1. Raasch , M. S. U.S. Patent, 2,979,435. 1961.Chem. Abstr.54(1960)
2. Johnston , J. D. German Patent, 1,065,659. 1959.Chem. Abstr.55, 15820 a (1961)
3. Johnston , J. D. U.S. Patent, 3052397. 1962.Chem. Abstr.57, 14236 e (1962)
4. Gerjovich , H. J. U.S. Patent, 2983 762. 1961.Chem. Abstr.55, 19793 h (1963)