Alume

Alume is a term used in some texts as an alternative spelling of alum, the group of chemical compounds that are double sulfates of aluminum with a monovalent cation. The most common member is potassium aluminum sulfate, KAl(SO4)2·12H2O, which forms colorless to white crystals that are soluble in water. General formulations of alums have the formula MAl(SO4)2·12H2O, where M represents a monovalent metal such as potassium or ammonium. Alums historically crystallize from acidic solutions and are often produced commercially by combining aluminum sulfate with the appropriate sulfate salt and allowing crystallization to proceed.

Applications of alum include water purification, where alum acts as a coagulant to remove suspended particles; use in dyeing and textile finishing as a mordant to fix colors; use in leather tanning; and in food preparation as a firming or stabilizing agent in some pickles and confections. They have also served as topical astringents and antiseptics in medicinal and cosmetic contexts.

Safety and regulation: exposure to alum in crystalline form or dust can irritate the skin, eyes, and respiratory tract; ingestion of large quantities is harmful. Food-grade alum is regulated in many jurisdictions and should be used within permitted guidelines. Environmental considerations include careful disposal to avoid aquatic contamination.

While the spelling alume occurs in some older texts or regional variants, current chemistry commonly uses alum with no final e. See also alum, alumen, and related double sulfate minerals.