1. J. Grieg,Amer. J. Sci. 13 (1972) 1.
2. F. P. Glasser, J. Warshaw andR. Roy,Phys. Chem. Glasses 1 (1960) 39.
3. E. M. Levin, in ?Phase Diagram?, Vol. 3, edited by A. M. Alper (Academic, New York, 1970) p. 143.
4. M. Wanatabe, H. Noake andT. Aiba,J. Amer. Ceram. Soc. 42 (1959) 593.
5. T. Tanaka,Phys. Rev. Lett. 40 (1978) 820.