OXYGENATED COMPOUNDS OF NITROGEN. 



dry nitric oxide and oxygen, and shaken them incessantly, the 

 heat liberated and the increase of weight was measured and the 

 amount of trioxide and pentoxide formed was ascertained. 

 The weight of pentoxide formed is always very slight, it has 

 been taken account of in the calculations according to the data 

 on the following pages. 



The following was found upon full calculation, 



2NO + 4- BaO = (IST0 2 ) 2 Ba, dissolved : + 28'0 Cal. 



3. Barium Nitrite. In order to pass from barium nitrite in 

 solution to nitrous acid, it was necessary to make a special 

 study of barium nitrite itself, this salt being a perfectly 

 pure and well-defined body, and intended to serve as starting 

 point for other experiments on the respective transformation 

 of the nitrous acid and of the nitrites into nitric acid and 

 nitrates. 



The barium nitrite was prepared by the reaction of nitrous 

 vapour (starch attacked by nitric acid) on a mixture of barium 

 carbonate and hydrate held in suspension in water. The barium 

 nitrite obtained was several times recrystallized, and its purity 

 verified by analysis. 



This salt crystallizes in brilliant needle-shaped prisms, 

 gathered together without order. Very slow spontaneous 

 evaporation yields large, confused twin crystals, which have the 

 appearance of a rather acute, double hexagonal pyramid. This 

 is in reality a limiting form, belonging to the system of the 

 straight rhomboidal prism, and analogous to that of potassium 

 sulphate. The following are some thermal data relative to this 

 salt : 



One equivalent (N0 2 ) 2 BaH 2 0, 123'5 grms. dissolved in 60 

 times its weight of water absorbs at 12, 4'3 Cal. 



The dissolving of the anhydrous salt (N0 2 ) 2 Ba = 114*5 grms. 

 absorbs at 12, - 2'84 Cal. 



It follows from these figures that the reaction (N"0 2 ) 2 Ba solid 

 + H 2 liquid = (N0 2 ). 2 BaH 2 solid, liberates -f T46. 



The very weak solution of barium nitrite, decomposed by 

 dilute sulphuric acid, liberates for 1 equivalent, + 7*9 Cal. 



Very dilute nitrous acid is set free under these conditions 

 without very sensible formation of nitric acid, as is proved by 

 adding potassium permanganate to it. Further, the formation 

 of barium sulphate, according to experiments made under the 

 same conditions of dilution and temperature, liberates 4- 18'50 ; 

 starting from sulphuric acid and the diluted base. 



From these figures we may conclude that, N 2 3 very diluted . 

 + BaO diluted = Ba(N0 2 ) 2 diluted, liberates + 10'6. This is 

 3 '2 Cal. less than nitric and hydrochloric acid, which shows 

 that nitrous acid must be ranked among the weak acids. 



Dilute hydrochloric acid completely displaces nitrous acid 



