| 摘要 |
1,272,812. Glass composition. PILKINGTON BROS. Ltd., B. PARKER, R. J. PARRY, and J. S. RUTHERFORD. 12 Aug., 1970 [29 Aug., 1969], No. 43096/69. Heading C1M. A phoria-free optical glass comprises in weight per cent B 2 O 3 19-25; SiO 2 12-20; La 2 O 3 17-27 and BaO 35-43 the said constituent together forming at least 95% by weight of the glass. The glass may also contain up to 5% by weight of at least one material of the group consisting of Al 2 O 3 , As 2 O 5 and CaO. The glass is prepared by melting a batch including boric acid, South African quartz and barium carbonate, maintaining it at 600‹ C. for twelve hours, cooling the glass to 500‹ C. at the rate of 20‹ C. per 24 hours for five days, and then allowing it to cool naturally to ambient temperature. |
