SOLUBLE GLASS. 613 



SOLUBLE GLASS. 



The silicates of soda and j^otasli differ from the other silicates grouped 

 under the general name of glass in being soluble in water ; hence they are 

 known as soluble glass, water-glass, liquid quartz, etc. While ordinary 

 glass has heen known from very ancient times, these peculair compounds 

 are quite new to us, having been accidentally discovered by the late Prof. 

 Fuchs of Munich, in the year ]818, while experimenting with a view to the 

 preparation of pure silica. In 1823, when the Munich theatre was rebuild- 

 ing after its destruction by fire, the Bavarian government appointed a 

 scientific commission to consider by what means the woodwork and stage 

 fixtures might be rendered incombustible; and Fuchs, in connection with 

 Pettenkofer, after careful investigation, settled upon soluble glass as the 

 best agent for the purpose. It has since been much nsed in this way, though 

 for textile fabrics the tungstate of soda has come to be preferred, in apply- 

 ing soluble g-lass it is necessary to begin with a weak solution, and to let 

 the first coat dry thoroughly before putting on a second, which may be more 

 concentrated. A wash of lime is sometimes used between the two coats. 



When the soluble glass is applied to surfaces of plaster and limestone, 

 an interesting chemical reaction takes place, resulting in the formation of 

 silicate of lime. A vitreous surface is thus produced, impervious to moisture 

 and unaffected by atmospheric agents. Soluble glass is also used as a ve- 

 hicle for mineral colors in a kind of fresco-painting, known as stereochromy, 

 which is intended to withstand exposure to the weather. The famous fres- 

 coes by Ivaulbach in the Museum of Berlin were done in this way. It is 

 also coming to be employed for preparing paints for ordinary use, and there 

 are factories exclusively devoted to the manufacture of this class of 

 pigments. 



One method of making artificial stone is b}' moistening fine sand with a 

 solution of silicate of soda, pressing the mixture into mould, drying it and 

 exposing it to a high temperature. The silicate fuses and cements the grains 

 together into a mass resembling sandstone. Al^J desired color may be im- 

 parted to the stone by the admixture of metallic oxides previous to the 

 moulding process. Thousands of tons of the silicate are consumed for this 

 purpose in England. 



Another important ajjplication of soluble glass is in calico-printing, where 

 it is now extensively used as a mordant. It is even more in demand in 

 soap-making, for which it has advantages over resin, on account of its alka- 

 line character. It also enters into the composition of fire-proof cements for 

 stoves and other iron-work, and especially for putting up iron fronts for 

 buildings. 



In this brief notice we have mmtioned only the leading uses of this val- 

 uable substance. The demand for it in the arts is daily increasing, and it 

 is probable that its commercial and industrial applications are destined to 

 be immensely extended in the future. — Boston Journal of Chemistry. 



