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I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
spring, E , which in turn holds the filtration apparatus and filter stick in place. Flask B is of very thin glass, for its rests against the filter stick to hold it in place and a heavy flask would break during centrifugation. Filter C is as described above, except that the lower part is as short as possible. I t rests on a soft tin collar,
D.
Vsing this assembly, accurate solubilitr dptcrminwtionq may
Vol. 16, No. 6
be made with organic solvents or corrosive solvents, since no rubber is present to absorb any portion of the solvent. LITERATURE CITED
(1) Craig, L. C.. IND.ENG.CREM., ANAL.ED., 12, 773 (1940). (2) Ing, H. R., and Bergmann, M., J. Bid. Chem., 129, 603 (1939). (3) Moore. S.. and Stein, U’.H., Ibid., 150, 113 (1943).
Semimicrodetermination of Arsenic in Insecticides MARK D. SNYDER AND WALLACE M. McNABB Department of Chemistry and Chemical Engineering, University of Pennsylvania, Philadelphia, Pa.
T
HE procedure presented below represents an extension to insecticidal arsenicals of the method recently described (4) for the semimicrodetermination of arsenic in organic compounds, the arsenic being precipitated as element by action of hypophosphorous acid and determined iodometrically with the aid of Koppeschaar’s bromide-bromate solution. This method is believed to be applicable to any properly prepared solution of arsenic free from interfering substances, such as organic material or metals precipitatable by hypophosphorous acid. It was found that arid-soluble arsenicals (Paris green, lead arsenate, calcium arsenate) could be analyzed thus, following dissolution of the samples in aqueous hydrochloric acid, In presence of organic material, a preliminary decomposition similar to that described for the analysis of organic arsenicals (2, 4) may be necessary. This was the case with the commercial insecticide currently marketed under the name “Victory 76”, stated to contain calcium arsenate together with sulfpr, nicotine, organic compounds with carbon contents from CIOto Cia, and inert material. Decomposition by nitric and sulfuric acids (4) was shown to be a suitable preparation for the determination of arsenic in this insecticide. An alternative decomposition by bromine was found to be more rapid and to lead to acceptable results, but is judged to be less satisfactory because the decomposition liquid contained suspended dark-colored material, prewmably organic bromination products, the presence of which interfered visually a t the time the arsenic was reduced and precipitated. PROCEDURES
SUBSTANCES SOLUBLEIN HYDROCHLORIC ACID, Dissolve a weighed sample (0.5 to 2 grams) of dried material in a minimal volume of 6 N to 12 N hydrochloric acid, transfer the solution to a 500 ml. volumetric flask, and dilute to the mark. Transfer an aliquot portion containing about 15 mg. of arsenic to the flask of an all-glass decomposition apparatus with reflux tube, such as that described for use in the determination of arsenic or mercury in organic compounds (9, 4). If a sufficiently sensitive balance is available-e.g., a semimicrobalance-weigh out the whole sample, of such size as t o contain about 15 mg. of arsenic, and dissolve in hydrochloric acid. To the solution in the flask add and dissolve rapidly 3 grams of sodium hypophosphite (XaHzPO2.HzO), and then add concentrated hydrochloric acid sufficient to increase the acid concentration to about 6 N . Attach the condenser and heat the flask with a small flame, completing the analy*is as described (4). ARSENICALMIXTURESCONTAINISG ORGAXICMATTER. Decomposiiion by il‘itric and Sulfuric Acids (recommended procedure). Weigh accurately a sample of suitable size (to contain about 15 mg. of arsenic; 0.5 gram of Victory 76) and transfer to the decomposition flask. Add 25 ml. of concentrated nitric acid and warm t,he mixture for several minutes, Add 20 ml. of concentrated sulfuric acid, evaporate the mixture to fumes, then add more nitric acid and again evaporate to fumes. Allow the liquid to cool partially and introduce 1 gram of ammonium sulfate. When evolution of gas ceases, heat the liquid gently for 5 minutes. Cool, add about 50 ml. of water, and heat until the solution (7learsor is slightly opalescent. Add 3.5 ml. of concent,rated hydro-
rhloric acid, then 3 grams of sodium hypophospite, and continue as described (4). Decomposition of Victory 76 by Bromine. Tranqfer weighed sample to the decomposition flask, add 2 ml. of liquid bromine. and swirl the mixture for about 5 minutes. Add 50 ml. of 6 AV hydrochloric acid and heat moderately until nearly all the excess bromine is expelled (hood). To the cooled solution add 10 ml. of concentrated hydrochloric acid and 3 grams of sodium hvpophosphite, and complete the analysis as indicated above. RESULTS
Analytical iesults for the four materials mentioned are presented in Table I, which includes also comparative results obtained by the familiar distillation procedure (1) selected as an umpire method. DISCTJSSIOK. Results by the reduction method show satisfactory levels of precision and accuracy, and are substantially identical with results by the distillation method. The reduction procedure is the more rapid, requiring about 40 minutes (exclusive of any needed preliminary decomposition), as compared 6 t h the 2 to 3 hours required for the distillation procedure.
Table
I. Determination of Arsenic i n Some Insecticides
Material
Araenic Found Reduction method Distillation method
%
%
Paris green
42.81 42.77 Av. 4 2 . 7 9
Lead arsenate
20.25 20.18 20.15 Av. 2 0 . 1 9 26.65 26.72 26.73 Av. 2 6 . 7 0
42.75 42.72 42.57 Av. 4 2 . 6 8 20.23 20.27 20.30 Av. 2 0 . 2 7 26.84 26.77 Av. 2 6 . 8 1
Calcium amenate
HNOs-H:SOr Bromine decomposition decomposition 3.57 3.64 3.50 3.55 3.60 3.60 Av. 3 . 5 6 3.59 Prelimmar> decomposition by HNOrHaSO4.
Victory 76 insertiriae
0
3.62“ 3.57” Av. 3 . 6 0
ACKNOWLEDGMENT
Grateful acknowledgment is made to J. J. McGlynn, who executed a series of confirmatory analyses by the reduction and distillation methods. LITERATURE CITED
(1) Assoc. Official Agr. Chem., Official and Tentative Methods of Analygis, 5th ed., pp. 44-5, 1940. (2) Levine and McNabb, IND.ENG.CHEM., ANAL.ED.,15, 76 (1943). (3) Sloviter. McNabb, and Wagner, Ibid., 13, 890 (1941). (4) h2.. 14. 516 (1942).
