ACETYLENE.* Chemical Properties. C,Hr- carbon 92.25 per cent, hydrogen 7.75 by weight. At atmospheric pressure and 60° F., the volume of one pound of acetylene is 14.53 cubic feet. Acetylene requires 11.92 volumes of air or 2.5 volumes of oxygen for its com plete combustion. Acetylene is a colorless, tasteless gas; when chemically pure it has a sweet ethereal odor; when in commercial form traces of impurities impart to it a pungent odor suggesting garlic. Acetylene is an unsaturated hydro-carbon. It exists in a state of unstable chemical equilibrium and owing to this fact it combines very energetically, having low igni tion temperatures, namely, 804° F. in air and 782° F. in oxygen, compared with about 1200° for other gases under similar conditions.
When mixed with the proper Rroportions of air and ignited, acetylene will give rise to a so-called gas explosion, as will any other combustible gas or combustible solid if in a state of sufficiently minute subdivision. The explosive range for acetylene under ordinary conditions is from 3 per cent of acetylene and 97 per cent of air to 24 per cent of acetylene and 76 per cent of air, the point of maximum explosibility being 12 per cent of acetylene and 88 per cent of air. Unlike other gases, how ever, acetylene possesses high endothermic energy, greater than that of any other ordinary substance. By this it is meant that the ele ments forming actylene may be considered as being in a state of chemical stress and capable of giving rise to a very considerable amount of heat by the mere act of their separation. In other words, an endothermic substance will give more heat when burned as a compound than can be obtained from burning its separate ele ments in the uncombined state. The carbon and hydrogen forming one cubic foot of acety lene would produce 1,248 heat units if they were burned separately. One cubic foot of acetylene, however, formed from the same car bon and hydrogen will produce 227 heat units more than this amount, making a total of 1,475 per cubic foot. The 227 heat units represent endothermic energy. Owing to this endother mic energy, acetylene acquires true explosible properties and will dissociate with explosive violence without admixture of air or oxygen if it is compressed slightly in excess of 20 pounds per square inch and ignited. Owing to this
property, insurance, police, transportation and fire authorities prohibit the manufacture, stor age and transportation of acetylene at a pres sure exceeding 15 pounds per square inch, ex cept when the acetylene is compressed into cylinders containing a porous substance having a degree of porosity which will prevent the propagation of an explosion.
Acetylene, at atmospheric pressure, is solu ble to the extent of about volume for vol ume in water. It is also soluble in vary ing proportions in alcohol, chloroform, benzene, paraffin, olive oil, ether, carbon bisulphide, etc. It is soluble to a remarkable extent in acetone, which liquid will dissolve 25 times its own volume of acetylene at atmos pheric pressure and an additional 25 volumes for each atmosphere of pressure to which the acetylene may be subjected. Commercial ad vantage is taken of this property and acetylene under pressure is now stored and transported in cylind is which arc packed with a porous substance soaked with acetone. The porous mass empiuyed in such cylinders generally con sists of asbestos in the form of blocks built up and reinforced with silicate of soda, or of a mixture of charcoal, kieselguhr and cement, molded into the cylinders. Cylinders contain ing acetylene compressed into a porous sub stance of a proper degree of porosity, or com pressed into a porous substance soaked with acetone, or other suitable solvent, are safe and their use is permitted. Acetylene stored in this way is commonly known as dissolved acety lene. The use of acetylene dissolved in ace tone gives to this gas a portability and a uni versality not possessed by any other lighting or heating agent. Cylinders of acetylene are now carried on motor cycles, trucks and small boats, and they are obtainable at country stores as well as in the cities. This has resulted in the education of thousands of people in the use of gas who used to depend upon the liquid fuels for their light and heat.