46
ANALYTICAL CHEMISTRY
(13) Davis, M. M., and Schumann, P. J., J . Research Natl. Bur. Standards, 39, 221 (1947). (14) Dietsel, R., and Paul, R., Arch. Pharm., 273, 507 (1935). (15) Evans, R. N., and Davenport, J. E., IND.ENQ.CHEM.,ANAL. ED.,3, 82 (1931). (16) Ferreira, R. de C., J . Chem. Phys., 19, 794 (1951). (17) Folin, O., and Flanders, F. F., J . Am. Chem. Soc., 34,774 (1912). (18) Folin, O., and Flanders, F. F., J . Bid. Chem., 11, 257 (1912). (19) Folin, O., and Wentn-orth, A. H., Ibid., 7, 421 (1909-10). (20) Fritz, J. S.,ANAL.CHEX.,22, 578 (1950). (21) I M . , p. 1028. (22) Fritz, J. S., and Lisicki, N. RI., Ibid., 23, 589 (1951). J . Chem. Phys., 7, 93 (1939). (23) Gordy, W., (24) Hall, N. F., Chem. Rers., 8, 191 (1931). (25) Hall, N. F., and Conant, J. B., J . Am. Chem. Soc., 49, 3047 (1927). (26) Hall, N. F., and Werner, T. H., Ibid., 50, 2367 (1928). (27) Hammett, L. P., and Deyrup, A. J., Ibid., 54, 2721 (1932). (28) Hammett, L. P., and Dietz, N., Jr., Ibid., 52, 4795 (1930). (29) Hantssch, A., Ber., 60B, 1933 (1927). (30) Hantssch, A., Z . Elektrochem., 29, 221 (1923). Ber., 62B, 975 (1929). (31) Hantzsch, A., and Voight, W., (32) Herd, R. L., J . Am. P h a r m . Assoc., 31, 9 (1942). (33) Higuchi, T., and Concha, J., J . Am. P h a r m . Assoc., Sci. Ed., 40, 173 (1951). (34) Higuchi, T., and Concha, J., Science, 113, 210 (1951). (35) I n d . Eng. Chem.. 43, No. 8, 186 (1951). (36) Izmailov, N. A., Zhur. Fiz. K h i m . , 24, 321 (1950). (37) James, J. C., and Knox, J. G., Trans. Faraday Soc., 46, 254 (1950). (38) Jurecek, M., Chem. Listy, 44, 134 (1950). (39) Kahane, E., Bull. soc. chim. France, 18, 92 (19*51). (40) Kahlenberg, L., J. Phys. Chem., 6 , 1 (1902). (41) Khait, G. Ya., Farmatsiya, 8, 26 (1945). (42) Kolthoff, I. M., ANAL.CHEM.,21, 101 (1949). (43) Ibid., 22, 65 (1950). (44) Kolthoff, I. M., J . Phys. Chem., 48, 51 (1944). (45) Kolthoff, I. M., and Gauss, L. S.,J . Am. Chem. Soc., 60, 2516 11Q.181. \__--,.
(46) Ibid., 62. 249 (1940). (47) Kolthoff, I. hi., and Rosenblum, C., “Acid-Base Indicators,” New York. Macmillan Co., 1937. (48) Kolthoff, I. M., and Sandell, E. B., “Textbook of Quantitative Inorganic Analysis,” p. 518, New York, Riaemillan Co., 1937. (49) LahIer, V. K., and Downs, H. C., J . Am. Chem. Soc., 53, 888 (1931). (50) Lavine, T. F., and Toennies, G., Am. J . M e d . Sci., 185, 302 (1933).
