A systematic analysis of the common anions

sophomore class of the National Central University,. Nanking, China,and have proved to be satisfactory. ALTHOUGH the progress of micro-analysis has f~...
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A SYSTEMATIC ANALYSIS of the COMMON ANIONS* TING-PING CHAO National Central University, Nanking, China

Based ufion the solubilities of their calcium, barium, nickel, and silver salts, twenty-six common anions are divided into fcve groups. Detailed procedures for the systematic separation and identification of the anions are suggested. Such pocedures have been adofited by the sophomore class of the National Central University, Nanking, Chine, and have proved to be satisfactory.

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are easily soluble but whose barium salts hardly dissolve in slightly alkaline solutions, namely, sulfite,g sulfate, and chromate. Group I11 contains those anions whose calcium and barium salts are easily soluble but whose nickel salts hardly dissolve in slightly alkaline solutions, namely, sulfide, cyanide, ferrocyanide, ferricyanide, and arsenite.1 Group IV contains those anions whose calcium, barium, and nickel salts are easily soluble but whose silver salts hardly dissolve in slightly alkaline solutions, namely, thiosulfate, thiocyanate, iodide, bromide, chloride, borate,$ silicate,$ arsenate,§ and arsenite. 5 Group V contains those anions whose calcium, barium, nickel, and silver salts are all soluble. This group may further be divided into two subdivisions. Subdivision A contains those anions which are detected from the filtrate of Group IV, namely, chlorate, hypochlorite, nitrite, borate,$ and acetate. Subdivision B contains those anions which are detected from some of the original sample, namely, nitrate, carbonate,! and

LTHOUGH the progress of micro-analysis has been so marked that the trend in modern analytical chemistry is toward the use of "spot tests" or "drop reactions" with separate portions of the sample, yet a systematic method of group precipitation is still useful, especially in cases where the quantity of sample available for analysis is small and the composition of the sample is entirely unknown. As the detection of anions is as important as that of cations, the group system in qualitative analysis should not be confined to cations. While a number of attempts have been made to systematize the analysis of anions (23, 25, 29, 30, 31, 32), the first successful one was that of Duschak and Sneed (12). However, in view of the L a L 1 " L C . y 2 fact that the common inibns such as silicate, acetate, arsenate, arsenite, oxalate, and tartrate are not inEXPERIMENTAL I . Procedure for the Analysis of Group I cluded in their system, their method leaves considerable T o the slightly alkaline solution of the unknown substance or room for improvement (Note 1). In order to improve prepared solution made in the usual manner, add a slight investigation the the method as far as possible, the excess of 2 N Ca(NO& solution until the precipitation is complete. was undertaken. Stir the mixture vigorously and let it stand for ten minuter, then Before the detailed procedures for the systematic filter (Nate 2). Reserve the filtrate for Group II-V, and treat analysis of anions were attempted, the solubilities of t h ~ ~ f ~ ~ ~ ~ c ~ , " ~ I ~ thoroughly, ~ ~ P i t a tthen e treat it with the calcium, barium, nickel, and silver salts of every HOAc and heat the mixture to boiling. The precipitate is theredivided into three phases, analyse each phase respectively as anion were carefully tested (2). ~~~~d upon the by follows. solubility tests, twenty-six common anions are divided p h s e : pass the liberated gas first through bromine water, and then through lime water. (A white precipitate forms into five groups. the lime water which may redissolve again and indicates the G~~~~ I contains those anions whose calcium salts in presence of carbonale.) (Note 3.) Acidify the bromine water with hardly dissolve in slightly alkaline S O ~ U ~ namely, ~ O ~ S , HCI and then add BaCI. solution, shake, and allow it t o stand. (The formation of a white precipitate indicates the presence of carb0nate.t . , sulfite, oxalate, fluoride, silicate. ~ h o s ~ h a t e . stdfite.) arsenate,f and tartrate. Solid g h r e : Wash the undissolved residue thoroughly ~. with Group I1 contains those anions whose calcium salts hol r a t & (Sotc 4). then divide it into two purrions. &..-&-..A"

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*Presented before the Third Annual Meeting of the Chinese Chemical Society a t Nanking, Kwangsi, China, August 12-15, 1935. t If N%COa has been used in preparing the solution, the detection of carbonate should be made on a portion of the original sample. $ Those anions marked by $ are precipitated only in concentrated solutions. 8 Those anions marked by Q may be detected a second time in the system, for they are not completely precipitated in the preceding groups.

