Brick

Brick was made from clay in very ancient times, and is found in Babylonian and Egyptian ruins. All clays consist essentially of a hydrated silicate of aluminium with, usually, some free silica, iron, lime, magnesia and potash. The clay is mixed into a pasty condition with water in the "pug mill," and then moulded to shape, either in a wet plastic, or in a semi-dry condition. In the latter case they are taken direct to the kiln to be baked, in the former they require drying first. The time of baking or "firing" varies with different kinds of clay from 40 to 150 hours. The fire bricks for building furnaces, etc., require to be of very refractory clay and should contain but little iron or alkaline oxides.