| 摘要 |
803,927. Glass compositions. PITTSBURGH PLATE GLASS CO. Sept. 21, 1956 [Oct. 21, 1955], No. 28899/56. Class 56. A green glass containing iron oxide ; for an ophthalmic crown glass, to have an index of refraction N D of about 1À523, a softening point of about 1330‹F. and a coefficient of thermal expansion of about 89-93 x 10<SP>-7</SP> per ‹C. between 25‹C. and 300‹C., consists in per cent. by weight: 65-75 SiO 2 , 7-10 Na 2 O, 7-10 K 2 O, 5-8 CaO, 2-4 MgO and 2À8-5 Fe 2 O 3 , the sum of Na 2 O and K 2 O being 15À5-17À5 and the sum of CaO and MgO being 7-10À5. Up to 2 per cent. of refining agents may be used, such as Na 2 SO 4 , AS 2 O 5 and Sb 2 O 3 . |