( I ) Firit portion: I p i t t stron~ly~n a n~cltclerucihlc (Sote 5 ) . thpn fuw it with NaOlI. and dizest [he fused masswith water. ~ c i d i f vthe water extract with dilufe HNO.. then add a few dr&s of (Nil.)?hlnO, solution, and warm (if ncceasary). (If thc soiutmn turns yellow, thc presence of rtlicdle is indirstrd.) Cwl, add a few droos of hen7idine aretatr and a n cxcesr of solid Na0.4,. ..-.. (Deep blie coloration indicates the presence of silicate.) (11) Second portion: Dry it thoroughly, then pour 5 cc. of N HSO, onto it. (IIA) Filtrate: Catch it in a small beaker, and heat it almost to the boiling point; then add a little MnSO, solution, and a few drops of 0.1N KMnO, solution. (Decolorization of the KMnO, solution indicates the presence of omlolc.) ~~

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(IIB) Residue: Wash the residue from the H 8 0 4 treatment thoroughly, then dissolve it in concentrated HCI. Add to it a few drops of KMn04, then a slight excess of NaHSO. solution. To the resulting solution add zirconium purpurin reagent (Note 6 ) . (The pink color of the reagent turning yellow, rndicates the presence of jluoride.) (IIC) Liquid phase: To the resulting solution obtained in the HOAc treatment, add a slight excess of HlCsO4solution, filter, and reject the residue. Divide the filtrate into two unequal portions. (IICa) Smaller portion: Make alkaline with NaOH and add 5 cc. in excess. Then add three oer cent. HIOl and evaporate the n.irture until it isaltwst dry ( S o i c 7). Takc up wth r w u c r:+tci. add two or thrce drops of .V C.. Test the precipilatefor silicate by the same procedure as desc;ih;d in I (Note 9). To the filtrate add a slight excess of Mg(NO& reagent. Stir the mixture vigorously, and let it stand for ten minutes, then filter. (IICbi) Precipitate: Redissolve in HNOa, and divide the resultine solution into two nortions. ~

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solution of the precipitati.(Residue turning dark red, presence of arsenate.) Wash the residue thoroughly, dissolve it in HCI, then add CCL and KI. (Violet color in the CCL layer is a confirmation of the presence of arsenote.) (IICblii) Second portion: (a) If arsenate is absent. Add (NHAMaO, solution, warm, and let stand for a few minutes. ( A y&s. preripirare indicates the p~esencc4 pBosph!r, ( . I ) If arrc.n;xrr is i,rv.rnt. i:mporarc thr second portion of the s o h tion until ir is nlmujt drv. lakc uo mirh HCI. and saluratc i t with ~~~-~ HzS. Heat it to boiling and pass in H a s ;gain. Filter off the precipitate, and repeat the treatment with H d until no more precipitate forms. Then filter and evaporate the filtrate i m t t o drvn-as Take un with dilute HNO,. and test this solu~~~

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1 larner ort ti on, and resen-c the combined filtrates for Group 111-9

