BRARY IVMSITYOI A DETAILED COURSE OF QUALITATIVE CHEMICAL ANALYSIS OF INORGANIC SUBSTANCES, WITH EXPLANATORY NOTES. B ARTHUR A. NOYES, PH.D., PROFESSOR OF CHEMISTRY IN THE MASSACHUSETTS INSTITUTE OF TECHNOLOGY. THIRD REVISED AND ENLARGED EDITION. NEW YORK: THE MACMILLAN COMPANY. LONDON : MACMILLAN & Co., Ltd. 1899, COPYRIGHT, 1897, BY ARTHUR A. No YES. PREFACE. SOME explanation of the origin and purpose of the present work *s necessary. It arose out of the difficulty experienced in attempt- ing to give a thorough course of qualitative analysis in limited time to large classes of students. The smaller text-books on the sub- ject are too elementary in character to use in connection with such a course ; they devote too little attention to the precautions to be observed to insure delicacy of the reactions, to the difficulties en- countered by the student in actual work, and to the modifications of the process required in special cases. On the other hand, the manual of Fresenius, though complete and very valuable as a work of reference, is confusing to beginners on account of the complex- ity of its arrangement and insufficient explanation of the purposes of the various operations. The attempt has been made in the fol- lowing pages to present an almost equally thorough scheme of qualitative analysis in a more concise and readily intelligible form. The process of analysis here given was based originally on that of Fresenius, but it has undergone a number of important modifi- cations suggested by experience with it in the laboratory. Among these may be specially mentioned the directions for the prepara tion of the substance for analysis and those for testing for acids, which have been made as distinct and definite as possible ; for it is with these two parts of the process that the greatest difficulty is usually experienced. The methods of separation of the metals also differ somewhat from those of Fresenius, a different process being given for arsenic, antimony, and tin, and the choice between 4 PREFACE. the two methods of analysis of the aluminum and iron groups being made to depend on a preliminary test for phosphates. The most characteristic feature of the book, however, will be seen to be the method of presentation of the subject. Through- out the part devoted to the description of the process of analysis the matter is comprised under two distinct headings the method of Procedure and the Notes upon it. The former consists exclu- sively of very detailed directions for carrying out the separations and special tests. The latter serve : first, to criticise the process and to point out the conditions to be fulfilled in order to insure delicacy of the tests ; second, to show the purpose of each oper- ation and reagent, where this is not sufficiently obvious ; . third, to explain abnormal results arising either from previous errors in the analysis or from the existence of conditions not provided for in the general scheme ; and fourth, to suggest modifications of the process desirable in special cases. In the part devoted to the analysis for metals the description of each group is preceded by a brief tabular outline of the process, intended only to indicate the principles of the separation, not to serve as a working basis. Besides this description of the process of analysis the book con- tains a separate part giving the Directions for Laboratory Work which have been used in connection with it. The author desires to express the opinion that the plan followed here and in the manual of Eliot and Storer of analyzing by the regular process solutions known to contain all the metals of each group is a far better preparation for the subsequent analysis of unknown sub- stances than the more usual method of studying the reactions of each metal separately ; for, however valuable the knowledge of the additional reactions involved in the latter method may be r it is found in practice that the performance of such a large num- ber of independent tests in disconnected form makes but little impression on the mind of the student and causes confusion and loss of interest. Even where it is desired to teach the chemistry of the metals in connection with a course of qualitative analysis PREFACE. 5 it is in the author's opinion better to do so as a supplement to the scheme of separation, in the form of additional reactions of the various metals. The laboratory work should be accompanied by lectures or recitations in which the process of analysis is taken up and discussed in detail. In conclusion, the author desires to express his great indebt- edness to Prof. T. M. Drown for his encouragement and valuable advice in regard to the general features of the book, and to Mr. W. S. Davenport, Instructor in Qualitative Analysis at the Institute, through whose cordial cooperation and numerous sug- gestions it has been greatly improved, not only in general char- acter, but also in matters of detail. PREFACE TO THE THIRD EDITION. IN this edition a number of changes suggested by recent inves- tigations and by the continued use of the book in the laboratory have been made. In accordance with the researches of Fresenius, a much more delicate method of detection of the alkaline-earth metals has been introduced. The barium carbonate process in the presence of alkaline-earth phosphates has been simplified. The methods of detection of metals and acids in the dry way have been extended and more fully discussed ; and practice with them has been introduced into the Directions for Laboratory Work. On the other hand, in the case of complete analyses, it is directed to confine the preliminary dry examination to the closed- tube test a modification discussed on page 65. Finally, for the convenience of teachers, an appendix has been added showing the strength of reagents to be employed. Objection has been raised to the system of instruction fol- lowed in this book on the ground that the omission of prelimi- nary " reaction " work gives the student too narrow and limited an 6 PREFACE TO THE THIRD EDITION. acquaintance with chemical facts. In reply to this objection, and especially in the interest of a reform of what the author believes to be a vicious method of instruction, the following remarks may be added to those which have been made on the subject in the preceding Preface. In the first place, it should be borne in mind that the introduction of an 'excessive amount of mate- rial is a common defect in modern education, and that the number of chemical facts involved in the systematic scheme of analysis is as great as can be properly assimilated by the stu- dent in the time usually devoted to the course. Secondly, it is to be considered that qualitative analysis is a satisfactory method of teaching a part of descriptive chemistry chiefly be- cause it unites into a connected whole a great variety of isolated facts, and because it makes evident to the student a practical use of the information presented to him ; but these advantages evi- dently do not apply to facts not directly related to the process of analysis. And thirdly, the additional knowledge which it is most desirable that the general student of descriptive chemistry should acquire when time permits, is not a more extended ac- quaintance with metathetical test-tube reactions, which involve for the most part merely questions of solubility, but rather a knowl- edge of new principles and new methods of manipulation infor- mation that would be much better given by a course in inorganic preparations. ARTHUR A. NOYES. Boston, March, 1897. PART I. DIRECTIONS FOR LABORATORY WORK. SEPARATION OF THE METALS INTO GROUPS. i. As an example of the method of separation of the metals into groups, prepare a solution of Pb(NO 3 ) 2 , Cu(NO 3 ) 2 , Zn(NO 3 ), Ca(NO 3 ) 2 , Mg(NO 3 ) 2 , and KNO 3 , by mixing together in a beaker about 5 cc. of each of these solutions. Add to it HC1 little by little, as long as a precipitate continues to form (2 or 3 cc. at most) ; filter, and wash with cold water, till the washings (which should be added to the filtrate) are no longer acid to litmus paper. Heat the filtrate to boiling, and pass H 2 S into it until it smells strongly of the gas, after removing it from the delivery tube, blow- ing away the gas collected on the surface, and shaking the liquid. Shake, heating at the same time ; allow the precipitate to settle and filter ; wash with hot water till free from acid, throwing the washings away. Add to the filtrate 10 cc. of NH 4 C1, NH 4 OH till slightly alkaline, and colorless (NH 4 ) 2 S, until the solution after shaking blackens a piece of filter paper moistened with lead ace- tate held above it. Heat and shake the solution till the precip- itate settles quickly ; filter, and wash with hot water containing a little (NH 4 ) 2 S. Add (NH 4 ) 2 CO 3 to the filtrate as long as a pre- cipitate forms ; filter, and wash the precipitate. To one portion of the filtrate add Na 2 HPO*. Evaporate the remainder of the filtrate nearly to dryness, and try the color imparted to the flame, using a platinum wire. State in the note-book in the case of this and all subsequent experiments the reason of each operation and the purpose of the 8 DIRECTIONS FOR LABORATORY WORK. addition of each reagent. Write every reaction occurring in the process. Name the other metals which, if present, would be precipitated in this experiment by each of the group reagents. See page 15. Read the General Directions, pages 13-14. 2. As an example of the separation of the copper and tin groups, pass H 2 S into a hot solution Of HgCl 2 and AsCl 3 until the liquid is saturated. Filter, and wash the precipitate ; warm some of it in a porcelain dish with 10 or 12 drops of (yellow) (NH 4 ) 2 S X diluted with a little water; filter, and add HC1 to the filtrate till slightly acid. For the sake of comparison, add HC1 to 10 or 12 drops of pure (NH 4 ) 2 S X diluted with water. (Read the notes on page 19.) COPPER GROUP. 3. Prepare a solution of Pb(NO 3 ) 2 , AgNO 3 , and HgNO 3 , using 10 cc. of each solution. Proceed with the separation as directed on pages 16 and 17. 4. In order to become familiar with the color and appearance of the various sulphides, add H 2 S water to solutions of PbCl 2 , HgCl 2 , BiCl 3 , CdCl 2) Cu(NO 3 ) 2 , each taken separately, and previously acidified with a few drops of HC1. In the case of HgClo, try the effect of adding a small quantity of H 2 S at first, then of adding an excess, shaking in each case. 5. Prepare a mixed solution of these five substances; dilute with water, and proceed according to pages 17-22, omitting the treatment with (NH 4 ) 2 S X described on page 19. TIN GROUP. 6. Pass H 2 S into separate solutions ot As?Cl 8 , SbCl 3 , SnCl 2 , and SnCl 4 ; also into a cold and then into a hot solution oi Na 3 AsO 4 acidified with HC1. Note the color and appearance of the precipitates. 7. Prepare a mixed solution of AsCl 3 , SbCl*, and SnCl 2 , using 10 cc. of each. Dilute with 100 cc. of water ; heat to boiling, and pass in H 2 S till saturated. Filter, and proceed with the- precip- itate according to pages 24 and 25. DIRECTIONS FOR LABORATORY WORK:. ALUMINUM AND IRON GROUPS. 8. Ferrous and Ferric Salts. Add KCNS, K 3 Fe(CN) 6 and K 4 Fe(CN) 6 to separate portions of FeSO 4 solution. 9. Add the same reagents to separate portions of FeCl 3 solu- tion. Contrast the results obtained in the two cases. 10. Try the following experiments illustrating methods of oxi- dizing ferrous to ferric salts, and read in this connection pages 27-29. a. Boil 2 to 3 cc. of FeSO 4 solution with a small quantity of HN0 3 . b. Boil 2 to 3 cc. of FeSO 4 solution with an excess of bromine water. c. Add HC1 and a few crystals of KC1O 3 to a little FeSG 4 solu- tion, and heat. In each of these three cases, dilute a portion of the solution thus obtained with water, and test it with K 3 Fe(CN) 6 to see whether the iron has been completely oxidized. If this is found not to be the case, add more of the oxidizing agent to the remainder of the solution, and boil again. 11. Try the following experiments illustrating the reduction of ferric salts : a. Pass H 2 S into a solution of FeCl 3 . b. Add HC1 and a piece of zinc to a little FeCl 3 solution in a test tube. c. Add H 2 SO 3 to a little FeCl 3 solution, and heat. In each case continue the action till the solution is decolorized, and then test a portion with KCNS to show that complete re- duction has taken place. 12. Behavior towards General Reagents. To solutions of alum, chrome alum, FeSO 4 , FeCl 3 , Zn(NO 3 ) 2 , MnSO 4 , NiSO 4 , and Co(NO 3 ) 2 , each taken separately, add NH 4 OH, first in small quantity, and then in moderate excess. To solutions of FeSO 4 and MnSO 4 add an equal volume of NH 4 C1, and then add NH 4 OH. 13. Repeat the experiments, using NaOH in place of NH 4 OH. 14. Add colorless (NH 4 ) 2 S in small quantity to solutions of the 'iame substances. 15. Separation in the Absence of Phosphates. Prepare a mixed solution of alum, FeSO 4 , Zn(NO 3 ) 2 , MnSO 4 , NiSO 4 , and Co(NO,) 2l "nd analyze it as directed on pages 31-33 and 36-38. to DIRECTIONS FOR LABORATORY WORK. 16. Experiments Illustrating the Behavior of Phosphates. Dis- solve some CaCO 3 in dilute HC1, boil a few minutes to expel the CO.J, and add NH 4 OH till alkaline. Note that no precipitate forms; then add (NH 4 ) 2 CO 3 . 17. 'Dissolve some Ca 3 (PO 4 ) 2 in dilute HC1, add NH 4 OH till alkaline ; filter, and add (NH 4 ) 2 CO 3 to the filtrate. 1 8. Dissolve another portion of Ca 3 XPO 4 ) 2 in dilute HC1, add 10 to 15 cc. of FeCl 3 solution, add NH 4 OH till alkaline; filter, and add (NH 4 ) 2 CO 3 to the filtrate. Explain fully the significance of these three experiments in the note-book. Read carefully pages 34 and 35 in this connection. 19. Separation in the Presence of Phosphates. A solution con- taining the phosphates of barium, strontium, calcium, and magne- sium, and salts of iron, chromium, aluminum, manganese, and zinc, will be found prepared in the laboratory. (Nickel and cobalt are omitted, since their separation is exactly the same as in the absence of phosphates.) Take 50 cc. of this solution, and proceed with it according to pages 29-30 and 40-43, omitting, however, the anal- ysis of the alkaline-earth sulphates. ALKALINE-EARTH GROUP. 20. Prepare a mixed solution of BaCl 2 , SrCl 2 , Ca(NO s ) 2 , and Mg(NO 3 ) 2 , and proceed with it according to pages 44-47. ALKALI GROUP. 21. Add H 2 PtCl 6 to separate solutions of KC1, NaCl, and NH 4 C1. 22. Warm a little solid NH 4 C1 with CaO moistened with water ;. note the odor of the gas, and its action on red litmus paper. ACIDS. 23. General Tests. Add BaCl 2 to a solution of Na 2 HPO 4 , and to one of Na 2 SO 4 . Then add HC1. State in the note-book the other acids which, if present, react in the same manner as either of these. See pages 51 and 52. 24. Add AgNO 3 to separate solutions of K 2 CrO 4 , Na 2 SO 4r Na 2 HPO 4 , Na 2 B 4 O 7 , (NH 4 ) 2 C 2 O 4 , Na,CO 3 , NaCl, KBr, KI, KCN, and Na 2 S. Note the color of each precipitate. Then add HNOs to each in moderate quantity. See page 53. DIRECTIONS FOR LABORATORY WORK. u 25. Special Tests. Try with the solid salts and solutions pre- pared for the purpose in the laboratory all the special tests for acids described on pages 55-64. Make the reduction tests for chromates with a small quantity of K 2 CrO 4 solution, (i) by adding HC1 and a lump of zinc, (2) by adding considerable strong HC1 and boiling, (3) by acidifying with HC1 and passing in H 2 S. DRY REACTIONS. 26. Heat in a closed tube, as described on page 66, each of the following substances: (i) Ni(NO 3 ) 2 .6H 2 O ; (2) KHC 4 H 4 O 6 ; (3) HgO; (4) NH 4 C1; (5) FeS 2 ; (6) KC1O 3 ; (7) ZnSO 4 . 27. Try the test with concentrated H 2 SO 4 , described on page 70, with the following substances: (i) KHC 4 H 4 O 6 ; (2) KI ; (3) KBr; (4) NH 4 C1; (5) Na 2 S 2 O 3 ; (6) KNO 3 ; (7) NaC 2 H 3 O 2 . 28. Heat on charcoal, as described on page 68, the following substances : (i) KC1O 3 ; (2) ZnO ; (3) BiOCl ; (4) PbS ; (5) As 2 O 3 , (using a very small quantity) ; (6) CuSO 4 . 29. Try the NaPO 3 bead test described on page 69, with : (1) Mn0 2 ;- ( 2 )FeS0 4 ; (3) Cr 2 (SO 4 ) 3 ; (4) (CuSO 4 ) ; (5) feldspar. 30. Try the flame test described on page 70, with : (i) Na 2 SO 4 ; (2) K 2 SO 4 V (3) CaSO 4 ; (4) SrSO 4 ; (5) BaSO 4 ; (6) CuSO 4 . Omit the moistening with H 2 SO 4 . 31. Examine with the spectroscope the salts provided for the purpose. Record the position on the scale of the characteristic lines of each element. Then analyze spectroscopically the un- known mixtures. See page 71. UNKNOWN SUBSTANCES. 