JULY 15, 1939
ANALYTICAL EDITION
Summary
The following modifications and improvements have been made in the dithizone method for the determination of lead in biological material described by Hubbard : The use of hydroxylamine in the initial extraction prevents the oxidation of the dithizone and permits the elimination of the second extraction step of the Hubbard method. Washing the first chloroform extract removes extraneous entrained salts and improves the test for bismuth. Filtrations through cotton and through paper have been eliminated from the procedure without loss of accuracy, and with a resultant saving of time and decrease of opportunities for contamination. The addition of the standard dithizone solutions and the development of the mixed color in all the samples of a series before the photometric readings are made save time and do not affect the accuracy of the analyses.
403
Purification of reagents and elimination of contamination have made possible a blank of 0.1 microgram, which is believed to be the lowest yet reported. Literature Cited (1) Behrens, B., and Taeger, H., 2.ges. ezptl. Med., 96,282 (1935). (2) Cholak, J., IND. ENG.CHEM.,Anal. Ed., 7, 287 (1935). (3) Cholak, J., and Story, R. V., Ibid., 10,619 (1938). (4) Clifford, P. A,, J . Assoc. Oficial Agr. Chem., 20, 191 (1937). (5) Clifford, P. A., private communication. (6) Clifford, P. A., and Wichmann, H. J., J . Assoc. Oficial Agr. Chem.. 19. 130 (1936). ( 7 ) Hubbard, D. M., IND. ENQ.CHEM.,Anal. Ed., 9, 493 (1937). (8) Ibid., 11, 343 (1939). (9) Laug, E. P., J. Assoc. Oficial Agr. Chem., 21,481 (1938). (10) Wilkins, E. S., Jr., Willounhbs, C. E., Kraemer, E. O., and Smith, F. L., 2nd, IND.E
