1. Welcher, F. J.Organic Analytical Reagents, 1955,3, 355–400 (D. Van Nostrand Co., Inc., New York).
2. Sandell, E. B.Colorimetric Determination of Traces of Metals, II Ed., 1950, pp. 142; 357. (Interscience Publishers, Inc., New York).
3. Mathers, F. C. and Prichard, C. E.Proc. Ind. Acad. Sci., 1934,43, 125–27;C.A., 1934,28, 7196.
4. Furman, N. H.Ind. Eng. Chem., 1923,15, 1071–73;C.A., 1923,17, 3463.
5. Pinkus, A. and Claessens, J.Bull. soc. Chim. Belg., 1927,31, 413–33;C.A., 1927,21, 3174