312 HEATS OF FORMATION OF THE CYANOGEN SERIES. 



experiments of this order and from the value at present adopted 

 for the formation of ammonia (p. 242), was found to be equal 

 to 24'3. This relates to liquid hydrocyanic acid. We get 

 then, according to this method 



H + C + N = HCN (gas) - 30. 



9. In short, the following numbers have been obtained for 

 the formation of hydrocyanic gas 



By the first method (detonation) 30-2 



By the second method (formic acid and ammonia) ... 28*3 



By the third method (mercuric cyanide and chlorine) ... 30'0 



Mean ... - 29'5 



This mean value will be adopted to express the heat absorbed 

 by the combination of the elements 



H + C (diamond) + N = HCN (gas) - 29-5 Gal. 



HCN (liquid), we should get 23-8 



. HCN (in solution) 23'4 



10. From these figures it follows that cyanogen and hydro- 

 cyanic acid are both formed from their elements with absorption 

 of heat. This circumstance explains, as has already been said, 

 the character of cyanogen as a compound radical, and, in a more 

 general manner, the tendency of cyanogen and hydrocyanic 

 acid to form direct combinations and polymeric compounds, 

 and to give rise to complex reactions. The fresh determi- 

 nations which are here published confirm the views which 

 were expressed by the author on this subject twenty years 

 ago, with regard to cyanogen, acetylene, and endothermal com- 

 binations. 1 



11. It will be remembered that cyanogen, hydrocyanic acid, 

 acetylene, etc., may be regarded as following the general rule 

 applicable to chemical compounds, i.e. as being formed with 

 disengagement of heat; if we assume that the carbon, when 

 under the form of diamond or charcoal, does not correspond to 

 true elementary carbon, the latter would be comparable to 

 hydrogen, and would probably be in the gaseous state, charcoal 

 and diamond representing its polymeric forms. In passing 

 from the gaseous to the polymeric and condensed state, the 

 elementary carbon would give off a considerable quantity of 

 heat, which is greater than that absorbed in the formations of 

 acetylene (- 30'5 for C = 12) and cyanogen (-37'3). 



The quantity of heat developed by the condensation of the 

 elementary carbon might even be estimated at 4- 42*6 for 

 diamond and + 39*6 for charcoal, if we assume that the successive 

 formation from the gaseous carbon of the products of the two 



1 " Annales de Chimie et de Physique," 4 e se*rie, torn. vi. pp. 351 et 433. 