32. After completing the above preliminary work, ask for un- known substances for analysis. Test the solubility of the first five (or ten) substances in water and dilute HC1, and in addition apply to them only the dry tests described on pages 65-70, and report as far as possible the nature of their constituents. Make complete analyses of the remaining substances as follows : Note first the physical properties, make the closed tube test described on page 66, get the substance into solution (pages 72-80), and analyze the solu- tion for metals according to pages 16-49. Prepare a solution for the analysis for acids (pages 81-83), and test for these according to pages 52-64. Describe the behavior of the substance through- 12 DIRECTIONS FOR LABORATORY WORK. out the course of the analysis in the note-book. In reporting the results of the analysis of complex substances, do not simply enu- merate the metals and acids found, but indicate the relative quan- tities of the various components, and state, if possible, the name of the substance. Compare its properties with the description of it given in the larger text-books in the library. PART II. THE PROCESS OF ANALYSIS. GENERAL DIRECTIONS. THE first aim of the student in analytical work should be to secure absolute certainty as to the correctness of his results ; the next, to carry out the processes of analysis with rapidity. To attain these ends, the analyst must not only thoroughly understand in all their bearings the various operations which he performs, but he must also possess skill in manipulation. Thoughtless or unin- telligent following of directions on the one hand, and lack of neat- ness or thoroughness in the performance of the operations on the other, are equally sources of error. The student will acquire the necessary knowledge by practice, if accompanied by a careful study of the principles of the process and by the habit of asking himself the purpose of each operation. The details of manipula- tion will be learned from practice and instruction in the labora- tory. The following general directions, which apply throughout the whole scheme of analysis, should be always observed : Precipitation. In precipitating a solution always add the re- agent gradually and only until a further addition produces no fur- ther precipitate. This can be determined in all cases by allowing the precipitate to settle, or by filtering a little of the liquid, and adding to the clear solution another drop of the reagent. In many cases, for example in precipitating with hydrogen sulphide, ammo- 14 GENERAL DIRECTIONS. nia, or ammonium sulphide, it is more simply determined by the odor or color of the solution, since the reagent can impart its characteristic properties to the solution only when an excess of it has been added. By adding the reagent in this way, two impor- tant results are attained : first, it avoids an unnecessary excess of the reagent, by which the precipitate may be somewhat dis- solved, the solution diluted, and subsequent tests made less deli- cate ; and second, the precipitation is thus proved to be complete. This second result is so essential that any uncertainty in regard to it is entirely inadmissible. It is not enough for the analyst to be lieve that he has added the reagent in sufficient quantity to pro- duce the desired result he must conclusively prove that such is the case by adding more of it to the filtrate. Washing Precipitates. Always wash a precipitate until the wash water will no longer give a test for ?.ny substance known to be present in the filtrate. The object of precipitation being to sepa- rate one or more bodies from others in solution, it is obvious that this result is only incompletely attained, if the precipitate is not entirely freed from the liquid in which it was thrown down. For example, if the precipitate produced by hydrogen sulphide is not thoroughly washed, metals of the succeeding groups will be pres- ent in it, and will cause confusion and perhaps error by their unexpected appearance in the course of the analysis of the pre- cipitate. Here, again, the analyst must not merely guess that the precipitate is thoroughly washed, he must invariably convince him- self of it by making appropriate tests. If the filtrate contains free acid or alkali, it is done very simply by testing the wash water with litmus paper ; if it contains chloride, by testing with silver nitrate, etc. On complete precipitation by the various reagents, and on proper washing of the precipitates, the success of an analysis very greatly depends. Impurities in Reagents. Bear constantly in mind that the sub- stances to be tested for may be present in the reagents as im- purities. In any case where this seems possible, make sure in regard to it by testing the reagent directly. The habit of thus making blank tests with reagents is an exceedingly important one to acquire ; for the neglect of this precaution is often the cause of serious errors. DETECTION OF THE METALS. SEPARATION OF THE METALS INTO GROjLJPS. Outline of the process. Solution containing all the metals : add HCl. Precipitate : Filtrate : add IhS. AgCl, HgCl, Precipitate : Filtrate: add NH^O Hand (NH<. PbCl 2 . HgS, PbS, Bi 2 S 3 , CdS, CuS,As 2 S 3 , Sb 2 S 8 ,SnS, Precipitate : Filtrate : SnS,. Add (NH^S^. A1O 3 H 3 , add (NH^COz. CrO 8 H 3 , Residue : Solution: CoS, XiS, Precipitate : Filtrate ; HgS, PbS, (NII 4 ) 3 AsS4, FeS, ZnS, BaC0 3 , Mg, K, and Bi 2 S 3 , CdS, (NH 4 ) 3 SbS 4 , MnS. SrCO 3 , Na salts. CuS. (NH i) 2 SnS 8 . CaC0 3 . Definition of the groups according to Freseniits. GROUP I. Alkali Group. Metals not precipitated by any of \ le general reagents: K, Na, NH 4 . GROUP II. Alkaline-earth Group. Metals not precipitated by sulphides either in acid or alkaline solution, but precipitated by carbonates : Ba, Sr, Ca, Mg. GROUP III. Aluminum Group. Metals not precipitated by H 2 S in acid solution, but precipitated by (NH 4 ) e S as hydrates: Al, Cr. i6 DETECTION OF THE METALS. GROUP IV. Iron Group. Metals not precipitated by H 2 S in acid solution, but precipitated by (NH 4 ) 2 S as sulphides : Fe, Co, Ni, Mn, Zn. GROUP V. Copper Group. Metals precipitated by H 2 S in acid solution, whose sulphides are insoluble in (NH 4 ) 2 S X : Ag, Pb, Hg, Bi, Cu, Cd. GROUP VI. Tin Group. Metals precipitated by H 2 S in acid solution, whose sulphides are soluble in (NH 4 ) 2 S X : As, Sb, Sn, (Au, Pt). PRECIPITATION AND SEPARATION OF LEAD, SILVER, AND MERCUROUS MERCURY. Outline of the process. Precipitate : AgCl, HgCl, PbCl 2 . Add hot water. Residue : AgCl, HgCl. Add NHOH. - \" Solution Add H-iSO^ to one part. : PbCl 2 . Add H^S to another. Residue : NH 2 Hg Cl + H g , Solution: add HNO*. Precipitate: AgCl. Precipitate : PbSO 4 . Precipitate : PbS. Procedure. Add to the cold solution dilute HC1 little by little as long as the precipitate continues to increase ; let it stand a few minutes ; filter, and wash with a small quantity of cold water, adding the washings to the nitrate. Notes. i. Non-formation of a precipitate proves absence of silver and mercurous mercury, but not of lead, as PbCl 2 is somewhat soluble in water. The more HC1 added, the more complete will be the precipitation of the lead; for it, like most chlorides, is less soluble in dilute HC1 than in water. 2. A great excess is to be avoided, as it interferes with the H 2 S precipitation of the copper and tin groups. PRECIPITATION WITH HYDROGEN SULPHIDE. 17 3. Moreover, strong HC1 dissolves all three of the chlo- rides quite readily. 4. If the solution is concentrated and strong HC1 is added, certain chlorides soluble in water but less soluble in HC1 may precipitate ; for example, BaCl 2 , NaCl, etc. 5. Dilute HC1 may also precipitate BiOCl or SbOCl, but these dissolve readily on the addition of more HC1. 6. HC1 may precipitate from a solution originally alkaline many other substances, namely, any substance held in solu- tion by an alkaline solvent; for example, As 2 S 3 from (NH 4 ) 2 S solution ; AgCN or Ni(CN) 2 from KCN solution ; silicic acid from sodium silicate ; or metallic hydrates from solution in caustic alkalies. Such precipitates, if not dissolved by more HC1, must be treated according to the process used in pre- paring the solution of a substance for analysis. Procedure. Pour boiling water through the filter and test one portion of the tiltrate with H 2 SO 4 , and another with H 2 S. If lead is present, wash the precipitate with hot water till the wash water no longer reacts for lead. Then pour NH 4 OH through the filter, and acidify the filtrate with HNO 3 . Notes. i. If the PbCl 2 is not completely washed out, it changes on addition of NH 4 OH to a white basic salt, which passes through the filter and gives a turbid filtrate, which becomes clear, however, when HNO 3 is added. 2. AgCl unites with NH 4 OH to form a soluble double compound, which is destroyed by HNO 3 with reprecipitation of AgCl. 3. The black residue on the filter is probably a mixture of NH 2 HgCl and finely divided Hg: 2 HgCl + 2 NH 4 OH = NH 2 HgCl + Hg + NH 4 C1 + 2 H 2 O. PRECIPITATION OF THE COPPER AND TIN GROUPS. Procedure. Pass H 2 S into the hot, slightly acid solution, until the odor of the gas is distinctly perceptible after shak- ing. Heat to boiling, allow the precipitate to settle, filter, and wash the precipitate with hot water till free from acid. 1 8 DETECTION OF THE METALS. Dilute a small portion of the filtrate with two or three times its volume of water, and pass in more H 2 S. Notes. i. In addition to the sulphides of these groups a white precipitate of free sulphur is formed, if the solution con- tains any strong oxidizing agent ; for example, nitric acid or a nitrate, a chlorate, a chromate, or a ferric salt. If a chro- mate is present, the solution changes in color from red to green ; if a ferric salt, the solution becomes colorless. 2. It is useless to pass H 2 S into a solution containing much HNO 3 or aqua regia. If, therefore, these acids have been used in dissolving the substance, the solution should be evaporated almost to dryness and the residue dissolved in water and a little HC1, before passing in H 2 S. 3. The solution must be slightly acid to prevent the pre- cipitation of Zn, Co, and Ni ; but too much acid prevents tfte precipitation of the metals of the copper and tin groups, espe- cially of cadmium, lead, antimony, and tin. One part of acid (1.12 sp. gr.) to 20 or 25 of water is a suitable concentration. If much more dilute than this, some zinc will be precipitated. 4. Complete precipitation may fail from two causes : use of an insufficient quantity of H 2 S or presence of too much HC1. Therefore always test the filtrate by passing more H 2 S and by further dilution. 5. Dilution with water before passing H 2 S may cause precipitation of BiOCl or SbOCl. It is not necessary nor advisable to redissolve these precipitates by addition of more HC1 ; for H 2 S changes them readily to sulphides. 6. Arsenic, in the higher state of oxidation, is precipitated by H 2 S very slowly indeed in the cold, and not very rapidly, hot. The precipitate is As 2 S 5 : 2H 3 AsO 4 -f- 5H 2 S = As 2 S 5 + 8H 2 O. The slow formation of a yellow precipitate is there- fore a strong indication of arsenic, and when it occurs the solution should be kept nearly boiling during precipitation. 7. Colors of the Sulphides. Black or brownish black : Ag 2 S, HgS, PbS, Bi 2 S 3 , CuS, SnS. Yellow: CdS, As 2 S 3 , As 2 S 5 , SnS 2 . Orange : Sb 2 S 3 , Sb 2 S 5 . Mercuric salts give at first a white precipitate consisting of a double compound (HgCl 2 .2HgS), which turns yellow, red, and finally black with more H a S, owing to conversion to HgS. Lead salts give a SEPARATION OF COPPER AND TIN GROUPS. 19 red precipitate of analogous composition when precipitated by H 2 S from a solution containing considerable HC1. SEPARATION OF THE COPPER AND TIN GROUPS. Procedure. Warm a portion of the H 2 S precipitate, or tne whole of it, if small in amount, with ten or twelve drops of yellow (NH 4 ) 2 S X diluted with a little water. Filter, and add HC1 to the filtrate till it reacts acid with litmus paper If the precipitate which forms is colored yellowish or orange, treat the remainder of the H 2 S precipitate in the same way, using rather more (NH 4 ) 2 S X , and repeating the treatment with successive portions of it till the filtrate from the last treatment is precipitated white by HC1. Wash the residue insoluble in (NH 4 ) 2 S X with water till the wash water no longer reacts alkaline. Collect on a filter the precipitate obtained by the addition of HC1 to the (NH 4 ) 2 S X solution, wash it #nce or twice with water, and dry it as much as possible by s action. Notes. i. If the H 2 S precipitate has not been thoroughly washed, the (NH 4 ) 2 S X will precipitate metals of the aluminum And iron groups contained in the solution adhering to it, and these will appear in the separation of the copper group. 2. Yellow ammonium sulphide must be used, for the color- less closs not dissolve SnS. A pure white precipitate after neutralization with HC1 is taken as proof of the absence of As, Sb, and Sn, hence the use of very little (NH 4 ) 2 S X at first; for, otherwise, the large amount of separated S would conceal the color of small quantities of As 2 S 5 , Sb 2 S 5 , and SnS 2 . 3. The sulphides dissolve in (NH 4 ) 2 S X with formation of salts of sulpho-acids : As ? S 8 + 3(NH 4 ) 2 S X = 2(NH 4 ) 3 AsS 4 + (3* 5)S. SbaSs + 3(MH 4 ) 2 S X = 2(NH 4 ) 3 SbS 4 + (8* 5)S. SnS -f (NH 4 ) 2 S X = (NH 4 ) 2 SnS 3 + (* 2)S. 4. When KC1 is added to these compounds, the higha sulphides are precipitated, for example : (NH 4 ),Sr,S 8 + WOl *= SnS 2 + 2NH 4 C1 + H 2 S. 20 DETECTION OF THE METALS. 5. CuS dissolves somewhat in (NH 4 ) 2 S X , but much less in Na 2 S x . HgS dissolves readily in Na 2 S x , but not in (NH 4 ) 2 S X . Hence, when the preliminary examination or the color of the solution indicates Cu, and there is no reason to suspect Hg, use Na 2 S x . 6. When Cu is present, and (NH 4 ) 2 S X is used, a liver- colored precipitate is obtained on neutralizing with HC1. SEPARATION OF MERCURY, LEAD, BISMUTH, CADMIUM, AND COPPER. Outline of the process. Precipitate : HgS, PbS, Bi 2 S 3 , CdS, CuS. Boil with HNO$. Residue: HgS. Dissolve in HCl and KCIOz ; add SnCl*. Solution: add H^SO^ Precipitate: PbS0 4 . Filtrate: add NHOH. Precipitate : Bi0 3 H 3 . Dissolve in HCl, and add to H^O. Filtrate : add KCNandH^S. Precipitate: HgCl. Precipitate: CdS. Solution: KCN.CuCN. Precipitate : B50C1. Procedure. Boil the residue from the (NH 4 ) 2 S X treatment in a porcelain dish with dilute HNO 3 (i part of acid 1.2 spec, grav., and 3 of water) for ten minutes, or until dissolved, replacing the acid which evaporates. Filter and wash. Notes. i. HgS remains undissolved; the other sulphides dissolve. The reactions are : 3PbS + 8HNO 3 = 3Pb(NO 3 ) 2 + 3S + 2NO + 4H 2 O, etc. 2. A black residue is not necessarily HgS, but may be S with PbS, CuS, or Bi 2 S 3 inclosed in it. The confirmatory test for Hg should therefore always be tried. COPPER GROUP. 21 3. Continued action of strong HNO 8 converts HgS to Hg(NO 3 ). 2 2HgS, a white insoluble compound. A heavy white or yellow residue should therefore be tested for Hg. 4. Dilute HNO 3 oxidizes PbS partly, and strong HNO 8 oxidizes it almost entirely to PbSO 4 : 3PbS + 8HNO 3 == 3PbSO 4 + 8NO + 4H,O. The insoluble residue may there- fore contain PbSO 4 as well as HgS ; but owing to the solubil- ity of PbSO 4 in HNO 3 , some Pb will always pass into the filtrate. 5. The insoluble residue may also contain oxides of tin and antimony, especially the former, if the (NH 4 ) 2 S X treatment has been insufficient. Procedure. To confirm the presence of Hg, dissolve the residue by heating with HC1 and a small crystal of KC1O 3 . Boil to expel the excess of chlorine, and add a little SnCl 2 solution. Notes. i. If the excess of chlorine is not expelled before adding SnCl 2 , the reduction of the HgCl 2 is prevented. 2. The reaction between KC1O 3 and HC1 is approximately as follows : 2KC1O 3 4HC1 = 2KC1 C1 2 2C1O 2 2H 2 O. Procedure. To the filtrate from the HgS add about 5 cc. of strong H 2 SO 4 , and evaporate in a porcelain dish till the white fumes of H 2 SO 4 come off thickly. After cooling add about 50 cc. of water and pour into a beaker ; note whether the solution is at all turbid, and if so, filter it. Notes. i. PbSO 4 is slightly soluble in HNO 3 ; hence the need of expelling it. 2. PbSO 4 is slightly soluble in concentrated H 2 SO 4 ; hence the dilution before filtering. 3. PbSO 4 is less soluble in dilute H 2 SO 4 than in H 2 O ; it is therefore advantageous to have the acid present in slight excess. n\ 22 DETECTION OF THE METALS. 4. Ammonium salts, for example NH 4 NO 3 , also dissolve PbSO 4 ; hence the need of thoroughly washing out the (NH 4 ) 2 S X before dissolving the H 2 S precipitate in HNO 3 . 5. A very minute precipitate of PbSO 4 not otherwise notice- able may be detected by giving a rotary motion to the beaker, thus causing the precipitate to collect in the center. Procedure. To the filtrate from the PbSO 4 add NH 4 OH till alkaline, and then, if a precipitate forms, a small quantity more, in order to redissolve CdO 2 H 2 and CuO 2 H 2 . Heat gently, filter, and wash the precipitate. Dissolve it by pour- ing a little strong HC1 through the filter; evaporate the solution to one or two drops, and pour into a beaker of water. Notes. i. If the H 2 S precipitate has been insufficiently washed, A1O 3 H 3 , FeO 3 H 3 , etc., may precipitate on the addition of NH 4 OH. 2. If the lead has not been completely removed by close adherence to the above directions, it also will precipitate at this point. 3. The formation of a precipitate by NH 4 OH must there- fore never be taken as proof of the presence of Bi, but the confirmatory test must always be tried. 4. Reaction : BiCl 3 + H 2 O BiOCl -f 2HC1. 5. The more completely the HC1 is removed by evapora- tion, the more delicate will be the test for Bi. Time is some- times required for the precipitation of the BiOCl. 6. Sb and Sn salts like those of Bi are precipitated by H 2 O, but these should not be present in the solution at this stage of the analysis. Tartaric acid prevents the precipita- tion of Sb salts by H 2 O, but not that of Bi or Sn salts. Procedure. Unless distinctly blue, test a small portion of the filtrate from the BiO 3 H 3 for Cu by acidifying with acetic acid and adding K 4 Fe(CN) 6 . If the ammoniacal solution is blue, add KCN little by little till the blue color due to the Cu is completely discharged, and then pass in H 2 S for a few seconds. COPPF f GROUP. 2 3 Motes. i. Cd is -.i^o precipitated by K 4 Fe(CN) 6 ; but the precipitate is white. 2. The precipitation with K 4 Fe(CN) 6 is a more delicate ^est for Cu than the blue coloration with NH 4 OH. 3. A potassium cuprous cyanide (KCN.CuCN) is formed oy the ac^on of the KCN, and this compound is not decom- posed by H 2 S. Cd forms with excess of KCN the double salt 2KCN.Cd(CN) 2 , which is decomposed by H 2 S. 4. A yellow coloration with H 2 S does not indicate Cd. A yellow precipitate must be obtained. 5. A black precipitate (due to HgS, PbS, FeS, etc.,) is sometimes obtained in testing for Cd with H 2 S, owing to some previous error in the analysis. To determine whether Cd is present in it, filter it off, wash it, and boil it several minutes with an excess of dilute H 2 SO 4 (one part of acid to four of water) ; filter, dilute the filtrate, and saturate it with H 2 S. H 2 SO 4 of this strength dissolves CdS, changes PbS to insoluble PbSO 4 , but does not affect CuS or HgS. ADDITIONAL REACTIONS OF METALS OF THE COPPER GROUP. 1. Behavior towards the Alkalies. All metals of this group are precipitated both by NaOH and NH 4 OH. Excess of NaOH dissolves only the Pb precipitate. Excess of NH 4 OH dissolves Ag 2 O, CdO 2 H 2 , and CuO 2 H 2 . The precipitates are hydroxides in the case of Bi, Cd, and Cu, the oxide in the case of Ag, and basic salts in the case of Pb. Hg gives with NaOH, Hg 2 O (black) and HgO (yellow); while with NH 4 OH substituted ammonium compounds are formed, e.g., NH 2 Hg 2 NO 3 and NH 2 HgCl. 2. Mcrcurous arid Mercuric Salts. These are distin- guished (i) by HC1, which precipitates the former and not the latter; (2) by NH 4 OH, which gives a black precipitate with the former and a white one with the latter. The reac- tions are : 2HgNO 8 + 2NH 4 OH = NH 2 Hg 2 NO 3 + NH 4 NO 3 + 2H 2 O. HgCl 2 + 2NH 4 OH = NH 2 HgCl -f NH 4 C1 + 2H,O. DETECTION OF THE METALS. SEPARATION OF ARSENIC, ANTIMONY, AND TIN. Outline of the process. Precipitate: As 2 S 5 , Sb 2 S 5 , SnS 2 . Add strong HCl. Residue : ^8285. Dissolve in HCl and KCIOz ; add NHOH, NHCl, and MgCl z . Solution : SbCls, SnCU, (and small amount of HsAsC^). .Place in hydrogen generator. Residue : Sn. Dissolve in strong HCl and add HgCl* Gas evolved : SbH 3 (and AsHg) Pass through a hot tube. Precipitate : MgNH 4 AsO 4 . Deposit: Sb (and As). Treat with NaOCL Precipitate : HgCl. Residue : Solution : Sb. (H 3 AsO 4 ). Procedure. Heat gently (not to boiling) the precipitated sulphides, dried as much as possible by suction, with strong HCl (1.2 spec, grav.) as long as the vapors blacken paper moistened with Pb(C 2 H 3 O 2 ) 2 and NH 4 OH. Dilute with a little water, filter, and wash the undissolved residue. Dis- solve it in a little HCl with addition of a crystal (or two) of KC1O 3 , heat to expel the excess of chlorine, add NH 4 OH till alkaline, filter if turbid, and then add enough more NH 4 OH to form one third the volume of the solution ; add magnesia mixture, stir, and if no precipitate forms at once, allow it to stand over night. Notes. i. The separation of As 2 S 5 , Sb 2 S 5 , and SnS 2 by HCl is not perfect. Some Sb 2 S 5 and SnS 2 may remain undis- solved, and small quantities of arsenic pass into solution. It is to prevent the latter as far as possible that the acid is only warmed, not boiled. In case there is reason to believe that the precipitate 2. consists mainly of As 2 S 5 , warm it first with a saturated solu- tion of (NH 4 ) 2 CO 3 (made by dissolving the finely ground solid TIN. GROUP. 