III. Procedure for the Analysis of Group 111 Tothe filtrate from Group 11, add aslight excess of 2 f i Ni(NO& solution, and let it stand for ten minutes with frequent shaking. Add some paper pulp, shake, then filter through a double filter. Reserve the filtrate for groups IV-V, and treat the precipitate as follows. Pour NH40H over the nickel precipitate in a casserole, stir vigorously, and then filter. (A) Precipitate: Treat with 5 cc. of dilute HCI and a little zmc. (I) Liberated gas: Test it immediately with a piece of filter ) ~ turns paper soaked with Ph(OA& solution. (If P ~ ( O A Cpaper hlack. the zOresence o f sulfide ir indimled.) (11) The mixture: F k e r off any residue and the excess of the un&d zinc. Pass H d into the filtrate. If no precipitate forms, warm the solution and pass H 8 into it again. (A yellow precipitate, indication of arsenits.) Filter, redissolve the precipitate in NHAOH.and then acidifv the resulting solution with HC1. ~

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(11~62)Fitrate: ~ c & y with HCI, and pass in H d . A yellow precipitate may he A%S.. Filter and redissolve the precipitate in NH40H, then acidify the resulting solution again with HCI. (Yellow precipitate, presence of arrenite.)

II. Procedures for thc Analysis of Group I1 Before the svstematic analvsis of Grouo 11. a ~reliminarvtest for the prese& of thiosulf&e (Note li) i4 &de as follows. Take a portion of the original or prepared solution, add Ca(NOd9, Ba(NOs)., and Ni(NO& solutions; let the mixture stand for ten mlnutes with frequent shaking, then filter, and eject the precipitate. T o the filtrate add AgNOs solution, a light-colored precipitate gradually turning yellow, brown, and finally hlack shows the presence of thiosulfate. (The preliminary test far thiosulfate may be omitted if sulfite has been found in Group I.) As to the procedure for the analysis of Group 11, two cases may arise. (a) Thiosulfate is absent, or sulfite has already been found in Group I. (b) Thiosulfite is present and sulfite bas not been found in Group I. (A) Case A: T o the filtrate from Group I add a slight excess of 2N Ba(NO& solution, and let it stand for ten minutes with frequent shaking. Add some paper pulp, shake, then filter through a double filter. Reserve the filtrate for Group III-V. and treat the precipitate as follows. Boil the barium precipitate with HCI. Three phases are thereby obtained. (I) Gaseous phase. Pass the liberated gas into same bromine water (Note 12). acidify the latter with HCI, and then add BaCL solution. (A white precipitate indicates the presence of sulfife.) (11) Solid phase. Wash the undissolved residue thoroughly with hot water until free from chloride. Transfer the residue to a test-tube, add Hg(NOs)* reagent, and warm gently (Note 13). (Residue turning yellow color, presence of sulfalc.) (111) Liouid ohase. If the resulting solution ohtained in the HCI tieatkent k yellow, chromate ma? be present this filtrate to about 2 cc., make it alkaline d t h acidify with HdO,. Cool, then add 2 cc. o of three ner cent. H,09. (Blue coloration in-the ether layer, ~~~~~

(B) Case B: Divide the filtrate from Group I into two unequal portions. Treat the larger portion as described in (A), and the smaller portion as follows. Acidify with HOAc and then make it alkaline with NKOH. Next add a slight excess of N SdNOI)? solution. boil. let stand

sofuiion. (~esidueturning blue, presence of f e w - or f k c y a -

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the mixture, repeatedly if'nece-ry; and gdd t6 the filtrate a freshly prepared FeSOd solution. (Dark blue precipitate, presence of ferriiyaiide.) (11) Filtrate: Acidify it with HNOI, filter, and eject the filtrate. Pour (HN&S repeatedly on the precipitate, and evaporate the resulting solution just to dryness. To the residue add 2 cc. of dilute HCI, and then 2 cc. of Fe(NOda solution. (Red coloration, presence of cyanide.)

