Page:Popular Science Monthly Volume 7.djvu/575

Rh bath almost without being touched. Then came another difficulty—that of preventing an already highly-heated combustible liquid taking fire upon the entrance of the still more highly-heated glass. The latter difficulty was met by placing the tempering bath in direct communication with the heating oven, and inclosing it so as to prevent access of air; and the former by allowing the heated glass articles to descend quickly by gravitation, from the oven to the bath.

The apparatus used by M. de la Bastie is shown in the accompanying illustrations, in which Fig. 1 is a front view, and Fig. 2 a vertical section, of furnace for annealing glass objects; Fig. 3 a sectional plan of the oven for annealing flat plates. The working oven, a, is heated by a furnace, b. The bottom of the oven, c, and the slope to the bath, are made in one piece of refractory material, and are very smooth on the surface. At the side of the oven is a preparatory oven, communicating by a passage in the separating wall. In this oven the glass is partially heated before being placed in the main oven, a. The products of combustion are carried away in the direction of the arrows through the chimney. When the oven, a, is sufficiently heated, the ash-pit and fire-doors are closed, and rendered air-tight by luting,



and the fire is maintained by small pieces of fuel introduced by a hole in the fire-door. The draught is then stopped by lowering the chimney-cap, or closing the damper. The vertical damper, f, is then raised, so that the flame passes by the flue, g, to a second chimney, passing thus along the slope and heating it, and also opening communication from the oven, a, to the bath, h, which is filled with the oleaginous compound. It is covered from the external air by a lid, and within it is a basket of fine wire gauze, k, hung from brackets. A tube, l, contains a thermometer, m, to indicate the temperature; and by this tube the contents of the bath may be added to, or any excess may overflow by the discharge-pipe, n. A plug, o, on the cover may be removed to