WATER-GLASS, or SoulmE GLASS. A term applied to alkaline silicates containing an excess of alkali and soluble in water. Three varieties of water-glass are in use, viz.: (1) Potash, seater glass. or potassium silicate, prepared by fusing together three parts of silica (sand) and two parts of potassium carbonate, with a small quan tity of charcoal, in an ordinary reverbatory fur nace, the product being soluble in four or five parts of boiling water. (2) S'odu ienter-glass, or sodium silicate, prepared by melting together fifteen parts of silica (powdered quartz), eight parts of sodium carbonate, and one part of pow dered charcoal, beating for five or six hours, then cooling, powdering, and extracting with five or six times its weight of boiling water. Thus is obtained the original water-glass in vented by Fuchs of :Munich. who first described it in 1825. (3) The so-called double water-glass consists of a mixture of both of the foregoing. It may he made by fusing together 100 parts of silica, 2S parts of potassium carbonate. 22 parts of sodium carbonate, and 6 parts of powdered charcoal. These substances find extensive prac
tical application. Wheu used in the form of varnish or paint they produce a fireproof and waterproof surface. When applied as a coating to a surface containing lime, they combine with the latter, forming an infusible silicate or artificial stone. This process has been taken advantage of for the preservation of frescoes, and is known as `stereochromy.' It has also been utilized for the manufacture of artificial stone, and of a cement. for consolidating siliceous sand into a hard, durable artificial sandstone, capable, before it is fired, of being molded into any desired form. Owing to its cleansing proper ties, water-glass is sometimes used as an in gredient of certain soaps. It is also employed in the manufacture of earthenware, and as a substitute for dung in the dyeing and printing of fabrics. Consult Fenehtwanger, A. Prac tical Treatise on Soluble or Water glass (New York, 1870).