25 salt in cold water), filter, treat the precipitate with strong HC1 as above directed, and acidify the (NH 4 ) 2 CO 3 filtrate with HC1. (NH 4 ) 2 CO 3 dissolves As,S 5 without difficulty, but dis- solves Sb 2 S 5 and SnS 2 only slightly. 3. If a yellow turbidity (Sb 2 S 3 or SnS 2 ) appears on diluting the HC1 solution with v;ater, it shows that the H 2 S has not been completely expelled. 4. On the addition of NH 4 OH any antimony or tin not dissolved out of the mixed sulphides by the strong HC1 will be precipitated as hydrate. 5. MgNH 4 AsO 4 like MgNH 4 PO 4 is somewhat soluble in water, but much less so in NH 4 OH. Hence the solution should be concentrated and an excess of NH 4 OH added. The precipitate is crystalline, and adheres to the sides of the vessel, especially along the lines rubbed with the glass rod. 6. REACTIONS : As 2 S 5 + 10C1 + 8H 2 O = 2H 3 AsO 4 + 5S + 10HC1. H 3 AsO 4 + 3NH 4 OH = (NH 4 ) 3 AsO 4 + 3H 2 O, (NH 4 ) 3 AsO 4 + MgCl 2 = MgNH 4 AsO 4 + 2NH 4 C1. Procedure. Place a piece of platinum and some zinc in a flask fitted with a thistle and delivery tube, and add some dilute HC1. Cause the gas to pass through a tube contain- ing dry CaCl 2 , and then through a hard glass tube drawn to a capillary at the end and at two intermediate points. After the air has been expelled (proved by collecting some of the gas in a small test tube and igniting it), light the gas at the end of the apparatus, and heat the hard glass tube just back \ of the first capillary with a small Bunsen flame. Continue this for a few minutes t ) see that no mirror forms ; then pour in the solution of SbCl 3 and SnCl 4 little by little. Note whether any deposit forms in the capillaj-y^ and whether the platinum in the generator becomes blackened. After some minutes pour out the liquid in the generator, wash the resi- due by decantation with water, boil with strong HC1 till en- tirely dissolved, dilute the solution, and add HgCl 2 . Break off the hard glass tube just beyond the mirror, and immerse it in a test tube containing NaOCl solution. Note whether the mirror dissolves wholly or in part. DETECTION OF THE METALS. Notes. i. SnCl 4 is reduced by nascent hydrogen to metal- lic tin, which deposits on the zinc. A part only of the Sb deposits on the platinum, the remainder being further reduced to SbH 3 . The H 3 AsO 4 is reduced to AsH 3 without precipita- tion of arsenic. 2. Heat decomposes SbH 3 and AsH 3 into antimony or arsenic and hydrogen. 3. As small quantities of As 2 S 5 are dissolved by strong HC1, a deposit in the capillary, unless accompanied by dis- tinct blackening of the platinum, must not be considered proof of the presence of Sb. The test with NaOCl removes all doubt, however ; for an arsenic mirror dissolves almost in- stantly, forming H 3 AsO 4 , while antimony remains unaffected for a long time. Even when the deposit consists of both metals, it is easy to detect the presence of both ; for arsenic, being more volatile, deposits in the part of the capillary more remote from the flame, and this part of the mirror is seen to dissolve completely on treatment with NaOCl. This reagent serves therefore not only to confirm the presence of antimony but also to detect traces of arsenic so small as not to be shown by the test with MgCl 2 and NH 4 C1. 4. The presence of an element may be established in three ways : (i) by isolation of the element itself ; (2) by for- mation of one of its characteristic compounds ; (3) by causing a change to take place in some other substance. The test for tin with HgCl 2 is one of the few examples of the last method. ADDITIONAL REACTIONS OF METALS OF THE TIN GROUP. 1. Arsenic and antimony may be detected in the original solution, even while other metals are present, by the generator test above described ; and where minute quantities are to be detected, that test should be employed, since the color of their sulphides may be concealed by the sulphur separated from the (NH 4 ) 2 S X . 2. Arsenites and arseniates are distinguished (i) by H 2 S, which in the cold precipitates the former instantly, and the Matter only very slowly; (2) by AgNO 3 , which in perfectly OXIDATION AND REDUCTION. 27 neutral solution gives a yellow precipitate with the former t and a brown one with the latter ; (3) by magnesia mixture, which precipitates only arsenic acid. 3. Stannous and stannic salts are distinguished (i) by HgCl 2 , which gives a precipitate of HgCl or Hg with the former, and none with the latter; (2) by H 2 S, which gives a brownish-black precipitate with the former, and a yellow one with the latter. 4. Detection of Arsenic in Wall Papers, Fabrics, etc. Cut the material into small pieces and treat it as described in note 6, , on page 74. OXIDATION AND REDUCTION. As many of the metals of the aluminum and iron groups exist in two or more different states of oxidation, a few gen- eral remarks on oxidation and reduction may be made with advantage at this point. A substance is said to be oxidized when oxygen or some other acid element or radical is added to it, or when hydrogen or some other basic element or radical is taken from it. A substance is said to be reduced when the reverse takes place. The oxidation of one substance involves the simultaneous reduction of some other substance. In the following examples the substance oxidized is placed first: 4FeO 2 H 2 + O 2 + 2H 2 O = 4FeO 8 H s . 3PbS + 8HNO 3 = 3PbSO 4 + 8NO + 4H 2 O. H 3 As0 3 + C1 2 + H 2 = H 3 As0 4 + 2HC1. SnCl 2 + 2HgCl 2 = SnCl 4 + 2HgCl. 2K 4 Fe(CN) 6 + C1 2 = 2K 3 Fe(CN) 6 + 2KC1. In the application of the definition of oxidation it is im- portant to distinguish between the addition of an element and the substitution of one element or radical for another. For example, PbO dissolves in HNO 3 , forming Pb(NO 3 ) 2 and H 2 O. This is not an oxidation, but a simple metathesis ; for the two NO 3 groups are not added, but simply take the place of their equivalent, one oxygen atom. But in the reaction : 3Pb + 8HN0 3 = 3Pb(N0 8 ) 2 + 2NO + 4H 2 O, the lead is 28 DETECTION OF THE METALS. oxidized, the NO 3 groups being added to it, and the HNO S is reduced to NO. The following additional reactions are given to illustrate further this distinction. The first reaction of each pair is an oxidation and reduction; the second, a metathetical change : MnO 2 + 4HC1 = MnCl 2 + CJ 2 + 2H 3 O. MnO + 2HC1 = MnCl 2 + H 2 O. SbCl 3 + 3H = Sb + 3HC1. SbCl 3 + H 2 O SbOCl + 2HC1. 2K 2 CrO 4 + 16HC1 = 2CrCl 3 + 3C1 2 + 4KC1 +- 8H 2 O. 2K 2 CrO 4 + 2HC1 = K 2 Cr 2 O 7 + 2KC1 + H 2 O. In order to write reactions involving oxidation and reduc- tion, consider first the oxides corresponding to each of the substances taking part in the reaction and known to be pro- duced by it. It will then be evident, on the one hand, how many oxygen atoms the oxidizing agent furnishes, and on the other, how many are required for the substance oxidized, thus showing the relative number of molecules of each entering into the reaction. The method is illustrated by the following examples : Oxidation of FeSO 4 with HNO 3 . The FeSO 4 is known to be oxidized to Fe 2 (SO 4 ) 3 and the HNO 3 to be reduced to NO. Write the symbols of these compounds dualistically, regard- ing them as composed of the anhydride of the acid united with water or the oxide of the metal. FeSO 4 = FeO, SO 3 ; Fe 2 (S0 4 ) 3 = Fe 2 3 , 3SO 3 ; and 2HNO 3 = H 2 O, N 2 O 5 . Then 2FeO + O = Fe 2 O 3 and N 2 O 5 = 2NO -f O 3 . That is, 2HNO 3 furnish 3 atoms of oxygen, and i atom of oxygen oxidizes 2 atoms of iron from the ferrous to the ferric condition. Hence 2HNO 3 oxidize 6FeSO 4 . If the ferric compound thus formed is to remain in solution, free acid of some kind must be added. Its amount is readily seen by inspection. The reactions are the following : 6FeS0 4 + 2HN0 3 + 3H 2 SO 4 = 3Fe a (^O 4 ). + 2NO + 4H 2 0. 6FeSO 4 + 2HNO : + 6HNO 3 = 2Fe 2 (SO 4 ) 3 + 2Fe(NO 3 ), + 2NO + 4H 2 O. ALUMINUM AND IRON GROUPS. 29 Reduction of K 2 Cr 2 O 7 with SnCl 2 . SnCl 2 corresponds to SnO ; SnCl 4 to SnO 2 ; SnO 2 = SnO + O. K 2 Cr 2 O 7 = K 2 O, 2CrO 3 ; CrCl 3 corresponds to Cr 2 O 3 ; 2CrO 3 = Cr 2 O 3 + O 3 . Therefore 3SnCl 2 reduce lK 2 Cr 2 O 7 , and the reaction is : K 2 Cr 2 7 + 3SnCl 2 + 14HC1 == 2CrCl 3 + 2KC1 + SSnCU + 7H 2 0. Oxidation of MnO 2 H 2 by KC1O 3 in presence of Na 2 CO,> KC1O 3 =:KC1 + O 3 . MnO 2 H 2 = MnO, H 2 O. Na,MnO 4 = Na 2 O, MnO 3 . MnO 3 = MnO -f- O 2 . Hence : 2KC1O 3 + 3MnO 2 H 2 + 3Na 2 CO 3 = 2KC1 + 3Na 2 MnO 4 + 3CO 2 + 3H 2 O. The most important oxidizing agents from an analytical point of view are : Cl, Br, and J solutions, HNO 3 , KC1O 3 , K 2 Cr 2 O 7 , and KMnO 4 . The mos: important reducing agents in solution are nascent hydrogen, H 2 S, H 2 SO 3 , SnCl 2 and oxalic acid (H 2 C 2 O 4 ) ; at a high temperature, C, KCN, starch and other organic bodies. It is well to remember what the usual reduction products of the important oxidizing agents are : Cl and Br are reduced to HC1 and HBr; HNO 3 is reduced to NO; KC1O 3 to KC1, K 2 Cr 2 O 7 and KMnO 4 in acid solution to chromic and manga- nous salts respectively. It should be added, however, that the reduction product of an oxidizing agent is not under all circumstances the same. For example, HNO 3 is reduced by certain metals to N 2 O and NH 3 ; ,KMnO 4 in neutral solution is reduced only to MnO 2 , not to MnO. ALUMINUM AND IRON GROUPS. Preliminary Tests. Procedure. Boil one quarter of the filtrate from the H 2 S precipitate until the excess of H 2 S is expelled. Add a little HNO 3 and boil again to oxidize the iron. Divide this solu- tion into two unequal portions. Add to the larger portion 10 cc. of NH 4 C1, and NH 4 OH to slight but distinct alkaline reaction ; heat to boiling, and allow to stand some minutes if no precipitate separates at once. Note whether a precipitate 30 ^Hfc DETECTION OF THE METALS. forms and what its color is. Then add, without filtering, colorless (NH 4 ) 2 S in small quantity. If NH 4 OH produces a precipitate, test the rest of the solution which has been boiled with HNO 3 for H 3 PO 4 by adding an equal bulk of (NH 4 ) 2 MoO 4 solution, stirring, and allowing it to stand some minutes. Notes. i. If NH 4 OH produces no precipitate, it proves the absence of iron, chromium, and aluminum, and the spe- cial tests for these elements may then be omitted in the subsequent analysis. 2. This conclusion is reliable, however, only when the directions are exactly followed ; for A1O 3 H 3 dissolves slightly in excess of NH 4 OH, CrO 3 H 3 dissolves in the cold (giving a pink solution) but is precipitated on boiling, and a small precipitate of any of the three is easily overlooked, owing to its transparency, unless time is allowed for the precipitate to gather in flocks. 3. Moreover, non-volatile organic matter, such as sugar, tartaric acid, etc., must not be present, for it prevents entirely the precipitation of these three elements by NH 4 OH. 4. Phosphates of alkaline-earth metals, if present, are also precipitated by NH 4 OH. The advantage in testing for H 3 PO 4 at this point will be made clear later, and the cases in which it is useless to try the test will be discussed. 5. The color of the NH 4 OH precipitate indicates which of the metals are present. A1O 3 H 3 is white and transparent ; CrO 3 H 3 , greenish blue ; and FeO 3 H 3 , reddish brown. 6. The color of the sulphides is also important : FeS, NiS, and CoS are black; ZnS is white; and MnS is flesh-colored, but turns brown on standing in the air. If the (NH 4 ) 2 S pre- cipitate is pUre white, the subsequent tests for iron, nickel, and cobalt may be omitted. 7. The H 2 S must be completely expelled at the beginning; otherwise, (NH 4 ) 2 S is formed, and the NH 4 OH test is of no value. 8. In whatever condition the iron was originally present, it is in the form of a ferrous salt after the treatment with H 2 S : 2FeCl 3 + H 2 S = 2FeCl 2 + 2HC1 + S. The solution is ALUMINUM AND IRON GROUPS. ^ 31 boiled with HNO 3 , since ferrous iron is not precipitated by NH 4 OH in the presence of ammonium salts. 9. A black precipitate with NH 4 OH shows incomplete ex- pulsion of the H 2 S, or incomplete oxidation of the iron. 10. NH 4 C1 is added to prevent the precipitation of MgO 2 H 2 and MnOoH 2 , which otherwise are precipitated by NH 4 OH. Aside from this it is useful, for it greatly promotes the sepa- ration of A1O 3 H 3 . and of all the sulphides. 11. If manganese is present the solution rapidly becomes brown after the addition of NH 4 OH, owing to the absorption of oxygen and precipitation of MnO 3 H 3 . 12. (NH 4 ) 2 S changes FeO 3 H 3 to FeS, but has no effect on A1O 3 H 3 and CrO 3 H 3 . A1 2 S 3 , Cr 2 S 3 , and Fe 2 S 3 are not formed in the wet way. 13. Even if present originally as chromate, the chromium will be precipitated by NH 4 OH, owing to reduction of the chromate by H 2 S. Precipitation of the Aluminum and Iron Groups. Procedure. If the preliminary tests show the presence of metals of the aluminum or iron groups, place the rest of the filtrate from the H 0j S precipitate in a flask, add 15 or 20 cc. of NH 4 C1, NH 4 OH till barely alkaline, and (NH 4 ) 2 S until the liquid after shaking causes blackening of a piece of Pb(C 2 H 3 O 2 ) 2 paper held above it. Heat to boiling, and shake until the precipitate will subside readily. Filter, and wash immediately with water containing a very little (NH 4 ) 2 S. Notes. i. The notes given under the preliminary tests on the preceding page apply here also. 2. Colorless (NH 4 ) 2 S is used instead of yellow (NH^S*, as the excess of 'sulphur is troublesome in the subsequent examination of the nitrate. For the same reason care should be taken to avoid using an excess of (NH 4 ) 2 S. 3. The nitrate from the (NH 4 ) 2 S precipitate should be colorless or light yellow. A brown or black color indicates the presence of nickel, whose sulphide dissolves somewhat in excess of (NH 4 ) 2 S, from which it should be precipitated by acidifying with acetic acid, boiling, and filtering through a DETECTION OF THE METALS. new filter. A pink color indicates chromium dissolved in excess of NH 4 OH, from which solution it is thrown out on boiling. A green color is due to traces of finely divided FeS in suspension, which separate on standing. 4. All five sulphides oxidize rapidly in the air to sulphates ; hence the addition of (NH 4 ) 2 S to the wash water. 5. NH 4 OH slowly absorbs C!O 2 from the air; hence if the solution is allowed to stand for some time before filtering, BaCO 8 , SrCO 3 , and CaCO 3 may precipitate. Separation of Nickel and Cobalt. Outline of the process. Precipitate : A1O 3 H 3 , CrO 3 H 3 , CoS, NiS, FeS, MnS, ZnS, [Ba 3 (PO 4 ) 2 , Sr 3 (PO 4 ) 2 , Ca 3 (PO 4 ) 2 , MgNH 4 PO 4 ]. Treat with dihite HCl. Residue : CoS, NiS, (FeS in small amount). Dissolve in aqua regia and add Nff^OH. Precipitate : Fe0 3 H 3 . Filtrate : expel NH salts, add KNO^ and Precipitate : Co(NO 2 ) 3 . 3KNO 2 . Solution: add NaOH. Precipitate: NiO 2 H 2 . Test in borax bead. Solution. Procedure. Treat the (NH 4 ) 2 S precipitate in a dish with cold dilute HCl, made by diluting one part of acid (1.12 spec, grav.) with five of water ; stir, filter when dissolved or after standing a few minutes, and if a black residue remains, wash it thoroughly. Separate it from the filter, or, if small in amount, incinerate the filter in a porcelain crucible, and dissolve the residue in a little aqua regia. Dilute, add NH 4 OH in moderate excess, and filter. Add to a small portion of the filtrate a drop or two of (NH 4 ) 2 S. If a black precipitate is produced, evaporate the remainder to ALUMINUM AND IRON GROUPS. 33 dryness, ignite till the ammonium salts are expelled, and test a little of the residue in a borax bead in the flame of the blowpipe. Dissolve the residue in a little aqua regia, evaporate to two or three drops, add 50 cc. of KNO 2 solu- tion and HC 2 H 3 O 2 to strongly acid reaction. Allow the mixture to stand some hours in a warm place, filter, add NaOH to the filtrate till alkaline, and if a precipitate forms, filter, and test the precipitate in a borax bead in the oxidiz- ing flame. Notes. i. The acid used is cold and dilute to avoid dis- solving NiS and CoS ; but even then quite appreciable quan- tities of these sulphides sometimes dissolve, and Ni and Co are met with later in the course of the analysis. 2. A small black residue after the HC1 treatment is not necessarily NiS or CoS, but it may be FeS inclosed in sulphur. 3. Moreover, metals of the copper group, if incompletely precipitated by H 2 S, appear at this point as sulphides, and may be mistaken at first for Co or Ni. 4. Action of aqua regia : 3HC1 -f HNO 3 = C1 2 + NOC1 -\- 2H 2 O. But the whole of the chlorine is available if a substance on which it can act is present: 3NiS -\- 6HC1 -|-' 2HN0 3 = 3NiLl a + 2NO + 4H 2 Q + 3S. 5. NH 4 OH is added to precipitate the iron, which, me- chanically inclosed, may have escaped the action of the dilute HC1. The addition of (NH 4 ) 2 S then shows whether the residue consisted entirely of FeS, or whether NiS and CoS were also present. 6. The borax bead test generally proves the presence of one or other of the two metals. It is especially delicate as a test for cobalt ; but in the presence of much nickel the blue color characteristic of cobalt may be obscured, and a negative result must therefore not be taken as evidence of the absence of that metal. If cobalt is absent, the color of the bead produced in the oxidizing flame violet while hot, reddish brown when cold proves the presence of nickel. 7. When either metal is found to be present, the tests for the other must be made with great care; for the two metals occur very commonly together. 34 DETECTION OF THE METALS. 