Meaning of iron alum in English:

iron alum

Pronunciation /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.