Page:Popular Science Monthly Volume 49.djvu/810

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THE advent of the electric light, the Siemens-Lungren regenerative burner, and the Welsbach incandescent mantle, all within a comparatively short period, threw the lighting industry into a very unsettled condition. There had begun, however, to appear some order out of the chaos. As the special advantages of the different systems were recognized, the purposes to which each was best adapted were noted. The development of the industries was going on very satisfactorily, when a new competitor appeared in the shape of acetylene. It is now stated that Mr. Edison and Nikola Tesla are independently working out still another system, based on the vacuum-tube phenomena; a subject in which Mr. D. McFarlan Moore claims also to have made a great step in advance by the invention of his vacuum vibrator. Vacuum-tube lighting, however, is still in the laboratory, and, while surprising tales are told of its great beauty and high efficiency, it is too soon to even prophesy intelligently regarding it. Acetylene has, however, during the last few years been much discussed, and considerable data are available regarding it; so that an inquiry into its history and value as a practical illuminant is of interest.

Acetylene (C2H2) was first described by Edmund Davy, who obtained it accidentally by the action of water on a mass of carbonized tartar and charcoal powder, with which he had attempted to prepare potassium. He called the new gas Klumene. Some years later it was rediscovered by Berthelot, who obtained it by passing ethylene through a red-hot tube; he noted its occurrence in coal gas, and later succeeded in making it by passing a powerful electric current between two carbon poles in an atmosphere of hydrogen.

The resulting mixture of acetylene and hydrogen was passed into an ammoniacal solution of cuprous chloride, and the insoluble copper compound thus obtained, which is extremely explosive and has recently caused several serious accidents, was then treated with hydrochloric acid, which liberated acetylene.

Acetylene is a colorless gas, having a rather disagreeable odor, somewhat resembling garlic and phosphorus. The peculiar odor noticed when the burners of a gas stove strike back is due to the formation of acetylene. Its specific gravity when compared with air is 0·91 (ordinary coal gas has a specific gravity of about 0·607). At 0°, and under a pressure of 21·5 atmospheres (322·5 pounds per square inch), it becomes a mobile, highly refractive liquid. Water at 18° dissolves its own volume of the gas. When ignited at an ordinary burner it gives a smoky, dull flame, and with oxygen