alum (1), alym

[In Sw. alun; Dan. allun; Dut. alu in; Ger. alaun; Fr. alum; Sp. alumbre; Port. alumen; Ital. allume. From Lat. alumen = alum.] 1. Chem . The name given to double salts of sulphate of aluminium with sulphates of pota ium, sodium, ammonium, or of other monatomic metals, as silver, thallium, cæsium, rubidium. They crystallise in octohedra. Potash alum, Al2K2(SO4)4+24H2O, is prepared by the decomposition of a shale containing iron pyrites, FeS2, which is gently burnt and exposed to the air in a moist state; it oxidises and forms sulphates, and, on the addition of a potash salt to the solution obtained by water, alum crystallises out. Alum has a sweet astringent taste, reddens litmus paper, and di olves in its own weight of boiling water. Sodium alum is very soluble. Ammonium alum is often prepared by adding the ammonia liquor of gas-works instead of potash. Alum is used in dyeing and in preparing skins, . Alums can be also formed in which ferric or chromic sulphates replace aluminium sulphate, as pota io-ferric sulphate, FeK2(SO4)4+24H2O, and ammoniochromic sulphate, Cro(NH4)2(SO4)4+24H2O. These crystallise in the same form, and cannot be separated from each other by crystallisation. Alum is used in medicine as an astringent in doses of ten to twenty grains. Burnt alum is alum deprived of its water of crystallisation by heat; it is used externally as a slight escharotic. and oyle Of tartre, alym, glas, berm, wort, and argoyle." Chaucer: C. T., 12,740, 12,741. 2. Mineralogy. Dana makes Alum the type of a group of minerals, cla ed under his "Oxygen Compounds-Hydrous Sulphates," and places under it Tschermigite and Kalinite. Ammonia Alum : A mineral, called also Tschermigite (q. v.). Feather Alum : A mineral, called also Halo trichite (q.v.). Iron Alum : A mineral, called also Halo trichite (q.v.). Magnesia Alum: A mineral, called also Picker in gite (q. v.). Manganese Alum: A mineral, called also Apjohnite (q. v.). Native Alum: A mineral, called also Kalinite (q. v.). Soda Alum : A mineral, called also Men do zite (q.v.). 3. Art : Saccharine Alum is a composition made of common alum, with rose-water and the white of eggs boiled together to the consistence of a paste, and thus capable of being moulded at pleasure. As it cools it grows as hard as an ordinary stone. IMG:content-0426.png:[blocks in formation] 173 recommends it in diseases which on their removal leave debility behind. The tincture may be locally applied with much advantage in sore throats and ulcerations of the mouth. (Lindley: Veg. Kingd.) 2. Heuchera American a and Heuchera cortusa , plants of the Saxifrage order, both of which figure in the American pharma copœia.