1. Dhar, J., Indian J. Phys., 7, 43 (1932).
2. Dhar, J., Proc. Nat. Inst. Sci. India, 15, 11 (1949).
3. Kitiagorodsky, A. I., Acta Physiochim. U.R.S.S., 2l, 575 (1946).
4. Hargreaves, A., and Hasan Rizvi, S., Proc. Chem. Soc., 122 (1961).
5. For example, Cruickshank, D. W. J., Acta Cryst., 9, 915 (1956).