COMBUSTION OF CYANOGEN. 161 



is one of the most important in chemistry. The knowledge of 

 the heats of formation of these oxides offers the more interest 

 as the two first are formed with absorption of heat from their 

 elements, while the three others are, on the contrary, formed 

 with liberation of heat from nitric oxide, which plays the part of 

 a true radical. A knowledge of the heats of formation of these 

 bodies is, moreover, indispensable to the theoretical study of 

 explosive substances, of which they go to form the greater part. 

 Unfortunately, the exact determination of these quantities pre- 

 sents great difficulties, as is the case with combinations which 

 cannot be brought about by direct synthesis. 



The figure deduced by Favre and Thomsen, namely 267 Cal., 

 from the action of chlorine on ammonia, was found to be wide 

 of the truth by the author, who estimated it at 12*2 Cal., and 

 this last figure has since been confirmed by Thomsen, so that all 

 values up to that date in which the formation of ammonia 

 intervenes have to be corrected by 14*5 Cal. But, before 

 applying such a correction to the heat of formation of the 

 oxides of nitrogen, the author endeavoured, with success, to 

 measure this more directly by comparing the heat of combustion 

 of methene and of cyanogen when burnt in oxygen and in 

 nitric oxide respectively. The results obtained were practically 

 identical, and the method admits of rapid and exact manipula- 

 tion, and the figures obtained are therefore incomparably more 

 valuable than the previous ones based on no less than nine 

 experimental data. The following are the details of the 

 experiment. 



The combustible chosen was cyanogen or ethylene. It was 

 found that the slow combustion of a mixture of cyanogen, 

 ethylene or carbon disulphide with nitric oxide always pro- 

 duced an abundance of nitrous vapours; but this is avoided 

 by detonating the cyanogen and nitric oxide in the calorimetric 

 bomb. 



1. Combustion of Cyanogen by free Oxygen. 



The explosion of the following gaseous mixture: 26 grm. 

 CN + 2 = C0 2 + N liberated + 131'0, and + 1307, the mean 

 being : + 130*9 ; explosion at constant volume. 



Hence we obtain the heat absorbed in the union of carbon 

 (diamond) and nitrogen. 



C (diamond) + N" = CN absorbs - 36'9. 



In another series of experiments made by burning a jet of 

 cyanogen in oxygen at constant pressure -I- 131 '6, for the heat 

 of combustion, and - 37'6, for the heat of formation, were the 

 figures obtained. The numbers found, whether at constant 

 pressure or at constant volume, can therefore be regarded as 

 identical, which one would expect, as the combustion of 

 cyanogen by free oxygen does not give rise to any change of 



M 



