1. Ballentine, R.: Ind. Engng. Chem., anal. Edit.13, 89 (1941).
2. Basu, K. P., and M. C. Nath: J. Indian chem. Soc. 15, 133 (1938); cf. Z. analyt. Chem. 118, 186 (1939/40).
3. Birch, T. W., L. J. Harris and S. N. Ray: Biochemic J. 27, 590 (1933); cf. Z. analyt. Chem. 102, 150 (1935).
4. Borsook, H., W. H. Davenport, C. E. P. Jeffreys and R. C. Warner: J. biol. Chemistry 117, 237 (1933).
5. Brown and W. B. Adam: J. Sci. Food Agric. 1, 50 (1950).