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2. Burstall, F. H., and G. R. Davies and coworkers: J. chem. Soc. (London) 1950, 516.
3. Datta, S. K.: Chemist-Analyst 50, 104 (1961); cf. Z. analyt. Chem. 192, 420 (1963).
4. Datta, S. K., u. S. N. Saha: Z. analyt. Chem. 194, 340 (1963).
5. Lederer, M.: Science (Lancaster, Pa.) 110, 115 (1949); Australian J. Sci. 11, 174 (1949).