200 



OXYGENATED COMPOUNDS OF NITROGEN. 



nitric oxide which will not be redissolved. Lastly, the contact 

 of the same quantities of substances, effected by degrees, will 

 not give rise to nitric oxide, or if so, only to a very small 

 extent. 



6. Nitric acid. We have said that anhydrous nitric acid 

 manifests a certain tendency to be spontaneously decomposed at 

 the ordinary temperature, and this appears to be due to the 

 action of light. A few rays of sunlight are sufficient to cause 

 an abundant liberation of oxygen and nitric peroxide. Sponta- 

 neous decomposition also takes place in diffused light, but very 

 slowly. This decomposition is accelerated with rise in tempera- 

 ture, without, however, being very rapid up to 43. It is 

 endothermal, for it absorbs 2*0 ; for N 2 5 gas = 2N0 2 + 0, 

 and is not reversible, dry nitric peroxide not absorbing oxygen 

 at any temperature, as has been proved by exact analysis. It is 

 well known that light also decomposes monohydrated nitric 

 acid. 



7. Heat liberated in the various oxidations effected by nitric 

 acid. The oxidation of the metals and other oxidisable bodies 

 by nitric acid gives rise, according to circumstances, to the four 

 lower oxides of nitrogen, to nitric peroxide, nitrogen itself, to 

 hydroxylamine, ammonium nitrate, and ammonia, the ultimate 

 term of the reduction of nitric acid by hydrogenated bodies. 

 The following is the method of calculating the heat liberated. Q 

 being the heat supposed to be produced by the union of an 

 equivalent of free oxygen (0 = 8 grms.) with the oxidisable 

 body, the latter being changed, further, either into an oxide or 

 soluble salt, we shall have 



It will be seen that the heat liberated constantly increases from 

 nitric peroxide to nitrogen according as the reduction becomes 

 more complete, without, however, attaining to the heat which 

 free oxygen would produce. When hydrogen comes into play, 

 the formation of hydroxylamine and ammonia diminishes, on the 

 other hand, the heat liberated. 



