralized ; mix with carbonate of baryta in excess, add solution of soda or potash, and boil. This pro- cess gives the alumina in solution, the phosphoric acid in a precipitate of phosphate of baryta. Dissolve this preci- pitate in hydrochloric acid, decompose by sulphuric acid, filter, and test the filtrate with sulphate of magnesia, with addition of chloride of ammonium and ammonia." Frese- nius. 211. Phosphoric acid may be detected in almost all salts and most minerals containing it, in the following way : " If some molybdate of ammonia is mixed in a test-tube with hydrochloric acid or nitric acid in sufficient quantity to redissolve the precipitate which forms at first, and a little of a very dilute fluid containing phosphoric acid is then added, and the mixture boiled, the fluid acquires an ^'n- tensely yellow colour, and after some time a yellow preci- pitate separates, which is insoluble in hydrochloric acid. As the yellow compound is decomposed by free phosphoric acid, an excess of the fluid containing the phosphoric acid 86 THE SPECIAL PROPERTIES must be carefully avoided. The yellow precipitate may, when it has subsided, be perceived even in dark-coloured fluids. " Fresenius. 212. PHOSPHATE OF THE SESQTTIOXIDE OF CHROMIUM behaves in the same way with reagents as the sesquioxide, with this exception, that it is insoluble in acetic acid, in which reagent the latter is soluble. The presence of phos- phoric acid, when combined with sesquioxide of chromium, may be detected, in the same way as when this acid is combined with alumina. To ascertain whether sesqui- oxide of chromium and the phosphate of the sesquioxide of chromium are both present in the precipitate produced by boiling the fixed alkaline solution, dissolve the pre- cipitate produced on boiling in ^hydrochloric acid, add an alkaline acetate in excess ; if a precipitate is produced, the PHOSPHATE is present, filter off", and to the filtrate add ammonia in excess ; if a precipitate is produced the OXIDE is present. 213. PHOSPHATE OF IRON behaves in the same way with reagents as the peroxide, with this exception, that it is insoluble in acetic acid, in which reagent the latter is solu- ble. Sulphide of ammonium decomposes PHOSPHATE OF IRON,* precipitating the metal in the state of sulphide whilst the acid remains in solution in combination with the ammonia. The phosphoric acid is therefore sought for in the filtrate and not in the precipitate, when the sulphide of ammonium has been employed as the precipitating reagent. The same method may be employed for the detection of phosphoric acid when combined with iron, as is employed when this acid is in combination with alumina. * The phosphates of alumina and chromium are not decomposed by sulphide of ammonium, they are precipitated unchanged by that reagent. OF THE FOURTH GROUP. 87 214. PHOSPHATE OF LIME (bone earth 3CaO, P0 5 ) is soluble in acetic acid. This salt may be decomposed in several ways. The following are those which are most ap- plicable in qualitative analysis : 1. Dissolve the phosphate in a small quantity of hydrochloric acid ; add to the solu- tion acetate of potash, and after that a few drops of per- chloride of iron (consult paragraph 425). PHOSPHATE OP IRON will be precipitated, whilst the LIME will remain in solution along with the excess of the perchloride of iron employed. To detect the LIME, throw down the iron by sulphide of ammonium, and add to the nitrate oxalic acid. If a precipitate be produced, lime is present. 2. Dissolve the phosphate in a small quantity of nitric acid; add to this solution subnitrate of mercury, and then ammonia slightly in excess ; PHOSPHATE OF MERCURY along with the excess of SUBOXIDE OF MERCURY will be precipitated, whilst the LIME will remain in solution, from which solution it will be thrown down on the addition of oxalic acid. Boil the mixed precipitate of phosphate of mercury and suboxide of mercury in sulphide of ammonium ; filter, and to the nitrate add chloride of ammonium and sulphate of magnesia; if a precipitate be produced, it proves the presence of phos- phoric acid. The above remarks upon PHOSPHATE or LIME apply to the corresponding salt of BARYTA, STRONTIA, and MAGNESIA. 215. OXALATE OF LIME is insoluble in acetic acid. By ignition, this salt, like all the other oxalates, is decomposed, a carbonate being left. To separate the oxalic acid from the lime, add to a nitric solution of this salt subnitrate of mercury. OXALATE OP MERCURY will be precipitated, whilst the lime, in the state of nitrate, will remain in solution along with the excess of subnitrate of mercury employed. To detect LIME, precipitate the mercury by ammonia, and 88 THE SPECIAL PROPERTIES. add to the filtrate oxalic acid. OXALATE OF MEBCTJKY is decomposed by boiling it in sulphide of ammonium, the metal being precipitated as sulphide, whilst the acid remains in combination with ammonia, in which solution it may be detected on the addition of any soluble lime salt. The above remarks apply to the corresponding SALT or BABYTA and STRONTIA. 216. The following precautions are to le attended to in the analysis of this section : Before dissolving the precipi- tate produced by ammonia, it must be completely freed by washing from all trace of that reagent. Frequently a small precipitate will appear after boiling the caustic soda solu- tion, when oxide of chromium is absent ; the presence of this member must therefore in all cases be confirmed by other tests. Alumina and phosphate of alumina are some- times overlooked by the operator, from his neglecting to add acetic acid in excess. The precipitate produced by caustic soda, after being well washed, should be dissolved in as small a quantity of nitric acid as possible, to which solution a moderate quantity of tartaric acid should be afterwards added, and finally ammonia in excess ; the solu- tion ought, after the addition of these reagents, to be well agitated, and time allowed for the separation of the preci- pitate. In testing for phosphoric acid in the ammoniacal solution, a precipitate will frequently be formed on the addition of sulphate of magnesia when phosphoric acid is absent. To distinguish the phosphate precipitate from this, the precipitate produced ought to be dissolved in tartaric acid, and ammonia added in excess. If a precipitate again appears, after agitating the liquid and allowing it to stand, it must be due to the presence of phosphoric acid. The precipitate produced by ammonia in the tartaric acid solu- tion must be well washed before dissolving it in dilute nitric ACID e cold. ^ .C J p .S r /3 S | S3 35 t-i -i ts ^ ^ fi.^ g^; p- I -I g^ gJ S5 B-s U : c >, MBIN A, W Q 3 fc ' -o| H PS'S-g ^^8 PH H-I lsl E ^ a ?. K ZSil^ |-s, 5 Is g & ^ BiS WO. S 6|H JH pq p w^ a M S ^* 90 THE SPECIAL PROPERTIES acid. A slight turbidness will generally be formed on the addition of nitrate of mercury to the nitric acid solution, even in the absence of oxalic acid, owing to the nitric acid containing a slight trace of chlorine. 217. The following is another method for the separation of the members of the fourth group and the phosphates and oxalates which are precipitated along with them by the group reagent ; the precipitate produced by ammonia, after being well washed, is ignited upon a piece of platinum foil, or in a small crucible ; if one or more of the three oxalates (baryta, strontia, and lime) are present, they will be con- verted by the ignition into carbonates; dissolve the ignited precipitate in as small a quantity of boiling dilute hydrochloric acid as possible; if it dissolves with effervescence, one or more of the three oxalates are present ; examine the solution in this case according to par. 218. If the solution is unattended with effervescence, the three oxalates are absent ; examine the solution in this case ac- cording to par. 219. 218. When the solution is attended with effervescence add ammonia in excess to the solution, warm, and filter ; the filtrate will contain the base or bases originally com- bined with oxalic acid ; examine for these bases in the way directed in the second group, par. 130 ; wash the precipi- tate very well, then dissolve it in as small a quantity of boiling dilute hydrochloric acid as possible ; examine the solution according to par. 219. 219. Add one of the fixed alkalies in excess in the cold to the hydrochloric acid solution ; if PHOSPHATE OF IRON, or PEROXIDE OF IRON, or any of the PHOSPHATES OF THE ALKALINE EARTHS are present, they will be precipitated; whilst ALUMINA and SESQUIOXIDE OF CHROMIUM and their PHOSPHATES will be retained in solution, ; examine the pre- OF THE FOURTH GROUP. 91 cipitate according to par. 221, and the solution according to par. 220. 220. Boil the fixed alkaline solution for some time ; if a precipitate is produced, it is due to the presence of SESQUI- OXIDE OF CHKOMIUM, or its phosphate ; filter when a preci- pitate is produced, add to the filtrate, or to the solution, without filtering, when no precipitate has been produced,* acetic acid in excess, PHOSPHATE ALUMINA, if present, will be precipitated; add to the filtrate ammonia in excess, when ALUMINA, if present, will be precipitated. Dissolve the chromium precipitate in as small a quantity of boiling dilute hydrochloric acid as possible, add an alkaline acetate in excess, PHOSPHATE OF CHEOMIUM, if present, will be precipitated ; to the filtrate add ammonia in excess ; if SES- QTTIOXIDE OF CHEOMIUM be present, it will be precipitated by the ammonia. 221. After the precipitate produced by the fixed alkali has been well washed, it must be dissolved in as small a quantity of boiling dilute hydrochloric acid as possible, then add one of the alkaline acetates in excess, and boil for some minutes ; the PHOSPHATE OF IRON and the OXIDE (the latter as basic per-acetate), will be precipitated, if present, whilst the PHOSPHATES OF THE ALKALINE EARTHS will remain in solution; examine the solution according to par. 222, and examine the precipitate for phosphoric acid in the following way: Digest the precipitate in sulphide of ammonium for a few minutes, then filter, and examine the filtrate for PHOS- PHORIC ACID, according to par. 422. To ascertain whether there was any iron, uncombined with phosphoric acid, add to the original solution an alkaline acetate ; filter, and to * If no precipitate is produced on boiling the fixed alkaline solution, a portion of the precipitate produced by the group reagent ought to be examined for chromium, in the way directed at par. 192. 92 THE SPECIAL PROPERTIES the filtrate add ferrocyanide of potassium. If a blue pre- cipitate is formed, it proves that all the IRON did not exist as phosphate. 222. To the solution add sesquicliloride of iron, drop by drop ; if no precipitate is produced on the addition of the first two drops, the PHOSPHATES or THE ALKALINE EARTHS are absent ; if a precipitate is produced, continue the addi- tion of the perchloride of iron until the solution is of a slightly reddish colour, then boil until the excess of iron is removed from the solution, then filter, and examine the nitrate for BARYTA, STRONTIA, LIME, and MAGNESIA in the usual way. 223. "When substances are examined, the nature of which is a sufficient proof that the oxide of chromium and its phos- phate, and the phosphates of baryta and strontia, and the oxalates of baryta, strontia and lime must be absent, as in the case of soils, natural and artificial manures, &c. ;* the last method may be much simplified ; the precipitate, produced by the group reagent, need not be ignited, the free alkali need not be added in the cold, and after its addition the mixture may be boiled, in order to hasten the filtration ; and lastly, lime and magnesia are the only alkaline earths which have to be sought for. 224. When substances are examined, the nature of which is a sufficient proof that oxalate of lime is the only oxalate, and that phosphate of lime and phosphate of magnesia are the only phosphates of the alkaline earths which can be pre- sent, as in the case of guano, urine, urinary deposits, &c.,f a simpler method may be employed for detecting and * Guano generally contains oxalate of lime, examine the ammonia precipitate of this manure according to par. 224. f Of course in such substances as guano, urine, and urinary deposits, oxide of chromium and its phosphate cannot be present. OF THE FOURTH GROUP. 93 separating these salts than the one given in Table V : after having separated them from all the other sub- stances in the way directed in Table V, dissolve the precipitate produced by ammonia in the tartaric acid solution in a small quantity of hydrochloric acid, and to this solution add acetate of soda in excess. OXALATE OF LIME, if present, will be precipitated, whilst the phosphates of lime and magnesia will remain in solution. Filter, and to the filtrate add oxalic acid, which will precipitate the LIME existing originally as PHOSPHATE in the state of OXA- LATE. PHOSPHATE OF MAGNESIA will be precipitated from this filtrate on the addition of ammonia in excess. 225. The BORATES and FLUORIDES of BARYTA, STRONTIA, and LIME, are also precipitated by ammonia ; but they are not completely precipitated by ammonia in the presence of chloride of ammonium ; therefore, a portion at least of the bases of these salts will be found as a member of the second group, and the acids in these salts will be discovered in the ordinary examination of the acids, for these reasons we have not included these salts in the group ; but it is necessary for the student to know that, when present in considerable quantities, they are in part precipitated by ammonia, as otherwise their precipitation by ammonia might occasion him much perplexity. APPENDIX TO THE FOURTH GROUP. 226. SESQUIOXIDE OF URANIUM (U 2 O 3 ). This oxide is of a brick-red colour, its hydrate is yellow ; by ignition it loses part of its oxygen, being converted into TJ 3 4 , the colour of which is a very dark green, approaching black. The sesquioxide dissolves in acids, forming salts, the solu- tions of which have a fine yellow colour, and redden blue litmus paper. Hydrosulphuric acid reduces this oxide to 94 THE SPECIAL PROPERTIES the state of protoxide, which attracts oxygen from the air, becoming converted into the sesquioxide again : oxidizing agents have the same effect. 227. Sulphide of ammonium precipitates, from alkaline solutions of this oxide, black SULPHIDE OF FEAisriuM, which subsides slowly, and is readily soluble in acids, even in acetic acid. 228. The volatile and fixed, alkalies precipitate this oxide from its solutions completely, in the form of a yellow pre- cipitate, which is insoluble in an excess of the reagent. 229. Carbonate of ammonia produces a yellow precipitate, which is soluble in an excess of the reagent, but is deposited again from this solution on boiling. It differs from ses- quioxide of iron in its behaviour with this reagent, which it so closely resembles with the other reagents in its behaviour. 230. Ferrocyanide of potassium produces in solution of this oxide a fine brown-red precipitate j this is a very deli- cate test for uranium. 231. TITANIC ACID (Ti O 2 ). This acid, although com- paratively a rare substance, occurs in some iron ores, and as it is considered by some to improve the quality of the iron, we have given, on this account, a short description of its properties, and the mode of detecting it. 232. The anhydrous acid varies in colour, according to the mode of its preparation ; it sometimes appears as a white powder, which, when heated, acquires during the time it is heated, a yellow tint, and sometimes it appears in the form of small lumps of a reddish-brown colour. The hydrated acid (Ti 2 , HO) is white. The anhydrous acid is insoluble in water and acids, with the exception of concentrated sul- phuric acid, which dissolves it with the aid of heat ; when fused with bisulphate of soda, the fused mass dissolves com- pletely in a large quantity of cold water ; when fused with car- OF THE FOURTH GROUP. 95 bonate of soda it combines with the soda, forming titanate of soda, which, on the addition of water, is decomposed into soda, which dissolves in the water, and bititanate of soda, which is insoluble in that liquid, but which is soluble in hydrochloric acid. 233. The hydrated acid in the moist state, and also when dried at a temperature not exceeding 212 E., is soluble in dilute acids, especially hydrochloric and sulphuric. When the acid solutions of titanic acid are greatly diluted with water, and boiled for a long time, the titanic acid is com- pletely precipitated as a white powder, insoluble in dilute acids; this precipitate possesses the marked property of passing through the filter when washed, unless an acid or chloride of ammonium is added along with it. It is preci- pitated from its acid solutions* in the form of a milky- white precipitate by the volatile and fixed alkalies and their carbonates, by carbonate of baryta, and by sulphide of am- monium ; the precipitate is insoluble in an excess of the precipitant ; but if it has been precipitated by any of these reagents in the cold, and washed with cold water, it is soluble in dilute hydrochloric or sulphuric acid. 234. When the solution of titanic acid in hydrochloric acid does not contain too much free hydrochloric acid when, for example, it has been prepared in such a way that part of the titanates treated by the hydrochloric acid has remained undissolved, and has been filtered from the solu- tion diluted with water the solution of the acid behaves with the reagents named in , , and c, in the way described in these paragraphs. (a) Infusion of galls produces in the solution a reddish orange-yellow precipitate of T ANN ATE or TITANIC ACID. * Not in the presence of tartaric acid, or other non-volatile organic matter. 96 THE SPECIAL PROPERTIES (5) Ferrocyanide of potassium gives a dense orange-brown precipitate ; the precipitate is soluble in an excess of the precipitant. (c) White precipitates are produced by adding to the solution dilute sulphuric, arsenic, phosphoric, or tartaric acid, but more especially oxalic acid ; these precipitates are com- pletely redissolved in an excess of the precipitating acid, and likewise by hydrochloric acid ; the precipitate produced by oxalic acid is the most insoluble. 235. If a strip of ZINC, IRON, or TIN be introduced into a solution of titanic acid in hydrochloric acid, the solution will become blue ; and from this, a reddish or violet preci- pitate will separate, which gradually oxidizes into the white titanic acid. 236. Pure titanic acid, where fused with microcosmic salts in the inner blowpipe flame, gives, after continued exposure, a bead which assumes a violet hue on cooling; this reaction, which is rendered easier on addition of metallic tin, disappears in the outer flame. If iron be present, a yellow or blood-red bead will be produced in the reducing flame. 237. Titanic acid, from its great similarity to silicic acid, is frequently overlooked in the analyses of silicates, although it occurs in many instances in some quantity. When me- tallic zinc is fused in conjunction with minute quantities of titanic acid, after the combustion of the zinc and clearing of the bead on cooling, a very distinct colouration is always produced, whereas, the button of microcosmic salt and titanic acid gives no reaction in the ordinary way. By this test, titanic acid may be found in pig-iron, and in most cases, when any residue is left by treating silica with hydro- fluoric acid (Eiley). OF THE FIFTH GROUP. 97 FIFTH GKOUP. PROTOXIDE OF TIN. PEEOXIDE or TIN. OXIDE OF ANTI- MONY. AESENIOUS ACID, ARSENIC ACID. PEEOXIDE OF GOLD. PEEOXIDE OF PLATINUM. 238. All the members of this group possess, in a greater or less degree, the character of acids. Arsenious and arsenic acids are soluble in water ; the rest are insoluble, not only in water, but likewise in nitric acid. They are all readily soluble in concentrated hydrochloric acid. In the state of sulphides they behave with different reagents in the following manner: The protosulphide and bisulphide of tin, with the sulphide of antimony, are insoluble in nitric acid, but dissolve readily in concentrated hydrochloric acid; whereas sulpharsenious and sulpharsenic acids are insoluble in hydrochloric acid, but are easily soluble in concentrated nitric acid. These different sulphides are readily dissolved by the alkalies and alkaline sulphides, from which solutions they are again precipitated unaltered on the addition of any acid in excess. The sulphides of gold and platinum are insoluble both in hydrochloric and nitric acid, but are easily soluble in aqua regia (a mixture of the two acids). They also dissolve with difficulty in the alkalies and alkaline sulphides. 239. As gold and platinum are seldom met with in ordi- nary analysis, and as .many of their properties render them perfectly distinct from the rest of the members, it has been found of advantage to subdivide the group. The first divi- sion comprises the OXIDES of TIN, ANTIMONY, and AESENIC ; the second, the OXIDES of GOLD and PLATINUM. 5 98 THE SPECIAL PROPERTIES FIRST DIVISION. 240. The precipitate produced bj the general reagent, after having been well washed, must be treated with a dilute solution of carbonate of ammonia* Both SULPHIDES of ARSENIC, being soluble in that reagent, will pass into solu- tion ; whilst the SULPHIDES of ANTIMONY and TIN, being insoluble, will remain undissolved. The solution must be separated from the insoluble sulphides by nitration. If a yellow precipitate be produced on the addition of hydro- chloric acid to the nitrate, one or both SULPHIDES of ARSENIC must be present. The substance which was insoluble in carbonate of ammonia, after having been well dried, must be mixed with three parts of nitrate of ammonia^ and the mixture projected in small portions into a porce- lain crucible containing two parts of nitrate of ammo- nia in a state of liquefaction. After all fuming has ceased, the residue should be gently ignited for a short time and then allowed to cool. The residue must be subse- quently heated with a saturated solution of tartaric acid. If complete solution takes place, OXIDE of ANTIMONY only can be present. If a portion remain undissolved by the tartaric acid, it indicates the probable presence of TIN. When complete solution does not take place, the liquid must be filtered, and to the filtrate must be added hydrochloric acid, and subsequently hydrosulpTiuric acid. If an orange-red- coloured precipitate be formed, OXIDE of ANTIMONY is pre- sent. The substance insoluble in tartaric acid must be ex- * See Appendix A. f When the amount of precipitate is so small that little or nothing can be detached from the filter, the precipitate as well as the filter, after having been cut into small pieces, must be mixed up with the nitrate of ammonia, and subsequently projected into the crucible. OF THE FIFTH GROUP. 99 amined for tin by fusing it with carbonate of soda and cyanide of potassium, as directed under the special remarks of the peroxide of that metal. 241. The following precautions must be attended to in ana- lysing this group : The mixed precipitate must be agitated in a test-tube for a few seconds only, with a dilute solution of carbonate of ammonia,* and then quickly filtered. When only a slight trace of arsenic is present, the carbonate of ammonia solution, on the addition of hydrochloric acid, will simply assume a slight yellow colour, no distinct precipitate being formed. When arsenic is present, the original solution must be examined to ascertain in what state it exists, whether as arsenious or arsenic acids. SPECIAL REMARKS. 242. OXIDE OE TiK (SnO). This oxide is black, its hydrate being white. Nitric acid and nitrates in a state of fusion convert it into the peroxide. The protosalts of tin are colourless, and are decomposed by heat. The soluble neutral salts redden litmus paper, and are decomposed, in the presence of much water, into soluble acid and insoluble basic salts. The addition of water therefore to the protosalts of tin produces a milkiness which disappears on the addition of hydrochloric acid. Sulphide of tin (SnS) is of a dark brown colour. 243. The alkalies and their carbonates throw down from solutions of this oxide the HTDEATE (SnO, HO), which is easily soluble in solutions of the fixed alkalies, but insolu- ble in ammonia and the alkaline carbonates. * According to Blyth, the dilute solution must be prepared by dis- solving one ounce of solid carbonate of ammonia in twelve fluid ounces of water. Vide Blyth's < Outlines of Chemical Analysis.' 100 THE SPECIAL PROPERTIES 244. All protosalts of tin are powerful reducing agents, from the great affinity they have for an additional quantity of oxygen. Many metallic oxides, such as the oxides of gold, silver, and mercury, are reduced to the metallic state in their presence ; whilst other oxides, such as peroxide of iron and oxide of copper, are reduced to a lower degree of oxidation. 245. Perchloride of gold produces in solutions of proto- salts of tin, containing a small quantity of free nitric acid, a beautiful PUEPLB PRECIPITATE (purple of Cassius). 246. If a solution of a PROTOSALT OF TIN is added to a mixture of ferricyanide of potassium and sesquichloride of iron, Prussian Hue precipitates immediately, owing to the reduction of the ferricyanide. This delicate test for a proto- salt of tin can only be conclusive in cases where there are no other residuary agents present. 247. Solution of perchloride of mercury produces in solu- tions of protoxide of tin a white precipitate of protochloride of mercury, owing to the protosalt of tin withdrawing half the chlorine from the perchloride of mercury. If sufficient quantity of the tin-compound be present, it removes, after a time, all the chlorine from the mercury ; the colour of the precipitate then becomes gray. Since this reaction takes place even in highly dilute solutions, and in the presence of much free hydrochloric acid, it is very valuable for the detection of oxide of tin. 248. PEROXIDE or TIN (SnO 2 ). This oxide is of a light straw colour; its hydrate is white. Nitric acid converts metallic tin and its protoxide into the hydrated peroxide, which is deposited in the form of a white powder. A peroxide of tin is likewise precipitated from persalts of tin, on the addition of caustic soda to their solutions. These hydrates, although they have the same composition, are OF THE FIFTH GROUP. 101 perfectly distinct in their chemical properties. The one formed by the action of nitric acid is insoluble, both in acids and the fixed alkalies ; the other is soluble in these reagents. These modifications are capable of being trans- formed into each other. The insoluble one is rendered solu- ble by fusion with the carbonated alkalies ; the soluble is converted into the insoluble form by ignition. Bisulphide of tin (SnS 2 ) is of a yellow colour. The usual mineral of this metal is the peroxide (tin stone Sn0 2 ). 249. The alkalies and their carbonates precipitate from solutions of persalts of tin the HYDEATE, which is soluble in the fixed caustic alkalies, but insoluble in ammonia and the alkaline carbonates. 250. If per- or proto-compounds of tin be mixed with equal parts of carbonate of soda and cyanide of potassium, and the mixed mass be subjected, upon a charcoal sup- port, to the inner blowpipe flame, ductile metallic grains of TIN will be obtained, unaccompanied by any incrustation upon the charcoal. 251. OXIDE OF ANTIMONY (Sb0 3 ). The oxide occurs either in the form of white brilliant crystalline needles or as a grayish white powder, assuming the one or the other of these forms according to its mode of preparation. It fuses at a gentle red heat, and, when exposed to a higher temperature, volatilizes unaltered. The solubility of this oxide in tartaric acid distinguishes it from the other mem- bers of the group. When fused along with nitrates, it is converted into a higher oxide (antimonic acid, SbO 5 ). 