MEraCAL SCHOOL LUIBMAllSY Gift of the R.B. Cooke Company, Digitized by the Internet Archive in 2007 with funding from IVIicrosoft Corporation http://www.archive.org/details/briefintroquantanaOOmedirich BRIEF INTRODUCTION TO Qdalitative Analysis FOR USE IN INSTRUCTION IN CHEMICAL LABORATORIES. BY LUD WIG j^EDICUS, PROFESSOR OF CHEMISTRY IX THE UNIVERSITY AT WURZBURG. TRANSLATED FROM THE TENTH AND ELEVENTH GERMAN EDITION, WITH ADDITIONS. BY JOHN MARSHALL, PROFESSOR OF CHEMISTRY AND TOXICOLOGY IN THE DEPARTMENT OF MEDICTNE OF THE UNIVERSITY OF PENNSYLVANIA. M5 ' . FIFTH EDITION. [ D R. J. p. ^ Jj PITILADELPHTA AND LONDON: PRINTED BY J. B. LIPPINCOTT COMPANY. 1904. Copyright, 1891, by John Marshall. Copyright, 1903, by John Marshall. TRANSLATOR'S PREFACE. The merit of Medicus's "Qualitative Analysis," and its popularity, which is shown by its having already passed through five editions in the German language, led to this translation. The translator has taken the liberty of rearranging the elements in the first part of the book into groups, to corre- spond with their precipitation by group reagents, and also of adding two tables and amplifying the text to the extent of about forty pages. J. M. Philadelphia, 1892. PREFACE TO THE SECOND EDITION. In the second edition a number of additions and changes have been made in the parts treating of the methods of pro- cedure in the separation of the bases into groups. A table showing the solubility of many of the salts of the commonly occurring metals has also been added. J. M. Philadelphia, 1892. PREFACE TO THE FOURTH EDITION. Some chancres in the text have been made in the fourth edition, and an additional method for the separation of the members of the third group has been inserted. J. M. Philadelphia, 1896. 8 PREFACE TO THE FIFTH EDITION. In this edition, which is from the tenth and eleventh German edition, there have been incorporated some general introductory remarks on the theory and behavior of ions. Changes have been made in various parts of the book to correspond with the theory of ions. In the fourth edition two methods were given for the separation of the bases of the third and fifth groups. Experience in the laboratory has determined which of the two methods of separation seemed better adapted for use by students, and, therefore, in the case of both of these groups the method which seemed least adapted was omitted from the present edition. To the Appendix have been added two examples of the behavior of the rare elements contained in thorite and lead selenide. J. M. Philadelphia, 1903. CONTENTS. PAGE iNTROCrCTION 7 I. — Properties of the Bases 15 I. Group: Silver, Mercurous Salts, and Lead 15 II. Group : Mercuric Salts, Copper, Bismuth, Cadmium, Arsenic, Antimony, Tin, Gold, and Platinum 22 III. Group: Iron, Chromium, Aluminium 46 IV. Group : Manganese, Zinc, Nickel, and Cobalt 54 V. Group : Barium, Strontium, and Calcium 62 VI. Magnesium, Potassium, Sodium, Ammonium, and Lithium 66 II. — Properties of the Acids 73 I. Group : Sulphuric Acid, Hydrofluosilicic Acid 73 II. Group: Sulphurous Acid, Hyposulphurous Acid, Phos- phoric Acid, Boric Acid, Hydrofluoric Acid, Carbonic Acid, Silicic Acid, Chromic Acid, Arsenic Acid, Arseni- ous Acid 75 III. Group : Hydrochloric Acid, Hydrobromic Acid, Hydriodic Acid, Hydrocyanic Acid, Hydroferrocyanic Acid, Hydro- ferricyanic Acid, Sulphydric Acid, Nitrous Acid, Hypo- chlorous Acid 88 IV. Group : Nitric Acid, Chloric Acid 101 Appendix : Acetic Acid, Oxalic Acid, Tartaric Acid . . . 103 III. — Preliminary Examination 107 (a) Preliminary Tests in the Dry Way 107 1. Examination in the Reduction-Tube 107 2. Examination on Charcoal 110 3. Examination in the Flame 114 4. Examination by means of Microcosmic Salt, or Borax . .114 (J) Preliminary Tests for Acids 116 1* 5 6 PAGE IV.— Solution and Fusion 120 1. Dissolving Oxides and Salts 121 2. Dissolving Metals and Alloys 127 3. Sulphides of the Heavy Metals 128 4. Cyanides 128 5. Silicates 130 V. — Detection of the Bases in the Wet Way 133 Precipitation of the Different Groups 133 First Group 136 Second Group 139 Third Group 141 Fourth Group 143 Fifth Group 144 Sixth Group 145 Separation of the Bases contained in the Group Precipitates . . 146 Separation of the First Group 146 Separation of the Second Group 148 Separation of the Third Group 159 Separation of the Fourth Group 164 Separation of the Fifth Group 165 Separation of the Sixth Group 168 VI. — Examination for Acids 174 VH. — Appendix, Behavior of the Compounds of the Kare Ele- ments 191 Examples for Practice in Testing for the Rare Elements .... ]or> INTRODUCTION. When the chemist has to examine some compound or mixture of unknown composition, he may put the questions, What elements are contained in the former ? What are the component substances of the latter? The processes which he must use in order to obtain the answers to these ques- tions, i. e.y to ascertain the elements and component sub- stances, belong to the domain of Qualitative Analysis. Qualitative analysis aims only to determine what sub- stances are actually present, and leaves undetermined the amounts present. To ascertain the amounts is the province of Quantitative Analysis. The object of this book is to treat of the systematic pro- cedure for the detection of the bases and acids, together with the requisite preliminary tests and the methods of solution and decomposition. The systematic procedure, however, is preceded by a brief description of the behavior of the more important bases and acids. The behavior of the rarer ele- ments is briefly described and illustrated by examples in the Appendix. The atomic weights ^^^ are expressed first as compared with Oxygen = 16, and second, in parentheses, as compared with Hydrogen = 1. General Remarks. — All salts (the true salts, like KCl and KNO3, and also the hydroxyl salts or bases, as KOH, and the hydrogen salts or acids, as HCl) when in aque- ous solution are more or less separated into their ions. Sufficiently diluted solutions of potassium chloride, for ex- 4- ample, contain the ions ; i. e., potassium as cation (K or K'), International. 8 on the one hand, and chlorine as anion (CI or CV), on the other hand. It is these ions which enter into the reaction and are detected in most of the analytical changes. One is able to detect the presence of chlorine in potassium chlo- ride by means of argentic nitrate — i. e., by the silver ion which is present in the argentic nitrate solution — according to the equation : KCl 4- AgNOg -= AgCl + KNO3, i. e., CV + Ag • = AgCl or CI + Ag = AgCl. The silver cation combines with the chlorine anion to form insoluble argentic chloride. However, it is impossible in the same manner to detect the presence of chlorine in potassium chlorate (KCIO3), because the aqueous solution of this substance contains no chlorine ions, but contains the anion of chloric acid, the chlorate ion CIO3 or CIO3'. In this case the presence of chlorine may be detected by the silver ion if the potassium chlorate be fused previous to its being dissolved in water. In the fusion oxygen separates from the compound according to the equation : KC103=KCl-f03. On dissolving the fused mass in water and treating the solu- tion with argentic nitrate, argentic chloride is precipitated, showing that the solution must have contained chlorine ions. Only the ions show the characteristic reactions of salts in aqueous solution. The extent to which salts in aqueous solution are disso- ciated is variable : there are salts which in dilute solutions are practically completely dissociated — for example, potas- sium chloride ; there are also others which are only slightly dissociated — for example, mercuric chloride ; while practi- cally no dissociation whatever occurs with mercuric cyanide 9 in aqueous solution, the solution giving no response to the usual reactions for cyanogen and for merciury. Of the salts, the neutral salts are most strongly disso- ciated. In aqueous solution of average concentration most neutral salts are dissociated to the extent of over one-half of the content of the solution. The salts most strongly dis- sociated are those with univalent ions : salts with ions of greater valence are proportionately less readily dissociated into their ions. Greater variations with respect to the degree of dissociation occur in the case of the acids (hydro- gen salts) ; and accordingly diiferentiation may be made between strong, moderately strong, and weal?: acids ; likewise between strong and weak bases (hydroxyl salts). As to which particular ions for the time being come into play during analytical decompositions, mention will be made under the respective acids and bases : it will be observed, for example, that in conjunction with the mercurous ion Hg* there is the mercuric ion Hg * *, with the ferrous ion Fe * ' the ferric ion Fe * * * , and that the manganate ion of the salts of manganic acid (Mn04'') is distinct from the permanganate ion of the salts of permanganic acid (MnO^'). It will also be found that in most of the zinc reactions the zinc ion Zn ' ' takes part ; while, on the other hand, the zincate ion ZnOg" takes part in the formation of the soluble compound (a zin- cate) produced when zinc hydroxide is dissolved in an aqueous solution of an alkali. In the case of tartaric acid, for example, it will be found that the ion C^H^Og'' is in combination in neutral salts of that acid, while the ion C4H50g' is in combination in acid salts, and that the latter ion may be employed for the detection of the potassium ion. In potassium ferrocyanide the iron cannot be detected by the usual reactions for that element, because in this com- pound the iron is not present as ferrous ion, but as a ferro- 10 cyanogen ion ; a similarly constituted ion, ferricyanogen ion, is also present in potassium ferricyanide : these complex ions enter unchanged into the reactions occurring in aqueous solutions. Although of identical composition, they yield different reactions — for example, with iron salts : the ferro- cyanogen ion Fe(CN)g"" is entirely different from the ferri- cyanogen ion Fe(CN)g'''. Similar complex ions are recog- nized as existing in all so-called complex salts : in the so-called platinic chloride, or more correctly hydrochlor- platinic acid, there is present the ion PtClg" in combination with 2H' ; this ion forms with two potassium ions (2K') the difficultly soluble salt Kg* PtClg", potassium chlorplatinate. Ammonia, too, forms complex ions with many metals — for example, Cu(NH3)4", Zn(NH3)4**, and the solubility of argentic chloride in ammonium hydroxide likewise depends upon the formation of a complex ammonia ion. The electrolytic dissociation of compounds is in some cases incomplete ; as, for instance, with mercuric chloride, HgClg. Nevertheless, the total quantity of chlorine may be precipitated from an aqueous solution of mercuric chloride by means of argentic nitrate. How, then, is this possible ? Suppose the electrolytic dissociation of a salt be expressed — for simplicity using potassium chloride — by the equation : KCI7 > K-4-CF (in which the symbol of double arrows denotes that the reaction is reversible— i. e., it may follow the direction of either arrow), there will then be exhibited for this trans- formation an illustration of the Law of Mass-action : c 7 — ^^ constant, or ,- o.c ' b In this case a represents the number of undecomposed mole- cules of potassium chloride ; b, the number of potassium 11 cations; and c, the number of chlorine anions. Now, the law states that for all temperatures the relation of the undis- sociated portion («) to the dissociated portions (6, c) is con- stant ; there is always a definite condition of equilibrium. If, then, a solution of argentic nitrate is added to a solution of potassium chloride, insoluble argentic chloride is formed, in which each silver ion has combined with a chlorine ion. Hence, for the time being, the status of equilibrium corre- sponding to the foregoing mass-action equation 7 — = K, becomes disturbed, and may be restored only on condition that new ions of chlorine (and potassium) be dissociated from the potassium chloride. This then continually occurs upon further addition of argentic nitrate until practically all of the potassium chloride is dissociated and all the chlorine is precipitated as argentic chloride. In analogous manner the decomposition proceeds in the case of mercuric chloride ; along with the precipitation of the dissociated chlorine ion by the silver ion disturbances of equilibrium occur, and these must be continually equalized according to the equation : HgCi,^— ±Hg-*+cr + cr, in the direction of the upper arrow until practically all of the chlorine is precipitated by the silver. Without considering here similar cases (for instance, the precipitation of sulphides by means of hydrogen sulphide), there are other applications of the law of mass-action which may be discussed. In the precipitation of silver by chlorine, or chlorine by silver, advantage is taken of the insolubility of argentic chloride. However, no salt is wholly insoluble, and even in the precipitation of argentic chloride the clear liquid above the precipitate of argentic chloride is saturated with argentic 12 chloride ; the liquid contains dissolved argentic chloride together with chlorine ions and silver ions, because the dis- solveil argentic chloride is partly dissociated : AgCl = Ag*-f CI'. Here, too, the equation — =: K holds good. If the concen- 6.C tratiou of the silver ions in the clear liquid above the pre- cipitate be increased by the addition of argentic nitrate solu- tion, b is increased ; and consequently, since - — remains con- b.c stant, a is also increased — that is, inasmuch as AgCl is only very slightly soluble the precipitation is rendered more com- plete. Therefore, the solubility of a salt may be diminished by increasing the concentration of one of the ions of the salt in the solution — that is, by the addition of an excess of the salt wliich produced the precipitate. The same result is achieved in the precipitation of silver by means of hydro- chloric acid when an excess of the acid is employed, thus increasing the amount of chlorine ions in the liquid. Again, the law of mass-action comes into play in connec- tion, for instance, with the ferric salts, with the decompos- ing, hydrolytic action of water. The neutral ferric salts in aqueous solution are, to a certain extent, separated by hydrol- ysis, as, for example : FeCla + UOn- > FeC1.0H -f HCl ; Fe(C2H302)3+ 2HOH7 > Fe(aH.O.)(OH),+ 2UCJIfi,. Here, again, the reaction, as indicated by the double arrows, being reversible, complete decomposition of ferric acetate may be practically effected in the direction of the upper arrow by the addition of water and warming the liquid — that is, all of the iron will be precipitated as basic ferric 13 acetate. Conversely, in the direction of the lower arrow, the reaction occurs in cold solutions (and also by the addi- tion of an excess of acetic acid). In this case, therefore, the ferric solution employed must be very dilute and hot in order that the precipitation shall be complete, and must be filtered while hot, so that the precipitate shall not redissolve in the liquid. In this category also belongs the precipitation of basic salts from solutions of antimony and bismuth. The reaction of salts depends also, under certain con- ditions, upon hydrolysis. Hydrogen salts (acids) in general have an acid reaction and change blue litmus to red. The intensity of the reaction depends upon the strength of the acid — i, e.y the amount of acid which separates into its anion and hydrogen, the reaction being due to the hydrogen ion. Hydroxyl salts (bases) likewise exhibit stronger or weaker alkaline reaction — i. c, they change red litmus to blue, the alkaline reaction being due to the hydroxyl ion. Neutral salts in general have no reaction upon blue or red litmus ; if, however, they be hydrolytically separated, the reaction of the separated portions is produced, salts of the strong acids may yield an acid reaction, and salts of the strong bases may yield an alkaline reaction. The transpositions which occur in reactions may be ex- pressed by equations. They may be written to represent the transposition of ions, as, for example : PtCV' + K-::=K2PtCl«; or they may be written as ordinary aggregated equations, as, for example : H^PtClfi + 2KC1 = K^PtCle + 2HC1. For the sake of simphcity, and in conformity with previous editions, the aggregated equations will be retained in this edition. I. PROPERTIES OF THE BASES. FIRST GROUP. Metals precipitated as chlorides by HCl, hydrochloric acid : Silver, Mercury (in the mercurous condition), and Lead, (cations Ag ', Hg ', and Pb '). SILVER, As (ARGENTUM). Atomic weight, I07.93 (107.12); valence, 1. White, glittering metal ; specific gravity, 10.57 ; melting- point, 954° C. AgNO^j argentic nitrate, may be employed in making the tests, 1. HCl, hydrochloric acid, or a soluble chloride precipitates white, curdy AgCl, argentic chloride. At first the liquid becomes milky in appearance, due to the finely-divided par- ticles of precipitate in suspension, but on shaking or heating the liquid the precipitate collects in curdy masses and the liquid becomes clear. On exposure to sunlight the precipitate turns violet and finally black, due to the liberation of a slight quantity of chlorine. The precipitate is insoluble in HNO3, nitric acid, but dissolv'CS on agitation in NH^OH, ammonium hydroxide, due to the production of a complex argent-ammonia cation, with the formation of argent-ammonium chloride : AgCl + 2NH,OH -= Ag(NH3)2Cl + 2H2O, from which solution it may be reprecipitated by the addition of nitric acid : 15 16 Ag(NH3)2Cl + 2HNO3 - AgCl + 2NH,N03. It is also dissolved by KCN, potassium cyanide : AgCl + 2KCN =- KAg(CN)2 -f- KCl, and in the absence of free acid by 'Nix.^S.fl.^j sodium hyposul- phite (thiosulphate). 2. NaOH, sodium hydroxide, as well as KOH, potassium hydroxide, precipitates brownish-gray Agfi, argentic oxide, insoluble in excess of either reagent. 3. NH4OH, ammonium hydroxide (very dilute), added a drop at a time, precipitates brownish-gray AggO, argentic oxide, readily soluble in a slight excess of the reagent, due to the production of the complex argent-ammonia cation Ag(NH3)2*, which forms Ag(NH3)20H, argent-ammonium hydroxide : AgP + 4NH,0H = 2Ag(NH3)pH + SHp. 4. HgS, hydrogen sulphide, precipitates black AggS, argen- tic sulphide, insoluble in dilute acids and in (NH4)2S, ammo- nium sulphide. On being boiled with nitric acid the precipi- tate dissolves, with the formation of AgN03, argentic nitrate. Argentic sulphide is also soluble in potassium cyanide with the formation of potassium argentic cyanide, the compound of the complex anion Ag(CN)2' : Ag2S + 4KCN = 2KAg(CN)2 + K2S. 5. (NH4)2S, ammonium sulphide, precipitates black AggS, argentic sulphide, insoluble in dilute acids. 6. K2Cr04, potassium chromate, produces a purplish-red. t precipitate of AggCrO^, argentic chromate, soluble in am-' monium hydroxide and in nitric acid. 7. NagHPO^, sodium hydrogen phosphate, precipitates yellowish, flocculent AgaPO^, argentic phosphate, soluble in ammonium hydroxide and in nitric acid. 8. KI, potassium iodide, precipitates yellowish, curdy Agl, argentic iodide, insoluble in dilute nitric acid, and very sparingly soluble in ammonium hydroxide. 17 9. KCN, potassium cyanide, precipitates white, curdy AgCN, argentic cyanide, soluble in excess of the reagent and in ammonium hydroxide, insoluble in dilute nitric acid. 10. Compounds of silver fused with ^3^003, sodium car- bonate, in the reducing blowpipe flame on charcoal yield a white, ductile globule of metallic silver, usually without an incrustation. Occasionally a slight reddish-brown incrusta- tion of argentic oxide is produced on the globule. MERCURY, Hg (HYDRARGYRUM). Atomic weight, 200 (198.5) ; valence, I. Silver-white metal ; specific gravity, 13.59 ; solidifies at —39.4° C. and boils at 357.2° C. Mercury forms two series of compounds, named respec- tively mercurous and mercuric compounds. HggO, mercu- rous oxide, may be taken as the type of the mercurous, and HgO, mercuric oxide, as the type of the mercuric compounds. BEHAVIOR OF MERCURY IN THE MERCUROUS CONDITION. HgNO^y mercurous nitrate^ may be employed in making the tests. 1. HCl, hydrochloric acid, or a soluble chloride precipi- tates from solutions of mercurous salts white pulverulent HgCl, mercurous chloride (calomel), insoluble in water and in cold dilute acids, easily soluble in nitro-hydrochloric acid (aqua regia), with the formation of HgClg, mercuric chloride (corrosive sublimate) : 3HgCl + HNO, + 3HC1 = 3HgCl, -f NO + 2H2O. Ammonium hydroxide converts the HgCl, mercurous chlo- ride, into black NHgHggCl, dimercurous ammonium chlo- ride, insoluble in excess of the reagent : 2HgCl + 2NHPH = NH^Hg^Cl + NH.CI + 2H2O. 6 2* 18 2. NaOH, sodium hydroxide, or KOH, potassium hy- droxide, precipitates bh\ck HggO, mercurous oxide, insohible in excess of the reagent. 3. NH4OH, ammonium hydroxide, produces in solutions of mercurous salts a black precipitate containing nitrogen, depending in composition npon the mercurous salt employed and the conditions under which precipitation has occurred. For example, on adding ammonium hydroxide to a solution of HgNOg, mercurous nitrate, black NH2Hg^,N03, dimer- curous ammonium nitrate (mercurius solubilis Hahnemanni), is formed : 2HgN03 -f- 2NH4OH =-- NH^Hg^NO,, + NH.NOs + 2H2O. The precipitate is insoluble in excess of the reagent. 4. HgS, hydrogen sulphide, as well as (NH4)2S, ammonium sulphide, produces a black precipitate, consisting of a mix- ture of HgS, mercuric sulphide, and metallic mercury (not HggS, mercurous sulphide). On boiling this precipitate with concentrated nitric acid, a white compound composed of HgS, mercuric sulphide, and Hg(N03)2, mercuric nitrate [Hg3S2(N03)2],^^^ insoluble in nitric acid, is formed, while the liquid (filtrate) contains Hg(N03)2, mercuric nitrate. Yellow ammonium sulphide, (NH4)2S^, converts the mixture of HgS and metallic mercury wholly into HgS, mercuric sulphide. Yellow sodium sulphide, NagS^., as well as yellow potassium sulphide, K2SJ,, converts the mixture into HgS, mercuric sul- phide. The precipitate is soluble in nitro-hydrochloric acid. 5. SnCl2, stannous chloride,^^^ added in very small quantity to a concentrated solution of a mercurous salt, precipitates, precisely as any other soluble chloride, white HgCl, mercu- S-HgNO, ' SnCl2, stannous chloride, used as a reagent, always contains some free HCl, hydrochloric acid. 19 rous chloride. When SnClg is added in excess, a grayish precipitate of finely-divided metallic mercury is formed : SnCl^ -f 2HC1 + 2HgN03 = Hg2 + SnCl^ -f- 2HNO3. 6. KI, potassium iodide, added in small quantity to a solution of a mercurous salt, precipitates greenish flocculent Hgl, mercurous iodide, which in excess of the reagent dis- solves, with the separation of metallic mercury and the for- mation of soluble KaHgl^, potassium mercuric iodide ; therefore, when much potassium iodide is added to a dilute solution of a mercurous salt, there immediately appears a grayish precipitate of metallic mercury. 7. A drop or two of a solution of a mercurous salt placed on clean copper foil produces a discoloration, due to the de- position of metallic mercury, which upon being gently rubbed with the finger becomes silvery white and mirror-like in ap- pearance. On heating the foil over a flame the deposit dis- appears, due to the volatilization of the mercury. 8. Mercurous salts (with the exception of HgCl, mercu- rous chloride, which volatilizes unchanged), when heated in a small dry glass reduction -tube with dry Na2C03, sodium car- bonate, yield a sublimate consisting of globules of metallic mercury. LEAD, Pb (PLUMBUM). Atomic weight, 206.9 (205.35) ; valence, H. Bluish-white metal ; specific gravity, 11.3; melting-point, 334° C. Pb(C2H^02)2j pluinbic acetate J may be employed in making the tests, 1. HCl, hydrochloric acid, or a soluble chloride precipi- tates, iu solutions not too dilute, white flocculent (sometimes crystalline) PbC^, plumbic chloride; soluble at 12.5° C. in 20 135 parts of water, and at the boilinj^-point in 30 parts of water. On cooling the hot saturated aqueous sohition, the lead salt crystallizes in glistening rhombic needles. It is insoluble in ammonium hydroxide; soluble with difficulty in dilute acids; easily soluble in strong hydrochloric acid, particularly on heating. 2. NaOH, sodium hydroxide, as well as KOH, potassium hydroxide, precipitates white, flocculent Pb(0H)2, plumbic hydroxide (mixed with a slight quantity of basic lead salt), — insoluble in ammonium hydroxide; slightly soluble in water ; and easily soluble in excess of sodium or potassium hydroxide, with the formation of NajPbO^, sodium plum- bite,^*^ or KgPbOg, potassium plumbite (as a sodium or potassium compound of the anion Pb02"). Pb(OH)2 + 2NaOH== Na^PbO^ + 2H2O. 3. NH4OH, ammonium hydroxide, precipitates white, floc- culent Pb(OH)2, plumbic hydroxide, insoluble in excess of the reagent. 4. HgS, hydrogen sulphide, or (NH4)2S, ammonium sul- phide, precipitates black PbS, plumbic sulphide, insoluble in dilute acids. Boiling nitric acid converts it into Pb(N03)2, plumbic nitrate ; boiling fuming nitric acid oxidizes it to PbS04, plumbic sulphate, which is slightly soluble in nitric acid. On rapidly passing HgS, hydrogen sulphide, into a dilute solution of lead containing free hydrochloric acid, cinnabar-red PbgSClg, plumbic sulphochloride,^^^ is often pro- duced. By the further addition of HgS, the plumbic sulpho- chloride is converted into black PbS : 2PbCl2 + H2S = Pb^SCl^ + 2HC1 ; Pb^SCl^ + H^S = 2PbS -f- 2HC1. ^0-Na. ^Pb-01. 21 5. KgCrO^, potassium chromate, as well as K2Cr207, potas- sium dichromate, precipitates yellow PbCrO^, plumbic chro- mate (chrome-yellow), insoluble in water and in HC2H3O2, acetic acid, difficultly soluble in nitric acid, easily soluble in sodium or potassium hydroxide : PbCrO, + 4NaOH = Na2CrO, + Na2Pb02 + 2H2O. 6. H2SO4, sulphuric acid, precipitates white, pulverulent PbS04, plumbic sulphate, soluble in 22,800 parts of pure water at ordinary temperature, less soluble in water containing sulphuric acid, more soluble in the presence of hydrochloric or nitric acid. The precipitate is soluble in warm concentrated sulphuric acid, and separates on diluting the solution with water. It is easily soluble in NH4C2H3O2, ammonium acetate, and in the presence of ammonium hydroxide in (NH4)2C4H40g, neutral ammonium tartrate, and from these solutions the lead may be precipitated by K2Cr04, potassium chromate, as yellow PbCrO^, plumbic chromate. 7. KI, potassium iodide, produces in solutions not too dilute a yellow, pulverulent precipitate of Pbl2, plumbic iodide, soluble in 1235 parts of cold water and in 194 parts of boiling water. The plumbic iodide separates from a hot saturated solution, to which a small quantity of HC2H3O2, acetic acid, has been added, in glistening, golden-yellow, six- sided plates. 8. Na2HP04, sodium hydrogen phosphate, precipitates white, flocculent Pb3(P04)2, plumbic phosphate, soluble in nitric acid and in sodium hydroxide, insoluble in acetic acid. 9. Na2C03, sodium carbonate, precipitates in cold solutions neutral PbCOg, plumbic carbonate, and in boiling solutions basic carbonates, in which (PbC03)2,Pb(OH)2 predominates, soluble in an excess of the reagent. 10. Compounds of lead fused witli sodium carbonate in the reducing flame on charcoal yield a white, ductile globe of 22 metallic lead together with a yellow incrustation of PbO, plumbic oxide. SECOND GROUP. Metals precipitated from acid solutions as sulphides by HgS, hydrogen sulphide : Mercury (in the mercuric condition), Copper, Bismuth, Arsenic, Antimony, Tin, Cadmium, Gold, and Platinum, (cations Hg " , Cu ", Bi * * ', As " *, As , Sh"\ Sb , Sn", Sn"\ Cd * *, Au *, An* * *, and Pf , Pt • • • ', and the anions SnO/', SnO/', SnS,'^, ; SbOg''', SbO/'^ SbS/'',SbS/''; AsO/, ASO3''' AsO/'', AsS/'^ AsS/'')- The sulphides of arsenic, antimony, and tin are soluble in alkaline sulphides with the formation of sulpho-salts. These sulphides, namely, AS2S3, AsgSg, SbaSg, Sb2S5, and SnSg, enter into combination with sulpho-bases ; for example, ammonium sulphide, to form soluble sulpho-salts. The sulpho-salts are combinations of sulphur-containing anions with metallic ions. The behavior of the metals when heated with nitric acid, and the formation of oxides, are described under the heading "Dissolving of Metals and Alloys," page 127. Tin is soluble in hydrochloric acid; antimony is most readily dis- solved by nitro-hydrochloric acid. MERCURY, Hg (HYDRARGYRUM). Atomic weight, 200 (198.5) ; valence, 11. BEHAVIOR OF MERCURY IN THE MERCURIC CONDITION. HgCl2, mercuric chloride ^ or Hg(^N0^2y 'i^i^i'curic nitrate, may he employed in making the tests. 1. HgS, hydrogen sulphide, and also (NHJgS, ammonium sulphide, produce in solutions of mercuric salts a white pre- 23 cipitate of Hg3S2Cl2^'> or Hg3S2(N03)2/'^ which, on the further addition of the reagent, becomes yellow, then brown, and finally is converted into black HgS, mercuric sulphide : 3HgCl2 + 2H2S = Hg3S2Cl2 4- 4HC1 ; Hg3S2Cl2 + H2S = 3HgS + 2HC1. HgS is not dissolved by ammonium sulphide ; sometimes, however, on being treated with ammonium sulphide, it is converted from black HgS into red HgS (cinnabar). NagS, sodium sulphide, and KgS, potassium sulphide (par- ticularly in the presence of sodium or potassium hydroxide), dissolve mercuric sulphide, with the formation of Na2HgS2 ^^^ or K2HgS2<'\ salts of the anion HgS2'0- Mercuric sulphide is insoluble in boiling hydrochloric acid or in nitric acid, but by the continued action of hot concen- trated nitric acid it is converted into the white insoluble double salt Hg3S2(N03)2 (as in the case of HggS, mercurous sulphide). Nitro-hydrochloric acid dissolves mercuric sulphide, with the formation of HgClg, mercuric chloride : 3HgS + 6HC1 + 2HNO3 = 3HgCl2 + 2NO + 4H2O + S3. 2. NaOH, sodium hydroxide, and KOH, potassium hy- droxide, produce a brownish-red precipitate of a basic salt, which, upon further addition of the reagent, is converted into yellow HgO, mercuric oxide. As mercuric cyanide is not dissociated in aqueous solution, no precipitate is produced when NaOH or KOH is added to its aqueous solution. 3. NH4OH, ammonium hydroxide, produces a white pre- cipitate; thus, in a solution of HgCl2 mercuric chloride, white NHgHgCl, mercuric ammonium chloride, is produced : S_HgCl S_HgNO, ^^S-HgCl. ^^S-HgNOj. »Hg<«^'' 'Hg<^^ 24 HgCl^ + 2NH,OH = NH^HgCl + NH.Cl + 2H2O. 4. SnCla, stannous chloride, added in small quantities to mercuric chloride or to mercuric salts containing a very slight quantity of free hydrochloric acid, precipitates white HgCl, mercurous chloride, which, on the addition of more stannous chloride, is reduced to gray, finely-divided, metallic mercury (very delicate reaction). 5. KI, potassium iodide, precipitates red Hglg, mercuric iodide, soluble in excess of the reagent, with the formation of K2Hgl4, potassium mercuric iodide, the potassium com- pound of the anion Hgl/'. 6. A drop or two of a solution of a mercuric salt placed on clean copper foil produces a discoloration, due to the depo- sition of metallic mercury, as in the case of mercurous salts. On gently rubbing the spot it becomes mirror-like in appear- ance, and on heating the foil the spot disappears, due to the volatilization of the mercury. 7. Many of the mercuric salts, when heated in a glass re- duction-tube, sublime undecomposed, as, for example, HgClg, mercuric chloride (corrosive sublimate), while others yield sublimates which, because of an admixture of basic salts, are colored yellow. If the white (or yellow) sublimate be covered with dry sodium carbonate and again heated, red mercuric oxide is produced, which, on being more strongly heated, breaks up into metallic mercury and oxygen. COPPER, Cu (CUPRUM). Atomic weight, 63.6 (63.1 ) ; valence, I, II. Reddish metal ; specific gravity, 8.94 ; melting-point, 1054° C. CuSO^y cupric sulphate, may be employed in making the tests, 1 . HjS, hydrogen sulphide, or (NH4)2S, ammonium sulphide, precipitates black Cu8, cupric sulphide, insoluble in dilute 25 acids, insoluble in NagS, sodium sulphide, and in KgS, potas- sium sulphide. Ammonium sulphide (particularly the yellow ammonium sulphide) dissolves traces of the precipitate, with the formation of Cu,Sj(NR,),= {CuSU^}i,\S,. Boiling nitric acid dissolves CuS, with the formation of Cu(N03)2, cupric nitrate. It is also soluble in KCN, potassium cyanide, forming the potassium compound of the complex ion Cu(CN)2' : 2CuS + 4KCN = 2KCu(CN)2 + K^S^. The precipitate (CuS), when moist and exposed to the air, readily absorbs oxygen, with the formation of CuSO^, cupric sulphate. 2. NaOH, sodium hydroxide, or KOH, potassium hy- droxide, produces in cold solution a voluminous flocculent precipitate of bluish- white Cu(OH)2, cupric hydroxide, insol- uble in excess of the reagent, but easily soluble in ammonium hydroxide. The precipitate, on being boiled with excess of sodium or potassium hydroxide, loses water and forms black CuO, cupric oxide. On adding sodium or potassium hydrox- ide to copper solutions containing non-volatile organic acids, and particularly containing such organic substances as glucose, (grape sugar,) glycerin, etc., and agitating the liquid, the bluish-white cupric hydroxide at first produced is immediately dissolved, with the production of a deep-blue liquid. ^'^ 3. NH4OH, ammonium hydroxide, added in small quanti- ties, produces a bluish-white precipitate of a basic salt, which ^ This property is made use of in the preparation of an alkaline copper solution in which cupric sulphate solution is added to a strong sodium hydroxide solution containing KNaC^H^Og, potassium sodium tartrate (Rochelle salt), the whole forming a deep-blue liquid (Fehling's solution), which is employed as a reagent for the detection of glucose (grape sugar). On boiling Fehling's solution to which a solution containing glucose has been added, insoluble red Cu^O, cuprous f)xide, or yellow CuOH, cuprous hydroxide, separates. B 3 26 is soluble in an excess of the reagent, producing a deep-blue so- lution, due to the formation of Cu(NH3)4S04, cupric ammonium sulphate, a compound containing the complex cupric ammonia cation Cu(NH3)4 * * (very delicate reaction). Strongly acid solu- tions are not generally precipitated by ammonium hydroxide. 4. Na2HP04, sodium hydrogen phosphate, produces a bluish-green, flocculent precipitate of Cu3(P04)2, soluble in ammonium hydroxide. 5. K4Fe(CN)g, potassium ferrocyanide, precipitates brown- ish-red Cu2Fe(CN)g, cupric ferrocyanide (very delicate reac- tion). 6. KCN, potassium cyanide, added in excess to a neutral or ammoniacal solution of a salt of copper, produces a color- less solution of KCu(CN)2, potassium cuprous cyanide : Cu(N03)2 + 2KCN - Cu(CN)2 + 2KNO3; 2Cu(CN)2 + 2KCN = 2KCu(CN)2 + 2CN. The copper of this potassium salt of hydrocuprocyanic acid^'^ is not precipitated by hydrogen sulphide (correspond- ing to the iron in potassium ferro- and ferricyanide, which is not precipitated by the ordinary reagents). 7. KI, potassium iodide, produces in solutions to which ferrous sulphate has been added a white precipitate of Cul, cuprous iodide (a compound of the cation Cu ' ) : 2CUSO4 + 2FeS04+ 2KI -= 2CuI + Fe,{80,), -f K^SO^. 8. KCNS, potassium sulphocyanide, followed by the addi- tion of H2SO3, sulphurous acid, produces a white precipitate of CuCNS, cuprous sulphocyanide: 2CUSO4 -h 2KCNS + H2SO3 4 H2O = 2CuCNS + K^SO^ + 2H2SO4. ' HCu(CN)„ the complex cupro-cyanogen anion Cu(CN)''2 in combi- nation with the cation H ' . 27 9. A bright piece of iron (knife-blade) free from grease placed in a solution of copper is soon covered with a reddish deposit of metallic copper. 10. Compounds of copper mixed with sodium carbonate and strongly heated on charcoal in the reducing flame yield reddish spangles or globules of metallic copper. 11. Compounds of copper fused in a bead of borax, ^326^07, held in a loop of platinum wire in the oxidizing flame of the blowpipe, yield a bluish-green bead. Fused in a bead of sodium ammonium ])hosphate, NaNH^HPO^ (microcosmic salt), they yield, in the oxidizing flame, a bluish-green bead, which, when heated in the reducing flame, becomes reddish brown and opaque, due to the presence of separated metallic copper. The addition to the bead of a little metallic tin facilitates the reduction. BISMUTH, Bi. Atomic weight, 208.5 (206.9) ; valence. III. Reddish-white metal ; specific gravity, 9.82 ; melting-point, 270° C. Bi(NO^)^ or BiCl^ may he employed in making the tests. 1. HgS, hydrogen sulphide, or (^114)28, ammonium sul- phide, precipitates brownish-black BigSg, bismuth sulphide, insoluble in dilute acids and in ammonium sulphide. It is dissolved by boiling nitric acid, forming Bi(N03)3, bismuth nitrate. 2. NaOH, sodium hydroxide, KOH, potassium hydroxide, or NH4OH, ammonium hydroxide, precipitates white, amor- phous BiO-OH, bismuth hydroxide, insoluble in excess of the reagent. 3. KgCrO^, potassium chromate, precipitates yellow, crys- talline (BiO)2Cr04, basic bismuth chromate, insoluble in sodium hydroxide, soluble in nitric acid. 28 4. A clear solution of a bismuth salt, when poured into a large quantity of water (provided the bismuth solution does not contain too much free acid), produces a milky turbidity, due to the separation of a white basic salt of bismuth. BiClg, bis- muth chloride, yields BiOCl, bismuth oxychloride. Bi(N03)3, bismuth nitrate, yields first BiONOg, bismuth oxynitrate, and afterward, especially on heating the liquid, (BiO)2N030H/*^ A few drops of hydrochloric acid or of NH^Cl, ammonium chloride, added to a bismuth nitrate solution before it is poured into the water, cause the separation of the bismuth as BiOCl, bismuth oxychloride. The reaction with Bids is the more delicate. Tartaric acid does not interfere with this reaction. 5. SnClg, stannous chloride, dissolved in a solution of sodium hydroxide, produces a black precipitate of BiO, bis- muth oxide : 2Bi(N03)3 + Na2Sn02 + 6NaOH = 2BiO -f Na^SnOg + 6NaN03 + 3H2O. 6. Bismuth salts, mixed with sodium carbonate and heated in the reducing flame on charcoal, yield brittle globules of me- tallic bismuth and a yellow incrustation of BigOg, bismuthous oxide. ARSENIC, As (ARSENICUM). Atomic weight, 75. (74-. 4) ; valence, III, V. Steel-gray non-metal; specific gravity, 5.72 at 14° C. Arsenic forms two compounds with oxygen, — AS2O3, arsen- ious oxide or anhydride, and AS2O5, arsenic oxide or anhy- dride. 1 Bi— O— NOo II Bi— O— OH. 29 BEHAVIOR OF ARSENIC IN THE ARSENIOU6 CONDITION, — AS ARSENIOUS ACID. As^O^, arsenious oodde, which, when dissolved in water , forms H^AsO^, arsenious add, may be employed in making the- tests. 1. HgS, hydrogen sulphide, precipitates, from warm solu- tions acidulated with hydrochloric acid, yellow AsgSg, arseni- ous sulphide, which is soluble in ammonium sulphide and in (NH4)2C03, ammonium carbonate, but is insoluble in hydro- chloric acid. Dissolved in ordinary colorless ammonium sulphide it forms (NHJ3ASS3, ammonium sulpharsenite, a compound of the anion AsSg'^', and from this solution it may be reprecipitated by acids as AS2S3, arsenious sulphide : 2(NH,)3AsS3 + 6HC1 = As^S, + 6NH,C1 + 3H2S. Dissolved in yellow ammonium sulphide it forms (NH4)3AsS4, ammonium sulpharseniate, a compound of the anion AsS^'''. From this solution it is precipitated by acids as AS2S5, arsenic sulphide : AS2S3 + 3(NH,)2S -+82 = 2(NH,)3AsS4 ; 2(NH4)3AsS, + 6HC1 = AS2S5 + GNH^Cl + 3H2S. Ammonium carbonate dissolves AS2S3 with the formation of ammonium sulpharsenite and ammonium arsenite, the latter being a compound containing the anion AsOg' : , AS2S3 + 2(NH4)2C03 = (NH,)3AsS3 + NH4ASO2 + 2CO2. Acids reprecipitate it from this solution as AS2S3 : (NH,)3AsS3 + NH,As02 + 4HC1 = AS2S3 + 4NH,C1 + 2H2O. AS2S5, arsenic sulphide, dissolved in ammonium carbonate forms ammonium sulpharseniate and ammonium arseniate, the latter being a compound containing the anion AsO^''', or HAsO/' : 4AS2S5 + 12(NH,)2C03 + 3H2O - 5(NH,)3AsS, + 3(NH,)2HAsO, + 3NH,HC03 -f- 9CO2. 