Merck,E. Patent: DE632257 , 1934 ; Fortschr. Teerfarbenfabr. Verw. Industriezweige, vol. 22, p. 622 Full Text Show Details Merck and Co. Inc. Patent: US2149279 , 1935 ; Full Text Show Details Kushner et al. Journal of the American Chemical Society, 1952 , vol. 74, p. 3617,3618,3620