172 OXYGENATED COMPOUNDS OF NITROGEN. 



But under these conditions a portion of the two gases is 

 always changed into nitric peroxide, and it does not seem 

 possible to obtain nitrogen trioxide without having at the same 

 time the products of its transformation, N0 2 and NO, the 

 whole constituting a system in equilibrium. 



However, by increasing the proportion of nitric oxide, that of 

 the nitrogen trioxide is increased. But we are limited in this 

 respect by the necessity of operating upon a volume of oxygen 

 sufficient to give notable calorimetric effects. 



By carrying out the reaction by the aid of a system ot 

 concentric bulbs (see p. 168), containing a known volume of the 

 two dry gases (about 400 cub. cms. of NO), the heat liberated was 

 measured, the proportion of NO and N0 2 formed was deter- 

 mined by absorbing the products in a weak alkaline solution, 

 the weight of oxygen employed affording a verifying equation. 



The products being known as well as the heat of formation of 

 NOa, we can calculate the heat of formation of the nitrogen 

 trioxide. The datum which results from these measurements, 

 though less accurate than that of the other oxides of nitrogen, is 

 nevertheless useful. 



From the mean of three experiments, 2NO -f = N 2 3 gas 

 liberates -f- 10*5 Cal. Hence the fixation of a second equivalent 

 of oxygen, that is, the transformation of the nitrogen trioxide 

 into nitric peroxide in the gaseous state, viz. N 2 3 + = 2N0 2 

 gas liberates + 19'0 - 10*5 = 8'5. 



8. The fixation of a third equivalent of oxygen, transforming 

 the peroxide into nitric anhydride. 2N0 2 + = N 2 5 gas 

 liberates + 2;0. 



The heat liberated by the same weight of oxygen, at the 

 ordinary temperature, decreases according as the oxygen in- 

 creases in the compound of nitrogen, starting with nitric oxide, 

 a fact which is demonstrated by the series of numbers -f 10 f 5 

 + 8-5 + 2-0. 



The latter figure is in keeping with the slight stability of 

 nitric anhydride, a compound which cannot be formed from 

 nitric oxide by direct synthesis. 



9. Direct measurements, independent of all analysis, show that 

 the same volume of oxygen, in the presence of an equal or more 

 than double volume of nitric oxide, in sealed bulbs, liberates 

 the more heat the greater the volume of nitric oxide, and conse- 

 quently that of the nitrogen trioxide formed. This result con- 

 tributes with the preceding ones to prove that the heat liberated 

 in the formation of nitric peroxide gas is not double that 

 liberated by the nitrogen trioxide gas, contrary to the relation 

 existing between the weights of oxygen successively fixed. 



Finally the formation of a nitrous gas from its elements at 

 the ordinary temperature, calculated from the above data 



N 2 + 3 = N 2 3 gas, absorbs -*22'2. 



