Coal-dust
Commonly called sea-coal facing is ground from bituminous coal that has been selected for its freedom from slate, sulphur, or any other substance of a deleterious nature. When this dust is mixed with the sand, it breaks up and separates the fusible elements contained therein, and that which is not separated is more or less impregnated with the gas produced. Fusing of the sand is by this means partially prevented by reason of the hydrogen and carbon which the sea-coal contains. Experience teaches just how much coal-dust is required for this purpose; but it is seldom that more than one of coal to six of sand can be used, as any higher percentage will produce a too open mixture which results in streaked blotches on the castings, caused by the molten iron searching out the surplus coal and consuming it. See FACING-SAND; FACING.