1. Lench, A.: Australian Dept. Supply, Defence Standards Labs. Rept. No. 218, 1–19 (1955).
2. Mitchell, C. A.: Analyst 58, 279 (1933); cf. Z. analyt. Chem. 104, 365 (1936).
3. Musil, A., u. W. Haas: Mikrochim. Acta (Wien) 1957, 803; cf. Z. analyt. Chem. 163, 433 (1958).
4. Penkova, E. F., A. V. Gladkova and T. V. Novikova: Zavodskaja Laborat. 22, 918 (1956); cf. Z. analyt. Chem. 156, 57 (1957).
5. Ramachar, T. L.: J. Indian chem. Soc. 18, 507, 563, 605 (1941).