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CHAPTER VI. 



THE HEAT OF FORMATION OF HYDROGENATED COMPOUNDS OF 



NITROGEN. 



1. HEAT OF FORMATION OF AMMONIA. 



1. THE heat of formation of ammonia, of nitric oxide, of water, 

 of carbonic acid, and of hydrochloric acid, constitute, perhaps, 

 the most important data of thermo-chemistry. The three last 

 have been, for the last forty years, the subject of numerous 

 direct measurements on the part of the most skilled experi- 

 mentalists ; they may therefore be looked upon as known within 

 one or two per cent, of their absolute value. In the foregoing 

 chapter the heat of formation of nitric oxide has been given, and 

 we may now proceed to study that of ammonia. Before the 

 author's last researches it was only known in a somewhat 

 unsatisfactory manner; two measurements only had been 

 taken of it, and these by an indirect process without control. 



2. It is by making chlorine act upon diluted ammonia, and 

 then weighing the chlorine absorbed, that Favre and Silbermann, 

 and afterwards Thomsen, endeavoured to estimate the heat of 

 formation of ammonia. They assumed that the reaction worked 

 upon the whole of the chlorine according to the following 

 formula, which is admitted in the elementary treatises, but in 

 none of these works is the quantitative realisation of this 

 equation verified by the calorimeter 



4NH 3 dilute + 301 gas = N gas + 3NH 4 C1 dilute. 



Favre and Silbermann obtained results which, for fourteen 

 grammes of nitrogen, gave 



N + H 3 = NH 3 gas + 2273 Cal. 

 U + H 3 + water = NH 3 dissolved + 3147. 



Thomsen, having repeated the same experiment, obtained 

 different results 



