1. Patent No. 802490 Federal Republic of Germany, 17g, 5/02 (1956).
2. Patent No. 914861 Federal Republic of Germany, 17g, 5/02 (1956).
3. Patent No. 627725 India, 6B1 (1956).
4. Patent No. 2730957 USA, 103–153 (1956).
5. Patent No. 751062 Britain, 102(1)A (1958).