Bricks
Good common bricks have about the following composition: silicia 3/5, alumina 1/5, lime, magnesia, soda, iron, potash, and water being included in the other fifth. The American brick varies in size from 7 3/4 to 8 1/2 inches long, 4 to 4 1/2 wide, and 2 1/4 to 2 1/2 thick. English bricks average 9 inches long, 4 1/2 wide, and 2 1/2 thick. A too severe fire in the kiln fuses the brick and causes hard clinkers; on the other hand, insufficient burning causes a soft brick unfit for use. See FIRE-BRICK.