30 From this solution acids reprecipitate it as AS2S5 : 5(NH,)3AsS, + 3(NH,)2HAsO, + 21HC1 - 4AS2S5 -f 21NH,C1 + 12Hp. 2. AgNOa, argentic nitrate, added to an aqueous solution of arsenious acid and very dilute ammonium hydroxide added drop by drop produces a yellow curdy precipitate of Ag3As03, argentic arsenite, soluble in nitric acid with the formation of arsenious acid and argentic nitrate, and in am- monium hydroxide with the formation of complex argentic ammonia compounds. 3. CuSO^, cupric sulphate, added to an aqueous solution of arsenious acid, and very dilute ammonium hydroxide subsequently added drop by drop, produces a greenish floc- culent precipitate of CuHAsOg, cupric arsenite (Scheele's green), soluble in excess of ammonium hydroxide and in acids. If, however, sodium hydroxide, or potassium hydroxide in excess, instead of ammonium hydroxide, be added to the solution of arsenious acid, followed by the addition of a few drops of dilute cupric sulphate solution, a blue solution is produced from which on being heated reddish-brown CugO, cuprous oxide, will separate : NaaAsOa + 2CuSO, + 4NaOH = Cu^O + NaaAsO, + 2Na2SO, -h 2H2O. (Distinction from arsenic acid. The anion AsOg''' is con- verted into the anion AsO^'".) 4. Marshes Test. — When a few drops of a solution of ar- senious acid or a soluble arsenite are placed in an apparatus in which hydrogen is being evolved, the nascent hydrogen reduces the arsenical compound, and gaseous AsHg, hydrogen arsenide (arsenuretted hydrogen), is evolved with the free hydrogen : H3ASO3 + 3Zn -f 3H2SO4 = AsHg -f 3ZnSO, + 3H2O. When this mixture of hydrogen and hydrogen arsenide is 31 slowly passed through a glass tulxi heated to incipicDt red- ness, the hydrogen arsenide is decomposed, and the arsenic is deposited in the metallic state on the inner surface of the tube just beyond the heated part, as a lustrous brown, gray, or black coating. For this purpose the apparatus of Marsh, Fig. 1, is best adapted. Fig. 1. The apparatus consists of a small generating flask. A, a drying-tube, By^^^ containing small pieces of calcium chlo- ride, and a reduction-tube, (7, of hard glass, contracted at intervals. The metallic zinc and concentrated sulphuric acid (diluted with about four volumes of water) used in the operation must be free from arsenic, and therefore the following con- trol test should always be made to determine their purity. Zinc is placed in the flask A, and the drying-tube By to- gether with the reduction-tube C, is connected with the flask. Dilute sulphuric acid (1-4) is introduced through the funnel-tube until the zinc is covered. When, after some minutes,^^^ the evolved hydrogen has expelled the air from the * The drying-tube is sometimes dispensed with, and the reduction-tube connected directly with the delivery-tube of the flask. ^ If the action is slow, as is usually the case when pure zinc is em- ployed, it may be accelerated by the addition of a few drops of platinic chloride. Some observers, however, state that traces of arsenic may be retained by the precipitated platinum. 32 entire apparatus/*^ the flame of a Bunsen burner is applied to that part (at D) of the reduction-tube l^etvveen the contracted portion and the drying-tube, and the tube then heated to 'incipient redness. After the flame has been applied for sev- eral minutes, the contracted i)art of the reduction-tube is ex- amined for the presence of a brownish, gray, or black lus- trous deposit. Should such a de[)osit be found, it indicates that either the zinc or the sulphuric acid, or both, are con- taminated with arsenic and therefore unfit for use in the test. If no deposit is produced by the above test, the application of the heat is continued, and the solution containing arsenic is introduced into the flask, through the funnel-tube. After the lapse of some minutes the contracted part of the tube immediately beyond the flame is examined for the presence of a brownish, gray, or black deposit.^^^ A deposit having formed, the reduction-tube is detached (leaving it open at both ends, to permit the free access of air), inclined over a small flame, and gently heated at the part containing the deposit. The arsenic volatilizes, combines with oxygen, and deposits beyond the part heated, as AsgOg, arsenious oxide, in minute octahedral crystals.^^^ 1^ the gas is ignited as it escapes from the contracted end of the tube, and the temperature of the flame is reduced by holding a piece of cold porcelain in it, incomplete combustion ' Unless the air is expelled, an explosion, which may cause pei-sonal injury, is likely to occur when the flame is applied to the reduction- tube. 2 Antimony yields a deposit much resembling in color tliat produced by arsenic. The arsenical deposit is soluble in fresh NaOCl, sodium hypochlorite, whereas the antimony deposit is insoluble in that reagent. ^ The antimony deposit volatilizes and yields a white sublimate, which is generally amorphous, or consists of minute granules and opaque gran- ular masses; but it may occasionally contain a very small number of well-defined octahedral crystals of Sb^Oj, antinH.nious oxide. 33 occurs, and the arsenic is deposited on the porcelain in the metallic state in lustrous brown, gray, or black spots : 2ASH3 4- O3 == As2 + 3H2O. The arsenical deposit is soluble in fresh NaClO, sodium hy- pochlorite. (Distinction from antimony.) As2 + 3NaOCl + 3H2O = 2H3ASO3 + 3NaCl. As hydrogen arsenide is exceedingly poisonous, it should not be allowed to escape in the room, but should be decom- posed by igniting it as it escapes from the tube, or conducting it into a solution of argentic nitmte, whereby reduction of the silver salt occurs with the separation of metallic silver, the arsenic remaining in solution : AsHg + 6 AgN03 4- SU.O = 6Ag -f H3ASO3 + 6HNO3. 5. Beinsch's Test. — Metallic copper reduces arsenious oxide in acid solution to metallic arsenic, which is deposited on the copper as CugAsg, cupric arsenide. The arsenical solution is acidulated with about one-seventh of its volume of hydro- chloric acid, a clean piece of copper foil placed in the solution, and the whole heated and kept almost at the boiling-point for several minutes. In this hot solution the arsenic is deposited on the foil as a grayish or black coating. The foil is taken from the liquid and im- mersed several times in water to wash oif the hydrochloric acid, then pressed (without rubbing) between filter paper to free it from adherent moisture, and finally completely dried by being heated in a porcelain dish on a water- bath. It is then placed in a reduction-tube near the contracted part, the tube inclined, and the part containing the foil gently heated over a small flame (Fig. 2). 34 Volatilization of the arsenic and combination with oxygen take place, and octahedral crystals of AsgOg, arsenious oxide, are deposited in the cooler part of the tube. 6. Arsenious oxide heated in a reduction-tube sublimes unchanged, and is deposited in the cooler portion of the tube in octahedi-al crystals. Heated in a dry reduction-tube with charcoal, a grayish or black mirror-like deposit of metallic arsenic is formed in the cooler part of the tube : AsA + Q^^As^ + SCO. 7. Arsenious oxide or compounds of arsenic heated on charcoal in the reducing flame produce a garlic-like odor. (The arsenious oxide is first reduced to metallic arsenic, which volatilizes and combines with oxygen to form AS2O3, which sometimes collects as an incrustation on the charcoal.) 8. Arsenious oxide or an arsenite, mixed with six times its bulk of a dry mixture consisting of equal parts of sodium carbonate and potassium cyanide and heated in a reduction- tube, is reduced, with the formation of a ])lack glistening sublimate of metallic arsenic in the cool part of the tube : AsPs + 3KCN = As, + 3KCNO. BEHAVIOR OF ARSENIC IN THE ARSENIC CONDITION, — AS ARSENIC ACID. AS2O5, arsenic oxide, which forms H^AsO^, arsenic acidy when dissolved in water, or Na^AsO^, sodium arseniate, may be employed in making the tests. 1. HgS, hydrogen sulphide, conducted into the solution does not at first produce a precipitate in cold solutions, but reduces the arsenic acid to arsenious acid. Heating the solu- tion facilitates the reduction : H3ASO, -f H^S = H3ASO., -I- HP -[- S. Continuing the addition of hydrogen sulphide, AS2S3, arsen- ious sulphide, is precipitated : 2H3ASO3 + 3H2S = AS2S3 -j- 6H2O. 35 The final precipitate is therefore a mixture of arsenious sul- phide and sulphur (AS2S3 + S). If the acidulated arsenic acid solution be heated to 70° C. and hydrogen sulphide be conducted into the solution, yellow AsgSg, arsenic sulphide, will at once be precipitated. 2. AgNOg, argentic nitrate, added to a solution of arsenic acid which has been exactly neutralized with ammonium hydroxide, or to an arseniate, precipitates reddish-brown AggAsO^, argentic arseniate, soluble in nitric acid and in ammonium hydroxide : H3ASO, + 3AgN03 -h 3NH,OH = AggAsO, + 3NH,N03 -f 3H2O. 3. CUSO4, cupric sulphate, added to a solution of arsenic acid, followed by the addition of ammonium hydroxide drop by drop, or to an arseniate, produces a bluish-green precipi- tate of CuHAs04, cupric arseniate, soluble in an excess of ammonium hydroxide and in acids. 4. The behavior of arsenic acid in Marsh's test or Reinsch's test, in the reduction-tube, mixed with charcoal, and on char- coal itself is identical with arsenious acid. 5. MgSO^, magnesium sulphate, added to a solution of ar- senic acid or an arseniate, followed by the addition of NH4CI, ammonium chloride,^^^ and ammonium hydroxide (magnesia mixture), precipitates white, crystalline MgNH4As04 + 6H2O, ammonium magnesium arseniate : H3ASO4 -h MgSO^ + 3NH4OH = MgNH^AsO^ + (NH4)2S04 -f 3H2O. In concentrated solutions the precipitate forms immediately, and in dilute solutions gradually ; but is always perceptibly crystalline. It is soluble in 15,293 parts of cold water and 1 The addition of ammoniuin chloride is for the purpose of preventing the precipitation of magnesium hydroxide. 36 less soluble in water containing ammonium hydroxide ; easily soluble in dilute acids, from which solutions it is reprecipitated by the addition of ammonium hydroxide. 6. NH4HM0O4, ammonium molybdate, added to a solution of ai'senic acid rather strongly acidulated with nitric acid, and the whole gently warmed, produces a yellow i)recipitatc of, possibly, (NH4)3As04(Mo03)i2, ammonium molybdoarseni- ate, soluble in ammonium hydroxide and reprecipitated from this solution by nitric acid. The ])resence of hydrochloric acid or of chlorides interferes with the delicacy of the reaction. 7. KI, potassium iodide, added to a solution of arsenic acid acidulated with hydrochloric acid, is decomposed with the liberation of free iodine : H3ASO, + 2KI + 2HC1 =- 21 -h H3ASO3 f 2KC1 + H^O. On agitating the liquid with carbon disulphide or with chlo- roform the iodine will be extracted, imparting a pinkish- violet color to the carbon disulphide or chloroform. 8. To detect arsenic acid in the presence of arsenious acid (providing the compounds are soluble in water) their behavior with magnesia mixture (compare above, 5) is made use of; arsenious acid produces no precipitate with magnesia mixture. In case the compound is insoluble in water, it is dissolved in hydrochloric acid, and the arsenious acid is precipitated in cold solution with hydrogen sulphide. The resulting arseni- ous sulphide is removed by filtration, the filtrate is warmed, and hydrogen sulphide again conducted into the liquid. The production of a precipitate indicates the presence of arsenic acid. ANTIMONY, Sb (STIBIUM). Atomic weight, 120.2 (119.3) ; valence, III, V. Silvery- white metal ; specific gravity 6.7 ; melting-point, 425° C. 37 Antimony forms two typical compounds with oxygen, — Sb203, antimonious oxide, and SbgO^, antimonic oxide. BEHAVIOR OF ANTIMONY IN THE ANTIMONIOUS CX)NDITION. SbCl.^, antimonious chloride, may be employed in making the 1 . HgS, hydrogen sulphide, produces in solutions of anti- monious salts which are not too strongly acidulated an omnge- red precipitate of Sb2S3, antimonious sulphide, insoluble in dilute acids, soluble in concentrated hydrochloric acid (without the separation of sulphur) and also in ammonium sulphide and in sodium or potassium sulphide; insoluble in ammonium carbonate (distinction from arsenic). When dissolved in colorless ammonium sulphide it forms (NH4)3SbS3, ammonium sulphantimonite, a compound of the anion SbSa"' : Sb^Sg + 3(NH,)2S == 2(NH,)3SbS3 ; and when dissolved in yellow ammonium sulphide it forms (NH^)3SbS4, ammonium sulphantimonate, a compound of the anion SbS/^' : Sb^Sj + 3(NH,)2S + 82 = 2(NH,)3SbS,. Hydrochloric acid precipitates from the sulphantimonite so- lution Sb2S3, and from the sulphantimonate solution SbgS^ : 2(NH,)3SbS3 + 6HC1 = Sb2S3 + 6NH,C1 + 3H2S ; 2(NH4)3SbS, + 6HC1 = ^\^, + 6NH,C1 + 3H2S. 2. NaOH, sodium hydroxide, as well as KOH, potassium hydroxide, produces a white voluminous precipitate of SbO-OH, antimonious hydroxide, readily soluble in an ex- cess of the reagent, forming NaSbOg, sodium antimonite, or KSb02, potassium antimonite, compounds of the anion Sb02'. On being boiled in the alkaline liquid the pre- cipitate of SbO-OH is converted into Sb203, antimonious oxide. 3. NH4OH, ammonium hydroxide, precipitates white 4 38 SbO-OH, antirnonious hydroxide, insoluble in an excess of the reagent. Tartaric acid prevents the precipitation. 4. On pouring a solution of an antirnonious salt, as, for example, SbClg, antirnonious chloride, into a large quantity of water, a white precipitate of a mixture of SbOCl, anti- rnonious oxychloride, and Sb405Cl2 is produced : SbClg + HP = SbOCl + 2HC1 ; 4SbCl3 + 5H2O = SbAClz + lOHCl. A milkiness is produced in water by even the slightest quan- tity of antirnonious chloride. Tartaric acid prevents the pre- cipitation by dissolving the precipitate with the formation of a complex compound : SbOCl + H^C.HA = (SbO)HC4HA + HCl. 5. Soluble salts of antimony, placed in a flask in which hydrogen is being generated from zinc and dilute sulphuric acid (1-4), are decomposed, with the formation of gaseous SbHg, antimonious hydride (antimonuretted hydrogen) : 2SbCl3 + Zufi + 3H2SO4 = 2SbH3 + 3ZnCl2 + SZnSO^. The apparatus of Marsh is best adapted for this purpose, and the same precautions as given under arsenic should be ob- served. (See page 31 .) On heating the reduction-tube of Marsh's apparatus to dull redness and slowly passing antimonious hydride through the tube, the compound is reduced, and a lustrous brown or black deposit of metallic antimony is formed in the part of the tube before the flame, or on both sides of the flame. If the gas be ignited as it escapes from the contracted end of the tube and the temperature of the flame reduced by holding a piece of cold porcelain in it, incomplete combustion will occur, and the antimony will be deposited on the porcelain in dull brownish or black spots : 2SbH3-hO,=-Sb2+3H20. 39 The deposit of metallic antimony is insoluble in fresh sodium hypochlorite (distinction from arsenic). The deposit of metallic antimony in the tube, on being gently heated over a small flame with free access of air/^^ vol- atilizes, combines with oxygen, and condenses in the cooler part of the tube as white SbjOg, antimonious oxide. The sublimate is usually entirely amorphous, but occasionally may contain octahedral crystals of antimonious oxide. 6. Compounds of antimony in acid solution are reduced on being heated with a piece of bright copper foil, with the deposition of the antimony as a grayish or black coating upon the copper. On washing the foil with water, drying, and gently heating it in a small reduction-tube over a flame, the antimony volatilizes, combines with oxygen, and deposits in the cooler part of the tube as amorphous SbgOg, antimoni- ous oxide, which may sometimes contain octahedral crystals of antimonious oxide. (See Reinsch's Test for Arsenic, page 33.) 7. Metallic zinc reduces antimonious solutions, the anti- mony separating as a black powder. If a drop of the anti- monious solution is placed on a piece of platinum foil and a small fragment of zinc is placed in the solution, the antimony is deposited on the foil as a brown or black adherent coating, insoluble in hydrochloric acid : 2SbCl3 + Zug = Sb2 + 3ZnCl2. 8. Compounds of antimony, when heated in the reducing flame with sodium carbonate on charcoal, yield a white, brittle globule of metallic antimony, usually coated with a white incrustation of SbgOg, antimonious oxide. ^ As in Marsh's test for arsenic. (See page 32.) 40 BEHAVIOR OF ANTIMONY IN THE ANTIMONIC CONDITION. SbClji, antimonic chlonde, may be employed in mciking the 1. HgS, hydrogen sulphide, precipitates from acid sohi- tions orange-red SbjSg, antimonic sulphide, insoluble in dilute acids and in ammonium carbonate, soluble in concentrated hydrochloric acid, forming SbClg, antimonious chloride (with the separation of sulphur) : Sh,S, + 6HC1 = 2SbCl3 -h 3H2S + S2, and soluble in ammonium sulphide and in sodium or potas- sium sulphide, with the formation or* sulphantimonates : Sb^Sg + S(NH,\S = 2(NH,)3SbS,. 2. The behavior of antimonic compounds is similar to that of antimonious compounds in respect to the tests with zinc and dilute sulphuric acid, copper foil and hydrochloric acid, and platinum foil and zinc. 3. To detect antimonious compounds in the presence of antimonic compounds, advantage is taken of the behavior of an alkaline solution of antimonious oxide with a silver solu- tion. On adding argentic nitrate to the alkaline solution and gently heating it, a precipitate composed of AggO, argen- tic oxide, and metallic silver is formed. Ammonium hy- droxide has the property of dissolving only the argentic oxide, leaving the metallic silver undissolved : KaSbOa + Ag^O =- KSbOg + Ag2. After washing the precipitate and then treating it with ammonium hydroxide, metallic silver will remain undis- solved in case an antimonious compound was originally present. To detect antimonic compounds in the presence of anti- monious compounds, the alkaline solution is acidulated with 41 hydrochloric acid, KI, potassium iodide, added, and then boiled ; in the presence of an antimonic; compound iodine is separated : SbCl^ + 2HI -= SbCls H- 2HC1 -\- I,. TIN, Sn (STANNUM). Atomic weight, 119. (118.1) ; valence, II, IV. Bluish -white metal ; specific gravity, 7.29 ; melting-point, 235° C. Tin forms two series of compounds, named respectively stannous and stannic compounds. SnO, stannous oxide, may be taken as the type of the stannous, and SnOg as the type of the stannic compounds. BEHAVIOR OF TIN IN THE STANNOUS CONDITION. SnCl^f stannous chloride^ may be employed in making the tests, 1. HgS, hydrogen sulphide (also ammonium sulphide), precipitates dark-brown SnS, stannous sulphide, insoluble in colorless ammonium sulphide, but easily soluble in yellow ammonium sulphide, with the formation of ammonium sulphostannate, (NH4)2SnS3, a compound containing the anion SnSg'' : SnS + (NH,)2S2 = (NH,).SnS3. From this solution acids precipitate yellow SnSg, stannic sul- phide : (NH4)2SnS3 + 2HC1 = SnS^ + 2NH,C1 + H^S. 2. NaOH, sodium hydroxide, as well as KOH, potassium hydroxide, precipitates Avhite Sn(OH)2, stannous hydroxide, soluble in excess of the cold reagent, with the formation of a compound containing the anion Sn02". On boiling a solu- tion of a stannous salt to which an insufficient quantity of sodium or potassium hydroxide has been added, the Sn(OH)2 is converted into black SnO, stannous oxide. 4* 42 3. NH^OH, ammonium hydroxide, precipitates white Sn(OH)2, stannous hydroxide, insoluble in excess of the reagent. 4. HgClg, mercuric chloride, added to an excess of SnClg, stannous chloride, j)roduces a grayisli ])recipitate of finely- divided metallic mercury : HgOa + SnClg = Hg -f- SnCl,. If, on the other hand, an excess of mercuric chloride be added to a stannous chloride solution, a white precipitate of HgCl, mercurous chloride, will be formed : 2HgCl2 + SnCl. = 2HgCl + SnCl, (a very delicate test and a means of distinguishing between stannous and stannic salts). 5. A fragment of metallic zinc placed in a solution of stannous chloride precipitates grayish metallic tin : SnCl2 + Zn = ZnCla + Sn. If performed on platinum foil (see 7 under Antimony, page 39) the tin whicli separates does not adhere to the platinum foil as a black coating (distinction from antimony). 6. Both stannous salts and stannic salts, when fused wdth sodium carbonate, or with a mixture of sodium carbonate and l)otassium cyanide, in the reducing flame on charcoal, yield white, ductile globules of metallic tin together with a slight incrustation of SnOg, stannic oxide. Stannic oxide moistened with Co(N03)2, cobaltous nitrate, and heated in the blowpipe- flame becomes bluish green in color. BEHAVIOR OF TIN IN THE STANNIC CONDITION. SnCl^j stannic chloride^ may be employed in making the tests. 1 . HgS, hydrogen sulphide, precipitates yellow SnSg, stannic sulphide, insoluble in ammonium carbonate, but soluble in 43 colorless and also in yellow ammonium sulphide, with the formation of (NH4)2SuS3, ammonium sulphostannate, a com- pound of the anion SnSg''. From this solution SnS^ is reprecipitated on the addition of acids. SnS2 is soluble in concentrated hydrochloric acid. 2. NaOH, sodium hydroxide, KOH, potassium hydroxide, or NH4OH, ammonium hydroxide, produces in sohitions of stannic salts white precipitates. The precipitate produced in hydrochloric acid solutions of ordinary SnOg, stannic oxide, is Sn(0H)4, stannic hydroxide, and is easily soluble in dihite sodium or potassium hydroxide, forming compounds contain- ing the anion Sn03" ; that produced in solutions of meta- stannic acid is metastannic hydroxide, only slightly soluble in excess of the reagent. 3. Na2S04, sodium sulphate, or NH^NOg, ammonium ni- trate, in saturated solution, added in excess to a hydrochloric acid solution of stannic oxide, precipitates the tin, particularly on the application of heat, as white Sn(OH)4, stannic hydrox- ide, or as (Sn(OH)4)„, metastannic hydroxide : SnCl, + 4Na2SO, + 4H2O = Sn(OH), + 4NaCl -f- 4NaHSO, ; SnCl^ + 4NH,N03 + 4H20=Sn(OH), + 4NH,C1 + 4HNO3. (Distinction from stannous salts.) 4. Metallic zinc reduces stannic salts in solution to metallic tin in the same manner as it reduces stannous salts. (See 5, page 42). CADMIUM, Cd. Atomic weight, 112.4- (111.6) ; valence, 11. Bluish-white metal ; specific gravity, 8.54 ; melting-point, 315° C. CdSO^y cadmium sulphate^ may be employed in making the tests. 1. H2S, hydrogen sulphide, or ammonium sulphide, pro- 44 duces a yellow precipitate of CdS, cadmium sulphide, in- soluble in dilute acids, in ammonium and sodium sulphides, and in potassium cyanide, soluble in boiling nitric acid, with the formation of Cd(N03)2, cadmium nitrate. 2. NaOH, sodium hydroxide, as well as KOH, potassium hydroxide, precipitates white Cd(OH)2, cadmium hydroxide, insoluble in excess of the reagent. 3. NH4OH, ammonium hydroxide, precipitates white Cd(OH)2, cadmium hydroxide, soluble in excess of the re- agent, probably with the formation of a colorless double salt of cadmium and ammonium, Cd(NH3)4S04, containing the complex cation Cd(NH3)4' '. 4. KCN, potassium cyanide, added to a neutral or ammo- niacal solution of a cadmium salt, precipitates wliite Cd(CN)2, cadmium cyanide, which is soluble in an excess of potassium cyanide, forming a colorless solution of K2Cd(CN)^ : CdSO, -f- 2KCN = Cd(CN)2 + K^SO^ ; Cd(CN)2 + 2KCN -= K2Cd(CN),. Hydrogen sulphide precipitates from this solution yellow CdS, cadmium sulphide. (This cyanide is the potassium compound of the anion Cd(CN)/' ; cadmium ions are dissociated from it, so that, in contrast with copper, the cadmium is precipitated.) 5. Cadmium compounds mixed with sodium carbonate and fused in the reducing flame on charcoal, yield yellow to brown incrustations of CdO, cadmium oxide. GOLD, Au (AURUM). Atomic weight, 197.2 (195.7) ; valence, I, MF. Yellow metal; specific gravity, 19.26; melting-point, 1035° C. AuCl^^ amnc Ghloride, may he employed in mahing the fesfa. 1. HgS, hydrogen sulphide, produces in a cold solution of 45 auric chloride a black precipitate of AugSg, auric sulphide, soluble in ammonium sulphide. From hot auric chloride solutions hydrogen sulphide pre- cipitates brownish metallic gold : 8 AUCI3 -f 3H2S + 1 2H2O = Aug + 24HC1 -f 3H2SO4. 2. NaOH, sodium hydroxide, and also potassium hydrox- ide precipitate reddish-yellow, amorphous Au(OH)3, auric hydroxide, soluble in excess of the reagent. 3. NH4OH, ammonium hydroxide, produces a reddish- yellow precipitate of (NH3)2Au203, ammonium aurate (fulmi- nating gold) : 2AUCI3 + 8NH,OH = (NH3)2Au A + 6NH,C1 + SH^O. 4. FeSO^, ferrous sulphate, precipitates in the presence of a free mineral acid, even in the cold, but especially on heating, metallic gold, brownish in color because of its finely-divided condition : 2AUCI3 + eFeSO^ = Au2 +2FeCl3+ 2Fe2(S04)3. 5. H2C2^4, oxalic acid, also precipitates metallic gold from auric chloride solutions : 2AUCI3 + 3H2C2O, -= Au2 + 6HC1 + 6CO2. The precipitation proceeds slowly, but is complete. WaVm- ing the solution facilitates the reduction. The presence of considerable free mineral acid interferes with the precipitation. 6. SnClg, stannous chloride, especially in very dilute solu- tion, added to auric chloride solutions, produces a purplish- red coloration or a purplish-red precipitate (purple of Cassius), consisting probably of a mixture of finely-divided gold and stannic oxide. 7. Compounds of gold fused with sodium carbonate or with bomx on charcoal yield yellow, glistening, ductile spangles of metallic gold. 46 PLATINUM, Pt. Atomic weight, 194-.8 (193.3) ; valence, II, IV. Tin-white metal; specific gravity, 21.46; melting-point, 1775° C. H2PtClQy hydrochlorplaiiniG acid (or PtCl^, platmic chlo- ride), may be employed in makiyig the tests, 1. HgS, hydrogen sulphide, produces in cold platinic chlo- ride solutions a brownish coloration, but after some time has elapsed a brownish-black precipitate of PtSg, platinic sulphide, separates. The precipitate appears at once on heating the solution. The precipitate is insoluble in hydrochloric acid and also in nitric acid, but soluble in nitro-hydrochloric acid (aqua regia) and also in ammonium sulphide. 2. KNO3, potassium nitrate, to which a drop of hydro- chloric acid has been added, or potassium chloride, added to a concentrated solution of platinic chloride, produces a yellow crystalline precipitate of KgPtCIg, potassium chlorplatinate, slightly soluble in water, insoluble in alcohol. The test is best made in a watch-glass, the liquid being stirred with a glass rod. Addition of alcohol facilitates precipitation. 3. NH4CI, ammonium chloride, produces a yellow crystal- line precipitate of (NH4)2PtClg, ammonium chlorplatinate, slightly soluble in water, insoluble in alcohol. This test is best made in a watch-glass as in 2, above. 4. Compounds of platinum heated in the reducing flame are reduced to spongy metallic platinum. THIRD GROUP. Metals precipitated as hydroxides by NH/)H, ammonium liydroxide : Iron, Aluminium, and Chromium (cations Fe' ', rV", Ar*-, Cr'--). 47 The members of this group, with the exception of iron, are also precipitated as hydroxides by (SH^^S, ammonium sul- phide, but are not precipitated from neutral or acid solutions by hydrogen sulphide : AICI3 + 3NHPH = Al(OH)3 -h 3NH,C1. 2CrCl3+ 3(NH,)2S + BHp = 2Cr(OH)3-j- SH^S + 6NH,C1. Chromic hydroxide is perceptibly soluble in cold anmio- nium hydroxide (imparting a reddish tint to the liquid), form- ing complex chromium ammonia hydroxides — combinations of the cation Cr(NH3)g* * * — which may be decomposed by boiling. Recently precipitated moist BaCOg, barium carbonate, also precipitates, even from cold solutions, the members of this group as hydroxides (together with basic salts) : 2AICI3 + 3BaC03 + 3H2O - 2Al(OH)3 + BaCl^ + 3CO2. The presence of tartaric acid, citric acid, and other organic substances prevents or at least retards the precipitation of the members of this group as hydroxides by the formation of complex compounds. IRON, Fe (FERRUM). Atomic weight, 55.9 (55.5) ; valence, H, III. Silver-white metal ; specific gravity, 7.84. Iron forms two typical series of compounds, named re- spectively ferrous and ferric compounds. FeO, ferrous oxide, may be taken as the type of the ferrous compounds, and FcgOg as the type of the ferric compounds. BEHAVIOR OF IRON IN THE FERROUS CONDITION. FeSO^j ferrous sulphate, may be employed in making the 1. NH^OH, NaOH, or KOH precipitates, in solutions of ferrous salts which are free from dissolved air, white 48 Fe(OH)2, ferrous hydroxide, which, by the absorption of oxygen, quickly changes in color to green, black, and finally to reddish brown. The presence of ammonium chloride or sulphate retards the precipitation, therefore it is incom- plete — due to the formation of (NH^)2FeCl4, as in the case of magnesium ; nevertheless, from these alkaline solutions, in consequence of the absorption of oxygen, black ferrous hydroxide and reddish-brown ferric hydroxide gradually separate. 2. (NHJgS precipitates black FeS, ferrous sulphide, insol- uble in excess of the reagent, easily soluble in hydrochloric acid and in nitric acid. Very dilute ferrous solutions are colored green by ammonium sulphide. Moist ferrous sul- phide is oxidized on exposure to the air and changes to reddish-brown Fe20(S04)2, basic ferric sulphate. 3. K4Fe(CN)g, potassium ferrocyanide, produces in ferrous solutions free from ferric salts a white precipitate, which quickly changes to bluish-white K2Fe(Fe(CN)6), potassium ferrous ferrocyanide (Everett's salt), insoluble in acids. On exposure to air the bluish-white precipitate gradually absorbs oxygen and changes to blue Fe^(Fe(CN)6)3, ferric ferrocyanide (Prussian blue) : 4K2Fe(Fe(CN)e) + O2 -f 4HC1 = Fe,(Fe(CN)e)3 + K,Fe(CN)e + 4KC1 + 2H2O. 4. K3Fe(CN)g, potassium ferricyanide, precipitates dark- blue Fe3(Fe(CN)6)2, ferrous ferricyanide (Turnbull's blue), insoluble in acids. 5. KCNS, potassium sulphocyanide, does not produce a claret-red coloration in solutions of ferrous salts free from ferric salts. (Distinction from ferric salts.) 6. Ferrous salts when warmed with nitric acid are oxi- dized to ferric salts, in which Fe' * is converted into Fe' * ', BFeSO^ -h 2HNO3 + 3H2SO, -- 3Fe2(SO J3 + 2NO + 4H2O. 49 7. Ferrous compounds and also ferric compounds when ignited with sodium carbonate on charcoal yield a black magnetic oxide. 8. All compounds of iron when fused in the oxidizing flame in a bead of borax yield while hot a yellow or reddish- brown bead, which on cooling becomes lighter in color or colorless. Fused in the reducing flame the bead becomes bottle-green in color. BEHAVIOR OF IRON IN THE FERRIC CONDITION. FeCl^jfei^ric chloride, may be employed in making the tests. 1. NH4OH, NaOH, or KOH, produces in solutions of ferric salts a voluminous reddish-brown precipitate of Fe(OH)3, ferric hydroxide, insoluble in excess of the reagent and in ammonium salts. 2. (XH4)2S precipitates black FeS together with free sul- phur : 2FeCl3 + 3(NH4)2S = 2FeS + S + 6NH,C1. 3. K4Fe(CN)g, potassium ferrocyanide, precipitates, even in exceedingly dilute solutions of ferric salts, blue Fe4(Fe(CN)g)3, ferric ferrocyanide (Prussian blue), insoluble in acids, but decomposed by alkalies. 4. K3Fe(CN)g, potassium ferricyanide, does not produce a precipitate in ferric solutions, but imparts a green or brown coloration to the solution. (See 3, page 96.) 5. KCNS, potassium sulphocyanide, produces an intense claret-red colomtion in ferric solutions, due to the formation of soluble Fe(CNS)3, ferric sulphocyanide. In exceedingly dilute solutions the color is pale red. On agitating the solu- tion with ether the ferric sulphocyanide will be extracted from the aqueous solution because the sulphocyanide is not dissociated. HgClg, mercuric chloride, destroys the colora- tion, soluble Hg(CNS)2 being formed. 50 6. NaC2H302, sodium acetate, added to a solution of a ferric salt which contains little free mineral acid, colors the solution dark red, due to the formation of Fe(C2H302)3, ferric acetate, which on boiling the sufficiently diluted solution hydrolyzes and separates with part of the acetic acid as a brownish-red flocculent precipitate of Fe(OH)2(C2H302), basic ferric acetate : Fe(C2H302)3 -h 2H2O = Fe(OH)2C2H302 + 2HC2H3O2. 7. Barium carbonate when added in moist condition pro- duces a precipitate of Fe(OH)3, ferric hydroxide. 8. H2S, hydrogen sulphide, reduces ferric salts in solution to ferrous salts, with the separation of sulphur : 2FeCl3 + H2S = 2FeCl2 + 2HC1 + S. 9. Metallic zinc and hydrochloric acid reduce ferric salts to ferrous salts ; sulphurous acid also acts as a reducing agent (conversion of Fe* * * to Fe' ') : 2FeCl3 + Zn = 2FeCl2 + ZnCla- 2FeCl3 + H2SO3 + H2O = 2FeCl2 + H2SO, + 2HC1. 10. For the behavior of ferric salts on charcoal and in the borax bead see under Ferrous Salts, 7 and 8, page 49. ALUMINIUM, AI. Atomic weight, 27.1 (26.9) ; valence, III. Tin-white metal; specific gravity, 2.56 (specific gravity of the hammered metal, 2.67) ; melting-point, about 700° C. Alj^SO^^j aluminium sulphate, or NH^Al{80^)2, ammonium alumiriium sulphate (ammonia alum), may he employed in making the tests. 1. NH4OH precipitates white gelatinous Al(OH)3, alumin- ium hydroxide, slightly soluble in an excess of the reagent. The precipitation is complete only when the excess of am- monia has been driven off by boiling the solution. 2. NaOH or KOH precipitates gelatinous A1(0H)3, 51 aluminium hydroxide, soluble in an excess of either reagent, with the formation of NagAlOg, sodium aluminate, or K3AIO3, potassium aluminate, due to the combination of the sodium or potassium with the trivalent anion AIO3"' : Al(OH)3 + 3NaOH = Na3A103 + SUfi. As aluminium hydroxide is insoluble in ammonium hydrox- ide (providing the latter is not present in great excess), the aluminium hydroxide may be reprecipitated from its solution as aluminate by the addition of ammonium chloride : Na3A103 4- 3NH,C1 = Al(OH)3 + 3NH3 + 3NaCl. Aluminium hydroxide is somewhat soluble in water, but not in water containing ammonium salts ; when in aqueous solu- tion it is believed to be in the colloidal state. Boiling does not decompose the aluminates. The solutions of aluminates have an alkaline reaction. 3. (NHjgS completely precipitates aluminium from its solution as Al(OH)3, aluminium hydroxide, with the evolu- tion of hydrogen sulphide. 4. Na2HP04, sodium hydrogen phosphate, precipitates in neutral solutions white gelatinous AlPO^, aluminium phos- phate, insoluble in acetic acid and in ammonium hydroxide, soluble in mineral acids and in sodium or potassium hydrox- ide, with the formation of aluminates : AlPO, + 6NaOH = Na3A103 + Na3PO,H- 3H.O. Ammonium chloride reprecipitates the aluminium phosphate from its solution in sodium or potassium hydroxide : Na3A103 H- Na3PO, + 6NH,C1 = AlPO, -f 6NaCl + 6NH3 -h 3H2O. 5. Na2S203, sodium hyposulphite, added to a neutral solu- tion of a salt of aluminium precipitates white gelatinous Al(OH)3, with the separation of free sulphur and liberation of SO2, sulphurous anhydride. Complete precipitation takes place only when the solution of the aluminium salt is dilute 52 and is boiled, after the addition of the hyposulphite, until the odor of sulphurous anhydride can no longer be detected : 2AICI3 + SNa^SA H- 3H2O - 2Al(OH)3 + 6NaCl + SSO^ + S3. 6. NaC2H302, sodium acetate, added in excess to a solution of an aluminium salt, and the solution diluted with water and boiled, produces a precipitate of Al(OH)2C2H302, basic aluminium acetate. Neutral aluminium acetate is first pro- duced when the sodium acetate is added, and this on boiling the liquid is converted by hydrolysis into insoluble basic aluminium acetate and acetic acid : Al2(SO,)3 + 6NaC2H302 = 2A1(C2H302)3 + 3Na2SO, ; A1(C2H302)3 + 2H2O = Al(OH)2C2H302 + 2HC2H3O2. 7. BaCOa, barium carbonate, when added in moist con- dition precipitates Al(OH)3, aluminium hydroxide. 8. Compounds of aluminium mixed with sodium carbon- ate and ignited on charcoal yield white infusible aluminium oxide ; on moistening the mass with cobaltous nitrate and again igniting, an infusible blue residue is obtained, due to the combination of CoO, cobaltous oxide, with AI2O3, alumin- ium oxide (Thenard^s blue). CHROMIUM, Cr. Atomic weight, 52.1 (51.7) ; valence, 11, ril. Light-gray crystalline powder; specific gravity, 6.81. CrC/3, chromic chloride, may he employed in making the tests. 1. NH4OH precipitates bluish-green or grayish-green ge- latinous Cr(OH)3, chromic hydroxide ; if the precipitation has taken place in a cold solution, a small quantity of chromic oxide will remain dissolved in the ammonium hydroxide ; on boiling this purplish solution all of the chromium is precipi- tated as chromic hydroxide. 2. NaOH or KOH precipitates from solutions of both the 53 green and the violet salts of chromium greenish flocculent Cr(OH)3, chromic hydroxide, soluble in an excess of the reagent, forming NagCrOg, sodium chromite, in consequence of the production of the anion CrOg'^', and imparting a greenish color to the solution : Cr(OH)3 -F 3NaOH = NagCrOa + SUfi. From this solution chromic hydroxide is reprecipitated by the addition of ammonium chloride or by long-continued boiling : NagCrOs + SHp = Cr(OH)3 + 3NaOH. The reaction with NaOH is reversible : Cr(OH)3 + SNaOH^^^NagCrOg + 3H2O. Th§ precipitated chromic hydroxide obtained by boiling its alkaline solution appears to be insoluble in sodium or potas- sium hydroxide. It is probably a chromic hydroxide some- what deficient in water of hydration. The solubility of chromic hydroxide in sodium hydroxide is very much re- tarded by the presence of ferric hydroxide. 3. NaC2H302, sodium acetate, will not precipitate chro- mium as a basic acetate, as in the case of aluminium. 4. (NH4)2S precipitates Cr(OH)3, chromic hydroxide, with the evolution of liydrogen sulphide : 2CrCl3 + 3(NH,)2S + GH^O = 2Cr(OH)3 + 6NH4CI + 3H2S. 5. Bromine water, or chlorine water, added to a chromium solution, which has previously been rendered alkaline with NaOH or KOH, and warmed, changes the green color of the solution to yellow, due to the formation of a chromate of the alkali : K3Cr03 + 3Br + 2KOH = K^CrO, + 3KBr + H^O. On neutralizing the solution with acetic acid and adding plumbic acetate, a yellow precipitate of PbCrO^, plumbic chromate, will be produced : K^CrO.-f Ph{C,lIf>,%= PbCrO, + 2KC2H3O2. 5* 54 In this case the anion CrOg"' is transformed into the chromate anion CrO^''. Also on boiling an alkaline (NaOH or KOH) solution of chromium with lead peroxide a yellowish coloration is imparted to the liquid, due to the formation of a chromate : 2K3Cr03 -h 3Pb02 = 2K2CrO, + 2PbO + K^PbO^. The lead oxide (PbO) remains in solution in the excess of alkali. On acidulating with acetic acid the lead separates as yellow PbCrO^, plumbic chromate : K^PbO^ + K^CrO, -f 4HC,H30, = PbCrO, + 4KC,JI,0, -f 2H,0. 6. A salt of chromium, fused on platinum foil with a mixture of sodium carbonate and potassium nitrate or potas- sium chlorate, yields a mass containing a salt of chromic acid — i. e.y a chromate ; on exhausting the mass with water a yellow solution of Na2Cr04, sodium chromate, and K2Cr04, potassium chromate, is obtained which, when acidulated with acetic acid and treated with plumbic acetate, yields a yellow precipitate of PbCrO.^, plumbic chromate : CrA + 2Na2C03 +03= 2Na2Cr04 + 2CO2 ; Na2Cr04 -f Pb(C2H302)2 = PbCrO^ + 2NaC2H302. 7. Compounds of chromium when ignited with sodium car- bonate on charcoal yield a green fused mass containing oxides of chromium. 