252. Some of the salts of antimony are decomposed by igni- tion ; some are volatilized unaltered. The soluble neutral salts redden litmus paper. When treated with a large amount of water, they are decomposed into soluble acid and insoluble basic salts. In this respect they resemble the 102 THE SPECIAL PROPERTIES salts of bismuth ; with this exception, that the insoluble basic salts of antimony dissolve in tartaric acid, whilst the corresponding salts of bismuth are insoluble. Sulphide of antimony (SbS 3 ) is of an orange-red colour. The principal mineral of this metal is the sulphide. 253. The alkalies and their carbonates throw down from solutions of antimony a bulky precipitate of OXIDE or ANTI- MONY, which is soluble in the fixed caustic alkalies and the alkaline carbonates, but insoluble in ammonia. 254. Metallic zinc precipitates from all solutions of salts of teroxide of antimony, if they contain no free nitric acid, metallic antimony as a black powder. But if the solution contains free nitric acid, teroxide of antimony precipitates together with the metal. If a few drops of a solution of antimony, containing some free hydrochloric acid, are poured into a platinum dish (the inside of a platinum crucible cover), and a small piece of zinc introduced, hydro- gen is evolved, and antimony separates, staining the part of the platinum covered by the liquid brown or black, even in the case of very dilute solutions. Cold hydrochloric acid fails to remove the stain, which, however, may be im- mediately removed by warm nitric acid. (Fresenius.) 255. If a solution of teroxide of antimony in one of the fixed alkalies is mixed with a solution of nitrate of silver, a deep-black precipitate of suboxide of silver forms with the grayish-brown precipitate of oxide of silver. Upon now adding ammonia in excess, the oxide is redissolved, whilst the suboxide is left undissolved (H. Ease). This very delicate test enables one to detect readily the presence of teroxide of antimony in the presence of antimonic acid. 256. If a solution of teroxide of antimony is brought into contact with zinc and dilute sulphuric acid, the zinc oxidizes not only at the expense of the water, but also at OF THE FIFTH GROUP. 103 the expense of the teroxide of antimony ; the antimony is, consequently, reduced to the metallic state : a portion of the antimony, however, at the moment of its reduction, enters into combination with some of the liberated hydro- gen, forming with that element a gaseous compound terhy- dride of antimony (SbH 3 ) . " If this gaseous compound be dried by passing it through a tube, the anterior portion of which is loosely filled with cotton wool, and the remoter part with chloride of calcium, and be then allowed to escape from a tube of hard glass drawn out to a fine point, the presence of antimony may be recognised by the follow- ing reactions : 257. " 1st. The gas will burn with a liluish-green flame, emitting white fumes of teroxide of antimony, which may be condensed in a cold beaker, dissolved in hydrochloric acid, and tested with JiydrosulpJiuric acid. 258. " 2d. If the inner surface of a porcelain capsule be depressed upon the flame, a Hack spot of metallic antimony will be deposited upon it, which is lustrous only when in thin layers. This coating of metal may be dissolved in aqua regia and tested. (The operator should take care to prove, before commencing this experiment, that the flame of the hydrogen itself deposits no spot upon porcelain.) 259. " 3d. The glass tube from which the gas issues should be heated with a spirit-lamp, in the centre; a lustrous mirror of antimony will be deposited on the in- side of the tube, immediately around the flame of the lamp, whilst the bluish-green tint of the hydrogen flame in great measure disappears. 260. " These reactions should be compared with those of terhydride of arsenic under similar circumstances. t 261. " If granulated zinc be boiled with a solution of antimony, to which a very large excess of potash has been 104 THE SPECIAL PROPERTIES added, the hydrogen which is evolved is free from terhydride of antimony." 262. If compounds of antimony, mixed with carbonate of soda and cyanide of potassium, be exposed, upon a charcoal support, to the reducing flame of the blowpipe, brittle grains of metallic antimony will be formed, accompanied with a white incrustation on the charcoal. 263. ARSENIOUS ACID (As0 3 ). There are two varieties of this acid, which are perfectly distinct in their physical characters and chemical properties. One, from its appear- ance, is termed the vitreous, and the other the milky variety; when heated, they volatilize in white inodorous fumes. " If the operation is conducted in a glass tube, a sublimate is obtained, consisting of small brilliant octahe- drons and tetrahedrons." Both kinds are more easily solu- ble in hot than in cold water. This acid is exceedingly poisonous; and, being altogether inodorous, almost desti- tute of taste, and readily obtainable, i& frequently employed as a poison. The best antidote is the moist and well- washed hydrated sesquioxide of iron. 264. This acid unites with bases, forming a class of salts called arsenites, which are all insoluble in water, with the exception of the alkaline arsenites. Sulpharsenious acid (AsS 3 ) is yellow, and soluble not only in the alkalies and alkaline sulphides, but likewise in the alkaline carbonates. 265. Nitrate of silver produces in neutral solutions of the arsenites a yellow precipitate of ARSEFITE or SILYEE (2AgO, AsO 3 ), soluble in nitric acid and ammonia. 266. If recently precipitated TERSULPHIDE OF ARSENIC is digested with sulphurous acid and acid sulphite of potash, the precipitate is dissolved ; upon heating the solution to boiling, the fluid turns turbid, owing to the separation of sulphur, which, upon continued boiling, is for the greater OF THE FIFTH GROUP. 105 part redissolved. The fluid contains, after the expulsion of the sulphurous acid, arsenite and hyposulphite of potash. Tersulphide of antimony and bisulphide of tin do not show this reaction. (JBunsen.) 267. Sulphate of copper produces in neutral solutions of the arsenites a yellowish-green precipitate of ABSENITE OF COPPER (2CuO, As0 3 ). 268. If to a solution of arsenious acid, or an arsenite, caustic potash be added in excess, and a few drops only of a dilute solution of sulphate of copper, and the liquid subse- quently boiled, a red precipitate of suboxideof copper (Cu 2 0) will fall down, whilst the solution will contain ARSENIATE OF POTASH. This test is particularly applicable in distin- guishing arsenious from arsenic acid. It cannot be em- ployed with safety as a direct means for detecting arsenious acid, as many organic substances possess the property of reducing protoxide of copper to the state of suboxide. 269. " If to arsenious acid, no matter whether in the solid form or in solution, some acetic acid is added, and then potash in slight excess, the mixture evaporated to dryness, and the residue heated to redness in a small tube or if a trace of arsenious acid is introduced into a narrow test- tube, and there covered with a somewhat larger quantity of acetate of soda, and heat applied part of the arsenious acid is reduced, but there forms at the same time ALKAESIN (oxide of cacodyl, C 4 H 6 AsO), which makes its presence immediately known by its equally characteristic and for- midable odour, which somewhat resembles that of sharp onions. This changes speedily to the not less characteristic odour of chloride of cacodyl, if the ignited contents of the tube are heated with a few drops of protochloride of tin." (JBunsen.) 270. If clean metallic copper is boiled in a solution con- 5 106 THE SPECIAL PROPERTIES taining arsenious acid, and acidified with hydrochloric acid, the copper becomes coated with a steel-gray film of metallic arsenic ; if the quantity of arsenious acid is considerable, the reduced arsenic will separate from the copper, when the liquid is boiled for a considerable time, in large Hack scales. As many other metallic oxides are reduced to their metallic state under the same circumstances, it is necessary to submit the crust to further examination. This test, which is called " Keinsch's test," is particularly useful for the detection of arsenic in organic liquids or solids. " The sus- pected liquid is simply to be acidulated with about one sixth of its bulk of hydrochloric acid, and boiled. The solid tissue must be cut up into very small pieces, and boiled for some time in a mixture of about one part of hydrochloric acid with six of water, until the whole is completely disin- tegrated ; then strained through muslin, or filtered through a previously wetted filtering paper. 271. " Into either of the above boiling liquids, dip the end of a piece of clean polished wire ; examine the wire from time to time, and as soon as its surface acquires a gray metallic discolouration, remove it, and add in its stead frag- ments of fine copper gauze, continuing the supply as long as the last added piece assumes any definite alteration in colour. 272. " Itemove the pieces of copper gauze, wash them in water, and dry them between folds of filtering paper ; the deposit will not rub off unless the amount of arsenic be very large. If the arsenic exists in but very small quantity, the colour of the precipitated metal is bluish ; otherwise, of a dark iron-gray tint. Holding the piece of gauze in the fingers, warm it over a flame, coil it up into a small compass, and introduce it into a reduction-tube; now apply heat cautiously ; the arsenic will volatilize, oxidize, and con- dense in the cold part, in the form of a white crystalline OF THE FIFTH GROUP. 107 sublimate. Several pieces of coated gauze may "be thus treated successively, until a sufficiently obvious sublimate of arsenious acid is procured ; by examination with a lens, or with the low power of a microscope, the crystals will be seen to consist of highly iridescent octo- and tetrahedra." (Odling's * Practical Chemistry.') 273. File off the piece of tube containing the sublimate, boil it for a minute or two in a little water ; test the water after the boiling for arsenious acid, one portion with hydrochloric and hydrosulphuric acids, and another portion with nitrate of silver. 274. Arsenic, as well as antimony (256), combines with hydrogen in its nascent state, forming an inflammable gase- ous compound, which burns with a bluish white flame, water and arsenious acid being formed ; water and teroxide of antimony being formed when terhydride of antimony is burned. When free access of air is prevented, the hydro- gen only is oxidized, metallic arsenic (or if it is terhydride of antimony, metallic antimony) being deposited in a finely divided state. 275. If, therefore, a solution of arsenious acid or an arsenite be brought into contact with zinc and dilute sul- phuric acid, the zinc oxidizes not only at the expense of the water, but also at the expense of the arsenious acid ; and the arsenic, at the moment of its reduction, enters into com- bination with the hydrogen, forming with that element the gaseous compound terhydride of arsenic (AsH 3 ) : this gase- ous compound was discovered by the late Mr. Marsh, and applied by him in the detection of arsenic. If the reduc- tion of the arsenious acid, and the conversion of the arsenic into terhydride of arsenic, be conducted in a flask fitted with an evolution-tube, the gaseous compound can then be subjected to the following experiments : The evolution-tube 108 THE SPECIAL PROPERTIES must consist of a drying-tube, into one end of which is fitted a narrow tube of hard glass. The drying-tube is placed nearest the flask, and it is half filled with cotton wool, and half with fragments of chloride of calcium ; the end nearest the flask is filled with the wool. The hard glass tube should be from six to nine inches long, and drawn out at one end, so as to form a jet, where the gas may be burned. The gas may be examined in the following manner : 276. 1st. " Terhydride of arsenic burns with a livid Hue flame, producing arsenious acid, which may be condensed in a cold beaker, dissolved in hot water, and tested (especially with nitrate of silver and with hydrochloric and hydrosulph- uric acids). 277. 2d. " By depressing the inner surface of a porcelain capsule* upon the flame, a black (generally) lustrous spot of metallic arsenic is obtained (this experiment should always be tried with the hydrogen flame,t before the arsenical solution is poured into the evolution-bottle) ; this spot may be tested by dissolving in concentrated nitric acid, evapo- rating just to dryness upon a sand bath, adding water, and afterwards nitrate of silver, with, if necessary, a little dilute ammonia, when a brick-red precipitate of arseniate of silver will be obtained ; an antimony spot, when treated in this way, generally gives a slight dirty-white precipitate with nitrate of silver. 278. " The incrustation of arsenic (whether on a porcelain surface or in a glass tube) may be dissolved by solution of * " The porcelain should not be allowed to remain in the flame for more than a second or two, since the minute spots would be dispelled if the porcelain were to become very hot." f "A great obstacle to the employment of Marsh's test is the diffi- culty of obtaining zinc and sulphuric acid perfectly free from arsenic, for which they should be very carefully tested previously to use." OF THE FIFTH GROUP. 109 chloride of lime, which does not affect the antimony incrus- tation ; this test may serve, to some extent, to distinguish the two metals, but is not adequate to the detection of traces of antimony in a mirror of arsenic.'* (Abel and 279. The properties and reactions just described enable us to distinguish pure arsenical stains and mirrors from antimonial stains and mirrors, but they do not enable us to detect arsenic with positive certainty in the presence of antimony. To obtain positive evidence, the following method ought to be employed : The central part of the glass tube (which ought to be free from lead) through which the gas passes should be heated to redness ; this effects the decomposition of the gaseous compound, the metal being deposited in a finely divided state. A feeble stream of dry hydrosulphuric acid gas must now be transmitted through the tube, the metallic mirror being heated from its outward to its inward extremity. If only arsenic be present, the yellow sulphide of that metal will be formed. If antimony only be present, the orange or black sulphide of antimony will be produced ; but if both metals be present, the corre- sponding sulphides will be formed ; and the sulphide of arsenic, being the more volatile of the two, will be the further removed from the flame. A stream of dry hydro- chloric acid gas must be passed through the tube without the application of heat : by this means the sulphide of antimony will be converted into volatile chloride, which will entirely disappear ; whilst the sulphide of arsenic will remain unaltered, and may be distinguished from any sulphur which may have separated, by dissolving readily in ammonia. 280. " If arsenites, or arsenious acid, or tersulphide of arsenic, are fused together with a mixture of equal parts of dry carbonate of soda and cyanide of potassium, the whole 110 THE SPECIAL PROPERTIES of the arsenic is reduced to the metallic state, and, if an easily reducible base, the latter also ; the eliminated oxygen converts part of the cyanide of potassium into cyanate of potash (KO, CyO). In the reduction of tersulphide of arsenic, sulphocyanide of potassium (K, CyS^) is formed. The operation is conducted as follows : Introduce the perfectly dry arsenical compound into the bulb of a small bulb-tube, and cover it with six times the quantity of a perfectly dry mixture of carbonate of soda and cyanide of potassium. The whole quantity must not more than half fill the bulb, otherwise the fusing cyanide of potassium is likely to ascend into the tube. Apply the heat of a spirit- lamp to the bulb, and continue this for a while, as the arsenic frequently requires some time for its complete sub- limation. The metallic mirrors are deposited on the cold part of the tube : they are of exceeding purity. They are obtained from all arsenites whose bases remain either alto- gether untouched, or are reduced to such metallic arsenides as lose their arsenic partly or totally upon the simple appli- cation of heat. This method deserves to be particularly recommended on account of its simplicity and neatness, as well as for the accuracy of the results attainable by its application, even in cases where only very minute quantities of arsenic are present. It is more especially adapted for the direct production of arsenic from tersulphide of arsenic, and is in this respect superior to all other methods hitherto suggested. The delicacy of the reaction may be very much heightened by heating the mixture in a stream of dry carbonic acid gas. A series of experiments made by Dr. V. Babo and myself has shown that the most accurate and satisfactory results are obtained in the following manner" (Fresenius) : 281. The apparatus consists of a flask or two-necked bottle capable of holding about eight or twelve fluid ounces ; OF THE FIFTH GROUP. Ill this flask or bottle is fitted with a funnel-tube, and a bent tube which dips into another and smaller flask. In the first flask carbonic acid is slowly generated from pretty large fragments of marble (no powder) and dilute hydrochloric acid ; it is conveyed by the conducting-tube into the smaller flask, which is partly filled with concentrated sulphuric acid, in order to dry the gas. The conducting-tube from the small flask is bent at right angles, and connected, by means of a cork, with the reduction-tube ; this latter tube is made out of a piece of hard glass tube (combustion-tube) some- what more than three eighths of an inch in diameter, and drawn out at one extremity to a long point ; the length of the body of the tube should be about four inches, that of the point at least two and a half inches. 282. A mixture of three parts of dry carbonate of soda and one part of cyanide of potassium is dried in the water bath ; one part of arsenical sulphide, or the arsenite, which has been also dried in the water bath, is mixed with about twelve parts of the well-dried mixture of carbonate of soda and cyanide of potassium. The mixture, before it has time to get damp, is put upon a narrow slip of card-paper bent into the shape of a gutter ; it is then introduced into the tube, and the latter is turned half round upon its axis ; the mixture falls upon the glass, and the gutter must be with- drawn. The mixture should be in the middle of the tube, and it ought not to occupy more than an inch . The reduc- tion-tube must now be fixed, by means of the cork, to the conducting-tube of the small flask, and a moderate stream of carbonic acid ought to be evolved, by pouring some hydrochloric acid into the large flask, by means of the funnel-tube. Heat the reduction- tube, in its whole length, very gently with a spirit-lamp, until the mixture is perfectly dry ; when all the water is expelled, moderate the gas stream 112 THE SPECIAL PROPERTIES so that only one bubble shall pass through the sulphuric acid in the small bottle in a second ; the gas stream may be moderated by pouring water into the large flask by means of the funnel-tube. When the gas stream is moderated, apply the flame of a spirit-lamp to the shoulder of the tube ; and when this part of the tube is red hot, apply the flame of a second and larger spirit-lamp, commencing at the end of the reduction-tube nearest the conducting-tube of the small flask, and heating along up to the mixture ; continue to apply the flame at the part where the mixture is, until all the arsenic is expelled. The far greater portion of the volatilized arsenic recondenses in the narrow part of the tube, whilst an extremely minute portion only escapes through the fine point, imparting to the surrounding air the peculiar odour of garlic. Advance the flame of the second spirit-lamp slowly and gradually up to the first, by which means the whole of the arsenic which may have condensed in the wide part of the tube is driven into the narrow part. When this end has been attained, close the fine point of the tube by fusion, and apply heat, proceeding from the closed point towards the part where the greater part of it is condensed ; by which means the extent of the mirror is narrowed, whilst its beauty and lustre are correspondingly increased. In this manner, perfectly distinct mirrors of arsenic may be produced from as little as the one three-hundredth part of a grain of tersulphide of arsenic. No mirrors are obtained by this process from tersulphide of antimony, nor from any other compound of antimony. 283. If a solution containing arsenious acid, or an arsenite, be mixed with a large excess of a concentrated solution of caustic potash, and boiled with fragments of granulated zinc, terhydride of arsenic is evolved, and may be readily recog- nised by allowing it to pass on to a piece of filter-paper OF THE FIFTH GROUP. 113 moistened with a solution of nitrate of silver; the paper assumes a purplish-black colour, even when a small quantity of arsenic is present. This test serves to distinguish arsenic from antimony. (Fleitmann.) 284. Arsenious acid, when mixed with a little carbonate of soda, and subjected to the inner blowpipe flame on char- coal, evolves a peculiar garlic odour, supposed to arise from a lower oxide. The vapours of arsenious acid, when sublimed from a piece of glass, possess no odour. 285. ARSENIC ACID (As0 5 ). This oxide is white; it is deliquescent and strongly acid, forming, with bases, a class of salts called arseniates, which are all insoluble in water, with the exception of the alkaline arseniates. It fuses at a low red heat without undergoing decomposition, but at a higher temperature is resolved into oxygen and arseni- ous acid, which volatilize. Sulphurous acid, aided by a gentle heat, reduces it likewise to this lower state of oxidation. The metal arsenic is found in nature principally as sulphide. 286. Nitrate of silver produces, in neutral solutions of the arseniates, a reddish-brown precipitate of ARSENIATE or SILVER (3 AgO, As0 5 ), soluble in dilute nitric acid and in ammonia. 287. Sulphate of copper produces, in neutral solutions of the arseniates, a greenish-blue precipitate of ARSENIATE or COPPER (2 CuO, HO, AsO 5 ). 288. Sulphate of magnesia, in the presence of chloride of ammonium and ammonia, produces, in solutions of the arseniates, a white precipitate of ABSENIATE OF AMMONIA AND MAGNESIA (2 MgO, NH 4 O, AsO 5 ), soluble in acids. 289. In those reactions which depend upon the reduction of the arsenic to the metallic state, arsenic resembles arsenious acid. 114 THE SPECIAL PROPERTIES SECOND DIVISION. 290. G-old and platinum produce reactions so decisive the former with chloride of tin, and the latter with chloride of ammonium that their presence may invariably be detected in the presence of all the other metals. The original solution may therefore in all cases be examined for these substances. 291. PEROXIDE OF G-OLD (Au0 3 ). This oxide is of a deep brown colour, its hydrate being somewhat lighter in colour. They both dissolve readily in hydrochloric acid, but are insoluble in dilute oxygen acids. Persulphide of gold (AuS 3 ) is black. 292. The salts of the protoxide of iron precipitate gold as a bluish-black precipitate, which acquires a metallic lustre when rubbed. 293. A solution of protochloride of tin and some bichloride produce, even in very dilute solutions of gold, a purple pre- cipitate (purple of Cassius), "the tint of which varies according to the quantity of gold present. The precipitate is insoluble in dilute acids ; the gold solution should be first mixed with the bichloride of tin, and the protochloride then added drop by drop. "When the quantity of gold is extremely minute, a, pink tinge pervades the solution. 294. " A very delicate method of applying this test is as follows : Sesquichloride of iron is added to protochloride of tin until a permanent yellow colour is produced ; the solution is then considerably diluted; the gold solution, having likewise been much diluted, is poured into a beaker, which is placed on a sheet of white paper ; a glass rod is dipped into the tin-iron solution, and afterwards into the gold solution, when, if even a trace of the precious metal be OF THE FIFTH GEOUP. 115 present, a blue or purple streak will be observed in the track of the glass rod. 295. "This purple-of-Cassius test has the advantage of being applicable even in very acid solutions." (Abel and Bloxam.) 296. PEROXIDE or PLATINUM (Pt0 2 ). This oxide is of a deep-brown colour, its hydrate is reddish brown. Both the oxide and its hydrate dissolve readily in hydrochloric acid, but with difficulty in the oxygen acids. Persulphide of platinum (PtS 2 ) is of a blackish-brown colour. 297. Chloride of potassium or ammonium produces, in solutions of platinum, yellow crystalline precipitates of POTASSIO-CHLORIDE OF PLATINUM and AMMONIO- CHLORIDE OF PLATINUM. The presence of free hydrochloric acid promotes the formation of these precipitates. Dilute solu- tions should be evaporated along with the chloride of potas- sium or ammonium and the free hydrochloric acid on the water bath to dryness, and the residue digested in weak spirits of wine until the excess of the alkaline chloride employed is dissolved. 298. Solutions of protochloride of tin produce, in solutions of binoxide of platinum, which contain much free hydro- chloric acid, a dark brown-red colour in exceedingly dilute solutions : the colour is yellow, and becomes darker on standing. This test is a very delicate one for platinum. The dark brown colour is owing to the reduction of binoxide or bichloride of platinum to protoxide or protochloride. 116 THE SPECIAL PROPERTIES SIXTH GKOUP. OXIDE or SILVER. SUBOXIDE OF MERCURY. OXIDE OF LEAD. PROTOXIDE OF MERCURY. TEROXIDE OF BIS- MUTH. OXIDE OF COPPER. OXIDE OF CADMIUM. 299. The oxides of this group are insoluble in water. They all combine with nitric acid, forming soluble salts ; many of them likewise form, with hydrochloric and sulphuric acid, soluble chlorides and sulphates ; but a few give, parti- cularly with the former acid, insoluble salts. This character permits of a sub-division of the group, which is fully exhibited under the head of its general properties. 300. In the state of sulphides they are insoluble, not only in the alkalies and alkaline sulphides, but likewise in the dilute mineral acids. They are therefore thrown down, both from their neutral acid and alkaline solutions, by sul- phuretted hydrogen. They are all decomposed and ren- dered soluble in boiling dilute nitric acid, with the exception Of PROTOSULPHIDE OF MERCURY. 301. The metallic radicals of these oxides possess the fol- lowing properties : Cadmium decomposes water at a red heat, and at common temperatures in contact with strong acids. Copper, lead, and lismutJi absorb oxygen at a red heat ; their oxides are therefore not decomposed by heat alone. They do not decompose water but at a very elevated temperature, and even then very feebly; neither do they decompose it in the presence of strong acids or bases. The affinity of mercury and silver for oxygen is very feeble, so much so that their oxides are decomposed by heat alone, at a more or less elevated temperature. These metals do not OF THE SIXTH GROUP. 117 decompose water, under any circumstances ; they have therefore no tendency to rust when exposed to the air. 302. This group may, as before noticed, be divided into two sections : 303. a. OXIDES which are precipitated by hydrochloric acid, viz., OXIDE OF SILYEE, SUBOXIDE OF MEECUEY, and OXIDE Or LEAD. 304. 5. OXIDES which are not precipitated by hydro- chloric acid, viz., PROTOXIDE OE MEECUEY, TEEOXIDE OP BISMTJTH, OXIDE OE CADMIUM, and OXIDE OE COPPEE. 305. The slight solubility of chloride of lead in water renders it impossible to confine this member exclusively to the first section a portion of the chloride, varying according to the amount of liquid present, always remaining dissolved. This is finally precipitated along with the members of the second section on the addition of hydrosulphuric acid. If attention be paid to the following facts, they will frequently remove a source of much confusion : 1. If lead has been discovered in the first section, a precipitate must always be obtained on passing hydrosulphuric acid through the filtrate, even if no other member of the group be present. 