ALT-ZABRZE, See ZABRZE.
ALUM (Lat. alumna, of unknown origin). A double salt consisting of a sulphate or selenate of the monovalent element or radicle, and a sul phate or selenate of a sesquioxide. that crystal lizes in the isometric system with twenty-four molecules of water. The principal alums of com merce contain potassium, ammonium, or sodium, and the sesquioxide of aluminum.
Potassium alum is a white, astringent. saline compound, found native as ketinitc. It is made by calcining carbonaceous shales, the residue from which is digested with sulphuric acid, yield ing alumin11111 sulphate; to this potassium sul phate is then added, the resulting crystals con stituting the alum. Another met hull consists in dissolving the alumina derived from the minerals cryolite or bauxite in sulphuric acid and treat ing the solution with potash or ammonia.
Ammonium alum is found native as wrigite, and is artificially made by combining am monium sulphate with aluminum sulphate as previously described. The low cost of ammonium
sulphate, obtained as a by-p•odnet in the manu facture of illuminating gas. has led to the sub stitution of this alum in commer•e for potassium alum. The properties of the ammonium and potassium alums are similar, though the am monium compound is less soluble in water.
Sodium alum is found native as ma cadosite, and is made by the eombination of sodium sul phate with aluminum sulphate.
Alum is used as mordant in dyeing, to clarify liquors of various kinds and especially water, to harden tallow, fats, and gypsum in the tan ning of leather; time ammonium alum is used in the manufacture of baking powders. A potas sium chromium sulphate, called chrome alum, and an iron aluminum sulphate called iron alum, are also used in the arts. Consult .T. Arctic. Acid, Vinegar, Alum, Ammonia, etc. (Phil adelphia. 1885).