1. Macey, H. H., Trans. British Ceramic Soc.47, 183, and 259 (1948).
2. Astbury, N. F., Proc. Royal Soc., Series A,258, 27 (1960).
3. Astbury, N. F. andF. Moore, Transactions of the VII International Ceramic Congress. Copenhagen, p. 3 (1962).
4. Moore, F., J. Scient. Inst.40, 228 (1963).
5. Astbury, N. F. andF. Moore, Materials Res. Stand.5, 178 (1965).