1. Swedish Patent, P. 94913 of September 20, 1937; Ghem. Zbl. II, 4354 (1939).
2. U.S. Patent, 2,402,560 of June 25, 1946: Chem. Abstrs. 40, 5595 (1946).
3. Belgian Patent 448,962 of February, 1943; Chem. Abstrs. 42, 209 (1948).
4. British Patent 580,357 of September 4, 1946; Chem. Abstrs. 41, 2077 c (1947).
5. U. S. Patent 2,419,943 of May 6, 1947; Chem. Abstrs. 41, 5336 a (1947).