ACET'YLENE from acetyl), 1IC=CIL A colorless gas composed chemically of carbon and hydrogen. It is present in small quantities in ordi nary illuminating gas, and has a eharaet eristic disagreeable odor somewhat resembling that of garlic. Its "critical temperature" is 37° C. (about 98°.6 F'.) ; that is to say, no matter how great the pressure to which it may be sub jected above 37° it will remain gaseous, while at :37° a certain pressure, called the "critical pressure," is necessary and sufficient to liquefy it ; the critical pressure of acetyhme is fiti at mospheres. Acetylene burns with a brilliant flame and is used as an illuminant. it is best made for scientific as well as for industrial pur poses by the action of water on the carbide of calcium (q.v.). It. is thus produced, for in stance, in bicycle "gas lamps." The various apparatus devised for the manufacture of acety lene produces it either in the gaseous state or, by immediate compression, in the liquefied state. We will distinguish two types of apparatus. In the first, the carbide is contained in an appropriate rcsereoir, into which water is introduced at a required rate. Such apparatus is rather inconvenient and somewhat dangerous, for the reason that in the mass of carbide con siderable rise of temperature may occur at the point immediately attacked by water; besides, a crust of lime may form on the surface of a lump of carbide, and when the water at last penetrates to the core of the lump a sudden and more or less violent reaction may ensue; all of which would naturally result in uneven genera tion of gas, variations of pressure, and, perhaps, the explosive inflammation of the gas. In the second type of apparatus. on the contrary, the carbide is thrown into a considerable MUSS of water, whereby undue elevations of temperature and irregularity of action are completely avoid ed. As the presence of impurities in acety lene adds considerably to the danger of using the gas, various methods of purification have been proposed. Now, the nature and quantity of im
purity in acetylene depends entirely on the com position of the carbide used in its manufacture, and a very pure acetylene has been produced on quite a large scale simply by employing a pure carbide. With air or oxygen acetylene forms extremely explosive mixtures; mere external friction of a vessel in which such a mixture is contained may cause an explosion. But even when isolated and pure acetylene is explosive if kept, under pressure of more than two atmos pheres: and it is very dangerous indeed when preserved in liquid form. It has, instead, been stored in solution in ordinary acetone, which absorbs considerable quantities of it. if the pressure under which the gas is dissolved in acetone is not very great, explosion can occur only in the gaseous volume above the surface of the liquid; the dissolved portion of the gas does not take part in the explosion. Under any circumstances, sudden compression of a volume of acetylene may cause an explosion. Acetylene is slightly, if at all, poisonous; it is certainly much less poisonous than ordinary illuminating gas.
Acetylene contains a high percentage of bon, and the amount of heat generated in its eombustion is very large. These are the causes to which its high illuminating power is due; for, in order that a flame may be luminous, it must contain a large amount of carbon aml its temperature must he high enough to keep those particles in a state of cen•e. In order that acetylene may yield a large amount of light, it must be properly burned. The numerous burners devised for this purpose are constructed with a view to burning either pure acetylene or mixtures of acetylene and other gases, such as nitrogen, car bonic acid gas, and especially marsh gas. We reproduce here the Punic] il burner, which, while adapted for use with pure acetylene. al lows it to he sufficiently mixed with air before it reaches the point a, where it begins to burn.