2. If only a small quantity of lead be present, hydrochloric acid may cause no precipitate, as a sufficient quantity of water may be present to dissolve the chloride formed. In this case, all the lead will be found in testing for the members of the second section. 306. First section. Boiling water, being poured upon the precipitate produced by hydrochloric acid, will remove the CHLOEIDE OF LEAD, if present, which is ascertained by sulphuric acid producing in the filtrate a precipitate of SUL- PHATE OF LEAD. If a residue remain after removing the chloride of lead by adding successively to the mixed chlorides fresh quantities of boiling water, until the last washings give * P | I 02 s a M I pq pr( -d H 2 g BEHAY -B 5 ** 4| 8 ft I S j s B"O ^ vT "2 B 3"- 1 P. a O- ,g "=<=> ra fl .*?; .2 in i ( 2 ^ .5 OS -2 cs -S m * O fl Jill M := O OJ < a 03 o S.-2 g g S S S 2 , of 4w, riidl ll!^ |i^.^- ^IsJ^s, s s Sulp no p n of ATE O soluble 2. ce o H rod oluti ULP ein ajfj 5? S e iM\ g***i l^lpa v ' - > C 3 cj **-! ^ 5 S protoxide decompo sence of an insol soluble a ^ s boi filssS rt >j rj es o ,a .S 120 THE SPECIAL PROPERTIES on the addition of sulphuric acid no further precipitate, it proves that either chloride of silver or sub chloride of mercury (calomel), or both, must be present. Ammonia being added to this residue, dissolves the CHLORIDE OP SILYER, whilst the SUBCHLORIDE or MERCURY is converted into a black compound. To detect the CHLORIDE OF SILVER in the ammoniacal solution, nitric acid must be added in excess, which, by destroying the solvent, causes the CHLORIDE or SILYER (if present) to be re-precipitated. 307. Second section. The precipitate produced by the general reagent, after being washed with distilled water until all trace of chlorine is removed, must be boiled in dilute nitric acid. If it all dissolves, with the exception of a light yellow mass of sulphur, PROTOXIDE OF MERCURY is absent ; but if, after boiling for some time, the undissolved mass presents a black appearance, it points out the probable presence of that member. Examine the black mass for peroxide of mercury, as directed in paragraph 308. To the acid solution, after it has been filtered from the yellow or black mass, and subsequently evaporated nearly to dryness, so as to remove the greater part of the free acid, must be added a little water, and then a few drops of dilute sulphuric acid, which will precipitate the LEAD as sulphate after the lapse of a longer or shorter time ; the solution must therefore be allowed to stand some time before ammonia is added. Ammonia being added in excess to the nitrate, throws down the BISMUTH. The ammoniacal nitrate, after being slightly acidulated with acetic acid, must be divided into two por- tions. COPPER is discovered, if it has not been already manifested by the blue colour of the ammoniacal solution, by ferrocyanide of potassium producing in one portion of the acetic solution a brownish-red-coloured precipitate. To the other portion of the acetic solution is to be added carbonate I OF THE SIXTH GROUP. 121 ef 'ammonia in excess, and heat applied ; by this means the CADMIUM, if present, will be precipitated. As this method for detecting and separating cadmium from copper is not a safe one if only small quantities of cadmium are present, we give the following method by Eresenius : To one por- tion of the acetic solution add hydrosulphuric acid in excess. The formation of a yellow precipitate denotes CADMIUM. If, on account of the presence of copper, the sulphide of cadmium cannot be distinctly recognised, allow the precipitate produced by the hydrosulphuric acid to subside, decant the supernatant fluid, and add to the precipitate a solution of cyanide of potassium until the sulphide of copper is dissolved. If a yellow residue is left undissolved, CADMIUM is present ; in the contrary case, not.* 308. If a black residue remain after boiling the mixed sulphides in nitric acid, it must be collected upon a filter, to separate it from the other members, and specially ex- amined for protoxide of mercury by one of the two follow- ing methods : 1st. After having dried the black mass thoroughly in a water bath, mix it with dry carbonate of soda, and proceed with the examination for mercury in the way described in paragraph 321. 2nd. Dissolve the black mass in as small a quantity of AQUA EEGIA as possible, then add ammonia in slight excess, and then a slight excess of hydro- chloric acid ; examine the solution, thus prepared, for mer- cury by means of copper wire, in the way described at paragraph 319. 309. The following precautions must be attended to in analysing this group : The means, both for separating and detecting the members of the first section, are so simple and positive, that no difliculty will be experienced by the * See Appendix B. 122 THE SPECIAL PROPERTIES student. It may, nevertheless, be as well to observe, that chloride of lead ought to be completely removed, before ammonia is added ; for if it is not, a white residue, which is nothing more than chloride of lead, may remain after the addition of ammonia, when mercury is absent, which may perplex the student. And if the chloride of lead be not completely removed before the addition of ammonia, the ammoniacal solution will appear turbid, owing to the separation of an insoluble basic salt of lead : this will not, however, interfere with the test for silver, since it (the basic salt of lead) redissolves upon the addition of nitric acid. The difficulties which occur in examining the second section will be easily overcome by a little attention. Many erroneous conclusions will be formed if the simple yet neces- sary precaution of washing the sulphuretted hydrogen pre- cipitate be neglected ; because a small quantity of the hydrochloric acid employed to precipitate the first section, being left behind, will be converted, on the addition of nitric acid, into aqua regia, which, by dissolving the proto- sulphide of mercury, may cause that member to be over- looked ; and should the mercury thus pass into solution, a compound of that metal will be precipitated on the addition of ammonia, which may be mistaken for bismuth. The precipitate must therefore, before it is treated with nitric acid, be washed with water until the wash-water, acidulated with nitric acid, gives 1 no precipitate with nitrate of silver. It is difficult to free the mass of sulphur, which separates on the addition of nitric acid, entirely from some of the imdecomposed sulphides ; and which, by communicating to it a black appearance, might lead to the belief that prot- oxide of mercury was present, even in the absence of that member. An experienced eye can generally distinguish between this mixture of undecomposed sulphide and sul- OF THE SIXTH GROUP. 123 >phur, and protosulphide of mercury, the former being light and flocculent, whilst the latter is dense and heavy ; but a safe and legitimate conclusion can only be arrived at by examining it specially for mercury. A varying amount of sulphuric acid is always formed by dissolving the sulphides in nitric acid : a portion of the lead will therefore be pre- cipitated as sulphate, and remain behind mixed up with the substance insoluble in nitric acid ; it is necessary, on this account, to examine the insoluble mass for this member, if it should not be met with in its proper place. As sulphate of lead precipitates from dilute solutions, and especially from those which contain much free acid, only after the lapse of some considerable time, the solution ought, after the addition of sulphuric acid, to be allowed to stand for a considerable time (an hour) before adding the ammonia. A precipitate will be formed on the addition of ammonia to the nitric solution, if either of these reagents contains a trace of iron, but this precipitate cannot be mistaken for bismuth if the following confirmatory test be applied : Dissolve the precipitate obtained by ammonia in the least ossible quantity of dilute hydrochloric acid, and evaporate just to dryness ; redissolve the residue in water containing a drop of hydrochloric acid, and then add a large quantity of water ; if a turbidness be produced, bismuth is present. s SPECIAL EEMAEKS. 310. OXIDE OF SILYEE. The colour of this oxide is brown. It is very soluble in nitric acid ; it combines with ammonia, giving rise to a dangerous compound (fulminating silver). Many of the salts of silver are colourless and in- soluble. The soluble ones do not affect vegetable colours, and are decomposed at a red heat. Many of them blacken 124 THE SPECIAL PROPERTIES on exposure to light ; and they are all decomposed with tho precipitation of metallic silver by many metals, such as zinc, iron, copper, &c., and other reducing agents. The principal minerals of this metal are the SULPHIDE (silver glance AgS), the CHLORIDE (horn silver AgCl), SULPHIDE OF SILYER and ARSENIC (3 AgS+AsS 3 ), and SULPHIDE or SILYER and ANTIMONY (3 AgS-f SbS 3 ) ; SILYER is also met with in the metallic state. It is likewise found in small quantities in most lead and copper ores. 311. When silver compounds, mixed with carbonate of soda, are subjected on charcoal to the inner blowpipe flame, brilliant metallic globules are produced, which are not attended with any incrustation. 312. OXIDE OF LEAD. This oxide is of a yellow or reddish-yellow colour. In commerce it frequently goes under the name of massicot, and when partially fused is called litharge. The hydrated oxide is of a white colour, and it speedily absorbs carbonic acid from the air. The best solvent, both for the oxide and its hydrate, is nitric or acetic acid. The salts of lead are frequently insoluble, and are colourless, if the constituent acids be so. The soluble neutral salts redden litmus paper, and are decomposed at a red heat. The principal minerals of this metal are the SULPHIDE (galena or lead glance Pb S) and the CARBONATE (PbO, C0 2 ). 313. Chromate of potash produces, in solutions of lead, a yellow precipitate of CHROMATE OF LEAD (PbO, CrO 3 ), soluble in the fixed alkalies, but insoluble iu nitric acid. 314. When lead compounds, mixed with carbonate of soda, are exposed upon charcoal to the inner blowpipe flame, ductile metallic globules "are formed, accompanied with an incrustation which is yellow whilst hot, but be- comes paler on cooling. OF THE SIXTH GROUP. 125 315. SUBOXIDE OF MEBCUBY. This oxide is black ; it is decomposed by heat, the mercury volatilizing in the metallic state. It forms no hydrate. The salts of the suboxide of mercury, when ignited, vola- tilize either with or without decomposition. The soluble neutral ones redden litmus paper ; some of them are de- composed by much water into soluble acid and insoluble basic salts. The colour of the neutral salts is white, the colour of the basic ones is yellow. They are reduced, like the silver salts, by many metals, such as zinc, iron, copper, &c., and by other reducing agents. 316. To obtain the mercury from the subsalts of this metal, they may be decomposed either by copper or pro- tochloride of tin, or by means of carbonate of soda, in the way described at 319, 320, 321. 317. PBOTOXIDE OF MERCUBY. This oxide is obtained in the form of a crystalline mass, nearly black whilst hot (at a red heat it is decomposed and entirely volatilized), but of a light red when cold. Its hydrate is yellow. Both the oxide and its hydrate are soluble in hydrochloric and nitric acid. The salts of the protoxide of mercury, when ignited, volatilize either with or without decomposition. The soluble neutral ones redden litmus paper. The sul- phate and nitrate are decomposed in the presence of much water into soluble acid and insoluble basic salts. The metals and other reducing agents which decompose the subsalts act in a similar manner upon the protosalts of this metal. 318. These two oxides differ not only in colour, but likewise in their behaviour with alkalies and hydro- chloric acid. The latter reagent is especially applicable for separating them, when they are present in the same solution; as subchloride of mercury (calomel) is 126 THE SPECIAL PROPERTIES insoluble, whilst the protochloride (corrosive sublimate') is soluble. 319. " Metallic copper, introduced into a solution of mercury, especially after acidification with hydrochloric acid, becomes covered with a white, lustrous coating ; when moderately heated, the copper regains its original colour, vapours of mercury being evolved : this test is ex- ceedingly delicate. Slips of copper wire, about an inch in length, may be used ; they should be cleaned by shaking for a few moments with concentrated nitric acid, and thoroughly washed. Half a dozen such slips should be boiled for three or four minutes in the solution, previously acidulated with hydrochloric acid; they are then well rinsed, dried by pressure between blotting-paper, and heated in a glass tube of one quarter of an inch diameter, constructed so as to allow the passage of a feeble current of air. A coating of minute globules of mercury is formed upon the cool part of the tube ; these may be united into larger globules by rubbing with a gla^s rod " (Abel and Bloxam). 320. If protochloride of tin be added in small quantity to salts of the protoxide of mercury, it reduces them to the state of suboxide, and, as a consequence, white snb- chloride of mercury precipitating ; but if it be added in excess, the salt of mercury (subsalts as well as protosalts) is completely decomposed, metallic mercury being thrown down as a gray precipitate, which may be united into glo- bules by heat and agitation but most readily by boiling the metallic deposit, after decantation of the supernatant fluid, with hydrochloric acid. 321. " Solid compounds of mercury, mixed with a large excess (at least twelve parts) of dry carbonate of soda, and heated in a perfectly dry tube of hard glass, having a OF THE SIXTH GROUP. 127 diameter of about one quarter of an inch, and expanded into a bulb at one end, furnish minute globules of metallic mercury, which are deposited on the cool part of the tube, and may be united into larger globules by rubbing with a glass rod. This test is exceedingly delicate ; in order that it may be perfectly successful, the mercury compound should be thoroughly dried (in a water bath), and the car- bonate of soda should be ignited immediately previous to use. In order to prevent the sublimation of undecom- posed mercury compounds, it is well to cover the mixture in the bulb-tube with a layer of pure carbonate of soda. (Abel and Rloxam). 322. The chief mineral of this metal is the PROTOSUL- PHIDE (cinnabar) ; it is likewise met with in the metallic state. 323. TEBOXIDE or BISMUTH. This oxide is of a yellow colour; when heated, it acquires, for the time, a deeper tint ; it fuses at a red heat. Its hydrate is white. They are both readily soluble in the dilute mineral acids. Most of the salts of bismuth are decomposed at a red heat. They are colourless, provided the constituent acid be so. The soluble neutral salts redden litmus paper, and one distin- guishing character which they possess is that of being decomposed by water into soluble acid and insoluble basic salts. This property is exhibited in the most decided man- ner by the chloride. To employ it as a confirmatory test, dissolve the precipitate in a small quantity of hydrochloric acid, evaporate nearly to dryness, and pour this solution into a large quantity of water. If bismuth be present, a milky turbidness will be produced. This metal is found principally in the native state. 324. Ckromate of potash throws down from solutions of bismuth the YELLOW CHEOMATE. This salt differs from the 128 THE SPECIAL PROPERTIES corresponding one of lead "by its solubility in dilate nitrics acid, and its insolubility in potash. 325. When compounds of bismuth, mixed with carbonate of soda, are exposed on charcoal to the inner blowpipe flame, brittle metallic globules are obtained, attended with a yellow incrustation of oxide of bismuth. 326. OXIDE or CADMIUM. This oxide is of a brown or yellowish-brown colour: its hydrate is white. They are both easily soluble in the dilute mineral acids. The salts of cadmium are colourless, provided the constituent acid be so. Most of them are soluble in water. The soluble neutral ones redden litmus paper, and are decomposed at a red heat. This metal occurs only in zinc ores. It is found as SULPHIDE in zinc blende, and as OXIDE or CARBONATE in calamine. 327. When compounds of cadmium, mixed with carbonate of soda or other reducing agents, are exposed on charcoal to the inner blowpipe flame, the charcoal becomes covered with a yellow or reddish-yellow incrustation of oxide of cadmium. 328. OXIDE or COPPER. This oxide is black ; its hydrate is of a light blue colour. They are both readily soluble in the dilute mineral acids. Most of the salts of this metal are soluble in water. The soluble ones redden litmus paper, and are decomposed at a red heat. In their anhydrous state, the salts are white ; in their hydrated state, they are of a blue or greenish-blue colour, which their solutions exhibit, even when much diluted. 329. This metal is sometimes found in the native state ; but it chiefly occurs in combination with sulphide of iron, constituting the COPPER PYRITES (Cu 2 S -f Fe 2 S 3 ), and in BLUE COPPER ore, or MALACHITE (2 CuO, CO 2 +HO). 330. Eerrocyanide of potassium throws down, even from dilute solutions of copper, a reddish-brown precipitate of OF THE SIXTH GROUP. 129 EERRO CYANIDE OE COPPER (2 Cu,Cfy), which is insoluble in dilute acids, but is decomposed by the fixed alkalies. 331. If bright metallic iron be introduced into a solution of a salt of copper, it becomes coated with a red deposit of that metal, provided the solution be neutral or only very slightly acid. 332. When any of the compounds of copper, mixed with carbonate of soda, are exposed on a charcoal support to the inner blowpipe flame, METALLIC COPPER is obtained, unac- companied with any incrustation on the charcoal. 130 CHAPTER III. THE GENERAL PEOPEETIES OF THE BASIC aEOUPS. 333. It will be seen by consulting the general table (7), that some of the reagents produce a precipitate with more than one of the groups ; the analysis must therefore be com- menced by removing those substances the general reagent of which produces no precipitate with the members of any other group under the same circumstances. Such a course will be adopted, if the reagents are employed in the order observed in the table. 334. PlEST DIVISION OP THE SlXTH GrKOTJP. The analysis must be commenced by adding to the solution hydrochloric acid, which precipitates the members of the first section of the sixth group when they are present. When a precipitate is produced, collect it upon a filter, wash it twice with cold water, and then examine it, according to the first section of table 6, and paragraph 306. The wash- water must be collected with the filtrate. Before adding the hydrochloric acid, consult paragraphs 342, 343, and 344. 335. SECOND DIVISION or THE SIXTH, AND THE WHOLE or THE FIFTH GEOTJP.* To the filtrate from the precipitate produced by hydrochloric acid, or to the solution with which * Gold and platinum are easily detected in the presence of all the metals (paragraph 290) ; Northcote and Church, in their ' Manual of Analysis,' recommend their separation from the solution, before pre- cipitating the other members of the fifth and the members of the sixth group, by sulphuretted hydrogen ; the following is their plan : The filtrate from the HC1 precipitate, or the solution which has failed to give a precipitate, is freed from HO, NO 5 (if present) by one or two evaporations on the water-bath with HC1 ; to the HC1 solution, which ought to be concentrated, a reasonable quantity of NH 4 C1 solution is THE GENERAL PROPERTIES. 131 it lias failed to give a precipitate, is to be added sulphide of hydrogen gas* (hydrosulphuric acid), until the solution smells strongly of the gas after it has been shaken and gently warmed for some time ; the remaining members of the sixth and all the members of the fifth group, when present, will be precipitated. When a precipitate is produced, collect it upon a filter and wash it with hot water until the wash- water is no longer acid to test-paper ; the wash- water need not be collected with the filtrate, but may be thrown away. Boiling caustic soda must be poured upon the washed pre- cipitate : the alkali dissolves out the members of the fifth group, whilst the members of the sixth group, being insolu- ble in the alkali, remain behind upon the filter. If a portion of the precipitate should be insoluble in the caustic soda, it must, after being well washed with hot water, be ex- amined for the members of the second division of the sixth group, according to table 6 and paragraph 307. To the caustic soda solution must be added hydrochloric acid in excess. If a precipitate is produced on the addition of the acid to the alkaline solution the colour of which is white, this arises merely from the separation of sulphur, none of the members of the fifth group being present ; if the pre- cipitate possess a yellow or orange colour, added, the liquid is then well agitated and allowed to rest for some hours; if Pt is present, a yellow crystalline precipitate of PtCl^ NH 4 C1 is formed. The nitrate is mixed with a reasonable quantity of a concentrated solution of HO, C 2 3 , and moderately heated for some hours. A precipitate, consisting of yellow spangles or of a brown yellow sponge, indicates Au. The filtrate is then treated with HS. * If the oxides of silver and lead, and suhoxide of mercury, had not to he sought for, we must nevertheless add hydrochloric acid to the solution to render it acid, before adding sulphide of hydrogen, in order to prevent the members of the third and fourth groups from being precipitated by that reagent, and to ensure the complete precipitation of the fifth group. 132 THE GENERAL PROPERTIES BINOXIDE OF TIN,* and ARSENIC, can only be present. If the colour of the precipitate is Hack., then all the members of the group must be sought for. The analysis of the pre- cipitate, after being well washed with hot water, must be conducted according to the directions given under the fifth group (240). Before passing the sulphide of hydrogen gas through the solution, consult paragraphs 345, 346, and 347. 336. THE FOURTH G-ROUP. If the directions given in the previous paragraph have been obeyed, the solution, which has now to be examined for the fourth group, will have a strong odour of sulphide of hydrogen ; if they have not been obeyed, they must le before proceeding to examine the solution for this or the following groups. The filtrate from the sulphide of hydrogen precipitate, or the solution with which it has failed to give a precipitate, must be boiled until every trace of sulphide of hydrogen is expelled. To ascertain when all the gas is expelled, hold a piece of bibulous paper, moistened with a solution of some soluble salt of lead, over the boiling liquid: when the lead-paper does not alter in colour, all the sulphide of hydrogen is expelled. If boiling the liquid causes a separation of sulphur, the solution, after the sulphide of hydrogen is expelled, must be filtered to free it from the sulphur ; a very small portion of the liquid must then be examined for protoxide of iron by ferricyanide of potassium.f When iron is present, the rest of the solution, to which no ferricyanide of potassium has been added, must be boiled with a few drops of nitric acid until all the iron is converted into sesquioxide,J which is accomplished when a * The colour of protosulphide of tin is a blackish brown. f Ferro- and ferricyanide of potassium precipitate a great many of the metallic oxides, besides the iron oxides, but with no other oxides but the iron oxides do they give Hue precipitates. When the fifth and sixth groups are not sought for, but we com- mence the analysis by examining for the members of the fourth group, OF THE BASIC GROUPS. 133 drop of the solution does not give a blue colour with ferricy- anide of potassium. To the solution, when the iron is peroxidized, must be added chloride of ammonium and ammonia ; the ammonia must be added until the solution, after it has been well shaken, smells of the volatile alkali. Nitric acid need noi> be added to the solution when it con- tains no iron, but the chloride of ammonium and ammonia can at once be added to it after it has been freed from the sulphide of hydrogen and sulphur. Warm the solution after the addition of the ammonia ; and when a precipitate is pro- duced, showing the presence of one or all of the members of the fourth group, collect it upon a filter, wash it with hot water until the wash-water does not turn red test-paper blue ; examine it then according to table 4 and paragraphs 189, 190, 191, and 192. Before adding the chloride of ammo- nium and ammonia, consult paragraphs 348, 349, 350, &c. 337. THE THIED G-EOTJP.* To the filtrate from the pre- cipitate produced by ammonia, or to the solution with which it has failed to give a precipitate, is to be added sulphide of ammonium in the cold.f If any of the members of the third we must not neglect to convert the iron, when any of it exists as prot- oxide, into sesquioxide, by boiling the solution with nitric acid. * Although protoxide of iron belongs, on account of its general . properties, to this group, we have placed it in the special table of the fourth group ; because, in separating the groups, it is converted by nitric acid into sesquioxide a member of the fourth group : we have thought it advisable, therefore, to contrast its special properties with those of the fourth. f When the student does not look for the members of the three pre- vious groups, viz., the sixth, fifth, and fourth, he must, before adding sulphide of ammonium to the solution, add chloride of ammonium and ammonia : in other words, he must add them to the solution which he has to examine for the members of the third group, if they (*. e., chlo- ride of ammonium and ammonia) have not been added in the previous course of the analysis. The chloride of ammonium is added, to pre- vent the precipitation of the magnesia by the ammonia. TABLE VII. BEHAVIOUR OF THE BASIC GIIOUPS FIRST GROUP. SECOND GROUP. THIRD GROUP. POTASH (KO), SODA First Subdivision. Second Subdivision. OXIDE MANGANfcSE (NaO), AMMONIA (NH 4 0). BARYTA (BaO), STRON- TIA (SrO), LIME MAGNESIA (MgO). * (MnO), OXIDE OF ZIMC (ZnO), OXIDE OF COB A LT ( CoO i, (CaO). OXIDE OF NICKEL (NiO), PROTOXIDE OF IRON (FeO). 1. HYDROCHLORIC 1. HYDROCHLORIC ACID does not precipitate the 1. HYDROCHLORIC ACID does not precipitate the members of tliis members of this group from their solutions, be- ACID does not precipitate cause their Chlorides are soluble. the members of this group from their solu- 4 group from their solu- tions, because their Chlo- tions, because their Chlo- rides are soluble. rides are soluble. 2. HTDROSULPHTJRIC 2. HYDROSULPHURIC ACID does not precipitate 2. HYDROSULPHURIC ACID does not precipitate the members of this the members of this group, either from their neutral acid or alkaline solutions, because their ACID does not precipitate t he members of this group, either from their neutral acid or alkaline Sulphides are soluble. group from their acid s olutions, because tlteir solutions, because tfieir Sulphides are soluble in Sulphides are soluble. dilute acids, even in the cold. 3. AMMONIA does not 3. AMMONIA does not* S.'AMMONIA precipi- 3. AMMONIA p.-cclpl-. precipitate either of the other two members of the group. precipitate the members of this division from their solutions. tates Magnesia partly from its solutions, as Hydrate (MgO, HO); tates the members of this! group as Hydrates. In an excess of the reagent, the presence of Salts of the Hydrates of Zinc, Ammonia prevents* the Nickel, and Cobalt are precipitation altogether. readily soluble, but the Hydrates of Manganese and Protoxide of Ironj are insoluble; but the presence of Salts of A,n- monia prevents the preci- pitation of the Manganese] and Oxide of Iron. 4. SULPHIDE or AM- MONIUM does not precipi- tate the other two mem- 4. SULPHIDE OF AMMONIUM does not precipitate the members of this group from their solutions, because their Sulphides are soluble. 