1. For many details Cf.T. J. M. Visser, Rheological properties of alkali borate glasses, Thesis Eindhoven, 1971.
2. Bray, P. J., andJ. G. O'Keefe, Phys. Chem. Glasses4, 37 (1963).
3. Beekenkamp, P., in: Physics of Non-Crystalline Solids, Ed.J. A. Prins, p. 512 (Amsterdam 1965).
4. Li, J. H. andD. R. Uhlmann, J. Non-Crystalline Solids3, 127, 205 (1970).
5. Lillie, H. R., J. Amer. Ceram. Soc.16, 619 (1933).