INDUSTRIAL AND ENGINEERING CHEMISTRY
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In this way it is possible to get a preliminary estimate of the approximate concentration of phosphorus in solution.
Literature Cited Alten, F., Weiland, H., and Loofmann, H., 2. PjZanzenernilhr. Dtingung Bodenk., 32 (A), 33-50 (1933).
Benedict, S . R., and Theis, R. C., J. Biol. Chem., 61,63-6 (1924). Deemer, R. B., and Schricker, J. A., J. Assoc. oficial Agr, Chem,, 16, 226-32 (1933).
Dreyspring, C., and Heinz, W., 2. PjZanzenernahr Dangung Bodenk., 35 (A), 362-74 (1934).
Feher, D., Phosphorsilure, 3, 429-61; 4, 508-29 (1933); 2. Pflanrenerntthr. Dtingung Bodenk., 33 (A), 320-35 (1934). Fiske, C. H., and Subbarow, Y., J. Biol. Chem., 66, 376-400 (1926).
Gerritz, H. W., IND. ENG.C H ~ MAnal. . , Ed., 7,116-18 (1935). Guyer, A,, and Likiernik, A,, Helu. Chim. Acta, 16, 1033-44 (1933).
Lewis, A. H., and Marmoy, F. B., J. SOC.Chem. Ind., 52, 17782T (1933). Liebknecht, O., and Gerb, L., Z. angew. Chem., 45, 744-5 (1932).
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(11) Osmond, F., Bull. 8oc. chim., 47,745-8 (1887). (12) Petrie, A. H. K., Australian J. EzptZ. Biol. Med. Sci., 11, 26-34 (1933). (13) Pett, L.’B., Biochem. J., 27, 1672-6 (1933). (14) Robinson, W. O., Dudley, H. C., Williams, K. T., and Byers, H. C., IND. ENG.CHEM.,Anal. Ed., 6,274-6 (1934). (15) Tananieff, N. A., and Potschinok, Ch. N., 2. anal. Chem., 88, 271-8 (1932). (16) Treadwell, W. G., and Hartnagel, I., Helv. Chirn. Acta, 15, 1023-9 (1932). (17) Tschopp, E., and Tschopp, E., Ibid., 15, 793-809 (1932). (18) Ward, R. R., Soil Sci., 24,85-97 (1933). (19) Yoe, I. H., “Photometric Chemical Analysis,” Vol. 1, pp. 91-3, New York, John Wiley & Sons, 1928. (20) Zinzadze, Ch., Chimie & Industrie, 27 (3-bis),841-3 (1932). (21) Zinradze, Ch., IND. ENQ.CHEM.,Anal. Ed., 7,230 (1935). (22) Ibid., p. 280. (23) Zinzadze, Ch., 2. PjZanzenernilhr. Ditngung Bodenk., 16 (A), 129-84 (1930): Ann. agron., 1,321-36 (1931). RECEIVED October 8, 1934. Read before the annual meeting of the Association of Official Agricultural Chemists, Washington, D. C., October 30,1934.
Colorimetric Methods for Determination of Arsenic in Phosphorus-Free Solutions CH. ZINZADZE, New Jersey Experiment Station, New Brunswick, N. J.
I
N ANOTHER paper (6)citations of the use of molybdenum blue methods for the determination of phosphorus i n different materials have been given. Deemer and Schricker ( I ) used this method for the determination of arsenic in plants. Slight changes and improvements which were found useful in connection with the determination of phosphorus are also applicable to the determination of arsenic. Only pentoxides (As205 and P206)give the blue-colored compounds with molybdenum blue. Arsenic pentoxide is much more easily reduced than phosphorus pentoxide and thus i t is possible to eliminate the influence of arsenic in the determination of phosphorus, but not vice versa. Consequently, the methods given in the previous paper can be used for the determination of arsenic only in solutions free from phosphorus pentoxide and containing not more than 2 mg. of ferric oxide and 10 mg. of nitrates, because sodium bisulfite reduces arsenic pentoxide and cannot be used in this determination. These methods areparticularlysuitable for arsenic distillates; distillation is described in detail by Deemer and Schricker (1). REAGENTS. With the exception of sodium bisulfite, the reagents used are exactly the same as for the determination of phosphorus (8). STANDARD ARSENICPENTOXIDI SOLUTION.Dissolve 0.0200 gram of pure anhydrous arsenic pentoxide in about 5 cc. of 2 per cent sodium bicarbonate and 100 cc. of distilled water; add 6 CC. of 1 N sulfuric acid and 3 drops of 0.1 N potassium permanganate and make up to a liter. This is 20 p. p. m. of arsenic pentoxide; 1 cc. = 0.02 mg. of AszOr. From this stock solution the standard solutions are prepared by taking appropriate aliquots in 50-cc. volumetric flasks.
perature; make up to 50 cc. with distilled water; mix well and measure the color in an ordinary or photoelectric colorimeter (a). The precautions here are the same as for the determination of phosphorus.
Reduction Method This method may be used when the molybdenum blue reagent method is inconvenient. For the determination of arsenic only stannous chloride can be used as a reducing agent; the three reducing agents mentioned in the previous paper (2) contain sodium bisulfite and are therefore not suitable. Prepare the standard or unknown as in the PROCEDURE. molybdenum blue reagent method up to the addition of the molybdenum blue reagent; add instead 5 cc. of molybdenum trioxide reagent; make up to 40 cc. with distilled water and mix; prepare all standard and unknown solutions exactly in this manner; then add rapidly in turn to each flask 5 cc. of stannous chloride solution while shaking; make up to 50 cc. with distilled water and mix thoroughly. After 20 minutes make comarisons. The determination should not stand longer than 6 Rours.
Detection of Arsenic by Drop Method To a few drops of solution add 1 drop of ten times diluted molybdenum blue reagent and boil very gently about 0.5 minute; or add one drop of molybdenum trioxide reagent and one drop of stannous chloride solution.
Aclrnowledgment The author wishes to express his sincere thanks t o John A. Schricker of the U. S. Department of Agriculture for helpful literary suggestions and criticism of the manuscript.
Molybdenum Blue Reagent Method
Literature Cited
Pipet 0.5 t o 30 cc. of the standard or unknown PROCEDURE. solution, corresponding to 0.005 to 0.3 mg. of As206, into a 50-cc. volumetric flask having a mark at 40 cc.; add 5 drops of alphadinitrophenol and neutralize with a 2 per cent sodium bicarbonate solution when acid, or with 1 N sulfuric acid when alkaline, t o a faint yellow; add 5 cc. of ten times diluted molybdenum blue reagent; make up to 40 cc. with distilled water and mix; heat on a steam bath for 30 minutes; allow to cool or cool to room tem-
(1) . . Deemer, R. B., and Schricker, J. A., J . Assoc. Oficial Agr. Chem., 16, 226-32 (1933). (2) Zinzadze. Ch.. IND. ENG.CHEM.,Anal. Ed., 7, 227 (1935). (3) Ibid., p. 280. R ~ C E I Y EOctober D 8, 1934. Read before the annual meeting of the ABsociation of 0 5 c i a l Agricultural Chemists, Washington, D. C., October 30, 1934.
