CARBON AND THE HYDROCAHlJoNS 359 



the lowest known member of the unsaturatecl hydrocarbon series of the 

 composition C,,H. );r As in composition it is equal to two molecules of 

 marsh gas deprived of two molecules of hydrogen, it is evident that it 

 illicit be, and actually can, together with hydrogen, be produced, 

 although but in small quantities, by heating marsh gas. On being 

 heated, however, olefiant gas is decomposed into charcoal and marsh 

 gas : C.,H 4 = CH 4 -|-C; and therefore in those cases where marsh gas 

 is produced by heating, olefiant gas, hydrogen, and charcoal will also be 

 formed, although only in small quantities. The lower the temperature at 

 which complex organic substances are heated, the greater the quantity 

 of olefiant gas found in the gases given off ; at a white heat it is en- 

 tirely decomposed into charcoal and marsh gas. If coal, wood, and 

 more particularly petroleum, tars and fatty substances are subjected to 

 dry distillation, they give off illuminating gas, which contains more or 

 less olefiant gas. 



Olefiant gas, almost free from other gases, 46 may be obtained 

 from ordinary alcohol (if possible, free from water), if it be mixed with 

 five parts of strong sulphuric acid and the mixture heated to slightly 

 above 100. Under these conditions, the sulphuric acid removes the 

 elements of water from the alcohol, C 2 H 5 (OH), arid gives olefiant gas, 

 C. 2 H G O=H. 2 O + C.,H,. The greater molecular weight of olefiant gas 

 compared with marsh gas points out that it may be comparatively 

 easily converted into a liquid by means of pressure or great cold ; 

 this may be effected, for example, by the evaporation of liquid nitrous 

 oxide. Its absolute boiling-point is +10, it boils at 103 (1 atmo- 

 sphere), liquefies at 0, at a pressure of 43 atmospheres, and solidifies 

 at 160. Ethylene is colourless, has a slight ethereal smell, is slightly 

 soluble in water, and somewhat more soluble in alcohol and in ether 

 (in five volumes of spirit and six volumes of ether). 47 



Like other unsaturated hydrocarbons, olefiant gas readily enters 



4(5 Ethylene bromide, C.^H 4 Br.,, when gently heated in alcoholic solution with finely 

 divided zinc, yields pure ethylene, the zinc merely taking up the bromine (Sabaneyeff). 



47 Ethylene decomposes somewhat easily under the influence of the electric spark, 

 or a high temperature. In this case the volume of the gas formed may remain the 

 same when olefiant gas is decomposed into carbon and marsh gas, or may increase to 

 double its volume when hydrogen and carbon are formed, CoH4 = CH. 1 + C = 2C + 2H ; >. 

 A mixture of olefiant gas and oxygen is highly explosive; two volumes of this gas require 

 six volumes of oxygen for its perfect combustion. The eight volumes thus taken then 

 resolve themselves into a mixture of eight volumes of the products of combustion, water and 

 carbon i i- anhydride, C..jH 4 + 3O., - 2CO._, + 2H..O. On cooling, after the explosion, diminution 

 of volume occurs because the water becomes liquid. For two volumes of the olefiant gas 

 taken, the diminution will be equal to four volumes, and the same for marsh gas. The 

 quantity of carbonic anhydride formed by both gases is not the same. Two volumes of 

 marsh gas give only two volumes of carbonic anhydride, and two volumes of ethylene give 

 four volumes of carbonic anhydride (2CO..,). 



