180 OXYGENATED COMPOUNDS OF NITROGEN. 



The results have been given above (pp. 168 to 171). They may 

 be summed up as follows : 



NO + = N0 2 gas ............... 



Liquefaction of N0 a ............... 



2N0 2 liquid + + H 2 + water = 2HN0 8 dilute ... 



+19-4 

 + 4'33 

 + 12-7 



We have therefore : 



2NO -f 3 + H 2 + water = 2HN0 3 dilute -f 364. 1 



These results are worthy of attention, but they do not appeal- 

 capable of great accuracy, owing to the uncertainty of the 

 reactions. 



5. To sum up the results of the different methods 



NO + 8 + water = HN0 3 dilute : by the nitrites ... + 35'9 

 by nitric acid ... + 34-4 



by nitric peroxide ... +36-3 



Mean ............ +35-5 



However, the accuracy of the three methods is very unequal, so 

 the value 3 5 '9 will be adopted, the method by which it was 

 obtained being most reliable, taking the two other figures as 

 mere verifications. 



6. Heat of formation of dilute nitric add from its elements. 

 This heat, calculated from nitrogen and oxygen, is easily deduced 

 from the preceding results, for it is sufficient to deduct from the 

 latter the heat absorbed in the formation of nitric oxide. 



N 2 4. Q 6 -f- H a O + water = 2 HN0 3 dilute liberates 4- 35'9 

 - 21-6 = -f 14-3 Gal. 



If we consider the integral formation of nitric acid from its 

 three elements, HN0 3 , we must add the heat of formation of 

 water, viz. + 34'5. Thus N 2 -f 6 + water = 2HN0 3 dilute 

 liberates -f- 48*8 Cal. Such a reaction, therefore, liberates heat. 

 Hence it can take place directly, and, in fact, it is observed 

 in the combustion of the hydrogen in the air, but it only affects 

 a small quantity. 



7. Heat of formation of nitric acid. It is sufficient to measure 

 the heat liberated by the solution of the liquid acid in a large 

 quantity of water, viz. + 7 '2. We have therefore 



N 2 + 8 + H 2 = 2HNO S liquid liberates + 7-1 



N 2 + 6 + H 2 = 2HNO, + 41-6 



To pass from the gaseous to the solid state, it is sufficient to 

 measure the heat of vaporisation and the heat of fusion at a low 

 temperature of nitric acid, HN0 3 = 63 grms. 



The result found for the heat of vaporisation is + 7'35, and 

 for fusion 0*6. 



1 Thomsen, following an analogous though not identical cycle, found 

 + 36-47. 