8. Fused in a bead of borax or of microcosmic salt, in either the oxidizing or the reducing flame, chromium com- pounds yield a yellowish-green bead, which becomes emerald- green on cooling. FOURTH GROUP. Metals precipitated as sulphides from neutral solutions by (NH4)2S, ammonium sulphide : Manganese, Zinc, Cobalt, and Nickel (cations Mn ", Zn* ', Co' *, Ni ' *). In addition to their being precipitated by ammonium sulphide as sulphides, they 55 are precipitated by ammonium hydroxide and sodium or po- tassium hydroxide as hydroxides. Certain of these hydrox- ides are soluble in an excess of the reagent — ammonium hy- droxide dissolves the hydroxides of cobalt, nickel, and zinc ; sodium or potassium hydroxide dissolves zinc hydroxide. Excepting ferric salts, they are, in general, not precipitated in the presence of ammonium salts. Hydrogen sulphide will not cause precipitation in their solutions if they contain free mineral acids. MANGANESE, Mn. Atomic weight, 55. (54.6); valence, II, III. Grayish-white metal ; specific gravity, about 8. MnSO^, manganous sulphate^ may be employed in making the tests. 1. (NH4)2S precipitates pale-salmon-colored MnS, manga- nous sulphide, containing water, easily soluble in acetic acid and in hydrochloric acid. (Occasionally, especially after standing some time, the pale-salmon-colored precipitate con- taining water is converted into green MnS, manganous sul- phide, which is free from water.) Manganous sulphide readily oxidizes on exposure to the air and becomes dark brown, due to the formation of HgMnO,, hydrated peroxide of manganese. 2. NaOH or KOH precipitates white Mn(OH)2, manganous hydroxide, insoluble in excess of the reagent. On exposure to the air the precipitate rapidly becomes brown, due to the formation of Mn(OH)3, manganic hydroxide. Manganous hydroxide is soluble in ammonium chloride, owing to the production of a double salt, whereas manganic hydroxide is insoluble in that reagent ; on this account anniionium chloride solutions of manganous hydroxide containing free ammonia 56 become brown on exposure to the air, due to the separation of manganic liydroxide : Mn(OH)2 + 4NH,C1 = (NHJ^MnCl, + 2H2O + 2NH3 ; 2(NH,)2MnCl, + 4NH3 + 5H2O + O ^ 2Mn(OH)3 + 8NH,C1. 3. NH4OH precipitates in neutral solutions, and also in solutions free from salts of ammonium, white Mn(OH)2, manganous hydroxide ; in the presence of salts of ammonium or of free acids, excess of ammonium hydroxide fails to pro- duce a precipitate, because of the formation of a soluble double salt of manganous hydroxide with the ammonium salts. The action of the oxygen of the air converts the solu- ble manganous salt into Mn(OH)3, manganic hydroxide, which separates as a brown precipitate. 4. Na2C03, sodium carbonate, or K2CO3, potassium carbo- nate, precipitates white MnCOg, manganous carbonate, but previously moistened barium carbonate does not produce a precipitate. 5. NaC2H302, sodium acetate, does not produce a precipi- tate in boiling solutions of salts of manganese. (Distinction from ferric salts.) 6. Bromine water added to an alkaline solution of a man- ganese salt produces a precipitate of brown hydrated peroxide of manganese : MnCl2 + 2NaOH + NaBrO = H2Mn03 + 2NaCl + NaBr. 7. Concentrated nitric acid and an excess of Pb02, lead peroxide, added to a solution of a manganese salt produce, on warming the liquid, a red solution, due to the formation of permanganic acid : 2MnS04 + 6HNO3 -h 5Pb02 -- 2HMnO, + 2PbS0, + 3Pb(N03)2 -f 2H2O. The red coloration is especially observable on permitting the excess of Pb02 to subside. 57 8. Compounds of manganese, fused on platinum foil with sodium carbonate and potassium nitrate, yield a bluish-green mass containing manganates of sodium and potassium, com- pounds of the divalent manganate ion MnO^'': 3Mn(OH)2 + Na2C03 + 4KNO3 = Na^MnO, + 2K2MnO, + 4NO + CO2 + 3H2O. The test is an exceedingly delicate one, and only a minute quantity of a salt of manganese need be used. On exhausting the mass with water, soluble KMnO^, potassium permanganate (a compound of the univalent per- manganate ion MnO/), and insoluble brown HgMnOg, hy- drated peroxide of manganese, are formed : 3K2Mn04 + 3H2O = 2KMnO, + H^MnOg + 4KOH. The potassium permanganate dissolves, imparting a purplish- red color to the water. 9. Compounds of manganese, fused in the oxidizing flame in a bead of borax or of microcosmic salt, yield an amethyst- colored bead ; fused in the reducing flame, the bead becomes colorless. ZINC, Zn. Atomic weight, 65.4 (64.9) ; valence, IF. Bluish-white metal ; specific gravity, 6.9 ; melting-point, 433° C. ZnSO^, zinc sulphate, may be employed in making the tests. 1. (NH4)2S precipitates white ZnS, zinc sulphide, easily soluble in hydrochloric acid, insoluble in acetic acid. 2. NaOH or KOH precipitates white, gelatinous Zn(OH)2, zinc hydroxide, soluble in excess of the reagent, with the formation of NaaZnOg, sodium zincate, or KgZnOg, potassium zincate, compounds of the zinc anion ZnOg'': Zn(OH)2 -h 2NaOH = Na2Zn02 + 2H2O. 58 These solutions, which have an alkaline reaction, yield a precipi- tate of ZnS, zinc sulphide, on the addition of hydrogen sulphide. 3. NH4OH precipitates in neutral solutions white floccu- lent Zn(OH)2, zinc hydroxide, soluble in excess of the reagent, with the formation of complex zinc ammonia compounds : Zn(0H)2 + 2NHPH = {^RX^nO^i + 2Hp. 4. K4Fe(CN)g, potassium ferrocyanide, produces a white flocculent precipitate of Zn2Fe(CN)g, zinc ferrocyanide, insol- uble in acids and in ammonium hydroxide. The precipitate while in suspension often has a pale-yellowish appearance, due to the color imparted to the liquid by the presence of an excess of potassium ferrocyanide. 5. NaaCO,, sodium carbonate, or K2CO3, potassium car- bonate, precipitates white basic zinc carbonate. Ammonium carbonate likewise produces a precipitate of white basic zinc carbonate, which is soluble in cold solutions in an excess of the reagent. Recently precipitated moist BaCOg, barium carbonate, fails to produce a precipitate. 6. NaC2H302, sodium acetate, does not produce a precipi- tate in boiling solutions of zinc salts. 7. Compounds of zinc, ignited with sodium carbonate in the reducing flame on charcoal, yield a coating of ZnO, zinc oxide, which is yellow when hot and white when cold. On moistening the deposit with cobaltous nitrate and again ignit- ing, the deposit becomes green in color. COBALT, Co. Atomic weight, 59. (58.56) ; valence, II, III. Steel-gray metal ; specific gravity, 8.6. Co{N0^2y cobaltous nitrate^ or CoCl^y cobaltous chloride, may be employed in making the tests. 1. (NH4)2S precipitates black CoS, cobaltous sulphide, in- 59 soluble in excess of colorless ammouium sulphide and in dilute hydrochloric acid; soluble in nitro-hydrochloric acid, with the formation of CoClg, cobaltous chloride : 3CoS + 6HC1 -[- 2HNO3 = 3C0CI2 + S3 + 2NO + 4H2O. 2. NaOH or KOH precipitates in cold cobaltous solu- tions a bluish basic salt, and in boiling solutions rose-red Co(OH)2, cobaltous hydroxide. Both precipitates become oxidized on exposure to the air and turn olive-green in color. They are insoluble in excess of the reagent. 3. NH4OH precipitates in cold cobaltous solutions a bluish basic salt, and in boiling solutions rose-red Co(OH)2, cobaltous hydroxide. Both of these precipitates are soluble in an excess of the concentrated reagent, imparting a reddish color to the liquid, which, on exposure to the oxidizing action of the air, soon changes to brown, owing to the production of cobalt am- monia ions. The presence of ammonium salts prevents the precipitation. 4. KCN, potassium cyanide, precipitates brownish- white Co(CN)2, cobaltous cyanide, soluble in excess of the reagent, with the formation of K4Co(CN)g, potassium cobaltous cyan- ide. On boiling this solution in tlie presence of an excess of potassium cyanide, or in the presence of an excess of potassium hydroxide (or of sodium hydroxide), or on adding bromine water, a precipitate of potassium cobaltic cyanide, K3Co(CN),;, the potassium compound of the com|)lex anion Co(CNy, is produced — /. r., the cobaltous cyanogen ion Co(CN),/''' is transformed into the cobaltic cyanogen ion Co(CN)/''. Acids added to this solution do not precipitate cobaltous cyanide : C0CI2 + 2KCN = Co(CN)2 -f 2KC1 ; Co(CN)2 + 4KCN - K,Co(CN)«. 2K,Co(CN), + O + HP -= 2K3Co(CN), f 2KOH ; 2K,Co(CN)e + 2Br -= 2K3Co(CN)« + 2KBr. 60 5. NaOH or KOH added to a solution of a cobaltous salt, followed by the addition of bromine water, precipitates on boiling the liquid (conversion of the cobaltous ion Co * ' into the cobaltic ion Co " *) brownish-black Co(OH)3, cobaltic hydroxide, insoluble in a mixture of ammonium hydroxide and ammonium chloride : 2Br + 2KOH = KBr + KBrO + Ufi ; KBrO -f- 2Co(OH)2 + Hp - 2Co(OH)3 + KBr. 6. KNO2, potassium nitrite, added in excess to a solution of a neutral salt of cobalt, to which sufficient acetic acid lias previously been added, produces, in concentrated solutions immediately and in dilute solutions slowly, a yellow crystal- line precipitate of K3Co(N02)6, potassium cobaltic nitrite, a combination of the complex ion Co(N02)6 with K3 : C0CI2 + 7KNO2 + 2HC2H3O2 = K3Co(N02)6 + 2KC2H3O2 + 2KC1 + NO + H2O. The presence of free acetic acid is necessary to liberate the nitrous acid (required in the oxidation in the transforming of Co * ' into Co * ' *) from the potassium nitrite. Free hydro- chloric acid must not be present ; in case of its presence in the solution, it should be neutralized by the addition of NaCgHgOg, sodium acetate, previous to the addition of the acetic acid (NaC2H302 -f HCl = NaCl + HC2H3O2). To insure complete precipitation of the cobalt, particularly in the case of dilute solutions, the solution should be allowed to stand in a warm place for about twenty-four hours. 7. Compounds of cobalt, ignited with sodium carbonate in the reducing flame on charcoal, yield dark metallic, magnetic spangles. 8. Compounds of cobalt, fused in a bead of borax or of raicrocosmic salt in either the reducing or the oxidizing flame, impart to the bead a beautiful sapphire-blue color. 61 NICKEL, Ni. Atomic weight, 58.7 (58.3); valence, II. Silver-white metal ; specific gravity, 8.9. NiSO^, nickelous sulphate ^ or NiCl^, niekelous chlonde, may be employed in making the tests. 1. (NH4)2S precipitates black NiS, nickelous sulphide, sol- uble in excess of ammonium sulphide (particularly in the presence of ammonia), imparting a brownish color to the solution. On boiling the ammonium sulphide solution of nickelous sulphide, it undergoes decomposition (particularly after the addition of acetic acid), with the separation of the previously dissolved nickelous sulphide. The precipitate is insoluble in dilute hydrochloric acid, but soluble in nitro- hydrochloric acid. 2. NaOH or KOH precipitates amorphous, apple-green Ni(OH)2, nickelous hydroxide, insoluble in an excess of the reagent. 3. NH4OH, added in small quantity, precipitates, in neu- tral solutions of nickelous salts free from ammonium salts, apple-green Ni(OH)2, nickelous hydroxide, soluble in excess of ammonium hydroxide, imparting a bluish color to the solution in consequence of the formation of complex coni- pounds of the nickel ammonia cation. 4. NaOH or KOH, added with bromine water and the liquid boiled, precipitates black Ni(OH).^, nickelic hydroxide, (conversion of Ni ' * into Ni ' ' '), soluble in a mixture of ammonium hydroxide and ammonium chloride. (Compare Cobalt, 5, page 60.) 5. KCN, potassium cyanide, precipitates light-green Ni(CN)2, nickelous cyanide, soluble in excess of the reagent, with the formation of K2Ni(CN)^, potassium nickelous cyan- ide ; on the addition of bromine water followed by j)otassium 6 62 hydroxide (or sodium hydroxide) to this sohition black nickelic hydroxide is precipitated (distinction from cobalt) : NiCl^ + 2KCN = Ni(CN)2 + 2KC1 ; Ni(CN)2 -i- 2KCN = K2Ni(CN)4 ; 2K2Ni(CN), + 18Br -t 6NaOH = 2Ni(OH)3 -f 4KBr + 8BrCN + 6NaBr. 6. KNO2, potassium nitrite (under the conditions given for cobalt, 6, page 60), fails to produce a precipitate in solu- tions of nickelous compounds. 7. Compounds of nickel, ignited with sodium carbonate on charcoal, yield dark magnetic, metallic spangles. 8. Compounds of nickel, fused in the oxidizing flame in a Dead of borax, yield a bead which is purplish red while hot and pale brownish yellow when cold. In the reducing flame the bead becomes gray and opaque, due to the separation of metallic nickel. Fused in a bead of microcosmic salt in the oxidizing or the reducing flame, salts of nickel yield a reddish-brown bead which becomes yellow or yellowish red on cooling. FIFTH GROUP. Metals precipitated as carbonates (compounds of the diva- lent anion CO3'') from neutral solutions by (NH4)2C03, ammonium carbonate : Barium, Strontium, and Calcium (cations Ba ' ', Sr * ', Ca ' *) : BaCl^ + (NH,)2C03 = BaC03 -f 2NH,C1. Complete precipitation does not take place in solutions which were originally acid, nor when ordinary commercial ammonium carbonate is employed, unless the solution is boiled after the addition of the ammonium carbonate. Com- mercial ammonium carbonate consists of equal molecules of NH4HCO3, acid ammonium carbonate, and XH2.CO.ONH4, 63 ammonium carbamate.^'^ Dissolving the commercial carbon- ate in water converts the ammonium carbamate into neutral ammonium carbonate : NH.HCOg + NH2.CO.ONH, -f H2O = NH.HCOg + (NHJ,C03. In precipitating with ammonium carbonate containing acid ammonium carbonate — /. e.j the univalent anion HCO3' — part of the precipitate will consist of acid salts— for example, Ba(HC03)2 — which are converted into neutral salts on boiling : Ba(HC03)2 = BaC03 + CO^ + H^O. The phosphates of the alkalies also precipitate (as phos- phates) the members of this group. The solubility, in water, of some of the compounds is as follows : of the hydroxides, barium hydroxide is quite soluble, strontium hydroxide is difficultly soluble, calcium hydroxide very difficultly soluble. Of the sulphates, barium sulphate is practically insoluble, strontium sulphate fairly soluble, calcium sulphate (CaSO^ -|- 2H2O) quite soluble. In absolute alcohol barium chloride and barium nitrate are insoluble ; calcium chloride and calcium nitrate are soluble ; strontium chloride is soluble, but strontium nitrate is insoluble. BARIUM, Ba. Atomic weight, 137.4(136.4); valence, 11. Silver-white metal ; specific gravity, about 4.0. BaCl2, baiium chloride y may be employed in making the tests. 1. (NH4)2C03, ammonium carbonate, precipitates white flocculent BaCOg, barium carbonate. The precipitate is ^ According to other views, commercial ammonium carbonate consists of one molecule of neutral and two molecules of acid ammonium carbon- ate, thus : (NH,)2C03 + 2NH^HC03. 64 easily soluble in dilute hydrochloric acid, in nitric acid, and in acetic acid, insoluble in pure water, slightly soluble in ammonium chloride, and, like all the carbonates of the alka- line earths, soluble in water containing carbonic acid. 2. H2SO4, sulphuric acid, and soluble sulphates, including solutions of calcium and strontium sulphates, precipitate white, finely-pulverulent BaSO^, barium sulphate, insoluble in acids. If the precipitation occur in a cold solution, the particles of the precipitate are so minute that they readily pass through a filter ; whereas, if the precipitation take place in a hot solution, and warm, dilute sulphuric acid be employed, the precipitate formed is composed of larger particles which are readily re- tained by a filter. 3. (NH4)2C204, ammonium oxalate, precipitates white, pul- verulent BaCaO^ + H2O, barium oxalate (compound of the divalent anion C2O4''), wliich when freshly precipitated is soluble in acetic acid and in Hfi./J^, oxalic acid. 4. Xa2HP04, sodium hydrogen phosphate, precipitates white flocculent BaHPO^, di-basic barium phosphate, soluble in hydrochloric, nitric, and acetic acids. 5. K2Cr04, potassium chromate, produces in neutral or acetic acid solutions of salts of barium, yellow BaCiO^, barium chromate (compound containing the chromate ion CrO/'), soluble in hydrochloric acid and in nitric acid. 6. Compounds of barium, held in the flame of a Bunsen burner by means of a platinum wire, impart a yellowish- green color to the flame. STRONTIUM, Sr. Atomic weight, 87.6 (86.94); valence, II. Yellowish metal ; specific gravity, 2.5. Sr(N0^2^ '"fft'ontimn nitrate^ may be employed in making the tesU. 1. (NHJgCOj, ammonium carbonate, precipitates white 65 SrCOg, strontium carbonate, easily soluble in dilute hydro- chloric acid, in nitric acid, and in acetic acid. 2. H2SO4, sulphuric acid, and soluble sulphates, including calcium sulphate, precipitate white, usually crystalline SrSO^, strontium sulphate, insoluble in alcohol. In dilute solutions, and also on using calcium sulphate as the precipitating re- agent, the precipitation takes place gradually. 3. (NH4)2C204, ammonium oxalate, precipitates white, pulverulent SrC204(4- 2JH2O), strontium oxalate, soluble with difficulty in acetic acid and in oxalic acid. 4. Na2HP04, sodium phosphate, precipitates white SrHPO^, di-basic strontium phosphate, soluble in hydro- chloric, nitric, and acetic acids. 5. K2Cr04, potassium chromate, precipitates, in not too dilute solutions of strontium, yellow SrCrO^, strontium chromate, soluble in hydrochloric acid and in nitric acid. 6. Compounds of strontium impart a crimson color to the flame. CALCIUM, Ca. Atomic weig-ht, 40.1 (39.8) ; valence, II. Silver- white metal ; specific gravity, 1.57. CaCl^, calcium chloride^ may he employed in making the tests, 1. (NH4)2C03, ammonium carbonate, precipitates white CaCOg, calcium carbonate, easily soluble in dilute hydro- chloric acid, in nitric acid, and in acetic acid. 2. H2SO4 and soluble sulpliates precipitate immediately, in concentrated solutions of salts of calcium, white, crystalline CaSO^ -f- 2H2O, calcium sulphate, insoluble in alcohol, but soluble in boiling hydrochloric acid. Precipitation takes place in dilute solutions either gradually or not at all. 3. (NH4)2C20^, ammonium oxalate, precipitates white pul- e 6* 66 verulent CaCgO^ + II2O (or from dilute solutions partly with SllgO), calcium oxalate, easily soluble in hydrochloric or in nitric acid, insoluble in acetic and oxalic acids. 4. Na^HPO^, sodium hydrogen phosphate, precipitates white CaHPO^, di-basic calcium phosphate, soluble in hydro- chloric, nitric, and acetic acids. 5. KgCrO^, potassium chromate, does not produce a pre- cipitate of CaCr04, calcium chromate, in dilute solutions of calcium salts. 6. Compounds of calcium impart a yellowish-red color to the flame. SIXTH GROUP. Bases not precipitated by any particular group reagent: Magnesium, Potassium, Sodium, Ammonium, and Lithium (cations Mg * * , K * , Na * , NH^ ' , Li *). The compounds of magnesium, potassium, sodium, ammo- nium, and lithium are, in general, soluble in water. In aqueous ammonia, in addition to NH3, there is present in part NH4OH, as evidenced by the fact that the liquid changes red litmus to blue. Magnesium (in the presence of ammonium chloride), potassium, sodium, and lithium are not precipitated by the group reagents HCl, H2S, NH4OH, (NH,)2S, and (NH,).C03. MAGNESIUM, Mg. Atomic weight, 24-. 36 (24-. 18); valence II. Silver-white metal; specific gravity, 1.75. MgSO^y magnesium sulphate, niaij he employed in making the tests. 1. NH4OH precipitates, in neutral solutions of salts of magnesium, part of the magnesium as flocculent Mg(OH)2, 67 magnesium hydroxide, leaving the other part in sohition as a double salt of magnesium and ammonium — /. f., a salt of the complex ion Mg(S04)2'' : 2MgSO. + 2NH,OH = Mg(OH), + (NH,),Mg(SO,),. This complex salt is not decomposed by a slight excess of ammonium hydroxide. Compounds of magnesium are not precipitated by ammonium hydroxide in the presence of an excess of ammonium chloride, the latter reagent having the property of dissolving magnesium hydroxide : Mg(OH)2 + 4NH,C1 = (NH,),MgCl, + 2NH,OH. This is one explanation of the behavior of magnesium salts with ammonia and ammonium salts ! The other explanation is as follows : magnesium hydroxide is somewhat, although very slightly, soluble in water, and then almost completely dis- sociated in the solution. In consequence of this constant, definite content of hydroxyl ions in the hydroxide solution magnesium is only partially precipitated from solutions by means of the likewise only slightly dissociated ammonia solu- tion, which contains but few hydroxyl ions ; ammonium ions are produced here in considerable amount, as the result of transpositions occurring in the liquid, which ammonium ions reduce the hydroxyl concentration below the mass necessary for precipitation. Ammonia compared with magnesium hy- droxide becomes a weaker base. Precipitation does not gen- erally occur where, in consequence of the addition of strongly dissociated ammonium salts, ammonium ions in considerable amount were originally present. 2. NaOH or KOH precipitates, particularly on boiling, white Mg(OH)2, magnesium hydroxide. 3. NagCOg, sodium carbonate, or K2CO3, potassium car- bonate, precipitates Mg4(C03)3(OH)2, basic magnesium car- bonate. (The carbonic acid liberated in the reaction retains part of the magnesium in solution as an acid carbonate ; this is 68 decomposed and precipitated as basic carbonate by boiling the solution.) The precipitate is soluble in ammonium chloride. 4. (NH4)2C03 produces no precipitate immediately, but after stiinding some time a crystalline precipitate of MgC03(NH4)2C03 appears. In the presence of a sufficient quantity of ammonium chloride the precipitation does not take place. 5. Na^HPO^ produces in concentrated solutions a white, flocculent precipitate of MgHPO^, di-basic magnesium phos- phate. If ammonium chloride and ammonium hydroxide are added to the solution of the magnesium salt, and after- wards sodium hydrogen phosphate added, a white, crystalline precipitate of MgNH4P04(-|- BHgO), ammonium magnesium phosphate, a compound of the trivalent anion PO^''', is pro- duced : MgSO, + Na^HPO, + NH.OH = MgNH.PO, + Na^SO, -|- The ammonium chloride is added to the solution in order to prevent the precipitation of the magnesium salt by the am- monium hydroxide. The precipitate is always crystalline; in dilute solutions it forms gradually, the formation is facili- tated, however, by gently rubbing the inner sides of the vessel with a glass rod. 6. Compounds of magnesium ignited on charcoal are some- what luminous in the flame. On moistening the mass with cobaltous nitrate and again strongly igniting, a pale-pink color, which is more evident on cooling, is imparted to the POTASSIUM, K (KALIUM). Atomic weight, 39.15 (36.86) ; valence, I. Silver-white metal ; specific gravity, 0.87 ; melting-point, 62.5° C. KNO^j potassium nitrate, or KCl, potassium chloride, may he employed in making the tests. 1. PtCl4, platinic chloride, or a solution of the same con- taining hydrochloric acid, forming HgPtClg, hydrochlorpla- tinic acid, precipitates from neutral or acid solutions yellow crystalline K^PtClg, potassium chlorplatinate, slightly solu- ble in water, insoluble in alcohol : H.PtClg + 2KC1 = K^PtClg + 2HC1 (a combination of the anion PtClg" with two cations of K*). The test is best made in a watch-glass, and the liquid should be stirred Avith a glass rod. In dilute solutions the precipitate forms slowly. The addition of a little alcohol and, if the potassium salt is not a chloride, a drop of hydro- chloric acid facilitates the precipitation. 2. NaHC^H^Og, acid sodium tartrate, produces, in rather concentrated neutral solutions of salts of potassium, a white, granular, crystalline precipitate of KHC^H^O^, acid potas- sium tartrate (a combination of the univalent anion HQH^Og' with the cation K *). Stirring the liquid with a glass rod or the addition of alcohol promotes the precipitation. If the po- tassium solution has an alkaline reaction, it must be neutral- ized with acetic acid previous to the addition of the acid so- dium tartrate. H2C4H40g, tartaric acid, may be used instead of acid sodium tartrate, but in using it NaCgHsOg, sodium acetate, must be added to the solution : KNO3 -f H2C4HA + XaQHA = KHC4HA + NaNOa + HC2H3O2. 70 In dilute solutions of potassium salts precipitation occurs only after standing some time. 3. Sodium cobaltic nitrite^'^ produces immediately in con- centrated solutions of potassium salts a yellow crystalline precipitate of K3Co(N02)6, potassium cobaltic nitrite (a com- bination of the complex anion Co(N02)/" with 3K' cations) : (NaNO^). + Co(N02)3 + 3KC1 - Kfio(NO,\ -f 3NaCl -f G — 3)NaN02. 4. Compounds of potassium impart to the flame a violet color. SODIUM, Na (NATRIUM). Atomic weight, 23. 05 (22.88); valence, I. Silver-white metal ; specific gravity, 0.97 ; melting-point, 95.6° C. NaCl, sodium chlomde, may be efinployed in making the tests. 1. K2H2Sb207, acid potassium pyroantimonate/^^ produces, in neutral or slightly alkaline concentrated solutions of salts of sodium, a white crystalline precipitate of Na2H2Sb207 (+ 6H2O), acid sodium pyroantimonate (a combination of the anion H2Sb207'' with 2Na* cations). In dilute solutions the precipitate forms only after the liquid has been standing some time. Gently rubbing the inner sides of the vessel with the part of a glass rod over which is slipped a piece of caout- chouc tubing facilitates the formation of the precipitate. If the sodium solution have an acid reaction, it should be neu- tralized with potassium carbonate before the addition of the potassium pyroantimonate. Metals other than sodium or * Prepared by treating a solution of sodium nitrite of about 10 per cent, strength with some cobalt(»us chloride and some acetic acid. 2 The solution of acid potassium pyroantimonate may be prepared by boiling for a short time 1 gram of the salt with 200 c.c. of water, allow- ing the liquid to cool and then filtering. 71 potassium should not be present, as they interfere by forming insoluble antimonates. 2. PtCl^, platinic chloride, HgPtClg, hydrochlorplatinic acid, or HaC^H^O^, tartaric acid, fails to produce a precipi- tate in solutions of salts of sodium. 3. Compounds of sodium impart to the flame an intense yellow color AMMONIUM, NH4. The cation NH^ in its behavior with anions corresponds to potassium and sodium. Another analogy between the ammo- nium ion and the metals is the existence of an ammonium amalgam. NH^Clj ammonium chloridey may be einployed in making the tests. 1. The ammonium salts (in combination with volatile acids) are characterized by their complete volatility when heated to high temperatures ; ammonium borate and ammo- nium phosphate, however, on being strongly heated leave a residue respectively of boric acid and of phosphoric acid. 2. PtCl4, platinic chloride, or a solution of the same con- taining hydrochloric acid, forming HgPtCle, hydrochlorplatinic acid, precipitates in concentrated solutions yellow crystalline (octahedra) (NH4)2PtClg, ammonium chlorplatinate, slightly soluble in water, insoluble in alcohol. The test is best made in a watch-glass, stirring the liquid with a glass rod. The addition of a little alcohol and, if the ammonium salt is not a chloride, a drop of hydrochloric acid hastens the formation of the precipitate. 3. NaOH or KOH added to a solution of a salt of am- monium liberates ammoniacal gas, on boiling the solution, w^hich may be detected by its odor; by its producing white clouds of ammonium acetate when a glass rod wet with acetic 72 acid is held above the liquid ; by its action upon turmeric paper moistened with water, which becomes brown when held above the liquid in which the liberation has occurred ; and by its action upon filter paper moistened with mercurous nitrate, which becomes black when held in the evolved gas (due to the formation of black NHaHggNOg. 4. HgC^H^Og, tartaric acid, or NaHC^H^Og, acid sodium tartrate, produces in concentrated solutions of ammonium salts white, crystalline ISTH^HC^H^Og, acid ammonium tartrate. 5. Sodium cobaltic nitrite produces a precipitate similar to the one produced in solutions of potassium salts, but the reaction is less delicate. (For conditions favoring precipita- tion see Potassium, 3, page 70.) LITHIUM, Li. Atomic weight, 7.03 (6.98); valence, I. Silver- white metal ; specific gravity, 0.59 ; melting-point, 180° C. LiCl, lithium chloride^ may be employed in making the tests. 1. Na-jCOg precipitates, in cold concentrated solutions of salts of lithium, white Li2C03, lithium carbonate. 2. NagHPO^ added to a concentrated solution of a salt of lithium produces a white, crystalline precipitate of LigPO^, lithium phosphate. 3. Compounds of lithium impart to the flame a carmine- red color. II. PROPERTIES OF THE ACIDS. FIRST GROUP. Acids which are precipitated by BaClj, barium chloride, from neutral and from acid solutions : Sulphuric Acid, Hydrofluosilicic Acid. SULPHURIC ACID, H^SO^. (Sulphuric acid combines with bases to form salts called sulphates.) MgSO^j magnesium sulphate, may be employed in making the tests. 1. The neutral sulphates (compounds of the anion SO^''), with the exception of barium, strontium, calcium, and lead sulphates, are easily soluble in water. Basic sulphates of the heavy metals are soluble in hydrochloric acid or in nitric acid. Lead sulphate and the sulphates of the alkaline earths are decomposed and converted into carbonates by sodium or potassium carbonate. 2. BaClg, barium chloride, precipitates, from solutions con- taining sulphates or free sulphuric acid, white, pulverulent BaS04, insoluble in acids. If the precipitation occur in a cold solution, the particles of precipitate are so minute that they readily pass through a filter ; whereas, if the precipitation take place in a hot dilute solution, the precipitate formed is com- posed of larger particles which are readily retained by a filter. 3. Pb(C2H302)2, plumbic acetate, precipitates white PbS04, plumbic sulphate, insoluble in dilute acetic acid, somewhat soluble in boiling concentrated acids. Plumbic sulphate is easily soluble in (NH4)2C4H406, ammonium tartrate; from D 7 73 74 this solution potassium cliromate precipitates the lead as yellow PbCr04, plumbic chromate. 4. Sulphates, fused with sodium carbonate on charcoal, yield a residue containing NagS, sodium sulpliide. On placing a portion of the mass on a clean silver coin and adding a few drops of water, a brownish or black stain of Ag2S is produced : Na^SO, + 4C = ]Sra,S + 4CO ; Na2S + Ag2 + 2H2O = Ag,8 -]- 2NaOH + H^. HYDROFLUOSILIC ACID, H2SiF6. (Hydrofluosilic acid combines with bases to form salts called silicofluorides.) JVcfg'S'ii^g, sodium silicofluorides may be employed in making the tests. 1. Most of the silicofluorides (compounds of the complex anion SiF^") are sokible in water; when gently heated with concentrated sulphuric acid they evolve gaseous SiF^, silicon fluoride, and HF, hydrofluoric acid : K^SiFg + H2SO, -: SiF, -f 2HF + K^SO,. If a piece of platinum foil containing a drop of water be inverted over the vessel in which the decomposition is eflected, the water becomes milky in appearance, due to the formation of insoluble HgSiOg, silicic acid : 3H2O + 3SiF, = H^SiOg + 2H2SiF6. 2. BaClj, barium chloride, precipitates, in solutions of hydrofluosilicic acid and of silicofluorides, crystalline BaSiFg, barium silicofluoride, insoluble in dilute acids. 3. KXO3, potassium nitrate, precipitates, in solutions that are not too dilute, translucent, gelatinous KgSiFg, potassium silicofluoride, soluble with difficulty in water, insoluble in alcohol. 75 4. NH^OH produces NH4F, ammonium fluoride, and £[28103, silicic acid, both of which are precipitated : 6NH,OH + H,SiF6 = H^SiO^ + 6NH,F -f- SH^O. SECOND GROUP. Acids which are precipitated by BaCla, barium chloride, in neutral solutions, the barium salts of which are soluble in hydrochloric acid : Sulphurous Acid, Hypo sulphurous Acid, Phosphoric Acid, Boric Acid, Hydrofluoric Acid, Carbonic Acid, Silicic Acid, Chromic Acid, Arsenic Acid, Arsenious Acid. SULPHUROUS ACID, HjSOg. (Sulphurous acid combines with bases to form salts called sulphites.) iVag^S'Og, sodium sulphite, may be employed in making the tests. 1. Of the neutral sulphites (compounds of the anion SO./'), only those of the alkalies are soluble in water ; the others are easily soluble in acids, with the evolution of SO2, sulphurous anhydride : BaSOa + 2HC1 = BaCl^ + SO^ i- Hfi. 2. Dilute acids decompose sulphites, with the evolution of SO2, sulphurous anhydride, which may be recognized by its odor (that of burning sulphur). The presence of sulphurous anhydride may be detected in gaseous mixtures by its be- havior with KIO3, potassium iodate. A piece of filter paj>er saturated with a solution of potassium iodate and starch paste, brought while wet in contact with gaseous mixtures contain- ing sulphurous anhydride, becomes blue in color, owing to the reduction of HIO3, iodic acid, to iodine, and the action of the latter on the starch. Bv means of the sulphurous 76 anhydride, in the presence of water, the iodic acid is reduced to HI, hydriodic acid (transformation of IO3' to I'). 3SO2 + 3H2O + HIO3 = HI + 3H2SO,. The hydriodic acid, by the action of the remaining iodic acid, is reduced, with the liberation of free iodine : SHI 4- HIO3 = I,+ SHp. (As the free iodine is reconverted by an excess of sulphurous anhydride into hydriodic acid : . I2 + SO2 + 2H2O = 2HI + H2SO,, an excess of the sulphurous anhydride causes a disappearance of the color.) 3. BaClg precipitates white BaSOg, barium sulphite, soluble in acids. 4. Pb(C2H302)2 precipitates white PbS03, plumbic sulphite, soluble in nitric acid. 5. AgN03, argentic nitrate, precipitates white AggSOg, argentic sulphite, soluble in nitric acid. On boiling the precipitate with water, it is decomposed into metallic silver and sulphuric acid, the liquid becoming gray in color, due to the separated metallic silver : Ag,SO, + H,0 = Ag, + H,SO.. 6. ZnSO^, zinc sulphate solution, containing a little Na2NOFe(CN)5, sodium nitroprusside, added to a solution of a sulphite which, if not neutral, has been neutralized with acetic acid, produces a red coloration ; or a flocculent, purplish-red precipitate, if the -solution contain a considerable quantity of the sulphite. When operating with dilute solu- tions of a sulphite, the test may be made more delicate by the addition of a few drops of potassium ferrocyanide solu- tion. (Distinction from hyposulphites.) 7. HgS conducted into a solution of sulphurous acid de- composes the latter, with the separation of sulphur and the probable formation of HgSgOg, pentathionic acid : 5SO2 + 5H2S = H^SA + S, -f 4H2O. 77 8. Sulpliites ignited with sodium carbonate on charcoal yield a yellowish residue containing sodium sulphide, as in the case of sulphates. A portion of the residue placed on a clean silver coin and moistened with a few drops of water pro- duces a brown or black stain of argentic sulphide on the coin. HYPOSULPHUROUS ACID, HjSjOg (THIOSULPHURIC ACID). (Hyposulphurous or thiosulphuric acid combines with bases :o form salts called hyposulphites or thiosulphates.) Na^S^O^j sodium hyposulphite^ may be employed in making the tests. 1. Most of the liyposulphites (thiosulphates) (compounds of the anion 8203^') are soluble in water. 2. HCl or H2SO4 added to a solution of a hyposulphite liberates HgSgOg, hyposulphurous acid, which quickly breaks up into sulphur, sulphurous anhydride, and water : Na,SA + 2HC1 = H2SA + 2NaCl ; H2S2O3 = SO2 + S + H2O. Thus hyposulphites, on the addition of either of the above acids, are decomposed and yield sulphurous anhydride, which may be recognized by its odor, and free sulphur. 3. BaCl2, barium chloride, produces in concentrated solu- tions of hyposulphites a white precipitate of BaSgOg, barium hyposulphite, soluble in a large quantity of water. It is also soluble in hydrochloric acid, with the evolution of sulphurous anhydride and the separation of sulphur. 4. Pb(C2H302)2, plumbic acetate, precipitates white PbSgOjj, plumbic hyposulphite, soluble in nitric acid. 5. AgNOg, argentic nitrate, precipitates white Ag2S203, argentic hyposulphite, soluble in excess of sodium hyposul- phite solution : Ag2S203 + Xa2S203 = 2NaAgS203. 78 The precipitiite becomes almost immediately yellow, then brown, and finally black, due to the formation of argentic sulphide : Ag^S A + HP = Ag,S + H^SO,. 6. FeCla, ferric chloride, immediately colors hyposulphite solutions reddish violet. (Distinction from sulphites.) 7. Hyposulphites ignited with sodium carbonate on char- coal yield a residue containing sodium sulphide, as in the case of sulphates and of sulphites. A portion of the residue placed on a clean silver coin and moistened with water pro- duces a brown or black stain of argentic sulphide. PHOSPHORIC ACID, HgPO^. (Phosphoric acid combines with bases to form salts called phosphates.) Na^HPO^^ sodium hydrogen phosphate , may he employed in making the tests. 1. The phosphates of the alkalies (compounds of the anions PO/'^ HPO/^ and H^PO/) are soluble in water; the phos- phates of other metals are soluble in acids. 2. BaClg, barium chloride, precipitates in solutions of the neutral phosphates white BaHPO^ or Ba3(P04)2, soluble in hydrochloric acid or in nitric acid. 3. Pb(C2H302)2, plumbic acetate, precipitates white Pb3(P04)2, soluble in nitric acid. 4. AgNOg, argentic nitrate, produces in solutions of the phosphates a light-yellow precipitate of AggPO^, soluble in nitric acid and in ammonium hydroxide. 5. NH4CI, ammonium chloride, NH^OH, ammonium hy- droxide, and MgS04, magnesium sulphate,^^> added in turn to a solution of a phosphate, produce a white, crystalline pre- » The three reagents composing the so-called "magnesia mixture." 79 cipitate of MgNHjPO^ + BHgO, ammonium magnesium phoaphate : NaaHPO^ + NH.OH + MgSO, = MgNH.PO, + Na,SO, + Hp. (The ammonium chloride is added to prevent the precipitation of the magnesium as magnesium hydroxide by the ammo- nium hydroxide.) The precipitate is sparingly soluble in pure water, and very slightly soluble in water containing ammonium hydroxide. In precipitating very dilute solu- tions the precipitate forms more rapidly when the inner sides of the vessel are gently rubbed with a glass rod. 6. NH4HM0O4, ammonium molybdate, added in excess, with a considerable quantity of nitric acid, to a solution of phosphoric acid or a phosphate, produces a yellow precipitate, probably of (NH4)3P04(Mo03)i2, ammonium phospho- molybdate, a compound containing the complex anion PO,(Mo03),/'^ 12NH,HMoO, + H3PO,+ 9HN03= (NHj3PO,(Mo03),3 + 9NH4N03-fl2H20. The precipitate is insoluble in dilute nitric acid, but easily soluble in ammonium hydroxide; it is reprecipitated from the ammoniacal solution by the addition of excess of nitric acid. The precipitate is also soluble in excess of a phosphate, and thus is explained the non-appearance of a precipitate when only a little ammonium molybdate is added to a solu- tion containing much phosphoric acid. In dilute solutions the precipitate forms slowly. The precipitation is hastened by warming the solution to a temperature of 40° C A higher temperature should be avoided. (Pyrophosphates (compounds of the anion PgO;'"') yield with argentic nitrate white precipitates of Ag4P20-, argentic pyrophosphate. Metaphosphates (compounds containing the anion PO3' — /. e., n(P03') ) likewise yield white precipitates 80 of AgPOg. Only the metaphosphates coagulate albumin. Sodium pyrophosphate may be obtained by strongly heating disodium phosphate : 'iNa^HPO^ = Na.P^O, + Hfi. Sodium metaphosphate may be produced by strongly heating sodium ammonium hydrogen phosphate : NaNH.HFO^ - NaPOa + NH3 + H^O.) BORIC ACID, H3BO3. (Boric acid combines with bases to form salts called borates.) Na^B^O^, sodium biborate (borax), may be employed in making the tests. 1. Of the borates (compounds containing various anions — for example, BO/, BO3''', and B,0/'), those of the alkalies are easily soluble in water. On treating warm concentrated solutions of borates with acids, colorless scales of boric acid slowly separate. Boric acid volatilizes with steam. 2. BaClg, barium chloride, produces in concentrated solu- tions of borates white Ba(B02)2, barium metaborate, easily soluble in excess of barium chloride and in ammonium chlo- ride : ^a^Bfi, + 2BaCl2 + H2O -= 2Ba(B02)2 + 2NaCl + 2HC1. 