1. E. B. Sandell, Colorimetric Determination of Traces of Metals. New York: Interscience. 1959. p. 444.
2. S. Hirano etA. Mizuike, J. Chem. Soc. Japan, Ind. Chem. Sec.1959, 62, N 10, 1447?1499, A 92?A 93;A. Mizuike, Talanta1962, 948.
3. G. G. Pierson, Ind. Eng. Chem., Analyt. Ed.6, 437 (1934);11, 86 (1939).
4. W. E. Caldwell etK. N. McLeod, Ind. Eng. Chem., Analyt. Ed.9, 530 (1937).
5. W. B. Pollard, Analyst62, 597 (1937).