CARBON AND THE HYDROCARBONS 71 



Is the lowest known member of the unsaturated hydrocarbon series of 

 the composition C n H 2u . As in composition it is equal to two molecules 

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

 it might be, and it actually can be, produced, although but in small 

 quantities, together with hydrogen, by heating marsh gas. On being 

 heated, however, olenant gas splits up, first into acetylene and methane 

 (3C 2 H 4 = 2C 2 H 2 + 2CE.,, Lewes, 1894), and at a higher tempera- 

 ture into carbon and hydrogen ; 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 entirely 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 ele- 

 ments of water from the alcohol, C 2 H 5 (OH), and gives olefiant gas ; 

 C 2 H 6 O = H 2 O -f C 2 H 4 . The greater molecular weight of olefiant gas 

 compared with marsh gas indicates 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 4 10, it boils at 103 (1 atmosphere), 

 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 



40 Ethylene bromide, C 2 H 4 Br 2 , 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 

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

 double its volume when hydrogen and carbon are formed, C 2 H 4 = CH 4 + C = 2C-f2H2. 

 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 eight volumes of the products of combustion, a mixture of water 

 and carbonic anhydride, C 2 H 4 + 3O 2 = 2C02 + 2H2O. On cooling after the explosion 

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

 olenant 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 

 ethyleue give four volumes of carbonic anhydride. 