8. The excess of NH 4 OH in which the NiO,H 2 and CoO 2 H 2 are dissolved and the NH 4 C1 must be completely expelled ; for nickel is not completely precipitated by NaOH in their presence. 9. The yellow precipitate obtained is tri-potassium cobalt/V nitrite : 3KNO 2 .Co(NO 2 ) 3 . It is decomposed by HCi and alkalies ; it is decidedly soluble in water, but almost insolu- ble in strong KNO 2 solution. Hence the need of expelling the acid by evaporation, of having the solution concentrated, and of adding a large excess of KNO 2 . The solution must be strongly acid with HC 2 H 3 O 2 to set free the HNO 2 re- quired for oxidizing the cobalt. Effect of the Presence of Chromium and of Alkaline* earth phosphates on the Method of Separation. General Remarks. Under certain circumstances to be now described, the precipitate produced by NH 4 OH and (NH 4 ) 2 S may contain metals of the alkaline-earth group as well as of the aluminum and iron groups. In that case a more com- plicated process providing for the detection of all these metals has to be used. Ba, Sr, Ca, and Mg are not ordinarily precipitated by NH 4 OH and (NH 4 ) 2 S ; for their hydrates and sulphides are soluble in water (except MgO 2 H 2 which dissolves in ammo- nium salts). But if there is present in the solution an acid radical which, combined with these metals, forms salts insol- uble in water and NH 4 OH, it is evident that such salts must be held in solution by an acid, and that they will be precipi tated when the acid is neutralized. Consider two examples ; CaCO 3 and Ca 3 (PO 4 ) 2 . Both these salts are insoluble in water, but dissolve in HCI, forming CaCl 2 ; the CO 2 , being volatile, escapes, while the H 3 PO 4 remains in solution. When, now, NH 4 OH is added, no precipitate forms in the former case, but Ca 3 (PO 4 ) 2 precipitates in the latter. It is evident, then, that it is unnecessary to try the pre- liminary test for phosphates described above when the sub- stance dissolves in water with a neutral reaction, or in any case in which no precipitate is produced by NH 4 OH before the addition of (NH 4 ) 2 S ; for under these circumstances the ALUMINUM AND IRON GROUPS. 35 (NH 4 ) 2 S precipitate can contain no alkaline-earth phosphates ; nor is it necessary in cases where the substance is unattacked by acids and has been fused with Na 2 CO 8 . Alkaline-earth metals are not necessarily completely pre- cipitated by NH 4 OH even when H 3 PO 4 is proved to be pres- ent, for the amount of the latter may not be sufficient to combine with the whole of the metal. Moreover, if triva- lent metals are simultaneously present, the H 3 PO 4 combines with them by preference, and the alkaline-earth metal may be found wholly or in part in the filtrate, there being no excess of H 3 PO 4 to combine with it, or an insufficient one. When phosphates are present, it is therefore necessary to look for alkaline-earth metals both in the (NH 4 ) 2 S and in the (NH 4 ) 2 CO 3 precipitates. Besides phosphates, the precipitate produced by NH 4 OH and (NH 4 ) 2 S may contain CaC 2 O 4 , SrC 2 O 4 , BaC 2 O 4 , or CaF 2 . These are, however, met with so rarely in actual analyses, that preliminary tests for oxalic and hydrofluoric acids are dispensed with. But in case these acids are found in the subsequent examination for acids, the (NH 4 ) 2 S precipitate must be again analyzed by the process used when H 3 PO 4 is present, in order to detect the alkaline-earth metals possibly in combination with them. Borates of alkaline-earth metals may also precipitate witn NH 4 OH, but never completely, owing to their solubility in water and ammonium salts. It is therefore desirable to have two distinct processes of separation of the aluminum and iron groups : a short one applicable in the great majority .of cases, and a longer one to be used when phosphates of alkaline-earth metals may be present, determined by the above considerations and by the preliminary test for H 3 PO 4 . For an entirely different reason the short process described below cannot be used when chromium is present. This proc- ess depends on the separation of the metals with NaOH, Fe and Mn being precipitated, and Al and Zn remaining in solu- tion. If, however, Cr is also present, Cr and Zn are precipi- tated with the Fe and Mn, owing to the formation of an insol- uble double compound of the oxides of the first two metals. The presence of Cr is shown by the green or purple color ?f the HC1 solution of the (NH 4 ) 2 S precipitate. Only wher DETECTION OF THE METALS. this sol? von is colorless should it be analyzed by the NaOH process. Tt is hardly necessary to add that, when the BaCO a process is used only on account of the presence of Cr, all those parts of It serving for the detection or removal of alka- line-earth metals may be omitted. Separation in the Absence ^" Chromium and of Phosphates, Outline oj* ! ? a: 5 ; > i-t Hr 1 O O C *.* *^ ~ ^ ' \ * k ^ *T s? " - > - ? ~ s< j* 8 c "j | fc ^ r ?v "j ^ t ^ f"D - * in o ] f 7 j ^ ft ^ e. j j i 1: 1 1 s . s " ^ " 1 1 < F . 1 s 1 ; > S _ n . hj o t ;1 s Nj 5 CM "^ s Q c N h- "l ^ P r j :hS" T3 1 y o ^ r< ft" * o H ^_ s ^ J -^ a T3 ' 9 a> ^^ ** Z I^S 10 ^^ O MI ^ ^ 2s~ "" G ? a *?> ^to^CO^" * ^ !j ? * -! 5 - 3 - ; ^ s? D 05 ^ Si Q !> " 1 P > M S> 2? o ^ fi &' ' ^ 1 ^ I-IH c s? s! N ^i > 3 ^ , 2 * O 1- S? 5 ^ ' a I' | * * 1 1 5 p J ? I "*. t r< D < * ( $ : %\ \ > D - ^H w 2 S? - r *"' ^* s^ i o B1 ^ W 2 ^ g 7 M ITJ . Q O* $ ^ ^ 3 n ? ^ S. " p- 1 Pill 1 If * rt & *" !^ K, "* ^ j^ i? " s 1 ^ &' ly i i | crq n ^ ^ i. 1 V O ffi ? ^ o ^ hd s, O O c/3 W 3 ^3 p p -( p o ^. n n o <-N ^| ' 1 Q * ^;P. s? P| || ^ 1 1 s ^ ^> 15 S^ ^ 1 * CT5 -! ^1 ^rj : ? ? r . ft' ^ & I O ^ ^ " , / 4 o DETECTION OF THE METALS. Procedure. Boil the solution of the (NH 4 ) 2 S precipitate in HC1 till the H 2 S is completely expelled. [Evaporate a third of it just to dryness. To the residue add 1020 cc. of dilute H 2 SO 4 and three volumes of alcohol. Allow the mixture to stand a few minutes, filter, and wash with a mix- ture of three volumes of alcohol and one of water. Dry the precipitate and fuse it on platinum foil with five times its bulk of Na 2 CO 3 . Boil the fused mass with water till disin- tegrated, filter, and wash the residue thoroughly. Dissolve it in dilute HNO 3 , and examine the solution for Ba, Sr, and Ca, as described on page 46.] Notes. i. The precipitate obtained after the addition of (NH 4 ) 2 S may consist of FeS, MnS, ZnS, CoS, NiS, A1O 3 H 3 , CrO 3 H 3 , A1PO 4 , CrPO 4 , Ba 3 (PO 4 ) 2 , Sr 3 (PO 4 ) 2 , Ca 3 (PO 4 ) 2 MgNH 4 PO 4 , BaC 2 O 4 , SrC 2 O 4 , CaC 2 O 4 , and CaF 2 ; also of borates of alkaline-earth metals, and silicic acid, if it has not been previously removed. All these substances except CaF 2 and H 2 SiO 3 dissolve readily in dilute HC1. 2.* A portion of the solution is tested for Ba, Sr, and Ca, at this point, since BaCO 3 is to be added to the remainder as a reagent. 3.* H 2 SO 4 precipitates Ba and Sr completely if allowed to stand a few minutes. Ca is also partly precipitated, if the solution is concentrated, but never completely until alcohol is added, owing to its slight solubility in water. 4.* Fusing with Na 2 CO 3 converts the sulphates to carbon- ates. If the Na 2 SO 4 produced is not washed out completely, the sulphates are again formed on treating with HNO 3 . 5.* If (NH 4 ) 2 CO 3 produces a precipitate in the filtrate from the (NH 4 ) 2 S group, the solution of that precipitate in HNO 3 should be united with the HNO 3 solution here ob- tained, in order to avoid two separate analyses for the alka- * line earth metals. Procedure. Boil the rest of the HC1 solution with a small quantity of HNO 3 , dilute a little of it and test with K 4 Fe(CN) 6 , added drop by drop, or with KCNS. (If Fe is present, test a freshly prepared solution of the original sub- stance in H 2 O or HC1 with K 3 Fe(CN) 6 and KCNS.) ALUMINUM AND IRON GROUPS. 4 Treat the remainder as follows: [Add FeCl 3 little by little, till a drop of the solution tested on a watch glass gives a yellow precipitate with NH 4 OH.] Evaporate the solution to a small bulk to expel most of the acid, add Na 2 CO 3 as long as the. precipitate which forms can be made to redis- solve on shaking. Place in a small flask, dilute with water to at least 200 cc., cool if still hot, and add BaCO 3 , avoiding a large excess. Allow the mixture to stand, with frequent C'haking, for half an hour. Filter and wash the precipitate. Notes. \. The solution tested with KCNS should be dilute and cold ; for otherwise the HNO 3 rapidly destroys the reagent. NO 2 is thereby formed, which itself gives a red color with KCNS. 2.* If FeCl 3 were not added, the phosphates of the alkaline- earth metals would precipitate when the solution is made neutral with BaCO 3 . But its addition causes precipitation of the H 3 PO 4 in the form of FePO 4 , and thus allows the bivalent metals to pass into the filtrate in the form of chlorides. 3.* The test with NH 4 OH shows when sufficient FeCl 8 has been added to combine with all the H 3 PO 4 ; for before that point is reached, white FePO 4 precipitates ; but as soon as an excess is present, brown FeO 3 H 3 precipitates with it. 4. BaCO 3 precipitates only the trivalent metals, aluminum, chromium, and ferric iron, leaving all the bivalent metals hi solution. 5. Na 2 CO 3 , on the other hand, being soluble, precipitates all the metals. The addition of enough to produce a perma- nent precipitate is therefore fatal to the separation. 6. The solution must be cold ; for BaCO 3 does precipitate from hot solutions certain bivalent metals. These are also precipitated if sulphates are present in the solution, since in- soluble BaSO 4 is thus formed. 7. The precipitate obtained by following the above direc- tions consists of the excess of BaCO 3 , of FePO 4 , of FeO 3 H 8 , A1O 3 H 8 , andCrO 3 H 3 . Reactions : 2FeCl 3 + 3BaCO 8 + 3H 2 O etc. Procediire. Dissolve the BaCO 3 precipitate in dilute HC1, heat to boiling, and add, without filtering, dilute 42 DETECTION OF THE METALS. H 2 SO 4 ; allow it to stand a few minutes, filter out the BaSO 4 , add to the filtrate NaOH to strong alkaline reaction, boil two or three minutes in a porcelain dish, filter, and test the precipitate for chromium by fusing on platinum foil with Na 2 CO 3 and KC1O 3 , boiling the fused mass with water, fil- tering, adding HC 2 H 3 O 2 to acid reaction, boiling to expel CO,, and then adding Pb(C 2 H 3 O 2 ) 2 . Test the filtrate from the NaOH precipitate for aluminum by acidifying it with HC1, adding NH 4 OH till very slightly alkaline, heating an.d allowing it to stand, if no precipitate is visible at first. Notes. i. Dilute HC1 is used for dissolving the BaCO 3 ; for BaCl 2 is insoluble in strong HC1. The solution should be at the boiling temperature when H 2 SO 4 is added; for the BaSO 4 is then less likely to pass through the filter. A slightly turbid filtrate need not, however, be again filtered. 2. By fusion with Na 2 CO 3 and KC1O 3 , CrO 3 H 3 is changed to Na 2 CrO 4 , which gives a yellow color to the fused mass. 3. If, however, Mn is present in the substance, enough of it is almost always retained in the BaCO 3 precipitate to give the characteristic green coloration of Na 2 MnO 4 on fusing. The yellow color of the Na 2 CrO 4 is then obscured, and it is necessary to dissolve the fused mass in water, to boil (with addition of a few drops of alcohol, if necessary), in order to reduce the Na 2 MnO 4 to MnO 2 , to filter, and add HC 2 H 3 O 2 and Pb(C 2 H 3 O 2 ) 2 . The HC 2 H 3 O 2 neutralizes the Na 2 CO3, and the Pb(C 2 H 3 O 2 ) 2 precipitates PbCrO 4 . 4. The precipitate produced by NaOH is usually very- bulky, owing to the nresenre of a large amount of iron, and a common mistake in testing for chromium is to fuse only a small portion of this precipitate. A large part or, better, the whole precipitate should be employed. It is best dried on the filter, whereby its volume is greatly reduced, before mix- ing with Na 2 CO 3 and KC1O 3 . 5. When Cr is present, small quantities of it sometimes precipitate in the test for Al, owing to insufficient boiling of the NaOH solution. It is distinguished by the green color of the precipitate after time has been allowed for its separation from the liquid. To test for Al in it, the precipitate should ALUMINUM AND IRON GROUPS. 43 be filtered off and dissolved in a little NaOH, the solution boiled and filtered, and the test for Al tried in the filtrate. 6. Consult notes 4 and 5 on page 38. Procedure. Acidify the filtrate from the BaCO 3 precipi- tate with a few drops of HC1, and boil two or three minutes to expel CO 2 . [Make slightly .alkaline with NH 4 OH and add (NH 4 ) 2 S, avoiding an excess. Filter out and wash any precipitate that may form, dissolve it in HC1, boil till the H 2 S is completely expelled], add NaOH till alkaline ; filter, test the precipitate for Mn by fusion with Na 2 CO 3 , and the filtrate for Zn by passing in H 2 S. [To the filtrate from the (NH 4 ) 2 S precipitate add (NH 4 ) 2 CO 3 and (NH 4 ) 2 C 2 O 4 ; filter; reject the precipitate ; concentrate the filtrate as much as possible, add to it one third its volume of NH 4 OH and a little Na 2 HPO 4 , stir, and allow it to stand over night if no precipitate appears at once.] Notes. i.* If the CO 2 is not expelled, the alkaline-earth carbonates will be precipitated when NH 4 OH and (NH 4 ) 2 S are added. 2. The (NH 4 ) 2 S precipitate consists of MnS and ZnS. If dark colored, it may contain small quantities of NiS and CoS r which were dissolved by the dilute HC1 used at first ; in that case it should be tested in a borax bead. FeS will also be precipitated here if the oxidation with HNO 3 was incomplete. 3 * (NH 4 ) 2 CO 3 and (NH 4 ) 2 C 2 O 4 are added to remove the Ba, Sr and Ca, which would otherwise precipitate with Na 2 HP0 4 in the Mg test. (NH 4 ) 2 C 2 O 4 is added since it pre- cipitates Ca more completely than (NH 4 ) 2 CO 3 . MgNH 4 PO 4 is somewhat soluble in H 2 O ; hence the solution must be concentrated, and contain a large quantity of NH 4 OH, in which the precipitate is less soluble. ADDITIONAL REACTIONS OF METALS OF THE ALUMINUM AND IRON GROUPS. Behavior towards the Alkalies. All metals of these groups are precipitated both by NaOH and NH 4 OH. Excess of cold f6 DETECTION OF THE METALS. 2. Ammonium salts considerably increase the solubility of the alkaline-earth carbonates in water, so that small quanti- ties of the metals might escape detection if (NH 4 ) 2 CO 3 were alone employed ; hence the further tests with (NH 4 ) 2 SO 4 , and (NH 4 )oCoO 4 for Ba and Ca respectively. Even if already detected in the (NH 4 ) 2 CO 3 precipitate, the traces of these metals must be so removed, as otherwise they will precipi- tate in the test for Mg. 3. The presence of ammonium salts is necessary, however, in order to avoid the precipitation of MgCO 3 (NH 4 )oCO 3 . For the same reason the solution should be moderately dilute and not stand long before filtering. Procedure. Dissolve the precipitated carbonates in a small quantity of dilute HNO 3 . Evaporate the solution to dryness in a small porcelain dish, and heat quite strongly on an iron plate until no odor of HNO 3 can be detected. As soon as it is. cold, rub the contents of the dish to powder by means of a pestle, add 5-10 cc. of a mixture of equal vol- umes of absolute alcohol and ether, and triturate with the pestle for two or three minutes. Filter, and add two drops of dilute H 2 SO 4 to the filtrate. Wash the residue on the filter with small quantities of the alcohol-ether mixture until the wash water shows no turbidity with a drop of dilute sul- phuric acid ; then dissolve it in 10-20 cc. of water, and filter if not perfectly clear. To a third of the solution add two or three drops of acetic acid, dilute it with 50 cc. of water, heat to boiling, and add gradually K 2 CrO 4 until present in slight excess. If no precipitate forms, add NH 4 OH and (NH 4 ) 2 CO 3 to the remaining two thirds of the aqueous solution. If a precipitate forms, treat the remainder of the solution in just the same way as the first third was treated, .unite the two portions, heat to boiling, and filter. Then add to the filtrate NH 4 OH and (NH 4 ) 2 CO 3 . Notes. i. In order that the separation of the nitrates by the alcohol-ether mixture may be complete, it is essential that they be completely anhydrous; for Sr(NO 3 ) 2 is very readily ALKALINE- EARTH GROUP. 47 soluble in water, and Ba(NO 3 ) 2 moderately so. The temper- ature, therefore, must be sufficiently high and long continued to effect dehydration ; it may reach 180 without injury, but too high a temperature would convert the nitrates to oxides. Since the nitrates are hygroscopic, they must not be left ex- posed to the air ; but they should be treated immediately with the solvent. 2. If the precipitate produced by H 2 SO 4 is very small, it may be due to a trace of Sr(NO 3 ) 2 dissolved, owing to the presence of water, by the alcohol-ether mixture. In that case, therefore, collect it upon a small filter, pour through the latter repeatedly 5 cc. of a hot, concentrated (25 per cent.) solution of (NH 4 )..>SO 4 , to which a few drops of NH 4 OH have been added, make barely acid with acetic acid, and add a few drops of (NH 4 )oC 2 O 4 . The formation of a precipitate shows conclusivel} the presence of Ca, for the minute quantities of SrSO 4 soluble in (NH 4 ) 2 SO 4 are not precipitated by (NH 4 ). 2 C,O 4 . 3. In order that the precipitation of BaCrO 4 may be com- plete, the quantity of free HC 2 H S O 2 present must be small The solution is diluted to prevent the precipitation of stron- tium. It is precipitated hot, since otherwise BaCrO 4 is liable to pass through the filter. A perfectly clear filtrate must always be obtained before adding (NH 4 ) 2 CO 3 . 4 In order to detect minute quantities of Ba, Sr, and Ca, it is advisable to examine the nitrates with the spectroscope before treating them with the alcohol-ether mixture. Procedure. Evaporate the filtrate from the (NH 4 ) 2 CO 3 (or (NH 4 ) 2 SO 4 and (NH 4 ) 2 C 2 O 4 ) precipitate in a porcelain vessel till ammonium salts begin to crystallize out. Acidify the liquid with HC1, filter, and add to a portion of it a third its volume of NH.OH and some Na 2 HPO 4 . Rub the sides of the tube with a glass rod, and if no precipitate appears, allow it to stand over night. Evaporate the remainder of the solution to dryness in a small porcelain disb, and ignite the residue not above a faint red heat until no more white fumes come off, taking care to heat the sides as well as the bottom of the dish. Dissolve 48 DETECTION OF THE METALS. in a little water, filter, and evaporate to dryness in a small beaker ; note the quantity of the residue, and introduce a little of it into a flame on a platinum wire. Dissolve in the least possible quantity of water, add a few drops of H 2 PtCl G , stir, and allow the solution to stand. Notes. i. Concerning the' precipitation of MgNH 4 PO 4 see note 4, page 43. All other metals except arsenic and the alkalies are also precipitated by Na 2 HPO 4 ; so the mag- nesium test can be made only after they are removed. The precipitate should be crystalline ; if flocculent it may consist of A1PO 4 , present here by reason of the solubility of A1O 3 H 3 in NH 4 OH and the use of too large a quantity of that re- agent in precipitating the aluminum and iron groups. 