Alum

n. [O. Fr. & Pr. alum, N. Fr. alum, Lat. alumen, It. alume, Sp. alumbre, Ger. alaun.] A double sulphate of alumina and potassa, containing one part by weight of sulphate of potash, one of ter-sulphate of alumina, and twenty-four of water. It is white, transparent, very astringent, and crystallizes easily in octahedrons. Ure.

(Dyeing.) To impregnate or steep in a solution of alum. Ure.