1. Verneuil, C.R. Acad. Sci., Paris, 135, 791 (1902); Ann. Chim. (France), 3, 20 (1904).
2. Laudise, R. A., and Ballman, A. A., J. Amer. Chem. Soc., 80, 2655 (1958).
3. Frémy, E., and Feil, C., see Smith, Herbert, Gemstones (Methuen, London, 1958).
4. See White, E. A. D., Quart. Rev. Chem. Soc., 15, 1 (1961).