2. , Presence of MgCl 2 does not interfere with the H 2 PtCl 6 test tor potassium. When present in large amount, however, it is sometimes desirable to remove it, in order to form, from the amount of residue left after ignition, an approximate idea of the quantity of alkali metals present. It is removed by adding BaO 2 H 2 to the solution from which the ammonium salts have been expelled, boiling, filtering out the MgO 2 H 2 , precipitating the barium from the filtrate with NH 4 OH and (NH 4 ) 2 O 3 , filtering, evaporating the filtrate, and igniting the residue to expel ammonium salts. By this same method all other metals (except arsenic) can be removed from a solution to be tested for alkalies. 3. Since ammonium salts, like those of potassium, give a precipitate with H 2 PtCl 6 , great care must be taken to remove them completely ; ignition above faint redness, however, vol- atilizes KC1 and NaCl. 4. No satisfactory precipitant for sodium is known. The flame test is so exceedingly delicate that only when the yellow color is intense and persistent is it to be taken as an indica- tion of sodium in appreciable quantity. At best, however, the flame test is very unsatisfactory ; it is therefore always advisable to determine approximately, as directed in the Pro- cedure, the amount of residue left after expulsion of the am- monium salts ; for, in this way, an idea can be formed of the amount of Na present, when Mg and K are absent, or when ALKALI GROUP. 49 present only in small amounts. If Mg or K are present in considerable amounts, it is even usually advisable to remove them by precipitation, and to determine the amount of Na in the filtrate by evaporation. Magnesium is best removed as described in note 2 above. To remove potassium, add H 2 PtCl 6 in the usual manner ; evaporate the filtrate to dryness, ignite the residue at a temperature below redness and treat it with water, filter the solution and finally evaporate it to dryness. By the ignition the Na 2 PtCl 6 and H 2 PtCl 6 are destroyed, Pt and NaCl alone remaining in the dish. 5. K 3 PtCl 6 is soluble in 100 parts of cold and 20 parts of hot water ; hence the need of having the solution cold and very concentrated, and of allowing it to stand. 6. Very small quantities of K and Na, like those Ba, Sr, and Ca, are best detected with the aid of the spectroscope. This method does not answer the ordinary purposes of anal- ysis, however; for it gives but little idea of the quantity of the element present, and does not distinguish unimportant traces from considerable amounts. Procedure. Test a portion of the original solid substance for ammonium salts by mixing it in a small beaker with solid CaO 2 H 2 moistened with a little water. Cover the beaker with a watch glass with a piece of moist red litmus paper adhering to the under side, and heat gently. DETECTION OF THE ACIDS. GENERAL REMARKS. The number of acids to be tested for is often restricted by the solubility of the substance taken in connection with the metals already found in it. A substance completely soluble in water containing a certain metal cannot contain any acid known to form an insoluble salt with that metal ; for example, a barium salt soluble in water need not be tested for sulphate, chromate, phosphate, oxalate, borate, carbonate, or fluoride; a barium salt soluble in dilute acids cannot contain sulphate. But, on the other hand, when the substance is insoluble, it is not safe to conclude that all acids forming soluble salts with the metals present are therefore absent; for the solution of such salts may be prevented by the presence of insoluble sub- stances which hold them back mechanically or by reason of chemical combination ; for example, Ba(NO 3 ) 2 is retained in this way by BaSO 4 . Moreover, many salts which when normal are readily soluble are insoluble when basic ; for example, basic lead nitrate, Pb(OH)NO 3 . In order to determine what acids are excluded by the solu- bility of the substance, the solubility of the various salts of the metals present must be considered. The following brief statement will be of assistance : 1. All K, Na, and (NH 4 ) salts are soluble in water (except K 2 PtCl 6 , (NH 4 ) 2 PtCl 6 , KHC 4 H 4 6 , and (NH 4 )HC 4 H 4 O 6 ). 2. All nitrates, chlorates, and acetates are soluble in watet (except certain basic nitrates and acetates). 3. All carbonates, phosphates, borates, oxalates, arseni- ates, and arsenites, except those of the alkalies, are insoluble or only slightly soluble in water, but are readily soluble in dilute acids. 4. All chlorides, bromides, and iodides, except the lead, silver, and mercurous compounds and HgI 2 , and all sulphates, except those of Ba, Sr, Ca, and Pb, are soluble in water. DIVISION INTO GROUPS. 5 The number of acids to be tested for is further limited in cases by the nature of the substance analyzed. For example, it is useless to test a mineral for organic and cyan- ogen acids, or, in general if insoluble in water, for nitrates, chlorates, bromides, and iodides; alloys contain no acids; etc. DIVISION OF THE ACIDS INTO GROUPS. The detection of the acids does not require, like that of the metals, their separation from one another. They are, nevertheless, divided into groups according to their behavior toward certain general reagents, which, however, serve to show the presence or absence of a whole group of acids, and not to separate one group from another. The acids are primarily divided into two classes : 1. Those whose salts blacken and emit a burnt odor when ignited in a closed tube ; that is, the organic acids. 2. Those whose salts do not behave thus ; that is, the inor- ganic acids. Notes. i. Blackening does not necessarily prove an organic acid. Starch, sugar, and other organic substances also char. 2. Blackening, unaccompanied by a burnt odor, is not due to organic matter. Cu, Co, and Ni salts may cause it, owing to expulsion of the acid and change to the black oxides. 3. The presence of organic matter is generally best de- tected by heating the substance suddenly to a high temperature. 4. Oxalic acid, an organic acid, is here classed with the inorganic ; for its salts do not char, or char but slightly. Organic Acids. These are exceedingly numerous, and no attempt to group them separately will be made. Acetic and tartaric acids, the two most commonly met with, are the only ones that will be considered in this course. Inorganic Acids. These including the two organic acids, acetic and tartaric, are divided into groups as follows : GROUP I. Sulphuric Acid Group. Acids precipitated from neutral solution by BaCl 2 . They are : H 2 SO 4 , H 2 CrO 4 , H 3 PO 4 , H 3 B0 3 , H 2 C 2 4 , HF, H 2 C0 3) H 4 SiO 4 , H 2 C 4 H 4 O. (HaSO,, H 2 S 2 3 , H 3 As0 3 , H 3 As0 4 .) 5* DETECTION OF THE ACIDS. GROUP II. Halogen Group. Acids precipitated from dilute HNO 3 solution by AgNO 3 . They are : HC1, HBr, HI, HCN, H 2 S, H 3 Fe(CN) 6 , H 4 Fe(CN) 6 . GROUP III. Nitric Acid Group. Acids not precipitated by BaCl 2 nor by AgNO 3 . They are : HNO 3 , HC1O 3 , HC 2 H 3 O 2 . Note. Though AgNO 3 precipitates none of the acids of the first group from an acid solution, it precipitates all of them except H 2 SO 4 and HF from a neutral solution. The acids of the second group are also precipitated by AgNO 3 in neutral solution. From an acid solution BaCl 2 precipitates only H 2 SO 4 . GENERAL TESTS. Procedure. If the solution is acid, make a portion of it slightly alkaline with NH 4 OH ; if it is alkaline with Na 2 CO 3 , acidify a portion with HNO 3 , boil it a few minutes to expel CO 2 , and make it alkaline with NH 4 OH ; add BaCl 2 and CaCl 2 , and if no precipitate forms at once, allow the solution to stand some minutes. If a precipitate forms, add HC1 in considerable quantity. Notes. i. Non-formation of a precipitate in neutral solu- tion proves the absence of all acids of the first group except H 3 BO 3 , which is precipitated by BaCl 2 and CaCl 2 only from rather concentrated solutions. 2. This conclusion is correct, however, only when no con- siderable quantity of ammonium salt is present ; for, with the exception of BaSO 4 and CaC 2 O 4 all these precipitates dissolve in ammonium salts somewhat, and some of them (the borate, fluoride, and tartrate) dissolve quite readily. 3. If the precipitate dissolves completely in HC1, H 2 SO 4 is absent ; if it is not completely soluble, H 2 SO 4 is present, and other acids of its group may also be present. Owing to the solubility of their Ba and Ca salts in ammonium salts, their presence or absence cannot be determined by filtering and neutralizing the filtrate from the BaSO 4 with NH 4 OH. 4. The precipitates are all white except the chromate. 5. CaCl 2 is added, since CaC 2 O 4 , CaF 2 , and CaC^O,* are more insoluble than the corresponding barium salts. GENERAL TESTS. 53 Procedure. Acidify a portion of the solution with HNO 8 , and add AgNO 3 . If a precipitate forms, filter it off and test the filtrate with more AgNO 3 to insure complete precip- itation. Then carefully pour a little dilute ammonia down the sides of the tube so as to form a layer on top. Note whether a precipitate forms at the junction, and what its color is. Notes. i. Non-formation of a precipitate in acid solution proves the absence of the halogen group. If no precipitate is obtained in neutral solution, all acids of the sulphuric acid group except H 2 SO 4 and HF are absent. 2. The color of the silver precipitates taken in connec- tion with their solubility in HNO 3 is an important indication. Agl, Ag 3 PO 4 , and Ag 3 AsO 3 are yellow; AgBr is yellowish white; Ag 3 AsO 4 and Ag 3 Fe(CN) 6 are brownish red; Ag 2 CrO 4 is dark red; Ag 2 S is black, and the remainder are white. Ag 2 CO 3 , white at first, rapidly turns yellow, and on boiling, brown owing to change to Ag 2 O. 3. All the precipitates with the exception of Agl, Ag 2 S and Ag 4 Fe(CN) 6 dissolve in NH 4 OH, most of them very readily; AgBr dissolves only sparingly. Therefore AgNO 3 precipitates chromates, phosphates, etc., only from a perfectly neutral solu- tion. As the whole solution is not easily made exactly neu- tral, the NH 4 OH is added on top, by which a neutral layer is formed at the junction. 4. Ag 2 C 2 O 4 dissolves in HNO 3 with some difficulty ; hence, if considerable HNO 3 is not added, it might be mistaken for a halogen compound. 5. A grayish brown precipitate of Ag 2 O, very soluble in HNO 3 , NH 4 OH, and NH 4 NO 3 , may form, even when no acids of the first and second groups are present. Procedure. Add a few drops of strong H 2 SO 4 to some of the finely powdered substance placed in a very small test-tube, and heat gently not enough to cause vola- tilization of the H 2 SO 4 . 54 DEFECTION OF THE ACIDS. Notes. i. Salts of the various acids give indications as follows : Chromates, sulphates, phosphates, and borates remain unchanged. Silicates remain unchanged, or decompose with separation of silicic acid. Sulphites evolve SO. 2 , recognized by its odor. Thiosulphates evolve SO 2 and give a precipitate of sulphur. Oxalates and carbonates effervesce, owing to escape of CO, (accompanied by CO in the case of oxalates). Fluorides evolve HF, which etches the watch glass on which the test is tried. Chlorides evolve HC1, recognized by its odor. Bromides and iodides evolve Br and I, recognized by their color and odor. Cyanides evolve HCN, recognized by its odor. Sulphides evolve H 2 S, known by its odor and reaction with Pb(C 2 H 3 2 ) 2 . Nitrates evolve HNO 3 , recognized by its odor. Chlorates evolve C1O 2 , a green gas which smells like chlo- rine and colors the I1 2 SO 4 intensely yellow. Acetates evolve HC 2 H 3 O 2 , known by its odor. Tartrates char and cause blackening of the H 2 SO 4 . 2. These indications should not be taken as conclusive, but should be confirmed by appropriate special tests. This is especially true where the results are negative, owing to the fact that certain insoluble salts are not decomposed as above stated. SPECIAL TESTS. By the considerations stated on pages 50 and 51, and by the BaCl 2 and AgNO 3 tests, the examination for acids is much simplified. Moreover, in the analysis for metals, the pres- ence of many acids, namely: H 2 CO 3 , H 2 S, HCN, H 2 SO 3 , H 2 S 2 O 3 , HC1O 3 , on addition of HC1 ; H 3 AsO 3 , H 3 AsO 4 , H 2 CrO 4 , by the action of H 2 S ; will generally have been demonstrated. For the acids not already detected, or not proved absent, special tests must be tried, as described below, SULPHURIC ACID GROUP. 55 SULPHURIC ACID GROUP. Chromic Acid. 1. Reducing agents, such as nascent hydrogen, strong HC1, H 2 S in presence of acid, reduce chromates to chromium salts, the color of the solution changing from yellow or red to green. In the presence of insufficient acid H 2 S effects only partial reduction, producing a brown precipitate of hydrated CrO 2 , which, in the analysis for metals, might be mistaken for a sulphide of the H 2 S group. 2. Pb(C 2 H 3 O 2 ) 2 precipitates PbCrO 4 , insoluble in HC 2 H 3 O 2 . 3. Acids change the yellow color of solutions of normal chromates to red, owing to formation of dichromates. Sulphuric Acid. The BaCl 2 test in presence of HC1 is conclusive for this acid. It is simply necessary to avoid the addition of much HC1; for this prevents the precipitation of small quantities of BaSO 4 , and may cause the precipitation of BaCl 2 . Sulphurous and Thiosulphuric Acids. These are detected by the action of H 2 SO 4 on the solid substance or on a concentrated solution of it. Phosphoric Acid. Procedure. Place 3 or 4 cc. of (NH 4 ) 2 MoO 4 solution in a test tube, and add to it not more than half as much of the solution to be tested, having first acidified the latter with HNO 3 . Allow the solution to stand, if no precipitate forms at once. Notes. i. The (NH 4 ) 2 MoO 4 is used in excess; for the precipitate is less soluble in it than in pure water. Dilute HNO 3 and NH 4 NO 3 also diminish its solubility; but HC1 and chlorides present in considerable quantity render the test less delicate. In alkaline solution the precipitate does not form. 2. The yellow precipitate is ammonium phospho-molybdate of complicated and somewhat variable composition (approxi mately (NH 4 ) 3 PO 4 .12MoO 3 ). 56 DECTECTION OF THE ACIDS. Procedure. Add enough NH 4 OH to fora? one third cht bulk of the solution, and then a little magnesia mixture (MgCl 2 , NH 4 C1, and NH 4 OH). Stir with a glass rod and allow the mixture to stand for some hours. Notes. i. The NH 4 C1 is added to the reagent to prevent the precipitation of MgO 2 H 2 . 2. H 3 AsO 4 gives a similar precipit&U. (See Note 5, page 25.) If present, it is first removed by passing H 2 S into the hot acidified solution. 3. The test is only applicable when NH 4 OH alone pro- duces no precipitate. If metals precipitated by NH 4 OH are present, the (NH 4 ) 2 MoO 4 test must be used. Boric Arid. Procedure. Add to the solid substance, obtained if neces- sary by evaporating the solution, concentrated H 2 SO 4 and C 2 H 5 OH. Warm the mixture, set fire to it, and note whether the borders of tne flame are colored green. Notes. i. The color is best seen at the moment when the alcohol is lighted. 2. Copper, if present, must be first removed with H 2 S. 3. In the presence of chlorides the test is unreliable ; for ethyl chloride, which also tinges the flame green, is formed by their action on the alcohol. 4. If a solution to be tested has to be evaporated, it must first be made alkaline, since H 3 BO 3 is volatile with steam. Procedure. Acidify the solution slightly with HC1, and partly dip a piece of turmeric paper in it, and dry. Note whether the dipped part assumes a red tint. Note. If the HC1 is not very dilute, it imparts a brownish black color to the turmeric paper, which obscures the H 3 BO 3 test. Oxalic Acid. Procedure. If the solution is neutral or alkaline, acidify with HC 2 H 3 O 2 , add CaSO 4 , and allow it to stand. If the solution is acid with HC1 or HNO 3 , first add a considerable quantity of NaC 2 H 8 O 2 , and then add CaSO 4 . SULPHURIC ACID GROUP. 57 . i. CaC 2 O 4 is nearly as insoluble in HC 2 H 3 O 2 as in H 2 O. The presence of that acid is necessary to prevent the precipitation of other calcium salts, such as CaCO 3 , Ca 3 (PO 4 ) 2 . CaF 2 , however, is also insoluble in HC 2 H 3 O 2 . 2. Mineral acids dissolve CaC 3 O 4 . NaC 2 H 3 O 2 neutralizes them with formation of their sodium salt and HC 2 H 3 O 2 , and is often employed for this purpose in other cases. Hydrofluoric Acid. This is commonly met with only in minerals and metal-, lurgical products. Procedure. , Mix the dry, finely powdered substance in a platinum crucible or on platinum foil with enough strong H 2 SO 4 to make a thin paste. Cover it with a watch glass coated on its convex face with beeswax through which some markings have been made with a pointed piece of wood. Fill the watch glass with cold water, and warm the mixture very gently, taking care not to melt the wax. After half an hour, melt off the wax and examine the glass for etchings. Notes. i. In order to detect small quantities of fluorine, a large excess of H 2 SO 4 should be avoided, the watch glass should fit the crucible or foil closely, and considerable time should be allowed. By breathing on the watch glass slight etchings, not otherwise noticeable, are made apparent. 2. The etching is due to the action of HF on the silicate of the glass, SiF 4 , a gas, being formed. 3. If the substance tested is not decomposed by H 2 SO 4 , or if it itself contains SiO 2 or silicate, it is evident that the test, if negative, is not conclusive. Another process, described on page 83, is then followed. Carbonic Acid. Procedure. Cover some of the finely powdered substance in a test tube with a little water ; boil to expel the air, and add HC1. If bubbles of gas escape, hold a drop of BaO 2 H 2 caught on the end of a glass rod just above the surface of the liquid, and note whether it becomes turbid. 5 8 DETECTION OF THE ACIDS. Silicic Acid. Procedure. Add HC1 to the solution, evaporate it to dry- ness, and ignite the residue at 125 in a hot closet for an hour or more. Moisten with strong HC1, warm, add water, and heat to boiling. If a residue remains undissolved, trans- fer it to platinum foil, add carefully one or two drops of HF and a drop of H 2 SO 4 , and heat until the acid is volatilized. Notes. i. For explanation see note 4, page 73. 