2. (Brande; Faraday.) Silica, 52%; oxide of lead, 34%; potassa, 34%. Crystal.
3. (Faraday.) Silica, 44·30%; oxide of lead, 43·05%; potassa, 11·75%; alumina, ·50%; oxides of iron and manganese, ·12%; (loss 28%). Heaviest of three samples of flint glass examined.
b. Materials used:—
1. Finest Lynn-sand (calcined, sifted, and washed), 51%; litharge (purest), 28% (or red lead, 29%), refined pearlashes (calcined before being weighed), 16%; nitre (purified), 43⁄4% arsenious acid and peroxide of manganese, of each, 1⁄8%. Very fine crystal.
2. (M. Payen.) Fine sand, 46%; red lead, 31%; purified carbonate of potash, 23%. French crystal.
3. (Geddes.) White Lynn-sand, 51%; red lead or litharge, 33%; refined pearlashes, 13%; nitre, 3%; a very little arsenious acid and peroxide of manganese. Ordinary English flint-glass. Crystal ‘cullet’ may be added at will to the above. This glass was originally prepared from powdered flints, a fact to which it owes its common name.
Glass, Optical. 1. (Crown glass.) Purest siliceous sand, 55%; carbonate of soda (dry), 12%; chalk (dry), 11%; carbonate of baryta, 22%.
2. (Flint glass.)—
a. By analysis:—
Silica, 44·30%; oxide of lead, 43·05%; potassa, 11·75%. This is Guinand’s ‘dense optical glass.’