aluminium

[In Ger. & Dut. aluminium. From Lat. alumen alum.] Chem. A tetratomic metal; symbol Al; atomic weight 274; sp. gr. 26; melts at red heat. It is a white, sonorous, ductile, malleable metal, not oxidised in the air, nearly insoluble in dilute sulphuric or nitric acid, readily soluble in HCl, and in solutions of potash or soda with evolution of H. It is used for instruments and ornaments; it forms a valuable alloy with copper, resembling gold, and not easily tarnished, called aluminium bronze. It is prepared by decomposing the double chloride of aluminium and sodium by metallic sodium. It forms one oxide, alumina, Al2O3 (q.v.). Its most important salts are alums (q.v.) and aluminium chloride, Al2Cl6, which is formed when aluminium hydrate is di olved in HCl, but upon evaporation HCl escapes and leaves Al2O3. It can be obtained by pouring Cl over a mixture of Al2O3 and carbon heated to redne . It is a transparent waxy substance, boiling at 180°. It forms double salts with alkaline chlorides, as AlCl6.2NaCl. Aluminium fluoride, AlgF6, also forms double salts, aluminium and sodium. Fluoride, Al2F6.6NaF, occurs as the mineral cryolite in Green land. Numerous silicates of aluminium occur as minerals [see CLAYS, FELSPAR, .]. The salts of aluminium are recognised by giving a blue colour when moistened with nitrate of cobalt, and heated before the blow-pipe. Alumina is precipitated from its solutions by caustic alkalies as a white precipitate, soluble in exce ; ammonia gives a similar precipitate, insoluble in exce ; alkaline carbonates precipitate the hydrate, and CO2 escapes; ammonia sulphide gives a white precipitate of aluminium hydrate. The salts of aluminium belong to the same cla as the ferric and chromic salts; oxides of aluminium, chromium, and sesquioxide of iron are precipitated with ammonia, [ANALYSIS.] The alumina and phosphate of aluminium are di olved by boiling with caustic potash; phosphate of aluminium is distinguished by being insoluble in acetic acid.