1. Nencki..Ber., 1874,7, 158.
2. Dixon..J. Chem. Soc., 1888,53, 411.
3. ----- ..Ibid., 1892, 509.
4. Steindorff and Paquin .. Ger. Patent, 5,282,203;C.A., 1933,27, 5160; U.S. Patent, 2,304,624;C.A., 1943,37, 2852.
5. Paquin..Angew. Chem., 1948,60 A, 267.