78 



KNOWLEDGE. 



[April 1, 1899. 



the manufacture of calcium carbide, and the production 

 from it of acetylene, is already an important one, and is 

 represented by over half-a-dozen journals in various 

 languages specially devoted to its interests. This gas has 

 always occupied a peculiar position among organic bodies, 

 from the fact that it is the lowest member of the important 

 group of compounds known as hydrocarbons ; and, further, 

 that it is the only hydrocarbon which can be produced 

 synthetically, and that it thus forms the starting point 

 from which other organic bodies have been built up. Its 

 singular properties and the manner of its decomposition, 

 under certain conditions, have also contributed to placing 

 it in a unique position. 



Acetylene was first prepared in an impure state by 

 Edmimd Davy, by the action of water on the mass obtained 

 by heating cream of tartar in an attempt to manufacture 

 metallic potassium. He called it " klumene," but, as he 

 made no investigation of its properties, it attracted no 

 interest until its re-discovery by Berthelot. who obtained it 

 in a state of purity. It may be prepared synthetically by 

 the action of hydrogen on carbon heated to whiteness by 

 the electric arc. It is also produced by strongly heating 

 or sparking marsh gas — many other bodies, including 

 benzene, being also produced ; or by the Incomplete com- 

 bustion of hydrocarbons, such as those in coal gas, as is 

 noticed when a Bunsen burner " burns back." 



These processes, however, are of scientific interest only, 

 as the amount of gas produced is but small in any case, 

 and the method of production which has given rise to the 

 acetylene " boom " consists in the action of calcium carbide 

 upon water. The carbide is now always produced elec- 

 trically, as described later on. 



Acetylene is a colourless gas about nine-tenths the 

 weight of air. It is stated to have a pleasant ethereal 

 odour when pure, but, as ordinarily prepared, it has a 

 strong unpleasant smell resembling that noticed when 

 ordinary iron filings are dissolved in dilute hydrochloric 

 or sulphuric acid. 



At eighteen degrees Centigrade it can be liquefied by a 

 pressure of eighty-three atmospheres, while at one degree 

 Centigrade only a pressure of forty-eight atmospheres is 

 required. It forms a mobile liquid, having a specific 

 gravity of 0-4.51 at zero Centigrade, and it has the lowest 

 refrangibility of any known liquid or solid, also the 

 greatest co-efficient of expansion. At eighteen degrees 

 Centigrade, water dissolves its own volume of acetylene gas, 

 carbon tetrachloride or turpentine dissolves twice its 

 volume, amyl alcohol three and a-half, benzene four, and 

 glacial acetic acid six times its volume, while acetone, 

 which has been proposed as a convenient means of storing 

 the gas in solution, dissolves no less than twenty-five 

 volumes at fifteen degrees Centigrade, at the ordinary 

 pressure, and three hundred volumes at twelve atmospheres 

 pressure, but the solubility is much less at higher tempera- 

 tures, and is only half as much at fifty degrees Centigrade. 

 Commercial acetylene is poisonous, though not so injurious 

 as carbon monoxide. The gas afifects the respiration and 

 weakens the heart and lungs. The pure gas is said to be 

 harmless when inhaled in small quantities, and Dr. Weyle 

 states that air containing nine per cent, of ordinary 

 acetylene may be breathed for a " long period " without 

 serious results. 



Among its other peculiarities, acetylene has the power 

 of combining with many metals with the production of 

 highly characteristic compounds, which are of importance 

 as bearing upon the dangers attending its use, and also as 

 afifording a convenient means of purifying it or of ascer- 

 taining its presence in admixture with other gases. The 

 most interesting of these compotmds is the acetjlide of 



copper, which is formed as a red precipitate when acetylene 

 is passed through an ammoniacal solution of cuprous 

 chloride. When diy, it explodes if struck or if heated to 

 one hundred to one hundred and twenty degrees Centigrade, 

 leaving a black velvety mass containing carbon and 

 metallic copper. This acetylide is so characteristic that 

 its production foims the most delicate test for acetylene, 

 as little as 0'005 of a milligramme being thus capable of 

 detection according to Berthelot. The well-known danger 

 of explosion, often from unascertained causes, may be 

 largely attributed to the lact that acetylene is an endo- 

 thermic compound — i.e., that the combination of carbon 

 with hydrogen to produce acetylene absorbs heat to the 

 extent of sixty-one thousand one hundred heat units. 

 Hence, any cause which gives rise to a sudden decomposition 

 of acetylene results in the evolution of great heat. The 

 decomposition of the gas by the induction spark at the 

 ordinary atmospheric pressm-e is not, however, rapid, and 

 takes place only where the spark acts. Liquid acetylene 

 appears to explode en masse under certain conditions, and, 

 as these are not clearly defined, it must be regarded as 

 highly dangerous. The explosions which have occurred 

 were so destructive as to prevent the possibiUty of deter- 

 mining the cause. 



Messrs. Berthelot and Vielle find that, under a pressure 

 of two atmospheres or more, even a platinum wire heated 

 by the electric current produces complete and explosive 

 decomposition of acetylene gas. The intensity of the 

 explosion increases with the initial pressure, and this 

 increase is very rapid as the pressure approaches the 

 liquefying point of the gas. Liquid acetylene may be 

 similarly exploded by a hot wire, but not by blows or 

 shocks, although the breakage of a cylinder of the liquid 

 by a blow is usually followed by an explosion, probably 

 induced by sparks from the friction of the broken metal. 

 These investigators are, however, of opinion that the 

 properties referred to need not prevent the domestic use of 

 acetylene if proper care is taken in the preparation and 

 manipulation of the gas, and it appears evident that the 

 purer the acetylene is the less danger exists of explosion 

 from friction and other causes. 



According to Prof Clowes, air containing any pro- 

 portion of acetylene between three and eighty-two per cent. 

 is explosive, and, as this is a far wider range than is shown 

 by any other combustible gas, there is little doubt that it 

 is in part due to the endothermic nature of acetylene. It 

 is stated by Grehau that the most explosive mixture 

 contains one volume of acetylene to nine volumes of air. 



Before considering the manufacture of calcium carbide 

 and acetylene on a large scale, it is of interest to note that 

 although many other metallic carbides exist, that of 

 calcium is at present the only one known which yields 

 acetylene in sufficient quantities to stand any chance of 

 competing with coal gas, electricity, etc., as a source of 

 Uluminattng power. In the case of aluminium carbide, 

 for instance, the action of water yields practically pure 

 methane (marsh gas), while the carbide of manganese, 

 under similar conditions, yields methane and hydrogen, and 

 that of uranium gives ofi' not only gaseous but also liquid 

 and solid products, mainly of the ethylene group. 



The best calcium carbide in the market is that pro- 

 duced by the Acetylene Illuminating Company at Foyers, 

 in Scotland, but the WiUson Company at Spray and 

 Niagara Falls, in America, the Neuhausen Aluminium 

 Company, in Switzerland, and many other companies, are 

 also large producers. The principle of manufacture is the 

 same in aU cases, and consists in passing a powerful 

 electric current, by means of large carbon electrodes, 

 through a mixture of carbon and lime. The best form of 



