HOW ALUMINUM IS PRODUCED.
ALUMINUM is the electrician's metal. It was discovered, or rather first isolated from the minerals of which it is a component, seventy-two years ago, by Wohler, in Germany. As lately as ten years ago it was so rare that it was justly classed as a precious metal. Then the electrical processes for its manufacture came into use, and to-day it is cheaper than any of the other metals excepting only iron, lead, and zinc. The method of its production is as simple as it is interesting. Two minerals, cryolite and bauxite, are used in the process, both of them compounds of aluminum. The former is found only in Greenland. Curiously enough it is green, a roughly crystalline substance which melts easily at a low red heat. It is, chemically speaking, aluminum fluoride. Bauxite, which is named after the town of Baux, in France, near which large beds of it have been found, is a white or yellowish clayey substance, consisting almost wholly of alumina, or aluminum oxide. In the modern process the cryolite is first melted in cast-iron tanks about the size and shape of an ordinary bath-tub, gas fires being used to supply the heat. Into the molten mass is stirred the bauxite, which has previously been cleaned and pulverized. At each end of each tank is an electrode consisting of a heavy carbon plate, and between these a very powerful current of electricity is passed. The current is sufficient to keep the contents of the tank heated to the melting point, and in a few minutes the metallic aluminum begins to collect at one of the carbon plates. The temperature of the bath being high enough to keep the metal melted, it collects in drops and flows to the bottom of the tank, from which it is drawn from time to time by removing a plug from a conveniently-situated hole. The metal is rapidly taking the place of brass and copper in many industries, notably as a conductor of electricity. For long-distance power-transmission lines it has many advantages. While it is more costly, pound for pound, than copper, yet it is so much lighter and comparatively so good a conductor of electricity, that a line built for it, for the same effective current-carrying power, weighs only half as much and costs ten per cent. less.—Selected.