1. Das, M. S., Ch. Venkateswarlu and V. T. Athavale: Analyst 81, 239 (1956); cf. Z. analyt. Chem. 155, 54 (1957).
2. Das-Gupta, P. N.: J. Indian chem. Soc. 6, 777 (1929); Analyst 55, 154 (1930); cf. Z. analyt. Chem. 83, 213 (1931).
3. Holness, H., and G. Mattock: Anal. chim. Acta (Amsterdam) 3, 320 (1949); cf. Z. analyt. Chem. 130, 249 (1949/50).
4. Přibil, R., and P. Schneider: Chem. Listy 45, 7 (1951); cf. Z. analyt. Chem. 137, 230 (1952/53).
5. Přibil, R., and J. Vorlíček: Chem. Listy 46, 216 (1952); cf. Z. analyt. Chem. 139, 130 (1953).