The German method of making the lamp filaments is to squirt a mixture of
tungsten powder and thorium oxide through a perforated diamond of the
desired diameter. The filament so produced is drawn through a chamber
heated to 2500 deg. C. at a velocity of eight feet an hour, which
crystallizes the tungsten into a continuous thread.
The first metallic filament used in the electric light on a commercial
scale was made of tantalum, the metal of Tantalus. In the period
1905-1911 over 100,000,000 tantalus lamps were sold, but tungsten
displaced them as soon as that metal could be drawn into wire.
A recent rival of tungsten both as a filament for lamps and hardener for
steel is molybdenum. One pound of this metal will impart more resiliency
to steel than three or four pounds of tungsten. The molybdenum steel,
because it does not easily crack, is said to be serviceable for
armor-piercing shells, gun linings, air-plane struts, automobile axles
and propeller shafts. In combination with its rival as a
tungsten-molybdenum alloy it is capable of taking the place of the
intolerably expensive platinum, for it resists corrosion when used for
spark plugs and tooth plugs.
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