1. Department of Industrial Chemistry, Faculty of Engineering, University of Tokyo, 7‐3‐1 Hongo, Bunkyo‐ku, Tokyo 113, Japan
2. Mikuni Company, Limited, 2480 Kuno, Odawara‐shi, Kanagawa 250, Japan
3. Osaka Gas Company, Limited, Torishima, Konohana‐ku, 554 Osaka, Japan