3. Pb(C2H302)2, plumbic acetate, precipitates in concen- trated solutions white Pb(B02)2, lead metaborate, soluble in excess of the reagent. 4. AgNOg, argentic nitrate, precipitates in concentrated solutions of neutral borates white AgBOg + JH2O, argentic metaborate, which is occasionally tinged with yellow, due to the presence of argentic oxide. In solutions of acid borates the precipitate is AggBgO,5. Both precipitates are easily soluble in nitric acid. By continued washing, and readily by 81 Ixiiling with water, both precipitates are decomposed into soUible boric acid and brown argentic oxide ; in dilute sohi- tions a brown precipitate of argentic oxide is directly pro- duced. 5. Boric acid, in the powdered condition, placed in a porce- lain dish and covered with alcohol gives a greenish flame on igniting the alcohol. Borates, in the powdered condition, impart the same greenish color to the flame, but must be moistened with a few drops of concentrated sulphuric acid before the addition of the alcohol. The greenish color im- parted to the flame is due to (C2H5)3B03, the ethyl ester of boric acid, formed in the reaction. Boric acid (without the addition of alcohol) when strongly heated on platinum wire imparts a greenish color to the flame. (Compounds of barium and of copper and compounds containing chlorine interfere with the test.) 6. Turmeric paper dipped in an aqueous solution of boric acid, or in a solution of a borate acidified with hydrochloric acid, and warmed until dry, becomes reddish brown in color. On bringing dilute sodium or potassium hydroxide solution in contact with the reddish-brown paper, the color becomes blue and then greenish black. HYDROFLUORIC ACID, HF. (Hydrofluoric acid combines with bases to form salts called fluorides.) KF, potassium fluoride, or NaF, sodium fluoride, may he employed in making the tests. 1. Of the fluorides (compounds of the anion F'), those of the alkalies are easily soluble in water ; the others are soluble only with great difficulty. / 82 2. BaClg precipitates from solutions of fluorides white BaF2, soluble in hydrochloric acid ; Pb(C2H302)2 precipitates white PbFg, easily soluble in nitric acid ; and AgNOg pre- cipitates white AgF, also easily soluble in water. 3. CaCl2, calcium chloride, precipitates white, gelatinous CaFg, calcium fluoride, almost insoluble in water, soluble with difficulty in mineral acids. 4. Hydrofluoric acid has the property of etching glass, forming with the silicic oxide of the glass volatile SiF^, silicon fluoride : Si02 + 4HF = SiF, + 2H2O. The test is performed in a platinum crucible covered with a watch-glass. The convex side of the watch-glass is covered with melted wax, and, after the wax has cooled, a design or figure is, by means of a sharpened piece of wood or the point of a knife-blade, graven of sufficient depth in the wax to expose an uncoated surface of glass. The pulverized fluoride is placed in the crucible, moistened with concen- trated sulphuric acid, quickly covered with the watch-glass (waxed side down), and the whole placed on a moderately warm iron plate or porcelain dish.^'^ After some time the watch-glass is taken from the crucible, and when the wax is removed the graven design will appear etched in the glass. 5. In decomposing fluorides containing considerable silicic acid with concentrated sulphuric acid, gaseous SiF^ is evolved, which, when conducted through a glass tube moistened with water, undergoes decomposition, rendering the water turbid, with the deposition of silicic acid : 3SiF, + 3H2O = H^SiOs -\- 2il^iF,. I The watch-glass should be filled with cold water, to jjrevent the melt- ing of the wax. 83 The result of the reaction is especially observable on drying the tube. CARBONIC ACID, HjCO,. (Carbonic acid combines with bases to form salts called car- bonates.) Na^CO^y sodium carbonate j may be employed in making the 1. The carbonates (compounds of the anion CO3'') of the alkalies are soluble in water ; the other carbonates are insolu- ble in water. Many of the latter are, however, soluble in water containing carbon dioxide, forming acid carbonates (compounds of the anion HCO3) : CaCOs + CO2 + H,0 = Ca(HC03)2. Carbonates in general readily dissolve in dilute acids, with effervescence (due to the liberation of carbon dioxide). The metal of the carbonate forms a salt with the acid used as a solvent : BaCOg 4- 2HC1 =- BaCla + CO2 + H^. 2. HCl or any dilute acid (except hydrocyanic acid), added to a carbonate either in solution or in the solid condition,^^^ produces effervescence, due to the evolution of carbon dioxide. The latter may be detected by inclining the test-tube in which the effervescence has taken place so as to pour only the gas- eous CO2 into another test-tube containing clear calcium hy- droxide solution. The CO2, being specifically heavier than air, displaces the air in the tube containing calcium hy- droxide, and, on closing the latter tube with the thumb and 1 The minerals magnesite (MgCO,), dolomite (CaCOgjMgCOj), and siderite (FeCOg) produce eflfervescence with a dilute acid only after being warmed. 84 agitating the liquid, a turbidity is produced, due to the for- mation of CaCOg, calcium carbonate : CO2 + Ca(OH)2 - CaCOg + H^O. 3. BaCla, barium chloride, precipitates white BaCOg, bariimi carbonate ; Pb(C2H302)2, plumbic acetate, precipitates white PbCOa ; both are soluble with effervescence in dilute acids. 4. AgNOg, argentic nitrate, precipitates white Ag2C03, argentic carbonate, which in a little time becomes yellowish, and on being boiled with an excess of sodium carbonate changes to brownish-gray AggO, argentic oxide. The argen- tic oxide is soluble in ammonium hydroxide and in ammo- nium carbonate. SILICIC ACID, H^SiOj. (Silicic acid combines with bases to form salts called sili- cates.) Na^SiO^y sodium silicate, may he employed in making the tests. 1. Of the silicates (compounds containing the various anions SiO/''^ SiOa'', Si20/', etc.), only those of the alkalies are soluble in water ; the others are partially soluble in con- centrated acids. The addition of an acid (as hydrochloric acid) to a solution of a silicate of an alkali causes the separation of silicic acid, which, if the solution is of sufficient concentration, appears as a gelatinous precipitate ; ammonium chloride also separates silicic acid from solutions of silicates of the alkalies : Na^SiOj + 2HC1 = H2Si03 + 2NaCl ; Na2Si03 + 2NH,C1 + 2H2O = H2Si03 + 2NaCl + 2NH,0H. The silicic acid separated in this manner is somewhat soluble in dilute acids. On evaporating the solution containing silicic acid — i.e.y the solution with the precipitate in suspension — to 85 the dryness of dust on a water-bath, the silicic acid loses water and amorphous silicic acids are produced, — i.e., poly- silicic acids, H2Si409, for example, which are entirely insolu- ble in water : 4H2Si03 = H^Si A -h 3H2O. On extracting the residue with water containing a little hy- drochloric acid, the metal which had originally been in com- bination with the silicic acid is dissolved as a chloride, while the silicic acid remains undissolved. Evaporation over a free flame is not advised, as thereby (because of the stability of silicic acid when heated) a part of the salt might be recon- verted into silicates, as, for example : H^Si A + 2NaCl = Na^Si A + 2HC1. For the methods employed in dissolving and disintegrating silicates insoluble in water, see Silicates, page 130. 2. BaClg, barium chloride, precipitates in solutions of silicates of the alkalies w^hite BaSiOg, barium silicate; Pb(C2H302)2, plumbic acetate, precipitates white PbSiOg, plumbic silicate ; AgNOa, argentic nitrate, precipitates yellow- ish Ag2Si03, argentic silicate ; all soluble in acids, the argen- tic silicate being also soluble in ammonium hydroxide. 3. NH4HM0O4, ammonium molybdate, together with an excess of nitric acid, added to a solution of a silicate pro- duces a yellowish coloration, and, in the presence of con- siderable ammonium chloride, a lemon-yellow precipitate. Warming facilitates the reaction. 4. On fusing a silicate with microcosmic salt in the loop of a platinum wire, the sodium metaphosphate which is produced dissolves the base, while the silicic acid remains undissolved and swims in small opaque particles in the otherwise trans- parent bead while the latter is in a state of fusion (" skeleton of silica") ; for example : CaSiOa + NaPOg = CaNaPO^ + SiO^. 86 Uncombined silicic acid produces the same result. The reac- tion is made more evident by coloring the bead with a com- pound of copper or of iron. ARSENIOUS ACID, H3ASO3. (See page 29.) ARSENIC ACID, HjAsO^. (See page 34..) CHROMIC ACID, HjCrO^. (Chromic acid combines with bases to form salts called chromates.) K,firO^^ potassium chromate, may be employed in making the tests. 1. Most of the chromates are insoluble in water. The chromates (compounds of the anion CrO^^Q of the alkalies (the neutral salts) are easily soluble ; the dichromates (the so-called acid salts, compounds containing the anion CrgOy'') are soluble, with the production of a reddish- yellow color. 2. BaCla, barium chloride, precipitates from solutions of chromates yellow BaCrO^, barium chromate, soluble with great difficulty in water, soluble in hydrochloric and in nitric acids. 3. Pb(C2H302)2, plumbic acetate, precipitates yellow, crys- talline PbCrO^, plumbic chromate (chrome-yellow), insoluble in water and in acetic acid, soluble in nitric acid and in sodium hydroxide, in the latter with the formation of Na2Cr04, sodium chromate, and NagPbOg, sodium plum- bite ; acetic acid reprecipitates lead chromate from the sodium hydroxide solution. 4. AgNOg, argentic nitrate, precipitates in solutions of chromates purplish-red AggCrO^, argentic chromate, and in solutions of dichromates purplish-red Ag2Cr207, argentic di- 87 chromate, both soluble in nitric acid and in ammonium hydroxide. 5. HgS, hydrogen sulphide, conducted into a solution of a chromate containing considerable free hydrochloric acid or sulphuric acid, reduces the chromate, with the formation of a soluble chromic salt and the separation of sulphur, the solution at the same time becoming green in color (conver- sion of the anion Cr04'' into the cation Cr* * ') : 2K2CrO, + SH^S + lOHCl --= 2CtC\, + S3 -|- 4KC1 + SHp. In case the acid is present in small quantity greenish Cr(OH)3, chromic hydroxide, or (especially on warming the solution) brown chromium chromate, is precipitated : 2K2CrO, + 3H2S + 4HC1 = 2Cr(OH)3 + S3 + 4KC1 + 2H2O; SK^CrO, + 3H2S + 6HC1 = (CrO)2CrO, + S3 + 6KC1 + 6H2O. The action of ammonium sulphide in neutral or alkaline solutions of chromates is similar to that of hydrogen sulphide. 6. On adding C2H5OH, alcohol, to a solution of a chromate or dichromate containing free hydrochloric or sulphuric acid, and warming the liquid, the chromate is reduced to a chromic salt, while the alcohol is oxidized to CgH^O, aldehyde ; in consequence, the liquid becomes green in color and the odor of aldehyde becomes evident : K^CrA + 4H2SO, + SC^H^OH = 2KCr(SO,)2 + SC^H.O + 7H,0. 7. On heating a chromate with concentrated hydrochloric acid chlorine is evolved and chromic chloride is produced : 2K2Cr04 + 16HC1 = 2CrCl3 4- 4KC1 + SHfl + 6C1. 8. H2O2, hydrogen dioxide, added in small quantity to a dilute solution of a chromate, rendered acid with hydro- chloric acid, produces a blue coloration in the solution due to the formation of perchroraic acid (HCrOg?). On agitating 88 the liquid with ethyl ether the latter extracts the perchromic acid from the water and becomes blue in color. Care should be taken not to use an excess of the chromate, otherwise the chromic acid and perchromic acid will, with the evolution of oxygen, be reduced to chromic oxide. 9. Chromates fused in a bead of borax or of microcosraic salt impart a yellowish-green color to the bead while hot, which becomes emerald-green on cooling. ' THIRD GROUP. Acids which are not precipitated by BaClg, barium chloride, but are precipitated by AgN03, argentic nitrate : Hydrochloric Acid, Hydrobromic Acid, Hydriodic Acid, Hydrocyanic Acid, Hydroferrocyanic Acid, Hydroferricyanic Acid, Sulphydric Acid (Hydrog^en Sulphide), Nitrous Acid, Hypochlorous Acid. HYDROCHLORIC ACID, HCI. (Hydrochloric acid combines with bases to form salts called chlorides.) NaCl, sodium cMoride, may be employed in making the tests. 1. The chlorides (compounds of the anion CI') are sol- uble in water, with the exception of argentic chloride, mercurous chloride, and plumbic chloride ; the latter, how- ever, being sparingly soluble in cold water. (For dissolv- ing insoluble chlorides, see Dissolving Oxides and Salts, page 121.) 2. AgN03, argentic nitrate, precipitates white curdy AgCl, argentic chloride, insoluble in dilute nitric acid, easily soluble in ammonium hydroxide. From its solution in ammonium hydroxide the argentic chloride is reprecipitated by nitric 89 acid. The precipitate is also soluble in KCN, |X)tassium cyanide, and in NagSgOs, sodium hyposulphite, with the for- mation of the complex anion AgSaOg' : Na^SA + AgCl -: NaAgSA + NaCl. When exposed to sunlight the precipitate changes in color to violet and then to black. 3. Pb(C2H302)2, plumbic acetate, precipitates, in hydro- chloric acid and in solutions of chlorides, white, sometimes crystalline PbCl2, plumbic chloride, sparingly soluble in cold water, easily soluble in hot water, from which, when in con- centrated solution, it crystallizes, on cooling, in glistening rhombic needles. Precipitation does not occur in very dilute solutions of chlorides. 4. On placing a dry mixture of a chloride and potassium dichromate in a small retort or tubulated fractionating flask, adding concentrated sulphuric acid, and carefully distilling the contents of the retort, Cr02Cl2, chlorochromic anhydride, as a brownish-red gas,^^^ is produced, which, when conducted into a receiving flask, condenses into a brownish-red liquid : 4KC1 + K2Cr207 + 6H2SO, = 2Cr02Cl2 + 6KHSO, + SUfi. Sodium hydroxide added to the brownish-red distillate pro- duces a yellowish solution of NagCrO^, sodium chromate^^^ (together with sodium chloride) : Cr02Cl2 + 4NaOH = Na2CrO, + 2NaCl -f- 2H2O. If the yellowish solution is acidified with acetic acid and plumbic acetate added, the production of a yellow precipitate of plumbic chromate gives indirect but conclusive evidence of chlorine. ^ Distinction from iodides, whioh furnish violet-colored vapors of free iodine. 2 Distinction from bromides, which do not impart a color to the liquid. 8* 90 HYDROBROMIC ACID, HBr. (Hydrobromic acid combines with bases to form salts called bromides.) KBvj potassium bromide^ may he employed in making the tests. 1. The bromides (compounds of the anion Br') in general are soluble in water. Argentic bromide and mercurous bromide are insoluble ; plumbic bromide is sparingly soluble in water. 2. AgNOg, argentic nitrate, precipitates yellowish-white, curdy AgBr, argentic bromide, insoluble in dilute nitric acid, sparingly soluble in dilute and more easily soluble in concen- trated ammonium hydroxide. The precipitate is easily soluble in potassium cyanide and in sodium hyposulphite. 3. Pb(C2H302)2, plumbic acetate, precipitates in hydro- bromic acid and in solutions of bromides white, crystalline PbBrg, plumbic bromide, sparingly soluble in cold water, more easily soluble in hot water. 4. Dry bromides, on being distilled in a retort with potas- sium dichromate and concentrated sulphuric acid (see under Chlorides, 4, page 89), yield brown vapors of bromine, which condense in the receiver as a brown distillate of bromine, free from chromium : 6KBr + K^Cr^Oy + TH^SO, =-- Cr2(SO,)3 -f 4K2SO4 + 7H2O -f- Brg. Sodium hydroxide added to the distillate decolorizes it, form- ing sodium bromide and NaBrO, sodium hypobromite : Br2 -f 2NaOH = NaBr -f- NaBrO -f- H^O. As sodium hypobromite solution is itself yellowish in color, it is well finally to add ammonium hydroxide, whereupon immediate and complete decolorization will occur : 2NH,0H + SNaBrO = N2 + 3NaBr + SHp. 91 5. Chlorine-water added in small quantity to a solution of a bromide liberates bromine, which remains dissolved in the water. On adding a small quantity of chloroform or of carbon disulphide (both of which are insoluble in water and sink to the bottom of the test-tube), closing the mouth of the tube with the thumb, and thoroughly shaking it, the chloro- form or carbon disulphide extracts the bromine and collects at the bottom of the tube as a yellowish or brownish liquid. The depth of coloration depends upon the quantity of bromine present. If an excess of chlorine- water is used, decolorization of the liquid occurs, due to the formation of HBrOg, bromic acid : Br2 + Cl,o = 2BrCl,; BrClg -f 3H2O = HBrOg -j- 5HC1. HYDRIODIC ACID, HI. (Hydriodic acid combines with bases to form salts called iodides.) Kly potassium iodide, may he employed in making the tests, 1. Most of the iodides (compounds of the anion I') are soluble in Avater ; the others are soluble in acids, with the exception of argentic iodide. Plumbic iodide is sparingly soluble in cold water. 2. AgNOg, argentic nitrate, precipitates yellowish, amor- phous Agl, argentic iodide, insoluble in nitric acid and in ammonium hydroxide, soluble in potassium cyanide and in sodium hyposulphite. 3. Pb(C2H302)2, plumbic acetate, precipitates in solutions of hydriodic acid and of iodides yellow, crystalline Pbig, plumbic iodide, soluble in hot water, from which, on cooling, it separates in glistening yellow, six-sided plates. 4. FeClg, ferric chloride, added to a solution of an iodide 92 causes a liberation of iodine in consequence of the conversion of Fe*" into Fe": 2FeCl3 + 2KI = 2FeCl2 + 2KC1 + L. 5. Dry iodides, distilled in a retort with potassium dichro- mate and concentrated sulphuric acid (see under Chlorides, 4, page 89), yield violet vapors of iodine -S^^ 6KH- K^CrA + 7H2SO, = Cr2(SO,)3+ 4K2SO,+ TH^OH- !«. The iodine contained in the distillate is soluble in sodium hydroxide, forming Nal, sodium iodide, and NalOg, sodium iodate, the distillate at the same time becoming colorless : Ifi + 6NaOH = 5NaI + NalOg + SHfi. 6. Chlorine-water added in small quantity to a solution of an iodide liberates iodine, which imparts a yellowish or brownish-yellow color to the solution. On adding a small quantity of chloroform or of carbon disulphide to the liquid, closing the tube with the thumb, and thoroughly shaking it, the chloroform or carbon disulphide will settle at the bottom of the tube, and be found to possess a pinkish-violet color, due to the free iodine extracted from the aqueous solution. The addition of an excess of chlorine water causes the oxidation of the iodine to iodic acid, with a consequent decolorization of the liquid : I,+ C% = 2IC1,; ICI5 + 3H2O = HIO3 + 5HC1. If, instead of chloroform or carbon disulphide, a drop of dilute starch paste is added, the solution becomes blue, due to the action of the free iodine upon the starch. The test is exceedingly delicate, and when considerable iodine is present the liquid becomes black upon the addition of the starch ; therefore strong solutions of iodides should be diluted before making this test. * Distinction from chlorine and bromine. 93 HYDROCYANIC ACID, HCN. (Hydrocyanic acid combines with bases to form salts called cyanides.) KCNy potassium cyanide^ may be employed in making the tests. 1. Of the cyanides (compounds of the anion CN'), those of the alkalies and of the alkaline earths are soluble in water (also mercuric cyanide) ; the cyanides of the heavy metals are insoluble in water, although many of them are soluble in potassium cyanide, with the formation of double salts, com- pounds of the complex anion Ag(CN)/ ; for example : AgCN + KCN = KAg(CN)2. By the addition of an acid to these solutions the cyanide of the heavy metal is usually but not invariably reprecipitated, with the evolution of hydrocyanic acid : KAg(CN)2 + HNOa = AgCN + HCN + KNO3. For methods of dissolving and fusing cyanides,, see 4, page 128. 2. AgNOa, argentic nitrate, precipitates in solutions of hydrocyanic acid and of cyanides white, curdy AgCN, in- soluble in nitric acid, easily soluble in ammonium hydroxide. From this solution it is reprecipitated by nitric acid : AgCN + NH3 =. NHgAgCN ; NHgAgCN + HNO3 = AgCN + NH,N03. Argentic cyanide is soluble in potassium cyanide ; therefore a precipitate appears only after an excess of argentic nitrate has been added. It is also soluble in sodium hyposulphite. On igniting argentic cyanide it breaks up into metallic silver and cyanogen gas (together with some argentic paracyanide) : AgCN = Ag + CN. 3. Pb(C2H302)2, plumbic acetate, produces in solutions of 94 cyanides a white precipitate of Pb(CN)2, plumbic cyanide, soluble in an excess of the reagent and in nitric acid. 4. If XaOH, sodium hydroxide, FeSO^, ferrous sulphate, and FeCls, ferric chloride, are adde^l in small quantities to a solution of hydrocyanic acid or to a cyanide, the mixture warmed, and finally acidulated with hydrochloric acid, a blue precipitate of Fe4(Fe(CN)g)3, ferric ferrocyanide (Prussian blue), is formed ; while the ferrous hydroxide first produced is dissolved by the acid. The ferrous sulphate with the sodium hydroxide produces Fe(OH)2, ferrous hydroxide : FeSO, + 2XaOH = Fe(0H)2 + Na^SO,, which, on being warmed with the cyanide solution, yields a ferrocyanide ; for example, with potassium cyanide it yields K4Fe(CX)g, potassium ferrocyanide : Fe(OH)2 -f- 6KCX = K,Fe(CN)6 + 2KOH, which combines with the iron of the ferric chloride to form blue ferric ferrocyanide (Prussian blue). 5. To detect hydrocyanic acid which is being evolved from a liquid, a drop of yellow ammonium sulphide and of ammo- nium hydroxide is placed on the concave side of a watch- glass, the watch-glass inverted and placed as a cover over the vessel in which the hydrocyanic acid is being evolved, so that the vapors of the acid coming in contact with the ammoniacal liquid can be absorbed. After some time the watch-glass is removed, placed on a water-bath, and warmed, whereby NH4CNS, ammonium sulphocyanide, is produced : HCN + (NHJ^Sg +NH,OH = NH.CNS + {^n,\^ + Hp, which remains as a dry residue on the complete evaporation of the liquid. This residue is dissolved in a little water ; a few drops of hydrochloric acid (to decompose any (NH^jgS remaining) and a drop of ferric chloride are added, whereby a claret-red coloration is pnxluced, due to the formation of Fe(CNS)3, ferric sulphocyanide. 95 6. When heated in a reduction-tube the cyanides of the heavy metals are decomposed ; the cyanides of the noble metals break up into metal and cyanogen gas ; other cyanides break up into metal, carbon, and nitrogen. Argentic and mercuric cyanides, in which the cyanogen cannot be detected by the ordinary reagents, can be recognized in this manner. Mercuric cyanide in aqueous solutions, when ti*eated with hydrogen sulphide, decomposes and forms mercuric sulphide and hydrocyanic acid. HCX and CX are virulent poisons. HYDROFERROCYANIC ACID, H^FeCCN^ (Hydroferrocyauic acid combines with bases to form salts called ferrocyanides.) K^Fe{CN)^, potassium ferroeyanide, may he employed in making the tests, 1. The ferrocyanides (compounds of the complex anion Fe(CN)g""), with the exception of those of the alkalies and of the alkaline earths, are mostly insoluble in water. Regard- ing their solution and fusion, see page 129. 2. AgXOj, argentic nitrate, precipitates white Ag^Fe(CX)j, argentic ferroeyanide, insoluble in nitric acid and in ammo- nium hydroxide, soluble in potassium cyanide. 3. Pb(C2H302)2, plumbic acetate, in solutions of ferro- cyanides precipitates white Pb2Fe(CX)g, plumbic ferroeyanide, insoluble in dilute nitric acid. 4. Ferrous salts (FeSO^, feri-ous sulphate) produce in solu- tions of ferrocyanides (when the ferroeyanide is in excess) a white precipitate, which, on exposure to the air, rapidly changes to bluish-white K2Fe(Fe(CX)g), potassium ferrous ferroeyanide (Everett's salt). When the ferrous salt is in excess, Fe2Fe(CX)g, ferrous fernx'yanide, is produced. 5. Ferric salts (FeCla, ferric chloride) precipitate dark- 96 blue Fe4(Fe(CN)g)3, ferric ferrocyanide (Prussian blue), insol- uble in acids. 6. CuSO^, cupric sulphate, precipitates brownish-red Cu2Fe(CN)g, cupric ferrocyanide. HYDROFERRICYANIC ACID, H3Fe(CN)6. (Hydroferricyanic acid combines with bases to form salts called ferricyanides.) K^Fe(CN)Q, potassium femcyanide, may he employed in making the tests. 1. Of the ferricyanides (compounds of the complex anion Fe(CN)g'''), those of the alkalies and of the alkaline earths are soluble in water, while those of the heavy metals are mostly insoluble in water. Regarding their solution and fusion, see page 129. 2. AgNOg, argentic nitrate, precipitates from solutions of ferricyanides reddish-brown Ag3Fe(CN)g, argentic ferri- cyanide, insoluble in nitric acid, soluble in ammonium hy- droxide and in potassium cyanide. 3. Ferrous salts (FeS04, ferrous sulphate) precipitate Fe3(Fe(CN)g)2, ferrous ferricyanide (TurnbulFs blue), insolu- ble in acids. Ferric salts fail to produce a precipitate, but cause a dark coloration ; possibly soluble Fe2(Fe(CN)6)2, ferric ferricyanide, is produced : 2FeCl3 + 2K3Fe(CN)g -. Fe,(Fe(CN)g)2 -F 6KC1. 4. CUSO4, cupric sulphate, precipitates greenish-yellow Cu3(Fe(CN)g)2, cupric ferricyanide. 97 SULPHOCYANIC ACID, HCNS. (Sulphocjanic acid combines with bases to form salts called sulphocyanides, also termed mlphocyanates.) KCNSy potassium sulphocyanide, may be employed in mak- ing the tests. 1. The sulphocyanides (compounds of the complex anion CNS') of the alkalies, of the alkaline earths, and of the heavy metals, with the exception of mercuric and argentic sulpho- cyanides, are soluble in water. 2. AgNOa, argentic nitrate, precipitates in solutions of sulphocyanic acid and of sulphocyanides white, curdy AgCNS, argentic sulphocyanide, insoluble in water and in dilute nitric acid, and which blackens when exposed to the direct rays of the sun. 3. Pb(C2H302)2, plumbic acetate, produces a yellowish crys- talline precipitate, Pb(CNS)2, plumbic sulphocyanide, which forms slowly, and on being boiled is converted into a white basic salt. 4. HgNOg, mercurous nitrate, produces a white precipitate of HgCNS, mercurous sulphocyanide, which on being boiled is resolved into gray, finely divided, metallic mercury and Hg(CNS)2, mercuric sulphocyanide. 5. FeClg, ferric chloride, produces an intense claret-red coloration, due to the formation of soluble Fe(CNS)3, ferric sulphocyanide. In exceedingly dilute solutions the color is pale red. HgCl2, mercuric chloride, destroys the coloration, soluble Hg(CNS)2, mercuric sulphocyanide, being formed. 98 SULPHYDRIC ACID, HjS (HYDROGEN SULPHIDE). (Sulphydric acid combines with bases to form salts called sulphides.) Na^Sf sodium sulphidCj may be employed in making the tests, 1. The sulphides (compounds of the anion S" and of the anion HS'), with the exception of those of the alkalies and of the alkaline earths, are insoluble in water. Most of them are soluble in hydrochloric acid and in nitric acid ; some are soluble only in nitro-hydrochloric acid. (See Sulphides of the Heavy Metals, page 128.) They may be recognized by their giving off hydrogen sulphide when dissolved in hydro- chloric acid, or by the separation of sulphur when dissolved in nitric acid or in nitro-hydrochloric acid. 2. AgN03, argentic nitrate, precipitates black AggS, argen- tic sulphide, soluble in nitric acid when warmed. 3. Pb(C2H302)2, plumbic acetate, precipitates in solutions of sulphides or of hydrogen sulphide black PbS, plumbic sulphide, soluble in nitric acid when warmed. 4. To detect hydrogen sulphide gas a strip of filter-paper is moistened with plumbic acetate and held in the atmosphere containing the gas. In the presence of hydrogen sulphide the paper becomes brown or black, due to the formation of PbS, plumbic sulphide. 5. A few drops of an alkaline solution of plumbic oxide (K2Pb02, potassium plumbite), added to a solution contain- ing hydrogen sulphide or a sulphide of a metal, produces a perceptible brownish coloration, even if only the slightest trace of the sulphide be present. 6. Na2NOFe(CN)5, sodium nitro-prusside, solutions are colored violet by sulphides, but not by solutions of free hydrogen sulphide. 7. Many of the sulphides of the metals, when heated in a reduction-tube, yield a sublimate of sulphur. Sulphides, 99 heated in a glass tube open at both ends and held obliquely in the flame, are oxidized, with the formation of SOg, sul- phurous anhydride. Ignited with sodium carbonate in the reducing flame on charcoal, they yield sodium sulphide, which, when placed on a clean silver coin and moistened with water, produces a black discoloration of argentic sulphide. (Nitrous acid combines with bases to form salts called nitrites.) KNO2, potassium nitntej may be employed in making the tests. 1. Most of the nitrites (compounds of the anion NO2') are soluble in water. Treated with hydrochloric or sulphuric acid they evolve brownish-red fumes of NO2, nitrogen dioxide. 2. AgNOg, argentic nitrate, precipitates white AgNOj, argentic nitrite, soluble with difficulty in water. 3. Pb(C2H302)2, plumbic acetate, colors solutions of nitrous acid yellow. 4. HgS, hydrogen sulphide, is decomposed by nitrous acid with the separation of sulphur : H2S + 2HNO2 = 2NO + S -h 2H2O. 5. FeSO^, ferrous sulphate, added to a solution of a nitrite containing a few drops of sulphuric acid,^*^ produces a brown or black coloration, due to the formation of NO, nitrogen monoxide, which enters into combination with the ferrous sulphate : 3FeSO, + H2SO, -I- 2HNO2 = FeSO,(NO)2 + Fe2(SO,)3 + 2H2O. Heating the liquid causes the coloration to disappear. ^ The nitrites of commerce usually contain free nitrous acid, and there- fore respond to the test without the addition of sulphuric acid. 100 6. KI, potassium iodide, (or Cdlj, cadmium iodide,) starch paste, and dilute sulphuric acid, added to a solution of a nitrite, immediately produce a blue coloration in the liquid. The nitrous acid liberates iodine from the hydriodic acid : 2HNO2 -f 2HI = 2NO + 2H2O + I2. The free iodine combining with the starch forms the blue compound. (In this test cadmium iodide or potassium iodide free from iodic acid should be used, as hydriodic and iodic acid undergo decomposition when together, with the liberation of iodine : 5HI + HIO3 = Ifi + 3H2O.) HYPOCHLOROUS ACID. HCIO. (Hypochlorous acid combines with bases to form salts called hypochlorites.) NaClOj sodium hypochlorite, may be employed in making the tests, 1. The hypochlorites (compounds of the anion CIO'), as a rule, contain chlorides, produced, during the preparation of the hypochlorite, by the action of the chlorine upon hydroxides : 2NaOH + CI2 = NaClO + NaCl + H^O. On the addition of acids they are decomposed, with the evolution of chlorine : NaClO + 2HC1 = NaCl -f- Cl^ + Ilfi ; NaClO + NaCl + H^SO, = Na^SO, + Cl^ + H^O. 2. AgNOg, argentic nitrate, added to a solution of a hypo- chlorite produces soluble AgClO, argentic hypochlorite, which immediately breaks up into white, insoluble AgCl, argentic chloride, and soluble AgClOg, argentic chlorate : 6AgC10 = 2AgC103 + 4AgCl. 3. Pb(C2H302)2, plumbic acetate, produces at first a white precipitate of PbCl,, plumbic chloride, which soon becomes 101 yellow and finally brown, due to the formation of PbO^, lead dioxide. (In like manner MnSO^, manganous sulphate, yields brown MnO(OH)2, hydrated peroxide of manganese.) FOURTH GROUP. Acids which are not precipitated by barium chloride or by argentic nitrate : Nitric Acid, Chloric Acid. NITRIC ACID, HNO3. (Nitric acid combines with bases to form salts called nitrates.) KNO^, potassium nitrate, may be employed in making the tests. 1. The nitrates (compounds of the anion NO3'), with the exception of a few basic salts, are soluble in water. Some nitrates (for example, Ba(N03)2, barium nitrate) are only sparingly soluble in nitric acid. 2. BaClg, Pb(C2H302)2, and AgNOg do not produce pre- cipitates in solutions of nitrates. 3. On placing a small crystal of FeSO^, ferrous sulphate, in a cooled mixture of concentrated sulphuric acid and a solution of a nitrate, a brownish-black ring is formed around the crystal. In the reduction of the nitric acid NO, nitrogen monoxide, is produced, which combines with the ferrous sulphate to form an unstable compound : 7FeS0, + 3H2SO, + 2HNO3 = [FeS0,(N0)2] + 3Fe2(SO,)3 + 4H20. The test is best made in a flat porcelain dish, or in a watch- glass placed on white paper. Heat destroys the black ring. 4. KI, potassium iodide, (or Cdlj, cadmium iodide,) starch paste, and dilute sulphuric acid, added to a solution of a nitrate, produce no reaction (distinction from nitrites), but, 9* 102 on placing a fragment of zinc in the liquid, nitrous acid is evolved, which, acting upon the potassium iodide, liberates the iodine, which with the starch produces a blue coloration : HNO3 +Zn + H2SO, = HNO2 + ZnSO, + Hfi ; 2HNO2 + 2HI = 2NO + 2H2O + I2. 5. Nitrates of the alkalies when heated in a reduction-tube are reduced to nitrites, with the evolution of oxygen : KN03 = KN02 + 0. The nitrates of the heavy metals when heated in a reduc- tion-tube evolve reddish-brown fumes of nitrogen dioxide : Pb(N03)2 = PbO + O + 2NO2. The latter reaction also takes place when a nitrate of an alkali mixed with cupric sulphate is heated in a reduction-tube : 2KNO3 + CuSO, = K2SO, +CuO + O + 2NO2. Nitrates deflagrate when ignited on charcoal. CHLORIC ACID, HCIO3. (Chloric acid combines with bases to form salts called chlorates.) KClO^y potassium chlorate, may be employed in making ilu tests. 1. The chlorates (compounds of the anion CIO3') are soluble in water. 2. BaClg, barium chloride, does not produce a precipitate in solutions of chlorates. Pb(C2H302)2, plumbic acetate, and AgN03, argentic nitrate, do not produce precipitates if the solution o£ the chlorate be free from chlorides. 3. On warming a solution of a chlorate with hydrochloric acid the liquid becomes greenish yellow in color, and greenish- yellow fumes of a mixture of chlorine and CI2O4, chlorine tetroxide (chlorine jxjroxide), are evolved : KCIO3 +6HC1 := KCl + Clg + 8H2O ; 2KCIO3 + 4HC1 = 2KC1 + CI2O4 + CI2 + 2H2O. 103 4. Concentrated sulphuric acid poured over a vei-y miall piece of a chlorate in a porcelain dish causes a decomposition of the chlorate, with the production of a perchlorate and chlorine tetroxide (chlorine peroxide) : 3KCIO3 + 2H2SO4 = 2KHSO, + KCIO4 + CIA + H2O. Great care should be used in making this test, and only small quantities of chlorate should be employed. Warming should be avoided, as explosions, which may cause personal injury, are likely to occur on the application of heat. 5. Chlorates heated in a reduction-tube undergo decomposi- tion, and are converted into chlorides, with the evolution of oxygen : KCIO3 = KCl + O3. (Bromates and iodates undergo a similar decomposition on being heated, forming respectively bromides and iodides, with the evolution of oxygen.) APPENDIX: OEGANIC ACIDS. Acetic Acid, Oxalic Acid, Tartaric Acid. (Acetic acid combines with bases to form salts called acetates.) NaC2lI^02, sodium acetate, may be employed in making the 1. Most of the acetates (compounds of the anion CH3COO', /. e., (C2H3O/) ) are easily soluble in water. 2. BaClg, barium chloride, and Pb(C2H302)2, plumbic acetate, do not produce precipitates in solutions of acetates. 3. AgN03 argentic nitrate, precipitates, in concentrated acetic acid or in concentrated solutions of acetates, crystalline AgCgHgOg, argentic acetate, soluble in a large quantity of water and in ammonium hydroxide. 104 4. FeClg, ferric chloride, added to a neutral acetate, or to acetic acid, which must afterwards be exactly neutralized with ammonium hydroxide, produces a reddish-brown solution of Fe(C2 1^302)3, ferric acetate : 3NaC2H302 + FeCl3 == Fe(C2H302)3 + 3NaCl. On warming this solution a precipitate of brownish-red Fe(OH)2C2H302, basic ferric acetate, separates, while the supernatant liquid becomes colorless : re(C,H30,)3 + 2H,0 = Fe(OH),C,HA + 2nC,Hf>,. 5. On adding sulphuric acid to a solution of an acetate and warming the liquid, HC2H3O2, acetic acid, is liberated, wiiich may be recognized by its odor of vinegar. 6. On adding CgHgOH, alcohol, to a cool solution of an acetate containing sulphuric acid and then w^arming the liquid, C2H5C2H3O2, ethyl acetate (acetic ether), is produced, which may be recognized by its characteristic apple-like odor : C2H,OH + H2SO, - C2H,HSO, + H2O ; C2H5HSO, + HC2H362 = C2H,C2H302 H- H2SO,. The alcohol should not be added while the liquid is hot, as violent ebullition might occur with consequent spurting of the liquid. 7. Acetates on being ignited are decomposed, without the separation of carbon, into volatile products (for example, acetone) and carbonates or oxides of the metals which were in combination as acetates. OXALIC ACID, H2C2O4. (Oxalic acid combines with bases to form salts called oxalates.) {NH^fifii, ammonium oxalate, may be employed in making the tests. 1. Of the oxalates (compounds of the anion C2O/' and of the anion HC2O/), those of the alkalies are soluble in water; most of the others are insoluble in water. 105 2. BaClg, barium chloride, precipitates in solutions of neutral oxalates white BaCgO^, barium oxalate, easily soluble in hydrochloric and in nitric acid. 3. CaClg, calcium chloride, precipitates from neutral solu- tions of oxalates white CaCgO^, calcium oxalate, soluble in hydrochloric and in nitric acid, insoluble in acetic acid. 4. Pb(C2 11302)2, plumbic acetate, precipitates white PbC204, plumbic oxalate, soluble in nitric acid. 5. AgNOg, argentic nitrate, precipitates white Ag2C204^ argentic oxalate, soluble in nitric acid and in ammonium hydroxide. 6. Concentrated sulphuric acid, on being warmed with oxalic acid or oxalates, decomposes them into water, COg, carbon dioxide, and CO, carbon monoxide : H2C2O, + H2SO, = H2O + CO2 + CO + H2SO,. On pouring the gases into a test-tube containing clear solution of calcium hydroxide (lime-water), closing the tube with the thumb, and shaking it, the production of a milky turbidity, due to the formation of calcium carbonate, indicates the presence of carbon dioxide. 7. Oxalates on ignition are decomposed into carbon mon- oxide and carbonates or oxides of the metals which were in combination as oxalates. Pure oxalates on being ignited do not become black in color : K2C20, = CO + K2C03. TARTARIC ACID, H2C4H4O6. (Tartaric acid combines with bases to form salts called tartrates.) KNaCJI^Q, potassium sodium tartrate, may be employed in making the tests. 1. The tartrates (compounds of the anion C^H^O/' and of the anion HC^H^O/) of the alkalies and some of the tar- 106 trates of the heavy metals are soluble in water ; the other tartrates are soluble in acids. 2. BaCIg, barium chloride, added in excess precipitates white BaC4H^Og, barium tartrate, soluble in hydrochloric and in nitric acid. 3. CaClg, calcium chloride, added in excess precipitates white, crystalline CaC^H^Og, calcium tartrate, soluble in hydrochloric, nitric, and acetic acids. The precipitate is also soluble in potassium or sodium hydroxides, forming a clear liquid, from which, on boiling, the calcium salt separates in gelatinous masses. Probably a salt, CaNa2C4H20g, is pro- duced in which the hydrogen atoms of the alcoholic hydroxyl of the taiiaric acid have also been replaced by a metal : CaQHA + 2NaOH = CaNa^C^HA + ^H^O. This compound, on being boiled with considerable water, is reconverted into the original calcium tartrate : CaXa2C4H206 -f 2H2O = CaC^HPe -f- 2NaOH. 4. Pb(C2H302)2; plumbic acetate, precipitates white PbC^H^Og, plumbic tartrate, soluble in nitric acid and in ammonium hydroxide. 5. AgNOg, argentic nitrate, precipitates in solutions of neutral tartrates Ag2C4H40g, argentic tartrate, soluble in nitric acid and in ammonium hydroxide. On boiling the pre- cipitate it is decomposed, with the separation of metallic silver. 6. KC2H3O2, potassium acetate, in the presence of free acetic acid produces in concentrated solutions of free tartaric acid, and of tartrates, a white precipitate of KHC^H^Og, acid potassium tartrate : Ufijifi, + KC2H3O2 - KHC^HA -^ HC2H3O2 ; Na^QHA -f KC2H3O2 + HC2H3O2 - KHC.HA + 2NaC2H,02. 