Acetylene has no toxic properties and may be taken into either the lungs or stomach with impunity, even when mixed in air in consider able proportions. Acetylene is a true gas, that is, it consists of only one chemical compound and is not a mixture of a number of gases each with its own peculiar characteristics, as is the case with most other illuminating and fuel gases. Under pressure, acetylene obeys Boyle's Law for the compression of gases and its Pres sure-Volume Curve is practically straight up to the liquefaction point, which at ordinary temperatures is 700 pounds per square inch. Owing, however, to the dangers in unabsorbed compressed acetylene this gas is never sub jected to pressures anywhere approaching its liquefaction point. Acetylene may be mixed with most ordinary gases with impunity, but if mixed with chlorine and subjected to sunlight, it will combine with considerable violence. Acetylene may be used as an enricher of other gases to increase their candle powers and calo rific values. It is employed for this purpose in European countries in the Pintsch gas used for train lighting. When added 'to an illuminat ing gas, acetylene will increase the heating value in direct proportion to its presence in the mixture and the illuminating value by about two candle power for each per cent of acetylene added. It cannot compete however in point of price with oil and other enrichers and for this reason is not ordinarily used for this purpose.
As stated above, acetylene obeys Boyle's Law for the behavior of true gases under vari ations of volume and pressure. It also obeys Charles' Law, governing the relation of tem perature to volume. However, if acetylene is subjected to a temperature in excess of 538° F., changes of great chemical complexity take place in its structure. For this reason, care must be taken not to overheat this gas in its generation or in the appliances in which it is used. Under the influence of heat acetylene will break up or rather double up — polymerize —into a vast number of hydro-carbons, rang ing from benzene (Cale) to heavy black tars according • to the degree of temperature. If once heated to the point where polymerization occurs, no amount of subsequent cooling or purification will restore the acetylene.
Acetylene has a density of 0.92, air being 1. Its atomic weight is 26. Its critical tem perature is 99° F., which means that the curve of power for compression reaches a straight line at this temperature and hence no amount of pressure will serve to liquefy, if in excess of this temperature. The critical pressure of acet ylene is 995 pounds per square inch.
Domestic and Commercial Uses.— Acety lene is used for isolated lighting plants throughout the country; homesteads, farms, churches, e lodges and similar institutions are illuminated with acetylene from generators de vised for the purpose. Owing to its relatively higher cost, acetylene does not compete in its present stage of development with electric or illuminating gas for city lighting. It is used quite extensively for cooking purposes in con nection with isolated lighting plants. Dissolved acetylene is used for buoy lighting and for other aids to navigation. Buoys carrying suf ficient gas to supply their lights continuously for 15 months are in use practically all over the world. These are veritable self-attending light ships. A large number of them are pro vided with °sun valves') which are actuated by the direct heat of sunlight, turning off the acetylene when the sun shines and turning it on again when darkness, fog or clouds intervene. There are some 360 acetylene buoys marking the channel of 'the Panama Canal. Owing to its low ignition temperature, acetylene cannot be compressed in an engine cylinder to a suffi ciently high point to render the engine effi cient; hence acetylene has never developed into a power proposition.
Acetylene is used in small portable lamps for mining purposes, the present acetylene min er's lamp being practically the first improve ment in mine illumination for 200 years. Prac
tically all the metal mines in the United States and its dependencies, as well as the coal mines which are not gaseous, are now lighted with acetylene. The acetylene cap lamp has about 18 candle power, head on, as compared with three-fourths candle power given by the old form of oil lamp, and its light can be directed to any spot desired by means of the reflector which is an integral part of the lamp. Acety lene is used to a very large and increasing ex tent for welding and cutting purposes, because of certain physical peculiarities now to be dis cussed. The theoretical temperature of any flame may be calculated from the amount of heat generated by the combustion of the fuel and the amount of heat absorbed by the prod ucts of the combination. Water vapor will absorb four times more heat for a given in crease in temperature than carbon dioxide and those fuels which burn to carbon dioxide have a higher flame temperature than those which burn to water vapor. The flame temperature of any hydro-carbon varies in proportion to the relative amounts of carbon and hydrogen of which it is composed. Acetylene has more car bon and less hydrogen than any other known substance, with the exception of the solid naph thalene which is devoid of the endothermic energy mentioned. This being the case, its products of combustion have a maximum of carbon dioxide and a minimum of water vapor. Added to this is the fact that acetylene pos sesses a very high endothermic heat content which gives off heat without producing any additional products of combustion. When the volume of the combustion products is reduced by the removal of the nitrogen from the air and when pure oxygen is used, the combustion of acetylene results in a higher flame temperature than that of any other substance known or rec ognized as possible in chemistry. The combus tion of acetylene with oxygen produces the acme of flame temperature — 7878° F. being the theoretical maximum. Owing ba radiation and convection losses, the actual available flame temperature is in the neighborhood of 6300° F. This gives to a blow pipe consuming- acetylene and oxygen the power to produce, in portable form and small compass, a temperature ap proaching nearly that of the electric arc. This has resulted in the wide employment of acety lene in conjunction with oxygen for the weld ing and cutting of metals. The oxygen cutting blow pipe, in which acetylene is commonly em ployed as the fuel gas, is used extensively for cutting steel bars, plates and ingots to shapes and lengths, and in wrecking work. The oxy acetylene cutting torch was employed in cutting up the Maine in Havana Harbor, and for cut ting out the Quebec Bridge. The cutting process has proven invaluable in fire fighting and in marine, mine and railroad rescue work, notable examples being the Equitable Building fire in New York and the Eastland disaster in Chicago. The process is used extensively in scrap yards and for all classes of demolition work. It is successfully employed for cutting steamships into sections where necessary, as in the case where a ship has to be transported through a lock which is too small to handle it. The oxygen-acetylene cutter has revolutionized wrecking and scrap yard practice in the past few years and the acetylene welding torch has produced great changes in the methods of metal construction during the same time. If a cut ting blow pipe is provided with a sheath of compressed air to force water away from its nozzle, cutting can be performed under water. It is said that the Germans used the process of cutting under water for freeing their subma rines from submarine nets. The under-water cutting blow pipe is commonly employed for cutting metal sheet piling under water. Acet ylene is used to a limited extent as a basis in the formation of chemical substances. This use, although it possesses considerable promise, is in the laboratory rather than in the commer cial stage at this writing.