1. Van Allan, J. A., and B. D. Deacon: Organic Synthesis, Vol. 30, John Wiley and Sons, Inc., New York (1950) p. 56.
2. Dutta, R. L.: Private communication.
3. Feigl, F.: Chemistry of Specific, Selective and Sensitive Reactions. Academic Press, Inc., New York (1949) p. 8.
4. Kuraš, M.: Collect. czechoslov. chem. Commun. 11, 313, 321, 367 (1939); Ž. obšč. Chim. 13, 95 (1938); 14, 49, 51, 145 (1939); 16, 124 (1941); cf.Z. analyt. Chem. 121, 39 (1941).
5. Majumdar, A. K., and M. M. Chakrabartty: Z. analyt. Chem. 155, 1, 7 (1957); 156, 103 (1957).