60 Biological Chemistry. 



If efchylene dibromide is treated with caustic alkalis 

 in alcoholic solution, all the bromine can be removed, and 

 the reaction can be represented by the equation 

 C 2 H 4 Br 2 + 2KOH = C 2 H 2 + 2KBr + 2H 2 O 



The gas acetylene is thereby obtained, which is also 

 unsaturated, and which is capable of uniting with no less 

 than four bromine atoms before a fully saturated com- 

 pound is obtained. This fact is graphically represented 

 by the use of the " triple " bond, thus 



CH 



or CH : CH 



III 



CJ 



The saturation by bromine can take place in stages 



CH CHBr CHBr CHBr 2 



||! +Br 2 = || and || -f-Br 2 = j 



CH CHBr CHBr CHBr 2 



(1) (2) 



(1) may be regarded as a " substitution " product of an 

 olefine ; (2) is a tetra-substitution product of a paraffin. 



Acetylene, the chief member of the series, can be 

 obtained, in addition to the method already described, by 

 a variety of processes. Theoretical interest attaches to 

 its direct synthesis from the elements, for it was shown 

 by Berthelot that the gas is produced when hydrogen 

 is led through a globe in which an electric arc is passing 

 between carbon poles. It is also formed by the incom- 

 plete combustion of methane, coal-gas, alcohol, and other 

 organic substances. It is most readily obtained, however, 

 by the action of water on calcium carbide. 



CaC 2 + 2H 2 = Ca(OH) 2 + C 2 H 2 



The carbide is obtained by heating together a mixture 

 of coke and calcium carbonate to a very high temperature 

 in the electric furnace. This product is made commer- 



