Fire bricks are used in places where a very high temperature is to be resisted, as in the lining of furnaces, fireplaces and tall chimneys. The ordinary fire brick used for the above purposes is made from a mixture of about 50 per cent raw flint clay and 50 per cent, plastic clay, the proportion varying with different manufacturers. The bricks are made both by the stiff mud and dry press processes, and also by the soft mud process with hand moulding. It is claimed that the last process gives the most perfect brick.

* H. A. Wheeler, E. M , in the Clay Worker, August, 1895.

Fire bricks, to admit of rapid absorption or loss of heat, should be open grained or porous, and at the same time free from cracks. They should also be uniform in size, regular in shape, homogeneous in texture and composition, easily cut and infusible.

Fire bricks are generally larger than the ordinary building brick.