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IV. Procedure for the Analysis of Group IV T o the filtrate from Group 111, add a slight excess of AgNOs solution. A light-colored precipitate gradually turning yellow. then brown, and finally black, presence of thiosulfate (Note 14). Shake the mixture vigorously, then filter. Reserve the filtrate for the sub-division A of Group V (Note 15), and treat the precipitate as follows. Treat the silver precipitate with HNOa, shake vigorously, then filter. (~ A l --Prerioitate: -~, ~ - - Divide it into two uneaual ~ o r t i o n s (I) ~mall&&tion: Treat it with a five ber cent. solution of N&$ boil, th'en filter, and eject the residue (6. 16). Acidify the filtrate with HNOI, add CCL and Fe (NOs)*sulution. and shske (Red rolnration in ~ the aoueous laver. Werence of thiocva~ . nole.) If the color of the aqueoud layer is br&n rather than red. and that of the CCL layer is violet, separate the CCI. and extract the aqueom znlurion wrcessivrly with fresh portions of CCL. Add murr Fe(SOa)aand now whether thc aqutuu. layrr is dccolorized. ( I f the aoucow laver ic srlll colored red, prereacr of ......\

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and powdered Kz%Os,and shake vkorously. (IIA) CC14layer: (Violet coloration, presence of iodide.)

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of'the ~ ~ c l a yise nro longer violet or slightly pink. Then to the ~ t e dHNO1; shake the mix-

ture vigorously, and a t the same time hold a fluorescein paper over it. (IIBa) CC14 layer: (Orange or yellow coloration. presnzce of bromide; fluorescein paper turning pink, further confirmation of bromide.) (Note 17.) If the result is inconclusive, warm the mixture gently and notice the color change again. (IIBb) Aqueous layer: Dilute it with water and boil it until bromine is completely expelled. Then add AgNOs solution. (White curdy precipitate, indication o j chloride.) Boil the mixture and stir it vigorously, then flter. Redissolve the precipitate in NH,OH, and then acidify it with HNOa. (White curdy precipitate, presence of chloride.) (B) Filtrate: May contain borate, silicate, arsenate, or arsenite. The detection of these anions a t this place is usually unnecessary. (Notes 18 and 19.)

