Soluble, Or Water Glass Glass , an artificial silicate of soda or potash, or a double silicate of both these alkalies. It may be formed by fusing 8 or 10 parts of dry carbonate of soda or potash with 15 parts of white sand or powdered quartz or flint. Nearly all glass is to a slight extent soluble in water, in consequence of the alkaline matter it contains; and the solubility is increased by raising the temperature of the water, which under pressure may he carried far above the boiling point. Water holding caustic alkalies in solution will attack glass vessels containing it in consequence of the formation of a soluble alkaline silicate. It is to this quality of solubility that feldspar ordinarily owes its value as a fertilizing ingredient of the soil; and it is from the affinity of caustic lime for silica that it may be used for liberating the alkali in the feldspar. Attention was first directed to soluble glass by Fuchs as a suitable composition for rendering combustible bodies fire-proof; and in 1824 portions of the new theatre in Munich were coated with it. He also employed it in the style of fresco painting called stereoehromy, for fixing the colors (see Fresco Painting); and it was used not only upon plastered walls, but with success by Echter directly upon the sandstone of the Strasburg minster.
Fuchs proposed to render-wood fire-proof, and even linen also, by means of it; to protect surfaces from the action of the weather; to prepare with it artificial stone; and to use it as a cement for glass and porcelain. But it appears to have been most successfully applied by Prof. Kuhlmann at Lille, who employed it to prevent the decay of walls and edifices, even when built of very inferior stone, and in print works and tapestry factories for fixing colors upon cotton and paper. In England it is employed in the fabrication of the celebrated Pansome artificial stone, described in the article Concrete and in Dr. F. A. P. Barnard's report of the Paris univer-sal exposition of 1867. Soluble glass is also employed by Baerle and co. of Worms for washing wool. Forty parts of water are mixed with one of soluble glass at a temperature of from 122° to 135° F., and the wool is stirred in the mixture for a few minutes. It is then rinsed in tepid water, when it is found perfectly clean, white, and odorless, without having lost any of its softness or other valuable qualities.