OPERATING BLAST FURNACES AND REDUCTION OF ORES.
The amount of stock that passes through a furnace the size of that seen in Fig. 10, page 49, every twenty-four hours is about 280 tons of ore,* 190 tons of coke, and 60 tons of limestone, a total of 530 tons. In filling a furnace by hand labor, two gangs of men are always
FIG. 7.— MODERN BLAST FURNACE WHERE HAND LABOR IS MINIMIZED.
employed, one at the top, and the other on the ground floor load the buggies and wheel them to the elevator, which ascends a distance of 70 to 100 feet in about twenty seconds. There being two cages to the elevator, an empty one is returned as the loaded onemay be said, are not obtainable. Several kinds of material have been tried in an effort to secure a lining for furnaces that would exceed the life of the general character of fire-bricks used. We have what are called 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