cation of other anions if they are not separated a t their proper places in the system. The purpose of the present investigation is to make up this deficiency. When the present investigation was nearly finished, another similar scheme suggested by Dobbins and Ljung was published (11). But according to the author's experience, many points in Dobbin's and Ljung's paper are open to question. 2. Due to their tendency to form super-saturated solutions, the precipitation of CaCIH~Osand Caa(As0p)z is exceedingly slow. But it may be hastened by vigorously stimng the mixture. V . Procedzrre for the Analysis of Sub-dinision A of Group V 3. If the solution has been treated with NazCOa Divide the filtrate from group IV into two unequal portions. a t the outset, the detection of carbonate should, of (A) Smaller portion: Make a preliminary test for chlorate and hypochlorite by adding a few drops more of AgNOs and then course, be made from some of the original sample, and hence this ion is also classified in Subdivision B of (chloridefree) NaNOn solution. (White precipitate, presence of chlorate or hypochlorite.) Group V. (B) Larger portion: Add slight excess of NazC08solution and filter off the precipitate. Divide the filtrate into five portions The detection may be made if the preliminary test for chlorate or hypochlorite is positive, or holding a drop of dilute solution of NazCOs colored by divide into three portions if the preliminary test is negative. some phenolphthalein in the gas escaping from the (I) e r s t portion: Add HOAc slowly until the solution is acid, Brz-water tube. (Red color of the drop decolorized and hod to expel co2. Then add P ~ ( O A + solution, bail, and let it standfor fiveminutes. (Brown~reci~itate,presenceofh~po-by the escaping gas, 9resence of carbonate.) (13.) chlorite.) 4. The anions soluble in HOAc should be completely (11) Second portion: Dilute with water, add HNOa, NaAs0~. then A ~ N Osolution, ~ and filter off the precipitate. TO the removed from the residue by thorough washing; otherfiltrate add a.few drops, more of AgNOs, and then (chloride free) wise, phosphate, arsenate, and tartrate will interfere NaNO, solutron. (Wh~teprec~pltate,presence of chlorate.) acid with the identification of silicate. Arsenite and tarThird portion: Acidify it with HOAc, add solution, and then --naphthylamine solution. (Red coloration, trate will reduce permanganate. vescnce of nitrite.) (Note 20.) 5. Since the reaction of silicate may be hindered by (IV) Fourth portion: Evaporate i t just t o dryness, add a little concentrated HCI and evaporate t o drynessagain (Note 21). the Presence of tartrate (I4, Z4) ; if tartrate is present, Take up with 3 cc. of Na*COasolution, heat, and filter if necessary. it must be removed. On strong ignition, tartrate is To the filtrate add 8 cc. of concentrated HCI and then 8 cc. of ethyl alcohol. If any salt separates, allow i t to settle, and decant decomposed. 6. During the early period of the present investigathe supernatant solution into a test-tube. Add two drops of an alcoholic solution of tumeric, and let it stand for ten minutes. tion, Noyes' method (26) was employed to identify (Orange or red coloration, presence of borate.) (28.) (5).Fifth portion: Acidify it with dilute HSO, and evaporate fluoride. But when the amount Of fluoride present is untd it a almost dry. Washit intaa test-tube with a little water, less than 10 mg., that method is not very sensitive. add C&OH and concentrated Hd04. warmif necessary After repeated unsuccessful attempts to identify small not boil.) (Fruity odor of ethyl acetate, presence of acetate.) amounts of fluoride by various methods (7, 15, 34), it (Note 22.) was finally decided to use the zirconium purpurin VI. Procedurefor the Analysis cf Sub-diuision B of Group V method (19). 7. Since arsenite and ammonium radical give simi(I) After the interfering substances have been removed (Note 23). evaporate the solution to be tested to a small volume, cool, lar reactions as does tartrate (8), they must be removed then add 5 cc. of concentrated HzS04,and let it cool again. Hold rethe test-tube containing the mixture in a slanting position and beforehand. The treatment with H2°2 pour down the side 5 cc. of a freshly prepared FeSOa solution. move arseuite and the evaporation with an excess of (Formation of a brown ring a t the junction, prcrence of nitrate.) N ~ O Hremoves ammonium radical. (11) Treat someof theoriginalsolutionor the original solid with 8. The HzSi03 precipitate formed during neutralizadilute HCI, and pass the liberated gas into lime water. NO^^ 3.) (A white precipitate or turbidity, presence of carbonate; if the tion is colloidal in character and is easily overlooked; precipitate or turbidity redissolves again, confirmation of car- consequently, the formation of this precipitate should bonate.) (111) Afterany interferingsubstances have been removed ( ~ o t e be carefully observed. Some needle-like crystals may 24). add two or three drops of N Co(N0.). solution t o the solution separate at this stage, due to the formation of a double to be tested and enough NaOH to render the solution alkaline, Of ammonium Oxalate and ammonium acetate. then add 5 cc. more of NaOH. Heat the solution to boiling, and filter if the solution is cloudy. (Deep blue coloration, presence o j But these crystals dissolve easily in pure water and can tortrote.) be separated from the ,H2SiO3precipitate by washing with water. NOTES 9. As dried CaSiOs is partly soluble in hot HOAc, 1. Although the presence of silicate, arsenate, and the amount of CaSiOa dissolved varies with the arsenite, oxalate, or tartrate is usually already known experimental conditions, the detection of silicate or detected during the preparation of solution for the should be made from both the residue and the filtrate systematic analysis of cations, or in the precipitation of the HOAc treatment. of Cu and Sn groups, or before the analysis of A1 and 10. A reprecipitation is carried out to free the Fe groups, yet these anions interfere with the identifi- magnesium precipitate from any occluded oxidants