7. Tartrates on being ignited are decomposed, with the production of an odor resembling that of burnt sugar, the separation of carbon and the formation of carbonates. III. PRELIMINARY EXAMINATION. (A) PRELIMINARY TESTS IN THE DRY WAY. The special tests for bases and acids (testing in the Wet Way) are always preceded by a short preliminary examina- tion (in the Dry Way), in order to obtain general information regarding the nature of the substance to be analyzed. It is hardly possible to determine the best method to be employed in the preparation of the substance for analysis without re- sorting to this preliminary examination. It should therefore never be omitted. When solutions are to be analyzed, a portion is evaporated to dryness at a moderate temperature (without ignition), and the residue used for the preliminary tests. 1. EXAMINATION IN THE REDUCTION-TUBE. To ascertain the behavior of the substance at higher tem- peratures, a small portion of it, or of the residue obtained by evaporation, is placed in a narrow glass tube closed at one end, and heated, at first slightly, afterwards more strongly, and then to redness. The occurrence of any of the following changes should especially be noted : 1. Separation of Carbon: Indicates the presence of organic compounds. Simultaneously a generation of empyreumatic vapors takes place, or, if nitrogen is present, an odor of burnt feathers is produced. 2. Elimination of Water : Indicates the presence of water of crystallization or of adherent moisture; frequently ^ 107 108 change of color occurs, as in the transformation of the bhie hydrous sulphate of copper (CuSO^ -|- SHgO) into the an- hydrous salt (CuSO^). Intumescence may take place as in the case of borax (Na^B^Oy -j- IOH2O), or decrepitation as in sodium chloride (in consequence of the violent expulsion of water confined between the lamellae of the crystals). 3. Change in Color: Indicates the presence of combina- tions of heavy metals. The change may be caused by the elimination of water (see 2, page 107), or by the conversion of salts into oxides; for example, cupric nitrate and cupric carbonate become black in color when heated, due to their conversion into cupric oxide : Cu(N03)2 =- CuO + 2NO2 + O ; CuC03 = CuO + C02. Many compounds differ in color when hot and when cold ; for example, oxide of zinc is yellow when hot and white when cold. 4. Formation of a Sublimate: Indicates the presence of volatile compounds. (a) White sublimate : Salts of mercury, ammonium salts, arsenious oxide, antimonious oxide. — On heating the sublimate with dry sodium carbonate, salts of mercury become red, due to the formation of mercuric oxide (frequently metallic mer- cury is produced at the same time) ; for example : HgCl2 + Na^COg = HgO + CO^ + 2NaCl. Ammonium salts evolve ammoniacal gas, which may be recognized by the odor, and by its coloring moistened tur- meric-paper brown, and red litmus-paper blue : WUfil + Na^COg = 2NH3 + CO2 + H2O 4- 2NaCl. Arsenical vapors and antimonious oxide are apparently not clianged when heated with sodium carbonate. The arsenic sublimes in octahedral crystals; the antimony forms an amorphous sublimate, which sometimes contains crystals. 109 (6) Yellow sublimate : Mercuric iodide (becomes red when stirred), arsenions sulphide. (c) Yellow to red : Compounds of mercury (formation of basic salts). (d) Yellow to brownish yellow : Sulphur (when hot col- lects in reddish-brown drops). Free sulphur, or sulphides rich in sulphur,— for example, SbgSg = SbgSg + Sg. (e) Gray to black : Mercury (globules) ; mercuric sulphide (black, red when rubbed) ; iodine (violet vapors, characteristic odor of iodine) ; arsenic (mirror). It is to be remembered that, in addition to the sublimates mentioned, quite a number of compounds exist which are more or less volatile, — for example, many chlorides. 5. Evolution of Vapors: (a) Colorless vapors should be tested for their reaction with litmus-paper. The acids frequently form clouds when escaping from the tube (in consequence of their changing from the anhydrous to the hydrous state). (6) Reddish-brown vapors : Nitrogen dioxide, bromine. Nitrogen dioxide, resulting from the decomposition of nitrates of the heavy metals, — for example, Pb(N03)2 = PbO -(- 2NO2 -f- O, — does not color starch-paper, and is recognized by its odor. Bromine, also recognizable by its odor, colors starch-paper reddish yellow. (c) Violet vapors : Iodine. Characteristic odor ; frequently simultaneous formation of a black sublimate. Colors starch- paper blue to brownish black. 6. Production of an Odor : (a) Odor of ammonia : Ammonium salts ; compounds of cyanogen or organic compounds containing nitrogen. (6) Odor of sulphurous anhydride : Resulting from the decomposition of sulphates. (c) Odor of cyanogen : Compounds of cyanogen. Cyan- 10 110 ogen gas burns when ignited, with a flame pinkish lavender in color : CN + O^^CO^ + N. (d) Odor of garlic : Compounds of arsenic, resulting from reduction. 7. Evolution of Oxygen (may be recognized by the flaring or re-igniting of a glowing stick held at the mouth of the tube) : Indicates the presence of peroxides, — for example, pyrolusite, MnOg : SMnOa-^MngO^ + Og; of mercuric oxide : HgO = Hg + 0; of salts rich in oxygen, — for example : KC103 = KCl + 03. 2. EXAMINATION ON CHARCOAL. To determine the behavior of substances in the reducing flame a small portion of the substance, generally mixed with dry sodium carbonate, is heated in a cavity in the charcoal by means of the reducing flame of the blowpipe/^^ The sodium carbonate is added in order to transform salts and sulphates into carbonates and oxides respectively, — for example : CaSO^ + Na2C03 = CaCOg + NaaSO, ; CuCla -f- Na2C03 = CuO + CO^ + 2NaCl. The addition of sodium carbonate is not necessary in the case of metals that form metallic globules, oxides, and salts which are easily decomposed, as the alkalies and their salts are ab- sorbed by the charcoal (because of their easy fusibility). The ^ The reducing flame is obtained by holding the blowpipe near the flame and by gentle blowing directing it upon the substance to be heated. The oxidizing flame is obtained by placing the blowpipe in the interior of the flame and blowing with force. Ill oxides of the remaining elements may be recognized by the following characteristics : 1. The oxides of the heavy metals heated in the reducing flame are reduced by the charcoal. The metals themselves are either volatile or non-volatile, may oxidize or not, and may be fusible or infusible ; therefore fused globules may be obtained, or infusible masses and incrustations, the latter resulting from the presence of metals that volatilize and oxidize. From plumbic oxide, for example, metallic lead is obtained : PbO + C:==Pb+CO, part of which volatilizes, combines with the oxygen of the air, and is deposited on the cooler part of the charcoal as an incrustation of yellow oxide : Pb + 0:=PbO. The metallic globules differ in their behavior in the oxi- dizing flame : some change into oxides and others remain unchanged. The ductility should also be ascertained ; for this purpose the globule is placed in a mortar and struck with the pestle ; those which are ductile are flattened into plates, while those which are brittle break into pieces and may be pulverized by subsequent rubbing. (a) Fused metallic globules, without incrustation, are produced : Yellow : gold, ductile, not oxidizable. White : silver, ductile, not oxidizable. Red : copper, ^'^ ductile, oxidizable. With incrustation, — White globule, incrustation yellow : Ductile : lead, oxidizable. Brittle : bismuth, oxidizable. White globule, incrustation white : Generally obtained as metallic spangles. 112 Ductile: tin/'^ oxidizable. Brittle : antimony, oxidizable. (b) Incrustation without metallic globule : White when cold, yellow when hot : zine. Yellowish red to brown : cadmium. (c) Gray, infusible masses : Iron Cobalt Nickel ] oxidizable. Manganese J Platinum : not oxidizable. (d) Neither globule nor incrustation : Volatile with odor of garlic : arsenic. Volatile without odor of garlic : mercury. In examining metallic globules it is to be remembered that in the presence of different metals alloys may be formed. 2. White infiLsihle masses remain on the charcoal if salts of the alkaline earths, magnesium or aluminium, are present. (By the action of Na2C03, carbonates and oxides are formed.) The white masses, moistened with a solution of cobaltous nitrate and strongly heated in the oxidizing flame, yield as follows : Aluminium : blue masses (infusible). Magnesium : pink-colored masses. Barium ^ Strontium I gray masses. Calcium J * Tin and antimony are obtained with difficulty in the form of globules when sodium carbonate is employed. Therefore on the appearance of a white incrustation a second test is made, in which, in addition to sodium carbonate, potassium cyanide is added to the salt, and the whole heated in the reducing flame. (KCN thereby changes into KCNO : for example, SnOj + 2KCN = Sn + 2 KCNO.) Compare also its behavior with cobalt solution, see 6, page 42. 113 The cobaltous nitrate on being heated is converted into co- baltous oxide : Co(N03)2 = CoO + 2NO2 + O, which combines with akiminium and magnesium compounds. With barium, strontium, and calcium, mixtures only of the oxides are obtained. Many silicates and phosphates which are fusible with diffi- culty, and also many borates and arseniates, may form blue masses when ignited with cobaltous nitrate ; frequently these double salts of cobalt are easily fusible. Zinc oxide, when ignited with cobaltous nitrate, becomes yellowish green in color ; antimonious oxide, a dirty green ; stannic oxide, bluish green. (Compounds of CoO are pro- duced with the different oxides.) 3. Green fused masses (consisting of chromic oxide) indi- cate salts of chromium and chromates. 4. Yellow or brown fused masses j consisting of sodium sul- phide, indicate the presence of compounds containing sulphur. A portion is placed on a silver coin and moistened with water to ascertain whether a black discoloration of Ag2S is produced. (See 7, page 98.) As the formation of sodium sulphide by the reduction of salts containing acids of sulphur requires time, and, like all alkali compounds, the sulphide impregnates the charcoal on continued heating, these tests must be made just after the reduction has taken place and before the sodium sul- phide has been absorbed by the charcoal. Many of the compounds containing sulphur, — for example, the sulphides, — when heated in a small glass tube open at both ends and held obliquely in the flame, yield sulphurous anhydride, which is easily recognized by its odor. 10* 114 3. EXAMINATION IN THE FLAME. If the presence of alkalies or alkaline earths is suspected, a small portion of the substance, or of the residue obtained by evaporation, is attached to a loop of clean platinum wire/^^ moistened with a drop of hydrochloric acid, and held in me flame of a Bunsen burner. The flame is colored by the salts of Potassium : violet. Sodium : intense yellow. Barium : yellowish green. Strontium : crimson. Calcium : yellowish red. It must be remembered that, if two or more of these ele- ments are present, one colored flame may conceal the other. Salts of copper and also boric acid color the flame green. For colored flames produced by the rare elements, see Ap- pendix. 4. EXAMINATION BY MEANS OF A BEAD OF MICRO- COSMIC SALT OR OF BORAX. A portion of sodium ammonium phosphate (microcosmic salt) is heated in a loop of platinum wire until it melts, and forms a bead. A very small portion of the substance to be examined is then attached to the clear bead, which is again heated in the oxidizing flame or in the oxidizing space of a Bunsen flame. The NaNH^HPO^ -f- 4H2O, sodium ammo- nium phosphate, when fused, first loses its water of crystal- lization and then changes into sodium metaphosphate : NaNH.HPO, = NaPOg + Hp + NH3. The sodium metaphosphate dissolves most of the oxides and salts (in the latter a replacement of the acids takes place), and forms beads, generally characteristic in color : ^ Or the wire may be dipped in the concentrated solution of the sub- stance to be examined. 115 CuO + NaPOg =- CuNaPO, ; CuSO, + NaPOg = CuNaPO^ + SO3. Some of the beads change color in the reducing flame or in the reducing space of the Bunsen flame (in consequence of the reduction of the phosphates); for example, the transparent bluish-green copper bead by reduction becomes brownish-red and opaque : CuNaPO^ + C = NaPOg + Cu + CO ; the violet manganic oxide bead in the reducing flame is con- verted into the colorless manganous bead : Mn2(NaP04)3 + C = 2MnNaPO, + NaPOg + CO. Borax (NaaB^O^ -|- lOHgO) with oxides and salts yields beads similar to microcosmic salt, which are likewise reducible : NaaB^O^ 4-CuO = 2NaB02 + Cu(B02)2 ; Na^B.O^ + CuSO, = 2]SraB02 + Cu(B02)2 + SO3 ; 2NaB02 H- Cu(B02)2 + C = Na^B.O^ + Cu + CO. The reduction of the oxide in the beads is often facilitated by adding a small piece of tin foil : 2CuNaP04 + Sn = Sn(NaPOj2 + Cu^. The following elements^^^ produce characteristic colomtions in the bead of microcosmic salt : Oxidizing Flame. Reducing Flame. Iron : yellow to dark red when Green to colorless, hot, light yellow to colorless when cold. Nickel : same as iron. As in the oxidizing flame.^^^ Cobalt: blue. Blue. Manganese : amethyst. Colorless. Chromium : green. Green. Copper : bhie-green. Brownish, opaque. ^For beads produced by the rare elements, see Appendix. 'For the behavior of nickel in the borax bead, see 8, page 62. 116 The remaining oxides yield colorless, transparent or trans- lucent, enamel-like beads. The behavior of silicic acid and of the silicates in the bead of microcosmic salt is characteristic. Silicic acid does not dissolve in the bead, but, while the bead is in a state of fusion, swims in distinctly outlined masses. The silicates are decom- posed in the bead, with the separation of undissolved silicic oxide : NaPOs -f CaSiOg = CaNaPO, + SiO^. (B) PRELIMINARY TESTS FOR ACIDS. Important conclusions regarding the presence or absence of certain acids may be drawn from the behavior of their salts with dilute and concentrated sulphuric acid, and also with alcohol and sulphuric acid. 1. If a portion of the substance or solution be placed in a test-tube and treated with dilute sulphuric add, there may be evolved : Colored Gases: Greenish-yellow chlorine in presence of hypochlorites (see 1, page 100). Moistened potassium iodide starch paper held in the fumes is colored blue. Reddish-brown vapors of nitrogen dioxide from nitrites (see 1, page 99). Colorless Gases recognized by their Odor: Sulphurous anhy- dride, odor of burning sulphur, from sulphites or hypo- sulphites ; in the presence of the latter, separation of sulphur also takes place (see 2, p. 77). Detection of sulphurous anhydride by potassium iodate (see 2, p. 75). Hydrocyanic acid, from many of the cyanides, recognized by its odor of bitter almonds, and also by the sulpho- cyanide reaction (see 5, page 94). 117 Acetic acid, odor of vinegar, in presence of acetates. Hydrogen sulphide, from many of the sulphides, blackens paper saturated with solution of plumbic acetate (see 4, page 98). Polysulphides evolve hydrogen sul- phide, Avith the separation of sulphur; sulpho-acids may also separate. (See pages 137, 138.) Colorless and Odorless Gas : Carbon dioxide is liberated with eifervescence from carbonates (to be confirmed with calcium hydroxide, see 2, page 83). 2. If a small portion of the substance or solution be treated with three or four times its volume of concentrated sulphuric acid and gently warmed, there may be evolved : Colored Gases : Greenish-yellow chlorine in presence of hypo- chlorites ; also when both chlorides and nitrates, or chlorides and peroxides are present. (When chlorides and nitrates are present, hydrochloric acid and nitric acid are simultaneously libemted and react upon each other (see d, page 123). When chlorides and per- oxides are present, the liberated hydrochloric acid acts upon the peroxides (see c, page 123). Greenish-yellow explosive mixture of chlorine and chlo- rine tetroxide, derived from chlorates (see 4, page 103). Brownish bromine together with hydrobromic acid de- rived from bromides ; the gas colors starch paper red- dish yellow. Brownish-red chromium oxychloride when chlorides and chromates are both present (see 4, page 90). Keddish-brown fumes indicate nitrites (see 1, page 99). Violet vapors of iodine from iodides. The vapors color moistened starch paper blue. Colorless Gases recognized by their Odar : Hydrochloric acid 118 vapors from chlorides ; pungent oclor, and render argentic nitrate solution (on glass rod) turbid (see 2, page 88). Hydrobromic acid (see above). Hydrofluoric acid from fluorides; of a strongly acid odor, etches glass (see 4, page 82). Nitric acid from nitrates, pungent odor. Red vapors arise when ferrous sulphate is added. Sulphurous anhydride, odor of burning sulphur, from sulphites and hyposulphites (see 2, page 75, and 2, page 77. — X. B. May also result from the reduction of the sulphuric acid employed). Hydrogen sulphide from sulphides (see 4, page 98). Acetic acid from acetates, odor of vinegar (see 5, page 104). Colorless and Odorless Gases: Oxygen (recognized by test with glowing wood, see 7, page 110) in presence of per- oxides, chromates, and permanganates ; for example : MnO, -h H2SO, = MnSO, + Ufi + O ; 2K2Cr04 + 5H2SO, = Cr2(S04)3 + 2K2SO, + SH^O + O3; 2KMn04 -f 3H2SO4 = 2MnS0, + K2SO, + SH^O + 0,. Chromates become green in color; permanganates are decolorized. Carbon dioxide from carbonates, effervescence (see 2, page 83). Carbon monoxide (bums with bluish flame) from organic substances, usually with blackening of the substance and the evolution of carbon dioxide and sulphurous anhydride, as in the case of tartaric acid. Carbon monoxide together with carbon dioxide is evolved from oxalic acid (without blackening, see 6, page 105). 119 From cyanides, ferrocyanides, etc. (Cyanides, page 128.) In presence of the latter a transitory bluish coloration appears. In the case of tartaric acid the odor of burnt sugar is produced. 3. If a portion of the substance be heated with concentrated sulphuric acid and alcohol^ there is produced, in the presence of acetates, ethyl acetate, which may be recognized by its apple-like odor (see 6, page 104). If the mixture be poured into a small dish and the alcohol be ignited, the flame will as- sume a green color in presence of boric acid (see 5, page 81). IV. SOLUTION AND FUSION, Solids must necessarily be in solution in order to make the tests in the Wet Way. The method employed in dissolving the solid depends upon the nature of the substance; with this in view, substances may be divided into the following five groups : 1. Oxides and salts (in general). 2. Metals and alloys. 3. Sulphides (of the heavy metals). 4. Cyanides (of the heavy metals). 5. Silicates. A distinction may be made between solution and fusion. Many salts cannot be directly dissolved in water or acids, but must undergo a special treatment to separate the acids from the bases, as in the case of barium sulphate ; the sul- phuric acid is separated from the barium by fusing with sodium carbonate. By fusion, new compounds of the bases and acids are obtained which are soluble in water or acids. In case a substance is not entirely soluble in any one of the solvents, it should be treated by each solvent in turn, and the solutions analyzed separately, as two simple analyses are more quickly made than one complex one. For example, the substance is first boiled with water, the solution obtained is filtered off and set aside for examination ; any residue insol- uble in hot water is treated witli nitric acid and the solution diluted with water and examined separately ; any residue re- maining after treatment with nitric acid is treated with hydro- chloric acid, the solution diluted with water and separately 120 121 examined. By this procedure a more distinct iusight into the nature of tlie substance to be analyzed is obtained. Hard bodies, minerals, etc., must be pulverized in a por- celain or agate mortar before they are dissolved. Very hard minerals are first crushed in a steel mortar, and the coarse powder thus obtained is afterwards pulverized in an agate moiiar. It is advisable to sift the powder through a linen cloth (previously washed and dried), remove the coarser particles and again pulverize them, and repeat the operation. If the substance to be analyzed be an organic compound or contain organic material (as shown by the preliminary ex- amination), the organic substance must be destroyed by igni- tion and the residue then dissolved in water (removing by filtration any separated carbon). 1. DISSOLVING OXIDES AND SALTS. (a) A portion of the substance to be dissolved is heated in a test-tube, with water. In case it enters into solution, a larger portion is dissolved and the liquid employed in testing for bases and acids. If the substance is apparently undis- solved, it is separated by filtration and the filtrate evapomted to dryness, to ascertain whether any of the original substance has entered into solution. (b) Substances insoluble in water are further tested as to their solubility in dilute nitric acid. An excess of nitric acid should be avoided, as many nitrates soluble in water are insoluble in excess of strong acids. On dissolving oxides with nitric acid, nitrates are formed, and on dissolving salts, nitrates of the bases are produced with the liberation of the acids which were in combination ; for example : Ca3(PO,), + 6HXO3 = 3Ca(N03)2 + 2H3PO, ; CUCO3 -f 2HXO3 = Cu(N03)2 + CO2 + H2O. F 11 122 Thus the presence of volatile acids becomes evident : Carbonic acid : effervesces ; odorless gas ; renders calcium hydroxide solution turbid (see 2, page 83). Hydrocyanic acid : odor of bitter almonds ; forms am- monium sulphocyanide with ammonium sulphide (see 5, page 94). Hydrogen sulphide : recognizable by its odor ; blackens paper saturated with solution of plumbic acetate (see 4, page 98). Sulphurous acid : odor of burning sulphur ; colors potas- sium iodate starch paper blue (see 2, page 75). Under certain conditions the presence of iodine, bromine, or chlorine may become evident (see 2, page 117). In using nitric acid as a solvent, acids which are soluble with difficulty may separate : Boric acid, crystalline, easily soluble in hot water ; silicic acid, gelatinous. Reddish-brown fumes of nitrogen dioxide result from the processes of oxidation ; for example, when mercurous com- pounds are converted into mercuric compounds : HgP + 6HNO3 = 2Hg(N03)2 + 2NO2 + 3H2O. These oxidations may interfere with the results of the analysis, especially when compounds of mercury are present. After the oxidation with nitric acid it is impossible to determine the original condition of oxidation of the salt ; for example, in the case of mercury, after oxidation it cannot be ascertained whether the salt was present originally as a mercurous or a mercuric salt. Salts of mercury which are insoluble in water or in moderately warm dilute nitric acid are decom- posed by boiling in sodium hydroxide (compare page 125, /). Compounds of arsenic should be dissolved, when pos- sible, in hydrochloric acid, in order to prevent tlie conver- sion of arsenious acid into arsenic acid. Plumboso-plumbic oxide (red lead) when treated with dilute nitric acid is decom- 123 posed into soluble plumbic nitrate and insoluble, brown lead dioxide : PbsO, + 4HNO3 = 2Pb(N03)2 + PbO^ + 2H2O. The latter is converted into plumbic chloride by concentrated hydrochloric acid. (c) Those substances which are insoluble in dilute nitric acid must be treated with concentrated hydrochloric acid. If in dissolving the substance in hydrochloric acid chlorine gas is evolved, peroxides and similar compounds, such as manga- nese dioxide, chromic acid, or permanganic acid, are present : MnO, + 4HC1 = MnCl^ + Cl^ + 2H2O ; 2Cr03 + 12HC1 =2CrCl3+ C\, +6Rfi ; Mn^O^ -h 14HC1 = 2MnCl2 + Cl^o + TH^O. Lead dioxide is converted into plumbic chloride, which crys- tallizes as the solution cools ; plumbic chloride is best de- composed with sodium carbonate (page 123, e). {d) Many compounds insoluble in nitric acid or in hydro- chloric acid are soluble in nitro-hydrochloric acid (aqua regia). In dissolving with nitro-hydrochloric acid chlorine^*^ is liberated, which is the active agent in effecting solution : 3HC1 H- HNO3 =-. CI3 + NO + 2H2O. Nitro-hydrochloric acid is prepared by mixing about three volumes of concentrated hydrochloric acid with one volume of concentrateii nitric acid ; the reaction takes place upon the application of heat. When nitro-hydrochloric acid is em- ployed as a solvent, oxidation necessarily occurs if the sub- stance is capable of being oxidized, as, for example, with compounds of mercury. (e) Many compounds that are insoluble in water and in acids are decomposed by boiling or fusing with carbonates of the alkalies, — that is, they are convei*ted into soluble com- * Besides (NOCl) nitrosyl chloride and (NOjCl) nitroxyl chloride. 124 pounds. Among them are plumbic sulphate, the sulphates of the alkaline earths, plumbic chloride, plumbic iodide, stannic oxide, etc. Of the sulphates, plumbic sulphate and calcium sulphate are easily decomposed by boiling in a solution of sodium carbonate. Precipitated strontium sulphate is also decom- posed in the same manner, although with more difficulty. Precipitated barium sulphate is only partly decomposed by boiling with sodium carbonate solution. These sulphates (as well as minerals) are readily decomposed by being fused with from four to six parts of sodium potassium carbonate.^^^ In these decompositions the acid of the substance fused unites with the alkalies, and the base is converted into a carbonate ; for example, with BaSO^ and NaKC03 the compounds NaKS04, soluble in water, and BaCOg, soluble in acids, are formed : NaKCOs + BaSO, = NaKSO^ + BaCOg. The fused mass is completely extracted with hot water and the insoluble residue (after separation by filtering) is dissolved in hydrochloric acid or nitric acid. The aqueous solution is to be examined for the acid, and the acid solution for the Plumbic chloride and plumbic iodide, etc., when boiled with a solution of sodium carbonate, are decomposed respec- tively into chloride and iodide of sodium and plumbic carbonate : ^ The double salt NaKCOg fuses more easily than the sodium or potas- sium salt alone. The fusion is best made in a platinum crucible, as porcelain is attacked by the alkali carbonates. The following substances should never be fused in a platinum crucible : potassium and sodium hydroxide, nitrates and cyanides of the alkalies, metals and metallic sulphides, or any substance from which a metal may be obtained by reduction or substances from which chlorine may be evolved. 125 PbCla + Na^COj = 2NaCl + PbCOg. (Plumbic carbonate is slightly soluble in sodium carbonate.) Stannic oxide (cassiterite) when fused with a carbonate of an alkali is converted into a stannate of the alkali, which is soluble in water and in hydrochloric acid : SnO. + K2CO3 = K^SnOg + CO, ; K2Sn03 + 6HC1 = SnCl, + 2KC1 + 3H,0. Fusion is continued until carbon dioxide ceases to be evolved. As stannic oxide is acted upon only wdth great difficulty by sodium carbonate, it is best fused in a silver crucible wdth sodium or potassium hydroxide,^^^ and the fused mass treated with water and hydrochloric acid, as mentioned above. (/) Many substances are unacted upon by the carbonates of the alkalies, but are readily decomposed on being boiled with sodium or potassium hydroxide ; for example, mercury and silver compounds. An oxide of the metal is formed, while the acid remains in solution in combination with the alkali. The oxide after being washed is dissolved in nitric acid. 2HgCl 4- 2NaOH = Hg^O + 2XaCl + H^O. In dissolving compounds of mercury cold dilute nitric acid should be used, in order to avoid the oxidation of mercurous salts to mercuric salts. (Mercuric iodide, which partly redis- solves in a carbonate of an alkali, — i.e., in the iodide of the alkali which is formed, — should be dissolved in nitro-hydro- chloric acid.) {g) Compounds of fluorine (for example, fluor spar) are decomposed by being gently heated with concentrated sul- phuric acid in a platinum crucible : 1 Or it may be fused in a porcelain crucible with three parts of sodium carbonate and three parts of sulphur to one part of the substance, and the fused mass, after cooling, extracted with water. The yellow solution con- tains the tin as sulphostannate, NajSnSg ; the insoluble residue, containing sulphides, is to be examined further according to 3, page 128. 11* 126 CaF^ + H2SO, = CaSO, + 2HF. The hydrofluoric acid is recognized by its etching glass (see 4, page 82) ; the residue in the crucible, consisting of sul- phates, is dissolved in hydrochloric acid or, if necessary, fused with sodium carbonate. Silicates containing fluorine, if treated in this manner, yield silicon fluoride, according to the reaction : 2CaF2 + Si02 + 2H2SO, = SiF, + 2CaSO, + 2H2O. If the evolved gas be conducted through a glass tube moist- ened with water, silicic acid together with hydrofluosilicic acid is produced : SSiF^ + 3H2O ^ 2H2SiF6 + H2Si03. The silicic acid will appear, either directly or on drying the tube, in the form of a white coating (see 5, page 82). (h) Chromic oxide, chromite, aluminium oxide, and ferric oxide are best fused by mixing them with ten parts of acid potassium sulphate. If the heat applied is not too great, neutral sulphates (together with basic salts) are formed : AlA + 6KHSO, = A\,{SO,), + SK^SO^ + SH^O, which, on cooling, may be dissolved by water or hydrochloric acid. Chromite is best fused with acid potassium sulphate, and the fused mass obtained again fus^d with potassium chlorate and potassium carbonate, to convert the chromic oxide into chromic acid : Cr2(S04)3 + 3K2CO3 = Crfi^ + 3K2SO, + 3CO2 ; Cr203 + 2K2CO3 + KCIO3 = 2K2CrO, + KCl + 2CO2. The fused mass yields potassium chromate when extracted with water ; the residue, consisting of ferric oxide (with some chromic oxide) is dissolved in hydrochloric acid. ^ (i) Carbon (charcoal, graphite) and sulphur are recognized by their appearance and their behavior when heated. 127 2. THE DISSOLVING OF METALS AND ALLOYS. Metals and alloys are cut into small preces, or filed, and the cuttings or filings are heated with strong nitric acid until brownish fumes cease to be produced on further addition of acid. The excess of acid is evaporated on a water-bath and the residue is heated with water and a small quantity of nitric acid. Most of the metals enter into solution as nitrates, gold and platinum remain unchanged, tin is converted into white meta-stannic acid, and antimony into its oxides. A. If complete solution has occurred the solutica is diluted with water and treated with hydrochloric acid ; should precipitation occur, the pre- cipitate is collected on a filter and examined according to Separation of First Group (page 146). The filtrate, or the solution in which hydro- chloric acid failed to produce a precipitate, is evaporated to dryness on a water-bath, the residue is moistened with hydrochloric acid, and again evaporated to dryness. The residue is then moistened with hydrochloric acid and dissolved in water, and the solution examined according to Second Group, p. 148, and the succeeding group reagents. The yellow ammonium sulphide treatment of the hydrogen sulphide precipitate in the Second Group may be omitted. B. If a white residue remain after treatment with water and nitric acid, the liquid is diluted with water, filtered, and the filtrate treated according to A above. The white residue, which may contain tin, antimony, and arsenic (the latter in the presence of tin, as arseniate of tin), is washed with hot water until free from acid, and is then heated with an excess of yellow ammonium sulphide, whereby tin, antimony, and arsenic are dissolved as sulpho-salts,(i) and the solution is examined according to I , p. 152. If after treating the white residue with yellow ammonium sulphide an insoluble residue remain, it is heated with strong nitric acid, and if it fail to dissolve it is treated with nitro-hydrochloric acid, which dissolves gold and platinum as chlorides. (2) The solution is evaporated to dryness, the residue dissolved in water, and treated according to Second Group, p. 148. I Sn(0H)4 + 3(NH4)2S = (NH4)2SnS3 + 4NH3 + 4H2O; SbgOa + 6(NH4)2S + 83 = 2(NH4)3SbS4 + 6NH3 + SHjO; SbgOi + 7(NH4)2S + S = 2(NH4)3SbS4 + 8NH3 + mjO; SbaOfi + 8(NH4)2S = 2(NH4)3SbS4 + IONH3 + 5HjO; AsgOe + 8(NH4)2S = 2(NH4)3AsS4 + IONH3 -f SHjO. « Au + 3HC1 + HNO3 = AUCI3 + NO + 2H2O ; 3Pt + 12HC1 + 4HN08 -= SPtCU + -iNO + SHsO. 128 3. SULPHIDES OF THE HEAVY METALS. The sulphides of the heavy metals generally possess a metallic lustre ; like the metals they are treated with concen- trated nitric acid, whereby most of them are dissolved as nitrates : CuS + 4HNO3 = Cu(N03)2 + S + 2NO2 + 2H2O. The procedure is as given under 2, page 127. The sulphur which separates first is oxidized by the nitric acid to sulphuric acid. The insoluble residue, in addition to the oxides of tin, antimony, and arsenic, may contain PbSO^, BiONOg (formed on treating the nitrate with water), and HgS. This residue is treated with yellow ammonium sulphide, which dissolves tin, antimony, and arsenic. Any residue remaining is filtered off and treated with nitric acid to dissolve the lead and bis- muth (which at this stage may be found again as sulphides), and any residue of mercuric sulphide is collected on a filter and dissolved by nitro-hydrochloric acid : 3HgS + 6HC1 + 2HNb3 =: SHgCl^ + 2NO + 4H2O + S3. Finally, silicious gangue, barite, etc., may remain, which should be examined according to 5 (page 130) and 1 (page 121) respectively. The sulphides are easily recognized by their appearance, and also by their behavior in the preliminary examination. 4. CYANIDES. The simple cyanides, which are insoluble in water, may be decomposed into chlorides and hydrocyanic acid, by boiling with concentrated hydrochloric acid. Argentic cyanide and mercuric cyanide, in which the cyan- ogen cannot be detected by the ordinary methods, may be readily recognized by their ]>ehavior when heated, as they separate into metal and cyanogen. If the cyanide is heated 129 in a narrow glass tube, the escaping cyanogen may be ignited, burning with a pinkish-lavender flame. The gas is also rec- ognizable by its odor of bitter almonds. Mercuric cyanide may be decomposed by dissolving in water and passing hy- drogen sulphide through the solution ; mercuric sulphide is precipitated and hydrocyanic acid enters into solution. The insoluble compounds of ferrocyanogen and ferricy- anogen are decomposed by boiling with sodium carbonate or sodium hydroxide ; sodium ferrocyanide and ferricyanide respectively are formed, together with an insoluble carbonate or an oxide of the metal : Pb2Fe(CN)6 H- 2Na2C03 = Na,Fe(CN)6 + 2PbC03 ; Cu2Fe(CN)6 + 4NaOH = ]S'a4Fe(CN)6 + 2CuO + 2H2O. The aqueous solution is filtered and the filtrate tested for the acid, while the carbonates or oxides are dissolved in dilute nitric acid. If sodium hydroxide is employed as the decom- posing agent, lead, zinc, and aluminium, and also arsenic, antimony, and tin, may enter into solution. In such cases a portion of the alkaline solution is tested for lead, zinc, and aluminium by saturating the solution with hydrogen sul- phide, thereby precipitating the first two metals as sulphides and the last as hydroxide. The filtrate from any precipitate which may have been produced, or the clear solution if no precipitate was produced by hydrogen sulphide, is acidulated with hydrochloric acid to precipitate arsenic, antimony, and tin as sulphides. If sodium hydroxide is used in decomposing the ferri- cyanide, sodium ferricyanide is formed, providing the metallic oxide produced in the operation is not further oxidizable : Cu3(Fe(CN)6)2 + 6NaOH = 2Na3Fe(CN)6 + 3CuO + SHp. If, however, the separated oxide is capable of further oxida- tion, this oxidation takes place, accompanied by the reduction of the sodium ferricyanide to sodium ferrocyanide : 130 Fe,{Fe(Cl^\\ + 8NaOH = 2Na3Fe(CN)e + 3Fe(OH)2 + 2NaOH ; 2Na3Fe(CN)6 + 3Fe(OH)2 + 2NaOH = 2Na,Fe(CN)g + 2Fe(OH)3+Fe(OH),. Consequently, in such cases to detect the acid the substance is fused, whenever possible, with sodium carbonate. To detect alkalies in ferrocyanogen and ferricyanogen com- pounds, the latter are decomposed into sulphates, carbon monoxide, and ammonium sulphate, by being heated with concentrated sulphuric acid : CuK2Fe(CN)6 + GH^SO, + GH^O = FeSO, + CuSO, + K2SO, + 6CO + 3(N.H,)2SO,. 5. SILICATES. Before silicates can be analyzed they must be finely pul- verized (page 121). (a) Silicates soluble in water or silicates that may be decom- posed by acids are best decomposed by being boiled with con- centrated hydrochloric acid ; by this procedure silicic acid and chlorides of the respective metals are formed ; for example : K2Si03 + 2HC1 = H^SiOg + 2KC1. Boiling is continued until complete decomposition has taken place, and no gritty particles are detected on stirring with a glass rod. The solution is then evaporated to the dryness of dust on a water-bath (see 1, page 84), to convert the solu- ble silicic acid into insoluble amorphous silicic acid. The dry residue is then moistened with a little concentrated hydro- chloric acid, to convert any basic chlorides (of Fe, Al, Mg, etc.) into neutral chlorides, thereby rendering them soluble ; finally the chlorides of the bases are extracted with water and dilute hydrochloric acid. (b) Silicates that are not decomposed by acids must either be fused with a carbonate of an alkali or decomposed by 131 hydrofluoric acid. To determine which method should be employed, the silicate is tested for the presence of an alkali. For this purpose a small portion of the powdered silicate, moistened with hydrochloric acid, is placed on a platinum wire and held in the non-luminous flame of a Bunsen burner, to observe whether a color is imparted to the flame (sodium, yellow ; potassium, violet). If alkalies are absent the method of decomposition by means of sodium carbonate is to be em- ployed ; whereas if alkalies are present, in order to test for them, the silicate must be decomposed with hydrofluoric acid. (c) In case the fusion is to be made with sodium carbonate (preferably with sodium potassium carbonate), one part of the finely pulverized substance is thoroughly mixed with six parts of sodium potassium carbonate, placed in a platinum cruci- ble, and the mixture fused by means of the blast-lamp. The silicate is decomposed by the carbonate of an alkali, with the production of a silicate of the alkali (or at least silicates that are decomposed by acids) and a carbonate of the metal : CaSiOs -I- XaKCOg -■ NaKSiOg + CaCOg ; CaSi A + 2NaKC03 -= 2NaKSi03 + CslCO, -f CO^. On disintegrating the fused mass with hydrochloric acid, ac- cording to a, page 130, silicic acid remains insoluble, and the chlorides of the metals together with sodium chloride and potassium chloride enter into solution. (d) In using hydrofluoric acid as a solvent the finely pulver- ized substance is placed in a platinum crucible, and treated witli the pure acid^'^ until a thin paste is formed. The mixture is stirred with a platinum wire (not with a glass rod) and digested, at a very gentle heat, until the substance is completely dissolved. By this treatment the silicates are converted into fluosilicates : ^ The hydrofluoric acid must he free from alkalies, and, when possible, freshly distilled in a platinum still. 