1. MacEwan, D. M. C., Nature, 154, 577 (1944).
2. Bradley, W. F., J. Amer. Chem. Soc., 67, 975 (1945).
3. See, for example, Hendricks, S. B., Amer. Min., 23, 295 (1938).
4. Nagelschmidt, G., "The Mineralogy of Soil Colloids" (Tech. Comm. No. 42, Imperial Bureau of Soil Sci.), 12.
5. Hendricks, S. B., Amer. Min., 23, 295 (1938).