NITRIC PEROXIDE. 167 



deduced from them, thus : 2NX3 + O 4- water = N 2 3 dilute 

 + 28-0 - 10-6 = 174 Cal. 1 



From this figure, and from the heat of formation of nitric 

 oxide, is deduced the formation of dilute nitrogen trioxide from 

 its elements, nitrogen and oxygen. N 2 4- O 3 + water = N 2 3 

 dilute, absorbs 4*2 Cal. 



The experiments relative to the formation of nitrogen trioxide 

 might be quoted here, but these experiments will be more con- 

 veniently described after those relating to nitric peroxide. The 

 numerical result will suffice at present : 



i(Na + 8 ) = i(NaOa) gas absorbs - 111 Cal., or for N 2 3 

 - 22-2 Cal. 



7. Formation of the nitrites from their elements. According 

 to the above numbers, the thermal formation of the nitrites from 

 their elements liberates 



Salt Salt 



dissolved. anhydrous. 



Potassium nitrite, N + 2 + K = KN0 2 ... + 887 ... 



Sodium nitrite, N + 2 + Na = NaN0 2 ... +84-0 ... 



Ammonium nitrite, N 2 + 2 + H 4 = NH 4 N0 2 +60-0 ... +64-8 



Barium nitrite, 2 N 2 + 3 + BaO = Ba(N0 2 ) 2 + 26*8 ... + 29'6 



Silver nitrite, N 2 + 2 + Ag = AgN0 2 ... +2-7 ... +11-4 



5. HEAT OF FORMATION OF NITRIC PEROXIDE. 



1. The heat of formation of this body was measured by two 

 inverse methods, and according to three distinct processes, 

 intended to control one another, viz. 



(1) By synthesis or by the direct reaction of nitric oxide on 

 oxygen, both gases being employed in equivalent ratios. 



(2) By the transformation of the already formed nitrogen 

 tetroxide into nitric acid by means of chlorine and water. 

 By the transformation of the same nitric peroxide into barium 

 nitrate by means of barium dioxide, whence we pass by calcula- 

 tion to the transformation effected by means of free oxygen. 

 The heat liberated by the direct metamorphosis of nitric oxide 

 and oxygen into dilute nitric acid, being known from former 



1 Favre had estimated this quantity at -6'6 Cal. from erroneous data. 

 Thomsen calculated + 18'2, relying upon the union of three more exact 

 thermal data, one derived from the reaction of nitric oxide, and oxygen form- 

 ing nitric peroxide (+ 19'57), another from the dissolving of the latter body 

 in water (+ 7*75), a solution which he supposes to give rise to nitric acid and 

 nitrous acid in equal equivalents, the last datum being deduced from the 

 reaction of chlorine on the same solution, which it changes entirely into nitric 

 acid. This method is much more complicated than the one applied above, 

 and is founded on less sure reactions. However, the results coincide 

 sufficiently. 



2 The heat of formation of this salt has been given from baryta only, the 

 heat of oxidation of barium being unknown. In the transformation of barium 

 nitrite as well as in that of the nitrate, this datum moreover suffices for all 

 calculations relative to explosive substances, as these calculations can always 

 be established from the baryta itself. 



