FORMATION OF AMMONIA FROM NITRIC ACID. 201 



8. We give also the figures relating to nitrogen trioxide. 



N 2 3 dilute = 



N 2 2 + yielded, .liberates Q-17'4 



N 2 + 2 (Q- 3-0) x 2 



N 2 + 3 (Q + 1-4) x3 



N 2 H 6 2 + 4 yielded /3H 2 supplemented! (Q-20-1) x 4 

 2NH3 + O.J \ in the reaction) / (Q-13'0) x 6 



It is well known that nitrogen trioxide oxidises bodies more 

 easily than nitric acid. This difference is accounted for by the 

 state of dissociation characteristic of nitrogen trioxide (pp. 196 

 and 197). 



The formation of ammonia in oxidations effected at the 

 expense of nitric acid is equally deserving of our attention. 



It is a secondary reaction, for it seems to be produced only 

 by the action of free hydrogen (spongy platinum) or by a metal 

 capable of liberating the hydrogen of water by dissolving in 

 more or less diluted acids, which requires the subsidiary relation 

 Q > 34-5. 1 



In order to form a proper idea of the conditions of this 

 formation, it is well to distinguish the general function of dilute 

 acids, the water in these compounds tending to be destroyed by 

 the metals with liberation of hydrogen, from the special function 

 in virtue of which nitric acid produces ammonia. Take dilute 

 sulphuric or hydrochloric acid in presence of a metal capable of 

 setting free its hydrogen, and a small quantity of nitric acid 

 to intervene, we shall provoke the following reaction : 



HN0 3 dil. + 8H = NH 3 dil. + 4H 2 0, which liberates + 248*2, 

 or 41*4 Cal. for every equivalent of oxygen (0 = 8 grms.) 

 eliminated. The ammonia combining with the excess of 

 sulphuric acid, the heat liberated will be raised by -f 12*4, which 

 makes altogether for each equivalent of oxygen + 43*5. 



1 Or rather Q > 34'5 - S, S being the heat of solidification of hydrogen, for 

 it would be necessary to compare the metal and hydrogen under the same 

 physical state. 



