ALUM

AL'UM, noun [Latin alumen.]A triple sulphate of alumina and potassa. This substance is white, transparent and very astringent; but seldom found pure or crystallized. This salt is usually prepared by roasting and lixiviating certain clays containing pyrites, and to the lye adding a certain quantity of potassa; the salt is then obtained by crystallization. alum is of great use in medicine and the arts. In medicine, it is used as an astringent; internally, in hemoptoe, diarrhea, and dysentery; externally, as a styptic applied to bleeding vessels, and as an escharotic. In the arts, it is used in dyeing to fix colors; in making candles, for hardening the tallow; in tanning, for restoring the cohesion of skins.

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alum. Alum, n. the sulphate of alumin and potash, a salt composed of sulphuric acid, alumin, and potash

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Al″um (�), 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. ☞ 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.