182 OXYGENATED COMPOUNDS OF NITROGEN. 



without difficulty. Light accelerates its decomposition, as does 

 also heat, though even at 43 it is not very rapid. This 

 change into nitric peroxide and oxygen is endothermic, and is 

 not reversible. 



The following is the analysis of these crystals : 5 '5 55 grms. 

 of crystals weighed, and dissolved in water, yielded a solution 

 which, according to alkalimetric test, contained 5 '54 grms. of 

 nitrogen pentoxide ; no appreciable quantity of nitrogen trioxide 

 was present (reaction of potassium permanganate). A large 

 quantity having been prepared, its action on water in the 

 calorimeter was studied, taking it successively under the three 

 states, solid, liquid, and gaseous. 



Solid state 



crystallised + H 2 -f water at 10 = 2HN0 3 dilute 

 + 8-34 Cal. 



Now 



N 2 5 H 2 pure + water at 10 = 2HN0 3 dilute liberates + 

 718 Cal. ; 



therefore 



N 2 5 solid + H 2 liquid = 2HN0 3 pure and liquid liberates 

 + 116 Cal. 



This quantity of heat is very small, as might be expected, 

 owing to the contrary thermal effect produced by the liquefaction 

 of the anhydrides. 



Hence, the action of the solid anhydride on water is not very 

 violent, which confirms in another way the above result. The 

 union of the solid anhydride with atmospheric aqueous vapour 

 is likewise slower than that of bodies said to be very hygroscopic. 

 In fact, at the ordinary temperature, the anhydride evaporates 

 without leaving any appreciable quantity of dilute acid. The 

 following reaction refers to the solid state 



N 2 5 solid + BaO solid = Ba(N0 3 ) 2 solid liberates + 407. 



This quantity of heat is less by + 10*3 than that liberated by 

 the formation of barium sulphate starting from the anhydrous 

 acid and the anhydrous base, both being solid, viz. + 51*0. 



Liquid state. Heat of fusion was determined by two 

 methods : 



(1) By the solidification of the dissolved acid contained in 

 a tube, immersed in the calorimeter. 



(2) By dissolving directly the solid acid in water. 



The following figures result from determination of the above 

 methods : 



N 2 5 ( = 54 grms.) liquid, in becoming solid, liberates + 414, 

 or, for N 2 8 ( = 108 grms.), + 8'28. 