(51) Lavine, T. F., and Toennies, G., J . B i d . Chem., 101, 727 (1933). (52) Lewis, G. N., “Valence and Structure of Atoms and Molecules,” New York, Chemical Catalog Co., 1923. (53) Lowry, T. M., Trans. Faraday Soc., 20,13 (1924). (54) Luder, W. F., Chem. Revs., 27, 547 (1940). (55) Luder, W.F., and Zuffanti, S., “Electronic Theory of Acids and Bases,” New York, John Wiley & Sons, 1946. (56) Markunas, P. C., and Riddick, J. A., ANAL. CHEM.,23, 337 (1951). (57) Moore, T. S., J . Chem. Soc., 1907, 1373, 1379. (58) Moss, M. L., Elliott, J. H., and Hall, R. T., ANAL.CHEM.,20, 784 (1948). (59) Nadeau, G. F., and Branchen, L. E., J . Am. Chem. Soc., 57,1336 (1935). (60) Palit, S. R., TSD. ENQ.CHEX.,ANAL.ED., 18, 246 (1946). (61) Palit, S.R., J . I n d i a n Chem. Soc., 19, 271 (1942). (62) Palit, S.R., Oil & Soap, 23, 72 (1946). Palit, S. R., and McBain, J. W.. I n d . Eng. Chem., 38, 741 (1946). Pauling, L., “Nature of the Chemical Bond,” 2nd ed., Ithaca, N. Y., Cornell University Press, 1940. Ralston, R. R., Fellows, C. H., and Wyatt, S. K., IND.ENG. CHEM.,ANAL.ED.,4, 109 (1932). Ruehle, A E., Ibid.. 10, 130 (1938). Seaman, W., and Allen, E., ANAL.CHEM.,23,592 (1951). Seltz, H., and McKinney, D. S., I n d . Eng. Chem., 20, 542 (1928). Selts, H., and Silverman, L., IND.Eso. CHEM.,ANAL.ED., 2, 1 (1930). Tomicek, O., Collection Csechoslov. Chem. C o m m u n s . , 13, 116 (1948). Trautner, E. RI.,and h‘eufeld, C. E., Australian Chem. I n s t . J . & Proc.. 13.70 (1946). Trautner, E. M.,and Shaw, F. H., Ibid., 12, 232, 405 (1945). Virasoro, E., aev. facultad Guim. ind. y agr. (Univ. nacl. litoral, Santa Fe, UVJ.), 19, No. 32, 102 (1950). Vorlander, D., Ber., 36, 1485 (1903). (75) Ibid., 67B, 145 (1934). Ibid., 66B, 1789 (76) Vorlander, D., Fischer, J., and Felicitas, W., (1933). (77) Wilson, H. N., J . SOC.Chem. Ind. (London), 67, 237 (1948). (78) Wittmann, G., Angew. Chem.. A60,330 (1948). and Hammett, L. P., J . Am. Chem. SOC.,57,2289 (79) Wooten, L. il., (1935) (80) Wooten, L. A., and Ruehle, A. E., IND.EX. CHEY.,A N A L .ED., 6, 449 (1934). I
I
RECEIVED Xorember 1, 1931.
AMPEROMETRIC TITRATIONS H. A. LAITINEN University of Illinois, Urbana, I l l .
F
ROM the number of papers that have appeared since the first review in 1949 (@), it is evident that the amperometric titration method is gaining momentum and is rapidly attaining maturity as a widely accepted analytical method. Several general and review papers have been published (3, IO, 23, S I , 32, 35, 40,59, 65, 80). APPARATUS AND METHODOLOGY
Delahay (14), Ringbom ( 6 7 ) ,and Gentry and KerTson (91) described circuits suitable for amperometry. Heyrovskj. (28) has suggested an oscillographic technique for end-point detection. Rius and Serrano (69) used a milliammeter with the dropping mercury electrode in the titration of solutions of relatively high concentration. Parks and Lykken (60) have described the adaptation of amperometric titrations t o operations on a reduced scale. Laitinen and Burdett ( 4 3 ) designed a cell with a shielded dropping electrode for the continuous passage of nitrogen during a titration. Berman, Saunders, and Winder (2) suggested a vibrating mercury electrode for polarographic measurements with
moving solutions, but did not apply it to amperometric titrations. Elofson and Mecherly (17) designed a special cell for use a t low temperatures. Vibrating platinum electrodes have been used by Harris and Lindsey ( 2 7 ) and by Rosenberg, Perrone, and Kirk (70). Vyakhirev ( 7 9 ) used lead electrodes for the titration of sulfate with lead. Tomicek, Blazek, and Roubal ( 7 7 ) performed amperometric titrations with bromine in glacial acetic acid. Lyalikov (50) titrated silver nitrate with potassium hydroxide in fused nitrate, using a platinum indicator electrode. Fused potassium nitratepotassium hydroxide mixtures proved superior t o fused potassium hydroxide as a reagent because of their less hygroscopic character. A technique somewhat related t o the amperometric and deadstop methods has been recently devised by Reilley, Cooke, and Furman (64), and named the derivative polarographic titration. The electromotive force necessary for the passage of a constant, predetermined current is measured. This quantity is related t o the slope of the current-voltage curve a t the zero current point. Ringbom (68) has devised a technique involving the use of “amperometric indicators.” A small amount of polarographi-