such as CrOl= or Fe(CN)SZ which otherwise interfere with the final test of arsenate. 11. In case thiosulfate is present in large quantity i t may be precipitated in Group I1 and the identification of sulfite by testing the liberated gas becomes open to question. In this case, a separation of these two ions has to be made (9). 12. Owing to the adsorption phenomenon, sulfite may be wholly precipitated as calcium salt, and consequently it is not always found in Group 11. When it has been found in Group I, a further detection of i t in Group I1 is unnecessary. 13. In view of the fact that most of the common anions are capable of undergoing oxidation and reduction and the oxidation-reduction reactions are generally promoted either by increasing the hydrogenion concentration or by increasing the temperature of the solution, the test-solution during the group separation was invariably made slightly alkaline and was in no case heated to boiling. Such experimental conditions, however, favor the formation of very small particles of the precipitates, especially in the case of barium sulfate. Consequently it is necessary to use paper pulp in filtering barium sulfate and from the residue on the filter paper, it is difficultto know whether BaS04 is present or not. For this reason, a confirmatory test with mercuric nitrate reagent (10) was found to be indispensable. 14. In case a large amount of light-colored precipitate renders the detection for thiosulfate inconclusive and a t the same time thiocyanate is known to be absent, the presence of thiosulfate can he identified by converting i t into sulfate by means of bromine water from a separate portion of the filtrate of Group 111. If thiocyanate is also present, a less sensitive test (by treating it with acid to liberate free sulfur) is the only resort. 15. If nitrite is present in the filtrate of Group IV, the latter will change to a black color on standing, owing to the reduction of AgNOa to metallic silver. In this case, the AgNOa must be removed a t once by treating the filtrate with an excess of Na&03 solution [as described in (V, B)]. 16. Although the detection of iodide by means of KlSz03is very delicate, yet, if a large amount of iodide is known to he present i t is preferable to use Fe(N0a)s or NaNOz as the oxidant. In this case, the treatment with NH40H and HOAc is unnecessary and the removal of iodide (before the identification of bromide) can he effected by boiling instead of continuous extraction with CC14. (The latter process is tedious, and it is also necessary to use a large quantity of CCL.) 17. In the identification of bromide the yellow color in the CCl4 layer should persist for at least three to

four minutes. A similar color due to an oxidationproduct of thiocyanate is easily decomposed within one minute by agitating the mixture (18). The trouble arising from the slowness of the oxidation and volatilization of the Brz as it is formed (22) can be overcome by the fluorescein paper test (17, 36). 18. Although silver borate scarcely dissolves in neutral or slightly alkaline solution and may be precipitated in Group IV, yet it hydrolyzes very easily with the formation of silver oxide and boric acid which goes into the filtrate of Group IV. For this reason, borate is not generally found in Group IV, hut in the Subdivision A of Group V. 19. The precipitation of CaSiOa, C ~ ~ ( A S OCa~)~, (ASO~)~, and Ni(AsO& is by no means complete. Small amounts of silicate, arsenate, and arsenite ions still remain in the solution and are usually further precipitated as silver salts in Group IV. However, enough quantities of CaSiOa and C a 3 ( A ~ 0have ~ ) ~ been precipitated in Group I and N ~ ( A S Oin ~ )Group ~ 111 so that positive results can be obtained in their proper places. 20. During the early period of this investigation, the thiourea test (27)was used to identify nitrite. But, when the amount of nitrite present is very small, the diazo reaction method (1) seems much better. However, in case nitrite is present in large quantity, a dark red precipitate instead of red coloration is always formed. 21. In case the conflicting substances such as nitrite, chlorate, or hypochlorite are absent, the evaporation with HC1 is unnecessary, since there is considerable loss of boric acid in evaporating acid solutions. 22. Although methods for identifying acetate are many (3,5,20,21, 33,35), none of them has proved to be satisfactory. As the ester formation test is simple, i t has been adopted in this procedure. 23. The following anions interfere with the identification of nitrate, and must first be removed: NO1-, B r I-, Fe(CN)k, Fe(CN)g, AsOz-, Cr0,-, and C103-. Nitrite can be destroyed by conversion into unstable ammonium nitrite (4) or by a diazo-reaction (I). Chlorate and chromate can be reduced by H2SOs. The removal of Fe(CN)$, Fe(CN)g, Asoz-, Br-, I-, and C1- can be effected by treating with AgsSO4. 24. Tartrate ion, when present in less than 10 mg. per 20 cc. of solution, cannot be precipitated by any of the group-reagents. For this reason, the detection of tartrate should be made from some of the original sample. Sulfide, arsenite, and ammonium radical interfere with the detection of tartrate. The removal of arsenite and ammonium radical has been described in Note 7. Sulfide can be removed by evaporation with an excess of HlS04.

