ACETYLENE.

A colorless gas of the composition HC CH, used for welding and flame cutting of metals and for producing other chemicals. It contains 92.3% carbon and is therefore nearly gaseous carbon. When pure, it has a sweet odor, but when it contains hydrogen sulfide as an impurity, it has a disagreeable odor. Acetylene burns brightly in air, and was widely used for theater stage lighting before the advent of electric light. When mixed with oxygen as oxyacetylene for flame cutting and welding, it gives a temperature of 6332 F (3500 C). In air it is an explosive gas. The maximum explosive effect is with a mixture of 7.7% gas and 92.3% air. Acetylene has a specific gravity of 0.92. It is nontoxic and is soluble in water, alcohol, or acetone. It liquefies under a pressure of 700 lb/in ² (4.8 MPa) at 70 F (21 C). It is easily generated by the action of water on calcium carbide, but the newest methods involve pyrolysis, or cracking, of hydrocarbons, principally methane. It is also recovered from ethylene feedstock prior to polymerization. About 80% of acetylene usage is for synthesis of industrial chemicals, such as vinyl chloride, vinyl acetate, acrylonitrile, polyvinylpyrrolidone, trichloroethylene, and acetic acid. Acetylenic alcohols and diols include propargyl alcohol, butynediol, butenediol, butanediol, and butyrolacetone; these are used in metal pickling and plating and for making agricultural chemicals, polyesters, and vinyl esters. It is marketed compressed in cylinders, dissolved in acetone to make it nonexplosive. One...