1. Megaw, H., Z. Kryst., 87, 185 (1934).
2. Unmack, A., abstracts of papers at Stockholm meeting of International Union of Crystallography, June 1951; also private communication.
3. Frank, F. C., Phil. Mag., 42, 1014 (1951).
4. Vand, V., Nature, 168, 783 (1951).
5. Stumpf, H. C., Russell, A. S., Newsome, J. W., and Tucker, C. M., Indust. Eng. Chem., 42, 1398 (1950).