ALUMINIUM

(Al =27), bluish silver white, malleable, ductile trivalent metallic element of low sp. gr. (c.2.6) and high conductivity of heat and electricity, m.p. about 700°. Itis widely distributed, but only in compounds, constituting about 7 per cent. of the earth’s crust. Its principal minerals are the silicates kaolin, felspar, and mica, and cryolite diaspore (AIO.OH). Davy was able to obtain an iron alloy by the electric decompositi on of alumina (aluminium oxide Al.O:) with an iron wire in 1809 and called the element ‘alumium,’ but it was first isolated by Wohler in 1827, by reducing the chloride with pota ium. With the cheapening of electric power it has become po ible to obtain aluminium on a commercial scale. The HallHéroult proce , now in general use, consists of electrolyzing alumina (obtained from bauxite), di olved in molten cryolite in an iron ‘cell’ lined with carbon, the cast-iron bottom and the already reduced aluminium forming the cathode connected with the negative pole of the dynamo, and adjustable carbon rods dipping into the mixture forming the anode. Large aluminium works have been established at the Falls of the Rhine (Neuhausen and Rheinfelden), Niagara Falls, and the Falls of Foyers. The metal is becoming used more and more extensively for parts of engines, in boat-building, for cooking utensils, parts of airships and aeroplanes, for various electrical and scientific apparatus, aS a substitute for lithographic stone, and together with powder iron oxides in the thermite proce of ed welding and soldering. Numerous alloys of aluminium have been manufactured, which are being increasingly employed account of their greater strength and on hardne (e.g.) magnalium (aluminium and magnesium) and aluminium bronzes a ‘and 2.5 to 10 per cent. aluminium). The great amount of heat developed by the combustion of aluminium has naturally to proposals for its use in led compositions, because, alex plosive the product of combustion though (Al.0;) is a solid, the gases produced from other ingredient s of the explosive composition would be raised to such a high temperature that great pre ure result. /Ammonal is a well-known must of an explosive containing example is aluminium. An intense white light when aluminium burns, so produced it is used in flash-light compos it i ons that photographic purposes, or for illumifor star compositions for rockets or nating shells.