ALUMINIUM The aluminium content of the earth appears to be concentrated near the earth's surface. F. W. Clarke and H. S. Washington estimate that the earth as a whole contains only 1.79% of alu minium, but that the outer crust, to a depth of io m., contains 8.05%. This is equivalent to an aluminium oxide content of 15 to 16%. The ores of aluminium are employed for the production of aluminium, alumina, aluminous abrasives, cement, aluminium chloride, alum, etc. From economic considerations those ores are employed which yield the maximum number of units of alumina per unit of cost. For this reason the pre-eminent ore is bauxite, which contains 5o to 6o% of alumina. The bulk of the world's aluminium is produced from alumina extracted from bauxite by digestion with caustic soda—the well known Bayer process. In 1929 about four tons of bauxite would produce a ton of aluminium. Bauxite of commercial grade is available in extensive deposits in Europe, North and South America, Asia and Africa, but the bulk of the production comes from the first three of these continents. E. C. Eckel, upon the assumption that the available bauxite per square mile of area is the same in other continents as in Europe, has estimated the world's bauxite reserves as about 2,500 millions of tons. In 1937 the world's production of bauxite was about 3,700,000 tons. After allowing for substantial annual increases in consumption, therefore, the world's supply will last a long time.
The aluminium industry was in 1928 using the purest bauxite, particularly with respect to silica, and much of the world's supply of bauxite is less desirable for the Bayer process. However, there
are other processes being developed which can handle lower grades. Among these are the electric furnace process of C. M. Hall as recently developed by Aluminum Company of America, as well as the processes of Pedersen and Haglund. Other ores of alumin ium, particularly certain of the silicates, are proving susceptible to treatment by processes now under development, so that when they become economically important they can be utilized. This will still further extend the available supplies of aluminium ores. The consumption index of aluminium is increasing more rapidly than some of the older, commonly used metals. Up to 1929 aluminium had competed principally with copper and other non-ferrous metals on a price per volume basis. With the greater realization, however, of the economic value of the lightness and strength of aluminium and the development of strong, light alloys, aluminium competition with other metals increased materially, accompanied by continually improving production and fabrication methods. Uses of the compounds of aluminium, as in the abrasive, cement, and chemical industries have also expanded. For all these growing demands, the supply of aluminium appears ample for many years to come. (J. D. E. ; X.)