4. SULPHIDE OF AM- MONIUM precipitates alii the members of this! bers of this group from group from neutral and their solutions, because alkaline solutions, as their Sulphides are solu- Sulphides. ble. 5. CARS ON ATE OF AM- 5. CARS ON ATE OF AM- 5. CARBONATE OF AM- 5. CARBONATK OF AM- MONIA does not precipi- tate either of the other MONIA precipitates the members of this division MONIA precipitates Mag- nesia only partly, and MONIA precipitates all the members of this two members of this from their solutions as the presence of Salts of group ; but they are all, group from their solu- tions. Carbonates; the presence of Salts of Ammonia does not interfere with the Ammonia prevents the precipitation altogether. with the exception of Manganese and Oxide of Iron, readily soluble in an precipitation. excess of the reagent. 6. ARSENIATE or AM- 6. ARSENIATE or AM- 6. ARSENIATE or AM- 6. ARSENIATE OF AM- MONIA does not precipi- tate either of the other MONIA precipitates the members of this division MONIA precipitates Mag- nesia from its neutral and MONIA precipitates the members of this group two members of this from their neutral and | alkaline solutions, as Ar- from their neutral solu- group from their solu- alkaline solutions, as seniate; violent agitation tions, as Arseniates. tions. Arseniates. promotes the formation of the precipitate. The precipitate is more solu- ble in hot than cold water. * The phosphates and oxalates of baryta, strontia, and lime, and phosphate of magnesia, are soluble in dil miuenil acids, but insoluble in water and the alkalies; consequently, when their acid solutions are rendered neutral or alkaline by nrn'mpuia, t keif salts are precipitated ; therefore when baryta, strontia, and lime are in combination with phospho'ric and oxalic acids, and when magnesia is in combination with phosphoric acid, they are precipitated in combination with these acids by ammonia, from their acid solutions, along with the members of thefo , .h group. WITH THE GENERAL REAGENTS. FOURTH GROUP. FIFTH GROUP. SIXTH GROUP. ALUMINA (AL>0 3 ), SESQUIOXIDE CHRO- MIUM (CrgOg), SESQUI- OXIDE OF IRON (FegOg). ARSENIOUS ACID (AsOs), ARSENIC ACID (AsOs), TEROXIDE OFANTIMONY (Sb0 3 ), OXIDE OF TIN (SnO), BINOXIDE OF TIN (SnOo), TEBOXIDE OF GOLD (Au0 3 ). BINOXIDE OF PLATINUM (Pt0 2 ). Second Subdivision. OXIDK OF LE\D (PbO), PROTOXIDE OFMERCURY (HgO),TEROXIDKOFBlS- MUTH (Bi0 3 ), OXIDE or CADMIUM (CdO), OXIDE OF COPPER (CuO). First Subdivision. OXIDE OF SILVER (AgO), SUBOXIDE OF AlER- CURY (Hg. 2 0), OXIDE OF LEAD (PbO). 1. HYDROCHLORIC 1. HYDROCHLORIC 1. HYDROCHLORIC 1. HYDROCHLORIC ACID does not precipitate ,he members of this ACID does not precipitate the members of this ACID does not precipitate the members of this divi- ACID precipitates the members of this division group, because their Chlorides are soluble. group, because their Chlorides are soluble. sion of the group, because their Chlorides are so- of the group, becaiise their Chlorides are insolu- luble. ble. Chloride of Lead is slightly soluble in water ; it is more soluble in hot than cold water. 2. HYDROSULPHURIC 2. HYDROSULPHURIC 2. HYDROSULPHURIC ACID 'precipitates all the ACID does not precipitate any of the members of his group from their ACID precipitates all the members of this group from their acid solutions, members of this group from their neutral, alkaline and acid, solutions, as Sulphides. acid solutions, because as Sulphides. Sulphide of Iron is readily oluble in acids, and the Sulphides of Aluminum and Chromium are not brmed in the humid way. 3. AMMONIA, even in 3. AMMONIA precipi- 3. AMMONIA precipitates the members of this he presence of its Salts, tates some of the mem- group ; but in an excess o f the reagent, the oxides >recipitates the mem- )ers of this group as Tydrates* which an bers of this group. 'of Silver, Cadmium, and Copper redissolve readily ; the rest are insoluble in an excess of the reagent." xcess of the reagent does not redissolve. 4. SULPHIDE OF AM- 4. SULPHIDE OF AM- 4. SULPHIDE OF AMMONIUM precipitates all MONIUM precipitates all .he members of this MONIUM, if added in ex- cess, does not precipitate the members of this group from their neutral and alkaline solutions, as Sulphides. group from neutral and the members of tins alkaline solutions ; Ses- group from their solu- quioxide of Iron, as Pro- tosulphide ; Alumina and tions, because their Sul- phides are soluble in the Sesquioxide of Chromi- Alkaline Sulphides. um, as Oxides. 5. CARBONATE OF AM- MONIA precipitates all 5. CARBONATE OF AM- MONIA precipitates some 5. CARBONATE OF AMMONIA precipitates all the members of this group from their solutions ; and the members of this of the members of this an excess of the reagent does not redissolve them, group from their solu- group, as Oxides. with the exception of Copper. tions as Oxides ; an excess of the reagent does not redissolve them. 6. ARSENIATE OF AM- 6. ARSENIATE OF AM- 6. ARSENIATE or AMMONIA precipitates the MONIA precipitates the members of this group MONIA precipitates some of the members of this members of this group tions, as Arseniates. from their neutral solu- from their neutral solu- group from their neutral tions, as Arseniates. solutions, as Arseniates. * When phosphate of irou and phosphate iilumiua are pre phates, and not as Hydrates, by ammonia. it in a solution, they are precipitated KB Phus- 136 THE GENERAL PROPERTIES group are present, a precipitate will be produced by the sulphide of ammonium. When a precipitate is produced, collect it upon a filter, and, after washing it well with hot water, examine it according to table 3 and paragraph 165, if the precipitate is of a light colour ; but if it is black, paragraph 166. Before filtering the whole of the solution, when a preci- pitate is produced by sulphide of ammonium, add to that portion of the liquid which has been filtered a little more sulphide of ammonium ; if the reagent produces a further precipitate, add some to the unfiltered as well as to the filtered portion, then filter it, and again test the filtrate with sulphide of ammonium. If the sulphide of ammonium cause no precipitate in the filtered liquid, proceed with the filtra- tion, as the group has been completely precipitated. Before adding any sulphide of ammonium to the solution, consult paragraphs 351, 352, and 353. 338. ElEST DIVISION OF THE SECOND GrKOUP. To the filtrate from the precipitate produced by the sulphide of ammonium, or to the solution with which it has failed to give a precipitate, is to be added carbonate of ammonia ;* the solution must then be gently warmed for some time, * When the student does not look for the members of the four pre- vious groups, viz., the sixth, fifth, fourth, and third, he must, before adding the carbonate of ammonia to the solution, add chloride of am- monium and ammonia : in other words, he must add them to the solu- tion which he has to examine for the members of the second group, if they (i. e., chloride of ammonium and ammonia) have not been added in the previous course of the analysis. The chloride of ammonium is added to prevent the precipitation of the magnesia by the carbonate of ammonia ; any ammoniacal salt may be employed, the acid of which forms no insoluble compound with magnesia or the other members of the group. The carbonate of ammonia employed being generally a sesquicarbonate, a portion of the alkaline earths is apt to be dissolved by the excess of carbonic acid. The ammonia is added to prevent this : it does so by converting the sesquicarbonate into a neutral carbonate. OF THE BASIC GROUPS. "but not boiled. If one or all of the members of this divi- sion are present, a precipitate will be produced by the car- bonate of ammonia, especially after warming the solution. When a precipitate is produced, collect it upon a filter, wash it with hot water, and afterwards examine it according to table 2 and paragraphs 130, 131, 132, and 133. Before adding the carbonate of ammonia, consult paragraphs 354 and 355. 339. SECOND DIVISION OP THE SECOND GROUP. The nitrate from the carbonate of ammonia precipitate must be tested with a little more carbonate of ammonia before we attempt to look for magnesia. If on the further addition of carbonate of ammonia a precipitate is produced, it must be filtered ; the precipitate must be examined, along with the previous precipitate, for baryta, strontia, and lime, and the filtrate must be again tested with carbonate of am- monia. The filtrate from the carbonate of ammonia preci- pitate, or the solution with which it has failed to give a pre- cipitate, must be divided into two parts. To one part of the solution, which must be quite cold, must be added arseniate of ammonia ;* the liquid, after the addition of the reagent, ought to be shaken very violently ; and if, after time (one or two hours) has been allowed for the formation of the precipitate, no precipitate should appear, this part of the solution can be thrown away ; the other part of the solution must be examined for potash and soda in the way pointed * When the student does not look for the previous groups and the first section of this group, he must, hefore adding the arseniate of am- monia to the solution, add chloride of ammonium and ammonia. The chloride of ammonium is added to prevent the precipitation of the magnesia by the ammonia. The ammonia is added because arseniate of magnesia and ammonia is less soluble in water containing ammonia than in pure water. 138 THE GENERAL PROVES/TIES out in paragraph 340. When arseniate of ammonia produces a precipitate in one part of the solution (consult paragraph 341), the two portions of the solution must be mixed together ; a further quantity of arseniate of ammonia must be added ; the liquid, after the addition of the reagent, must be shkken very violently ; and, after time has been allowed for the complete precipitation of the magnesia, the liquid must be filtered. To the nitrate must be added a little more arseniate of ammonia ; if this should cause a further precipitate, the solution must be again filtered and the filtrate again tested with arseniate of ammonia. The excess of the arsenic acid must be got rid of in the filtrate before we can test for the non-volatile alkalies. When, therefore, the filtrate gives no further precipitate with arseniate of ammonia, sulphide of ammonium containing an excess of sulphur* must be added in sufficient quantity, and the solution evaporated to one half its bulk ; hydrochloric acid must then be added, slightly in excess, and the solution filtered from the precipitated sulpharsenic acid (AsS 6 ). The filtrate must then be exa- mined for potash and soda in the way described in the following paragraph. Before adding the arseniate of am- monia, consult paragraph 356. 340. THE FIRST GROUP. The second portion of the solution in which magnesia has been found to be absent, and the filtrate from the sulpharsenic acid precipitate (when magnesia has been present in the solution under examina- tion), are each examined in the following way for potash and soda: The solution is evaporated to dryness, and ignited until all fuming has ceased. As a slight quantity * To obtain sulphide of ammonium containing an excess of sulphur, heat some of the ordinary sulphide of ammonium with some flowers of sulphur ; filter the solution if all the sulphur does not dissolve, and use the nitrate. OF THE BASIC GROUPS. 139 of the ammoniacal salt frequently becomes detached from the sides of the vessel during the process of ignition, however long the ignition may be continued, it will remain unvolatilized, as it does not become sufficiently heated. It is necessary, therefore, after all fuming has ceased, to re- move the lamp, allow the vessel to cool, and, when cold, to wash down from the sides of the vessel any unvolatilized ammoniacal salt with the smallest possible quantity of water ; the liquor must then be evaporated, and the ignition continued until all fuming ceases. During the ignition, the dry matter frequently assumes a black or brown colour ; this is owing to the ammoniacal salts, which have been added during the course of the analysis, containing organic matter. Should this black matter not be destroyed during the ignition, it will be got rid of on dissolving the residue which remains after the expulsion of the ammoniacal salts in water, and filtering the solution; the organic matter, being rendered insoluble by the heat, will remain behind upon the filter. After all the ammoniacal salts have been expelled, as much lolling water as would fill a small-sized thimble should be poured into the vessel, in order to dis- solve the fixed alkalies if they are present. The liquid must then be filtered through a very small filter, and the clear filtered liquid examined for potash and soda according to paragraph 100 ; and paragraph 102 ought to be con- sulted. We always look for ammonia in a portion of the original solution. Before examining for the alkalies, consult paragraph 357. 341. As magnesia does not alter or modify in the least the colours which potash and soda impart to the blowpipe flame, it is not necessary to separate magnesia, when it is present, from the solution, in order to look for the fixed alkalies ; all that is required is to evaporate to dryness that 140 THE GENERAL PROPERTIES portion of the solution to which no arseniate of ammonia has been added, and continue the ignition until all the am- moniacal salts which have been added in the course of the analysis are expelled ; after their expulsion, as much foiling water as would fill a small-sized thimble should be poured into the vessel, in order to dissolve the fixed alkalies, if they are present. The liquor must then be filtered through a very small filter, and the clear filtered liquid examined for soda and potash by the blowpipe flame ; when soda is pre- sent, CartmelTs method (paragraph 112) must be adopted for the detection of potash. PARTICULAR OBSERVATIONS REGARDING THE PRECIPITATES PRODUCED BY THE GENERAL REAGENTS, AND THE PRECAUTIONS TO BE ATTENDED TO IN EXAMINING THE SOLUTIONS. 342. Precautions to be attended to in examining for the first section of the Sixth Group. Before adding hydro- chloric acid to any solution under examination, it is neces- sary to ascertain, by test-papers, whether the solution is acid, neutral, or alkaline. When it is one of the two former, a few drops of the acid will generally be sufficient ; if alka- line, the acid must be added until it is decidedly in excess. When a precipitate is produced, add the acid, drop by drop, until it ceases to increase; then add a few drops more, shake the mixture, and filter. When no precipitate is pro- duced, a few drops of the acid will in most cases be sufficient, since our only object in adding it then is to acidify the solution, in order to prevent the precipitation of the mem- OF THE BASIC GROUPS. 141 bers of the third and the members of the fourth group by sulphide of hydrogen. When an evolution of gas takes place on the addition of the hydrochloric acid, consult para- graph 362. 343. As oxide of silver is not precipitated, under certain circumstances, by hydrochloric acid and as a precipitate may be produced on the addition of hydrochloric acid, in the absence of the oxides of silver, lead, and sub oxide of mer- cury it is requisite to notice, 1st, the substances which interfere with the precipitation of the oxide of silver ; 2d, the substances which may be precipitated, and under what condition the precipitation takes place. 1st. When proto- nitrate of mercury is present in the solution, oxide of silver, if present, will not be precipitated by the hydrochloric acid, because chloride of silver is soluble in a solution of proto- nitrate of mercury, especially if the solution is hot and concentrated: on the addition of water, and cooling, the solution may deposit shining yellowish-white crystals, which are pure chloride of silver. "When protonitrate of mercury is suspected to be present, acetate of ammonia ought to be added to the solution after the addition of the hydrochloric acid, as this ensures the complete precipitation of the chlo- ride of silver. 2nd. The precipitate* may be occasioned by the presence of some salt of antimony or bismuth, as the chlorides of these metals are decomposed by much water into soluble acid and insoluble basic salts. This precipitatef * If the hydrochloric acid employed contain a trace of sulphuric acid, and baryta he present in the fluid under examination, a slight trace of insoluble sulphate of baryta will be formed, which may be dis- tinguished by the difficulty experienced in separating it from the fluid by nitration. f Hydrochloric acid precipitates, of the inorganic acids, boracic acid, and of the organic acids, benzoic and uric acids, if the solution is very concentrated. The two former are dissolved by hot water, and the uric acid by heating with nitric acid. 142 THE GENERAL PROPERTIES may also arise from the presence of some substance inso- luble in water, but soluble in the caustic, carbonated, or sulphuretted alkalies, or in an alkaline cyanide for ex- ample, phosphate of alumina, or alumina dissolved in caustic soda, sulpharsenious acid dissolved in carbonate of ammonia, tersulphide of antimony dissolved in an alkaline sulphide, cyanide of nickel dissolved in an alkaline cyanide ; or the precipitate may be due to silicic acid, some alkaline silicate being present. If the precipitate is due either to antimony or bismuth, it will redissolve on the addition of a few drops more of hydrochloric acid. When silicic acid is the sub- stance thrown down, the precipitate will appear very gelati- nous, and will remain undissolved on the further addition of acid ; a fresh portion of the original solution must there- fore be acidulated with nitric acid, and evaporated to dry- ness to render the silicic acid insoluble ; the ignited mass may then be digested with dilute nitric acid, and filtered. * The analysis of the filtrate must then be conducted in the regular way, by adding to it hydrochloric acid, &c. If the precipitate should be due to the presence of any of the other substances, a fresh portion of the original solution ought to be taken, and nitric acid added to it until it is decidedly acid. If the precipitate does not disappear on the addition of the acid, the solution ought to be warmed ; if this should fail to dissolve the precipitate, it must be collected upon a filter, and examined as a substance inso- luble in water and acids (see par. 591.) The analysis of the solution or' filtrate must then be conducted in the regular way, by adding to it hydrochloric acid, &c. 34<4<. As the chlorides of lead, silver, and subchloride of * The precipitate left upon the filter must be examined for silicic * T,^ 4 s ^-e I 4 os . s e i, SS -u acids form with baryta lubility of the baryta pr .2 ** ill 157 ft . 9 g tj 3 w H ^ O 1 s H ^ PH ( ( OQ ft" M ^ o 1 5 P^ PM 03 o O pq H a 3 o . Q t^ w o M CO P *7 ^ PH O * HH PH O i-5 a Q H H s W PH p o o 1 DIDE < 1 s o M 1 ft" o GO s ft O ^5 ^ s g M O - te O % w O g W 3 W 3 M H 3 0) if! ^ PH p a E cc p hH O O a PH ACIDS HYDEOSU S h^ O 158 THE SPECIAL TESTS 381. HYDEOCYAKIC ACID. This acid can be distin- guished from all other acids by the tests described in para- graphs 452 and 454 ; if, however, protoxide of mercury has been discovered in testing for the bases, the process de- scribed in paragraph 455 must be employed. 382. AESEXIOUS ACID, AESE^IC ACID, CHEOMIC ACID. As these acids are discovered in testing for the bases, no experiments require to be made for their detection when testing for the acids. 383. SULPHUEIC ACID. The presence or absence of this acid is ascertained on testing a part of the solution with the general reagent, chloride of barium ; no further test is needed to prove its absence or presence. 384. BOEACIC ACID. This acid can be detected, in most cases, by the method described in paragraph 416 ; but the most certain test is the one described in paragraph 417. 385. PHOSPHOEIC ACID. "When the phosphates are solu- ble in ammoniacal solutions (and the student can decide this when he knows what bases are present), this acid can be detected by the method described in paragraph 422, but the most certain tests are 425 and 426, especially the last. The student must, however, remember that arsenic acid gives precipitates with these reagents, similar to those given by phosphoric acid. When arsenic acid is present, it must, on this account, be removed from the solution by sulphide of hydrogen, or be reduced to the state of arsenious acid, before testing for phosphoric acid. 386. OXALIC ACID. This acid is detected by the method described at 433 ; but very minute quantities of it are more securely detected by boiling the substance with a solution of carbonate of soda, for some time ; subsequently filtering, and the filtrate acidifying with acetic acid, and then adding to it a solution of sulphate of lime (432). FOR THE INORGANIC ACIDS. 159 387. HYDROFLUORIC ACID. Test for this acid, when silicic acid is absent, by the method described at 435 ; when silicic acid is present, by the one described at 437 or 438. 388. SILICIC ACID. To test for this acid, evaporate the solution to dryness with an acid, and proceed as directed at 442 or 443. 389. HYDROCHLORIC ACID. "When hydrocyanic acid and hydrobromic acid are absent, the presence of this acid is proved by the insolubility of the silver precipitate in nitric acid, and by its solubility in ammonia ; when hydro- cyanic acid is present, and hydrobromic acid absent, its presence is proved, if, after igniting the silver precipitate, which is insoluble in nitric acid, but soluble in ammonia, a whitish residue remains, which is insoluble in nitric acid. When hydrobromic acid is present, no matter whether hydrocyanic acid is present or absent, the presence of hydrochloric acid can only be ascertained by the test described at 448. 390. HYDROBROMIC ACID. When hydriodic acid is pre- sent, it must first be precipitated, by the solutions of copper and iron (469), from the liquid, before we can test for bro- mine ; when this has been accomplished, the test described at 458 can be applied : in the absence of iodine, this test for bromine can be applied at once to the original solution. 391. HYDRIODIC ACID. Iodine is best discovered by the test described at 468. 392. NITRIC ACID. The tests described at 473 and 474 are the most characteristic of this acid. 393. CHLORIC ACID. The presence or absence of this acid is proved by the tests described at 479 and 480. CARBONIC ACID (CO 2 ). 394. This acid exists at the common temperature and 160 THE SPECIAL PROPERTIES pressure as a colourless, inodorous, and non-inflammable gas. Being heavier than the atmosphere in the proportion of 1'5 to 1, it can be decanted from one vessel to another like a liquid. It reddens blue litmus paper, previously moistened with water, which after a time returns to its original colour, owing to the acid having volatilized. It is soluble in cold water, but when the solution is heated the gas escapes. 395. The neutral alkaline carbonates are the only neutral salts of this acid which are soluble in pure water. The car- bonates are decomposed by all free acids soluble in water (hydrocyanic and hydrosulphuric acids excepted), with evolution of carbonic acid. 396. To detect carbonic acid, add to the solution or solid substance under examination hydrochloric acid; and warm the solution, if sufficient gas for detection cannot be procured without. Should any gas be evolved, allow it to accumulate by placing the thumb on the mouth of the test- tube, and afterwards decant it (taking care not to allow any of the liquid to pass over along with it) into another test-tube half filled with lime-water. A white precipitate of CARBONATE or LIME will be produced, if carbonic acid is present. 397. Many of the insoluble carbonates dissolve in water containing free carbonic acid from which solutions they are precipitated on boiling, the free acid being expelled. It is in this state that most of the lime and magnesia in spring and river water exist. The incrustrations which are formed in the vessels in which such waters are boiled are due to the precipitation of these carbonates occasioned by the removal of the free carbonic acid. Carbonic acid is best detected in waters by adding to them lime-water ; by this means not only is the CARBONATE OF LIME which is formed OF THE INORGANIC ACIDS. 161 precipitated, but also that which pre-existed in the solution. This process is employed on a large scale for softening hard waters (waters impregnated with earthy matter). 398. All the carbonates, with the exception of those of the alkalies, lose their acid upon ignition, the metal being left either in an oxidized or uncombined state, ac- cording to its greater or less affinity for oxygen. The alka- line carbonates and bicarbonates affect test-paper in the manner of a free alkali. 399. The following precautions must be attended to in testing for this acid : When the substance is in the solid state, it should be reduced to fine powder; and a little water should be added prior to the acid, to displace the air in its pores, otherwise an apparent effervescence will ensue from the expulsion of air. In the case of alkaline carbo- nates, the decomposing acid must be added until the solu- tion reddens blue litmus paper that is, until the acid is in excess ; otherwise, the carbonic acid set free may combine with some of the undecomposed carbonate, forming with it a bicarbonate, no effervescence consequently taking place. JSTo decomposition takes place on the addition of strong nitric acid to carbonate of baryta, especially the native car- bonate, because nitrate of baryta is insoluble in the strong acid. Water must therefore be added, as well as the acid, for the decomposition to be effected in this and many other cases. HYDKOSULPHTJKIC ACID (Sulphuretted Hydrogen HS). 400. This acid exists at the common temperature and pressure as a colourless inflammable gas possessing a highly offensive odour resembling that of rotten eggs. It burns with a blue flame, the products of combustion being sul- phurous acid and water. It is soluble in water, three 162 THE SPECIAL PROPERTIES volumes of which dissolve one volume of the gas ; this solution reddens litmus paper. On exposing the gas in a state of solution to the air, it is decomposed, water being formed, and sulphur in a highly divided state being sepa- rated. 401. Most metallic sulphides dissolve with decomposition in hydrochloric acid, in which case SULPHURETTED HYDRO- GEN is evolved, which from its characteristic smell is easily recognised. When the quantity is so minute that the smell fails to afford a sufficient proof, it may be detected by holding a piece of paper moistened with a solution of any soluble SALT OF LEAD over the mouth of the test-tube, as a brown or black coating of SULPHIDE OF LEAD will be formed upon the paper. 402. When sulphides are dissolved in nitric or nitro- hydrochloric acid, SULPHURIC ACID is formed along with a separation of sulphur, which may be recognised by its colour, and also its behaviour upon ignition. In the case of sulphides, therefore, which, from their insolubility in hydrochloric acid, must be dissolved in nitric or nitro- hydrochloric acids, the sulphur is converted into sulphuric acid, and not given off as sulphuretted hydrogen. 403. To ascertain whether the sulphur existed in an un- oxidized state, when nitric or nitro-hydrochloric acid has been employed as the solvent of the substance under exami- nation, a small portion of the original substance, in fine powder, must be fused with a little solid hydrate of potash or soda, in a platinum spoon, by means of the blowpipe flame. The fused mass must then be dissolved in a little water and filtered ; a bright strip of silver (or polished coin) is put into the solution, and the fluid warmed. If a sulphide were present, a brownish-black film of sulphide of silver would form upon the metal. This film may be OF THE INORGANIC ACIDS. 163 removed afterwards by rubbing the metal with leather and quicklime. 