Glass made with Cryolite

FLUORIC AND FLUOSILICIC ACID.

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The use of fluorine compounds has been considerably developed by the same inventor, in connection with M. Marechal,in engraving on ghut»; fluoride of an alkali with sulphuric acid being employed to engrave glass without destroying the polish, and employing a hydrofluate of the fluoride of silicon when a dead surface is desired: these methods of furnishing the hydrofluoric acid are but a modification of known processes. We are doubtless to expect something in the future from the introduction of these compounds in the arts. Already cryolite, the natural fluoride of aluminum and sodium, is being largely applied in the manufacture of an opaque glass, and it is desirable to present, in some detail, an account of the process as described in the American Journal of Pharmacy, May, 1868:

GLASS FROM CRYOLITE.

"The application of cryolite to this new porcelain or opaque glass, promises to be one of those discoveries, simple in themselves, that may materially affect the course of trade and manufacture. This material (which is simple glass, so far as the mode of working is concerned) is furnished at less than the cost of the cheapest ordinary white or flint glass. It can be worked or formed with the facility attending working common brown or pressed glass, and any article of any shape that can be made from glass can be made from it, and the product exactly resembles the finest French porcelain in appearance and beauty, but far surpasses it, as well as glass, in toughness, strength, and capability of standing sudden changes of temperature. The ingredients used in its manufacture consist of cryolite 10 pounds, white sand 20 pounds, and oxide of zinc 5 pounds; the dirty discolored oxide, worth less than half the price of the white oxide of commerce, answers very well for this purpose. The infusion of the ingredients is effected at the same heat, and in the usual manner practiced in the flint-glass factories. In this manner can be made not only the articles ordinarily made of glass or porcelain, but also tiles, mantel-pieces, moldings, statuary ware, mortars, pill-tiles, evaporating dishes, funnels, ointment jars, and, in fact, any and every thing capable of being cast, blown, or molded whilst in a melted state, and at a mere trifling cost. The business of making these articles from cryolite is as yet in its infancy. One establishment in this city alone [Philadelphia], and the only one yet in operation, is working exclusively on it, consuming from 500 to 1,000 tons of cryolite per annum; but its use will necessarily become general, either as a specialty or in connection with the ordinary white or transparent glass. Having obtained from the factory of this 'hot-cast porcelain' several mortars, funnels, and evaporating dishes, and tested them fully and satisfactorily, they were found to have their advantages over the ordinary ware now in use. The mortars presented at all times a much whiter color, and withstood more pounding or trituration than the Wedgewood mortar commonly used; and the evaporating dishes resisted the heat of both the sand and water baths; at the same time we were able to purchase them at about one half the cost of ordinary porcelain. Not only these bulky and useful articles are manufactured, but also the finest parlor ornaments and lamp-shades are made and decorated, and finished in a most beautiful manner, at the establishment which is situated in the upper part of Kensington, on York avenue, in Philadelphia."