132 CaSiOs + 6HF = CaSiFg + SHp ; CaSiA + 12HF = CaSiFfi + H2SiF6 + 5H2O. When completely dissolved concentrated sulphuric acid is added and heat applied, gently at first, but afterwards more strongly, to drive off the excess of acid. The sulphuric acid converts the fluosilicates into sulphates, while hydrofluosilicic acid is evolved : CaSiFfi + H2SO4 = H^SiFfi + CaSO,. The residue of sulphates is dissolved in water and a little hydrochloric acid. When this method is employed to decompose silicates con- taining barium, strontium, or calcium, it is necessary — espe- cially with barium and strontium, — to afterwards fuse the residue containing the barium, strontium, or calcium sulphate with a carbonate of an alkali (page 123, e). In mineral analyses it is often of interest to ascertain whether the minerals contain, in addition to the silicates not decomposable by acids, others that may be decomposed, thus making separation possible With this in view, after having mechanically separated the gangue and any other impurities from the mineral proper, it is finely pulverized, treated with hydrochloric acid, the solution evaporated to dryness as above described (page 130, a), and the chlorides resulting from the decomposed silicates dissolved in water. The insoluble residue, which may contain silicic acid and undecomposed silicates, is boiled with sodium carbonate, which dissolves the silicic acid derived from the decomposed silicate. After acidulating the sodium carbonate solution with hydrochloric acid, evaporating to dryness, and extracting with hot water, the silicic acid re- mains as a light, white powder. If a residue remain after boiling a second time with sodium carbonate, it is to be con- sidered an undecomposable silicate, which is to be further tested according to b, c, and r/, pages 130 and 131. V. DETECTION OF BASES IN THE WET WAY. If the substance to be analyzed is a solid it is to be dis- solved, as before described (page 121). To test for bases in organic substances the latter should be incinerated and the bases extracted from the ash by water or acids. Organic acids, etc., interfere with a number of the reactions used in the detection of bases. The reaction of solutions to be examined should be tested with litmus and turmeric paper to ascertain whether they are neutral, acid, or alkaline. A number of substances may be present in acid solutions, which, in neutral solutions, may be disregarded ; for example, in the Third Group, acid solutions must be tested for phosphates and oxalates, whereas if the so- lutions are neutral the tests for these acids need not be made. Regarding combinations that may arise during the exam- ination of alkaline solutions see h, page 138. PRECIPITATION OF THE DIFFERENT GROUPS. To separate the bases into groups the following group reagents are employed in turn : 1. Hydrochloric acid. 2. Hydrogen sulphide (in presence of HCl). 3. Ammonium hydroxide (in presence of NH^Cl). 4. Ammonium sulphide (in presence of NH^Cl). 5. Ammonium carbonate. By each of these reagents a series of bases called a group is precipitated. Bases that are not precipitated by group reagents are classed as a sixth group. (See Sixth Group, page 145.) The rare elements are not considered in this plan. 12 133 134 TABLE I.— GROUP PRECIPITATIONS. Gboup I. Metals precipitated by Hy- drochloric Acid. as white, curdy AgCl, argentic chloride. Mercurous saMs, as white, pulverulent HgCl, mercurous chlo- ride. Lead, as white PbCla, plumbic chloride. Group II. Metals precipitated in Acid Solution by Hydrogen Sulphide. Lead, as black PbS, plumbic sulphide. Mercwic salts, as black HgS, mercuric sulphide. Copper, as black CuS, cupric sulphide. Bismuth, as brownish-black BigSa, bismuthous sul- phide. Stannous salts, as brownish-black SnS, stannous sulphide. Cadmium, as yellow CdS, cadmium sulphide. Arsenic, as yellow AS2S3, arssnious sulphide (mixed with sulphur if precipitated from arsenic acid solutions). Stannic salts, as yellow SnSa, stannic sulphide. Antimonious salts, as orange-red Sb2S3, antimonious sul- phide. Antimonic salts, as orange-red Sb2S5, antimonic sulphide (together with 81)283 and sulphur). Gold, as black AU2S3, auric sulphide. Platinum, as brownish-black PtSg, platinic sulphide. Group III. Metala precipitated by Am- monium Hydroxide in presence of Ammonium Chloride. Iron, as reddish- brown Fe(0H)3, ferric hydroxide. Chromium, as bluish- or grayish -green Cr(0H)8, chromic hydrox- ide. Aluminium, as white, gelatinous Al(0H')8, aluminium hy- droxide. In presence of phosphoric acid iron and alumin- ium respectively are pre- cipitated as phosphates, — thus : Iron, as white FeP04, ferric phosphate. Aluminium, as white AIPO4, aluminium phosphate. In presence of phosphoric acid or oxalic acid cal- cium, strontium, and barium are precipitated as phosphates or oxa- lates, as white Ca3(P04)2, SrCaOi, etc. Magnesium in the pres- ence of phosphoric acid is precipitated in this group as white MgNH4P04, ammonium magnesium phosphate. In presence of iron, man- ganese may be precipi- tated as white Mn(0H)2, manganous hy- droxide, changing to brown Mn(0H)3, manganic hy- droxide. 135 TABLE I.— GROUP PRECIPITATIONS.— Om^mwecf. Group IV, Metals precipitated by Ammonium Sulphide in presence of Ammonium Chloride. Manganese, as light-salmon-colored MnS, manganous sul- phide. Zinc, as white ZnS, zinc sulphide. Nickel, as black NiS, nickelous sulphide. Cobalt, as black CoS, cobaltous sulphide. Group V. Metals precipitated by Am- monium Carbonate. Barium, as white BaCOs, barium carbonate. Strontium, as white SrCOs, strontium carbon- ate. Calcium, as white CaCOs, calcium carbon- ate. Group VI. For which there is no Spe- cial Group Reagent. Magnesium. Potassium. Sodium. Lithium. Ammonium, 136 If on the addition of the reagent a precipitate is formed, it is filtered off and carefully washed. The filtrate should be tested to ascertain whether the precipitation was complete, — that is, whether no precipitation takes place on further addi- tion of the reagent. The precipitate must be collected only on properly-cut filters which fit closely to the inner surface of the funnel, and the liquid in which the precipitate is sus- pended should be poured down a glass rod into the filter. The precipitates should be thoroughly washed before proceed- ing with the further examination. Concentrated solutions should be diluted with water before the examination is commenced. Solutions containing much free acid should be boiled to expel the excess of acid and then diluted with water before the examination is commenced. This dilution may cause turbidity, in consequence of the for- mation of basic salts or oxychlorides of bismuth, antimony, or mercury. These, however, may be redissolved by the addition of a little nitric or hydrochloric acid. The filtrate, including the wash-water, from each group pre- cipitation is reserved for treatment with the succeeding group reagent. If no precipitate is produced by a group reagent, it indicates that the metals of that particular group are absent. The solution is then treated with the succeeding group reagent. FIRST GROUP. (a) Neutral or acid solutions are treated Avith a few drops of dilute hydrochloric acid. There will be precipitated : Silver, as white, curdy AgCl, argentic chloride. Mercury (in the mercurous condition), as white, pulveru- lent HgCl, mercurous chloride. Lead,, as white crystalline PbClg, plumbic chloride. If a precipitate is produced, it is collected on a filter and 137 examined according to Sepamtion of the First Group, page 146. The filtrate, or the solution in which hydrochloric acid failed to produce a precipitate, is treated with the Second Group reagent, page 139. Lead is incompletely precipitated, as it is slightly soluble in water ; therefore a test for it must also be made in the second group. The solution in which the precipitation takes place must be cold, as plumbic chloride is easily soluble in hot water and might remain in solution ; moreover, small quantities of mercurous salts might be overlooked in the presence of nitric acid, as, when hydrochloric acid and nitric acid are both present and the solution is warm, mercurous chloride is transformed into soluble mercuric chloride. Furthermore, it should be observed whether the precipitate redissolves on the addition of an excess of the hydrochloric acid. On the addition of dilute hydrochloric acid, dilute solutions of compounds of bismuth yield a white precipitate of BiOCl, bismuth oxychloride, which on the further addition of hydrochloric acid is redissolved as BiClg, bismuthous chlo- ride. Compounds of antimony, especially K(SbO)C4H40g, potassium antimonious tartrate, with dilute hydrochloric acid form SbOCl, antimonious oxychloride, which is soluble in an excess of the acid as SbClg, antimonious chloride. KHC^H^Og, acid potassium tartrate, if it should have sepa- rated, would be redissolved on the further addition of hydro- chloric acid : KHC^HA + HCl = H^C.HA +KC1. Furthermore, there may be precipitated in the first group : boric acid (crystalline), organic acids, and sulphur. (Sulphur separates from hyposulphites and polysulphides : Na^SA + 2HC1 = 2NaCl + S + SO^ + H^O ; (NHJ^Ss -f 2HC1 = 2NH4CI H- S2 + H2S. In the first case sulphurous anhydride, in the latter case hy- 12* 138 drogen sulphide, is evolved with the sulphur. Poly sulphides are always alkaline in reaction.) Attention should be paid to any gases evolved on treat- ment with hydrochloric acid (with reference to the manner of distinguishing them see pages 116 to 119 and 121, 6.) Sul- phurous anhydride must be driven off by heating; other- wise, on the addition of hydrogen sulphide, separation of sulphur would occur (together with the formation of pen- tath ionic acid) : 5SO2 + 5H2S -= H^SA + S5 + 4H2O. Chlorine, nitrogen dioxide, etc., should also be expelled by heating the liquid. (b) Alkaline solutions should be treated with hydrochloric acid until acid in reaction, and any formation of precipitates or evolution of gases observed. From alkaline solutions there may separate : 1. Sulphur and sulphides of the metals, accompanied by the evolution of hydrogen sulphide. The sulphides are the following sulpho-acids : AsgSg, AsgSg, SbgSg, Sb2S5, SnS^ : they should be tested according to the directions given in the chapter treating of them under the second group (see B, page 152). Under certain conditions CuS, HgS, and NiS might also be encountered at this stage. The filtrate from the sulphur or the sulphides which have separated may be examined directly for the metals of the fifth and sixth groups. 2. Cyanides of the heavy metals (which were dissolved in cyanides of the alkalies), with the evolution of hydrocyanic acid. Concentrated hydrochloric acid is added to the liquid containing the precipitate and the whole heated. The cyanides are thereby converted into chlorides, which finally dissolve, argentic chloride alone remaining undissolved. The solution is then examined for the presence of metals of the second, 139 third, and subsequent groups; argentic chloride in the residue is confirmed by testing its solubility in ammonium hydroxide. 3. Silicic acid : gelatinous ; should be confirmed in the bead of microcosmic salt (see 4, page 85). The solution, together with the precipitate, is treated with an excess of hydrochloric acid, and evaporated to dryness on the water- bath to render the silicic acid insoluble. The residue is extracted with water and a little hydrochloric acid (page 130, a), and the filtrate examined for bases. It usually contains nothing but the alkalies. 4. Precipitates of plumbic hydroxide, aluminium hydrox- ide, chromium hydroxide, and zinc hydroxide may be formed, but on acidifying with hydrochloric acid will immediately disappear, being converted into soluble chlorides. SECOND GROUP. The acid filtrate from the first group precipitate, or the solution in which hydrochloric acid failed to produce a pre- cipitate, is warmed and hydrogen sulphide conducted into the acid solution until a distinct odor of the gas is observable in the liquid. There will be precipitated : Lead, as black PbS, plumbic sulphide. Mercury (in the mercuric condition), as black HgS, mer- curic sulphide. Copper, as black CuS, cupric sulphide. Bismuth, as brownish-black BigSg, bismuthous sulphide. Gold, as black AujSg, auric sulphide. Platinum, as brownish-black PtSa, platinic sulphide. Cadmium, as yellow CdS, cadmium sulphide. Arsenious compounds, as yellow AS2S3, arsenious sulphide. Arsenic compounds, as yellow AsgSj, arsenious sulphide (with sulphur). 140 Antimonious compounds^ as orange-red SbgSg, antimoni- ous sulphide. Antlmonic compounds, as omnge-red SbgSg, antimonic sulphide (together with SbaSg and S). Stannous compounds, as brownish-black SnS, stannous sulphide. Stannic compounds, as yellow SnSg, stannic sulphide. If a precipitate is produced, it is collected on a filter and examined according to Separation of the Second Group, page 148. The filtrate, or the solution in which hydrogen sul- phide failed to produce a precipitate, is treated with the Third Group reagent, page 141. From solutions containing hydrochloric acid, when hydro- gen sulphide is not present in sufficient quantity, lead is pre- cipitated as red Pb2SCl2, plumbic sulphochloride, which is converted by further addition of hydrogen sulphide into black PbS. In solutions of mercuric salts white precipitates of double salts (for example, Hg3S3Cl2) are formed, which on continuing the addition of hydrogen sulphide become yellow, then brown, and finally are converted into black HgS. Arsenious acid is precipitated at once, arsenic acid gradually ; the precipitation is accelerated, however, by heating (see 1, page 34). Sulphur may also separate when hydrogen sulphide is intro- duced into the solution. This separation may be caused by : 1. Chlorine, bromine, iodine, nitrous acid, nitrogen dioxide, etc. (in consequence of their oxidizing action upon hydrogen sulphide) ; for example : Cl2 + H2S-=2HCl + S; N2O3 + H2S = 2NO + H.O -h S. On passing hydrogen sulphide into solutions containing an excess of nitric acid or nitro-hydrochloric acid, sulphur is separated. The excess of acid should be driven off by 141 evapomtion and, after diluting with water, the introduction of hydrogen sulphide should be repeated. 2. Sulphurous acid (page 137). 3. Ferric salts, in consequence of their reduction to ferrous salts : 2FeCl3 + H^S =- 2FeCl2 + 2HC1 + S. Decolorization of the solution results from the reduction. 4. Chromic acid and chromates, in consequence of their reduction to chromic salts : 2H2CrO, + 3H2S + 6HC1 =-2CrCl3+ SUfi + S3. The solution changes in color from yellow to green. By repeated introduction of hydrogen sulphide accompanied by renewed additions of hydrochloric acid, the chromic acid is completely decomposed. If the acid is not added in sufficient quantity, a precipitate is formed consisting either of green chromic hydroxide : 2H2CrO, + 3H2S =2Cr(OH)3+ S3 + 21Ifi, or of brown chromium chromate : SH^CrO, -h 3H2S = (CrO)2CrO, + S3 + 6Rfi. 5. Permanganic acid and permanganates, in consequence of their reduction to manganous compounds : 2HMnO, + 5H2S + 4HC1 = 2MnCl2 + S^ + SH^O. The purplish-red solution is decolorized. The procedure is the same as in 4, page 141. (If the hydrochloric acid is not added in sufficient quantity, brown precipitates are formed.) THIRD GROUP. From the filtrate of the second group, or from the solution in which hydrogen sulphide failed to produce a precipitate, the hydrogen sulphide is expelled by boiling. A small quantity of nitric acid is added and the solution warmed to oxidize the bases, ammonium chloride and afterwards ammo- 142 niiim hydroxide (the latter in not too great excess) are added, and the solution is boiled until the odor of ammoniacal gas can no longer be detected. There will be precipitated : Iroy}j as reddish-brown Fe(OH)3, ferric hydroxide. Chromium, as bluish-green Cr(OH)3, chromic hydroxide. Aluminium, as white gelatinous Al(OH)3, aluminium hydroxide. In the presence of phosphoric or oxalic acid, — Ferric phosphate, FePO^ (white). Alum,inium phosphate, AlPO^ (white). Phosphates and oxalates of cal- \ Ca3(P04)2, etc. (white). eium, strontium, barium, i CaC204, etc. (white). Ammonium magnesium phosphate, MgNH4P04 (white). If a precipitate is produced, it is collected on a filter and examined according to Separation of the Third Group, page 159. The filtrate, or the solution in which ammonium hy- droxide failed to produce a precipitate, is treated with the Fourth Group reagent, page 143. In presence of iron some manganese may be precipitated as Mn(0H)2, manganous hydroxide. The hydrogen sulphide must be expelled, so that, on the addition of the ammonium hydroxide, ammonium sulphide may not form and thereby precipitate the fourth group with the third. By means of the nitric acid ferrous salts are converted into ferric salts ; in presence of ammonium chloride the fer- rous salts are not precipitated, or are precipitated only incom- pletely. If the oxidation is not complete, a greenish precip- itate is obtained in the presence of ferrous salts, which, when exposed to the air, oxidizes and gradually changes to black and finally to reddish-brown (ferric hydroxide). In solutions containing silicates the ammonium hydrox- ide may precipitate gelatinous HgSiOa, silicic acid. H2SO1 143 may possibly be formed (by the oxidation of the H2S passed into the solution), and precipitate barium and strontium as sulphates. Ammonium chloride is added to prevent the pre- cipitation of manganese and magnesium (see 3, page 56, and 1, page 66). The ammonium chloride should be added in excess, — but not too great excess, as thereby the precipitation of the fifth group is unnecessarily rendered more difficult. After the addition of the ammonium hydroxide it is neces- sary to boil the liquid until the odor of ammonia disappears, in order to completely precipitate aluminium and chromium (see 1, page 50, and 1, page 52). By this procedure the excess of ammoniacal gas is expelled ; but the boiling should not be continued too long, as the solution may become acid (in con- sequence of the decomposition of NH4CI with the liberation of NH3). FOURTH GROUP. To the filtrate from the third group (to which ammonium hydroxide is again added), or to the solution in which ammo- nium hydroxide, in presence of ammonium chloride, failed to produce a precipitate, colorless or slightly yellow ammo- nium sulphide is added. There will be precipitated : Manganese, as light-salmon-colored MnS, manganous sulphide. Zinc, as white ZnS, zinc sulphide. Nickelj as black NiS, nickelous sulphide. Cobalt, as black CoS, cobaltous sulphide. If a precipitate is produced, it is collected on a filter and examined according to Separation of the Fourth Group, page 164. The filtrate, or the solution in which ammonium sul- phide failed tu produce a precipitate, is treated with the Fifth Group reagent, page 144. 144 Xickelous sulphide is slightly soluble in an excess of yellow ammonium sulphide, imparting a brown color to the solution. The nickelous sulphide is completely separated on boiling the solution, especially after the addition of acetic acid. Ammo- nium sulphide might also precipitate iron as ferrous sulphide, in case the iron were held in solution by organic substances. FIFTH GROUP. From the filtrate of the fourth group, or from the solution in which ammonium sulphide failed to produce a precipitate, the ammonium sulphide is expelled by boiling, any sulphur which may have separated is filtered off, ammonium hydrox- ide and ammonium carbonate are added to the filtrate, and the whole is boiled as long as carbon dioxide is evolved. There will be precipitated : Barium, as white BaCOg, barium carbonate. Strontium, as white SrCOg, strontium carbonate. Cahdum, as white CaCOg, calcium carbonate. If a precipitate is produced, it is collected on a filter and examined according to Separation of the Fifth Group, page 165. The filtrate, or the solution in which ammonium car- bonate failed to produce a precipitate, is examined according to the directions given under Separation of the Sixth Group, page 168. On the addition of commercial ammonium carbonate, acid carbonates soluble in water — as, for example, Ca(HC03)2 — are produced (page 62), which, on boiling, are converted into neutral, insoluble carbonates, with the liberation of COg and H,0: Ca(HC03)2 = CaCOj + CO2 + H2O. The carbonates are soluble in an excess of ammonium chlo- ride on long-continued boiling : CaCOa + 2NH,C1 = CaCl^ + 2NH3 + CO2 + Hp. 145 SIXTH GROUP. In this group are classed magnesium, potassium, sodium, and lithium. Ammonium is also classed with this group, but the test for it must be made in the original substance presented for analysis. (With reference to their separation see Separation of the Sixth Group, page 168.) With this group may also be found the ferro- and ferri- cyanides of the alkalies, cobalticyanides of the alkalies, etc., from which the iron and cobalt are not precipitated by the ordinary reagents. Furthermore, aluminium may have re- mained in solution, because of the presence of organic sub- stances. These compounds are to be treated with concen- trated sulphuric acid (page 130) and separated by the regular group precipitations. 13 146 SEPARATION OF THE BASES CONTAINED IN THE GROUP PRECIPITATES. The group precipitates thus obtained are now examined separately. The precipitates of the second and fourth groups must be examined immediately, as they oxidize when exposed to the air. Precipitates of the third group must be quickly filtered, in order to prevent the formation and precipitation of manganic hydroxide ; for example : 2(NH,)2MnCl, + 4NH,OH + Hp + O -^ Mn^COH), + 8NH4CI. If no precipitate is formed in the third group, ammonium sulphide should be added rapidly, to prevent the separation of manganic hydroxide. If arsenic or tin be founa in the second group, a portion of the filtrate is reserved for the tests for acids and the other portion is used in testing for bases. The filtrate, including the wash-water, from each group precipitation is reserved for treatment with the succeeding group reagent. If no precipitate is produced by a group reagent, it indicates that the metals of that particular group are absent. The solution is then treated with the succeeding group reagent. SEPARATION OF THE FIRST GROUP. The precipitate produced by hydrochloric acid (page 137) is collected on a filter and, after having been washed with cold water, is treated while on the filter with hot water ; any plumbic chloride present is dissolved by the hot water, and may be tested for in the cooled filtrate by the addition of 147 sulphuric acid ; the formation of a white precipitate of PbSO^ indicates the presence of lead. Argentic chloride and mer- curous chloride would remain on the filter, undissolved by the hot water. Any residue remaining on the filter is washed with hot water until free from lead (test washings with sulphuric acid, provided lead has been found), and then treated, while on the filter, with ammonium hydroxide : mer- curous chloride is converted into black, insoluble NHgHggCl, dimercurous ammonium chloride, indicating the presence of mercury in the mercurous condition, while argentic chloride is dissolved by the ammonium hydroxide as Ag(NH3)2Cl, argent-ammonium chloride, and passes through the filter with the filtrate into the vessel below. The ammoniacal filtrate is treated with nitric acid until acid in reaction. A white precipitate of AgCl indicates the presence of silver. To detect small quantities of argentic chloride in the pres- ence of mercurous chloride, the dry mixture of the chlorides is heated in a small glass tube : mercurous chloride will vola- tilize, while argentic chloride remains as a horn-like mass, which may be further tested on charcoal with the blowpipe. 148 TABLE II.— SEPARATION OF THE FIRST GROUP. The precipitate, which may contain AgCl, HgCl, PbCl,, is treated, while on the filter, with hot water. CooUd Filtrate. PbClj. Treat with HjSO^ : Insoluble Residue. AgCl, HgCl. Treat with ammonium hydroxide : white precipitate of PbSO^ indi- cates presence of lead. Filtrate. Residue. Ag (as Ag(NH3),Cl). Treat with HNO3: Hg as black NH^HgjCl indi- white, curdy pre- cipitate of AgCl indicates pres- cates presence of mercurous salts. ence of silver. SEPARATION OF THE SECOND GROUP. Of the sulphides of the second group some are basic and others acid in character ; therefore some of them are unacted upon by ammonium sulphide, while others are dissolved as sulpho-salts. BoMC Sulphides — Insoluble. Lead sulphide. Mercuric sulphide. Cupric sulphide. Bismuthous sulphide. Cadmium sulphide. Acid Sulphides — Soluble. Arsenious sulphide. Antimonious sulphide. Antimonic sulphide. Stannous sulphide. Stannic sulphide. Auric sulphide. Platinic sulphide. (Cupric sulphide is slightly soluble in ammonium sulphide, insoluble, however, in sodium sulphide and in potassium sulphide. Mercuric sul- phide is insoluble in ammonium sulphide, but soluble in sodium sulphide and in potassium sulphide containing free alkali. Stannous sulphide is insoluble in colorless ammonium sulphide, but easily soluble in yellow ammonium sulphide.) 149 I. To ascertain whether sulphides of both basic and acid divisions or of only one division are present, the precipitate produced by hydrogen sulphide (page 139) is collected on a filter, washed, and then examined regarding its behavior with ammonium sulphide. For this purpose a small portion of the precipitate is taken from the filter, placed in a test-tube, treated with ammonium hydroxide and then with yellow ammonium sulphide, and slightly warmed, any residue re- maining undissolved is filtered off, and the filtrate is acidified with dilute hydrochloric acid, to ascertain whether a sulpho- salt is present in the solution, — that is, whether a (colored) precipitate of a sulphide is formed. (a) If, on the addition of dilute hydrochloric acid to the filtrate no precipitate appears, or only a milkiness due to the separation of sulphur from the yellow ammonium sul- phide is produced, none of the sulphides have entered into solution in the ammonium sulphide, and, therefore, basic sul- phides only are present. Consequently the remainder of the precipitate produced by hydrogen sulphide should be treated according to directions given under A, page 150. (6) If the precipitate is completely dissolved by the am- monium sulphide, acid sulphides only are present, and the remainder of the precipitate produced by hydrogen sulphide should be examined according to B, II., page 152. (c) If a portion of the precipitate remain undissolved and another portion enter into solution in ammonium sulphide, as shown by the production of a colored precipitate on acidi- fying the ammonium sulphide filtrate with dilute hydro- chloric acid as before described (I., page 149), the entire re- mainder of the precipitate produced by hydrogen sulphide is treated with ammonium hydroxide and ammonium sulphide, warmed, the insoluble part filtered off and examined accord- ing to a, page 150, while the solution (filtrate) is treated ac- 13* 150 cording to I., page 162, or, if the presence of gold or plati- num is suspected, according to C, page 1 54. A. FURTHER SEPARATION OF THE BASIC SULPHIDES. (a) The thoroughly washed precipitate of the basic sul- phides is taken from the filter, placed in a porcelain dish, and boiled with dilute nitric acid (adding fresh portions of water to replace that lost by evaporation) until no further change takes place in the precipitate. Lead, bismuth, copper, and cad- mium will enter into solution as nitrates ; mercuric sulphide remains insoluble as a heavy black powder. The mercuric sulphide is filtered off and examined according to c, page 150, and the filtrate is examined according to d, page 151. (6) If the precipitate of sulphides is completely dissolved by the dilute nitric acid (with the exception of sulphur, which floats on the surface of the liquid), mercury was not present. Complete solution having taken place, the nitric acid solution is examined according to c?, page 151. (c) The mercuric sulphide* on the filter is washed, removed from the filter, placed in a porcelain dish, and treated with nitrohydrochloric acid, which, on being heated, dissolves and converts the mercuric sulphide into mercuric chloride. After evaporating the excess of acid and diluting with water, this 1 White PbSO^ (see 4, p. 20, and 6, p. 21) as well as white Hg3S2(N03)2 (see 4, page 18) may be precipitated with the mercuric sulphide. Should this occur, the precipitate is treated with ammonium acetate, which dis- solves the plumbic sulphate, and if an insoluble residue remain, the liquid is filtered. The presence of lead in the filtrate may be shown by the for- mation of a yellow precipitate of plumbic chromate on the addition of acetic acid and potassium chromate. The insoluble residue on the filter is dissolved in nitro-hydrochloric acid, the excess of acid expelled by evapo- ration, the solution diluted with water and tested for mercury with stan- nous chloride. The production of a grayish precipitate indicates the presence of mercury. 151 solution yields with stannous chloride a white precipitate of HgCl, or a gray precipitate of metallic mercury. {d) The excess of acid is evaporated from the nitric acid so- lution obtained as before described, the solution diluted with a small quantity of water, and then treated with dilute sulphuric acid : lead is precipitated as white plumbic sulphate. The plumbic sulphate is filtered oflF, and the filtrate, or the solu- tion in which sulphuric acid failed to produce a precipitate, is treated with an excess of ammonium hydroxide. If bismuth is present a white precipitate of BiO-OH, bismuth hydroxide, insoluble in an excess of the reagent, is produced. As a con- firmatory test the precipitate should be collected on a filter and dissolved in dilute hydrochloric acid ; if, on adding the solu- tion to a large quantity of water, a separation of white bismuth oxy chloride takes place, the presence of bismuth is fully estab- lished. Copper and cadmium are also precipitated by ammo- nium hydroxide, but redissolve in an excess of the reagent. If the solution is colored blue, copper is present. To test for cadmium the solution is decolorized by potassium cyanide, and hydrogen sulphide conducted into the liquid ; a yellow pre- cipitate of CdS indicates the presence of cadmium. If the ammoniacal solution is colorless, it is treated directly with hydrogen sulphide to ascertain whether a precipitate of yellow cadmium sulphide is produced. (As plumbic sulphate is soluble in concentrated nitric acid and also in salts of ammonium, it might be overlooked in the presence of an excess of nitric acid or in consequence of the incomplete elimination of ammonium sulphide (before dis- solving in nitric acid), and thus interfere with the tests for other substances. At the point v/here bismuth is precipitated by ammonium hydroxide, ferric hydroxide, aluminium hy- droxide, etc., may also be precipitated, especially if the original precipitate produced by hydrogen sulphide has not been suffi- ciently washed. With copper may be found nickel and 152 cobalt; with cadmium, zinc. Plumbic hydroxide might also be precipitated here by ammonium hydroxide.) B. FURTHER SEPARATION OF ACID SULPHIDES. I. The ammonium sulphide solution may contain the sul- pho-salts (NHJgAsS^, (NH,)3SbS„ (NH,)2SnS3, and may yield on the addition of hydrochloric acid a yellow or orange-red precipitate of AsgSg, SbaSg, SnSg. If no precipitate, or only a milkiness, due to the separation of sulphur from the am- monium sulphide, is produced, it indicates the absence of sulphides of arsenic, antimony, and tin. (Any black SnS which may have been present originally would be precipitated here as yellow SnSa ; see 1, page 41.) II. The colored precipitate of acid sulphides is collected on a filter and thoroughly washed. The separation of the three sulphides may be accomplished by either of two methods, — by hydrochloric acid or by ammonium carbonate. The separation by ammonium carbonate is preferable in case the preliminary examination indicated the presence of arsenic. A. Separation by Hydrochloric Acid. — (a) The remainder of the precipitate of sulphides, a portion of which was found to be completely soluble in ammonium sulphide, or the pre- cipitate obtained by the addition of hydrochloric acid to the ammonium sulphide solution (after having been pressed be- tween sheets of filter paper to remove the excess of moisture), is treated with concentrated hydrochloric acid and warmed : antimony and tin enter into solution as chlorides, while arsenic sulphide and sulphur remain undissolved. (Cupric sulphide would also be dissolved by the hydrochloric acid. A test for it may be made by treating a few drops of the solution with ammonium hydroxide ; the production of a blue coloration indicates the presence of copper.) (b) To test for antimony, a few drops of the hydrochloric 153 acid solution are placed on platinum foil and a small piece of zinc is placed in the liquid. If antimony is present, a black deposit of metallic antimony is formed which adheres to the platinum foil. To test for tin which may be present as stannic chloride, a fragment of metallic zinc is placed in the remainder of the hydrochloric acid solution ; if both tin and antimony are present, they are precipitated as a spongy metallic mass. When the precipitation is complete, the super- natant liquid containing zinc chloride is poured off and the metallic powder remaining is treated with moderately concen- trated hydrochloric acid, which dissolves the tin as stannous chloride, leaving . the antimony undissolved. The antimony is removed by filtration, and the solution of stannous chloride thus obtained yields with mercuric chloride a precipitate of either white mercurous chloride or of gray metallic mercury (see 4, page 42). On dissolving the sulphides in hydrochloric acid, arsenic sulphide (together with sulphur) remains undis- solved. To confirm the presence of arsenic, the arsenic sul- phide is dissolved in warm concentrated nitric acid, the solu- tion evaporated to dryness on a. water-bath, and the residue, containing arsenic acid, dissolved in water. Ammonium chloride, ammonium hydroxide, and magnesium sulphate are then added, to ascertain whether crystalline MgNH^AsO^, ammonium magnesium arseniate, is precipitated. The precipi- tate is always crystalline : in very dilute solutions it forms only after standing some time. B. Separation by Ammonium Carbonate. — If the remainder of the precipitate of sulphides, or the preci[)itatc obtained by the addition of hydrochloric acid to the ammonium sulphide solution, is supposed io contain much arsenic sulphide, it is collected on a filter, thoroughly washed with water, and then digested with a concentrated solution of ammonium carbonate. Arsenic sulphide enters into solution (see page 29), while 154 SbaSg, antimonic sulphide, and SnSg, stannic sulphide, remain undissolved, and after being collected on a filter and washed are dissolved in hydrochloric acid and separated according to 6, page 152. The ammonium carbonate solution of arsenic sul- phide is evaporated to dryness on a water-bath, and the residue treated with concentrated nitric acid to oxidize the arsenic to arsenic acid. The solution is again evaporated to dryness, the residue dissolved in water, and the arsenic precipitated with magnesia mixture as MgNH^AsO^, as under h, p. 152. (To determine whether the arsenic, antimony, or tin existed in the ic or ous conditions, see the pages treating of the special reactions of these metals. It is, of course, understood that, in testing for arsenic acid in the presence of phosphoric acid, hydrogen sulphide is the only reagent that can be employed.) C. FURTHER SEPARATION OF ACID SULPHIDES IF THE PRESENCE OF GOLD OR PLATINUM IS SUSPECTED. The ammonium sulphide solution may contain the sulpho- salts (NHJaAsS,, (NH,)3SbS„ (NH,)2SnS3, (NHJgAuSa, (NH4)2PtS3, and may yield on the addition of hydrochloric acid a yellow, orange-red, or brownish-black precipitate of AS2S5, SbgSg, SnSg, Au2S3,PtS2. If no precipitate, or only a milkiness (due to the separation of sulphur from the ammo- nium sulphide), is produced on adding the hydrochloric acid, it indicates the absence of sulphides of arsenic, antimony, tin, gold, and platinum. The colored precipitate is collected on a filter, thoroughly washed, dried, and then mixed with twice its bulk of a dry mixture consisting of equal parts of sodium carbonate and potassium nitrate. This mixture is introduced, in small portions at a time, into a porcelain crucible contain- ing two parts (compared with the quantity of precipitate) of potassium nitrate, which is kept just at the point of fusion. The temperature must not be of such a degree as to decom- pose the potassium nitrite resulting from the fusion of the 155 potassium nitrate, as, when the precipitate is added, sodium stannate instead of stannic oxide may be formed. When cool, the fused mass is extracted with water containing alcohol and filtered. Any insoluble residue is treated according to a, page 155. The alcohol is evaporated from the filtrate, which may contain arsenic, and then ammonium hydroxide, ammo- nium chloride, and magnesium sulphate are added. A white crystalline precipitate of ammonium magnesium arseniate, which may appear immediately or after some time, indicates the presence of arsenic. (a) The residue, insoluble in alcohol, which may contain metallic gold and platinum, stannic oxide, and sodium pyro- antimoniate, is boiled with a concentrated soluti ^n of sodium hydroxide, diluted with water, and filtered. Any insoluble residue is treated according to 6, page 155. The filtrate, which may contain tin as sodium stannate, is acidulated with hydrochloric acid, concentrated by evaporation, and a piece of metallic zinc placed in the solution to precipitate the tin The precipitate is collected on a filter, dissolved in hydro- chloric acid, and mercuric chloride added to the solution. The production of a white precipitate of mercurous chloride or gray metallic mercury indicates the presence of tin. (b) The residue, insoluble in sodium hydroxide, which may contain gold, platinum, and sodium pyroantimonate, is boiled with concentrated hydrochloric acid, slightly diluted with water, and then filtered. A portion of the filtrate, which may contain antimonious chloride, is placed on platinum foil and a fragment of metallic zinc placed in it. The production on the platinum of a brown or black adherent coating indi- cates the presence of antimony. The residue insoluble in concentrated hydrochloric acid, which may contain metallic gold and platinum, is dissolved by heating with nitro-hydrochloric acid, the solution eva\x)- rated to dryness on a water-bath, the residue dissolved in 156 water, and the solution boiled with ferrous sulphate and then filtered. The insoluble residue of gold on the filter is fused on charcoal with the blowpipe to obtain the gold in the form of a yellow metallic globule. The filtrate, which may contain platinic chloride, is heated, and, while hot, hydrogen sulphide is passed into the solution. The precipitate is collected on a filter, dissolved by heating with nitro-hydrochloric acid, and evaporated to dryness on a water-bath. The residue is dissolved in a small quantity of water, placed in a watch-glass, ammonium chloride added, and the liquid stirred with a glass rod. A yellow, crystalline precipitate of ammonium chlorplatinate indicates the pres- ence of platinum. 157 2 2 ^B^.'2B<^% •o < g S ©Hj ^' ff C fD ^2 o2 2 ^ clO *i ■^ OB QifP r^ I—! B^S' S- 2; o S"o 2 ^"^j fl §.1 S^ M «♦ DOaS 2.0" 50 . 13 • £• g 2 7 3 "^^^ * S« 2 p O sr a "• O » (C 3 PB r (? ?B — • H 1^ -• . .X CO 02 a-_ -.a--2 --t.. ^5» i <^ ffi rTr.i •-• 2- :;• i <^ i j3 oS-sj (K! o 2. •^ o -^^S cr.^-3 2.0C i o-S. i§p? ^%'^i2 2. 3 ^i-ri3 3 ^ 2.:?2 The pi PbS nied wi '*Ki. w S%-2. 1— 1 HH iol a prod uS, J nium 1 t?cl M 3 O.J' h> H E^CC' s' M " g'^ ^ ^ !=: 7: a H 3 ccS^ R'^ i^ r/j iJ^^ r^ Si^o- 3- cr ^ <« GpS ^i^^ BtGCO § 0.3 2 P's r C1 B. 5* ^ I 14 158 o (A O Q o H o GQ H o o O a> O Vi OJ t^ -^ -^ ^ air. 111 .« 2 S ^ t - S CC "o* W *• O fl fl O o a. oJDfi ■^^ CO '3 =- S o 3 « •— to ;15 ;^ .2 •- '^ ^rQ 0.2 ^■> ^ s > w r "^ o o M H I pq 5|.i 3 o ^ CO p,rt © .