alulet (alulet)

taining more or le carbonaceous material (remains of seaweeds, etc.), with which is a ociated an easily decomposed and frequently occurring compound of sulphur and iron (marcasite). The decomposition of this substance gives rise to an efflorescence of alum, usually potash alum, which is a compound of pota ium sulphate and aluminium sulphate. - Burnt alum, alum from which the water of crystallization has been driven off by heat. Also called dried alum, alumen exsiccatum. - Concentrated alum, normal aluminium sulphate, Al2(SO4)3, which is prepared on a large scale by treating roasted clay with oil of vitriol, and crystallizing out the sulphate form ed. It is largely used in dyeing. Also called patent alum. - Cubic alum, or basic alum, the mineral alum-stone. Earth of alum. See earth. - Roman alum, a variety of potash alum prepared from the mineral alum-stone, of special value to dyers, since it contains no soluble iron salts. Also called rock - alum and roc he - alum.