47
V O L U M E 24, NO. 1, J A N U A R Y 1 9 5 2 cally active substance is added t o serve as an indicator for titrations involving substances not yielding suitable polarographic waves. ION COMBINATION REACTIONS
The determination of sulfate in a zinc plating bath by titration with 1 N lead in the presence of ethyl alcohol t o decrease the solubility of lead sulfate has been described by Korshunov and Sazanova (41). Vasil’ev and Getsova (78) found acetone preferable over ethyl alcohol in the determination of sulfate in fluoride and d u m i n a t e solutions. Lead electrodes have been used by Vyakhirev ( 7 9 ) for the titration of solutions 0.1 X or more in sulfate ion with lead ion. I t was necessary t o wait 20 t o 30 seconds after each addition for a steady current. Lead ion has been used as a reagent for tungstate ion in 50% ethyl alcohol medium by Kalvoda and Zyka (SO). The same authors investigated the titration of thallium with iodide and with dichromate in acetone-water medium, and silver ion with thiocyanate, ferrocyanide, and nitroprusside. The titration of lead ion with dichromate, using a milliammeter switched in only a t the movement of measurement, was described by Rius and Serrano (69). The results were correct within &5%. The titration of phosphate with uranyl ion has been applied by Boos and Conn (4)t o the determination of total phosphorus in organic compounds. Ferrocyanide has been used by several investigators as a precipitating reagent for copper. Chovnyk and Klebs (11) recommended the use of a hydrochloric acid solution in the presence of 1.0 t o 1.5 ‘121 potassium salt t o approach the composition 5Cu2Fe(CS)6.K4Fe(CN)& I n the absence of alkali metal the precipit a t e was Cu2Fe(CS)G, but, the curves were irregular and poorly reducible. Riccoboni and Goldschmied (66) reported Cu2Fe( c s ) 6 as the product, but in the reverse titration obtained &Cu3[Fe(CS)6]2in neutral solution and the normal salt in the presence of acid or ammonium chloride. Kalvoda and Zyka (SO) titrated copper in 1 N acetic acid or 0.5 iV acetic-0.5 AVnitric acid. They found irregular behavior in the presence of potassium salts. Simer, Hamm, and Lee ( 5 7 )titrated zinc in 1.7 M ammonium acetate, and indium in 0.1 11 potassium chloride with potassium ferrocyanide, obtaining in both cases the normal salt, rather than the double potassium salts. Riccoboni and Goldschmied (66) found zinc t o give the normal salt in neutral or ammoniacal medium, but obtained E(~Znt[Fe(CN)612in acid solution. Butenko and Rynskaya (8) used a rotating platinum electrode t o titrate zinc with ferrocyanide. Best results were obtained in acid solution. Sodium or potassium salts led t o high results. Potassium ferricyanide was used as a precipitant by Chovnyk and Kuz’mina (12) who observed iSi3[Fe(CN)&a s the product in the titration of 0.01 kf nickel sulfate under various conditions of electrolyte. The sensitivity could be increased by use of the rotating platinum electrode. Zinc in hydrochloric acid or potassium chloride solution, and copper alone and in the presence of ferric iron (using fluoride as a complexing agent) likewise gave the normal ferricyanides. Liberti and D e Cesaris (48)described the titration of copper with thiocyanate in slightly acid or neutral solution, after reduction t o copper(1) with hydroxylamine. Fluoride was titrated with thorium ion by Luzina (49). Amounts of 0.005 t o 1 nig. of fluoride could be successfully determined. Aluminum, magnesium, arsenate, and phosphate interfered. Fluoride was titrated with 0.2 N lead nitrate in the presence of chloride t o precipitate lead chlorofluoride by Petrow and Kash (61). Cnder suitable conditions, as little as 0.5 nig. of fluoride could be determined t o a n accuracy of 0.5% or better. Fluoride has been used as a reagent by Ringhom and Wilkman, who used ferric chloride as a n “amperometric indicator” (68). Aluminum was titrated t o A1F3--- a t p H 2.5 t o 3.5. To determine magnesium, the sample was added t o a measured excess of
