Alum

in its general sense a double salt pro- duced by the combination of the sulphate of an wkali metal with the sulphate of a triatomic metal of the aluminium group. Asa cla the alums are marked by identity of crystalline form, ready so lability in water, astringent taste, and acid reaction. They also contain the same quantity of water of crystallisation. The term alm, in its special sense, invariably denotes ordinary potash alum, symbol K,So,Al,(So,)3.24Aq.