LITERATURE CITED

(1) BLOM, Ber., 59, 121 (1926); C h m . Abstr., 1368 (1926). J. Chinese Chem. Soc., 4,433 (1936). (2) CHAO,

(3)

CURTMAN, BROGGI, AND FOURMAN, Chem. News, 120, 230 (1920).

(4) (5) (6) (7)

(8) (9j (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21)

CURTW AND LIEBOWITZ, ihid., 132, 293 (1926). AND HARRIS.I.Am. Chem. Soc., 39, 1315 (1917). CURTMAN AND HARRIS, ihid., 38, 2622 (1916). CURTMAN CURTMAN. "Qualitative chemical analysis," The Macmillan Co., New York City. 1931, p. 377. ibid.. D. 449. CURTMAN. iw.;b. 468. CURTMAN; DENmss, Bull. soc. chzm.. (4), 33.36 (1918). AND LJUNG.J. CHEMEDUC.,12, 586 (1935). DOBBINS AND SNEED, ibid., 8, 1177,1386 (1931). DUSCHAK Mikrochemie. 8, 131 (1930). FEEL AND KRUNMOLZ, Ber., 62B, 1138 (1929). FEIGLAND KRUMHOLZ, FISCHER.Z. ma1. Ckem., 104, 344 (1936). FREsENIUs. "Introduction to oualitative chemical analvsis." 17th ed.' F. Viewep und' Sohn. Braunschweip. .19Zi, p. 466. GANAssrNI, Boll. ckim. farm.. 43, 153 (1904). HEISIG,Ind. Eng. Chem.. Anal. Ed., 7, 248 (1935). KoLrHosa AND STWSBY,ihid., 7, 118 (1934). KRUGER AND TSCHIRCH, Bn., 6ZB, 2776 (1929). M C A L P ~ EAND SOULS."Qualitative chemical analysis," 2nd ed., D. Van Nostrand Co., New York City, 1933, p. 451.

(22) MCALPMEAND SOULE,ibid., p. 572. (23) MORGAN, "Qual Analysis," p. 275 (1924). (24) NIEUWENBURG AND DULFER,"A short manual of svstematic qualitative analysis," p. 41 (1933). (25) NOYES,"A course of instruction in qualitative chemical analysis of inorganic substances," 9th ed., The Macmillan Co.. New York Citv. 1927. D. 144. (26) NOYES,ibid., p. 157. (27) NOYES,ibid., p. 159. (28) NOYES.ibid.. O. 1fiO. (30) REEDY,"~lementary q&itative' anaiysis," McGraw-Hill Book Co., New York City, 1924, p. 90. (31) SCOTT,"Qualitative chemical analysis," 5th ed., p. 224

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SEARS,"A systematic qualitative chemical analysis." 2nd ed., John Wiley & Sons, Inc., New York City, 1926, p. 102. AND KLYACHRS, I. RUSS.Phyr. Chem. SHPITALSKII, KATZEN, Soc., 61, 1497 (1929); Chem. Abrtr., 24, 1317 (1930). STONE, J. CHEM.EDUC.,8,347 (1931). TSCHIRCH,Oeslerr. Chem.-Ztg., 34, 38 (1931): Ckem. Abdr., 25, 2665 (1931). TSENG.I. Chinese Chem. Soc., 3, 33 (1935).