404. When the sulphides of the heavy metals are heated in contact with air, sulphurous acid is evolved : the metal being left in some cases uncombined, and in others as an oxide. The sulphides of the alkalies and alkaline earths are converted by this process into sulphates. As the student is made familiar, in passing through the basic groups, with the properties of the various sulphides, their solubility or insolubility in water, the alkalies, and the various acids, their colour, &c., it is unnecessary to notice them here. CHROMIC ACID (CrO 3 ). 405. Chromic acid is a solid coloured acid occurring in the form of beautiful crimson needles, which deliquesce rapidly when exposed to the air, the solution possessing a deep red- brown tint. This acid is decomposed, upon ignition, into sesquioxide of chromium and oxygen. All its salts are coloured; the neutral chromates possessing a yellow, and the acid or bichromates a red colour. Most of the salts are insoluble in water ; they are nearly all soluble in nitric acid. 406. Chromic acid, whether in its free or combined state, is reduced by hydrosulphuric acid to the state of SESQUI- OXIDE OE CHEOMIUM ; water and some oxide of sulphur is formed in this decomposition, along with a separation of sulphur. The change of colour which attends this decom- position, viz., the conversion of a yellow or red coloured solution to a green one, is so characteristic that it cannot be mistaken. 407. Alkaline chromates may be prepared from insoluble chromates by fusing the latter in conjunction with alkaline carbonates. 164 THE SPECIAL PROPERTIES 408. When testing for the bases, we always find the chromic acid as sesquioxide of chromium, since hydrosul- phuric acid reduces it to that state. SULPHURIC ACID (Oil of Vitriol) (HO, S0 3 ). 409. Anhydrous sulphuric acid (S0 3 ) is a white feathery crystalline mass, which, when exposed to the air, emits dense white fumes. It is destitute of acid properties until it has combined with water and passed into the hydrated state. The hydrated acid is a heavy, colourless, oily fluid, which possesses a strong affinity for water, producing, when mixed with it, a great degree of heat. Its affinity for water is so great, that it decomposes organic substances when placed in contact with them, removing their hydrogen and oxygen, whilst the carbon is left behind as a black coaly mass, a portion of which dissolves in the acid and communicates to it a brown tint. If heat is applied, the carbon is oxidized at the expense of the sulphuric acid, carbonic acid and sulphurous acid being formed: these facts may be illus- trated by pouring some strong sulphuric acid upon white sugar. Sulphuric acid, at temperatures below its boiling- point (572 F), displaces all other acids from their combi- nations with bases, but above that temperature it is itself displaced by the non-volatile acids. 410. Most of the sulphates, with the exception of the sulphates of baryta, strontia, and lead, are soluble in water. The alkaline sulphates and the three just named are the only salts of this acid which are not decomposed on simple ignition. 411. Sulphates in dilute solutions containing organic matter are gradually converted into sulphides. "Water con- taining a sulphate may therefore, after it has been kept a long time in a bottle or any closed vessel, be found to con- OF THE INORGANIC ACIDS. 165 tain sulphuretted hydrogen, although originally it was per- fectly free from that gas. 412. Sulphate of baryta, from its insolubility in acids, is at once distinguished from all the other baryta salts ; any soluble salt of baryta is therefore the best and most delicate test for SULPHURIC ACID. 413. Insoluble sulphates are completely decomposed by fusion with alkaline carbonates, an ALKALINE SULPHATE being produced along with a CARBON ATE or an OXIDE of the METAL. 414. When a sulphate, mixed with charcoal and carbo- nate of soda, is fused upon a charcoal support by the inner blowpipe flame, sulphide of sodium is produced. If the fused mass, moistened with water, be placed upon a piece of silver, a brown stain of sulphide of silver will be formed. BORACIC ACID (BO 3 ). 415. This acid is best obtained by adding to a boiling concentrated solution of biborate of soda (borax) strong sulphuric acid, until the liquor becomes sour to the taste : on cooling, the greater part of the boracic acid separates from the solution in the form of colourless crystalline scales, .containing water. "When ignited, they fuse to an anhy- drous glassy mass, which, on exposure to the air, absorbs water, swells, and becomes opaque. This acid, in the anhy- drous state, is a colourless fixed glass, fusible at a red heat ; the hydrate (2 B0 3 , 3 HO) is a porous white mass ; in the crystalline state (2 B0 3 , 3 HO + 3 aq.) it presents small scaly laminae. The hydrated acid is much more soluble in hot than cold water. "When an alcoholic or an aqueous solu- tion of this acid is evaporated, a portion of the acid vola- tilizes with the vapours of the solvent, but alone it is per- fectly fixed at a red heat. One peculiar property which 166 THE SPECIAL PROPERTIES this acid possesses is that of affecting turmeric paper in the manner of a free alkali ; it acts, however, upon blue litmus paper like other acids. All the borates, with the exception of the alkaline ones, are almost totally insoluble in pure water; they dissolve readily in acids, and in water con- taining ammoniacal salts. They are not decomposed upon ignition : they are colourless, and all of them, even the acid salts, manifest an alkaline reaction. 416. An alcoholic solution of boracic acid burns with a green-coloured flame, which becomes more distinct upon stirring the mixture. To detect a borate, add to the sub- stance under examination strong sulphuric acid and alcohol or wood naphtha ; ignite the mixture subsequently. If a borate be present, the borders of the flame will appear green, which becomes more distinct upon stirring, and the delicacy is further increased by repeatedly extinguishing and rekindling the flame. The only substance which at all interferes with this test is copper, the salts of which impart the same colour to the flame. This metal, if present, must therefore be got rid of by sulphuretted hydrogen, before testing for boracic acid. 417. A solution of one part of borax in one thousand parts of water, very slightly acidified with hydrochloric acid, imparts to turmeric paper, after drying, a distinctly brown tint (H.Rose), This method may therefore be employed in place of the usual method for the detection of boracic acid. The slip of paper ought only be dipped half into the fluid, and it ought to be dried at a gentle heat. PHOSPHOBIC ACID (3 HO, P0 5 ). 418. Anhydrous phosphoric acid (PO 5 ) appears under the form of white flakes, which rapidly absorb moisture from the atmosphere. It has a great affinity for water, with OF THE INORGANIC ACIDS. 167 which it combines in three different proportions, forming three distinct acids, which have the following constitution Tribasic phosphoric acid (3 HO, P0 5 ). Bibasic phosphoric acid (2 HO, P0 5 ). Monobasic phosphoric acid (HO, PO 5 ). 419. Each of these acids forms, with bases, a distinct class of salts. 420. The tribasic acid, which is the most important, is the only one treated of in this work. It appears in the form of colourless crystals, which deliquesce rapidly in the air. AVhen strongly heated in an open platinum vessel, it vola- tilizes without a residue. 421. The neutral phosphates, with the exception of the alkaline ones, are nearly all insoluble in water. The action of heat converts the tribasic phosphates into bibasic or mo- nobasic salts, according to the number of atoms of basic w^ater expelled. 422. Sulphate of magnesia, or any soluble magnesian salt, produces in aqueous solutions of the phosphates, if con- centrated, a white precipitate of PHOSPHATE or MAGNESIA (2 MgO, HO, P0 5 ). A salt much more insoluble in water is produced by adding chloride of ammonium, ammonia, and then the magnesian salt ; in this way PHOSPHATE OF MAG- NESIA AND AMMONIA (2 MgO, NH 4 O, P0 5 ) is precipitated, which is slightly soluble in pure water, but almost insoluble in water containing ammonia. In dilute solutions it only appears after much agitation and the lapse of some time; agitation promotes its formation in all cases. This test can only be applied when the phosphates are soluble in ammo- niacal solutions. 423. Acetate of lead produces a white precipitate of PHOSPHATE or LEAD (3 PbO, PO 5 ), which is soluble in 168 THE SPECIAL PROPERTIES nitric acid. If this precipitate, after being dried, is heated in the outer flame of the blowpipe, it becomes distinctly crystalline on cooling. This test is very characteristic, not only on account of the crystalline structure of the bead, but also from the circumstance that the phosphate of lead is the only salt of that metal which is not reduced to the metallic state when heated in the inner blowpipe flame. It is evident that, to render this test of any value, the phosphate of lead must be freed thoroughly, by washing, from all acetate of lead. 424. Nitrate of silver throws down, both from solutions of phosphates containing one or two atoms of fixed base, as well as from phosphates containing three atoms of fixed base, a light yellow precipitate of phosphate of silver (3 AgO, PO 5 ), which is readily soluble in nitric acid and in ammonia. If the solution contained a phosphate contain- ing three atoms of fixed base, the fluid in which the preci- pitate is suspended will manifest a neutral reaction, whilst the reaction will be acid if the solution contained a phos- phate containing one or two atoms of fixed base. The acid reaction is occasioned by the nitric acid receiving, for the three equivalents of oxide of silver which it yields to the phosphoric acid, only 2 or 1 eq. of fixed base, and 1 or 2 eq. of water; and as the latter does not neutralize the acid properties of the nitric acid, the solution becomes acid. Monobasic and bibasic phosphate of silver is white ; conse- quently, a tribasic phosphate, containing 1 or 2 eq. of fixed base, yields, after ignition, a white precipitate with nitrate of silver (AgO, PO 5 , or 2 AgO, PO 5 ). 425. " If to a solution containing phosphoric acid and the least possible excess of hydrochloric or nitric acid a tolerably large amount of acetate of soda is added, and then a drop of sesquichloride of iron, a yellowish -white flocculent-gela- OF THE INORGANIC ACIDS. 169 tinous precipitate of PHOSPHATE OF SESQUIOXIDE OF IEON is formed. An excess of sesquichloride of iron must be avoided, as acetate of sesquioxide of iron (of red colour) would thereby be formed, in which the precipitate is not insoluble. This reaction is of importance, as it enables us to detect the phosphoric acid in phosphates of the alkaline earths : to effect the complete separation of the phosphoric acid from the alkaline earths, a sufficient quantity of ses- quioxide of iron is added to impart a reddish colour to the solution, which is then boiled (whereby the whole of the sesquioxide of iron is thrown down, partly as phosphate, partly as basic acetate), and filtered hot. The filtrate con- tains the alkaline earths as chlorides. If you wish to detect, by means of this reaction, phosphoric acid in pre- sence of a large proportion of sesquioxide of iron, boil the hydrochloric acid solution with sulphite of soda, until the sesquichloride is reduced to protochloride, which reduction is indicated by the decoloration of the solution ; add car- bonate of soda, until the fluid is nearly neutral ; then acetate of soda, and finally, one drop of sesquichloride of iron. The reason for this proceeding is, that acetate of protoxide of iron does not dissolve phosphate of ses- quioxide of iron. 426. " If some molybdate of ammonia is mixed in a test- tube with hydrochloric or nitric acid, in sufficient quantity to redissolve the precipitate which forms at first, and a little of a very dilute fluid containing phosphoric acid is then added, and the mixture boiled, the fluid acquires an in- tensely yellow colour, and after some time a yellow preci- pitate separates, which is insoluble in hydrochloric acid. The exact composition of this precipitate is not yet ascertained ; we only know that it contains MOLTBDIC ACID, AMMONIA, and a little PHOSPHOEIC ACID. Application of heat greatly 8 170 THE SPECIAL PROPERTIES promotes the reaction. This reaction is so delicate that the phosphoric acid may be detected by its means in almost all salts and most minerals containing it. As the yellow com- pound is decomposed by free phosphoric acid, an excess of the fluid containing the phosphoric acid must be carefully avoided. The yellow precipitate may, when it has subsided, be perceived even in dark-coloured fluids. 427. " In phosphate of alumina the phosphoric acid may be detected also by one of the two following methods : 428. " Add carbonate of soda to the hydrochloric acid solution until the free acid is nearly neutralized ; mix with carbonate of baryta in excess ; add solution of soda or potash, and boil. This process gives the alumina in solu- tion, the phosphoric acid in a pfecipitate of phosphate of baryta. Dissolve this precipitate in hydrochloric acid, de- compose by sulphuric acid, filter, and test the filtrate with sulphate of magnesia, with addition of chloride of ammo- nium and ammonia. 429. " Mix the hydrochloric acid solution with tartaric acid; add ammonia in excess; and finally, to the clear solution, chloride of ammonium and sulphate of magnesia. If a precipitate forms only after some time, this cannot be considered a safe indication of the presence of phosphoric acid, as, under the circumstances named, a precipitate of tartrate of magnesia, resembling the phosphate of magnesia and ammonia, may form in a solution of the proper degree of concentration, though no phosphoric acid is present. The precipitate must therefore be tested for phosphoric acid, which is done by dissolving it in nitric acid, evaporating the solution, with addition of some pure nitrate of potash or soda, to dryness, igniting the residue, then heating with hydrochloric acid, filtering the solution, and mixing the filtrate with ammonia in excess. The formation of a crystal- OF THE INORGANIC ACIDS. 171 line precipitate of phosphate of magnesia and ammonia con- firms the presence of phosphoric acid." (Fresenius.) OXALIC ACID (HO, C 2 3 , or HO, O). 430. Oxalic acid crytallizes from its aqueous solutions in four-sided prisms. These crystals contain three atoms of water, of which one is essential (HO, C 2 O 3 + 2 aq.). When warmed, the 2 atoms of non-essential water (water of crys- tallization) are given off", and the hydrate of oxalic acid re- mains as a white powder, which melts at 350, and, when further heated, sublimes & portion, however, being decom- posed. It is very soluble in water, and highly poisonous. It is usual to place it in the list of organic acids ; but since its salts upon ignition leave no carbonaceous residue, it has been included in the list of inorganic acids. 431. All the oxalates are decomposed at a red heat, the oxalic acid being resolved into carbonic acid and carbonic oxide. If the base with which the acid is combined be an alkali or an alkaline earth, it is left as a carbonate ; the other bases are left either in an oxidized or metallic state, according to their greater or less affinity for oxygen. 432. Lime-water and all the soluble salts of lime produce in solutions of oxalic acid and the oxalates, even if highly diluted, a white precipitate of OXALATE OE LIME, which is insoluble in acetic acid. 433. When concentrated sulphuric acid is added to dry oxalic acid or an oxalate, it withdraws the constitutional water in the one case and the base in the other from the anhydrous acid (C 2 3 ), which, being incapable of existing alone, splits up into CAEBONIC ACID and CAEBONIC OXIDE. The two gases escape with effervescence ; and if a light be applied as they issue from the mouth of the tube, the car- bonic oxide will burn with a blue flame. 172 THE SPECIAL PROPERTIES HYDBOFLTTOBIC ACID (HF). 434. This acid is best obtained by the action of concen- trated sulphuric acid on fluoride of calcium (fluor spar). The powdered mineral is gently heated with the acid in a retort of lead, and the acid condensed in a receiver of the same metal. It is obtained in the form of a very volatile liquid, strongly acid and corrosive, fuming in the air. It burns the skin like red-hot iron, causing a sore which is not easily healed. It is distinguished from all other acids by dissolving insoluble silicic acid and the silicates which are insoluble in the other acids ; on this account it cannot be prepared or kept in glass vessels. 435. " If a finely pulverized fluoride, no matter whether soluble or insoluble, is heated in a platinum crucible with concentrated sulphuric acid, the crucible covered with the convex face of a watch-glass, coated on that side with bees' - wax, which has been removed again in some places by tracing lines in it with some pointed instrument,* the hol- low of the glass filled with water, and the crucible gently heated for the space of half an hour or an hour, the exposed lines will, upon the removal of the wax, be found etched into the glass. If the quantity of hydrofluoric acid disen- gaged by the sulphuric acid is very minute, the etching is often invisible upon the removal of the wax ; it will, how- ever, in such cases reappear when the plate is breathed upon. This reappearance of the etched lines is owing to the unequal capacity of condensing water which the etched * The coating with the wax may be readily effected by heating the glass cautiously, putting a bit of wax upon the convex face, and spreading the fused mass equally over it. The instrument used for tracing the exposed lines should not be too hard ; a pointed piece of wood answers best. The removal of the wax coating is effected by heating the glass gently, and wiping the wax off with a cloth. OF THE INORGANIC ACIDS. 173 and the untouched parts of the plate respectively possess." (Fresenius.) This method cannot be adopted if the substance containing the fluorine is not decomposed by sulphuric acid, or if silicic acid is present ; the silicic acid must be got rid of, in the way to be described, before we can discover fluorine. 436. If nascent hydrofluoric acid meet with silicic acid, the two compounds are mutually decomposed, FLUOKIDE OF SILICON (SiF 3 ) and water being formed. Should the com- pound examined contain therefore silicic acid as well as fluorine, fluoride of silicon, and not hydrofluoric acid, will be disengaged by the sulphuric acid. Fluoride of silicon in the pure state is a colourless gas, which has a suffocating acid smell, and which emits fumes in contact with the air. It is largely soluble in water, but is thereby partially decom- posed ; silicic acid is deposited in the gelatinous state, and a combination of fluoride of silicon and of hydrofluoric acid is dissolved (hydrofluosilicic acid HE, SiF 3 ). Fluoride of silicon does not attack glass. The glass, when damp, becomes covered with a very adhesive coating of silica, which impairs the transparency of the glass, owing to the decomposition of the fluoride of silicon. It is necessary to notice the action of bases upon hydrofluosilicic acid, as the method next to be described cannot be well understood without this knowledge. Hydrofluosilicic acid combines with the basic metallic oxides, and forms with them a class of salts called silicofluorides. In order, however, to obtain these silicofluorides, it is necessary to have the acid in ex- cess, or at any rate to use as much of it as is necessary to saturate the base ; for when an excess of base is employed, the hydrofluosilicic acid is decomposed, the silicon separates in the form of silicic acid, and a fluoride remains in solu- tion. 174 THE SPECIAL PROPERTIES 437. The method for detecting fluorine in the presence of silicic acid is founded upon the fact just stated that when a fluoride, combined or mixed with silica, is heated with sulphuric acid, the fluorine and silicon are evolved in combination as fluoride of silicon. This method is appli- cable to all silicated fluorides which are decomposable by sulphuric acid. Boil the substance under examination with concentrated sulphuric acid in a flask, retort, or test-tube, to which is attached a bent tube ; conduct the gases evolved into a solution of ammonia; heat, filter, evaporate in a platinum crucible to dryness, and examine the residue by the method described in 435. If the substance under examination contains only a slight trace of fluorine and no other volatile acid, it is better to add a very little marble to the substance, so as to ensure a continuous slight evolution of gas. When the sulphuric acid boils, all the fluoride of silicon is given off. 438. " Compounds not decomposable by sulphuric acid must first be fused with four parts of carbonate of soda and potash. The fused mass is treated with water, the solution filtered, the filtrate concentrated by evaporation, allowed to cool, transferred to a platinum or silver vessel, hydrochloric- acid added to feebly acid reaction, and the fluid let stand until the carbonic acid has escaped. It is then super- saturated with ammonia, heated, filtered into a bottle, chloride of calcium added to the still hot fluid, the bottle closed, and allowed to stand at rest. If a precipitate separates after some time, it is collected on a filter, dried, and examined by the method described in 435." (H. Eose.) 439. If a fluoride mixed with bisulphate of potash is heated in a test-tube, hydrofluoric acid is disengaged, which is easily detected by the etching of the glass. OF THE INORGANIC ACIDS. 175 SILICIC ACID (Silica Si0 3 ). 440. The anhydrous acid is met with in two states crystalline and uncrystalline, or amorphous. In both these states it is insoluble in water and all acids with the excep- tion of hydrofluoric acid. The hydrated acid is slightly soluble in water and the ordinary acids ; it is rendered anhydrous and insoluble by heat. Its aqueous solution does not redden blue litmus paper, or possess any taste ; the presence of the acid can only be detected with certainty by evaporating the solution to dryness, and thus obtaining it in its insoluble form, as a gritty, whitish powder, which remains undissolved when the dry mass is treated with water or dilute acids ; its presence should be further confirmed by testing the gritty powder with carbonate of soda before the blowpipe flame, as directed at 445. The amorphous silicic acid and the hydrate dissolve in hot aqueous solutions of the fixed caustic and carbonated alkalies, but the crystalline acid is insoluble in these reagents. The crystallized acid is, as has been stated, dissolved by hydrofluoric acid ; it is also rendered soluble by fusing it with the fixed carbonated alkalies, a basic silicate being obtained, which is soluble in water, and from which acids separate it in the hydrated state. If there is sufficient water to dissolve it, when it is thus separated from basic bodies, it does not precipitate ; but if there be not sufficient water present, then a portion of the acid, varying with the amount of water, precipitates, owing to its being a solid body. Silicic acid, when quite pure, is a colourless or white powder, which is more or less gritty ; it is infusible and unalterable in the hottest blow- pipe flame, but fuses in the flame of the oxyhydrogen blow- pipe. 441. The alkaline silicates are the only salts of this acid 176 THE SPECIAL PROPERTIES which are soluble in water. Some of the silicates insoluble in water are dissolved with decomposition by hydrochloric or nitric acids ; some of them, that are not even affected by these acids when the mixture is boiled, are decomposed by concentrated sulphuric acid. The silicates, which are not acted upon by any acids but hydrofluoric acid, are decom- posed by fusion with the alkaline carbonates, and also with hydrate of baryta. 442. The solution of the alkaline silicates is decomposed by all acids, even by carbonic acid. If there is not suffi- cient water present to dissolve the silicic acid when the silicate is decomposed, a part of it precipitates as hydrate, in the form of a gelatinous mass. If a solution of an alka- line silicate be evaporated to dryness along with a slight excess of hydrochloric or nitric acid, and if the dry mass be ignited for some little time and then treated with dilute hydrochloric or nitric acid, the other substances dissolve, whilst the whole of the silicic acid remains undissolved as a gritty powder of a whitish colour. On adding chloride of ammonium to a concentrated solution of an alkaline silicate, a gelatinous precipitate* takes place. 443. The silicates decomposable by hydrochloric or nitric acid ought to be reduced to the finest powder, before acting upon them with either of the acids; when the acid is added, the silicate must be digested in the acid at or near the boiling point for some time. To effect the complete sepa- ration of the silica from the bases and other acids, the acid mixture is evaporated to dryness, the silicate is thus com- pletely decomposed, but the heat must be continued until there is no longer the least trace of acid fumes, in order to * Is this precipitate, which is always looked upon as hydrated silicic acid, a silicate of ammonia, corresponding to the titanate of ammonia discovered by Rose ? OF THE INORGANIC ACIDS. 177 render the whole of the silicic acid insoluble ; the dry mass is then boiled with dilute hydrochloric acid ; the solution containing the bases and other acids is filtered off from the insoluble silica, which is examined according to 445. 444. The decomposition of the silicates, which are not decomposable by hydrochloric or nitric acid, is best effected by fusing them with four times their weight of a mixture of carbonate of soda and carbonate of potash. The silicate must be reduced to the finest powder, and then intimately mixed with the alkaline carbonates, also in a state of fine powder ; the mixture is then to be heated, by means of a gas lamp or Berzelius spirit-lamp, in a platinum crucible, until the mixture is in a state of fusion. The crucible is then allowed to cool ; and when cold or nearly so, and still containing the fused mass, it is put into an evaporating dish containing dilute hydrochloric acid. When the fused mass is detached from the crucible, remove the crucible and evaporate the mixture to dryness, and ignite just in the same way as the solution in 443 is directed to be treated. The fixed alkalies cannot of course be sought for in that portion which has been fused with the alkaline carbonate ; to ascertain whether they are present, another portion of the silicate must be fused with hydrate of baryta. For this purpose " mix one part of the very finely pulverized sub- stance with four parts of hydrate of baryta ; expose the mixture for half an hour, in a platinum crucible, to the strongest possible heat of a good Berzelius spirit-lamp or to a gas lamp, and treat the fused or agglutinated mass with hydrochloric acid and water until it is dissolved. Pre- cipitate the baryta and all the bases in the silicate, with the exception of magnesia and the alkalies, with ammonia and carbonate of ammonia ; filter, evaporate to dryness, ignite, dissolve the residue in water, precipitate again with 8 178 THE SPECIAL PROPERTIES ammonia and carbonate of ammonia, filter, evaporate, ignite ;" then test for potash and soda in the usual way. If the substance should contain magnesia, this will have to be got rid of by arseniate of ammonia before testing for potash and soda. 445. When silicic acid is fused with carbonate of soda before the blowpipe, a transparent colourless bead is formed, while carbonic acid is expelled. A small quantity of soda ought only to be employed, as an opaque bead is produced when it is added in excess. HYDROCHLORIC ACID (Muriatic Acid, HC1). 446. This acid is a transparent and colourless gas, of a pungent, acid, suffocating smell, and fuming strongly with moist air. It ife absorbed in large proportions by water, forming the common liquid hydrochloric acid, which is a mere solution of the gas in water. 