1. British Patent No. 1,200, 103, 1967.
2. J. Kendall, E.D. Crittendon, and H.K. MIller: J. Am. Chem. Soc., 1923, vol. 45, p. 963.
3. U.I. Shvartsman: Western Inst. Chem., Akad. Nauk URSR, 1940, vol 7, p. 1: also Fig. 1314 Phase diagram for ceramists, American Ceramic Society Inc., 1964.
4. A. Chretien and E.C.R. Lous: Hebd. Seances Acad. Sci., 1943, vol. 217, p. 451.
5. R. Midorikawa: J. Electrochem. Soc. Jpn., 1955, vol. 23, p. 72.