458 M. De Wilde on Acetylene. 



a mixture of hydrogen and bisulphide of carbon. The action is 

 slower, however, than in the preceding case. 

 . The formation of acetylene in a mixture of carbonic oxide and 

 hydrogen is still more difficult; the passage of the electric spark 

 must be continued for ten hours. 



De Wilde describes* several experiments which he had under- 

 taken with a view of obtaining a ready means of preparing ace- 

 tylene. Dutch liquid, chloride of ethylene, C 4 H 4 CI 2 , may be 

 regarded as consisting of acetylene and hydrochloric acid; and 

 it might possibly, under the influence of heat, decompose into 

 acetylene and hydrochloric acid, according to the equation 



C 4 H 4 C1 2 =C 4 H 2 + 2HC1. 



When the vapour of chloride of ethylene is passed through a 

 porcelain tube heated to bright redness, a portion does indeed 

 decompose in this manner, but the quantity formed is so small 

 as to render this mode of formation of little use ; in fact 100 

 grms. of the liquid only yielded about 2 litres of the gas. 



A well-known experiment consists in mixing ethylene gas and 

 chlorine, and setting fire to the mixture, by which a large quan- 

 tity of carbon is deposited, — it being assumed that the mixture 

 is decomposed into carbon and hydrochloric acid : 



C 4 H 4 + 4C1=C 4 + 4HC1. 



De Wilde has shown that in this case some acetylene is formed. 

 He also found, independently of Berthelot, that acetylene is 

 formed in the incomplete combustion of ethylene and of coal- 

 gas, but, as Berthelot observes, did not establish the general 

 character of this reaction. 



The remarkable property which platinum -black and spongy 

 platinum possess of condensing large quantities of gas, led De 

 Wilde to try the experiment whether hydrogen could not in this 

 way be fixed on certain organic compounds. An experiment 

 was first made with acetylene. A small quantity of compressed 

 platinum-black of the size of a pea was introduced into a mea- 

 sured quantity of hydrogen in a jar of this gas standing over 

 mercury ; the platinum was then removed and placed in a mea- 

 sured volume of acetylene. An immediate absorption is set up, 

 which is complete after the lapse of half an hour. Numerous 

 experiments showed that when the hydrogen was in excess, two 

 volumes of hydrogen absorbed exactly one volume of acetylene; 

 the odour of acetylene completely disappeared, and its presence 

 could scarcely be detected by means of ammoniacal solution of 



* Bulletin de la Societe Chimique, March 1866. 