447. When a chloride is heated with peroxide of man- ganese (Mn0 2 ) and sulphuric acid, chlorine gas is evolved, which may be recognised by its ODOUR and GREENISH-TEL- LOW COLOUR. 448. When a chloride is heated with chromate of potash and concentrated sulphuric acid, a brown gas is disengaged, which condenses into a blood-red liquid, CHROMATE OF CHLORIDE OF CHROMIUM (CrClg, 2 Cr0 3 ). On the addi- tion of ammonia in excess, the colour changes to a yellow, owing to the formation of neutral chromate of ammonia ; upon the addition of an acid, the yellow changes to a reddish-yellow colour, owing to the formation of an acid chromate. HYDROCYANIC ACID (JPrussic Acid, HC 2 N, or HCy). 449. This acid is the hydrogen compound of the radical OF THE INORGANIC ACIDS. 179 cyanogen (C 2 N), a compound composed of carbon and nitrogen. 450. In its anhydrous state hydrocyanic acid is a colour- less, volatile, inflammable liquid, possessing a strong odour resembling oil of bitter almonds. Water dissolves it in all its proportions : both in its concentrated and diluted state it speedily undergoes decomposition when exposed to the light. Being exceedingly poisonous, it requires to be used with care. 451. The cyanogen compounds of the metals of the alkalies and alkaline earths are soluble in water ; their solutions possess an alkaline reaction, and are decomposed, with the liberation of hydrocyanic acid, by the weakest acid. 452. If to a solution of free hydrocyanic acid or an alkaline cyanide potasli and a mixed solution of a per- and proto-salt of iron, be added, a greenish-blue precipitate will be produced, which, on the addition of hydrochloric acid, will redissolve, Prussian Ulue precipitating. If only a very minute quantity of hydrocyanic acid is present, the fluid simply appears green after the addition of the hydrochloric acid, and it is only after long standing that a trifling blue precipitate separates from it. 453. If to a solution of hydrocyanic acid potash is added in excess, and then finely pulverized peroxide of mercury, the latter dissolves as readily as it would in free hydrocyanic acid. Since peroxide of mercury is soluble in alkaline fluids only in presence of hydrocyanic acid, this reaction may be looked upon as a positive test for that acid, (Fresenius.) 454. When free hydrocyanic acid is added to sulphide of ammonium containing an excess of sulphur, the acid seizes upon some of the ammonia and sulphur, forming with them 180 THE SPECIAL PROPERTIES SULPHO CYANIDE OF AMMONIUM (NH 4 , CyS 2 ), which pOS- sesses, in common with all the other soluble sulphocyanides, the property of producing with persalts of iron a deep Hood-red colour. This test may be applied in qualitative analysis in the following way : Add a few drops of yellow sulphide of ammonium to the liquid supposed to contain the hydrocyanic acid ; evaporate at a gentle heat (not above 212 E), until the excess of sulphide of ammonium has com- pletely volatilized, which is ascertained by the smell ; then test the solution with a drop or two of sesquichloride of iron. This test is exceedingly delicate. " If an acetate is present, the reaction takes place only upon addition of hydrochloric acid." (Fresenius.) 455. " Neither of the above methods will serve to effect the detection of cyanogen in cyanide of mercury. To detect cyanogen in that compound, the solution is mixed with sulphide of hydrogen; sulphide of mercury precipi- tates, the solution then contains free hydrocyanic acid." Examine the solution, after the precipitation of the mer- cury, for hydrocyanic acid, either by the method described in 452 or 454. HYDROBROMIC ACID (HBr). 456. Hydrobromic acid is a gas which resembles very closely in its properties hydrochloric acid gas. It emits in the air white fumes, which are denser than those produced by hydrochloric acid gas. It is decomposed by chlorine, bromine being set free, and hydrochloric acid formed : the liberated bromine appears under the form of reddish vapours ; or if in more considerable proportions, it condenses into drops of a similar colour. Hydrobromic acid gas is extremely soluble in water ; the solution is colourless, and, both in the concentrated or in the dilute state, it very much resent OF THE INORGANIC ACIDS. 181 bles concentrated or dilute hydrochloric acid. When, how- ever, hydrobromic acid gas contains any free bromine, which it dissolves in large quantities, the liquid acid has a dark reddish colour. 457. Bromides are decomposed by chlorine, nitric and concentrated sulphuric acids, with the liberation of bromine, which communicates to the liquid a yellowish-red colour. Bromine is soluble in ether, and imparts an orange colour to starch paste. 458. To detect bromine in any compound, add an aqueous solution of chlorine gas ; the bromine, being set free, will communicate a yellowish-red tint to the liquid, unless the quantity be very minute ; an excess of chlorine should be avoided, since it converts the bromine into the colourless chloride of bromine. If the solution be now agitated with ether, it will remove all the bromine from the liquid, dis- solving it, and forming a yellow-coloured solution. If the ethereal solution, which has been carefully decanted or removed by a pipette, be agitated with potash, the colour will disappear, bromide of potassium and bromate of potash being formed. By evaporating this solution to dryness and igniting the residue, the bromate of potash will be con- verted into bromide of potassium. On heating the bromide along with peroxide of manganese and sulphuric acid in a small retort, TELLOWISH-EED VAPOUES will be evolved unless the quantity be very minute. These vapours, when brought in contract with starch paste, will communicate to it an ORANGE-YELLOW COLOUR, which disappears on expo- sure to the air. 459. Solid bromides, when distilled with BICHROMATE OP POTASH and CONCENTRATED SULPHURIC ACID, yield pure bromine, which becomes colourless, or nearly so, when treated with excess of ammonia ; by this means it is dis- 182 THE SPECIAL PROPERTIES tinguished from chlorochromic acid, which it resembles in colour. HYDRIODIC ACID (HI). 460. This acid and its compounds resemble in their pro- perties the corresponding compounds of chlorine and bro- mine. The pure acid is gaseous. It is extremely soluble in water, and the solution, which is colourless, resembles in properties that of hydrochloric and hydrobromic acids ; but it is more easily decomposed than the two latter compounds by the substances which have an affinity for hydrogen, and also by those substances which have an affinity for the other constituent, hydrogen being set free as mercury, for instance. The colourless solution turns speedily to a reddish brown when in contact with the air, owing to the formation of hydriodous acid (HI 2 ) and water. Many of the iodides of the heavy metals are more insoluble in water than the cor- responding chlorides. 461. Subnitrate of mercury throws down from solutions of the iodides a yellowish-green precipitate of SUBIODIDE or MERCURY (Hg 2 I). 462. Proto chloride of mercury throws down a red pre- cipitate of PROTOIODIDE OF MERCURY (Hgl), which is SOlll- ble in an excess of the protochloride or of iodide of potassium. 463. Soluble salts of lead precipitate an orange-yellow precipitate of IODIDE OF LEAD (Pbl). 464. Iodine, in a free state, forms with starch, even in highly dilute solutions, a purple precipitate of IODIDE OF STARCH. If the iodine is in a state of combination with hydrogen or any metal, it is necessary to liberate it before applying the starch test. 465. Nitric acid liberates iodine from its hydrogen and OF THE INORGANIC ACIDS. 183 metallic compounds, nitric oxide being given off. The libe- rated iodine communicates a brownish-yellow tint to the solution ; and if it is concentrated, a portion of the iodine separates as a black precipitate. When solid iodides are heated with nitric acid, the iodine sublimes in the form of violet- coloured vapours, which condense upon the colder parts of the vessel as a blackish sublimate. 466. Chlorine gas likewise liberates iodine from its com- binations ; but if added in excess, they combine together, forming a colourless compound (chloride of iodine). 467. If iodides are heated with sulphuric acid and peroxide of manganese, the iodine sublimes in the form of violet- coloured vapours, which are easily recognised. 468. The best method of detecting iodine in a solution is to mix with the liquid a little starch-paste, and acidify it with HC1. A solution of nitr^e of potash is then to be added, when, if much iodine be present, a dark blue colour will be instantly produced ; if a very small quantity only as, for instance, the two or three millionth part then a few seconds elapse before the blue colour makes its appearance. Dr. D. Price, who invented this method states that he has, in this way, detected the -jo^io^o^h part of iodine dissolved in water as iodide of potassium. It is, he says, much more delicate than the other tests for iodides, as well as being free from the disadvantages to which they are more or less subject. If the experiment is made in a porcelain basin, the faintest indication of colour may be observed. 469. When a solution, containing 1 part of sulphate of copper and 2| parts of the sulphate of protoxide of iron, is added to a neutral or slightly alkaline solution of an iodide, a white precipitate of SUBIODIDE or COPPER (Cu 2 I) is formed. The sulphate of iron is added, to convert the 184 THE SPECIAL PROPERTIES sulphate of copper into a subsalt. The addition of ammo- nia promotes the complete precipitation of the iodine. Chlorides and bromides are not precipitated by this reagent. NITRIC ACID (HO, N0 6 ). 470. The hydrate of nitric acid, when pure, is a colour- less liquid, which fumes strongly in the air. It acts upon organic substances, destroying them quickly if concen- trated ; if they contain nitrogen, they are stained yellow by this acid. It oxidizes all the metals, with the exception of gold, platinum, and some of the rarer ones, being itself re- duced to the state of nitric oxide (NO 2 ), which, in contact with the air, is converted into red fumes of nitrous acid (]ST0 4 ). All the oxides treated of in this work dissolve in this acid, with the exception of binoxide of tin and oxide of antimony. 471. All the neutral nitrates are soluble in water ; a few basic salts are insoluble in that liquid. All the salts of this acid are decomposed by ignition, the alkaline nitrates yielding oxygen and nitrogen, and the rest oxygen and nitrous acid. 472. When nitrates are ignited in the presence of sub- stances capable of oxidation, a portion of the oxygen passes over to them, whilst an inferior oxide of nitrogen is evolved. In some cases the combination is attended with a violent detonation; in others, vivid scintillations accompany the combustion. 473. To detect nitric acid in a solution, add to it one fourth of its volume of concentrated sulphuric acid, and gently warm the solution ; a solution of a protosalt of iron must then be added, along with a few drops more of con- centrated sulphuric acid, when the liquid will become of a deep-brown colour, attended, most likely, with an energetic OF THE INORGANIC ACIDS. 185 disengagement of gas ; the colour, in this case, will soon disappear, for a reason presently to be named, but can readily be reinstated by a fresh addition of the solution of the protosalt of iron. Or the solution of the protosalt of iron may be added first to the solution of the nitrate, and then the concentrated sulphuric acid poured in, in such a way that it forms a layer at the bottom of the test-tube ; in this case the deep-brown colour will be produced at the contact-surface of the two liquids. The dark-brown colour 'is owing to the formation of a compound of binoxide of nitrogen (N0 2 ) and the protosalt of iron. This com- pound is destroyed by heat, with disengagement of the binoxide of nitrogen as gas hence the fading of the colour. It may therefore be better for the young student to add the protosalt of iron when the solution of acid and nitrate is quite cold. 474. When nitrates are heated with concentrated sulpli- uric acid, in the presence of copper turnings, binoxide of nitrogen is evolved, which, in contact with the air, forms red fumes, owing to its conversion into nitrous acid. This experiment ought to be conducted in a narrow test-tube. The colour is best observed by looking into the test-tube lengthways. 475. If a mixture of a nitrate with cyanide of potassium in powder is heated upon platinum foil, a violent deflagra- tion will ensue, owing to the sudden evolution of carbonic acid and nitrogen, produced by the oxidation of the cyano- gen. Very minute quantities of nitrates may be detected in this way. CHLORIC ACID (HO, C10 5 ). 476. This acid, in its concentrated state, appears in the form of a yellow oily liquid, the odour of which resembles 186 THE PROPERTIES that of nitric acid. The dilute acid is colourless and in- odorous. 477. All the chlorates are soluble in water. They are decomposed upon ignition, oxygen gas being giyen off and a metallic chloride left. When heated along with organic substances, they deflagrate with far greater violence than the nitrates. 478. To detect this "acid, add to a small quantity of the solid substance under examination a few drops of concen- trated sulphuric acid in the cold. The chlorate will be de- composed, SULPHATE OF POTASH and PEECHLOEATE OE POTASH (KO, C1O 7 ) being formed along with a GBEENISH- TELLOW-COLOTJEED gas (chlorous acid C10 4 ), which escapes. The application of heat must be avoided ; and the quanti- ties operated upon should be small, to prevent any loud and violent explosion taking place. 479. If the solution of a chlorate is coloured light blue, with some solution of indigo in sulphuric acid, a little dilute sulphuric acid added, and a solution of sulphite of soda dropped cautiously into the blue fluid, the colour of the indigo disappears immediately. The cause of this equally characteristic and delicate reaction is, that the sulphurous acid deprives the chloric acid of its oxygen, and the liberated chlorine decolourizes the indigo. (Fresenius.) 480. Upon heating chlorates with hydrochloric acid, the constituents of the two acids decompose, forming water, chlorine, and bichlorate of chlorous acid (C10 3 , 2 C10 5 ). The test-tube in which the experiment is made becomes filled in this process with a greenish-yellow gas, of a very disagreeable odour, resembling that of chlorine ; the hydro- chloric acid acquires a greenish-yellow colour. (Fresenius.) 481. If a mixture of a chlorate and cyanide of potassium is gently heated upon platinum foil, a very violent deflagra- OF THE ORGANIC ACIDS. 187 tion ensues, even with a minute quantity of chlorate. The experiment must only be made with very minute quantities of chlorate. ORGANIC ACIDS. 482. Organic acids cannot be detected with the same certainty and precision as the inorganic acids. To detect with certainty even some of those which we have given requires on the part of the analyst great skill and judg- ment. 483. PRELIMINARY EXAMINATION. A portion of the solid substance in powder must be heated nearly to boiling with concentrated sulphuric acid, except when chloric acid is present, as it would be dangerous in that case to warm the solution. We will first notice the changes produced by sulphuric acid on the inorganic acids, and then on the organic acids. 484. Inorganic Acids. Carbonic acid, hydrosulphuric acid, nitric acid, hydrochloric acid, and hydrofluoric acid are evolved from the carbonates, the sulphides, the nitrates, the chlorides, and the fluorides, by concentrated sulphuric acid. The vapour of nitric acid will generally have a brown colour ; the vapour of hydrofluoric acid will etch glass ; and the vapour of hydrochloric acid will fume in contact with air. A greenish gas, having a smell of chlorine, will be evolved if a chlorate is present, and the solution will become yellow ; vapours of bromine and iodine will be evolved if bromides and iodides are present ; oxygen will be evolved if chromic acid is present, and the solution will become green ; carbonic oxide will be evolved, and its presence may be proved by burning it, if cyanides or oxalates are present ; it will be attended, when the latter acid is present, with carbonic acid. The other inorganic acids give off 188 THE PROPERTIES no vapours on being treated with concentrated sulphuric acid. 485. Organic Acids* Tartaric, tannic, and gallic acids are immediately blackened when heated with concentrated sulphuric acid ; carbonic acid is evolved at the same time from tartaric, but not from the other two. Citric and uric acids are not blackened unless boiled with the acid for some time. Benzoic, succinic, and acetic acids are not blackened by sulphuric acid under any circumstances, but they vola- tilize and in an unchanged state. 486. PREPARATION or THE SOLUTION. "When the sub- stance under examination is soluble in water, or if it is in solution and the fluid is water, it requires a little prepara- tion before it can be examined with advantage for the organic acids, as it conduces much to the success of the examination if no other bases but the alkalies and alkaline earths are present. In order to remove the others, the solution has y sometimes to be treated with sulphuretted hydrogen and sulphide of ammonium ; but generally it is only necessary to boil the solution with a slight excess of carbonate of soda ; by this reagent all the bases but the alkalies are removed. After the solution has been boiled for some time it is filtered, and to the filtrate is added nitric acid very slightly in excess; the solution is then gently heated in order to expel the carbonic acid. After this, ammo- nia is added in very slight excess ; and when it is required to have the solution perfectly neutral, as in testing with nitrate of silver and sesquichloride of iron, the solution, which has been rendered slightly alkaline with ammonia, is boiled in an evaporating dish until it is neutral to test-paper. When salts of ammonia are present in the substance under exami- * Malic acid and formic acid are not included in the course. OF THE ORGANIC ACIDS. 189 nation, the solution must, supposing no other bases but the alkalies are present, be boiled with carbonate of soda until all the ammonia is expelled, and the solution is then ren- dered neutral in the way just stated. 487. If the substance under examination is insoluble in water, but soluble in acids, or if it is a solution, and the fluid is an acid, the dry substance or the solution, which- ever it may be, is boiled with a strong solution of car- bonate of soda, then filtered ; and the nitrate, after it has been neutralized in the way described in 486, is examined for the acids. SPECIAL TESTS FOB- THE ORGANIC ACIDS. 488. TARTARIC ACID. When this acid has been indi- cated by the general reagent, a special test may be made for it by adding to a neutral solution acetate, or some other salt, of potash, and then agitating the liquid very much, and allowing time for the formation of the insoluble bitar- trate of potash. 489. CITRIC ACID. This acid is best ascertained by the way described at 504. 490. BENZOIC ACID. This acid, in the presence of suc- cinic acid, is best detected by the method described at 511. 491. SUCCINIC ACID. This acid -is best detected, in the presence of benzoic acid, by the method described at 516. 492. GALLIC ACID. This acid is best detected, in the presence of tannic acid, by the method described at 523. 493. TANNIC ACID. This acid is best detected, in the presence of gallic acid, by the method described at 519. 494. ACETIC ACID. This acid is detected in the way described at 528. 495. URIC ACID. This acid is detected in the way de- scribed at 535. 190 ^ "p. Jz; -- S s O *0 g ^ ^ . 'S 2 S fcH >H ^ Q> ft ^ 3 5 H? *"' r^H O ^ S iJ H w H o w S fl ^ g M FQ H ! OEGANIC ACIDS WITH TH [TATED FROM NEUTRAL AND SLIG BY CHLORIDE OF BARIUM. TAETAKIC ACID, CITEIC ACID. are soluble in dilute hydrochloric acid. [TATED FROM NEUTRAL AND SLIG ' THE COLD BY CHLORIDE OF CA TARTARIC ACID. ne, is soluble in chloride of ammonium ; it s with chloride of calcium, by digesting thi PRECIPITATED ON BOILING THE THE CHLORIDE OF CALCIUM. PH 5_] P-i ^ H ^ K H o 1 HH ^ If 3 ^ CS " *^ w r^H PH PH ?H ^ O & . ^ i i ~" pi M tf J8 1 ^ n^ < o ^N ^H &> ^ M 1 W 11 O) g i i * S t| O & ^ 0) ^ -4J g S OJ e CS OS HH o e I 1 o .s 191 . i^j 1 -1 Jo P^ PH HH 2 .S > ^( S i-5 S i 02 w ^ fe s o u O 3 w 1 H S O O 1 PH 1 ^ 1 H ^H &D m S Q M o a 'S 43 C5 >H ^ * K PH O2 M ^ 1 1 PH i CJ PH 3 'o g S o p 02 C5 O! n to the points which require to be attended to, as pointed out in the table, it should be paitttuhity noticed whether the substance dtaengagee a peculiar odour, aa araenie and aul- phur might be deteetedbj the odours they prv^uoe - and it should abo be noticed whether the substance fowa; the oxidea and acids whkh fuse are the oxidea of antimony, bismuth, lead, and oxide of copper. "Most metaQie su)> phurets ft* when katt^bell^ the hornpipe upon chim^ and thb efEbet oftm takea place with a^phwdte of of whidiareinfuaible; but many of these rapidfy oxidiied duxing the operation, and of aulphurooa acid in the aame way as when in the open tube, and are thus converted into metattk oxides Moat metal* foae before the flame of the blowpipe; and aU of them, except those eaOed noble, are aubwqueaD% oxidiied by the exterior flame.*" 560. After this examination k complete, the imbalance moat atQi be retained in the charcoal for the examination with protanitrate of cobalt WITH CJLKBOXAXE OF SOBA ox . The aubstance (in powder) imAnr examination is mixed with an equal quantity of carbonate of aoda, and the mixture ia made into a paste with a drop of After it baa been dried at a moderate heat* it k the charcoal to the reducing flame of the blowpipe, the oxidizing flame spreading over the charcoal. Should no reduced metal make its appearance, alter exposure for two HI 44 *k* fl^B* A ' '* - ' " , ' * * , ' ' * * * ' ' ' ' -' - - ........ ^6&MJ ^rfjMM Ihia ^^ L* 4RBMIKHMK^ jj^^BI^Pw 9&&W ^wHP' WV hum am fc* i^lniil. ft Mwl fc* . ^^^^J ^^^^^^1^^^ ^^B^ ^^^&& ^^r^ I^MA^ j&j^A^^^u^^^v 4^rift MNi P x "^ ' tf g '/ ' - - '^' v"r ' " - ''-' '' ' V **mfm*ttr mA**.+~ifwitkaruat,w1**,i( hill III, ft Awmps rprl . J r OXIDE OF COBALT Melts into brown- ish-yellow drops when heated. Melts readily when heated. Formed from the oxidation of the sulphide. The substance OXIDE op COPPER .... blackens . -. | I OEGANIC MATTER . J Aci e Acid vapours evolved. Empyreuniatic vapours. Acid Vapours. r FLUOEIDES Etching the glass. r Yielding an odour SuLpmDES { ofsulphurousacid. Arsenious acid and the oxides of bismuth and antimony may have existed as such in the original substance, or they may have been formed in the operation from the oxidation of their metals or sulphides. 214 (3) COUESE OF BLOWPIPE OPEEATio^s. continued. Expose the substance to the inner blowpipe flame, on CHAECOAL. If deflagration ensue, the presence of a chlorate or nitrate is indicated. Substances which volatilize or pass off in vapour. MEBCUEY, ABSENIC, CAD- MIUM, ANTIMONY, ZINC, AMMONIA, SULPHITE, and LEAD partly. Substances which are not volatilized. SILTEB, COPPEE, BISMUTH, LEAD, TIN. GOLD, PLATINUM, COBALT, NICKEL, MANGANESE, IEON, ALUMINUM, CHEO- MIUM, BAEIUM, STEONTIUM, CALCIUM, MAGNESIUM, SODIUM, POTASSIUM, SI- LICA, &c. Colour of the different Substances which Substances Substances Sublimates. yield coloured which are which/kse. MEECUET, incrustations. infusible, or run into ZINC, ) White. LEAD, 1 LI BISMUTH, J g but become luminous. the charcoal. AMMONIA, ) ALUMINA, SALTS ANTIMONY, white, imparting BAETTA, or a greenish-blue colour to STEONTIA, THE FIXED the flame. LIME, and ALKALIES. CADMIUM, red brown. MAGNESIA and their salts. 215 COTJRSE or BLOWPIPE OPERATIONS. continued. Mix the substance with Carbonate of Soda, and expose the mixed mass to the inner blowpipe flame, on CHARCOAL. Heat the substance before the blow- pipe on PLATINUM WIRE, with a bead of BORAX. Heat the substance On CHARCOAL,with theblowpipeflame; then moisten it with a solution of PROTONITRATE OF Oxides and Combinations of Oxides which can be reduced Substances which give coloured beads. COBALT : again strongly to the metallic state. heat it in the outer Oxide of Character of the Metal. In the outer flame. flame. BISMUTH . Brittle. COPPER, 1 COBALT,/ blue - Substances which yield coloured masses /Brittle; vola- when thus treated. 1 tilizes in white NICKEL . . reddish. ANTIMONY/ fumes, yield- OXIDE OP "1 _ > fiTTGdl* | ing an incrus- IRON . . yellow. tation. SILTEE. ..(Malleable; j_ very white. MANGA- 1 . NESE, } Amethyst. ALUMINA, TIN . . . Malleable. CHROMIUM . green. SILICIC ACID, > blue. LEAD . . Malleable,very J COPPER f We11 known EE > \ colours of the GoLI) > 1 metals. In the inner flame. COPPER . . red. PHOSPHATES, J MAGNESIA . pink. These three are reduced, but COBALT . . blue. BlNOXIDE J abluish OF TIN 1 ^ een yield no metal- NICKEL . . gray. L colour. NICKEL, COBALT, TlUYKT lic beads; they are rendered magnetic, and IRON . . . green. XxCUJN j can therefore MANGA- 1 be at once NESE, / colourless. distinguished ' from the rest. CHROMIUM . green. To discover the reduced metal, remove the fused mass from the charcoal, and grind it up in a small mortar with water ; allow it to stand a minute, and then pour oif the water and the suspended matter in it, and continue to repeat the process until the metal remains at the bottom of the mortar, perfectly free from charcoal, &c. If it is brittle, it will be in the state of very small spangles; if malleable, it will have adhered to the mortar or pestle, or a portion of it, whilst the rest may be in large spangles. 216 CLASSIFICATION AND SOLUTION 577. "While the bead of borax is still hot, it is touched with a small quantity of the powder of the substance under examination, and that which adheres is fused into it. The operator must then observe 1st, whether the substance is soluble or insoluble in borax ; and 2nd, the colour of the borax bead in (1) the oxidizing flame and (2) in the reducing flame, both in the hot and in the cold state. In performing this experiment, care must be taken not in the first instance to dissolve up too large an amount of the oxide or other substance under examination. If a small quantity afford no distinct reaction, more may be easily added. If, how- ever, the colour of the bead be too intense to be clearly distinguished, the bead jnay be jerked off the wire, and that which still adheres fused up with a fresh quantity of borax, by which a paler and more transparent glass will be obtained. 578. TREATMENT WITH PEOTONITEATE OF COBALT. No explanation beyond that given in the table is required. 579. If the substance should be a metal or an alloy, the only blowpipe experiments which need be made are 1st, in the glass tube closed at one end ; 2nd, as regards its mal- leability ; and 3rd, heating a portion of the substance on charcoal in the reducing flame of the blowpipe. 580. "When the student has completed the different preliminary experiments, he will be able to arrange the substance under one of the three following divisions : 581. The solid substance under 1 examination is neither a pure metal nor an alloy, and is destitute of organic matter. 582. The solid substance under examination is neither a pure metal nor an alloy, but contains organic matter. 583. The solid substance under examination is either a pure metal or an alloy. OF SOLID SUBSTANCES. 217 584. Each of the three cases just named is separately considered under its respective head. 585. THE SOLID SUBSTANCE UNDER EXAMINATION is NEI- THER A PURE METAL NOR AN ALLOY, AND IS DESTITUTE OF ORGANIC MATTER. 586. Before a solid can be acted upon by reagents, it must be brought into a state of solution. For this purpose it is submitted to the action of different fluids, and the one in which it dissolves is termed its solvent. The solvents employed in qualitative analysis are water, hydrochloric, nitric and nitro-hydrochloric acids. Water, when it can be employed, is always to be preferred. 