1. Normann, W., DRP, Patent No. 141,029 (1902).
2. Bolton, E. R., E. J. Lush, EP 162, 270 (1920); Ibid. E. J. Lush, EP203, 218 (1922).
3. Mills, V., AP 2 520, 423–425 (1947).
4. Smith, F. G., JAOCS25, 328 (1948).
5. Bailey, A. E., Ibid.25, 644 (1949).