M. Berthelot on Acetylene. 457 



lighted at the mouth, gradually enters the jar. A very abun- 

 dant red precipitate of cuprous acetylene is formed, both in con- 

 tact with the flame and below. The experiment may be made 

 with chloride ofethyle, C 4 H 5 C1, and propylene, C 6 H 6 . 



With marsh-gas, C 2 H, acetylene is formed in like manner, 

 though with less brilliancy. Its formation under these circum- 

 stances is a direct proof of the condensation which marsh-gas 

 undergoes under the influence of heat. Thus 

 2C 2 H 4 = C 4 H 2 + 3H 2 . 



2. It is more especially in the case of volatile liquids that this 

 formation of acetylene in incomplete combustion is met with. It 

 may well be shown by means of ether, a few drops of which are 

 introduced into such a gas-jar as is mentioned above. Two or 

 three cubic centimetres of ammoniacal solution of cuprous chlo- 

 ride being added and the ether lighted, the jar is inclined almost 

 horizontally and turned round ; in a moment the entire inner 

 surface is lined with a blood -red coating of cuprous acetylene. 

 This is a beautiful lecture experiment; and the quantity of ace- 

 tylene formed makes it probable that a convenient method for 

 preparing acetylene may be based on this experiment. 



This experiment also succeeds with all neutral organic liquids 

 which do not mix with the reagent, and volatile below 60° or 80°. 



3. It may also be shown, in all cases of fuliginous flame, by 

 placing over the flame, at such distance as not to interfere with 

 the combustion, a funnel ; by means of an aspirator, a dry empty 

 gas-bottle is filled with the gaseous products of combustion by 

 aspiration. In a few minutes two or three cubic centimetres of 

 cuprous solution are poured into the flask, and the characteristic 

 precipitate is at once formed. 



This experiment may be made either with gases passed through 

 a narrow orifice before combustion, with very volatile liquids in- 

 flamed in a capsule, or with difficultly volatile liquids heated to 

 such a point in a capsule that they will take fire and burn con- 

 tinuously. Berthelot has tried in this way ordinary ether, ben- 

 zole (C 12 H 6 ), oil of turpentine (C 20 H 16 ), petrolene," stearic acid, 

 vegetable oils, and finally naphthaline. 



All gases and vapours of hydrocarbons are decomposed when 

 traversed by electric sparks ; and in a subsequent paper* Ber- 

 thelot shows that when hydrogen is simply mixed with a gas 

 containing carbon, and a series of sparks passed through the 

 mixture, acetylene is formed. Thus in a few minutes a quantity 

 of acetylene is formed in a mixture of cyanogen and hydrogen 

 gases when traversed by the electric spark. It is also formed, 

 and with deposition of sulphur, when the spark passes through 



* Bulletin de la Societe Chimique, March 1866. 



