1. M. Mousson, Compt. Rend.,6, 296 (1895).
2. V. I. Zabiyako, Tr. Ural'sk. Nauchn.-Issled. Khim. Inst., No. 1, 222 (1954).
3. W. Kroll, Z. Anorg. Chem.,102, 1 (1918).
4. L. Ya. Markovskii and G. V. Kaputovskaya, Zh. Neorgan. Khim.,3, 328 (1958).
5. E. E. Kotlyar and T. N. Nazarchuk, Zh. Analiticheskoi Khim.,15, 207 (1960).