Fire Clay

a variety of clay used in the making of glass retorts, glass pots, fire bricks, crucibles, and the like. When found it is always a stratum immediately beneath a layer of coal. It must be a pure compound of silica and aluminum, free from an appreciable quantity of alkali, iron, lime, or magnesia. Articles made from a good quality of fire clay may be exposed to a temperature at which glass melts and ordinary pottery crumbles. Fire bricks made of this clay are able to with-stand a heat at which ordinary bricks fuse and run into a glassy mass. In the various operations connected with blast furnaces and the different methods of making steel, it is requisite to have huge retorts, cupolas, crucibles, and fire-brick linings capable of withstanding 1,000 deg., 1,600 deg., 2,000 deg., 2,600 deg. and even 3,000 deg. of heat. See Brick; Pottery