FIRECLAY. Clay of highly refractory character, capable of resisting a very high temperature without fracture, fusion or softening. This quality is due to comparative freedom from flux ing impurities, such as soda, potash, lime, iron, and magnesia. There is no fixed standard of refractoriness for these clays, but no clay should be classed as a fireclay which has a fusion point below I,600° Centigrade.
Fireclays vary considerably in chemical composition, but gener ally the percentage of alumina and silica (taken together) is high, and the percentage of oxide of iron, magnesia, lime, soda, and potash (taken together) is low. Other materials, such as lime, bauxite, etc., are also used for the manufacture of firebricks where special chemical or other properties are necessary.
Fireclays are abundantly distributed in Great Britain and in the United States. A typical fireclay is composed of silica, 22% alumina, 2% oxide of iron, 2% potash, o.5% mag nesia, 0.5% lime, 5.5% water, 0.5% organic matter. See FIRE BRICK.