1. E. Wedekind, Ber. Dtsch. Chem. Ges. 43, 293 (1910).
2. J. Th. Davis, Am. Chem. Journ. 11, 26 (1899).
3. H. A. Hofmann, Ber. Dtsch. Chem. Ges. 43, 2631 (1910).
4. W. Crookes, Select Methods in Chem. Anal. 1905, 151.
5. L. Bourgeois, in E. Frémys Encyclop. chim. (Paris 1884), II, 137.