1. Note that Frdl. is an abbreviation for the following source where the patent reference can be found: Friedländers Fortschritte der Teerfarbenfabrikation, Berlin.
2. M. Spatz and B. Cross, U. S. Pat. 4,490,165(1984).
3. Sakano, T. Yokoyama, S. Kajiya, T. Minami, Y. Okazaki, H. Tokuda, H. Kawazura, M. Kumajura, T. Nakano, and A. Awaya, U. S. Pat. 4,490,393(1984).
4. D. Riedel, German Pat. 76,596.