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621,979. Optical glass. KODAK, Ltd Jan. 29, 1947, No. 2808. Convention date, Jan. 29, 1946. Drawings to Specification. [Class 56] Optical glass is made from a batch preponderantly of germanium oxide and containing at least 10 per cent. by weight alkali fluoride with or without titanium oxide. Preferred glasses having refractive indices above 1.70 and dispersive indices below 28 contain at least 15 per cent TiO 2 at least 15 per cent NaF and/or KF, and 38-70 per cent GeO 2 . The mixed anhydrous raw materials are stirred while heated in a covered platinum or " Vycor " (R.T.M.) crucible at 1100‹-1300‹C. when the GeO 2 is not over 85 per cent, but at higher temperatures and for a longer time when the GeO 2 or TiO 2 content is higher. The glass is poured into a mould heated to 420‹-460‹C. and cooled slowly. The composition by weight of some examples are (1) 15 per cent NaF, 20 per cent TiO 2 , 65 per cent GeO,; (2) 21 per cent NaF, 21 per cent TiO 2 , 58 per cent GeO 2 ; (3) 21 per cent KF, 23 per cent TiO 2 , 56 per cent GeO 2 ; (4) 30 per cent NaF, 30 per cent TiO 2 , 40 per cent GeO 2 ; (5) 20 per cent NaF, 10 per cent TiO 2 , 70 per cent GeO 2 ; and (6) 10 per cent NaF, 90 per cent GeO 2 . Some optical properties and the compositions in mols. per cent are given.
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