1. W. A. E. McBryde etJ. H. Yoe, Analyt. Chemistry20, 1904 (1948).
2. F. Vydra etJ. Celikovsky, Chem. Listy,51, 768 (1957).
3. E. B. Sandell, Colorimetric D�termination of Traces of Metals, 3eme �d., New York: Interscience. 1959. p. 497.
4. H. Peterson, Z. anorg. Chem.,19, 59 (1898).
5. F. A. Gooch etF. H. Morley, Amer. J. Sci.,8, 261 (1899).