1. Benedict, H.A. (1919), U.S. Patent 1, 294, 355.
2. Burlin, A. L., Leicester, S., and Holman, L. B. (1925), British Patent 251, 373.
3. Du Pont De Nemours & Co. (1945), British Patent 569, 974.
4. Naugatuck Chemical Co. (1931), French Patent 716, 953.