OPERATING BLAST FURNACES.
fillers.'' A view of this more modern plan of charging a furnace is shown in Figs. 7 and 8, and which are illustrations used by Mr. Walter Kennedy in the A merican Man ufacturer, J anuary 3, 1901. We also present cut Fig. 9, which .. was originally shown in the Journal of the Association of Engineering Societies, January, 1901.
In charging a furnace, the coke, limestone, and ore are generally dumped in the order mentioned and dropped independently of each other in the hopper H, Fig. 10. After the completion of each charge, the bell B is then lowered as indicated, and the material falls into the furnace shown, about as illustrated at the mound M M. After the delivery of the charge, the bell returns to its position, ready to receive the next supply of stock. There are several ways of oper-
FIG. IO.—ACTION OF STOCK DESCENDING A FURNACE,d silica, carbon, ganister, coke, magnesia, and asbestos bricks, all of which have been experimented with, and, to some degree, all have advocates of their utility in certain lines of work. Carbon bricks, it is claimed, have worn well, made of fine coke (poor in ash), or charcoal mixed with clay with tar as a binder. If such bricks contain more than 70 per cent of silica, as used for high temperatures, they are generally very friable and disintegrate with the least friction, so that bricks of this character would be suitable only for the lower body of a furnace. As clay is chiefly silicate of alumina, which is also a good substance to resist high temperatures, it works well as a binder with silica in making fire-bricks. The other substances in clay are iron oxide, lime, magnesia, potash and soda, which, to some degree, decrease the durability of fire-bricks. As fire-bricks come to the furnace or foundry they are often composed of about equal parts of silica and alumina. Bricks should contain silica or alumina in proportion to the amount of heat or friction they are if j