HYDROCYANIC ACID. 301 



obtained by the calorimeter; but this new addition is insig- 

 nificant. 



On calculation, the following values, referred to 26 grms. of 

 cyanogen, were obtained : 



Weight of cyanogen 

 consumed. 



419 grm 133-2 Cal. 



630 130-0 



574 131-3 



732 129-6 



Mean ... 131-6 



i.e. for 52 grms. (= C 2 N 2 ) -f 263'2 Cal. 



3. The author had also recourse to detonation in the calori- 

 metric bomb (p. 148). In this way, the value + 261*8 was 

 obtained. This result was obtained at constant volume, but 

 it also applies to combustion at constant pressure ; the com- 

 bustion of cyanogen not giving rise to any change of volume. 



It will be convenient to adopt the mean of the two results, 

 viz. -f 262 '5 Cal. Thomsen, who has repeated these experi- 

 ments quite recently, and after the publication of the above 

 results, obtained + 261'3, which comes as near as can be expected. 



Dulong had obtained in 1843 -f 270 Cal. : the discrepancy 

 in this value will not seem excessive, when we take into con- 

 sideration to what perfection calorimetric methods have been 

 brought since that time. 



From results made, it follows that 



C 2 (diamond) 4- N 2 absorbs 74*5. 



If the carbon is supposed to be in the condition of charcoal, we 

 should only get 68 - 5. Thus cyanogen, CN, like acetylene, 

 CH, 1 nitric oxide, NO, and all other substances acting as true 

 compound radicals, is a body formed with absorption of heat ; 

 a circumstance to which attention has already been called more 

 than once, as it seems calculated to account for the very 

 character of this real compound radical, which manifests in its 

 combinations an energy greater than that of its free elements. 

 The energy of these latter is increased by this absorption of heat, 

 instead of being weakened, as is the case in combinations that 

 give off heat, and this increase of energy renders the compound 

 system comparable to the more active elements. 



3. HYDROCYANIC ACID. 



1. The heat of formation of hydrocyanic acid is deduced by 

 means of three methods, or series of independent measurements, 

 the results of which agree. 



1 Acetylene and cyanogen are here considered under the same volume as 

 the simple radicals H and Cl. 



