Sherry Thompson, age 16, of Santa Cruz, Calif., for her question:

HOW IS TUNGSTEN USED?

Tungsten is a metallic element. The principal uses of tungsten are as filaments in incandescent lamps, as wires in electric furnaces and in the production of hard, tanacious alloys of steel. It is also used in the manufacture of spark plugs, electrical contact points and cutting tools and as a target in X ray tubes.

Tungsten is never found free in nature but occurs in combination with other metals, notably in the minerals scheelite and wolframite, which are the important tungsten ores.

To separate the element from its ore, the ore is first fused with sodium carbonate to yield sodium tungstate. The soluble sodium tungstate is then extracted with hot water and treated with hydrochloric acid to yield tungstic acid. The latter compound is washed and dried to produce an oxide which is refined in an electric furnace. The resulting fine powder is reheated in molds in an atmosphere of hydrogen and pressed into bars.

After being hammered and rolled at a temperature of 2,732 degrees Fahrenheit, the metal bars become compact and ductile, which means it is capable of being drawn out into wire or threads.