587. The student must particularly guard against adding too much of the solvent, especially if it be an acid. To avoid this, he must add it in small quantities at a time, and apply heat after each addition. The substance should, before being submitted to the action of solvents, be reduced to the state of a very fine powder, and fifteen or twenty grains employed for the analysis. The whole of the sub- stance must, however, never be employed, but always a portion kept in case of any unforeseen accident, or for con- firmatory experiments. 588. The powdered substance is boiled in ten times its amount of water. It all dissolves. Make the preliminary experiments described under the head of Liquids, and then proceed with the actual analysis. A portion remains undis- solved. Filter a few drops of the liquid, and evaporate them to dryness on platinum foil. If a large residue remains on evaporation, the whole of the solution must be filtered, and submitted to analysis. The insoluble residue, after being well washed with boiling water, must be examined according to 589. If no residue remains on evaporating the aqueous solution, or at all events a very slight one, pour the re- 10 218 CLASSIFICATION AND SOLUTION mainder of the water off, and treat the insoluble substance according to 589. 589. The substance which was partly or entirely insoluble in water, is boiled in concentrated hydrochloric acid.* It all dissolves. Add to the solution the water which was poured off, and then proceed with the analysis. A portion remains undis solved. Ascertain if anything has dissolved, by evaporating a portion of the fluid to dryness on platinum foil. Should this be the case, place the tube, with its contents, on one side, and proceed with the next experi- ment. 590. A fresh portion of the original substance is boiled in concentrated nitric acid. The substance dissolves.^ [Remove as much of the free acid as possible by evaporation ; dilute the concentrated solution with water, and then proceed with the analysis. It does not dissolve. Allow it to settle ; pour oft' one half the acid, add a like quantity of concentrated hydrochloric acid, and again boil. If a portion still remains undissolved, return to the strong hydrochloric acid mixture (589); filter, and examine the filtrate, if anything has passed into solution. The residue insoluble in acids, after being well washed, must be treated according to 591. 591. The usually occurring substances, which are insoluble in water and acids, are the sulphates of baryta, strontia, * If hydrochloric acid causes any effervescence, the evolved gas nmst be examined for carbonic, hydrosulphuric, and hydrocyanic acids, as di- rected under the " General Properties of the Acids/' f If the substance dissolves with the separation of a light -yellow coloured mass of sulphur, it points out the presence of a sulphide. When nitric acid is employed as the solvent, as much of the free acid as possible ought to be removed by evaporation, before passing hydro- sulphuric acid gas through the solution, as they decompose each other, the decomposition being attended with the separation of a large amount of sulphur. OF SOLID SUBSTANCES. 219 lime and lead, alumina, peroxide of iron and their phosphates, the chlorides of silver and lead, fluoride of calcium, silicates, silica, and sulphur. 592. A small portion of the residue, insoluble in water and acids, is heated on a slip of platinum foil. If sulphurous acid is evolved along with the volatilization of the whole of the substance, sulphur only can be present. "When other substances are present, add to another small portion a drop of sulphide of ammonium. If the colour remains white, silver, lead, and probably iron, are absent. 593. A small quantity of the dry residue, in the state of a very fine powder, is mixed with four times its weight of carbonate of soda and potash. The mixed mass is placed in a platinum crucible,* and heated over a Berzelius spirit lamp for about half an hour ; or, what is still better, the platinum vessel is placed within a Hessian crucible con- taining a little carbonate of magnesia, and exposed to a full red heat, for the same length of time, in a furnace. The magnesia is employed to prevent the platinum from coming in contact with the Hessian crucible. 594. On cooling, the fused mass is boiled with water, and filtered. The filtrate is to be examined for the acids and alumina, the residue for the fiases. 595. Examination of the filtrate. To one portion of the filtrate add hydrochloric acid until the solution is distinctly acid ; evaporate to dryness, and ignite until acid fumes are no longer evolved. To the dried mass add dilute hydro- chloric acid, and boil ; if a residue remains, silicic acid is present. To the filtrate from the silica add ammonia in * The compounds of the easily reduced metals, such as silver, lead, &c., must not be fused in platinum vessels, as they form alloys with that metal, which greatly injures or altogether destroys the platinum vessel : porcelain crucibles must therefore be employed in such cases. 220 CLASSIFICATION AND SOLUTION excess, and then warm the solution; if a precipitate is formed, it must be due either to alumina or its phosphate. After having filtered and washed the precipitate, examine it for alumina and phosphate of alumina, according to table Y. In the filtrate from the alumina precipitate, or in the solution which has failed to give a precipitate, test for phosphoric acid by adding chloride of ammonium, and then sulphate of magnesia. Acidulate another portion of the original filtrate with hydrochloric acid, and examine for sulphuric acid by adding chloride of barium. Ano- ther portion must be acidulated with nitric acid, and tested for chlorine by nitrate of silver. To detect fluo- rine, an examination must be made according to 437 or 438. 596. Examination of the residue. After having removed all the substances soluble in water, by repeated washings, dissolve the residue, if lead and silver are absent, in hydro- chloric acid, and proceed with the analysis in the usual way. If the residue does not completely dissolve in the acid, and the two metals just named are absent, it shows that a portion of the substance has not been decom- posed. "When this is the case, filter off, and examine the fil- trate. 597. "When the fixed alkalies are to be looked for in the insoluble residue, another portion, in fine powder, must be mixed with about four times its weight of carbonate of baryta, and fused in a platinum crucible, in the manner already described. On cooling, the fused mass is digested with dilute hydrochloric acid, and filtered. The filtrate is evaporated to dryness, and ignited ; the dry residue must be treated with water, and again filtered. The filtrate, after being freed from iron, alumina, baryta, lime, and magnesia, must be evaporated to dryness, to expel the OF SOLID SUBSTANCES. 221 ammoniacal salts which have been employed in their preci- pitation ; if a residue remains, it must be examined for potash and soda. 598. THE SOLID SUBSTANCE UNDER EXAMINATION is NEITHER A PURE METAL NOR AN ALLOY, BUT CONTAINS ORGANIC MATTER. 599. The presence of fixed organic matter* interferes with the detection of many substances. Thus, in the pre- sence of tartaric acid, which is a fixed organic acid, the oxides of aluminum, chromium, and iron, and many other metallic oxides, are not precipitated, by the alkalies ; alka- line citrates prevent the precipitation of acids, by bases, with which the acids form insoluble salts under ordinary circumstances ; a soluble salt of baryta will not produce a precipitate, even in a solution of a sulphate, if an alkaline citrate be present, unless the sulphate is present in the proportion of three or more equivalents for every one of the citrate. It is therefore necessary, after precipitating the fifth and sixth groups by hydrochloric acid and sul- phuretted hydrogen, to destroy the fixed organic matter, when it is present, which will have been ascertained in the preliminary examination. For this purpose, the filtrate from the sulphuretted hydrogen precipitate, or the solution which has failed to give a precipitate with this reagent, is evaporated to dryness, and ignitedf until all the organic matter has been destroyed, the residue must then be dis- * Organic substances are termed fixed when they cannot be distilled or volatilized without decomposition. f Many substances, especially alumina and oxide of iron, after ignition dissolve with very great difficulty even in the concentrated mineral acids. The residue may therefore require protracted boiling in acids, although the original substance dissolved in water or dilute acid very readily. 222 CLASSIFICATION AND SOLUTION solved in water and acids, and examined in the regular way. 600. Sometimes we are obliged to have recourse to the following method for destroying the organic matter, espe- cially in the case of solutions which have to be examined for poisons : The solid substance or solution is boiled with concentrated hydrochloric acid, to which chlorate of potash, in powder, is added gradually until the mixture becomes perfectly fluid ; the solution is then heated until all free chlorine is evolved, after which it is diluted with water and filtered. The filtrate must be examined in the regular way. The residue must be examined for chloride of silver. 601. THE SUBSTANCE TINDER EXAMINATION is A PUEE METAL OB AN ALLOT. 602. Nitric acid behaves with metals in the following manner : Grold and platinum are neither dissolved nor altered in the least degree by it. Tin and antimony are converted by nitric acid into oxides, which do not dissolve in or combine with an excess of the acid. The other metals are oxidized and converted by it into soluble nitrates. On account of the different behaviour, therefore, which nitric acid exhibits with the metals, it is usual to employ it as the solvent of alloys, &c. 603. To the metal or alloy under examination, which is placed in a small flask, is added concentrated nitric acid, and heat applied. One of the three following cases will then occur : 1. Complete solution takes place. 2. A white insoluble substance separates. 3. A metallic residue re- mains. Each of the three cases are considered separately in detail. 604. 1. If complete solution ensues, GOLD, PLATINUM,* * Alloys of silver and platinum, with the latter metal present in small proportion only, dissolve in nitric acid. OF SOLID SUBSTANCES. 223 TIN, and ANTIMONY* must be absent. After removing the greater part of the free acid by evaporation, dilute the solu- tion with water,f and proceed with the analysis in the regular way. Mercury, if present, will be found in the state of protoxide. 605. 2. If a white insoluble substance separates, TIN or ANTIMONY is indicated. After removing the greater part of the free acid by evaporation, dilute the solution with water, filter, and proceed with the filtrate in the ordinary way. The precipitate, after being well washed with water, is treated with a hot concentrated solution of tartaric acid. If it all dissolves, TIN is absent. The presence of ANTI- MONY is confirmed by hydrosulphuric acid producing in the tartaric acid solution, to which hydrochloric acid has been added, an orange-red precipitate. If the whole of the insoluble substance does not dissolve in tartaric acid, the solution is filtered. The filtrate is examined for antimony by the method just stated. The residue, after being well washed, is mixed with carbonate of soda and cyanide of potassium, and exposed on a charcoal support to the inner blowpipe flame. If tin is present, ductile metallic grains will be obtained. 606. 3. If a metallic residue remains, GOLD or PLA- TINUM is indicated. After removing the greater part of the free acid by evaporation, dilute the solution with water, filter, and examine the filtrate in the usual way. The metallic residue is dissolved in aqua regia. One portion of the solution is tested for GOLD by means of protosul- phate of iron (294). The other portion is tested for PLA- TINUM by means of chloride of potassium (297). * Very minute traces of antimony are often completely dissolved by nitric acid. f If the solution becomes turbid, on the addition of water, it indicates the presence of bismuth. APPENDIX. A. THE following method for the detection even of very small quantities of antimony and arsenic, in the presence of tin, has been proposed by Ansell : The sulphides, pre- cipitated from their solutions in alkalies or alkaline sul- phides, are dissolved in nitro-hydrochloric acid, and the solu- tion, thus obtained, poured into a hydrogen-apparatus so arranged as to allow the gas to be washed with a dilute solution of acetate of lead which absorbs any hydrochloric acid or sulphuretted hydrogen, and to pass the mixture of antimonide, arsenide, and free hydrogen, into a test-tube half filled with concentrated nitric acid, which converts the antimony and arsenic into antimonic, arsenious, and arsenic, acids ; the gas ought to be passed through the acid mode- rately slow. The nitric acid solution obtained after the gaseous mixture has passed for about a quarter of an hour, is evaporated ; and the residue is exposed to a tolerable heat upon the sand-bath, in order to expel the last traces of nitric acid, which is an essential condition of success, inasmuch as antimonic acid is slightly soluble in water containing nitric acid. The residue is now treated with warm water, which dissolves the arsenious and arsenic acids, but leaves undissolved the antimonic acid: to the solution is added nitrate of silver, and the solution is then very cautiously neutralized with ammonia, when a mixture SEPARATION OF CADMIUM FEOM COPPER. 225 of arsenite and arseniate of silver precipitates. The anti- monic acid, which did not dissolve in the water, is dissolved in as small a quantity of nitro-hydrochloric acid as possible, and the solution evaporated as far as possible, and then tested with sulphuretted hydrogen water, when, if any antimony is present, the liquid at once assumes an orange- yellow colour; and, on boiling, decidedly orange-yellow flakes are separated. In order to detect the tin, the me- tallic precipitate is washed off the zinc in the generating bottle, and boiled with hydrochloric acid, when chloride of tin is formed, which may be detected by the well-known re- action with chloride of mercury. To effect the detection of small quantities of arsenic, in presence of a large quantity of antimony, the above process may be advantageously modified by passing the washed gases into a solution of nitrate of silver instead of into nitric acid ; the whole of the antimony is precipitated as antimonide of silver, while every trace of arsenic remains in solution in the form of arsenious acid. On neutralizing the liberated nitric acid by ammonia, the characteristic yellow arsenite of silver is precipitated. If the gas has been passed for a long time, the solution is sometimes free from silver. In this case, the precipitate of arsenite of silver appears only after the addition of a drop of nitrate of silver. The separation of the antimony from the black precipitate, which is a mixture of metallic silver and antimonide of silver, is attended with difficulty ; to detect minute quan- tities of antimony, it is better, therefore, to follow the pro- cess first described. B. Dr. Hoffman has proposed the following method for separating cadmium from copper : Acidify the solution, if it is not acid, with hydrochloric acid ; then pass sulphuretted hydrogen through the solution. The two metals, if present, 10 226 APPENDIX. will be precipitated as sulphides ; the precipitate must be well washed, and then boiled with dilute sulphuric acid. The sulphide of cadmium is decomposed by the sulphuric acid, sulphate of cadmium being formed, which dissolves whilst the sulphide copper is undecomposed and undis- solved. Separate the two by filtration; test the filtrate for cadmium by sulphuretted hydrogen ; dissolve the sul- phide of copper in nitric acid; neutralize with ammonia, acidify with acetic acid, then add ferrocyanide of potassium. This is a good method : the only precaution to be attended to is, that the mixed sulphide must be washed rapidly, so that the sulphide copper may not become oxidized by expo- sure to the air. c. " The blowpipe experiments that require the assistance of charcoal may be divided into two classes. In the first class may be named the formation of beads with microcosmic salt, the trial of fusibility per se, and the roasting of the metallic compounds that contain such volatile elements as sulphur and arsenic. The second class of experiments is restricted to the fusion of minerals or metallic compounds with carbonate of soda, or with soda and borax, for the purpose of effecting particular combinations, or of procuring their metals in a state of regulus. For these two classes of experiments I make use of two different composition supports, the first of which I call Supports for Fusions, and the second, Supports for Reductions. They are alike in appear- ance. Each consists of two parts an upper or combustible portion, and a base or incombustible portion. The former is the proper substitute for the ordinary charcoal, the under portion acting only as a crucible in which the combustible portion is contained. I shall first describe the composition and formation of the supports, and afterwards show the way to use them. BLOWPIPE SUPPORTS. 227 " The incombustible portion of both supports is made of fine pipeclay and charcoal powder, mixed in equal parts by weight with as much water, slightly thickened with rice paste, as is sufficient to form a stiff plastic mass. " The combustible portion of the Support for Fusions con- sists of Charcoal, in fine powder . 12 parts. Eice flour . . . 1 Water, about 8 The rice is boiled in the water to form a paste, with which the charcoal is afterwards mixed into a mass of the consist- ency of dough. " The upper part of the Support for Seductions consists of the following mixture : Charcoal, in fine powder . 9 parts. Carbonate of soda, crystallized 2 Borax, crystallized . . 1 Kice flour . . . . \ Water, about . . . 8 The water is boiled, the soda and borax are dissolved in it, and the rice is then added to form a paste, with which the charcoal is finally incorporated, and the whole well kneaded into a stiff mass. The mould in which these compositions are pressed to form the supports is made of boxwood.* " The principal points which require attention to ensure success in this process are to have the materials in the state of a very fine powder, and the moist compositions of a proper degree of consistency. If they are too soft, the support * These moulds, and every other part of the apparatus, are sold by Mr. Griffin, and, I have no doubt, can be procured through any of the other dealers in chemical apparatus. 228 APPENDIX. will not quit the mould without losing its form ; if too dry, the particles of the support will not cohere. The proper state is found after a few trials. It is most convenient to begin by making the mixture too soft, and then drying it slowly till it is found to be hard enough to work easily. The composition is rolled into balls with the fingers. The moulds should be kept clean, and the forming parts of the pestle for the charcoal composition, and the ring, should be oiled. The point of the pestle for the clay composition must not be oiled, because grease prevents the adhesion of the combustible portion of the clay base. A pestle, made on purpose for the operation, is used to remove the finished support from the mould, by pressure on the clay foundation. " When the support is taken from the mould, it is placed on a hot plate or sand-bath to dry, after which the rough edges are taken off by a rasp. It is then ready for use. The bottoms of supports for reductions are painted with red ochre, mixed with rice paste, to distinguish these from the other kind. The size I have fixed upon is as follows : height, half an inch ; diameter at top, half an inch ; at bot- tom, two fifths of an inch. The weight is about 16 grains, consisting of 10 grains of clay crucible, and 6 grains of combustible matter. I have tried several other sizes, but this I find to be the most generally convenient. Never- theless, a higher temperature can be produced upon a smaller support ; and I find that large masses of charcoal are not essential, since many blowpipe experiments can be finished during the combustion of only two grains of char- coal. When in use, they are supported by a handle made of wire, turned into the form of a ring : a piece of tobacco pipe can be used for the handle of the wire support. " The following is the method of using these supports : " Firstly, the surface of one of the supports for fusion is BLOWPIPE SUPPORTS. 229 heated before the blowpipe flame. The support continues to burn like an ordinary pastile, till it is consumed down to the clay : in this respect the support has a superiority over common charcoal, which soon ceases to burn when removed from the fire. The ignited support is then to be rested upon a porcelain capsule, and a quantity of microcosmic salt, sufficient to form a bead, is placed on its red-hot surface. The salt instantly melts, and sinks into the central cavity, so as to form a bead ; the heat, the form, and the smooth- ness of the surface of the support, facilitating this part of the process. The salt is then heated before the blowpipe, till it is converted into a transparent, colourless bead. The support is again placed on the porcelain capsule, and the metallic substance intended to be incorporated with the bead is added to it. The support continuing to be red-hot, and the bead consequently continuing soft, the substance so added is immediately absorbed, and its loss by dispersion prevented ; whereas, upon common charcoal the fused salt solidifies soon after it is removed from the flame : and the substance added for examination, not adhering to it, is often blown away by the first blast from the blowpipe jet. The bead is now again fused, till the substance added to it is de- composed, and the resulting glass is observed to fuse quickly. It is then ready for examination ; but it is sunk in the bot- tom of the hollow of the support, and cannot be seen by transmitted light, unless the projecting sides of the support be removed. This is effected as follows : the support is placed, as before, on the porcelain capsule, and the operator blows with his mouth, without the blowpipe, strongly down upon its surface. The pastile then burns away rapidly, and the force of the blast disperses the ashes, until the whole rim of the support is consumed. The bead then appears situated on the summit of a cone, and can be examined either 230 APPENDIX. by reflected or transmitted light. It is also in a position adapted for exposure to the different action of the oxidating and reducing flames, so as to have the character of the in- cluded metal fully developed. If, finally, the charcoal is allowed to burn wholly away, the coloured bead can be lifted from the ashes and preserved in a glass tube for sub- sequent examination and comparison. " Secondly, if the surface of one of the supports for re- ductions be heated before the blowpipe, it becomes at first like the simple charcoal support ; but in proportion as the charcoal is consumed, the fluxes which were mixed with it, and which are not volatile, concentrate and fuse upon the surface of the residue. If, therefore, a reducible metallic compound is heated upon such a support, it becomes at once exposed to the reducing action of the high temperature, of the nascent oxide of carbon, and of the carbonate of soda, whilst any earthy matter that it may contain is vitrified by the attendant borax." Griffin. D. " The degree of fusibility is a very important point to ascertain, when the examination in question refers to the native combinations of silica and certain other minerals, for this characteristic feature displayed by the blowpipe is often the only one by which we may distinguish those which con- sist of earths, and which contain no notable quantities of metallic oxides, properly so called. Amongst the minerals most frequently met with, the following are infusible : Quartz, Zircon, Corundum, Cyanite, Tourmaline (both that Phenakite, which contains alumina Leucite, and even that which con- Talc, tains soda), Pyrophyllite, FUSIBILITY OF MINERALS. 231 Apatite, Gehlenite, Antophyllite, Staurodite, Refractory clays, Hydrate of alumina, Hydrate of magnesia, Sulphate of alumina, Carbonate of lime, Carbonate of magnesia, Carbonate of zinc, Allopliane, Spinell, Pleonast, Gahnite, Olivine, Cerite, Cymophane, Gadolinite (which, being heated,becomes suddenly luminous, as if it caught fire), Vitreous tin, Eutile, Titanic iron, Turquoise, Titaniferous oxide of iron, Chrome iron, Native oxides of iron, Tantalite, Tttrotantalite, Dioptase, Chondrodite, Topaz. " Amongst those which are almost infusible and only be- come rounded at the edges, the following may be named : Felspar, Albite, Petalite, Labradorite, Anorthite, Nepheline, Tubular spar, Pyroxene (which contains much magnesia), Epidote (which intumesces by the first impression of the heat), Euclase (which intumesces by the first impression of the heat), Emerald, Titanite, Sodalite, Calcareous scheelin, Meerschaum, Soapstone, Serpentine, Mica (some species, espe- cially those found in granite), 232 APPENDIX. Dichroite, Heavy spar, Celestine, G-ypsum, Apatite, Fluor spar. " The following are fusible : Zeolites (most of them in- tumesce) , Spodumene (which intu- mesces), Mejonite (which froths up before fusing), Eleolite, Amphibole (most of which boil up whilst in fusion), Pyroxene (those which con- tain no excess of mag- nesia), Idocrase (intumesces in fusing), G-arnet, Cerine, Orthite (boils in fusing), Ferruginous scheelin, Boracite, Hydroboracite, Datolite, Botryolite, Cryolite, Mica (several species, espe- cially those which con- tain lithia), Tourmaline (those which contain potash), Axinite (intumesces whilst fusing), Amblygonite, Lazulite, Haiiyne, Nosiane, Eudialite, Pyrosmalite." Rose's Manual of Analysis. E. Blowpipe Experiments ty Bunsen. The lamp invented by Bunsen, in which gas is burned without luminous or fuligenous flame, can be used to pro- duce all the reactions for which the blowpipe is usually employed, and with greater ease and certainty. In many cases reactions can be obtained, and even the approximative quantity of substances determined, which, with the ordinary BUNSEN S BLOWPIPE EXPERIMENTS. 233 blowpipe, are either impossible, or can only be effected by difficult and tedious processes. Fig. 1 represents the blowpipe lamp. A conical iron- plate chimney, 30 millimetres wide at the top, and 55 millimetres at the bottom, is so fixed on the supports a a a, that the tube of the burner b is in the axis of the chimney, and terminates 45 millimetres below the upper aperture. By this arrangement the flame has the form represented in the vertical section, fig. 2 ; a I a corresponds to the dark part of the ordinary luminous flame, and contains the unburned gas mixed with air. By arranging the supply of gas so that the point 5 is exactly level with the upper aperture, a flame is obtained of unvarying dimensions, which does not flicker, and may at all times be obtained, a dab is the burning cone of the flame, and is so little luminous as to be scarcely 234 APPENDIX. perceptible. In this cone the external mantle adac may be distinguished from the internal mantle a cab, by being of a more intense blue. The holder, fig. 3, serves to hold the test specimens, which must not be larger than a millet grain, and to expose them to the action of the flame. In the two tubes a a, which are lined with cloth, two glass rods 5 5, bent at right angles, move easily in any direction. On the ends of the rods are two glass tubes c, drawn out to solid ends ; in these are fused platinum wires, about 0*145 millimetres thick, bent at their extremities to fine loops. To allow these glass tubes to be firmly fixed to the glass rods, and yet allow them at the same time of being easily and gently pushed in and out, a silken thread, provided with a knot, is drawn through the whole length of the tube ; this silken thread acts as a spring, and causes the tubes to glide easily. To bring about this, an aperture is made in the sides of the tubes through which the thread is carried. BUNSEN'S BLOWPIPE EXPERIMENTS. 