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Page:Popular Science Monthly Volume 49.djvu/813

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789
ACETYLENE.

and production of high pressures and heat accounting for the various volcanic disturbances and the large natural deposits of petroleum and other carbonaceous material, which occur so abundantly in some districts.

Pure calcium carbide has a specific gravity of 2·262; in a dry atmosphere it is odorless, but upon exposure to moisture evolves the peculiar odor of acetylene. When exposed in lumps to the action of ordinary air it becomes coated with a layer of hydrate of lime, which protects the interior of the mass from further oxidation. It is not inflammable, and can be exposed to the heat of the ordinary blast furnace without decomposition. It is, in fact, a very stable compound, its ready decomposition under the action of water being quite at variance with its other chemical properties. It was first prepared by Woehler, in 1862, by fusing an alloy of zinc and calcium with carbon. He called it acetylene carbide. It forms a dark grayish or red dense mass, which upon fracture shows a crystalline metallic surface. The whole process of manufacturing acetylene, from the preparation of the lime and coke onward, is very simple, and the only reason why it is new as a commercial product is the difficulty of causing a combination between the calcium of the lime and the carbon of the coke. Nothing short of the temperature of the electric furnace (3500° to 4000° C.) will bring this about, and the comparative modernness of this apparatus accounts for the lateness of the calcium carbide. The chemistry of the process is as follows: Quicklime (CaO) and coke, or any other substance whose main content is carbon (C), are mixed and fused together in the electric furnace. The calcium (Ca) of the lime combines with part of the carbon (C) of the coke to form calcium carbide (CaC2); the oxygen (O) of the quicklime combining with another portion of the carbon to form carbonic oxide:

CaO + 3C = CaC2 + CO
Quicklime. Coke. Calcium
carbide.
Carbonic
oxide.

Carbonic oxide is a gas and is driven off, leaving calcium carbide and the various impurities in the furnace. The further reaction to form acetylene occurs when calcium carbide is subjected to the action of water:

CaC2 + 2(H2O) = Ca(OH)2 + C2H2
Calcium
carbide.
Water. Slaked lime. Acetylene.

The following description of the commercial manufacture of calcium carbide as conducted at Spray is based on a paper by G. de Chalmot, who for some time had personal supervision of the works of the Wilson Aluminum Company at Spray, N. C, and