— » « OJ § ®s CJ to M CO 3.S i S:^ I H G bJO &. 03 C X g © 1.2 8 1 .a ^' . 4." a ^.5^ .aj o o) 05 . 5 lllll .5 II Stic =^TS'^a^?n '^^ •X3 S c c c 03.2 OJ— o3 '2-2-l'Sg o o 03 oj S a> ;s ^ N •• S = 5? - ^ .-tStS"^ bCto >, fe: S 0^ G i §=«§".§ 2 fl o o'ot:3 H o C o s 0^ 3-5 g •s^ JSJS ^'^c "S -T-^ 5^0 o.e's S^!?^ 159 SEPARATION OF THE THIRD GROUP. Before proceeding with the separation of the members of the third group, the presence or absence of phosphoric acid (phosphates) and of oxalic acid (oxalates) in the precipitate produced by the group reagent, ammonium hydroxide, should be ascertained, because their presence or absence will determine which method of separation shall be employed. To obtain this information the procedure should be that described under B, page 160. The test for phosphates and for oxalates need be made in this group only when the original substance was dissolved in acid or when solutions having an acid reaction are presented for analysis. If the group precipitate did not contain phosphoric acid or oxalic acid, the separation of the members of the group should be made according to the method described under A, page 159. If, however, the group precipitate contained phosphoric acid or oxalic acid, or both, the separation of the members of the group should be made according to «, or 6, or c, pages 161 and 162, dependent upon whether phosphoric acid or oxalic acid, or both, are present. A. The thoroughly washed precipitate produced by am- monium hydroxide is removed from the filter, placed in a porcelain dish, covered with sodium hydroxide, bromine water added, and slightly warmed for about five minutes.<^> A reddish-brown, insoluble residue of ferric hydroxide re- ' It is necessary, during this treatment, that the liquid should contain an excess of sodium hydroxide, which may be determined by rubbing a drop of the liquid between the fingers and observing whether or not a slippery sensation is produced ; the reaction with turmeric or litmus paper is in this case of no value, as NagAlO, and NagCrO,, which may be formed here, are also alkaline in reaction. The production of a slippery sensation indicates the presence of an excess of sodium hydroxide. 160 maining after this treatment indicates the presence of iron. The liquid is filtered, and the filtrate (or the solution in which sodium hydroxide may have failed to produce a pre- cipitate) is treated according to a, page 160. The reddish- brown residue of ferric hydroxide is washed with water, dis- solved in hydrochloric acid, the solution diluted with water, and the presence of iron confirmed by the addition of potas- sium ferrocyanide ; the production of a blue precipitate con- firms the presence of iron. (a) The filtrate from the reddish-brown residue of ferric hydroxide is treated with an excess of ammonium chloride and warmed until the odor of ammonia is no longer percep- tible; the formation of a white, gelatinous precipitate of aluminium hydroxide indicates the presence of aluminium. The precipitate of aluminium hydroxide is filtered off and the filtrate is acidified with hydrochloric acid and treated with an excess of hydrogen sulphide, the solution is warmed several minutes, ammonium hydroxide is added, the liquid is again heated, and if chromium be present it will separate as a bluish-gray, gelatinous precipitate of chromium hydroxide, which may be confirmed by its imparting an emerald color to a bead of borax. B. If the original solution contained phosphoric or oxalic acids, the group reagent, ammonium hydroxide, would pre- cipitate the members of the third group, namely, iron, alu- minium, and chromium as hydroxides and phosphates, and the alkaline earths, namely, barium, calcium, strontium, and magnesium, were they present in the original solution, as phosphates and oxalates. Therefore, a preliminary examina- tion of the precipitate produced by ammonium hydroxide to ascertain whether or not phosphoric or oxalic acids are present should invariably be made before proceeding with the separa- 161 tion of the members of the group. For this purpose, separate portions of the precipitate produced by the group reagent, am- monium hydroxide, are examined according to the following methods : I. A portion of the precipitate is boiled with an excess of sodium carbonate. The liquid is filtered, the filtrate acidified with acetic acid, and calcium chloride is added. The pro- duction of a white, pulverulent precipitate of calcium oxalate indicates the presence of oxalic acid. II. A second portion of the precipitate is dissolved in nitric acid, ammonium molybdate added, and the solution warmed. The production of a yellow crystalline precipitate of ammonium phosphomolybdate indicates the presence of phosphoric acid. (a) If oxalic acid alone is present, the remaining portion of the precipitate produced by ammonium hydroxide is re- moved from the filter, placed in a porcelain crucible, or on a piece of platinum foil, dried, and then gently ignited to de- stroy the oxalic acid. The residue is dissolved in hydro- chloric acid, the solution diluted with water, and ammonium hydroxide added until the odor of ammonia is perceptible. The precipitate, which will consist of the bases which were originally in combination with the oxalic acid, is examined according to A, page 159. (6) If 2)hosphoric acid alone is present, the precipitate pro- duced by ammonium hydroxide is dissolved in hydrochloric acid. A small portion of the solution is diluted with water, and potassium ferrocyanide is added. The production of a blue precipitate indicates the presence of iron. Ferric chlo- ride is added to the remainder of the solution until a drop of the solution placed in a porcelain dish and treated with ammonium hydroxide yields a reddish-brown precipitate. The solution is nearly neutralized with sodium carbonate, I 14* 162 an excess of sodium acetate is added, the solution boiled for several minutes until a reddish-brown precipitate is pro- duced, and the liquid is then filtered while hot. The filtrate may contain the alkaline earths, and should be treated with ammonium hydroxide and ammonium carbonate, and any precipitate produced examined according to Separation of the Fifth group, page 165. The reddish-brown precipitate produced by boiling the solution with sodium acetate may consist of ferric phosphate, basic ferric acetate, and chromium and aluminium phos- phates and hydroxides. The precipitate is dissolved in hy- drochloric acid, the solution is cooled, and an excess of sodium hydroxide is added, thereby precipitating reddish- brown ferric hydroxide resulting from the ferric chloride previously added. The filtrate, which may contain alu- minium and chromium as phosphates and hydroxides, is boiled, whereupon chromium, if present, will separate as a bluish-gray precipitate of chromium phosphate or of chro- mium hydroxide, which is collected on a filter and the presence of chromium confirmed by its imparting an emerald color to a borax bead. The filtrate is acidified with acetic acid, and if aluminium be present in the solution as a phos- phate, it will separate as a white, gelatinous precipitate. If no precipitate should appear on acidifying the solution with acetic acid, excess of ammonium hydroxide is added and the solution is warmed. The production of a white, gelatinous precipitate of aluminium hydroxide indicates the presence of aluminium. (c) If both oxalic and phosphoric adds are present, the pre- cipitate is detached from the filter, placed in a porcelain cruci- ble, or on a piece of platinum foil, dried, and gently ignited to destroy the oxalic acid. The residue is dissolved in hydro- chloric acid and the solution examined according to 6, p. 161. 163 TABLE IV.— SEPAKATION OF THE THIRD GROUP. In the Absence of Phosphoric Acid or Oxalic Acid. The precipitate, which may contain Fe(0H)3, A1(0H)3, Cr(0H)3, is treated with an excess of sodium hydroxide, bromine water is added, and the mixture is warmed about five minutes and then filtered. Insol. Residue. Filtrate. Reddish-brown NagAlOg, Na^CrO^. re(0H)3. Add excess of ammonium chloride and boil Dissolve in hydrochlo- until the odor of ammonia is no longer per- ric acid and dilute ceptible and then filter. with water, add po- tassium ferrocj'^an- ide: blue Precipitate. Filtrate. re,(Fe(CN)e)3 White, gelatinous Na^CrO,. indicates presence of A1(0H)3 Acidulate with hy- iron. indicates presence of drochloric acid and aluminium. treat with an excess of hydrogen sul- phide. Warm sev- eral minutes, and add ammonium hy- droxide until odor of ammonia is per- ceptible, then warm the liquid until odor of ammonia is barely perceptible. Bluish- gray or greenish- gray Cr(0H)3 indicates presence of chromium . ( May be confirmed by its im- parting an emerald color to a borax bead.) 164 SEPARATION OF THE FOURTH GROUP. After washing the precipitate produced by ammonium sul- phide (page 143), while on the filter, with water containing hydrogen sulphide, the filter is pierced with a glass rod and the precipitate washed with cold dilute hydrochloric acid into a beaker placed below. Manganous sulphide and zinc sul- phide are dissolved by the dilute hydrochloric acid as man- ganous chloride and zinc chloride, while nickelous sulphide and cobaltous sulphide remain undissolved. The nickelous and cobaltous sulphides are collected on a filter and w^ashed with water containing hydrogen sulphide. The hydrochloric acid filtrate is warmed until the hydrogen sulphide is completely driven off, and then treated with sodium hydroxide in excess. Manganese is precipitated as white manganous hydroxide, which, when exposed to the air, rapidly changes to brown manganic hydroxide ; while zinc, at first precipitated as zinc hydroxide, is dissolved as Na2Zn02, sodium zincate. The manganous hydroxide is filtered ofip, and the alkaline filtrate treated with hydrogen sulphide, which precipitates zinc as white zinc sulphide. The mixture of nickelous sulphide and cobaltous sulphide remaining on the filter, insoluble in hydrochloric acid, is dis- solved by heating with nitro-hydrochloric acid. The greater part of the excess of acid is driven off by boiling, and the solution neutralized by adding sodium hydroxide drop by drop until a permanent precipitate of hydroxides is formed. Acetic acid in excess and sodium acetate are then added, fol- lowed by the addition of an excess of a concentrated solution of potassium nitrite. If cobalt is present, a yellow crystal- line precipitate of potassium cobaltic nitrite is formed, either immediately or after standing some time. After several hours the precipitate is filtered off, and the filtrate treated 165 with sodium hydroxide ; the formation of a pale-apple-green precipitate of nickelous hydroxide indicates the presence of nickel. (The precipitate of nickel should be tested in a bead of borax or of microcosmic salt ; see 8, page 62.) TABLE v.— SEPARATION OF THE FOURTH GROUP. The precipitate, which may contain MnS, ZnS, NiS, CoS, is treated with cold dilute hydrochloric acid and filtered : Insol. Residue. Filtrate. NiS, Cos. ZnCl^, MnClj. Dissolve in nitro-hydrochloric acid, Heat to drive off H„S, add ex- cess of NaOH, and filter: evaporate excess of acid, neutral- ize remainder with NaOH, add HCoHoOo in excess and then NaC^HgO^andKNO^: Precipitate. Filtrate. White Na,ZnO,. Treat with H,S: Precipitnte. Filtrate. Mn(OH)„ rapidly Yellow crvstalline NiCl^. changing to white K3Co(N0,)e Add NaOH : brown ZnS indicates presence pale-apple- Mn(0H)3 indicates pres- of cobalt. green indicates pres- ence of zinc. Ni(0H)2 ence of man- indicates pres- ganese. ence of nickel. SEPARATION OF THE FIFTH GROUP. The members of the Fifth Group may be separated accord- ing to the following method : A. The precipitate produced by ammonium carbonate (page 144), consisting of carbonates, is dissolved, while on the filter, with a small quantity of dilute hydrochloric acid, which converts the carbonates into chlorides. Only a small quantity of hydrochloric acid is used, so that the solution may be concentrated but only slightly acid. A small portion of the solution of chlorides is treated with a concentrated solution of calcium sulphate. (a) If upon the addition of the calcium sulphate no pre- 166 cipitate is formed, either immediately or after standing some time, barium and strontium are absent. The remainder of the hydrochloric acid solution (to which calcium sulphate has not been added) is treated with ammonium hydroxide and ammonium oxalate, when, if calcium is present, a white pre- cipitate of calcium oxalate is formed. (6) If on the addition of calcium sulphate a white precipi- tate is immediately produced, barium is probably present ; if a turbidity appear after some time, probably strontium only is present. In either case the remainder of the hydrochloric acid solution (which has not been treated with calcium sul- phate) is evaporated to dryness on a water-bath, and the residue pulverized and extracted with strong alcohol. Barium chloride remains undissolved, while strontium chloride and calcium chloride enter into solution. The liquid is filtered through a dry^^^ filter, and a portion of the residue on the filter is placed on a platinum wire and held in the Bunsen flame ; a green color imparted to the flame indicates the pres- ence of barium. The alcoholic filtrate is evaporated on a water-bath to ascertain (by a residue remaining) whether anything has entered into solution. Any residue (consisting of chlorides) remaining is evaporated twice to dryness with an excess of concentrated nitric acid (free from chlorine), which converts the chlorides into nitrates : SrCLj + 2HNO3 = Sr(N03)2 + 2HC1, and the residue of nitrates is then extracted with strong alco- hol as before described ; calcium nitrate enters into solution, while strontium nitrate, which remains undissolved, is col- lected on a filter, and a portion placed on a platinum wire and held in the Bunsen flame ; a crimson color imparted to the flame indicates the presence of strontium. The alcoholic fil- 1 A filter which has not been moistened witii water. 167 trate is now evaporated until free from alcohol, and any traces of strontium and barium are precipitated with a few drops of sulphuric acid/^^ and the liquid is filtered and tested for calcium with ammonium hydroxide and ammonium oxalate. The formation of a white precipitate indicates the presence of calcium. TABLE VI.— SEPAKATION OF THE FIFTH GROUP. The precipitate, which may contain BaCOg, SrCOg, CaCOg, is dissolved in a small quantity of HCl, and a portion of the solution treated with CaSO, : No precipitate is produced : Ba and Sr are absent. Treat the remainder of the HCl solution with NH4OH and(NHJ.,CA: white precipitate, CaCjO,, indicates presence of calcium. A white precipitate is produced. Evaporate the remainder of the HCl solution to dryness on a water-bath, pulverize the residue, extract with strong alcohol, and filter : Insol. Residue. BaCl^. Place a portion on platinum wire and hold in the flame: a green color imparted to the flame in- dicates pres- ence of bar- Filtrate. SrCl^, CaClj. Evaporate to dryness on a water- bath, evaporate residue twice to dryness with cone. HNO3, extract the residue with strong alcohol, and filter: Insol. Residue. Sr(NOg),. Place a portion on platinum wire and hold in the flame: a crimson color imparted to the flame in- dicates pres- ence of stron- tium. Filtrate. Ca(N0g)2. Evaporate un- til free from alcohol, add NH.OH and (NlijAO^: white precipi- tate, CaCjO^, indicates pres- ence of cal- * From concentrated solutions calcium also may be partly precipitated, although, because of its solubility, a considerable quantity of calcium sul- phate remains in solution. 168 SEPARATION OF THE SIXTH GROUP. If barium and calcium were found in the Fifth Group, traces of them may remain in the filtrate from that group, and must be removed before proceeding with the separation of the Sixth Group. For this purpose a few drops of dilute sulphuric acid are added to the filtrate to precipitate the barium, and ammonium hydroxide and ammonium oxalate added to precipitate calcium. If precipitates are formed, they are removed by filtration. A portion of the solution thus rendered free from barium and calcium, or the filtrate from the Fifth Group which originally contained no barium or calcium, is tested for magnesium with ammonium chloride, ammonium hydroxide, and sodium hydrogen phosphate. If magnesium is present, a white, crystalline precipitate of am- monium magnesium phosphate will appear, either immediately or after standing some time. If magnesium is not present, the remainder of the solution is examined according to I., page 1 68 ; if it is present, the solution is to be examined according to II., page 169. I. The remainder of the solution which does not contain magnesium is placed in a porcelain crucible or dish and evaporated to dryness on a water-bath ; it is then gently heated over a free flame until vapors of ammonium salts cease to be evolved. If no residue remain, potassium, sodium, and lithium are absent ; if a residue remain, it is tested, by means of the flame-test, for lithium. The pro- duction of a carmine-colored flame indicates the presence of lithium. If lithium be present, the residue is to be exam- ined according to III., page 170. If lithium be absent, the remainder is then dissolved in the least quantity possible of water, and the concentrated solution divided into two portions. 169 (a) One portion is placed in a watch-glass, treated with platinic chloride and a small quantity of alcohol, and stirred with a glass rod. If potassium is present, a yellow crys- talline precipitate of potassium chlorplatinate will be formed. (b) The second portion is tested for sodium by adding a clear, freshly-prepared solution of potassium pyroantimonate. Sodium salts yield with potassium pyroantimonate, either im- mediately or after standing some time, a white crystalline pre- cipitate of sodium pyroantimonate. The solution to be tested for sodium must not be acid in reaction, or flocculent anti- monic acid will be precipitated. If acid in reaction, the solu- tion should be exactly neutralized with ammonium hydroxide before making the test with potassium pyroantimonate.^^^ II. If magnesium is present in the solution, it must be re- moved before the tests for potassium, sodium, and lithium can be made. For this purpose the solution containing magnesium is evaporated to dryness on a water-bath, and the residue gently heated over a free flame until the vapors of ammonium salts cease to be evolved. The residue is then dissolved in water and a few drops of hydrochloric acid. (The presence of ammonium salts interferes with the precipitation of mag- nesium ; see 1, page 66. The residue does not completely dissolve in water, as part of the magnesium salts were con- verted into insoluble basic salts by the heating.) The solution is heated to the boiling point and barium ^ To detect small quantities of potassium, sodium, and lithium, ad- vantage may be taken of their behavior in the non-luminous flame. Sodium imparts a j'ellow color, potassium a violet color, lithium a oar- mine color, to the flame. To detect the potassium flame in the presence of the sodium flame (as the intense yellow .sodium flame obscures the weaker violet potassium flame), a piece of blue glass (cobalt glass) or an indigo prism (which absorbs the yellow rays) maybe employed. Viewed through blue glass or an indigo prism the potassium flame appears crim- son-red in color. H 15 170 hydroxide added, whereby magnesium hydroxide is precipi- tated : MgCl^ + Ba(0H)2 = Mg(OH)2 + BaCl^. (Any sulphuric acid which might be present would also be precipitated.) The magnesium hydroxide is filtered off, and the filtrate treated with ammonium carbonate to precipitate the barium of the barium chloride as barium carbonate. The barium carbonate is filtered off, the filtrate evaporated to dry- ness, and the residue gently heated in a porcelain dish or crucible until vapors of ammonium salts cease to be evolved and the residue tested by the flame test for lithium. If lithium be present, the residue is to be examined according to III., page 170. If lithium be absent, the residue is dis- solved in a small quantity of water and the solution divided into two portions and tested for potassium and sodium, as described und(H' a and b, page 169. III. If lithium has been detected by the flame test in the residue mentioned under I., page 168, or II., page 169, the residue is moistened with concentrated hydrochloric acid (which converts the bases into chlorides), and evaporated to dryness on a water-bath. The residue remaining is extracted with a mixture consisting of equal volumes of absolute alco- hol and ether. Lithium chloride enters into solution, leaving potassium chloride and sodium chloride undissolved. The liquid is filtered, the filtrate evaporated to dryness on a water-bath, and a portion of tlie residue placed on a plati- num wire and held in the non-luminous flame. If lithium is present, a carmine-red color will be imparted to the flame. The residue insoluble in alcohol and ether is dissolved in a small quantity of water and divided into two portions. One portion is placed in a watch-glass, platinic chloride and a few drops of alcohol are added, and the liquid is stirred with a glass rod. If potassium is present a yellow, crystalline pre- 171 cipitate of potassium chlorplatinate will be formed. The other portion is placed in a watch-glass and treated with a clear, freshly-prepared solution of potassium pyroantimonate and the liquid stirred with a glass rod. If sodium is present a white, crystalline precipitate of sodium pyroantimonate will be formed. To test for the presence of ammonium salts, a portion of the original substance or solution presented for analysis is placed in a test-tube, treated with a solution of sodium hy- droxide, and boiled. If ammonium salts are present ammo- niacal gas will be evolved, which may be recognized by its odor, by its changing turmeric paper, moistened with water, brown, and by its forming white clouds of ammonium acetate when a glass rod moistened with acetic acid is held in the atmosphere containing the gas. In using turmeric paper in this test care must be taken that the turmeric paper does not come in contact with the sides of the test-tube, as in such case the yellow paper may be changed to brown by sodium hydroxide which may be on the glass. Likewise care must be taken that in the ebul- lition of the liquid none of it is projected on the turmeric paper. 172 TABLE Vila. -SEPARATION OF THE SIXTH GROUP. A. Examination for Mg, K, Na, Li. Test the filtrate from the Fifth Group for traces of Ba with H0SO4 and for Ca with NH4OH and (NH4)2C204. If precipitates are produced, remove them by filtration. Test a portion of the solution free from Ba and Ca for Mg with NH4CI, NH4OH, and NaaHPO*: A precipitate is produced : MgNH4P04, indicating presence of magne- sium. Evaporate the remainder of the solution to dryness on a water-bath, gently heat resi- due over a free flame until vapors of ammonium salts cease to be evolved. Dissolve residue in water and a few drops HCl, boil, add Ba(OH)2. filter, add (NH4)2C03 to filtrate, filter, evaporate fil- trate to dryness on water- bath, and gently heat residue over a free flame until vapors of ammonium salts cease to be evolved. (Test the residue for lithium by the flame test (carmine). If lithium be present, proceed according to the separation under Table VII6.) A residue remains : KCl, NaCl. Dissolve in small quantity of water and divide into two portions. To one portion add PtCl4: a yellow, crystalline pre- cipitate, K2PtCl6, I indicates presence ' of pota.ssium. j To the other por- tion add clear, freshly - prepared solution of potas- sium pyroanti- monate : a white, crystalline pre- cipitate, Na^H2Sbj07, indicates presence of sodium. A residue does not remain : K and Na are ab- sent. No precipitate is produced. Evaporate the remainder of the solution to dryness on a water- bath, gently heat residue over a free flame until vapors of ammonium salts cease to be evolved. (Test the residue for lithium by the flame test (carmine). If lithium be present, proceed according to the separation under Table VII6.) A residue remains : KCl, NaCl. Dissolve in small quantity of water and divide into two portions. To one portion add PtCU: 'a yellow, crystalline pre- cipitate, K2PtCl6, indicates presence of potassium. To the other por- tion add clear, freshly-prepared solution of potas- sium pyroanti- monate : a white, crystalline pre- cipitate, Na2H2Sb207, indicates presence of sodium. A residue does not remain : K and Na are ab- sent. B. Examina- tion for Am- moniuni. Treat the original substance or solution with NaOH and boil : the evolu- tion of am- moniacal gas, recog- nized by its odor, etc., indicates presence of ammonium. 173 TABLE yiI6.— SEPARATION OF THE SIXTH GROUP (IN THE PRESENCE OF LITHIUM). K, Na, Li. If a residue remain (see Table Vila.), moisten with cone. HCl, evapo- rate to dryness on a water-bath, extract residue with a mixture of absolute alcohol and ether, and filter : Insol. Residue. < Filtrate. KCl, NaCl. LiCl. Divide into two portions. Evaporate to dryness on a water-bath. To one portion add PtCl4 : a yellow crys- Place a portion of the residue on a talline precipitate, clean platinum wire and hold in the KaPtClo, non-luminous flame : a carmine-red indicates presence of potassium. color imparted to the flame indicates To the other portion add clear, freshly- presence of lithium. prepared solution of potassium pvro- antimonate : a white, crystalline pre- cipitate, NasHaSbgOy, indicates presence of sodium. 15* VI. EXAMINATION FOR ACIDS. The examination for acids should always be preceded by the examination for bases and by the preliminary examination. (See pages 107, 108, and succeeding pages.) The number of acids to be taken into consideration depends upon the number of bases present and upon the results of the preliminary examination. Acids which form insoluble com- pounds with the bases found in the solution need not be sought for ; as, for example, if silver is found in the solution, hydrochloric acid cannot be present, or, if barium is found, it is useless to look for sulphuric acid. In neutral solutions containing heavy metals, only a limited number of acids are to be considered, as most of the salts of the heavy metals are insoluble in water. In solutions having an acid reaction all the acids are to be considered which, with the bases present, form salts soluble in acid solution. (For solubilities see Properties of the Acids, page 73 and succeeding pages, and also table on page 180.) If heavy metals (metals of the First, Second, Third, Fourth, and Fifth Groups) are present, they must, in many cases, be 174 175 removed before proceeding with the tests for acids. When possible, this is accomplished by the addition of an excess of sodium carbonate to the solution and boiling, thereby pre- cipitating the metals as carbonates or oxides. The precipi- tate is filtered off, and the filtrate is divided into two unequal portions. The larger portion is neutralized with nitric acid and examined according to A, page 176, and the smaller portion is acidulated with sulphuric acid and used in test- ing for nitric and acetic acids. It is advisable to gently heat the solution after acidulation, in order to completely expel carbon dioxide.^^^ Stannic oxide and arsenic are removed by precipitating with hydrogen sulphide. In this operation sul- phuric acid may result from the oxidation of the hydrogen sulphide. In such cases the original solution should be test-ed directly for sulphuric acid and hydrochloric acid. In the examination of solutions having an alkaline reaction, they should be neutralized with nitric acid or sulphuric acid before beginning the examination for acids. In case a pre- cipitate is produced the acid should be added in excess, the precipitate filtered off, and the filtrate neutralized with an alkali. (See page 122, b.) Salts which are insoluble in water are examined for acids by treating them directly (without first dissolving them) with a solution of sodium carbonate. When heated to boiling the acid enters into solution as a sodium salt, while the base remains as an insoluble oxide or carbonate. The liquid is filtered, and the filtrate containing the sodium salts is neu- tralized with nitric acid or acetic acid as above described. 1 If the carbon dioxide has not been completely expelled, precipitates of carbonates may be produced on the addition of the three group re- agents ; with barium chloride soluble barium bicarbonate might be formed, which would appear as a precipitate only after boiling. 176 In examining for acids when fusion is necessary, see the chapter on Sohition and Fusion, page 1 20. A. Separate portions of the sohition neutralized with nitric acid are first examined regarding their behavior with the three group reagents : one portion is treated with BaCla, a second with Pb( €211302)2, and a third portion with AgNOg. The acids ^^^ which produce precipitates with the group re- agents and the properties of the precipitates are given in the following table (page 178)c, In many cases reasonably cer- tain conclusions as to which acids are present may be drawn from the color of the precipitates and from the behavior of the latter with the difterent solvents, if at the same time it is considered which acids could possibly be present under the existing conditions; for example, if a precipitate soluble in nitric acid is produced by argentic nitrate, the presence of hydrochloric acid, hydrobromic acid, etc., is excluded. If the precipitate produced by barium chloride is insoluble in acids, sulphuric acid or hydrofluosilicic acid must be present. After having ascertained to which group or groups the acids belong, and obtaining reasonable information, by the solu- bility and color of the precipitate produced by the group reagents for acids, of the particular acids present, their pres- ence is to be confirmed by applying to the solution neutral- ized with nitric acid the special characteristic tests for acids given in the pages beginning with page 182. ' For a classification of the acids composing the four groups, see page 178 : in this classification oxalic acid and tartaric acid belong to the second group, and acetic acid to the fourth group. 177 NitHc acid, chloric acid, and acetic acid are not precipi- tated by the three group reagents ; therefore, special tests characteristic of these acids must be made. Eor the tests for nitric acid, see page 189 ; chloric acid, page 190 ; acetic acid, page 190. 178 TABLE VIII— BEHAVIOR OF THE ACIDS Pbecipitate in the presence of On the Addition of BaCl2. Group I. ( Sulphu7'ic acid Qroup II. Hydrojluosilicic acid: Sulphurous acid: . . Hyposulphurous acid: Phosphoric acid: Boric acid: . . Hydrofiuoric acid. Carbonic acid: . Silicic acid: Arsenious acid: Arsenic acid : Chromic acid: Oxalic acid: . [ Tartaric acid: QronpIII. - Hydrochloric acid : Hydrobroniic acid: Hydriodic acid : Hydrocyanic acid: Hydrqferrocyanic acid . Hydroferricyanic acid: Sulphydric acid: . . Nitrous acid : . . Hypochlorous acid , Sulphocyanic acid: {Nitric acid: Chloi'ic acid . Acetic acid: white (insoluble in HCl) .... white (insoluble in HCl) .... white (soluble in HCl : with evo- lution of SO2) white (soluble in large quant, of water ; soluble in "HCl : with evolution of SO, and separation of S) white (soluble in HCl) white (precipitated only in cone, solutions ; soluble in HCl) white (soluble in HCl) white (soluble in HCl : with effer- vescence) white (soluble in HCl) white (soluble in HCl) white (soluble in HCl ) yellow (soluble in HCl) .... white (soluble in HCl) white (soluble in HCl) 179 WITH THE GKOUP REAGENTS. On the Addition of Pb(C2H802)j. On the Addition of AgNOa. white (slightly soluble in HNO3) • white (soluble in HNO3) . . . . white (soluble in HNO3; with separation of S) ^ white (soluble in HNO3) . . white (soluble in excess of agent ; soluble in HNO3) with white (soluble in HNO3) white (soluble in HNO, effervescence) white (soluble in HNO3) white (soluble in HNO3) white (soluble in HNO3) yellow (soluble in HNO3) white fsoluble in HNO3) white (soluble in HNO3) white (crystalline, soluble in hot water) white (soluble with great difficulty in water) yellow (crystalline, soluble in hot water) white (insoluble in water ; soluble in HNO3) white (insoluble in HNO3) . . . white (soluble in HNO3; becomes gray on boiling) white (soluble in HNO3; rapidly becomes black) yellowish white (soluble in HNO3) white ^precipitated only from cone, solutions ; soluble in HNO3 ; de- composed by water) black (soluble in HNO3 ^^^ warm- ing) yellow coloration white (becomes brown, due to sep- aration of PbOj) white (soluble in HNO3 ; on boiling becomes yellow or brown) yellow (soluble in HNO3) yellow (soluble in HNO,) reddish brown (soluble in HNO3) purplish red (soluble in HNO3) white (soluble in HNO3) white (soluble in HNO3 ; separation of Ag on boiling) white (curdy, insoluble in HNO3) yellowish white (insoluble in HNO3) yellowish white (insoluble in HNO3) white (curdy, insoluble in HNOj) white (insoluble in HNO,) I yellowish white (insoluble in HNO3) black (soluble in HNO3 on warm- ing) white (soluble in large quant, of water) white (=AgCl) white (curdy, insoluble in dil. HNO3) 180 ■*.- O u -, a 'Sb-c . .rr -x: X "^.O tt u .5 s to 4) <»-=:^!: t- ':3 > o fl «^ -"^ 5 £j ^ •= <5 * ® a, ' ® • as 2"? o c 02 P^ 3S 0) ^, ;: = - 0) ^3 * >.::d i5o| 2 o "3,0 i Us ^ 05-3 p-i .2I IB t. .^ bO OS & ^^ °2 *1 II to ©3 ©X oT'i i S 6 ri «■ m C 2^« odid te, onat Arsei ©&^af e, I rsenia ate). Garb alate. nate. Iodide . lodat 'artrate e, Garb eniate, phate). nate, etate e). fl®2 TJ-jj t- y. S23 •E --i^^oC 0o2=^'0©j^3 0O-^ Sulphide, O Gyanide, O } (Arseniate, Iphite). Sulphide, G Iphate (Phospl iromate, Tartra Sulphide, lo Iphate (Phospl ornate. Tartrate Sulphide, C Oxalate (Chi Iphite, Ilyposu rseniate, Chron ate, Oxych Oxide, Sulp hate (Chromat , Iodide, Tartra Sulphide, C Arsenite, O rate. Cyanide, H ate, Chi xide, phate, ide, Su mate, A xynitr phate, Phosp Oxalate xide, phate, late. 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I J I ■« |-£ ^ III a . 2 ^ i 11 ill i L.i| I lii i . ^ ^ I 11 ill I § __o o 16 182 TESTS FOR ACIDS. Sulphuric Acid. (Sulphates.) Sulphates when fused (as in the preliminary examination) with sodium carbonate on charcoal and a portion of the fused mass is placed on a silver coin and moistened with water pro- duce a brownish or black stain on the coin. Barium chloride produces a white precipitate of barium sulphate, insoluble in acids. Plumbic acetate produces a white precipitate of plumbic sulphate, soluble in neutral ammonium tartrate. Tests for sulphuric acid should never be made in solutions which have been treated with hydrogen sulphide, because of the probability of the presence of sulphuric acid resulting from the oxidation of hydrogen sulphide. Tests for sulphuric acid can be made in acid solutions con- taining bases. Hydrofluosilicic Acid, {Silicofluorides.) Hydrofluosilicic acid is not precipitated by plumbic acetate, but is j^recipitated by potassium nitrate as gelatinous potas- sium silicofluoride (see 3, page 74). Sulphurous Add. (Sulphites.) Sulphites when fused with sodium carbonate on charcoal and a portion of the fused mass is placed on a silver coin and moistened with water produce a brownish or black stain on the coin. On acidulating a solution of a sulphite with hydrochloric acid, sulphurous anhydride is evolved, which may be recog- nized by its odor of burning sulphur and by its action upon moistened potassium iodate starch-paste paper, the latter be- coming blue, owing to the iodine separated by the sulphurous anhydride from the iodate acting upon the starch. 183 Argentic nitrate precipitates white argentic sulphite, soluble in nitric acid. On boiling the precipitate with water, it is decomposed, with the separation of finely-divided, gray metal- lic silver. To detect sulphurous acid in the presence of hyposulphur- ous acid, see 6, page 76. Hyposulphurous Acid. (Hyposulphites,) Hyposulphites when fused with sodium carbonate on char- coal and a portion of the fused mass is placed on a silver coin and moistened with water produce a brownish or black stain on the coin. Hydrochloric acid or sulphuric acid added to a hyposul- phite causes the evolution of sulphurous anhydride (odor of burning sulphur) and a milkiness due to the separation of sulphur. Argentic nitrate produces a white precipitate of argentic hyposulphite, which rapidly changes to brown and finally to black argentic sulphide. As argentic hyposulphite is soluble in an excess of a hyposulphite of an alkali, precipitation occurs only when an excess of the argentic nitrate is added. To detect sulphuric acid and other acids in the presence of hyposulphurous acid, the latter acid must be decomposed by gently warming with hydrochloric acid, the liquid filtered, and the tests for sulphuric acid and acids other than hydro- chloric acid made in the filtrate. .Phosphoric Acid. (Phosphates.) Ammonium chloride, ammonium hydroxide, and mag- nesium sulphate (magnesia mixture), added in turn to a solu- tion of a phosphate, produce a white, crystalline precipitate of ammonium magnesium phosphate. Ammonium molvbdate, added in excess with a consider- 184 able quantity of nitric acid, produces a yellow precipitate of ammonium phosphomolybdate. (If arsenic acid is present, it must be completely removed by precipitation with hydrogen sulphide before testing for phosphoric acid. With reference to the behavior of silicic acid with ammonium molybdate, see 3, page 85.) Bo)ic Acid, (Borates.) Turmeric paper dipped in an aqueous solution of boric acid, or of a borate acidified with hydrochloric acid, and warmed until dry, becomes reddish brown in color. Boric acid alone, or borates placed in a dish and moistened with a few drops of concentrated sulphuric acid, covered with alcohol, and the latter ignited, impart a greenish color to the flame. (Other substances, as copper, which might also im- part a green color to the flame should be removed before making the test.) Hydrofluoric Acid. (Fluorides.) Etches glass (see 4, page 82). Carbonic Add. (Carbonates.) On adding an acid to a carbonate, effervescence occurs, due to the evolution of carbon dioxide. The presence of carbon dioxide is confirmed by the production of a white turbidity or precipitate, due to the formation of calcium carbonate with clear calcium hydroxide solution (see 2, page 83). Silicic Acid. (Silicates.) A portion fused in a bead of microcosmic salt yields a bead in which the silica is not dissolved, but swims in the fused bead as small opaque particles (see 4, page 85). Arsenious Add. (Arsenites.) Arsenic Add. (Arseniates.) 