2. If the residue consists only of SiO 2 , it will completely volatilize on treatment with HF, owing to the formation of gaseous SiF 4 . In using HF take the greatest care not to get it on the hands nor to breathe it. HALOGEN GROUP. Hydrochloric Acid. The test relied upon in most analyses for the detection of this acid is simply the formation with AgNO 3 of a white pre- cipitate insoluble in HNO 3 , other halogens being proved ab- sent by the special tests for them. This method is simpler and far more delicate than to try special tests for chlorine. Such tests have to be resorted to, however, in some cases, when other halogens are present. Hydrobromic Acid. Procedure. Add to the neutral or slightly acid solution enough CS 2 to form a large drop at the bottom of the test tube ; then add a few drops of chlorine water, and shake the tube. Note. The CS 2 is added to dissolve the liberated bromine, thus making the test more delicate. The color is reddish brown if much bromine is present ; yellow if only a little. If care is not taken to avoid an excess of chlorine, the solu- tion will be decolorized, owing to formation of bromine chlo- ride, BrCl. Make sure that the chlorine water used smells strongly of the gas. HALOGEN GROUP 59 Hydriodic Acid. Procedure. Make the solution distinctly acid with HCl f add a drop of KNO 2 solution and enough CS 2 to form a large drop at the bottom of the test tube, and shake vigorously. Note. The HNO 2 liberates iodine and is itself reduced to NO. Chlorine water (as in the test for HBr) answers equally well in most cases, but is not so suitable for the detection of very small quantities of HI, since if used in excess it oxidizes the liberated iodine, thus destroying its color. Hydrocyanic Acid. Procedure, If the solution is acid, make it alkaline by the addition of NaOH ; then add solution of FeSO 4 and a few drops of FeCl 3 . Heat the mixture for a short time, and then acidify with HC1. Notes. i. On the addition of the iron salts a greenish black precipitate of ferrous-ferric hydrate forms, even in the absence of HCN ; but this dissolves when HC1 is added, the insoluble Prussian blue then becoming visible. If only traces of HCN are present, the liquid simply appears green at first and a slight blue precipitate separates on long standing. 2. The reactions in this process are : FeSO 4 + 6KCN = K 4 Fe(CN) 6 + K 2 SO 4 3K 4 Fe(CN) 6 + 4FeCl 3 = Fe 4 (Fe(CN) 6 ) 3 + 12KC1. Procedure. If the solution is acid, make it alkaline with NH 4 OH, and add one or two drops of (yellow) (NH 4 ) 2 S X . Heat on the water bath till a drop of the solution no longer reacts with Pb(C 2 H 3 O 2 ) 2 ; then acidify with HC1 and add a little FeCl 3 . Note. The reaction is : (NH 4 ) 2 S X + (x 1) KCN = (NH 4 ) 2 S + (* !) KCNS. Hydroferrocyanic and Hydrofefricyanic Acids. Procedure. Add to one portion of the slightly acid solu- tion a few drops of FeSO 4 , and to another portion a few drops of FeCl 3 . 6o DETECTION OF THE ACIDS. Hydrogen Sulphide. Procedure. Warm some of the finely powdered sub- stance in a test tube with dilute HC1, insert a piece of Pb(C 2 H 3 O 2 ) 2 paper in the top of the tube, and if no blacken- ing appears, add some pure powdered zinc ; cork the tube loosely, and allow it to stand. Notes. i. Some sulphides (for example, HgS, FeS 2 , etc.) are not decomposed by the acid alone. The nascent hydro- gen evolved from the zinc reduces these, however, with evolu- tion of H 2 S. 2. If sulphide is present in considerable quantity, it is detected in the preparation of the solution for analysis, either by the odor of H 2 S, if the substance is dissolved in HC1, or by the separated sulphur, if HNO 3 or aqua regia is used. ACIDS OF THE HALOGEN GROUP IN THE PRESENCE OF EACH OTHER. Iodides, cyanides, and sulphides are readily detected by the tests above described, even in the presence of other acids of the group. Hydrobromic in the Presence of Hydriodic Acid. Procedure. Add to the neutral or slightly acid solution CS 2 , and then chlorine water little by little, with constant shaking, until the violet color of the iodine disappears. Note. All the iodine is set free before any of the bromine. Excess of chlorine oxidizes it to iodic acid, which is colorless : the bromine is then set free and gives a red or yellow color to the CS 2 . Excess of chlorine also decolorizes it, as above stated ; hence the need of adding the reagent very slowly. Hydrochloric in the Presence of Hydrob^omic and Hydriodic Acids. Procedure. Mix the finely powdered substance intimately with dry powdered K 2 Cr 2 O 7 ; place in a small dry distilling NITRIC ACID GROUP. 6r flask, cover with concentrated H 2 SO 4 , and heat. Cause the vapors to pass into a test tube containing a little dilute NH 4 OH. Notes. i. When chlorides are present, deep red vapors of chromium oxychloride, CrO 2 Cl 2 , are evolved. The corre- sponding bromine compound is not formed, but free bromine escapes. The reactions in the two cases are : K 2 Cr 2 O 7 + 4NaCl -f- 3H 2 SO 4 = 2CrO 2 Cl 2 + K 2 SO 4 -f 2Na 2 SO 4 + 3H 2 O. K 2 Cr 2 7 + 6KBr + 7H 2 SO 4 = 3Br 2 + Cr 2 (SO 4 ) 3 + 4K 2 SO 4 + 7H 2 O. 2. NH 4 OH reacts with CrO 2 Cl 2 with formation of NH 4 C1 and (NH 4 ) 2 CrO 4 , which imparts a yellow color to the liquid. With Br, NH 4 Br and NH 4 BrO 3 are formed, both of which are colorless. 3. H 2 O decomposes CrO 2 Cl 2 ; hence the need of having the apparatus and the salts perfectly dry. 4. Care must be taken that none of the K 2 Cr 2 O 7 is carried over mechanically by frothing or spurting ; for this would of course give rise to a yellow coloration on the addition of NH 4 OH. 5. The presence of much HI interferes with this test for HC1. It is removed by precipitating with AgNO 3 , and treat- ing the precipitate with strong NH 4 OH, which dissolves AgCl readily and Agl only very slightly. The AgCl is reprecipitated by HNO 3 and boiled or fused with Na 2 CO 3 ; the solution is filtered and evaporated, and the test with K 2 Cr 2 O 7 and H 2 SO 4 made in the usual way. NITRIC ACID GROUP. Nitric Acid. Procedure. Mix the solution to be tested with an equal volume of strong H 2 SO 4 , cool, and pour a concentrated FeSO 4 solution cautiously down the side of the tube, so that the two liquids do not mix ; allow it to stand some minutes, if no color appears. 62 DETECTION OF THE ACIDS. Note. The H 2 SO 4 sets free HNO 3 from the nitrate; the HNO 3 is then reduced to NO by the FeSO 4 , and the brown ring is due to the formation of a compound of the two sub- stances last named. This compound is decomposed by heat. Procedure. Treat a small quantity of the dry substance with a few drops of phenolsulphonic acid, dilute with water, and make alkaline with NH 4 OH. Notes. i. Picric acid is produced by the action of HNO 3 on the phenol, and its formation is indicated by the intensely yellow color of its ammonium salt. 2. The test is exceedingly delicate, and serves to detect very minute quantities of HNO 3 . It is used, for example, in testing natural waters, these being first evaporated to dryness. Chloric Acid. Procedure. Add strong H 2 SO 4 to a little of the solid substance on a watch glass, and heat gently. Note. C1O 2 , a greenish yellow gas smelling like Ci, is evolved, which colors the H 2 SO 4 intensely yellow. The re- action is : 3KC1O 3 + 2H 2 SO 4 = 2KHSO 4 + KC1O 4 + 2C1O 2 + H 2 O. Procedure. Ignite the solid substance in a porcelain dish at a low red heat. Dissolve in water and add AgNO 3 . Note. This test is very delicate, but is applicable, of course, only in the absence or after the removal of chlorides Nitric in the Presence of Chloric Acid. Procedure. Mix the substance in a small porcelain dish with dry Na 2 CO 3 and ignite gently for five to ten minutes. Test in the usual way for HNO 3 . Notes. i. The presence of HC1O 3 prevents the reduction of HNO 3 in the FeSO 4 test, and gives a brown color to the phenol sulphonic acid ; it must therefore be removed. ORGANIC ACIDS. 63 2. The chlorate is converted to chloride by ignition ; the nitrate is unaffected or partially reduced to nitrite, which gives the same reaction with FeSO 4 . The use of too high a temperature would destroy the nitrate and nitrite. . 3. Nitrates except those of the alkali-metals are very easily decomposed by heat ; hence the addition of Nitric in the Presence )f Chromic Acid. Procedure. Warm the solution with addition of H 2 SO 3 till the color becomes a pure green. Add NH 4 OH and fil- ter ; test the filtrate with H 2 SO 4 and FeSO 4 . Nitric in the Presence of Hydriodic Acid. Procedure. Add Ag 2 SO 4 to the solution acidified with H 2 SO 4 , as long as a precipitate continues to form ; filter and test the filtrate for HNO 3 . ORGANIC ACIDS. Acetic Acid. Procedure. Add a mixture of equal volumes of alcohol and strong H 2 SO 4 to the solid substance placed in a test tube ; heat gently, and _iote the odor. Notes. i. The alcohol and acetic acid react in the pres- ence of H 2 SO 4 with formation of ethyl acetate, C 2 H 5 (C 2 H 3 O2), a volatile liquid with a- pleasant ethereal odor. 2. If the mixture is heated too hot, other products (ether, SOo, etc.) are formed by the action of the H 2 SO 4 on the C 2 H 5 OH, whereby the odor of the ethyl acetate is concealed. 3. Till perfectly familiar with the odor, the student in trying the test should always make a comparative experiment with a pure acetate. Tartaric Acid. Procedure. Evaporate the solution to the volume of a few drops, slightly acidify with HC 2 H 3 O 2 , add some KC 2 H 3 Oj solution, stir with a glass rod, and allow it to stand. 64 DETECTION OF THE ACIDS. Notes. i. The crystalline precipitate is KHC 4 H 4 O 6 , po- tassium acid tartrate, cream of tartar. The test is exceedingly characteristic, for no other potassium salt (except K 2 PtCl 6 ) is nearly so insoluble. It is not very delicate, however, owing to the slight solubility of the precipitate in water ; still, if care is taken to have the solution very concentrated, and if time is allowed, it is sufficiently so for most purposes. 2. Addition of C 2 H 5 OH greatly diminishes the solubility of the precipitate; before adding it, however, it is necessary to make sure that it alone (without KC 2 H 3 O 2 ) does not give a precipitate with the solution. 3. If the solution contains HC1 or HNO 3 , this should be removed by evaporating to dryness on the water bath, since strong acids readily dissolve KHC 4 H 4 O 6 . 4. If the solution contains potassium salts, the precipitate forms, of course, as soon as the HC 2 H 3 O 2 is added. In pre- paring the solution to test for tartrates, it is better to boil the substance, if insoluble, with K 2 CO 3 than with Na 2 CO 3 solu- tion ; for potassium salts diminish and sodium salts increase the solubility of KHC 4 H 4 O 6 . Procedure. Make the solution slightly alkaline witlr NH 4 OH, add CaCl 2 in excess, allow it to stand a short rime, filter, treat the precipitate in the cold with strong NaOH, dilute, filter if not clear, and heat the nitrate to boiling. Note. CaC 4 H 4 O 6 is precipitated from neutral or ammo- niacal solution by CaCl 2 . Presence of ammonium salts re- tards the precipitation. The solubility of the precipitate in cold NaOH and its reprecipitation on boiling are pauicularty characteristic of tartaric acid ANALYSIS IN THE DRY WAY. GENERAL REMARKS. The methods so far described make it possible to detect and separate the metals and acids only when in solutior. . Valu- able information in regard to the composition of a material may, however, often be obtained by making a few simple tests directly with the solid substance. Such tests are of value, first, as a pre- liminary indication of the presence of specific elements or com- pounds ; for the knowledge thus obtained often facilitates the pre- paration of the solution for analysis, and enables the subsequent analysis in the wet way to be more intelligently carried out. They are of value, secondly, as an independent method of analysis which may replace the more lengthy wet process in cases where information only in regard to the presence or absence of particular elements is desired, or where the facilities of a well-equipped lab- oratory are not available. Where a complete analysis in the wet way is to be made, it is usually not worth while to make all the tests described below ; for the physical properties of the substance, its behavior towards solvents, and the precipitates produced by the general reagents, indicate in most cases very quickly the nature of the metals present in considerable proportion. The closed tube test should, however, always be made ; for it shows at once the pres- ence or absence of organic matter and of water, and in many ca^es the nature of the acids contained in the substance. More- over, if any special difficulty is met with in getting the substance into solution, it is always advisable to try all the dry tests before proceeding. It should be understood, however, that these dry tests, especially when applied to complex substances with negative results 66 ANALYSIS IN THE DRY WAY. are not as delicate nor conclusive as those made in the wet way ; also that some of the reactions are readily obtained and correctly interpreted only after considerable experience. The student, therefore, should not at first draw too positive conclusions from the results SPECIAL TESTS. Procedure. Place a little of the finely powdered substance in a glass tube sealed at one end. Heat gently at first, and then to the highest heat of the flame. Note any change of appearance and any odor. During the heating apply a flame to the mouth of the tube, and insert in it a glowing wood- splinter or a smouldering bit of twine. Notes. i. The important indications furnished by this test are in regard to the presence of (i) organic matter, (2) water, (3) compounds of volatile metals and (4) in regard to the nature of the acid elements of the substance. The character- istic phenomena that may be observed are (i) carbonization, (2) formation of a distillate or sublimate, (3) evolution of a gas, (4) fusion or change of color. 2. Especial attention must be given to determining whether the substance carbonizes ; first, because, if organic matter is present it must be destroyed (as described on page 74), before proceeding with the detection of the metals ; and secondly, because, if organic matter is not present, the tests for organic acids may be omitted. For a fuller discussion of carboniza- tion see the notes on page 51. 3. As water is used in preparing the solution, its presence must of course be determined by a test made with the original substance. If present, it should always be reported. In order to detect it, keep the upper part of the tube as cool as possi- ble during the first part of the heating, so as to cause it to condense. It may be present in the substance as water of constitution, as in FeO 3 H 3 and Na 2 HPO 4 ; as water of crys- tallization, as in MgSO 4 .7H 2 O; as hygroscopic moisture on the surface ; and as water mechanically enclosed within the crystals. Speaking generally, the temperature required for the expulsion of water is lower in the order named. ANALYSIS IN THE DRY WAY. 67 4. The sublimates which may be obtained and the corre- sponding indications are : Black, accompanied by a garlic odor . . Black, forming minute globules when rubbed Black, becoming red when rubbed . . , Black, accompanied by violet vapors . . Reddish brown drops becoming / a yellow solid on cooling \ ' ' * As Hg or a compound of it. HgS. I. . . . S or a persulphide. Yellow S or As 2 S 3 . White, quite volatile , f An NH 4 salt, As 2 O 3 , HgCl, { HgCl 2 , or an organic acid. White, difficultly volatile Sb 2 O 3 . From all compounds of NH 4 , Hg, and As (except As 2 O 5 , arsenites, and arseniates) these components volatilize read- ily and completely. Therefore, if the substance containing them was for the most part insoluble, and was decomposed by fusion, they might escape detection altogether, if the closed tube test were omitted. 5. The gases that may be evolved and the compounds that they indicate are shown in the following table : Gas: Known by: Indicates : 2 N0 2 SO 2 NH 3 H 2 S CO CO 2 C1 2 ; Br 2 ; I 2 Inflaming a glowing splinter. Its odor, and brownish-red J color. ) Its odor. Its odor. ( Its odor and by blackening f } lead acetate paper. J Burning with a blue flame. ( Causing turbidity in a drop ) ] of BaO 2 H 2 . J Their odor and color. A chlorate, peroxide, or al- kali nitrate. A nitrate or nitrite. A sulphate, sulphite, or sul- ( phide. \ An ammonium salt, a cyan- ) ide or nitrogenous organic > matter. ) A moist sulphide. An oxalate. A carbonate, oxalate, or or- ) ganic matter. I A chloride, bromide, or iodide ANALYSIS IN THE DRY WAY. 6. The substance may undergo a change of color. Some of the indications are as follows : Original color : Color while hot: Color after cooling : Indication : White. Yellow. White. Zn. White. Yellow. Pale yellow. Sn. White or yellow. Brownish red. Deep yellow. Pb. White or yellow. Brownish red. Pale yellow. Bi. Yellow or brown. Black. Brownish red. Fe. Yellow or red. Green. Green. A chr ornate. Pink, green, or blue. Black. Black. Co, Ni, Cu. 7. If the substance fuses without volatilization or expulsion of aqueous vapors, or if it remains in a state of fusion after vola- tile matters have been expelled, it is probably a compound of an alkali metal. In that case try the color imparted by it to the flame. Procedure. Heat some of the dry powder in a small cavity on a piece of charcoal before the reducing flame of the blowpipe. Observe the odor evolved and the nature of the incrustation and of the residue in the cavity. JV0tes. i. The metals reduced to the metallic state and forming globules are Pb, Ag, Bi, Sb, Cu, and Sn. Bi and Sb are distinguished by their brittleness from the others ; Cu is known by its red color. (Au forms a yellow globule.) 