fluoride, giving MgFs-, after which an excess of aluminum was added, and titrated as above. Calcium was determined by precipitation as the fluoride. Ringbom and Wilkman (68) also determined calcium by titration with oxalate, using cadmium ion as the indicator ion. . The use of hexamminecobalt(II1) ion as a precipitant for ferrocyanide and pyrophosphate has been described by Laitinen and Burdett (44). The normal ferrocyanide \vas observed, but the ratio of cobalt t o pyrophosphate was 4 t o 3 only in the absence of sodium salts. In the presence of sodium ion, which is the recommended condition, the ratio was 1 t o 1, corresponding to the precipitate Co(h’H3)&aPIO7. The salt Co(i\TH3)6BrSOc proved t o be too soluble t o permit the titration of sulfate ion in the presence of an excess of bromide ion. OXIDATION-REDUCTION REACTIONS
The reaction beta-een ferrous iron and dichromate has been the subject of several recent papers. Kolthoff and Medalia ( 3 7 ) studied the titration of ferrous iron in 70 t o 80% acetone using the rotating platinum electrode a t a potential of $0.7 volt us. the saturated calomel electrode. While no constant diffusion current region was observed, the titration curves were satisfactory. Butenko and Bekleshova ( 6 ) determined manganese, chromium, and vanadium in steel by titration with ferrous sulfate after oxidation with persulfate t o determine the sumof manganese, chromium, and vanadium; after reoxidation with persulfate and destruction of the permanganate with chloride t o determine chromium and vanadium; and after permanganate oxidation and reduction of the excess with oxalate or nitrite t o determine vanadium. Grenberg and Genie ( 2 5 ) found this procedure t o give satisfactory results, using the rotating platinum electrode a t a potential of 1.0 volt. Parks and Agazzi (58),in a similar procedure, determined chromium and vanadium in steel and petroleum by oxidizing the chromium and vanadium with perchloric acid followed by permanganate. After determining the total chromium and vanadium, they reoxidized the vanadium with permanganate, destroyed the excess with sodium azide, and titrated again, using a rotating platinum electrode. The use of vanadium(I1) solution for the amperometric titration of ferric iron and of chromate ion in thiocyanate medium was mentioned by Meites ( 5 5 ) . Marks and Glass ( 5 1 )determined residual chlorine in water by titration with arsenite using a gold electrode. Total chlorine was determined by titration in the presence of iodide. I n the absence of iodide, only free chlorine was determined. Marks and Joiner ( 5 2 ) determined residual chlorine in sewage by treating the sample with a measured excess of phenylarsene oxide, followed immediately by potassium iodide. The unreacted phenylarsene oxide was titrated with iodine. Haller and Listek (26) determined various active chlorine compounds in n a t e r by amperonietric titrations. After the addition of sodium hydroxide, and adjustment of the p H t o 7 , an arsenite titration yielded the sum of chlorine and hypochlorite. .4 second portion made alkaline, adjusted t o p H 7 , and treated with iodide, was titrated with arsenite t o determine chloramine as well as free available chlorine. h third portion iTas adjusted t o p H 7 without the alkali treatment, treated with iodide, and titrated. Chlorine dioxide reacts with iodide t o yield chlorite. Consequently, one fifth of the oxidizing power of chlorite was determined in addition t o the above. Finally, the total oxidizing power was determined by adding iodide a t a pH of 2 and titrating with arsenite. Evans and Simmons ( 1 8 ) improved the sensitivity of the Winkler method for oxygen determination by adding an excess of thiosulfate and titrating with standard iodine. The amperometric end point for the iodine-thiosulfate reaction has been used by Laitinen and Burdett ( 4 5 ) . Rius and Serrano (69) titrated arsenite with bromate using a milliammeter connected momentarily during the measurement.
