178 OXYGENATED COMPOUNDS OF NITROGEN. 



first methods, owing to the complex nature of the thermal 

 reactions of permanganate. Their mean, however, is sufficiently 

 concordant. 



To sum up, the reaction 



Ba(N0 2 ) 2 dissolved + 2 = Ba(N0 3 ) 2 dissolved liberates 



According to the results obtained with gaseous chlorine ... + 22*1 

 barium dioxide ... + 21 '9 



potassium permanganate +21-1 



Mean +21-7 



This value is applicable not only to the oxidation of barium 

 nitrite, but also to the oxidation of all dissolved alkaline 

 nitrites. 



Hence from the knowledge of the heats of neutralisation 

 of nitrogen trioxide (4- 10*6) and nitric acid (-f 13*8) by 

 baryta : 



N 2 3 very diluted + 2 + H 2 = 2HN0 3 dilute liberates 

 + 18-5 Cal. 



For both the bodies gaseous we have, according to the data 

 given further on : 



NA gas + 2 = N 2 5 gas liberates + 10'5 Cal. 



Hence the change of the nitrogen trioxide into the pentoxide 

 liberates, when the action takes place, upon the gases, + 10 '5 ; 

 on the dissolved bodies, -f- 18'5 ; lastly, in presence of alkalis, 

 -f- 247. The great difference between the quantities of heat 

 liberated by one and the same transformation, according to 

 the state of the bodies, deserves attention, being due to the 

 difference in the heats of hydration and neutralisation of the 

 two acids. 



We will also give here the heats of oxidation of the solid and 

 anhydrous nitrites, which are easily calculated if their dissolving 

 heat be known. 



Dissolved salts. Solid salts. 



Ba(N0 2 ) 2 + 2 = Ba(N0 3 ) 2 liberates ... +21-7 ... +23-5 



NH 4 N0 2 + = NH 4 N0 3 liberates +21-8 ... +23-3 



AgN0 2 + = AgN0 3 liberates +20-3 ... + 17'2 



3. Second method. By nitric acid and barium dioxide. A 

 known quantity of concentrated and pure nitric acid is allowed 

 to absorb dry nitric oxide, the weight of which is determined 

 by a fresh weighing after having measured the heat liberated, 

 say Q for NO = 30 grms. The concentrated acid is contained 

 in a small tube, which is weighed and closed and plunged 

 into the calorimeter throughout the whole duration of the 

 absorption. A thermometer sensitive to 20^ of a degree gives 

 the temperature of the calorimeter; a smaller thermometer, 



