1. Lohaus, G. and Dittmar, W.:S. Afric. Patent, 6,906,039 (1968);C.A. 73, 120508a (1970).
2. Youngdale, G.A.:U.S. Patent, 4288 440 (1980);C.A.,96, 6596c (1982).
3. Todd, A. H.:Br. Patent, 1203 149 (1970);C. A. 73, 120509b (1970).
4. Gante, J. and Lust, S.:Ger. Offen. 1908 947 (1970):C.A. 73, 120510 (1970).
5. Meyer, H., Sitt, R., Thomas, G. and Krause, H.P.:Ger. Offen., 3015 219 (1980);C.A. 96, 6604d (1982).