2. The characteristic incrustations formed are the following : White, very volatile, at a distance from the cavity : As. White, volatile with some difficulty : Sb. Yellow when hot, white when cold : Zn and Sn. Yellow both hot and cold : Pb and Bi. Reddish brown : Cd. Dark red : Ag. 3. The evolution of a garlic odor indicates As, and of SO 2 , a sulphide. If the substance deflagrates, it is probably a chlorate or nitrate. ANALYSIS IN THE DRY WAY. 69 Procedure. Make a clear bead by fusing some NaPO 3 or (NH 4 )NaHPO 4 on the loop of a platinum wire, add to it a little of the substance to be tested, and heat it in the oxidizing flame of a Bunsen burner. Observe the color of the bead when both hot and cold. Then heat it in the reducing flame. Notes. i. The color imparted to the bead depends in many cases on whether it is heated in the oxidizing or re- ducing flame. To obtain an oxidizing action, heat the bead in the edge or at the top of the non-luminous flame of the Bunsen burner. To get a reducing action, cut off the supply of air to the burner enough to produce a small luminous cone in the interior of the flame, and heat the bead in this cone. 2. The following are the characteristic colorations which the cold bead may exhibit : Blue in both flames : Co. Green and in both flames : Cr. Greenish blue in the oxidizing, red and opaque in the reducing flame : Cu. Amethyst red in oxi- dizing, colorless in the reducing flame : Mn. Brownish red in the oxidizing flame while hot, yellow or colorless when cold : Fe or Ni. Enamel-white after cooling : Ba or Sr ; but many other metals produce this same effect, when a consider- able amount of the substance containing them is added to the bead. 3. One of the most important indications of the bead test is in regard to silicic acid. If this substance is pres- ent, it floats about undissolved in the melted bead as a semi- transparent skeleton. This distinguishes it from all metallic oxides. 4. By the action of heat NH 4 NaHPO 4 changes to NaPO 3 , sodium metaphosphate ; and it is far more convenient in practice to make the beads directly with the latter substance, which can be prepared from the former in quantity by igni tion. The colors imparted by different metals are due to the formation of double orthophosphates ; for example, MnNaPO 4 , CoNaPO 4 , etc. 5. Borax, Na 2 B 4 O 7 , is sometimes used in place of NaPO 3 . The colors produced are the same in most cases, but not in all. It is, however, in general less suitable than NaPO 8 ; for it does not show satisfactorily the silicic acid reaction. 7 o ANALYSIS IN THE DRY WAY. Procedure. Add a few drops of strong H 2 SO 4 to some of the finely powdered substance placed in a very small test- tube, and heat gently enough to cause volatilization of the H 2 SO 4 . Note. For the indications furnished by this test, see the notes on page 54. It is valuable especially as a means of detecting certain Volatile acids which may not be shown by the closed-tube test. Procedure. Introduce on the loop of a clean platinum wire a little of the substance moistened with H 2 SO 4 into the outer edge of the lower part of the Bunsen flame. As soon as the coloration has nearly ceased, moisten the sub- stance on the wire with HC1, and again introduce it into the flame. Observe the flame closely and continuously until the substance is burnt off. If it is colored yellow, look at it through a thick piece of blue cobalt glass. [Examine the flame by means of a spectroscope, and com- pare the spectrum as to the position of its lines with the spectra produced by pure compounds of the elements sus- pected to be present.] Notes. i. The characteristic flame colorations are as follows : Yellow: Na. Red : Ca, Sr, (Li). Violet : K, (Rb, Cs). Green : Ba, Cu, H 3 BO 3 , (Tl). 2. By proceeding as here directed elements may often be detected even in the presence of one another by their flame colorations ; for the alkali metals first volatilize, leaving be- hind the alkaline-earth sulphates, which can then be detected by moistening with HC1, since their chlorides are much more volatile than their sulphates. ' Moreover, the use of blue glass makes it possible to detect potassium in the presence of so- dium, for the yellow light caused by the latter metal is thus completely absorbed. It should always be proved, however, by testing with a pure sodium salt, that the blue glass is of sufficient thickness to cut off the sodium light completely. ANALYSIS JN THE DRY WAY. y x 3. The spectroscope is a valuable aid in qualitative an- alysis as a means of detecting elements present in such minute quantities that they are not revealed by the ordi- nary methods, especially in testing the purity of a sub- stance, in examining mineral waters, or any other material of which only a small amount is available, in detecting the rarer elements in minerals, etc. It may also, in special cases, be used with advantage as a substitute for the far more lengthy wet processes ; for example, in the analysis of the alkaline-earth group, or of the group of rare earthy metals : it is not, however, usually a satisfactory substitute for these ; for a good qualitative analysis should not only establish the presence or absence of the elements, but also determine roughly the relative proportions of those present, a thing which spectrum analysis (in its ordinary form) en- tirely fails to do. The elements, which give the most char- acteristic spectra when heated in the flame are Na, K, Li, Rb, Cs, Ba, Sr, Ca, Tl, In. PREPARATION OF THE SOLUTION. I. FOR THE ANALYSIS FOR METALS. Non-Metallic Substances. Procedure. Place about one gram of the finely powdered substance in a test tube, add considerable water, and heat to boiling. If the substance dissolves completely, test the, solution with litmus paper, and use it for the analysis for metals. If in doubt whether anything dissolves, filter a little of the liquid, and cautiously evaporate three or four drops to dryness on a small watch glass. If partial solution takes place, allow the substance to settle out, decant, and boil the residue with a fresh portion of water. If the sub- stance does not now dissolve, add to the water a few drops of HC1, and heat, noting carefully whether effervescence or evolution of any odor occurs ; if necessary, add, little by little, more HC1. In case dilute HC1 does not effect solu- tion, rinse the residue into a porcelain dish, decant the liquid, and boil for some time with strong HC1. If this does not suffice, add one third the volume of strong HNO 3 , and heat again. A residue remaining after continued action of aqua regia must be fused with Na^Og. Mix together the various liquids by which any of the substance has been dis- solved. If only dilute HC1 has had to be used, dilute the solution and pass in H 2 S directly. If much strong HC1 or any HNO 3 was necessary, evaporate the solution just to dryness, moisten the residue with a few drops of HC1, add considerable water, heat, and pass in H 2 S. For modifica- tions of this procedure in certain special cases, see the fol- lowing notes 4, 5, and 6. FOR THE ANALYSIS FOR METALS. 73 i. An acid reaction of the aqueous solution may be due to free acids, acid salts of strong acids, or to neutral salts of most metals of the H 2 S and (NH 4 ) 2 S groups. An alka- line reaction shows the presence of a soluble hydrate, carbon- ate, sulphide, phosphate, borate, or cyanide. It is to be noted that the terms "acid salt" and "neutral salt" refer only to the extent of the replacement of the hydrogen of the acid by the metal, and do not show the reaction towards litmus or other indicators. The latter depends on the relative strength of the acid and base. Examples : Na 2 CO 3 , Na 2 S, and even the acid salts, NaHCO 3 , Na 2 HPO 4 , react alkaline. ZaSQ*, CuCl 2 , etc., react acid. 2. It is desirable to use as little HC1 as possible in dis- solving the substance, since otherwise it is necessary to evap- orate the solution before passing in H 2 S. 3. HC1 may cause evolution of CO 2 , H 2 S, SO 2 , HCN, or Cl (from chlorates, chromates, or peroxides), thus indicating the nature of the acid present. 4. HC1 may also cause separation of gelatinous silicic acid. When this occurs, and even when it does not, if the sub- stance is a mineral or metallurgical product liable to contain silicate, the solution should be evaporated to dryness, and the residue ignited at 125 in the hot closet for at least an hour; the mass should then be dissolved in a little HC1, water added, the solution filtered, and the analysis proceeded with. This is done to remove the silicic acid, which in the hydrated condition dissolves to a considerable extent in acid, but which is dehydrated and made insoluble by ignition. This could, of course, be accomplished by direct ignition over the lamp ; but it is then very difficult to get A1 2 O 3 and Fe 2 O 3 again into solution. If the silicic acid is not removed, it precipitates on the addition of NH 4 OH, and may be mistaken for A1O 3 H 3 . 5. In case the preliminary examination indicates the pres- ence of lead or silver, treat the substance first with HNO S instead of with HC1; then decant and use aqua regia if neces- sary. Or if in any case HC1 has been tried, and has been found to leave a white residue resembling PbCl 2 or AgCl, treat a fresh portion of the substance with HNO 3 . 6. If the preliminary examination shows the presence of organic matter, this must be destroyed before proceeding, 74 PREPARATION OF THE SOLUTION since it interferes with the various tests, particularly with the precipitation of the trivalent metals by NH 4 OH. The methods used for destroying it vary with the nature of the substance, and directions cannot be given to cover every case. a. If the proportion of mineral matter is large, ignite the substance at a low temperature in a porcelain crucible till fully charred ; cool 1 , moisten with HNO 3 , and ignite again carefully at first, and then strongly. Repeat the addition of HNO 3 and ignition till the carbon is consumed. Boil the residue with a small quantity of strong HC1, dilute, filter, and proceed with the analysis as usual. This method is appli- cable, for example, to baking powders, which it is often neces- sary to test for Al. Mercury, ammonium, arsenious and anti- monious compounds are volatilized. b. If the substance is mostly organic, heat it in a porcelain dish on the steam bath for ten or fifteen minutes with a mix- ture of about equal parts of strong H 2 SO 4 and HNO 3 , then heat over a lamp till white fumes of H 2 SO 4 escape ; cool, add HNO 3 and heat again repeat this process till the H 2 SO 4 becomes light colored. Dilute with water, boil to expel SO 2 and filter. This method is suitable for destroying paper, fab- rics, foods, etc. The H 2 SO 4 solution so obtained may be put directly into a hydrogen generator and tested for As and Sb (page 25) ; for As and Sb in the higher form of oxidation, to which they are converted by the HNO 3 , are not volatile. In using this method bear in mind the insolubility of the sulphates of Ba, Sr, Ca, and Pb. c. If the substance contains oily or fatty matter, extract this by treating the substance two or three times with ether, and use the residue for analysis. Paints in oil, for example, are conveniently treated in this way. 7. If sulphides are present, and HNO 3 or aqua regia is used for dissolving, sulphur separates in the form of a light spongy mass, often black at first owing to inclosed matter, but becom- ing yellow on continued boiling. It may be tested by heating on porcelain when it burns with a blue flame and odor of SO 2 . 8. When strong acids have been used for dissolving the substance, on evaporating these a white residue insoluble in dilute HC1 is sometimes obtained. This may be SiO 2 , PbSO 4 , CaSO 4 , CaF 2 , or H 2 SnO 3 . If there is reason to think it may be PbSO 4 , treat it with (NH 4 )C 2 H 3 O 2 solution. (See FOR THE ANALYSIS FOR METALS. 75 note 2, filter, add (NH 4 ) 2 S to the filtrate, filter if a precipitate forms, wash, dissolve the precipitate in hot dilute HNO 3 , dilute and add HC1. AgCl is dissolved by KCN, and the Ag is pre- cipitated from that solution by (NH 4 ) 2 S. Do not attempt ta reprecipitate the AgCl by addition of acids to the KCN solu- tion ; for HCN gas, which is exceedingly poisonous, would be evolved. e. If the residue seems to be nothing but SiO 2 , treat it in a platinum crucible with a few cc. of HF, evaporate off the acid and note whether anything remains; if there is still a residue, try to dissolve it in HC1. In using HF, take great care not to get it on the hands nor to inhale the gas. 3. Fusion with Na 2 CO 3 decomposes most substances, and is especially useful analytically as a means of bringing insol- uble substances into a soluble form. A metathesis takes place ; the acid radical of the compound combines with the sodium, and a carbonate of the metal is formed ; or, if the carbonate is decomposed by heat, the oxide or the metal itself is obtained. The following are some examples : BaSO 4 -f Na 2 CO 3 = Na 2 SO 4 + BaCO 3 . Al 2 Si0 5 + Na 2 C0 3 = Na 2 Si0 3 + A1 2 O 3 + CO 2 . 4AgCl -f 2Na 2 CO 3 = 4NaCl + 4Ag + 2CO 2 + O 2 . The acid element or radical of the original compound is- therefore found in the aqueous, and the metallic element in the acid solution of the fusion. 4. In case a substance is dissolved only partially by acids, it may seem simpler to fuse the original substance with Na 2 CO 3 rather than the insoluble residue. This is, however, generally not the case ; first, because some substances, especially me- tallic sulphides and alkaline-earth phosphates, though readily soluble in acids, are only slightly decomposed by Na 2 CO 3 ;. secondly, because complete decomposition with Na 2 CO 3 is at best often difficult to attain, and therefore the amount of sub- stance treated should be as small as practicable ; and thirdly, because volatile metals, especially mercury, would be lost. 5. It is preferable to use platinum where admissible, for two reasons : First, it is much easier to obtain the requisite 7 8 PREPARATION OF THE SOLUTION , high 'temperature ; and secondly, Na 2 CO 3 attacks porcelain, so that subsequent tests for aluminum and silica are unreliable. Platinum vessels cannot be used, however, when readily re- ducible metals (Pb, Ag, Cu, Hg, As, Sb, Bi, Sn), sulphides, or phosphates together with organic matter, are present, as they would then be spoiled through the formation of fusible alloys. Alkali hydrates and nitrates in the fused condition, and any solution evolving chlorine, as aqua regia, also attack them. 6. The first and third reactions of note 3 are examples of cases where the aqueous and acid solutions must not be mixed. The second reaction, a type of case very commonly occurring, admits of it, however. The advantage of adding some of the aqueous solution to that used for the analysis for metals is that certain metals, those whose oxides are sol- uble in excess of alkali, may pass into the aqueous solution as sodium salts. 7. If the residue insoluble in acids contains stannic oxide, calcium fluoride, alumina, ferric oxide, or chromic iron, these substances would be little affected by fusion with Na 2 CO 3 , and would be found still insoluble in acids. Therefore, when the preliminary examination indicates the presence of any of these, it is better to make use of other fluxes than Na. 2 CO 8 . The choice depends on the considerations set forth in the follow- ing note. 8. Fluxes. Four kinds of fluxes may be distinguished : i. Alkaline fluxes, such as Na 2 CO 3 , which are suited for the de- composition of most salts, and especially of silicates. 2. Acid fluxes, especially KHSO 4 , which is used for the conversion of basic oxides (A1 2 O 3 and aluminates, Fe 2 O 3 , Cr 2 O 3 , etc.) into sol- uble sulphates. The silica of a silicate is lEereby separated in insoluble form. In using this flux take care not to con- tinue the heating till the sulphuric acid ceases to come off ; for insoluble basic sulphates then result. 3. Oxidizing fluxes, for example mixtures of Na 2 CO 3 with NaNO 3 or KC1O 3 , which serve to convert compounds of acid forming metals (like Cr, As) into soluble salts of their acids. Insoluble native sul- phides are also best treated in this way. 4. Reducing fluxes, for example a mixture of Na 2 CO 3 and KCN, which are some- times useful in separating reducible metals from their oxides, FOR THE ANALYSIS FOR METALS. 79 as Sn from native SnO 2 . Chromic iron is decomposed by fusing first with KHSO 4 , and then treating the undecomposed residue with Na 2 CO 3 and NaNO 3 . Procedure. To test for alkali metals in a silicate not acted on by acids, decompose the mineral without the use of alkaline carbonates as follows : Mix one part of the very finely powdered substance with six parts of pure CaCO 3 and one part of NH 4 C1, and heat the mixture to bright redness in a covered platinum crucible for half an hour, taking care to heat only the bottom of the crucible. Heat the sintered mass with water for half an hour, filter, add to the filtrate a little NH 4 OH, and (NH 4 ) 2 CO 3 in slight excess; heat to boiling, filter, and remove ammonium salts from the filtrate and test for K and Na as directed on page 48. Notes. i. Alkali silicates, though soluble in water when alone present, are often not dissolved out of double silicntes even by acids. Hence the need of a special test as above described. 2. CaCO 3 decomposes the silicate in the same way as Na 2 CO 3 . The NH 4 C1 serves to convert the alkali metals to chlorides. The aqueous extract obtained contains the hydrates and chlorides of Ca, K, and Na. The (NH 4 ) 2 CO 3 is added to precipitate the Ca. 3. If the whole crucible is heated to bright redness the alkali chlorides are lost by volatilization. The heat used should be sufficient to make the mixture sinter, but not fuse. Metals and Alloys. Procedure. Cut the alloy into small pieces, or hammer it out so as to expose as great a surface as possible. Heat about one gram of it with 25 cc. of strong HNO 3 (1.2 spec, grav.) as long as any action continues. If metal protected from further action of the solvent by the products of the reaction still remains, pour off the acid, treat the residue with water, and then with a fresh portion of strong HNO 3 . go PREPARATION OF THE SOLUTION If complete solution takes place, dilute with water and add HCL If a precipitate (PbCl 2 or AgCl) forms, filter it off and examine it in the usual manner for Pb and Ag. Evaporate the filtrate, or the solution in which HC1 pro- duces no precipitate, to dryness ; moisten the residue with HC1, and evaporate once again just to dryness to expel the HNOo. Dissolve the residue in water with addition of a o little HC1, pass in H 2 S, and proceed with the analysis as usual, except that the (NH 4 ) 2 S X treatment of the H 2 S pre- cipitate may be omitted. (See note 2.) If a white residue remains, dilute the HNO 3 solution with water, filter, and treat the filtrate as directed in the last para- graph. Wash the residue with hot water till free from acid, transfer it to a porcelain dish, and heat it with a consider- able quantity of (NH 4 ) 2 S X . The white residue should entirely dissolve ; if a small black residue consisting of sulphides of metals of the copper group remains, filter it off. Test this (NH 4 ) 2 S X solution for As, Sb, and Sn in the usual manner. In case the white residue left by the HNO 3 is large, and it is found to be very difficult to get it into solution in (NH 4 ) 2 S X , treat a fresh portion of the alloy with aqua regia, and pro- ceed with this solution as with the HNO 3 solution, except that the separation with (NH 4 ) 2 S X and the analysis of the tin group must in this case be carried out. Notes. i. The nitrates formed in dissolving the alloy, though readily soluble in water, are very little soluble in HNO 3 ; they may therefore precipitate on the surface of the metal, and prevent further action of the acid. 2. If the alloy is completely soluble in HNO 3 , Sn is absent and not more than a trace of Sb can be present. It is then unnecessary .to treat the H 2 S precipitate with (NH 4 ) 2 S X ; foi of the metals of the tin group only As and a trace of Sb can be present, and these are best detected by placing some of the solution from which the HNO 3 has been removed by evap- oration in a generator with zinc and HC1. If present, Sb and Sn are oxidized by HNO 3 to the white compounds, meta- stannic acid (H 2 SnO 3 ) and antimony oxide (Sb 2 O 3 , Sb 2 O 4 , or FOR THE ANALYSIS FOR ACIDS. 