235 If the loop of the platinum wire when moistened is slightly brought into contact with the powder or the grain of the substance to be examined, it adheres to it, and when some time warmed near the flame, and then introduced into it, the substance melts and fuses into a drop or bead. Spluttering substances must first of all be brought to a red heat in a covered platinum spoon. By means of the holder fig. 3, the substance under examination can thus be brought to any part of the flame required. The temperature of the flame depends mostly on the composition of the gas ; it will be found that the hottest part of the flame is in a zone of the external mantle adac, which extends a few millimetres above and below the diameter of the flame at b. This region, which may be called the melting-space, is used to determine the deport- ment of bodies at the temperature of 2300 C. The external edge of this melting-space acts as an oxidising flame, and the internal as a reducing flame. The latter is most powerful just below the point 5. The great constancy of the flame permits it to be used for determining the volatility of bodies at 2300 C. This is effected by melting on the platinum wire as much of the substance to be tested as will form, when seen under the microscope, a bead of 1 millimetre in diameter : with a little practice this is very easy. After the bead has been brought to the right size, and warmed by being brought near the flame, it can, by a very slight movement of the arms of the holder (fig. 3), be introduced into the melting-space of the flame, and the seconds which elapse until it has quite evapo- rated are counted by means of a pendulum or metronome. This point is generally so marked by a sudden alteration of the flame as to be determinable to half a second. Taking the volatility of carbonate of soda as unity, we 236 APPENDIX. may compare with it the volatility of equal bulks of other substances. If t Q be the time required for the evaporation of carbonate of soda, and # t 2 , t 3 , &c., that required for the evaporation of other substances, we obtain the values ~ ~ ~&C; as approximate measures for their volatility. *1 ^2> ^3> The following determinations of volatility will illustrate the use to which they may be applied in geological chemistry, more especially if the balance be used, as is necessary in very accurate determinations : Sulphate of soda . , . .077 Sulphate of lithia . . . O89 Sulphate of potash -,.',.. 1*21 Carbonate of soda . 1*00 Carbonate of lithia . . . . 1'70 Carbonate of potash .... 2'30 Chloride of sodium .... 6*57 Chloride of lithium .... 8'36 Chloride of potassium . . . 15*33 Boracic acid 0'84 Borate of soda . . . T02 Phosphoric acid .... 23'00 Bibasic phosphate of soda . . O12 All these substances are easily and completely volatile at 2300 C. Other substances under the same circumstances lose only a single constituent, and leave a non-volatile residue. For instance, the sulphates of lime, strontia, and baryta lose some of their S0 3 , and become alkaline ; the same is the case with the chlorides of calcium, strontium, and barium, and many other chlorides ; they are converted in an analogous manner into basic compounds. The silicates rich in alkalies lose considerable quantities of potash and 237 soda at 2300 C, at a temperature, therefore, much less than that of many lava streams. Besides these determinations of volatility, the flame can be used for many valuable blowpipe experiments, among which is the quantitative determination of soda in the pre- sence of lithia and potash. For the qualitative determination of soda in its volatile salts, it is enough to hold a small bead in the melting-space, and to illuminate with it a crystal of bichromate of potash. When the rays of the soda-flame are incident on this salt, it appears perfectly colourless, transparent, and with an adamantine lustre, But the following reaction is more delicate, and better suited to approximative quantitative determinations. A piece of paper about a centimetre square is coated with red iodide of mercury, and placed upon a small holder d (fig. 1), which is moveable on an arm c, also moveable, attached to the chimney. When the least quantity of soda, sulphate of soda, or chloride of sodium is introduced into the melting- space of the flame, the red iodide becomes white, with a faint tinge of fawn colour. The glaring contrast of these colours is apparent when the paper is lit up by being placed close to the red-hot wire and bead, and the wire then placed in the flame, that the bead only reaches the melting-space. Potash, lithia, and lime do not prevent this reaction. If the soda compound is dissolved in water, the experiment is made as follows : The capillary platinum wire d, fig. 3, is bent to a loop, and this is beaten out so as to form a small ring. If this be dipped in the substance under examina- tion, a drop of the liquid in the form of a lens adheres to it. If this drop is evaporated, without boiling, in the neigh- bourhood of the flame, as much solid substance remains as is necessary for the reaction. With solutions of various 238 APPENDIX. degrees of concentration, the time during which the change of colour of the paper is observed is proportional to the concentration of the liquids. With the same quantity of chloride of sodium diluted with 1, 2, and 4 parts of water, the duration of the change of colour was 1, 2, and 4 seconds. The reaction is extremely delicate. To determine its limit, 0'1865 gram, of salt were mixed with measured quantities of distilled water, and, each time, 2 milligrammes of the solution evaporated and exposed in the flame. "When the quantity of water had reached 1 kilogramme, the reaction was still quite distinct ; TT y^ of a milligramme of chloride of sodium may thus be detected without difficulty. To detect volatile potash compounds in the presence of soda, Cartmell's * reaction may be used. As Cartmell ;has observed, all substances which make flame luminous, and especially all organic substances which burn with separation of carbon, give the same violet colour, and must hence be first removed by heat. This test for potash is even more delicate than that for soda. Cartmell detected lithia in the presence of soda and potash, by comparing the mixed colour of the flames of those bases with that of the flame of pure potash, when both are viewed through an indigo solution. Bunsen has found that the discrimination of these bases in presence of each other is more easily effected by observing the succession of changes of colour, which the mixed flame produced by these substances experiences when the rays reach the eye after passing through gradually thicker layers of an indigo solu- tion. For this purpose a hollow plate-glass prism (fig. 4) is used, filled with indigo solution ; it is 40 millimetres high, and its principal section is a triangle, with two sides of * See paragraph 112, p. 49. 150 millimetres, and the other of 35 millimetres. The Iij.4. indigo solution is made by dissolving 1 part of indigo and 8 parts of fuming sulphuric acid, diluting with 1500 to 2000 parts of water, and filtering. In the following experiments the prism was moved hori- zontally before the eye, so that the rays of the flame always passed through gradually thicker layers of the medium. The alkaline substances, brought singly into the melting- space, exhibited the following changes : 1. Chemically pure chloride of calcium produces a yellow flame, which, even with very thin layers of the indigo solu- tion, passed through a tinge of violet into the original blue lamp flame. 2. Chemically pure chloride of sodium, the same. 3. Chemically pure carbonate or chloride of potassium appears of a sky blue, then violet, and at last of an intense crimson red, even when seen through the thickest layers of solution. Admixtures of soda or lime do not hinder the reaction. 4. hemically pure carbonate or chloride of lithium gives a carmine-red flame, which, with increasing thickness of the medium, becomes gradually feebler, and disappears before the thickest layers pass before the eye. Lime and soda are also without influence on this reaction. 240 APPENDIX. As, of all lithium compounds, the carbonate and chloride;, give the most intense coloured flame, it is only necessary to mark on the prism the place at which the lithia disappears, to obtain a space above this mark which transmits red potash rays, but never red lithia rays. As this part of the prism acts in the same way as a thick cobalt glass in detecting potash compounds in the presence of soda compounds, the cobalt glass can be dispensed with for determining potash. Lithia with an admixture of potash is detected by bringing a sample into the melting-space, and comparing its flame with that of a sample of pure potash placed side by side with it in the melting-space. With thin layers of the solution, the lithia flame appears redder than the pure potash flame ; with somewhat thicker layers the flames are equally red, if the proportion of lithia to potash be very small ; if the lithia be in excess, the intensity of the red lithia flame sensibly diminishes with thicker layers, while the red flame of potash is scarcely weakened. In this manner a few thousandths of lithia may be detected in the presence of potash. Soda has almost no influence on the reaction. These reactions succeed readily with the chlorides, the sulphates, the nitrates, carbonates, phosphates, and especially such combinations as show a sufficient degree of vola- tility at 2300 C. But with silicates and other non-volatile compounds such as are met with in nature, it is often diffi- cult to detect 3 or 4 per cent, of these alkalies. These reactions may, however, be applied to the silicates, by heating them in the melting-space with pure gypsum, by which there is formed silicate of lime, and a volatile alkaline sulphate which imparts a colour to the flame. If the reaction of a specimen both before and after the addition of gypsum be compared with a standard series of silicates, the proportion of alkali in which is known, the various alkaline BUNSEN'S BLOWPIPE EXPERIMENTS. 241 silicates (for instance, the members of the felspar family) may not only be recognised, but the relative quantity of potash, soda, and lithia approximative^ determined. The process adopted in these cases will be most readily understood by an example. Bunsen selects the discrimina- tion of the following minerals : Orthoclase and its varieties, Sanidine and Adularia ; Leucite, Labradorite ; Albite and Oligoclase, Anorthite, Nepheline, Hauyne, and Lasurstein ; Petalite, Lepidolite, and Triphane. These are divided into two groups those containing litMa, and those which do not contain that alkali. It is first ascertained to which of the two groups the sample belongs, by exposing it with gypsum in the melting-space side by side with a specimen of pure potash, and viewing the two flames through the indigo prism. If the sample contains lithia, its flame at that part of the prism at which the soda colour vanishes appears red against the cornflower-blue of the potash. With thicker layers of indigo, the red of the lithia gradually lessens in intensity, while the cornflower-blue of the potash passes through violet into red, which, with a certain thickness of the indigo layers, is quite like the colour of the lithia. If no lithia is found, the sample belongs to the first group ; in the other case, to the second. The individual minerals of the first group are recognised by comparing them with each other according to their relative proportions of potash and soda. A standard series of felspathic minerals is selected, and arranged according to the soda they contain. Bunsen uses the following series, and distinguishes them by the numbers placed over the analyses : 11 242 APPENDIX. 4 S -S .5 -3 a5 'S S 5 1 S J p 1 s f 1 1 1 1 '3 1 1 1 ^ Cl CO 10 o t- GO NaO 9.09 15.44 10.06 7.08 4,0 2.55 1.13 KO 4.94 7.03 8.0 1.06 0.62 22 MsrO 0.34 0.33 0.97 CaO "3.53 '" 1-77 ... 0.48 i'.b 12.02 17.22 MnO ... { MnO ) nfl , FeS03J- 6a 0.25 Fe^03 FeO, 0.86 0.95 063 0.6 FeO, 0.66 1.50 A1203 31.76 "33.28 18.65 19.99 18.5 34.66 30.50 23 SlO3 45.58 44.03 67.75 65.19 66.6 48.62 .48.75 54- SO3 5.89 Cl 0.42 s 0.95 HO 0.12 0.21 0.38 0.49 These silicates are heated, powdered, and arranged according to their numbers, in small bottles. If one of these standard silicates, and the sample to be tested, either with or without gypsum, be simultaneously placed side by side in the melting-space, so that, besides the tests themselves, small but equal lengths of the platinum wire are ignited, the iodide of mercury paper before the flame appears more or less bleached. If the sample be now removed from the flame, and the paper exhibits a distinct passage to red, the sample contains more soda than the standard silicate ; if the paper is white, the reverse is the case. By ascertaining in this manner between what two of the silicates the reaction falls, the proportion of soda in the silicate under examination can be approximatively determined to a few per cents. Although these quantitative estimations of soda can be made quickly and without difficulty, yet there are a few precautions which must not be neglected, to prevent mis- takes arising. The specimens to be compared (the test specimen and the standard silicate) must be as nearly equal as possible, as regards quantity, which is measured by the eye ; and then care must be taken that the lengths of the 243 platinum wire in the flame are also equal ; but, above all, the eye must be accustomed to distinguish the different brightnesses of the same tint from the changes in colour, which are very different. Inasmuch as the eye is not susceptible enough for the more intense bleaching of the iodide of mercury, in cases when the bleaching is intense, the paper must be illuminated so strongly by the flame of an ordinary candle, that a colour nearer to the red, but at the same time white, is produced. There is no quantitative blowpipe test for potash so accurate as that for soda. It suffices for all purposes to distinguish, according to the duration and intensity of the potash colouring, a slight, a strong, and a very strong potash reaction. The flames produced by oligoclase, orthoclase, and leucite, are used as the deciding points of comparison. The silicate to be tested for potash is mixed with gypsum, and one of the standard potash silicates is also mixed with gypsum in the same way as in testing for soda. The sub- stance under examination, and the standard silicate after gypsum has been added, are placed in the melting-space of the flame, and in such a manner that the coloured flames arising from them appear to the naked eye of the same size and appearance. The flames are then viewed through the indigo prism. The sample containing more potash is dis- tinguished by greater dimensions, more intense colour, and longer duration of the red flame, as well as by the occur- rence of the blue and violet colour in thinner layers of the solution. The following is a scheme of the behaviour of the above-mentioned standard silicates : 244 APPENDIX. WITHOUT GYPSUM. Lasurstein 1 J~ NaO : 1 more than 2. Nepheline 2 \ KO : not to be detected. 1 and 2 fusible. Nepheline 2 J NaO : 2 more than 3. Albite 3 1 KO : not to be detected. 2 and 3 fusible. Albite 3 f NaO : 3 more than 4. Orthoclase 4 \ KO : not to be detected. 3 and 4 fusible. Orthoclase 4 / NaO : 4 more than 5. Sanidine 5 \ KO : not to be detected. 4 and 5 fusible. Sanidine 5 f NaO : 5 more than 6. Labradorite 6 \ KO : not to be detected. 5 fusible in a bead. 6 fusible on the edges. Labradorite 6 f NaO : 6 more than 7. Anorthite 7 \ KO : not to be detected. 6 fusible at the edges. 7 fusible to a globule. Anorthite 7 f NaO : 7 about equal to 8, Leucite 8 \ KO : not to be detected. 7 fusible to a globule. 8 infusible. WITH GTPSTJM. NaO : 2 more than 1. KO : both very feeble and equal. NaO : 2 more than 3. KO : 2 more than 3. NaO : 3 more than 4. KO : 4 stronger than 3. NaO : 4 more than 5. KO : 5 scarcely more per- ceptible than 3. NaO : 5 more than 6. KO : 5 more than 6. NaO : 6 more than 7. KO : scarcely to be detected. 6 more than 7. NaO : 7 more than 8. KO : 7 scarcely to be de- tected. 8 very strong. The reason that lasurstein, which only contains 9 per cent, of soda, gives a stronger soda reaction than nepheline, which contains 15 per cent., is that it already contains sul- phuric acid, and can therefore only be compared with silicates containing no sulphuric acid when these are fused with gypsum, when, as is seen from the table, the anomaly disappears. One must be certain that the substance under examination contains no sulphuric acid, chlorine, and fluorine, as these substances by giving rise to the formation of volatile soda compounds render the reaction more delicate. Those silicates containing sulphuric acid are placed in a group by themselves, and compared in a similar way to the felspars, by the assistance of a special reagent scheme. The detection of sulphuric acid in the silicates is effected by 245 fusing a sample of the silicate with soda in the reducing flame, letting it cool in the dark part of the flame, and then testing it on polished silver. Chlorine and fluorine are tested for in a similar manner. In testing a sample, a splitter is brought into the flame, and by the intensity of the bleaching of the iodide-paper the place is approximatively determined. To come nearer to the number, a lighted candle is approached to the iodide- paper, and the distance observed at which the bleaching passes into red. The nearer the candle can be placed, the lower in the series is the silicate. With lasurstein, the candle can be brought within two or three inches without pro- ducing red. After this preliminary test, two, or at most three, comparative observations will show the place of the silicate. Lithia silicates must be tested for separately. The above soda scale cannot be used, as the lithia flame gives rays which redden the iodide-paper: this is not the case with potash. Lithia silicates can only be compared amongst themselves ; and lepidolite, petalite, and triphane are best used as reagents. Their deportment is as follows : 1 a Lepidolite. Easily fusible. In the oxidizing flame, yellowish red to the naked eye; in the reducing flame, yellow ; with the indigo prism a strong, and with gypsum a still stronger, lithia reaction ; tolerably strong potash reaction, still stronger with gypsum and the prism. Feebler soda reaction than 2 a and 3 a. The varieties richer in fluorine often give a stronger soda reaction than 2 a^and 3 a, especially with gypsum. 2 a Petalite. Pretty readily fusible, with intumescence ; no potash reaction; feeble soda reaction; with gypsum, stronger than 3 a, and feebler than 1 a. Otherwise like lepidolite. 3 a Tripliane. Puses without intumescence. Only with 11 246 APPENDIX. gypsum a feeble soda reaction, which is feebler than 2 a. On the other hand, a stronger lithia reaction than 2 a. Otherwise like petalite. The following is the composition of the minerals used in these reactions : LiO NaO KO MgO CaO MnO FeO SiOg" la. Lepidolite. 2.41 0.71 8.60 0.53 1.24 14.57 17.62 48.65 6.16 2 a. Tetalite. 3.30 1.19 3 a. Triphane. 5.47 0.46 0.14 0.15 0.50 18.58 77.79 trace 29.14 65-02 THE END. l-KINTED BY J. E. ADLAHD, BARTHOLOMEW CLOSE, B.C. BY THE SAMS AUTHOR. THE FIKST STEP IN CHEMISTEY. A NEW METHOD FOR TEACHING THE ELEMENTS OF THE SCIENCE. Third Edition. Illustrated with Engravings on Wood ; fcap. 8vo, cloth, 5s. This work is placed on the list of books recommended by the Committee of Privy Coun- cil for Education. " Beginners in the study of Chemistry are much indebted to Mr. Galloway, for the great pains he has taken in the book before us (' Manual of Qualitative Analysis'), and in his 'First Step in Chemistry/ to remove from the path of the student the many difficnlties and obstacles which hinder his early progress. These difficulties, so puzzling and discouraging to the pupil, are too often forgotten or neglected by the compilers of such text-books ; but our author has evidently devoted considerable and especial attention to them, and we think he has been successful in most materially facilitating the acquisition of sound knowledge in the first stages of chemical study." Philosophical Magazine. "We spoke favorably of Mr. Galloway's work on 'Qualitative Analysis,' and we are no less pleased with his ' First Step.' " Atke- " We have thus glanced at the principal features of Mr. Galloway's system of instruction, and although, as the book has now reached a third edition, it is pretty extensively known, we have done so because we believe that the principles of such a system cannot be too widely diffused, and that, if universally employed, not only would the beginner be spared much disappointment, but many more really practical chemists would be given to science. We have marked several portions of Mr. Galloway's book, the peculiar merits of which, did space permit, we should notice at length, but we think that our readers will, from the above resume, get an idea of its general plan, and for its details we refer them to the book itself. We cannot, however, conclude this notice, without reference to the chapter on the atomic theory, and that on isomerism, as examples of that clearness of explanation which is pre-eminently the characteristic of the whole work. Of the manner in which a subject may be treated so as to combine interesting reading with sound instruction in confessedly difficult subjects, the sections on light and electricity may be cited as illustrations. " In conclusion, we confidently recommend this little treatise to all who seek an introduction to chemistry, as a book which will, if properly studied, leave them in an infinitely better position than years of attendance upon lectures on the science, and with a practical know- ledge of all its fundamental truths." Dublin Medical Press. "We heartily commend this unpretending work to the heads of scholastic establishments, and to others who are anxious to initiate their pupils into the principles of a most fascinating and most useful branch of human knowledge." London Journal of Medicine. " The author of this manual complains, and with some justice, that the elementary works on the science of chemistry do not begin at the beginning, and, consequently, do not follow up the various stages in their natural and proper order. Chemistry should be taught as arith- metic This is the plan pursued by Mr. Galloway, and the arrangement of the subject is one of the distinctive features of his book. But besides this, he lays great stress on instruction by working examples ; to lay down rules simply would utterly fail as a method of teaching chemistry, just as much as it would fail in arithmetic. The exercises in this book are most abundant, and constitute its second recommendation. On the whole, we think it a very excellent work, and we recommend it to the notice of our readers." English Journal of Education. " This method of instruction seems likely to meet with considerable success in schools and other establishments, where a study of chemistry is not a chief branch of education, but must take its place by the side of Latin and Greek ; and, as such, it gives us pleasure in being able to cordially recommend this useful little book." The Chemical Neius. "We have seldom had an opportunity of witnessing so large an amount of valuable information compressed in so small a space ; and to the young student in chemistry, as well as the more matured one, we have no hesitation in strongly recommending the result of Mr. Gallo- way's labours." Morning Herald. "The plan of teaching adopted by Mr. Galloway differs very con- siderably from the plans hitherto laid down ; and the fact of a second edition of the work having been called for, is a proof that Mr. Galloway's system is highly appreciated by the public For interest and perspicuity, this is the most complete elementary treatise on chemistry which has yet appeared ; and we can confidently recom- mend its study to all those who wish to become acquainted with that valuable science." Morning Chronicle. " Enough has been said to show the scope and design of Mr. Gallo- way's ' First Step in Chemistry.' We recommend it to every beginner in the study of that science, as better fitted to smooth his first diffi- culties than any other work with which we are acquainted." Morning Post. 3 A MANUAL OP QUALITATIVE ANALYSIS. Third Edition, enlarged and improved. This work contains a new and simplified scheme of analysis. It is one of the TEXT-BOOKS in the examina- tion for certificates as Teachers of Science in the Depart- ment of Science and Art. " A most important feature of the system pursued consists in con- trasting the chief properties of the individual members of each group of substances, by placing a description of these properties in parallel columns ; thus the student, after experimentally demonstrating their behaviour with reagents, is enabled to devise for himself methods for the separation and individual detection of the different members of the group before him. We cannot but greatly admire this plan of teaching chemical analysis, which, whilst it calls into exercise the powers of observation, at the same time appeals to the judgment and reasoning faculties of the experimenter. The adoption of methods of study like this, cannot fail still further to increase the value of the natural sciences as instruments of intellectual discipline. We can confidently recom- mend Mr. Galloway's work as a valuable text-book, both to the regular laboratory student, and to the beginner who has not the advantage of professional instruction." The Philosophical Magazine. " This is really a valuable little book, we have not for a long time met with an introductory manual which so completely fulfils its inten- tion ..... The author before us has clearly ascertained all the obstacles lying in the way of the progress of the chemical student, and has used much judgment in his endeavours to obviate them." Aihe- " The author of this little treatise has wisely begun with the alphabet of his science ; and his explanation of terms, and his illustrations of simple phenomena, are very happily given. We cordially recommend this manual to every person desirous of making himself acquainted with the powers of chemistry." Literary Gazette. " We have before had to speak in terms of commendation on the first edition of Mr. Galloway's excellent work ..... On the whole, we repeat our conviction that no better guide can be had, for those who desire to prepare themselves for the wide and labour-rewarding field of chemical research, than Mr. Galloway's comprehensive ' Manual of Qualitative Analysis.'" Dublin Medical Press. " We see in these modifications of the usual process of analysis, as well as in the little manual in which they are described, much to com- mend them to favorable consideration." Pharmaceutical Journal. 4 " Mr. Galloway's book is a very good manual for the student of analytical chemistry, in which the author has pointed out and explained all those little difficulties which are so puzzling to the beginner, and has substituted a very simple scheme of analysis for the complex and cumbrous systems employed in some of the other treatises on Quali- tative Analysis. There are some points on which greater fulness would probably have been advantageous; these, however, may easily be extended in a future edition. The work, however, is a valuable addition to the treatises on the subject we already possess, and seems likely to find its way into our laboratories as a student's text-book." Monthly Journal of Medical Science. The following new work, by the same author, will shortly be published. THE SECOND STEP IN CHEMISTRY. The subjects treated of in this work will be taught in a series of progressive and practical exercises. The fol- lowing are a few of the subjects : The specific gravity of gases. The correction of gases for temperature, pressure, and tension of vapour. Combination by volume. Atomic volumes. The specific gravity of vapours. Application of the specific gravity of vapours to control the chemical analyses of substances. Unitary Notation. UNIV liL REC'D L