1. U.S. Patent (filed May 19, 1941) 2,452,080 (1948).
2. U.S. Patent (filed Aug. 11, 1948) 2,451,064 (1951).
3. U.S. Patent (filed May 18,1956) 2,862,234 (1958).
4. U.S. Patent (filed Nov. 6, 1958) 2,979,777 (1961).
5. and U.S. Patent (filed Feb. 14, 1962) 3,166,616 (1965).