48
ANALYTICAL CHEMISTRY
Goffart, Michel, and Pitance (24) titrated manganese(I1) t o the pyrophosphate complex of manganese( 111) using platinum and silver wire indicator electrodes. Goffart ( 2 2 ) described a similar titration of cerium( 111). TITRATIONS INVOLVING ORGANIC REAGENTS
Stock (75) determined milligram and microgram quantities of copper, zinc, or cadmium by titration with 8-quinolinol (oxine). Copper could be determined in the presence of cadmium, but not in the presence of zinc. Cadmium could be determined in the presence of either copper or zinc. Zan'ko and Panteleeva (88) titrated the sum of copper and zinc in an acetate buffer of pH 5 , and copper in the presence of zinc in a biphthalate buffer of p H 2.8. Iron when present precipitated in both buffers. Ishibashi and Fujinaga (29) titrated magnesium with oxine in an ammonium hydroxide ammonium chloride buffer a t a concentration of 0.001 M with a n accuracy of O . i % or better. Calcium was removed by adding an excess of ammonium oxalate. Quinaldic acid was used by Stock (73) in the determination of copper and zinc. Precipitation was SIOY a t room temperature but practicable at 60" C. Alternatively, an excess of reagent could be added and a back-titration performed a t room teniperature with copper or zinc solution. Under certain conditions, ly Copper could be copper and zinc could be s u c ~ e ~ s i v e titrated. determined in the presence of cadmium, but the determination of cadmium n-as not succeseful. Stock ( 7 4 ) titrated copper with quinoline-8-carboxylic acid without, interference from zinc, cadmiurn, ferrous iron, cobalt, nickel, or lead. Liberti and Cervone ( 4 7 ) titrated copper with 2-niercaptothiazole in amounts of 0.T t o 5 mg. with a n accuracy of 1%. Cadmium and manganese interfered. The reagent was assayed by titrating with silver ion, using the rotating platinum electrode. Calzolari (9) titrated copper with dimethyldithiohydantoin. In hot solution, a compound of 1 mole of copper t o 1 mole of reagent residue was obtained. Kolthoff and Liberti (36) determined copper(I1) and iron( 111) by titration with cupferron. Copper(I1) was titrated in various buffers of p H 5 to 6, while iron(II1) vias determined in citrate or tartrate huffers of pH 3 t o 4. Copper was determined in the presence of large amounts of iron(II1) by using a citrate buffer which was made 0.5 JI in potassium hydrogen fluoride. Iron could be determined in the presence of an equal or lesser quantity of copper by titration in 0.1 A' hydrochloric acid medium. The end point was found before the precipitation of copper began. Sandberg ( 7 1 ) described the tit,ration of cadmium with naphthoquinoline in the presence of iodide. Zinc does not interfere, but ferric iron must be reduced with hydroxylamine. Various heavy metals could be removed by reduction with iron wire. He also titrated iron(II1) with 5,7-dibromo-8-quinolinol, taking precautions t o prevent reduction of the iron by mercury. Copper and vanadium interfered. The titration of potassium ion with dipicrylamine in the presence of up to 15 times its concentration of sodium was also described. Butenko et al. (7) determined nickel in steel by titration with dimethylglyoxime using alcoholic or alkaline solutions. Pribil and hlatyska ( 6 2 )titrated bismuth, iron(III), nickel(lI), lead, zinc, and cadmium with the disodium salt of ethylenediaminetetraacetic acid (S'ersene) at various pH values and applied potential depending upon the metal ion being titrated. Bismuth could be determined in the presence of most ions a t a pH of 1 t o 2 . A procedure was norked out for the determination of bismuth in lead. DETERMINATIOS OF SULFHYDRYL COMPOUNDS
Benesch and Benesch (1)applied the silver titration method of Kolthoff and Harris (34),using the rotating platinum electrode, t o the titration of sulfhydryl groups in amino acids and proteins. Using a microburet with 0.001 S silver nitrate, amounts down t o 0.03 mg. of mercaptan sulfur could be successfully determined in
