1. Eegriwe, E.: Diese Z. 70, 400 (1927).
2. Fredrick, W. G.: Ind. Engng. Chem., anal. Edit. 13, 922 (1941).
3. Kuznecov, V. I.: C. R. Acad. Sci. URSS. 52, 231 (1946); Ch. Zbl. 1947 II, 1879.
4. Webster, S. H., and L. T. Fairhall: J. ind. Hyg. Toxicol. 27, 184 (1945).