238 HYDROGENATED COMPOUNDS OP NITROGEN. 



N + H 3 = NH 3 gas, -|- 26-71 Cal. 

 ]ST -f H 3 + water = NH 3 dissolved, + 3515 Cal. 



The difference is considerable, amounting to 4 Cal., or nearly 

 20 per cent. Thomsen tried to reconcile these figures by re- 

 calculating the figures of Favre and Silbermann, according to 

 his own data regarding the heat of formation of hydrochloric 

 acid and ammonium chloride. But corrections of this kind are 

 very problematical, 1 seeing that the figures of the above-men- 

 tioned writers form a complete whole : the cause of the divergence 

 is apparently quite a different one. 



3. In fact, some years ago, the author began to doubt the 

 accuracy of all these figures, in the course of his studies of the 

 heat of formation of the oxygen acids of the halogen elements. 2 

 Having measured that of the hypobromites, he thought it might 

 serve to determine that of urea, in accordance with the process 

 of analysis generally followed for that substance. But it was 

 desirable first to verify the reaction of the hypobromites upon 

 ammonia itself, and it was then found that extraordinary losses 

 of heat took place, quite irreconcilable with those that could be 

 calculated from the data that have been accepted with regard to 

 ammonia. The experiments were made, starting with pure 

 liquid bromine of a determined weight. It was dissolved in a 

 weak solution of soda, and the heat liberated was measured ; 

 then weak ammonia was also added in considerable excess, and 

 the second escape of heat was measured. The total result must 

 represent the transformation of the bromine, ammonia, and soda 

 into sodium bromide, water, and nitrogen 



6Br + 2NH 3 dilute + 3^0 dilute = 6NaBr + 3H 2 + N 2 . 



This is the thermal result observed, as obtained from the effect 

 of the two operations, performed one after the other 



(6Br acting on 3Na 2 0) dilute ......... +18-0 



NH 3 dilute acting on the hypobromite ... ... + 88'8 



Total ... + 106-8 



1 It would at least be as reasonable to correct Favre and Silberrnann's 

 results by the following considerations. Their data were almost all obtained 

 with the mercury calorimeter; now the unit employed by them in this 

 instrument was apparently too high by about one-tenth, according to the 

 error that they committed in the estimation of the heat of neutralisation of 

 nitric acid, hydrochloric acid, etc. All the quantities that enter into the calcu- 

 lation of the heat of formation of ammonia, and consequently this heat of 

 formation itself, should therefore be reduced in the same proportion. 



2 "Annales de Chimie et de Physique," 5' se*rie, torn. v. p. 333, hypo- 

 chlorites; torn. x. p. 377, chlorates; torn. xiii. pp. 18 and 19, bromates et 

 hypobromites ; p. 20, iodates. See Book II. chap. XII. of the present work. 