thioglycolic acid, cysteine, glutathione, and ergothioneine. Egg albumin, bovine serum albumin, human serum albumin, and various dialyzed sera were analyzed for sulfhydryl content. Frank et al. (20) reported low results in the titration of certain mercaptans by the silver titration method. Strafford, Cropper, and Hamer ( 7 6 ) showed that the low results were due t o oxidation. Rosenberg, Perrone, and Kirk (70) modified the Kolthoff and Harris method by using a vibrating platinum electrode and adding the solution from a horizontal microburet. Microgram quantities of cysteine and glutathione could be determined. Kolthoff and Harris (33) described a method for the determination of primary and tertiary mercaptans. All mercaptans react with silver in a molar ratio of 1 t o 1. Primary mercaptans are oxidized by iodine t o the disulfide, using 0.5 mole of iodine per mole of mercaptan, while tertiary mercaptans react with 1 mole of iodine t o form the sulfenyl iodide. Mixtures of primary and tertiary mercaptans reacted with less than the calculated amount of iodine because of the partial formation of a mixed disulfide. In the presence of a n excess of lead, the correct results were obtained because the mixed disulfide formation could be prevented by forming slightly dissociated mercaptides. The method is of limited accuracy because it is indirect and because some tertiary mercaptans react incompletely with iodine. Kolthoff and Stricks (38, 39) studied the reactions between copper(I1) and cysteine in the presence of sulfite, and devised an amperometric titration for traces of cysteine and cystine using the rotating platinum electrode. The diffusion current corresponded t o the reduction of copper(I1) t o copper(1) rather than to the metal. The over-all reaction is given by the equation 2Cu(II)
+ RS- + SO3--
= 2Cu(I)
+ RSSOa-
Cystine was determined by reduction t o cysteine using sodium amalgam. Mixtures of cysteine and cystine were analyzed by titrations run before and after sodium amalgam reduction. OTHER ORGANIC DETERRllNATIONS
Duyckaerts (16) determined 8-quinolinol (oxine) and phenol, by titration with potassium bromate using a platinum indicator electrode in a rotating vessel. .4n accuracy of 0.4 to 0.5% was achieved. Liberti ( 4 6 ) used a rotating platinum electrode t o follow the titration of p-anlinosalicylic acid with bromate in an acid solution containing bromide t o produce 3-amino-2,4,6-tribromophenol. m-hminophenol could be determined by the same method. Elofson et al (16, 17) used an amperometric method t o follow the titration of a coupler such as a pyrazolone or a naphthol with diazotized aromatic amines in well buffered solutions. A jacketed cell and buret were used t o permit titrations at 0 " t o 5" C. A dropping mercury electrode a t an applied potential of -0.2 t o -0.3 volt was used. COULOMETRlC DETER!+IINATIONS
Swift and coworkers have used an amperometric indication of the end point in several coulometric determinations with electrolytically generated reagents. Very sensitive determinations were worked out in favorable cases. Using electrolytically generated bromine, Sease, Siemann, and Swift ( 7 2 ) determined thiodiglycol, blyers and Swift ( 5 6 ) determined arsenite, and Brown and Swift ( 5 ) determined antimony(II1) by its oxidation t o antimony(V) in hydrochloric acid medium. Wooster, Farrington, and Swift (81) oxidized iodide to iodine bromide using a similar technique. Arsenite has been determined using electrolytically generated iodine (63) and chlorine (19). Meier, Myers, and Swift ( 5 3 ) have described the coulometric determination of chromate and vanadate by use of electrolytically generated copper(I), with an amperometric end point. Silver(I1) proved t o be an unsatisfactory intermediate for the
V O L U M E 2 4 , NO. 1, J A N U A R Y 1 9 5 2 coulometric determination of manganese(II), arsenic(III), or cerium( 111)because the rates of oxidation were too slow ( 5 4 ) . Cooke and Furman ( I S ) used electrolytically generated iron(II1 for the coulometric determination of cerium(1V) and chromium(TT), but used a potentiometric rather than an :iiupcromcAtric indication of the end point. LITERATURE CITED
Benesch, R., and Benesch, R. E., A r c h . Biochem.. 19, 35 ( 1 9 4 9 , (2) Berman, D. -4.. Saunders, P. .I.,and Winzler, R. J., AN.^., CHEY.,23, 1040 (1951). ( 3 ) Berth. C., Anal. Chim. A c t o , 5 , 1 (1951). (4) Boos, R.s.. alld Colin. J. n., .kN.iL. C H E M . . 23, 671 (1951). ( 5 ) Bronm, R. d.,and Sxift, E. H., J . Am. Chem. Soc.. 71, 2717 (1949). (6) Butenko, G. AI., and Bekleshova, G. E., Zamdskaya Lub., 16, 650 (1950). (7) Butenko. G. .I., and Stricks. Kalter. Ibid., 23, 763 (1951). (39) Kolthoff, I. h l . , and Stricks. X-alter, J . A m . Chem. Soc., 72, 1952 (1950j .
49 Korshiinov, I. A , T r u d y Komissil Anal. Khim., Otdel Khim. S a u k , A k a d . .Vauk S.S.S.R., 2 ( 5 ) , 96 (1949). Korshunov, I. ii., and Sasanora. L. X., Zatodskaya Lab., 13, 1172 (1917). h i t i n e n , H . .\., .\S.kI.. C H E X , 21, 66 (1949). Laitinen. H. -1.. nncl Burdett, L. IT., I h i d . , 22, 833 (1950). 7bid..23, 1265 (1951). lbid., p. 12009. I.iha,ti. A , , .ifti u w d , l t ( f d , , ('lussa sc;. .tis. mat. e nut., 8, 608 (1950).
