THE METAL OF THE FUTURE.

Otago Witness, Issue 3292, 18 April 1917, Page 54

THE METAL OF THE FUTURE.

When first exhibited at the Paris Exhibition of 1855, aluminium was regarded as a mere chemical curiosity, "silver made from clay," as it was popularly termed. When, however, severe tests demonstrated its superiority over other metals wherever lightness is synonymous Avith economy, the methods of manufacture were continually improved, until, in 1914, the price had fallen from £56 per lb to about £3 per hundredweight. The characteristics of the now well-known, shining, tin-white metal are such as to render it increasingly useful in all branches of the arts and sciences. It is not brittle like glass or porcelain, or poisonous like copper; it needs no enamel, does not rust, and,bulk for bulk, weighs but a fraction of other metals: These properties render it of_ the utmost value in aviation, in electrical engineering, in science, and in the home. Aluminium is an essential constituent of all clays, felspars, and granites. It occurs also in cryolite and bauxite, and in many precious stones. It is thus one of the commonest and most widely-distributed of elements. _ Practically the only source, however, is bauxite, "a more or less impure oxide. The manufacture of aluminium divides itself into two stages—first, the purification of the bauxite; and, secondly, its electrolysis in a bath of fused cryolite. The purification of the raw material is a costly and laborious process, to which is very largely due the comparatively high cost of the metal. The electrical smelting in Heroult or similar tiltingfurnaoes is now carried on very cheaply by the utilisation of water-power. Pure aluminium is in large demand as a base for heat-resisting paints, for cooking utensibj and for ornamental fittings. Aluminium wire is favoured for long-dis-tance electrical transmission, since for a given conductivity it is not so heavy as copper wire. Thermite, a mixture of aluminium powder and certain metallic oxides, is used in welding, and now finds a place in the manufacture of incendiary bombs, since ; by it 3 combustion, temperatures as high as 60OOdeg Fahrenheit are. easily obtained. In metallurgy aluminium is used for promoting soundness in steel ingots, and in the production of chromium and similar metals in a carbonfree state. The pure, metal is now being to a large extent replaced by certain of its alloys, the addition of only a small percentage of various metals, notably magnesium, producing a disproportionate increase in the tensile strength and resistance to corrosion. Magnalium is very extensively used in aeroplane, torpedoboat, and submarine fittings. Aluminium bronze, containing only about 5 per cent, of aluminium, ranks in strength with caststeel, ( and is hard, light, and elastic. Aluminium and its alloys can only be soldered with difficulty, but may be welded by autogenous soldering. As has been indicated, the most serious obstacle to the cheap manufacture of aluminium is the preliminary, purification of the native bauxite. A new' method, which promises to oust all others, has been devised by Dr Serpek. By this method, which is in use at the. works of the Societe General des Nitrures, in Savoy, the recovery of a most valuable by-product is made to pay very nearly the whole cost of purification. Natural bauxite Is heated in the electric furnace with small coal or coke. Over the mass a slow current of nitrogen passes, l-esulting in the formation of aluminium.nitride. The latter is then treated either with water under pressure or superheated steam, yielding pure alumina and giving off ammonia-gas, which is absorbed in sulphuric acid. , The sulphate of ammonia thus made is about 25 tons per 20 tons of alumina, reducing the cost of purification from £ls to £2 per ton. Incidentally, this is by far the cheapest method of ' fixing' atmospheric nitrogen, the cost for current being only one-half that of the 'nitrolime' process and a fifth that of the arc process. Serpek's method constitues a most important advance in the manufacture of aluminium. But as yet no economical and practical process has been devised for the extraction of aluminium from clay. Boundless possibilities lie before the research metallurgist in this direction. Such a discovery once made, the manufacture of aluminium will proceed on a scale commensurate with the steel industry; and while, of course, it cannot hope to oust iron as the most useful metal, aluminium will become a serious rival to it. —Chambers's Journal.