: either of two colorless or white crystalline double sulfates of aluminum used in medicine internally as emetics and locally as astringents and styptics: a: one KAl(SO4)2·12H2O that is a sulfate of aluminum and potassium—called also potassium alumb: one consisting of an ammonium aluminum sulfate NH4Al(SO4)2·12H2O—called also ammonia alum, ammonium alum
: any of various double salts isomorphous with potassium aluminum sulfate
Inorganic compound, any of a class of hydrated double salts, usually consisting of aluminum sulfate, water of hydration (an essential part of the crystal makeup), and the sulfate of another element. The most important alums are those of potassium sulfate (potassium alum, or potash alum, KSOAl(SO)24HO), ammonium sulfate, and sodium sulfate. Alums occur naturally in various minerals and can be prepared and purified by crystallization from their solutions. Most are white crystals with an astringent, acid taste. They are used as paper-sizing agents, flocculating agents in water treatment, mordants in dyeing, and in pickles, baking powder, fire extinguishers, and medicines.