185 Chromic Add. (Chromates.) These will have been detected in the preliminary exam- ination and in the examination for bases. Argentic nitrate added to a solution of arsenious acid, fol- lowed by the addition of ammonium hydroxide, drop by drop, or to a solution of an arsenite, produces a yellow, curdy precipitate of argentic arsenite, soluble in ammonium hydroxide and in nitric acid. Argentic nitrate added to a solution of arsenic acid, fol- lowed by the addition of ammonium hydroxide, drop by drop, or to a solution of an arseniate, produces a reddish- brown precipitate of argentic arseniate, soluble in ammonium hydroxide and in nitric acid. Arsenious acid may be detected in the presence of arsenic acid by its being immediately precipitated as arsenious sul- phide by hydrogen sulphide, whereas arsenic axjid is pre- cipitated only after continuing the introduction of hydrogen sulphide for some time. Arsenic acid is detected in the presence of arsenious acid by the formation of a white, crystalline precipitate of am- monium magnesium arseniate on the addition of magnesia mixture (see 8, page 35). Arsenious acid does not produce a precipitate with magnesia mixture. Chromic acid produces a yellow precipitate with plumbic acetate and a purplish-red precipitate with argentic nitmte (see 3, page 86, and 4, page 86). Oxalic Acid. (Oxalates.) Tartaric Acid. (Tarirates.) Produce white precipitates with calcium chloride. They may be distinguished when together by the behavior of their calcium salts : calcium oxalate is insoluble and calcium tar- trate soluble in acetic acid. 16* 186 Hydrochlonc Acid. (Chlorides.) Hydrobromic Acid. {Bromides.) Hydriodic Acid. (Iodides.) Hydrocyanic Acid. (Cyanides.) All are precipitated by argentic nitrate respectively as chloride, bromide, iodide, and cyanide of silver, and are dis- tinguished by the behavior of their silver salt with ammonium hydroxide. Argentic chloride and argentic cyanide are easily soluble in dilute ammonium hydroxide. Argentic bromide is soluble in concentrated ammonium hydroxide ; argentic iodide is insoluble in ammonium hydroxide. If the precipitate produced on the addition of argentic nitrate is insoluble in nitric acid but soluble in ammonium hydroxide, hydriodic acid is absent, but hydrochloric acid, hydrocyanic acid, and hydrobromic acid may be present. A test for hydrocyanic acid may be made by means of the Prussian-blue reaction (see 4, page 94), and for hydrobromic acid with chlorine- water and chloroform or carbon disulphide (see 5, page 91). If neither hydrobromic acid nor hydrocyanic acid is present, the solubility of the silver precipitate in ammonium hydrox- ide proves the presence of hydrochloric acid. If hydrobromic acid or hydrocyanic acid is present, the distillation test with potassium dichromate and sulphuric acid must be made for hydrochloric acid (see 4, page 89). If the precipitate is insoluble or only partly soluble in ammonium hydroxide, the presence or absence of hydriodic acid must be established by means of chlorine-water and chloroform or carbon disulphide (see 6, page 92). If a pink- ish-violet color is produced, chlorine- water is added drop by drop until either decolorization occurs (absence of hydrobro- mic acid) or the yellow color, due to the presence of bromine 187 (which was obscured by the pinkish-violet color produced by iodine), appears (see 5, page 91). The test for hydrocyanic acid should be made as before described (4, page 94). The distillation test for the detection of hydrochloric acid is to be employed when, in addition to hydriodic acid, hydrobromic acid or hydrocyanic acid is present. If hydrobromic acid or hydrocyanic acid is ab- sent, hydrochloric acid may be detected in the presence of hydriodic acid by the solubility of the silver precipitate in ammonium hydroxide. It should be remembered that chloride, bromide, iodide, and cyanide of silver are soluble in hyposulphites of the alkalies ; therefore in the presence of hyposulphites the hypo- sulphurous acid should be removed by gently warming with nitric acid. As argentic nitrate fails to produce a precipitate in solu- tions of mercuric cyanide, the presence of mercuric cyanide must be proved according to 4, page 128. Hydrqferrocyanic Acid. (Ferrocyanides.) Ferric chloride produces a dark-blue precipitate of ferric ferrocyanide (Prussian blue), insoluble in acids (see 5, page 95). Cupric sulphate produces a precipitate of brownish-red cupric ferrocyanide. Hydroferricyanic Acid. {Ferrieyanides.) Ferrous sulphate precipitates blue ferrous ferricyanide (TurnbulFs blue), insoluble in acids. Ferric chloride fails to produce a precipitate, but produces a dark coloration in the liquid, due probably to the produc- tion of ferric ferricyanide (see 3, page 96). Cupric sulphate precipitates greenish-yellow cupric ferri- cyanide. 188 Sulphocyanic Acid. (Sidphocyanides,) Argentic nitrate precipitates white, curdy argentic sulpho- eyanide, insoluble in water and in dilute nitric acid. Ferric chloride produces an intense claret-red coloration, due to the formation of soluble ferric sulphocyanide. The coloration in dilute solutions is pale red. Mercuric chloride destroys the coloration. Hydriodic add (iodides), hydrobromic add (bromides), and hydrochloric acid (chlorides) are detected in the presence of hydroferrocyanic acid and hydroferricyanic acid by means of chlorine-water and chloroform, and by distillation with potas- sium bichromate and sulphuric acid. To detect hydrocyanic acid in the presence of hydroferro- cyanic acid and hydroferricyanic acid, the solution is acidu- lated with hydrochloric acid, and calcium carbonate is imme- diately added until carbon dioxide ceases to be evolved. A test for hydrocyanic acid is then made by the ammonium sulphocyanide reaction (see 5, page 94). The hydrochloric acid liberates hydrocyanic acid as well as hydroferrocyanic acid and hydroferricyanic acid, but only the two latter pos- sess the property of decomposing carbonates to form salts; hydrocyanic acid, therefore, remains in the free state. Hydrogen Sulphide. (Sulphides.) The presence of sulphides is detected when making the preliminary examination. A soluble sulphide placed on a clean silver coin and moistened with a few drops of water produces a brownish or black stain on the coin. Nitric acid or nitro-hydfochloric acid decomposes sulphides, with the separation of sulphur ; hydrochloric acid causes the evolution of hydrogen sulphide if it should have any action at all. 189 Plumbic acetate produces in solutions of sulphides a black precipitate of plumbic sulphide. Sodium nitro-prusside solutions are colored violet by sul- phides, but not by free hydrogen sulphide. Nitrous Acid. (Nitrites.) On the addition of an acid to a nitrite, brownish-red fumes of nitrogen dioxide are evolved. On adding a few drops of sulphuric acid to a solution of a nitrite, cooling the liquid, and adding ferrous sulphate, a brown or black coloration is produced (see 5, page 99). Potassium iodide (or cadmium iodide), starch paste, and a few drops of dilute sulphuric acid added to a solution of a nitrite produce a blue coloration (see 6, page 100). Before testing for nitric acid in the presence of nitrous acid, the nitrous acid must be decomposed by being boiled a suffi- cient length of time with a solution of ammonium chloride : KNO2 + NH4CI = KCl + N2 + 2H2O. Hypoehlorous Acid. (^Hypochlorites.) Hydrochloric acid decomposes hypochlorites, with the evo- lution of chlorine. Plumbic acetate produces in solutions of hypochlorites at first a white precipitate of plumbic chloride, which soon becomes yellow and finally brown, due to the formation of lead dioxide (see 3, page 100). Nitric Acid. (Nitrates.) On adding a small quantity of concentrated sulphuric acid to a solution of a nitrate, cooling, and placing a crystal of ferrous sulphate in the liquid, a brownish or black ring is formed around the crystal (see 3, page 101). With potassium iodide (or cadmium iodide), starch paste, 190 and dilute sulphuric acid nitrates do not produce a blue discoloration unless a fragment of metallic zinc is added. (Distinction from nitrites. See 4, page 101.) Before testing for nitric acid in the presence of hydriodic acid or hydrobromic acid, the two latter acids must be re- moved by precipitation with argentic sulphate or with plumbic acetate, the precipitate filtered off, and the tests for nitric acid made in the filtrate. Chloric Acid. (Chlorates.) On warming a solution of a chlorate with hydrochloric acid the liquid becomes greenish yellow in color, and greenish- yellow fumes of a mixture of chlorine and chlorine tetroxide are evolved. Concentrated sulphuric acid poured upon a very small portion of a solid chlorate causes the evolution of chlorine tetroxide (see 4, page 103). Chlorates in the solid state on being strongly heated are converted into chlorides. On dissolving the residue in water and testing for a chloride with argentic nitrate, a white pre- cipitate of argentic chloride will be produced. (A chlorate itself, free from chlorides, does not yield a precipitate with argentic nitrate.) Acetic Acid. (Acetates.) On adding ferric chloride to a solution of an acetate and boiling the liquid, a brownish-red precipitate of basic ferric acetate is formed. Sulphuric acid added to an acetate and the liquid warmed liberates acetic acid, Avhich is recognized by its odor of vinegar. Alcohol added to a cooled solution of an acetate containing free sulphuric acid and then warmed produces acetic ether, which is recognized by its apple-like odor (see 6, page 104). APPENDIX. BEHAVIOR OF THE COMPOUNDS OF THE RARE ELEMENTS. The deportment of the rare elements and their compounds when subjected to the usual preliminary examination, as well as the behavior of these elements with the ordinary group reagents, will be treated of in the following pages. It is not intended to give a detailed description of the separation of the rare elements from one another or from the more fre- quently occurring elements, but in the latter part of the appendix a few examples are given of the separation of the rare elements in minerals which may be easily procured. I. BEHAVIOR IN THE PRELIMINARY EXAMINA- TION. (a) On heating the substance in a glass reduction-tube : Titanic acid becomes yellow to brown. Niohie acid becomes yellow. TantaUc acid becomes pale yellow. Selenium and selenides yield a reddish-brown sublimate : a portion heated in a tube open at both ends and held obliquelv in the flame gives a radish-like odor. 191 192 Tellurium sublimes ; heated in a tube open at both ends, it burns, producing dense white clouds. (6) On heating the substance with the blowpipe flame on charcoal, there are produced : Pused metallic globules : Gold : yellow, ductile, without incrustation. Thallium: white, ductile, yellow incrustation. Indium, : white, ductile, white incrustation. Incrustation, without metallic globule : Tellurium. Infusible metallic masses : Tungsten, Molybdenum^ Platinum^ Palladium, etc. White masses (When heated with cobaltous nitrate solution) : Titanie acid becomes yellowish green. Niobic acid becomes dirty green. TantaUc acid becomes flesh color. Beryllia becomes gray. Brownish-red masses : Selenixim compounds. Tellurium compounds. When placed on a silver coin and moistened with water, a brown or black stain is produced on the coin. When treated with hydrochloric acid, hydrogen sele- nide and hydrogen telluride are evolved. (c) On fusing tl>e substance in a bead of microcosmic salt the following colored beads result in the Reducing Flame, Green. Colorless. 193 Oxidizing Flame. Uranium : yellow when hot, yellowish green when cold. Cerium: reddish yellow when hot, lighter reddish yellow to colorless when cold. Didymium : colorless. Titanium : colorless. Niobium : colorless. Tungsten: colorless. Molybdenum : colorless. Vanadium : colorless. Gold and platinum are not dissolved in the bead of micro- cosmic salt. Amethyst changing to violet. Violet. Blue or violet. Blue. Black. Green. 0-2 3 (d) Examination in the flame. The non-luminous flame is colored by Lithium : carmine-red. Rubidium: violet. Gcesium: violet. Indium: bluish violet. Selenium: ultramarine-blue. Tellurium : blue bordered with green. Thallium: intense green. Molybdic acid: yellowish green. Lithium, rubidium, ccesium, indium, thallium, and gallium are best detected by means of the spectroscope. Erbium and didymium also furnish absorption spectra. I n 17 194 II. BEHAVIOR WITH THE GROUP REAGENTS. FIRST GROUP. Hydrochloric acid precipitates : Thallium : as white curdy TlCl, thallous chloride, solu- ble with difficulty in water. From alkaline solutions : Molyhdic axnd : as white H2M0O4, molybdic acid, soluble in an excess of hydrochloric acid. Tungdic acid : as white H2WO4, tungstic acid, insoluble in an excess of hydrochloric acid ; becomes yellow on boiling. Tantalic add : as white HTaOg, tantalic acid, soluble in an excess of hydrochloric acid, producing opalescence in the liquid. SECOND GROUP. Hydrogen sulphide precipitates : ii B 5 BS Palladium : as black PdS, palladious sulphide. Osmium : as brownish-black OsS, osmic sulphide Rhodium : as brown RhgSg, rhodic sulphide. Ruthenium : as brown RugSg, ruthenic sulphide. J (The liquid at first becomes azure-blue in color.) Gold: as black AugS, aurous sulphide, or AU2S3, auric sulphide. Platinum : as brownish-black PtS2, platinic sulphide. Iridium : as brown Ir2S3, iridic sulphide. Molybdenum : as brown M0S3, molybdic sulphide. (A small quantity of liydrogcn sulphide colors the solution bhie.) Selenium : as yellow, which on warming changes to reddish-yellow SeS2, selenic sulphide. Tellnriurn: as brown TeS^, tolhu'ic sulphide. The solution may become blue; in color if compounds of tungsten or ranadium arc present. 195 THIRD CROUP. Ammonium hydroxide in the presence of ammonium chloride precipitates : Uranium: as yellow (NH4)2Ur207(?), ammonium uranate. Indium : as white In(OH)3, indie hydroxide, soluble in NaOH. Beryllium: as white Be(OH)2, beryllic hydroxide, soluble in NaOH. Zirconium: as white Zr(OH)4, zirconic hydroxide, insoluble in NaOH. Thorium : as white Th(OH)4, thoric hydroxide, in- soluble in NaOH. Yttrium: as white Y(OH)2, yttric hydroxide, in- soluble in NaOH. Cerium : ^ Lanthanum : > as basic salts. Didymium : J Titanium : as white Ti(OH)4, titanic hydroxide. Tantalum : as white Ta02(0H), acid tantalic hydroxide, or as an acid ammonium salt. Niobium : as white Nb02(0H), acid niobic hydroxide, or as an acid ammonium salt. FOURTH GROUP. Ammonium sulphide precipitates : Thallium : as black TI2S, thallous sulphide. If the filtrate from the Fourth Group precipitate is treated with hydrochloric acid, there will bo precipitated : Tungsten : as brown W83, tungstic sulphide. 196 Vanadium: as brown vanadiiuu sulphide, containing oxygen and varying in composition. Molybdenum: as brown M0S3, molybdic sulphide. SIXTH GROUP. In this group may be found ; Lithium. Ccesium. Rubidium, (To be detected by means of the spectroscope.) III. EXAMPLES FOR PRACTICE, WOLFRAMITE. Wolfmmite may be recognized by the blue color it imparts to the bead of microcosmic salt in the reducing flame, and by the yellow residue of tungstic acid remaining when the finely- pulverized mineral is boiled with hydrochloric acid. The finely-pulverized wolframite is boiled with concentrated hydrochloric acid, and a few drops of concentrated nitric acid are added from time to time, until the undissolved resi- due is pure yellow in color and does not undergo further change. Tungstic acid remains undissolved as a yellow powder, w^hile the bases enter into solution as chlorides. The liquid containing the insoluble residue is evaporated to dry- ness on a water-bath, the residue extracted with water con- taining a small quantity of hydrochloric acid, filtered, and the filtrate tested for bases. The insoluble residue contains tungstic acid, and frequently silicic acid and niobic acid. The residue is treated with am- monium hydroxide, which dissolves the tungstic acid as an 197 ammonium salt, leaving an undissolved residue consisting of silicic acid and possibly niobic acid. This residue is thor- oughly washed with ammonium hydroxide, to render it free from tungstic acid, and then tested in a bead of microcosmic salt for niobic acid. The ammoniacal solution containing ammonium tungstate should give the following reactions : Hydrochloric acid precipitates white H2WO4, tungstic acid, which, on boiling, becomes yellow. Metallic zinc and an excess of hydrochloric acid impart to the precipitate of tungstic acid a blue color changing to brown (due to the formation of lower oxides of tungsten). Stannous chloride produces a yellow precipitate ; on adding hydrochloric acid and warming, the yellow color changes to blue. Ammonium sulphide added to the solution of ammonium tungstate produces no precipitate, but forms the soluble sulpho-salt (NH4)2WS4. On adding hydrochloric acid to this solution, brown WSg, tungstic sulphide, is precipitated. The supernatant liquid is generally blue in color. MOLYBDENITE. Molybdenite, when fused in a bead of microcosmic salt, yields a colorless bead in the oxidizing flame and a black bead in the reducing flame. It imparts a yellowish-green color to the non-luminous flame. When heated on cliarcoal, it yields a reddish-brown mass. It is soluble in nitro-hydro- chloric acid, imparting a green color to the liquid. On evaporating the excess of acid, diluting with water, and con- ducting hydrogen sulphide into the solution, a blue coloration is produced, and gradually brownish-black M0S3, molybdic sulphide, is precipitated. Molybdic sulphide is soluble in 17* 108 ammonium sulphide, which dissolves it as a sulpho-salt, (NH4)2MoSi, from which solution it is reprecipitated by hydrochloric acid as M0S3, molybdic sulphide. The filtrate from the precipitate produced by the intro- duction of hydrogen sulphide may still contain molybdenum in solution ; therefore, before testing for the metals of the Fifth Group, ammonium hydroxide is added to the solution, which is gently warmed, filtered if a precipitate be formed, and the solution, which now contains (NH4)2MoS4, is treated with hydrochloric acid, which precipitates the remaining molybdenum as molybdic sulphide. The molybdic sulphide reprecipitated in the Second Group from the ammonium sulphide solution by hydrochloric acid is collected on a filter, dried, and placed in an uncovered crucible, which is placed obliquely over the flame and gently heated, whereby the molybdic sulphide is oxidized and con- verted into molybdic acid, with the evolution of sulphurous anhydride. When the sulphurous anhydride ceases to be evolved, the yellow residue is dissolved in ammonium hy- droxide and the resulting solution of ammonium molybdate tested as follows : a small portion of the solution is tested for copper with a few drops of ammonium sulphide, and the remainder of the solution is used in making the tests for molybdenum. (The precipitated molybdic sulphide obtained from the Fourth Group is heated in an uncovered crucible and treated in the same manner.) Hydrochloric acid causes the precipitation of white H2M0O4, molybdic acid, soluble in an excess of hydrochloric acid. Stannous chloride produces in the hydrochloric acid solution of molybdic acid a blue coloration, changing to green and finally to brown ; metallic zinc produces a similar coloration, but not so promptly. The cliange in color in the two pre- ceding reactions is due to the reduction of molybdic acid. 199 Ammonium sulphocyanide added to the ammoniacal solu- tion, followed by the addition of hydrochloric acid and zinc, produces a carmine-red coloration (in consequence of reduction with the formation of sulphocyanides of the oxides). Concentrated nitric acid and sodium hydrogen phosphate added to the ammoniacal solution precipitate yellow am- monium phosphomolybdate. WULFENITE. Wiilfenite, when heated in the blowpipe flame on charcoal, yields a globule of metallic lead ; when fused in a bead of microcosmic salt, it yields a colorless bead in the oxidizing flauie and a black bead in the reducing flame. Wulfenite is soluble in hydrochloric acid with the sepam- tion, upon cooling, of crystalline plumbic chloride. The hydrochloric acid solution yields with hydrogen sulphide in the Second Group a precipitate of molybdic sulphide, soluble in ammonium sulphide, thus furnishing a means of separating it from plumbic sulphide, which is insoluble in ammonium sulphide. After precipitating the Fourth Group, the reddish- brown filtrate is treated with hydrochloric acid to precipitate the remainder of molybdic sulphide. The molybdic sulphide is further examined as given under Molybdenite, page 197. URANINITE (PITCHBLENDE). Uraninite, when fused in the bead of microcosmic salt, yields a yellow bead in the oxidizing flame and a green bead in the reducing flame ; treated Avith nitric acid it dissolves, leaving a residue of silicic acid and insoluble oxides (see page 116). The nitric acid solution yields in the Third Group a precipitate containing uranium, the uranium being precipi- tated as vellow ammonium uranate. In order to separate 200 uranium the precipitate of the Third Group is digested at a moderate heat with a concentrated sohition of ammonium carbonate ; uranium enters into solution as uranyl ammonium carbonate, Ur02C03 ((NH4)2C03)2, imparting a yellow color to the solution. The oxides of the other metals remain undissolved, and after being collected on a filter may be examined according to the usual scheme of analysis. To detect uranium a portion of the yellow filtrate contain- ing uranyl ammonium carbonate is acidulated with acetic acid and treated with potassium ferrocyanide : a reddish- brown precipitate of (Ur02)2 Fe(CN)g, uranyl ferrocyanide, indicates the presence of uranium. The remainder of the solution of uranyl ammonium carbonate is carefully concen- trated on a water-bath, and on cooling glistening yellow crystals of uranyl ammonium carbonate separate, which when strongly ignited leave a residue of dark-green uranous-uranic oxide, UrgOg. On treating the filtrate containing ammonium sulphide from the precipitate of the Fourth Group with hydrochloric acid, nickelous sulphide together with vanadic sulphide may be precipitated. If a precipitate is obtained by treatment with hydrochloric acid, it is collected on a filter, washed, dried, mixed with potassium nitrate, fused, and the resulting fused mass extracted with water, whereby vanadium as an acid vanadium salt enters into solution. On filtering, neutralizing the filtrate with nitric acid, and adding a concentrated solution of ammonium chloride, vanadic acid in combination with ammonium is gradually precipitated as a white ammonium salt. On collecting the precipitate on a filter, dissolving in water, and adding a small quantity of hydrochloric acid,^^^ * The solution becomes yellow <»r r*'d in color. 201 followed by the addition of metallic zinc, the solution becomes blue in color. RUTILE (TITANIFEROUS IRON). Rutile, when fused in a bead of microcosmic salt in the reducing flame, yields a violet- to blood-red-colored bead. Fused in the oxidizing flame (when a sufficient quantity of the mineral is employed) it yields microscopic tabular crystals of anatase (TiOg). The mineral is best decomposed by being fused with acid potassium sulphate at not too high a temperature. The fused mass after cooling is pulverized and dissolved in cold water : the titanium enters into solution as sulphate. The liquid is filtered and a portion of the filtrate tested with metallic zinc or tin for titanic acid : in the presence of titanic acid a pale violet or a blue coloration is imparted to the solution and afterwards a blue precipitate separates which gradually changes to white. On boiling the remainder of the precipitate for some time, me ta- titanic acid separates as a white powder. The meta- titanic acid is filtered oif and the filtrate diluted with water and again boiled and filtered. The filtrate is then tested for the remaining bases in the usual manner. BERYL. Beryl, when fused in a bead of microcosmic salt, slowly dissolves without the formation of a skeleton of silica. The fragment of beryl remains in the bead of microcosmic salt and gradually diminishes in size, forming, on cooling, an opalescent bead. Varieties of beryl containing chromium (for example, emeralds) impart a green color to the bead. As beryl is insoluble in acids, it must be decomposed by fusing with sodium potassium carbonate. The fused mass is 202 treated with hydrochlorie acid and evaporated to dryness on a water-bath, in order to separate silicic acid. The residne is extmcted with water containing a small quantity of hydro- chloric acid and filtered ; the filtrate contains BeClg, beryllium chloride. On the addition of ammonium hydroxide to the filtrate, Be(OH)2, beryllium hydroxide, separates as a white precipitate, and is collected on a filter and dissolved in an excess of sodium hydroxide. The sodium hydroxide solution contains sodium aluminate and sodium beryllate, and may also contain sodium chromite, in which case the solution would be green in color. If chromium is not present, the solution is treated with a considerable quantity of ammonium chloride, which precipi- tates aluminium hydroxide and beryllium hydroxide. On boiling the liquid for some time, beryllium hydroxide enters into solution as beryllium chloride, with the evolution of ammoniacal gas, while aluminium hydroxide remains un- dissolved, is collected on a filter, and, when lieated with cobaltous nitrate on charcoal, yields a blue mass. The fil- trate, which contains beryllium chloride, is treated with ammonium hydroxide to precipitate beryllium hydroxide. Beryllium hydroxide is soluble in an excess of ammonium carbonate, and from this solution it separates on boiling as a basic bervllium carbonate. The bervllium hydroxide, when heated with cobaltous nitrate in the oxidizing flame on char- coal, yields a gray mass. If chromium is present, the solution is diluted with water and boiled for some time : aluminium hydroxide remains in solution, while beryllium hydroxide and chromium hydroxide are precipitated. The precij)itate is collected on a filter, dried, and the beryllium hydroxide separated from the chro- mium hydroxide by fusing with a mixture of sodium carbon- ate and potassiiuii nitrate. On extracting the yellow fused 203 mass with water, beryllium oxide remains undissolved, while chromium enters into solution as a chromate of the alkali. CERITE. Cerite, heated in the blowpipe flame on charcoal, is infusi- ble, but becomes dirty yellow in color. Fused in a bead of microcosmic salt, it yields in the oxidizing flame a reddish- yellow bead, and in the reducing flame a colorless l^ead, together with a skeleton of silica. On heating a portion of the finely-pulverized mineral with hydrochloric acid, diluting with water, filtering, and adding oxalic acid to the filtrate, a white precipitate is produced. On heating the mineral with concentrated hydrochloric acid, evaporating to dryness on a water-bath, and extracting the residue with Avater and a few drops of hydrochloric acid, the bases enter into solution while silicic acid remains undis- solved. In the Second Group, in addition to other metals, molyb- denum may be precipitated as molybdic sulphide. (See Molybdenite, page 197.) Cerium, lanthanum, and didymium are precipitated by ammonium hydroxide in the Third Group as hydroxides : Ce(OH)2, La(OH)2, and Di(OH)2. Cerium hydroxide and lanthanum hydroxide are white. The former when exposed to the air oxidizes and becomes yellow ; didymium hydroxide is pink in color. On collecting the precipitate of the Third Group on a filter, dissolving in hydrochloric acid, and add- ing oxalic acid, cerium, lanthanum, and didymium are pre- cipitated as white oxalates insoluble in dilute acids ; the filtrate from the precipitate of oxalates may be examined for the remaining bases of the Third Group. The oxalates of cerium, lanthanum, and didymium when ignited yield a brown residue consisting of a mixture of 204 oxides (Cefi^, LaO, and DiO). On heating a portion of this mixture of oxides with concentrated sulphuric acid, sul- phates are formed which are soluble in water and impart a yellow color to the liquid. In this solution concentrated potassium sulphate produces a lemon-yellow precipitate con- sisting of a mixture of double salts. The remainder of the mixture of oxides is treated with hydrochloric acid and alcohol and then heated : the oxides are dissolved thereby, with the formation of chlorides (CeCl2, LaCl2, DICI2). If didymium is present, on passing a ray of light through the solution, the spectrum shows dark absorp- tion bands (four between Frauenhofer's lines D and F and two between F and G). On adding sodium acetate and passing chlorine through the solution, or on the addition of sodium hypochlorite, light- yellow CcgOyllg, cerium hydroxide, is precipitated, Avhich is soluble when warmed with hydrochloric acid, forming CeClg, with the evolution of chlorine. (For the separation of cerium, lanthanum, and didymium the reader is referred to more extensive works on qualitative analysis.) ' ' ZIRCON (HYACINTH). Zircon, heated in the blowpipe flame on charcoal, is infusi- ble, but becomes lighter in color. It is not dissolved in the bead of microcosm ic salt. It is decomposed by being fused for some time with sodium potassium carbonate. The fused mass is treated with hydro- chloric acid, evaporated to dryness on a water-bath (to render the silica insoluble), the residue extracted with water and hydrochloric acid and filtered. The filtrate contains zirco- nium as zirconium chloride. From this solution the zirco- nium is precipitated by ammonium hydroxide in the Third Group as Zr(OH)4, zirconium hydroxide. Zirconium hy- 205 droxide is insoluble in sodium hydroxide, but soluble in ammonium carbonate. From the solution in ammonium carbonate it is reprecipitated by boiling. On dissolving a portion of this precipitate in sulphuric acid and adding a concentrated solution of potassium sulphate, a wliite double salt of zirconium is precipitated. The hydrochloric acid solution is not precipitated by oxalic acid, but the neutral solution is precipitated by ammonium oxalate ; the precipitate redissolves in an excess of ammonium oxalate. Turmeric paper, moistened with the hydrochloric acid solution, becomes reddish brown in color when drv. LEPIDOLITE. Lepidolite when fused in a bead of microcosmic salt yields a skeleton of silica. When placed on a platinum wire and held in the non-luminous flame it imparts a carmine-red color to the flame, especially after moistening the lepidolite with a few drops of hydrochloric acid. Treated with concentrated sulphuric acid it responds to the fluorine reactions (see 4, page 82). A portion of the mineral is heated in a platinum crucible (without the addition of carbonates of the alkalies as a flux) until melted. The fused mass is pulverized and then decom- posed by being boiled with concentrated hydrochloric acid. The solution is evaporated to dryness on a water-bath to render the silica insoluble ; the residue is extracted with water and a few drops of hydrochloric acid, the insoluble silica filtered ofl^, and the filtrate examined for bases. Lithium belongs to the Sixth Group. The hydrochloric acid filtrate, obtained as described above, is treated with am- monium carbonate to precipitate tlic metals of the Fifth Group, and with sodium hydrogen phosphate to precipitate magnesium, filtered, the filtrate treated with barium chloride, 18 206 and the liquid again filtered. The filtrate now contains, in addition to the excess of barium chloride, the alkaline metals as chlorides. The liquid is evaporated to dryness, the residue gently heated over a free flame to expel ammonium chloride, and then placed in a small flask and extracted with a mixture of alcohol and ether. Lithium chloride enters into solution, while the chlorides of the other metals remain undissolved. The alcoholic solution is filtered and the filtrate evaporated to dryness on a water-bath ; the residue remaining consists of lithium chloride, which is recognized by its imparting a carmine-red color to the non-luminous flame and by the examination with the spectroscope. The residue, insoluble in the mixture of alcohol and ether, is dissolved in water, and sulphuric acid added to the solution to precipitate barium as barium sulphate, which is filtered off and the filtrate ex- amined for potassium and sodium. THORITE. Thorite when fused in a bead of microcosmic salt is dis- solved with the production of a skeleton of silica ; the bead is colored yellow, due to ferric oxide (and uranium oxide), and is opalescent while cooling. The finely pulverized mineral is heated with hydrochloric acid, evaporated to dryness, the dry residue moistened with hydrochloric acid and extracted with hot water and the liquid filtered. The filtrate is treated with hydrogen sulphide and the precipitated sulphides removed by filtration. The filtrate is treated with ammonium hydroxide, the precipitate which is produced is washed, by decantation, with water (test the filtrate), and then the precipitate is dissolved in hydrochloric acid and the solution treated with oxalic acid. The precipi- tate produced is washed, by decantation, witli hot water (test the filtrate), and finally, after having been boiled with water, 207 is collected on a filter, dried, and decomposed by incinera- tion. The thorium oxide thus obtained still contains oxides of cerium and ytterbium (and some manganese). It is now treated with sulphuric acid, and the mixture heated to expel the excess of sulphuric acid, and the residue, consisting of sulphates, is dried. The residue is then dissolved in ice-cold water, and the solution allowed to become of the temperature of the room, whereby thorium sulphate, contain- ing water, separates while the sulphates of cerium and ytter- bium remain in solution. The supernatant liquid is removed by decantation, the thorium sulphate is collected on a filter, washed with water, removed from the filter, and by careful heating rendered free from the water it contained. The thorium sulphate is now dissolved in ice-cold water, and from this solution the thorium is precipitated as Th(OH)^ thorium hydroxide, by the addition of ammonium hydroxide. LEAD SELENIDE. Lead selenide occasionally decrepitates when heated in a reduction tube, but undergoes no further change. When heated in a glass tube open at both ends selenium is given oif, which collects as a gray sublimate near the heated part of the tube, and as a red sublimate in the part of the tube beyond the gray sublimate ; at the same time an odor resem- bling that of decayed radishes is produced. When heated on charcoal it produces fumes having an odor similar to that of decayed radishes, fuses only imperfectly, and covers part of the charcoal with, primarily, an incrustation of selenium which, near the point where the heat was applied, is black, and at the outer edges red ; eventually, on continuing the heat, an incrustation of lead oxide is formed. On prolonged used of the blowpipe flame considerable volatilization occurs. 208 until finally a very small fused mass remains which, when portions are tested in the bead of microcosmic salt, occasion- ally furnishes evidence of the presence of iron, cobalt, or copper. Fused with sodium carbonate or charcoal, lead sel- enide produces a brownish-red mass, which on further fusion yields metallic lead, which occasionally contains silver. (On heating the globule of lead on a cupel of bone ash to remove the lead by absorption, a small globule of silver will remain, provided it was present in the lead selenide employed.) The very finely pulverized mineral is treated with dilute hydrochloric acid to remove calcite and siderite. The resi- due is collected on a filter and washed with water, and then it is digested with nitric acid, whereby PbSeOg, plumbic sel- enate, is produced. The solution thus obtained is evaporated to expel the nitric acid, and the residue, consisting of plumbic selenate, is treated with dilute sulphuric acid, whereby insol- uble plumbic sulphate is produced, and soluble H2Se03, selenic acid, remains in solution. The plumbic sulphate is removed by filtration, and the filtrate is diluted with water and a current of sulphurous anhydride is passed through, whereby sulphuric acid is produced and selenium separates as a red powder : PbSe -f 2HNO3 = PbSeOa + H^O + 2NO ; PbSeOg + H2SO4 = PbSO^ + H^SeOg ; H^SeOg H- 2SO2 + H2O = 2H2SO, + Se. INDEX. PAGE Acetates 103, 190 Acetic acid 103, 190 Acid, acetic 103, 190 arsenic 84 arsenious 29 boric 80, 184 carbonic 83, 184 chloric 102, 190 chromic 86, 185 ferricyanic 96, 187 ferrocyanic 95, 187 hydriodic ... 91, 186 hydrobromic 90, 186 hydrochloric 88, 186 hydrocyanic 93, 186 hydroferricyanic 96, 187 hydroferrocyanic 95, 187 hydrofluoric 81 hydrofluosilicic 74, 182 hypochlorous 100, 189 hyposu^phurous 77, 183 molybdic 194 niobic 191 nitric 101, 189 nitrous 99, 189 oxalic 104 phosphoric 78, 185 silicic 84, 184 sulphocyanic 97, 188 sulphuric 73, 182 sulphurous 75, 182 sulphydric 98, 188 tantalic l-*4 18* • 20<» 210 PAGE Acid, tartaric 105, 18") thiosulphuric 77 titanic 191 Acid sulphides, separation of 152 Acids, behavior with group reagents . 178 examination for 174 preliminary tests for 116 Aluminium 5q Ammonium 72 carbonate 62 Antimony 36 Marsh's test for 3j^ Keinsch's test for 39 in antimonic condition 40 in antimonious condition 37 Arsenic 28 Marsh's test for 30 Keinsch's test for 33 in arsenic condition 34 in arsenious condition 29 Arsenic acid 34 Arsenious acid 29 Barium 64 Bases, detection of, in the Wet Way 133 precipitation of groups 133 properties of 15 separation of First Group 146 Second Group 148 Third Group 159 Fourth Group 164 Fifth Group 165 Sixth Group 168 Basic sulphides, separation ol 150 Beryl 201 Beryllium 195 Bismuth 27 Borates 80, 184 Boric acid 80, 184 Bromides 90, 188 211 PAGE Cadmium 43 Caesium 196 Calcium 65 Carbonates 83, 184 Carbonic acid 83, 184 Cerite 203 Cerium ]95 Charcoal, examination on HO Chlorates 102, 190 Chloric acid 102 190 Chlorides 88, 186 Chromates 86, 185 Chromium 52 Cobalt 58 Copper 24 Cyanides 93^ 128, 186 Detection of bases in the Wet Way 133 Didymium I95 Dissolving metals and alloys 127 oxides and salts 121 Everett's salt 48, 95 Examination by microcosmic salt 114 for acids 174 in the flame 114 in the reduction-tube 107 on charcoal 110 Ferricyanides 96, 187 Ferrocyanides 95, 187 Flame, examination in 114 Fluorides 81 Gold ^ Group (acids) : First 73 Second 75 Tnird ^8 Fourth 101 212 Group (bases) : page First 15 Second 22 Third 46 ' Fourth 54 Fifth 62 Sixth 66 Group precipitations, table of 134 Beavy metals, sulphides of 128 Hyacinth 204 Hydriodic acid 91, 186 Hydrobromic acid 90, 186 Hydrochloric acid 88, 186 Hydrocyanic acid 93, 186 Hydroferricyanic acid 96, 187 Hydroferrocyanic acid 95, 187 Hydrofluoric acid 81 Hydrofluosilicic acid 74, 182 Hydrogen sulphide 98, 188 Hypochlorites 100, 189 Hypochlorous acid 100, 189 Hyposulphites 77, 183 Hyposulphurous acid 77, 183 Indium 195 Iodides 91, 186 Iridium 194 Iron 47 in ferric condition 49 in ferrous condition 47 Lanthanum 195 Lead 19 Lead selenide 207 Lepidohte 205 Lithium 72 Magnesia mixture 78 Magnesium ... • ■ 66 Manganese 55 213 PAGE Marsh's test , 30 Mercury 17 in mercuric condition 22 in mercurous condition 17 Metals and alloys, dissolving of 127 Microcosmic salt, examination by 114 Molybdenite 197 Molybdenum 194 Nickel 61 Niobium 195 Nitrates 101, 189 Nitric acid 101, 189 Nitrites 99, 189 Nitrous acid 99, 189 Organic acids . 103 Osmium 194 Oxalates 104 Oxalic acid 104 Oxides and salts, dissolving of 121 Palladium . 194 Phosphates 78, 183 Pitchblende 199 Platinum 46 Potassium » . • . 69 Precipitation of the bases : First Group 136 Second Group . , 139^ Third Group •• • 141 Fourth Group . „ 143 Fifth Group 144 Sixth Group 145 Preliminary examination • • 107 tests for acids 116 tests in the Dry Way • • 1^7 Properties of the acids • • 73 of the bases • • 1^ Prussian blue 49, 9b 214 PAGE Rare elements, behavior of 191 preliminary teste for 191 Reinsch's test 33 Rhodium 194 Rubidium 196 Ruthenium 194 Rutile 201 Selenides 191 Selenium 194 Separation of acid sulphides 152 of bases : First Group 146 Second Group 148 Third Group . 159 Fourth Group 164 Fifth Group 165 Sixth Group . 168 of basic sulphides 150 Silicates 84, 130, 184 Silicic acid 84, 184 Silicofluorides 74, 182 Silver 15 Sodium 70 Solubilities, table of 180 Strontium 64 Sulphates 73, 182 Sulphides 98, 188 of heavy metals 128 Sulphites 75, 182 Sulphocyanates 97, 188 Sulphocyanic acid 97, 188 Sulphocyanides 97, 188 Sulphuric acid 73, 182 Sulphurous acid 75, 182 Sulphydric acid 98, 188 Table of group precipitations 135 Table of solubilities 180 Tantalic acid 194 Tantalum 195 215 PACK Tartaric acid 105 Tartrates lOo Tellurium 194 Tests, preliminary, in Dry Way 107 Thallium 194 Thenard's blue 52 Thiosulphates 77 Thiosulphuric acid 77 Thorium 195 Thorite 206 Tin 41 in stannic condition 42 in stannous condition 41 Titanic acid 191 Titaniferous iron 201 Titanium 195 TurnbuU's blue 48, 96 Uraninite 199 Uranium 195 Vanadium 196 Wolframite 196 Wulfenite 199 Yttrium 195 Zinc 57 Zircon 204