Alum

n. [ OE. alum, alom, OF. alum, F. alun, fr. L. alumen alum. ] (Chem.) A double sulphate formed of aluminium and some other element (esp. an alkali metal) or of aluminium. It has twenty-four molecules of water of crystallization. [ 1913 Webster ]

☞ Common alum is the double sulphate of aluminium and potassium. It is white, transparent, very astringent, and crystallizes easily in octahedrons. The term is extended so as to include other double sulphates similar to alum in formula. [ 1913 Webster ]

‖n. [ L. ] (Chem.) Alum. [ 1913 Webster ]

n. [ L. alumen, aluminis. See Alum. ] (Chem.) One of the earths, consisting of two parts of aluminium and three of oxygen, Al2O3. [ 1913 Webster ]

☞ It is the oxide of the metal aluminium, the base of aluminous salts, a constituent of a large part of the earthy siliceous minerals, as the feldspars, micas, scapolites, etc., and the characterizing ingredient of common clay, in which it exists as an impure silicate with water, resulting from the decomposition of other aluminous minerals. In its natural state, it is the mineral corundum. [ 1913 Webster ]

n. (Chem.) A compound formed from the hydrate of aluminium by the substitution of a metal for the hydrogen. [ 1913 Webster ]

a. Combined with alumina. [ 1913 Webster ]

n. [ F. ] Alumina. Davy. [ 1913 Webster ]

a. Of or containing aluminium; as, aluminic phosphate. [ 1913 Webster ]

a. [ L. alumen alum + -ferous: cf. F. aluminifère. ] Containing alum. [ 1913 Webster ]