iron alum
/ˌʌɪən ˈaləm/noun
Chemistry. Each of two hydrated double sulphates of (ferric) iron and (respectively) potassium and ammonium, belonging to the series of alums and typically pale violet in colour.
- Formula: KFe(SO4)2·12H2O (with potassium); (NH4)Fe(SO4)2·12H2O (with ammonium)..
Origin
Mid 19th century. From iron + alum, perhaps after German Eisenalaun or French alun de fer.
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