168 



OXYGENATED COMPOUNDS OF NITROGEN. 



experiments, we deduce from the latter trials by difference the 

 heat which would be liberated by the metamorphosis of nitric 

 oxide and of oxygen into nitric peroxide. 



The first method, though simpler, is less exact than the 

 others from a consideration of the weight of the gases employed, 

 and of the quantity of heat produced. 



2. First process. Nitric oxide and oxygen. Two concentric 

 glass bulbs are enclosed one inside the other and sealed 

 separately, each containing one of the dry gases in the exact 

 ratio of 2 volumes nitric oxide (250 to 280 cub. cms.) to 1 

 volume of oxygen (see Fig. 30). 



The system is plunged into the water of the calorimeter, then 

 by a jerk of the hand the internal bulb is broken, leaving its 

 envelope intact. Both gases react at once, and the action is 

 allowed to complete itself. The nitric peroxide remains gaseous 

 even up to 10 or 15, because its tension in the bulb is less by 

 a third than the atmospheric pressure. The 

 latter circumstance slightly lowers the figures 

 which would be observed at the normal pres- 

 sure, viz. by 0-3 Cal. (p. 155). 



Operating in this way and calculating the 

 reaction at constant pressure 1 the following 

 was observed: 2NO + 2 = N" 2 4 gas + 19'6 ; 

 + 19-9 + 18-3 + 19-8 : mean + 194 Cal. 



3. Second process. Nitric peroxide, gaseous 

 chlorine and water. In principle, this reaction 

 is the following : N0 2 gas + Clgas -f H 2 + 

 water = HN0 3 dilute + HC1 dilute. 



The heat of formation of water (34*5 for 

 H 2 + 0) and that of dilute hydrochloric 

 acid + 39-3 for H + Cl + water = dilute 

 HC1 being taken as known. 

 In practice it has been found preferable to operate on liquid 

 nitric peroxide, and this led the author to determine its heat 

 of vaporisation, 2 viz. 4'33 Cal. for N0 2 = 46 grms. 



The weighing of liquid nitric peroxide may be performed 

 very accurately in a hermetically sealed bulb. 



In order to weigh chlorine directly in the same way, recourse 

 was had to the following artifice. Instead of allowing the nitric 

 peroxide and the chlorine to act directly on the water, the 

 chlorine was absorbed by a dilute solution of potash, the latter 

 being in excess, the heat liberated and the weight of chlorine 

 absorbed was determined by means of the vessel shown on 

 page 163. 



1 Thomsen obtained + 19-57 by introducing both gases simultaneously into 

 a chamber placed in a calorimeter. 



2 See the method employed (" Annales de Chimie et de Physique," 5 e seVie, 

 torn. v. p. 154). 



Fig. 30. 



