1. E. Zettnow, Pogg. Ann.130, 324 (1867).
2. W. F. Hillebrand, G. E. F. Lundell, H. A. Bright, andJ. I. Hoffman, Applied Inorganic Analysis, 2nd ed., New York: Wiley. 1953.
3. P. Luis, Mikrochim. Acta [Wien]1959, 536.
4. F. Feigl, Mikrochem.2, 188 (1924).
5. P. E. Williams andH. T. Briscoe, Chem. News145, 177 (1932).