184 OXYGENATED COMPOUNDS OF NITROGEN. 



is deduced from the foregoing data. Under the three states we 

 have 



N 2 + 6 = N 2 5 gas +0-6 



N 2 -f 6 = N 2 5 liquid + 1-8 



N 2 + O fi = N 2 6 solid +5-9 



10. The following table shows the thermal formation of the 

 oxides of nitrogen under the gaseous form, referred to the 

 ordinary temperature : 



N 2 + = (2v.)N 2 - 103. 



} - 11-3 

 N + = (4v.)NO - 21-6{ 



} +10-5 



N 2 + 3 = (2v.)N 2 3 -H-l, 



} + 8-5 

 N + 2 = (4v.)N0 2 - frtf 



\ + 2-0 



N 2 + 6 = (2v.)N 2 6 - 06' 



It will be seen that the progressive formation of the oxides of 

 nitrogen follows a peculiar course. It first absorbs a quantity 

 of heat nearly proportional for the first two, then liberates 

 quantities which go on decreasing. These bodies are here 

 given under the gaseous form, the only one which is really 

 comparable. The most stable compound, nitric peroxide, 

 corresponds neither to the maximum nor to the minimum of 

 the heat absorbed. In short, there exists no simple numerical 

 relation between the quantities of heat brought into action. 



The most general fact, following from the foregoing table, is 

 that the formation of all the oxides of nitrogen from their 

 gaseous elements absorbs heat, their decomposition must there- 

 fore liberate it. Nevertheless not one of them is explosive by 

 simple heating. But nitric oxide, formed with the greatest 

 absorption of heat, is decomposed into its elements with facility, 

 as will be established further on (see p. 191). The heat absorbed 

 in its formation renders it comparable to cyanogen ( 37*3 for 

 C 2 N 2 ) or to acetylene ( 30-5 for C 2 H 2 ). These three bodies can, 

 moreover, undergo a true explosion under the influence of the 

 sudden and violent shock of mercury fulminate (p. 66). These 

 three bodies indicate an aptitude for combination altogether 

 comparable, to that of the simple radicals. Hence from a 

 knowledge of these relations may be understood why the 

 formation of the oxides of nitrogen never takes place directly, 

 and why it requires the aid of a foreign energy, such as electri- 

 city, or of a simultaneous chemical action. 



It also explains the great energy of explosive mixtures and 

 compounds formed by the oxygen compounds of nitrogen. 



