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National Projector Carbons
slow. It may readily be formed in a variety of shapes, either in the initial plastic condition or later by machining in solid form. In graphitic form carbon is valuable as a lubricant. Carbon articles of graphitic composition can be used on many applications where an anti-frictional characteristic is necessary but where, due to temperature or other inhibiting factors, oil or grease lubrication is not feasible. The thermal conductivity of carbon, especially in nongraphitic form, is low as compared with that of most metals. While much higher in electrical resistance than the metals, carbon is a good conductor of electricity, a characteristic which adapts it to many uses in the electrical field. The contact resistance of carbon writh other elements of an electrical circuit is much higher than any metal, in which respect it is peculiar to other materials of good electrical conductivity.
The various industrial applications of carbon include carbon brushes, for motors and generators; welding carbon products; carbon anodes and electrodes, used in electro-chemical and electro-metallurgical industries; carbon Raschig rings, carbon tubes and carbon lining, used in handling and processing acids and other corrosive materials; dry cells; and numerous special applications among which may be mentioned switch and circuit breaker contacts, resistance discs, steam turbine packing, thrust rings for automobile clutches, back plates, diaphragms and granular carbon for telephones, electronic tube anodes and grids and, in the form of pure graphite powder, as a lubricant and a constituent of lubricating greases.
The original commercial application of carbon on an extensive scale was in the electric arc lamp. Here the peculiar characteristics of this element make possible a quality and intensity of illumination wrhich cannot be obtained in any other way. Possessing good electrical conductivity but low thermal conduc
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