Aluminum

or Aluminium, a silvery white metal about as hard as zinc. It may be hammered into sheets and drawn into wires. It rings when struck, and is a good conductor of heat and electricity. It does not rust in the air, and is harder to melt than silver. Aluminum oxide, known also as alumina, is found in nature as corundum, of which the ruby, the sapphire, and emery are varieties. Alumina is one of the principal ingredients of clay. Aluminum gives its name to alum and enters into a vast number of minerals and soils. It is one of the lightest of metals, and would be used in preference to iron in buildings, were not its separation from clay so expensive. Aluminum is used for the tips of lightning rods. The cap of the Washington Monument, weighing 100 ounces, which is also the tip of its lightning rod, is formed of this metal. Of late aluminum has displaced copper in part as a conductor through which to distribute electricity from power houses. Electricity generated at Niagara is carried by aluminum cables to Buffalo. Thin sheets of aluminum are used as a substitute for tinfoil. The metal is used also for hairpins, thimbles, ferrules, bands for canes and umbrellas, mirror frames, combs, backs for brushes, and many other articles. Bobbins of this metal are not subject to shrinkage. They are lighter than wood. The output of aluminum in the United States was only 83 pounds in 1883; in 1904 it was 8,600,000 pounds. Aluminum is separated from clay by electrolysis in an electric furnace, at a cost (1909) of about eighteen cents a pound. Beds of clay suitable for the purpose occur in Georgia, Alabama, and Arkansas. There are smelters at Niagara Falls and Pittsburg. In 1909 Europe produced about 30,000 tons; America, 15,000 tons. See Copper; Corundum; Sapphire; Clay