192 OXYGENATED COMPOUNDS OF NITROGEN. 



decomposed ; always in the same manner, the second reaction 

 slightly prevailing. Hence it will be seen that nitric oxide does 

 not and cannot appear in the electric decomposition of the 

 monoxide, since the latter always gives rise to an excess of free 

 oxygen. 



The proportion of nitric peroxide, formed in these experi- 

 ments, represented nearly one-seventh of the final volume, 

 a proportion which cannot be very far removed from that corre- 

 sponding to the final equilibrium produced by the spark in an 

 equivalent mixture of free nitrogen and oxygen, according to 

 experiments detailed further on. 



3. Nitric oxide. This gas is reputed one of the most stable. 

 It has, however, been taught that the spark (Priestley) or the 

 action of a red heat (Gay-Lussac) slowly decomposes nitric 

 oxide into nitrogen or nitric peroxide, and that in the presence 

 of mercury or iron there remains nothing but nitrogen (Buff 

 and Hoffmann, 1860). 



These opinions do not appear to be well founded. Mtric 

 oxide l contained in a sealed glass tube and brought to a dull 

 red heat, about 520, commences to decompose. At the end of 

 half an hour, the volume of the gas decomposed amounts to 

 nearly the quarter of the initial volume. The decomposed 

 portion was partly broken up into nitrogen monoxide and 

 oxygen 



2NO = N 2 + 0, a reaction liberating + H'3 Cal., 

 and partly into free nitrogen and oxygen 



2NO = N 2 + 2 , a reaction liberating -f- 21'6. 



The first reaction, that is the formation of nitrogen monoxide, 

 was predominant ; but the oxygen, gradually regenerated in 

 presence of an excess of non-decomposed nitric oxide, had 

 partially transformed it, at first, into nitrogen trioxide 



2NO -f = Na0 3 liberates + 10-5; 

 the total reaction, 



4NO = N 2 + N 2 3 , liberating + 217. 



Then, the oxygen increasing owing to a more advanced decom- 

 position, nitric peroxide is formed 



2NO + 2 = 2N0 2 liberates -f 19'0 ; 

 the total reaction, that is to say 



4NO = N 2 + 2N0 2 , liberating + 40'6 Cal. 



1 This gas was prepared by the reaction of nitric acid on a boiling solution 

 of ferrous sulphate ; it is the only reaction which yields it quite pure. The 

 use of copper and nitric acid, even very dilute and cold, always gives rise to 

 monoxide of which the proportion, variable with the length of duration ot 

 the reaction, may amount to more than a tenth of the volume of the gas 

 disengaged. 



