ALUMEN—ALUM
Derivation.—From alum slate, shale, schist, a native mixture of aluminum silicate and iron sulphide. This is roasted and exposed to the air, when the sulphur is oxidized into sulphuric acid and combined in part with aluminum and iron to form sulphates. The mass is lixiviated with water, and aluminum and iron sulphates together with sulphuric acid are recovered in solution. The solution is concentrated and to it is added potassium chloride. The double sulphate of potassium and aluminum (alum) is formed, which crystallizes out on cooling, while potassium sulphate and ferric chloride remain as by-products. Alum is purified by recrystallization.
Properties.—Large, colorless, octahedral crystals, sometimes modified by cubes or crystalline fragments; without odor, but having a sweetish and strongly astringent taste. On exposure to the air the crystals are liable to absorb ammonia and acquire a whitish coating. Soluble in nine parts of water, insoluble in alcohol.
Dose.—Horses and cattle, 2 to 4 dr.; sheep and pigs, 20 gr. to 1 dr.; emetic for dogs, 1⁄2 to 1 dr.