1. British Patent No. 1030338, cl. FIF (F05g) (1966).
2. PPR Patent No. 56131, cl. 59e, 6-02 (F05g) (1968).
3. US Patent No. 3804565, cl. 418-201 (F01 c 1/16) (1974).
4. Japanese Patent No. 8976, cl. 63B222.2 (1966).
5. Japanese Patent No. 1735, cl. 63B222.2 (1966).