2. White sand, 60%; potashes (good), 24%; common salt, 10%; nitre, 5%; white arsenic, 1%; peroxide of manganese, a little (1⁄12 to 1⁄10%); pale ‘cullet,’ at will (10 to 30%). Very pale. This is the ‘spread’ or ‘sheet window-glass’ in common use.
Glass, Chemical. Sp. gr. 2·390 to 2·396.—
a. By analysis:—
1. Silica, 72·80%; potassa, 16·80%; lime (with a trace of alumina), 9·68%; magnesia, 40%; traces of oxide of manganese and iron (and loss) ·32%. This is the difficultly fusible ‘Bohemian tube-glass,’ so valuable in chemical manipulations.
2. Silica, 69·3%; potassa, 15·8%; soda, 3%; lime, 7·6%; alumina, 1·2%; magnesia, 2%; oxide of iron, ·5%; oxide of manganese (and loss), ·6%. English chemical glass (without lead). More fusible than the last.
b. Materials used:—
1. Quartz (hyalin, in powder), 60%; calcined purified pearlash, 30%; fresh-burnt lime (very pure), 9%; nitre (dried), 3⁄4%; arsenious acid or peroxide of manganese, 1⁄4%. Said to be the proportions used in the production of a, 1 (above).
2. (M. Peligot.) Quartz, 711⁄2%; carbonate of potassa (or its equiv., dry), 20%; quicklime, 81⁄2%; (manganese, a little). Said to be the formula for the hardest and least fusible ‘Bohemian tube-glass.’ It is very intractable and infusible, except at a very high temperature; but the addition of an exceedingly small quantity of boracic acid, borax, or arsenious acid, causes it to flow into a glass possessing great brilliancy and hardness, and capable of being wrought at the highest heat of the ordinary furnace.
Glass, Crown, White window-glass. Sp. gr. 2·486 to 2·488.—
a. By analysis:—