1. E. H. Sprecht, A. Neuman and H. T. Neher, U.S. Pat. 2,773,063 (1956): assigned to Rohm & Haas.
2. CIBA Ltd., Br. Pat. 746,747 (1956).
3. E. H. Sprecht, A. Neuman and H. T. Neher, Br. Pat. 772,196 (1956); assigned to Rohm & Haas.
4. N. H. Shearer Jr. and H. W. Coover Jr U.S. Pat. 2,790,744-5 (1957); assigned to Eastman Kodak.