Bauxite
A ferric oxide, usually containing alumina 50.4, sesquioxide of iron 26.1, water 23.5. Some samples have more silica and less iron. The purest is called aluminum ore, and is used in the manufacture of that metal. It is very refractory, being practically infusible, although containing over 20 per cent of iron oxide, while 4 or 5 per cent of the latter in some clays renders them easily fusible. Bauxite bricks are made by adding about 8 per cent of clay and plumbago for binding to the calcined bauxite, the result being that as soon as intense heat is applied the plumbago partially reduces the iron and the brick is rendered practically infusible. These bricks are more durable than ordinary fire-bricks, will resist the most intense heat as well as the action of basic slags. They also become harder with use. See FIRE-BRICK; REFRACTORY MATERIALS.