1. For example, Barrer, R. M., and also Powell, H. M., Solvay Congress on Non-stoichiometry, Brussels (May 1956) (in the press). Cramer, F., “Einschlussverbindung” (Springer, 1954).
2. Barrer, R. M., Brennstoff. Chemie, 35, 325 (1954).
3. Palin, D. E., and Powell, H. M., J. Chem. Soc., 208 (1947).
4. van der Waals, J. H., Trans. Farad. Soc., 52, 184 (1956).
5. Smith, A. E., Acta Cryst., 5, 224 (1952).