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CHAPTER XL 



HEATS OF FORMATION OF THE CYANOGEN SERIES. 



1. HISTORICAL. 



series of compounds in chemistry are of greater importance 

 than that of cyanogen, owing to the nature of the compound 

 radical that constitutes the characteristic pivot of the series. It 

 is the only electro-negative radical that has, up to the present, 

 been isolated. The exceptional properties of simple cyanides, 

 with their resemblance to the salts of the halogen elements, and 

 the still more singular properties of the double cyanides, add to 

 the interest of the cyanogen series. Several of the compounds 

 derived from it are employed in the manufacture of explosives. 



In 1871, 1875, and finally in 1879 and 1881, the author 

 devoted long courses of experiments to the thermal study of 

 this series, which are published in the " Annals de Chimie et 

 de Physique," 5 e serie, torn. v. p. 433; and torn, xxiii. pp. 

 178, 252. 



These experiments, which were commenced during the spring 

 and summer of 1871, partly at Versailles and partly at Paris, in 

 the midst of the tumults of that year of trouble, presented 

 great difficulties and even serious dangers, for it was necessary 

 to use pure hydrocyanic acid and liquefied cyanogen chloride, 

 which are the most poisonous substances known. 



The calculation of the fundamental quantities is based 

 principally on the measurements that were made of the heats 

 of formation of cyanogen, hydrocyanic acid, potassium cyanate, 

 and cyanogen chloride. The experiments on which the calcula- 

 tion of these quantities was based will be given in full. But 

 various alterations have been made in the values deduced from 

 them, principally on account of the complication caused in the 

 calculations by the intervention of the heat of formation of 

 ammonia. It has already been shown (pp. 237-242) to what 

 degree the former estimates of this quantity were inaccu- 

 rate, and the methods employed to rectify them. In 1882, 