81 Sb 8 O 5 , according to the strength of the acid and temperature). Traces of the latter dissolve in HNO 3 . 3. If the alloy contains at the same time P or As, these elements are also found in the white residue in the form of Sii 3 (PO 4 )4 and Sn 3 (AsO 4 ) 4 respectively. 4. In order to detect P in an alloy completely soluble in HNO 3 , it is only necessary to add some of the solution to an excess of (NH 4 ) 2 MoO 4 . To detect it in the white residue, acidify some of the (NH 4 ) 3 S X solution of the latter with HNO 3 , filter out the precipitate, and add the filtrate to an excess of (NH 4 ) 2 MoO 4 solution. 5. In the analysis of an alloy all the operations serving for the detection or removal of Cr, Ba, Sr, and Ca are omitted, since these metals are never present. Moreover, K and Na need be tested for only when the alloy decomposes hot water. 6. A black residue consisting of C or Si may remain on treating the alloy with HNO 3 . C is found principally in alloys containing Fe, and Si in the newer alloys of Al. 7. An insoluble residue may also consist of the rare metals Au and Pt. They dissolve in aqua regia. 2. FOR THE ANALYSIS FOR ACIDS. Salts and Industrial Products. Procedure. If the substance is soluble in water, and only alkaline-earth and alkali metals are present, dissolve about one gram, and use this aqueous solution for the various tests ; if, however, other metals are present, add Na^Og to the solution as long as a precipitate continues to form. If the substance is insoluble and metals not precipitated by H 2 S are present, boil a gram of the finely powdered substance with 10 cc. of strong Na 2 CO 3 solution for ten or fifteen minutes, replacing the water which evaporates. Filter off the precipitate or residue, and make half of the filtrate slightly acid with HNO 3 . (If a precipitate forms when the solution is neutral, filter it off.) Boil this solution for two or three minutes to expel the CO 2 , and use it for the BaCl 2 and AgNOg tests, and for those special tests which may. be made in the presence of free HNO 3 . Acidify fresh portions 82 PREPARATION OF THE SOLUTION of the Na 2 CO 3 solution with HC 2 H 3 O 2 for the oxalic (and tartaric) acid test, and with H 2 SO 4 for the nitric acid test. If the substance is insoluble, and only metals precipitated by H 2 S are present, suspend a gram of the finely powdered sub- stance in water, saturate with H 2 S, heat to boiling, and filter ; boil the filtrate till the H 2 S is completely expelled, and use it for the BaCl 2 and AgNO 3 tests and for the various special tests. If not already detected or proved absent, test the original substance for H 2 S and H 2 CO 3 . Notes. i. All metals except arsenic and the alkalies are precipitated from solution by Na 2 CO 3 in the form either of carbonate, basic carbonate, or hydrate. Boiling with Na 2 COs decomposes almost all salts more or less completely, the acid radical going into solution in combination with sodium, and the metal being precipitated as carbonate or hydrate. Many of these carbonates and hydrates dissolve somewhat in the excess of Na 2 CO 3 employed, and they are then precipitated when the alkali is nearly neutralized. 2. The removal of the metals by Na 2 CO 3 is necessary ; foi otherwise the solution cannot be made alkaline, for example with NH 4 OH, without the production of a precipitate ; more- over, their presence interferes in other ways with some of the special tests. 3. The Na 2 CO 3 must be completely neutralized and the CO 2 expelled before testing with BaCl 2 and AgNO 3 ; other- wise BaCO 3 and Ag 2 CO 3 will precipitate. 4. The removal of the metals with H 2 S where possible has the advantages that it is more complete than that with Na 2 CO a , and that no additional salts or acids are introduced into the solution. In the presence of chlorates it is inapplicable ; for the H 2 S is then oxidized, and the tests for HC1O 3 , HC1, and H 2 SO 4 are valueless; in the presence of nitrate the test for H 2 SO 4 is unreliable. Minerals and Metallurgical Products. Procedure. Try the special tests for H 2 S and H 2 CO 3 with a portion of the finely powdered dry substance. Boil another portion with HNO 3 for two or three minutes, ;!iiute, FOR THE ANALYSIS FOR ACIDS. 83 filter if not entirely dissolved, and test the filtrate for H 3 PO 4 with (NH 4 ) 2 MoO 4 , and for HC1 with AgNO 3 . Test for H 2 SO 4 , if sulphides are absent, by adding BaCl 2 to some of the HNO 3 solution ; if the substance is not com- pletely soluble in HNO 3 , test also the aqueous solution obtained from the fusion of the insoluble residue in prepar- ing for the analysis for metals (page 76) by acidifying with HC1 and adding BaCl 2 . If sulphides are present, boil some of the original substance with strong Na^CC^ solution for some minutes, dilute, filter, acidify with HC1, and add BaCl 2 . The presence or absence of H 2 SiO 3 has been already determined in the preliminary examination by the NaPO 3 bead test, or in the course of the analysis for metals. Test for HF (with H 2 SO 4 ) and for H 3 BO 3 (with H 2 SO 4 and C 2 H 5 OH), if silicates are absent, with separate portions of the original substance. To test for these acids, if sili- cates are present, fuse at least a gram of the substance with four or five parts of Na 2 CO 3 , boil the fused mass with water, and filter. Slightly acidify a little of the filtrate with HC1, and test it for H 3 BO 3 with turmeric paper ; evaporate half of the remaining filtrate to dryness, and test for H 3 BO 3 with H 2 SO 4 and C 2 H 5 OH. Acidify the other half of the filtrate with HC 2 H 3 O 2 , allow it to stand, filter off the precipitate, add CaCl 2 , allow the liquid to stand, collect the precipitate on a filter, and test it in the usual manner for HF. Notes. i. Boiling with Na 2 CO fails to decompose many insoluble minerals, slags, etc. Moreover, it is necessary to test these substances for only a comparatively small number of acids; namely, for H 2 S, H 2 CO 3 , H 2 SiO 3 , H 2 SO 4 , H 3 PO 4 . H 3 BO 3 , HF, and HC1 ; for the other acids do not occur in them, or occur very rarely. For these reasons a different method of treatment has been given. 2. H 2 S and H 2 CO 3 , if present, are usually detected at the beginning of the analysis on treating the substance with acids. It is only for traces that it is sometimes necessary to test more carefully here. 3. Many phosphates are decomposed very incompletely by 84 PREPARATION OF THE SOLUTION. boiling, and even by fusing, with Na 2 CO 3 ; but they all dissolve without difficulty in HNO 3 , and are therefore best tested for in this solution. 4. All chlorides except AgCl can also be tested for in the HNO 3 solution. If Ag has been found among the metals, the solution obtained by boiling or fusing with Na 2 CO 3 must also be tested for HC1. 5. Sulphides are partially oxidized to sulphates both by boiling with HNO 3 and by fusing with Na 2 CO 3 . Therefore the substance is boiled with Na 2 CO 3 , or, if completely soluble, a HC1 solution of it may be prepared, in order to test for H 2 SO 4 in the presence of H 2 S. 6. In the presence of silicates the tests for H 3 BO 3 and HF, if made with the original substance, would be unreliable, because the mineral may not be decomposed by H 2 SO 4 ; and in the case of HF, also because this acid, if set free, may be entirely converted to SiF 4 by the silica of the mineral. 7. By fusing such a mineral, Na 2 SiO 3 , NaBO 2 , and NaF are obtained in solution. Silicic acid is precipitated on acid- ifying with HC 2 H 8 O 8 , and CaF 2 on the addition of CaCl s . .APPENDIX. PREPARATION OF REAGENTS. ACIDS. n Acetic : sp. gr. 1.044 ; m * x ne part of the glacial acid with 2^ parts of water. Aqua regia : mix i part HNO 3 with three parts of con- centrated HC1. Hydrochloric, concentrated : sp.gr. 1.12. Hydrochloric, dilute : mix one part of the concentrated acid with 4 parts of water. Hydrochloroplatinic : 100 grams H 2 PtCl 6 .6H 2 O to the liter, Hydrogen sulphide : saturated solution. Phenolsulphonic: dissolve 150 grams of phenol in 600 grams of concentrated H 2 SO 4 . Sulphuric, concentrated: sp. gr. 1.84. Sulphuric, dilute : mix i part of the concentrated acid with 4 parts of water. Sulphurous : saturated solution. rrtoo* AMMONIUM SALTS. Acetate : add 1000 cc. NH 4 OH (sp. gr. 0.90) to 1250 cc. glacial acetic acid. Carbonate : dissolve 250 grams in a liter of water and add 100 cc. NH 4 OH (sp. gr. 0.90.) Chloride : 100 grams to the liter. Hydroxide : sp. gr. 0.96 ; mix i part NH 4 OH (sp. gr. 0.90) with 2 parts water. Molybdate : mix 100 grams MoO 3 with 400 cc. cold dis- tilled water and add 80 cc. of ammonia (0.90 sp. gr.). Filter, and pour this solution with constant stirring into a mixture of 300 cc. HNO 3 (1.42 sp. gr.) and 700 cc. water. Oxalate : 40 grams (NH 4 ) 2 C 2 O 4 ,2H 2 O to the liter. Sulphide (colorless) : saturate 1500 cc. NH 4 OH (sp. gr. 0.90) with H 2 S ; then add 1000 cc. NH 4 OH (sp. gr. 0.90) and 2000 cc. of water. Persulphide (yellow) : add 50-75 grams of sulphur to col- orless (NH 4 ) 2 S. Sulphate 1250 grams to the liter. 86 APPENDIX. BARIUM SALTS. Chloride : 20 grams BaCI 2 .2H 2 O to the liter. Hydroxide : 50 grams BaO 2 H 2 .8H 2 O to the liter. CALCIUM chloride : 100 grams CaCl 2 .6H 2 O to the liter. FERRIC chloride : 100 grams FeCl 3 to the liter. FERROUS sulphate: dissolve 200 grams FeSO 4 .7H 2 O in a liter of water; place scraps of iron in the solution, and add a few drops of H 2 SO 4 from time to time. LEAD acetate : 100 grams Pb(C 2 H 3 O 2 )2.3H 2 O to the liter. MAGNESIUM ammonium chloride : dissolve 90 grams MgCl 2 .6H 2 O and 240 grams NH 4 C1 in a liter of water, and add 50 cc, NH 4 OH (sp. gr. 0.90) to the solution. MERCURIC chloride : 50 grams to the liter. POTASSIUM SALTS. Acetate : saturated solution. Chromate : 100 grams to the liter. Ferricyanide : 10 grams to the liter. Ferrocyanide : 15 grams to the liter. Nitrite: 500 grams to the liter. Sulphocyanate : 100 grams to the liter. SILVER SALTS. Nitrate : 25 grams to the liter. Sulphate : saturated solution. SODIUM SALTS. Acetate : saturated solution. Carbonate : 150 grams of the anhydrous salt to the liter. Hydroxide : 100 grams (Solvay) NaOH to the liter. Hypochlorite : add 500 grams of bleaching powder and 245 grams of anhydrous Na 2 CO 3 to 4000 cc. of water ; allow the precipitate to settle and decant the solution. Phosphate : 100 grams Na 2 HPO 4 .i2H 2 O to the liter. Sulphide : saturate a 10 per cent. NaOH solution with H 2 S, and dissolve 50 grams of sulphur in i liter of the solution. STANNOUS chloride : heat an excess of granulated tin with concen- trated HC1, adding scrap platinum to facilitate the solution. Dilute with an equal volume of water, and keep the solution in well-stoppered bottles containing metallic tin. INDEX. ACETATES, detection, 54, 63 solubility, 50 Acids, detection, 50 detection in salts, 81 detection in minerals, 82 division into groups, 51 general tests, 52, 53 Alkalies, precipitation of metals by, 2 3> 3' 43 Alkali-group, detection in silicates, 79 separation, 48 carbonates, occurrence, 32 carbonates, properties, 46 Alkaline-earth group, separation, 46 group separation from iron group, 3 r > 40 nitrate-s, properties, 46 sulphates, properties, 40 Alkaline solutions, precipitation by acid, 17 Alloys, analysis, 79 Aluminum, detection, 37, 42 Aluminum group, behavior with alka- lies, 30, 43 precipitation, 31 preliminary tests, 29 separation, 36, 38 separation fr<>m copper group, 17 Aluminum hydroxide, occurrence, 19, 22, 38 hvdroxide, properties, 30, 44, 48 phosphate, occurrence, 48 Ammonium, detection, 49, 67 magnesium arseniate, properties, 25, 56 magnesium phosphate, properties, 43, 48, 56 phosphomolybdate, properties, 55 platinichloride, properties, 48 salts, solubility, 50 salts, solvent action, 22, 31, 34, 46, 52, 64 Antimony, detection, 25, 67 hydride, properties, 26 oxide, occurrence, 21 oxychloride, occurrence, 17, 18 sulphide, properties, 18, 19 Arseniates and' arsenites distinguished, 26 solubility, 50 Arsenic, detection, 24, 25, 67, 68 detection in paper, fabrics, etc., 74 hydride, properties, 26 sulphide, properties, 18, 26 Arsenious sulphide, properties, 18, 19 BARIUM, detection, 40, 46, 69, 70 chloride, occurrence, 17 chromate, properties, 47, 52 Bismuth, detection, 22, 68 oxychloride, occurrence, i/, 18 oxychloride, properties, 22 sulphide, occurrence, 20 sulphide, properties, 18 Bivalent and trivalent metals sepa- rated, 41 Blowpipe reactions, 33, 68 Borates, detection, 56, 83 of alkaline earths, occurrence, 35 solubility, 50 Borax bead test, 69 Bromides, detection, 54, 58, 67 detection in presence of iodides, ^o solubility, 50 CADMIUM, detection, 22, 68 ferrocyanide, properties, 23 sulphide, properties, 18, 23 Calcium, detection, 40, 46, 70 tartrate, properties, 64 Carbonates, detection, 54, 57, 73 solubility, 50 Chlorates, as oxidizing agents, 18, 24, 29 decomposition by ignition, 62, 63, 68 detection, 54, 62, 67, 73 solubility, 50 Chlorides, detection, 54, 58, 67, 84 detection in presence of oth^r halogens, 60 solubility, 16, 17, 50 88 INDEX. Chromates, as oxidizing agents, 18, 29 detection, 55, 68, 73 Chromic iron, decomposition, 79 Chromium, detection, 42, 69 effect on iron-group separation, 35 hydroxide, properties, 30, 32, 37 oxychloride, properties, 61 Closed tube test, 66 Cobalt, detection. 33. 68, 69 hvdroxide, properties, 34 occurrence, 37, 43 sulphide, properties, 30, 33 Copper, detection, 22, 68, 09, 70 ferrocyanide, properties, 22 occurrence. 20 sulphide, properties, 18, 20 Copper-group, behavior with alkalies, 2 3 precipitation, 17 separation, 20 separation from other groups, 16, '9 sulphides, occurrence, 33 sulphides, properties, 20 Cyanides, detection, 54, 59, 67, 73 DRY analysis, 65 FERRIC and ferrous salts distinguished, 44 ferrocyanide, properties, 37 hydroxide, occurrence, 19, 22 hydroxide, properties, 30, 31 salts, as oxidizing agents, 18 Ferricyanides, detection, 59 Ferrocyan des, detection, 59 Ferrous sulphide, occurrence, 23, 33, ' 38, 43 properties, 30 Flame tests. 40, 48, 70 Fluorides, detection, 54, 57, 83 effect on iron-group separation, 35 Fluxes, properties, 78 Fusion, decomposition by, 77, 78 HALOGEN-ACID-GROUP, detection, 53 special tests, 58 Hydroxides, colors, 23, 30 solubility, 23, 30, 31, 43 IMPURITIES in reagents, 14 Incrustations on charcoal, 68 Insoluble substances, 74, 76 substances, treatment, 75, 76, 80 Iodides, detection, 54, 59, 67 solubility, 50 Iron (see also " ferric and ferrous ") detection, 37, 40, 68, 69 Iron-group, behavior with alkalies, 43 precipitation, 31 preliminary tests, 29 separation, 36, 38 separation from copper group, 17 sulphides, properties, 30, 32 L.EAD, detection, 17, 21, 68 chloride, properties, 16, 17 chromate, properties, 42, 55 sulphate, occurrence, 20, 23, 38 sulphate, properties, 18, 21 Litmus, significance of reaction with, 73 MAGNESIUM, detection, 43, 47 ammonium phosphate, properties, 43. 48, 56 hydroxide, properties, 31 removal, 48 Manganese, detection, 37, 43, 69 hydroxide, properties, 31 sulph de, properties, 30 Mercuric and mercurous salts distin- guished, 23 oxide, properties, 23 sulph'de, occurrence, 23, 67 sulphide, properties, 18, 20, 21, Mercurous chloride, properties, 17, 25, 27 oxide, properties, 23 Mercury, detection, 17, 21, 23, 67 Metals, division into groups, 15 reducible on charcoal, 68 removal from solutions, 48, 82 Metaphosphate bead test, 69 Minerals, detection of acids in, 82 solution for analysis, 72 NICKEL, detection, 33, 68, 69 hydroxide, properties, 34 occurrence, 37, 43 Nitrates, as oxidizing agents, 18, 29 decomposition by heating, 63 detection, 54, 61, 62, 63, 67, 68 Nitric-acid-group, properties, 52 special tests, 61 ORGANIC acids, special tests, 63 matter, detection, 51, 66 matter, removal, 74 matter, solvent action, 30 Oxalates, detection, 54, 56, 67 of alkaline earths, occurrence, 35 Oxidation and reduction, 27, 28 of ferrous salts, 28, 30 of sulphides, 18, 21, 32, 33 Oxidizing agents. 29 INDEX. PERMANGANATES, properties, 29, 44 Phosphates, detection, 54, 55, 83 effect on iron group separation, 35 of al kaline earths, occurrence,3O,34 solubility, 50 Phosphorous, detection in alloys, 81 Platinum, in alloys, 81 vessels, use of, 77 Potassium, detection, 48, 70 acid tartrate, properties, 50, 64 platinichloride, properties, 48 removal, 49 salts, solubility, 50, 64 Precipitation, directions for, 13 by water, 22 Preliminary examination, 65 REACTION towards litmus, 73 Reactions of oxidation, method of writing, 28 Reagents, preparation, 85 Reducing agents, 29 Reduction and oxidation, 27* 28 of ferric salts, 30 on charcoal, 68 SILICATES, detection, 54, 58 detection of alkalies in, 79 Silicic-acid, bead test, 69 occurrence, 17, 38, 73 removal, 73 solubility, 58 Silicon fluoride, properties, 57 Silver, detection, 17, 68 chloride, properties, 17, 6l, 77 iodide, properties, 61 salts, properties, 53 sulphide, properties, 18 Sodium, detection, 48, 70 chloride, occurrence, 17 platinichloride, properties, 49 salts, solubility, 50 Solubility, general statement of, 50 Solution of nonmetallic substances, 72 of metals and alloys, 79 for analysis for acids, 81, 82 Spectrum analysis, 49, 71 Stannic and stannous salts distin- guished, 27 oxide, occurrence, 21 sulphide, occurrence, 25 sulphide, properties, 18, 24 Strontium, detection, 40, 46, 69, 70 sulphate, properties, 47 Sublimates in closed tube, 67 Sulphates, detection, 52, 55, 83 solubility, 47, 50 Sulphides, as reducing agents, 18, 29, colors of, 18, 30 detection, 54, 60, 67, 68, 73 Sulphites, detection, 54, 67, 73 Sulphur, occurrence, i8,.i9, 31,36,44, 74 Sulphuric-acid group, detection, 52, 53 group, special test, 55 test for acids, 53 TARTRATES, detection, 54, 63 Thiosulphates, detection, 54 Tin (see also " stannic ") . detection, 25, 68 Tin-group, behavior with nitric acid, 80 precipitation, i" separation, 24 separation from copper group, 19 WASHING precipitates, directions for, 14 Water, precipitation by, 18, 22 detection, 66 ZINC, detection, 37, 43, 68 hydroxide, properties, 38 occurrence, 18, 36 sulphide, properties, 30 ' J.