1. Mackay, A. L., Min. Mag., 32, 545 (1960).
2. Böhm, J., Z. Anorg. Allg. Chem., 149, 203 (1925).
3. Mackay, A. L., Min. Mag., 33, 270 (1962).
4. Kolthoff, and Moskovitz, J. Amer. Chem. Soc., 58, 777 (1936).
5. Feitknecht, W., Fourth Intern. Symp. Reactivity in Solids (edit. by de Boer), 583 (Elsevier, Amsterdam, 1960).