Libeh. .I,, m r l C'ervonc. E.. I / ~ i d .8, , 613 (1950). Libwti, .1., and De C'esaris. E., A n n . Chim. ( R o m e ) , 40, 593 (1950).
Luzina, G. S.,Znioilako2jn L o b , 15, 1212 (1949). Lyalikov, T.8..Z h u r . S n r r l . Khim.,5 , 323-9 (1950). Marks, H. C . . and Glass. J. R., J . A n i . Water W o r k s Assoc., 34, 1227 (1942). hlarks, H. C , , and Joiner, R. R.. ah.^^. CHEY.,20, 1197 (1948). Rfeier. D. J.. Myers, R. J., and Swift, E. H., J . Ani. Ckem. Soc., 71, 2340 (1949). Meier, D. J . . and Swift, E. I f . , Ihid.. 72, 5331 (1950). Meites, L.. J . C'i~cm.Editcofiorz. 27, 458 (1950). Myers. R. J., and Swift, E. H.. J . A m . C h ~ n n .Sor., 70, 1047 (194h 1.
Kimer. E. L., Hamni, R. E., and Lee, G. E., ;\SAL.
CHEY..22,
790 (1950).
Parks, T. D,, and .1gazzi, E. I., Ihid., 22, 1179 (1950). Parks, T. D., and Lykken, L., Ibid., 22, 1444 (1950). Parks, T. D.. and Lykken, L., Petroleum Refine?, 29, S o . 8, 85; s o . 9, 112 (1950) Petrow, H. G.. and S a s h , L. K., -4s.~~. CHEM.,22, 1274 (1950). Pribil, R., and Slatyska, B., Chem. L i s t y , 44, 305 (1950). Ramsev. \T. C.. Farrington, P. 9.. and Swift. E. €1.. SAL. C H E l f . , 22, i 3 2 (1950). Reilley, C. S.,Cooke, IT, D.. and Furman, N. H., Ibid , 23, 122 (1951j . Riccoboni, L., S f t i . reale id. LCrteLo s c i . . 102, 797 11943). Riccoboni, L., and Goldschmied, P., Proc. X I t h I n t e r n . C'ongr. Pure and A 4 p p / i c ~C'hem. l ( L o n d o n ) , 1 , 199 (1947). Ringboni, A , , Tek. T i d . , 77, 755 (1947). Ringhom, .I.. and Iyilkman. B., A c t a Chem. Scand., 3 , 22 (1949). Rius. A , . aiid Serrano, F., Arkales rrnl .soc. espaii. fis. u quirn., 45B, 501 (1949). Rosenberg. S.. l'errone, .J. C.. and Kirk. P.L.. . ~ s . A L . CHEM.,22, 1186 (1950). Sandberg, B.. S l e n s k Kern. Tid., 58, 197 (1946). Pease, J. IT.,Siemann, C., arid Swift, E. H., .Is.\L. C H E i f . . 19, 197 (1947). Stock. J. T . , .f. C'iiem. Soc., 1949, 1793. Ihid.,p. 2470. Stock, J. T., .lIetcillurgin, 40, 179, 229 (1949). Strafford, S . , Cropper, F. R.. and Hamer, A , , A n a l y s ! , 55, 55 (1950).
Tomicek, O . , Blazek, .4.,and Roubal, Z.. Chem. Zoesfi. 4 , 479 (1950). Vasil'ev, K. -4., aiid Getsova. S. T.,Z a t o d s k a y a Lab.. 15, 1414 (1949). Tyakhirev, D. A , , Ibid.,13, 1167 (1947). IT-olff, J. P., BUZZ. nzens. ITERG (Insf. tech. 4 f u d ~ se! rechrichea corps gras), 3, 418 (1949). n-ooster. K . S . , Farrington, P. S., and Swift, E. H., ASL. CHEM., 21, 1157 (1949). .\., and Panteleeva, L. I., Zhur. Anal. Khim., 6 , 109 (1951).
Zan'ko,
R E C E I V EOctober D 2 2 , 1951.
