Glass is a compound of silica (silicic acid) with the oxide of an alkaline metal, obtained by fusion. In its usual form it is brittle, transparent, non-crystalline, insoluble, and fusible; but it sometimes exhibits other qualities. The principle of its production is very simple, although skill and experience are necessary to insure excellence. Silica (commonly under the form of sand) is heated with carbonate of potassa or soda and slaked lime or oxide of lead, until the mixture fuses and combination takes place. When the mass becomes perfectly limpid and free from air bubbles, it is allowed to cool until it assumes the peculiar tenacious condition for working.

The fusion is performed in large crucibles of refractory fire-clay; in making lead glass, the crucible is covered with a dome, and an opening left in the side, through which the materials are put in and the melted glass withdrawn. Carbonates and other crystalline matter used in glass making, require to be dry. (See No. 2065 (Colored Fires).) Certain mineral oxides give glass a variety of color, sometimes of a very undesirable kind. Should the paste contain traces of iron, instead of producing white glass there will be only the common bottle-glass ; and if the iron be in larger proportions, the dark green shade will be the result. On the contrary, add a certain quantity of oxide of lead to a pure base of potash, and the beautiful crystal glass is formed; a still larger dose, and the diamond paste, with its wonderfully dispersive power, will deceive many an unpracticed eye.

2340. Peligot's Bohemian Tube Glass

2340.  Peligot's Bohemian Tube Glass. The component parts of this glass are 711/2 parts quartz, 20 parts dry (see No. 2065 (Colored Fires)) carbonate of potassa (or its equivalent), 81/2 parts quicklime, and a little manganese. It is very intractable and difficult to melt, but the addition of a very small quantity of borax, boracic acid, or arsenious acid, causes it to flow into a glass of great brilliancy and hardness, and capable of being wrought at the highest heat of the ordinary furnace.

2341. Bottle Glass

2341.    Bottle Glass. Dry Glauber salts, 11 pounds; soaper salts, 12 pounds; 1/2 bushel of waste soap ashes; sand, 56 pounds; glass skimmings, 22 pounds; green broken glass, 1 cwt.; basalt, 25 pounds. This mixture affords a dark green glass. Or: Yellow or white sand, 100 parts; kelp, 30 to 40 parts; lixiviated wood ashes, from 160 to 170 parts; fresh wood ashes, 30 to 40 parts; potter's clay, 80 to 100 parts; cullet, or broken glass, 100 parts. If basalt be used, the proportion of kelp may be diminished.

2342. Broad, or Green Window Glass

2342.   Broad, or Green Window Glass. Dry Glauber salts, 11 pounds; soaper salts, 10 pounds; 1/2 bushel of lixiviated soap waste; 50 pounds of sand; 22 pounds of glass-pot skimmings; 1 cwt. of broken green glass.

2343. Crown, or White Window Glass

2343. Crown, or White Window Glass. Pure sand, 100 parts; dry sulphate of soda, 50 parts; dry quicklime, in powder, 17 to 20 parts; charcoal, 4 parts. The product is white and good.