Soluble Glass.

Scientific American 23, 1.12.1866

MESSRS. EDITORS: — In your valuable paper of the 17th inst., you state that the silicates of soda and potash have been known for more than a century. I beg to differ with you in opinion. Although it is known that as early as 1640 it was observed by von Helmont, that a compound consisting of quartz, sand, and a surplus of alkali was liquefied when exposed to the air, yet those definite combinations of silica with soda or potassa, which we call soluble glass, were not prepared until 1825; they were discovered by the German chemist Fuchs. There are four kinds of soluble glass: -
1. The silicate of soda;
2. Silicate of potassa;
3. Silicate of soda and potassa, and
4. Soluble glass for fixing colors, mainly a combination with silica saturated double silicate. For the preparation of these various kinds of silicates, Fuchs has given the following prescription:—

Silicate of potassa, 45 parts quartz, 30 parts potassa, 3 parts charcoal.
Silicate of soda, 45 quartz, 23 calcined soda, 3 charcoal, or 100 quartz, 60 calcined glauber salt, 15 charcoal.
Double silicate, 100 quartz, 28 potassa, 22 soda, 6 charcoal.
The ingredients here named are to be ground, thoroughly mixed, and then melted together, whicil operation is conducted best in a glass furnace; the melted mass is at last boiled in water and the thereby obtained liquor forms the soluble glass. The last of the above named kinds is obtained by melting together 30 parts of calcined soda with 20 parts of quartz, and mixing the liquid obtained with silicate of potassa.

Soluble glass has since its discovery been proposed for quite a number of applications, both in industry and arts. Many of these, not being practical, have, been abandoned, but its applicability for making inflammable bodies fire-proof, when coated or impregnated with it, is of real value; it may for this purpose previously be mixed with ground clay, chalk, blastfurnace slags, feldspar or other similar substances.

Soluble glass may also be mixed with colors, forming fireproof paints. We hear that this manufacture is carried on by the "Atlantic Quartz Company," in West Philadelphia, on quite a large plan.

The soluble glass has also given birth to a new kind of fresco painting, named by Fuchs "stereochromy." In this kind of painting the soluble glass forms the ground and also the binding of the colors, which are really silicified with it, and stand, therefore, the atmospheric influences, which destroy so easily common frescoes. For stereochromic colors these are recommended: fine white, chrome green, cobalt green, chrome red, the American vermilion, iron minium, sulphide of cadmium, ultra marine, ocher, terra di sienna, and umber. Sulphide of mercury, the old vermilion, cannot be used, getting brown, and, finally, black, by exposure to light.

If wished, I shall give a full description of this interesting mode of painting in another issue.

- Adolphus Ott.

Philadelphia, Nov., 1866.

[We shall be pleased to receive the description mentioned by our correspondent—EDS.