FORMATION OF NITRITES. 



163 



According to theory this number is the same at constant 

 pressure. 



It follows from these figures that the formation of nitrogen 

 monoxide from nitrogen and free oxygen at constant pressure 

 N 2 + = N 2 absorbs + 34'1 - 44'4 = - 10'3 ; or for N 2 + 

 = N 2 44 grms. - 20*6 Cal. 



The heat absorbed in the formation of the monoxide ( 10*3) 

 is practically one half of the heat absorbed in the formation of 

 nitric oxide ( 21*6). 



4. HEAT OF FORMATION OF DISSOLVED AND ANHYDROUS 

 NITROGEN TRIOXIDE, AND THE NITRITES. 



1. The heat of formation of nitric oxide being known, it 

 is easy to obtain from it those of the higher oxides ; for it is 

 easy to change nitric oxide, under conditions of calorimetric 

 experiments, into nitrogen pentoxide, tetroxide, and trioxide. 



2. Conversion of nitric oxide into nitric acid by several 

 methods. One method consists in first forming a nitrite and 

 afterwards oxidizing it. In regard to the formation of nitrites, 

 nitric oxide and oxygen react very rapidly upon each other, 

 upon contact with an alkaline base, and are changed almost ex- 

 clusively into nitrites whatever be the relative proportions of 

 the two gases. 1 



This experiment was made in a closed vessel (Fig. 29) of a 

 capacity equal to 800 cub. cms. 

 almost filled with baryta water, the 

 strength and weight of which was 

 accurately measured. 



This vessel served as a calori- 

 meter; it was surrounded by an 

 envelope, as in the annexed figure. 



A calorimetric thermometer, 9, 

 was plunged into the vessel, pass- 

 ing through a large tube, K, at the 

 upper orifice of which it was fixed 

 by a small cork, b. The vessel itself 

 was closed by a large cork, pierced 

 with four holes, one for the passage 

 of the tube, K, another for that of 

 a tube, t, conducting the nitric 

 oxide and dipping into the liquid, 

 a third hole (hidden by the large 



Fig. 29. 



tube in the figure) received another tube for supplying the 



oxygen, lastly a tube, s, for carrying away the excess of the gases. 



Having introduced separately into the calorimetric apparatus 



1 " Annales de Chimie et de Physique," 5 e srie, torn. vi. p. 193. 



M 2 



