[L,. alumen.] A white saline compound used in dyeing and many other industrial processes. Chemically it is known as a double sulphate of potassium and aluminium. It has an astringent and sweetish taste, turns vegetable blue colors red, dissolves in water and melts when heated. When more strongly heated it loses its water of crystallization, leaving the white substance known as burnt alum, which is used as a caustic. It has many highly important uses in the arts, as a mordant in dyeing, etc., and in medicine it is of great use as an astringent in stopping bleeding. Wood and paper which have been dipped in a solution of alum are less liable to catch fire.