1. E. F. Gross and V. A. Kolosova, ZhFKh,26, 1673, 1952.
2. P. Jellyman and J. Procter, J. Soc. Glass Technol.,39, 173, 1955.
3. Ya. S. Bobovich and T. P. Tulub, Opt. i spektr.,2, 174, 1957.
4. V. A. Florinskaya and R. S. Pechenkina, ZhSKh,46, 850, 1963.
5. Ya. S. Bobovich and T. P. Tulub, UFN,66, 3, 1958.