188 OXYGENATED COMPOUNDS OF NITROGEN. 



14Br (gas) -f water, the final state is arrived at by the following 

 cycle : 



N 4 + 5 + Ag 4 = N 4 5 Ag 4 . 



7(H 2 + 0) = 7H 2 liberates + 34-5 x 7 ... =241-5 



4Br gaseous + water = 14Br dissolved ... + 29'0 



Beaction (for Ag 4 ) + 59*3 



x + 329-8 

 the final state being 



2HN0 3 dilute + lOHBr dilute -f 4AgBr. 

 The same final state may be arrived at by the following cycle : 



2(H + N + 8 ) + water = 2(HN0 3 ) dilute ... + 97-6 

 10(H + Br gas) + water = lOHBr dilute ... +167-5 

 4(AgBr gas) = 4AgBr + 55'4 



+ 320-5 

 Both thermal sums being equal, it follows that 



x = -9-3 Cal. 

 This is the heat absorbed in the reunion of the elements 



Ag 4 + N 4 + 5 . 



We have further, starting with nitrogen, oxygen, and silver 

 oxide 



2Ag 2 + N 4 + 3 , - 16-3 Cal. 



6. Heat of formation of hyponitrous acid. To pass to the acid 

 itself, we measured the heat liberated in the reaction of dilute 

 hydrochloric acid on silver hyponitrite, viz. for one equivalent 

 of silver, Ag, contained in this compound. 



+ 8 '' 



which makes for Ag 2 + 17 '88. 



The hyponitrous acid exists, moreover, after this operation, or 

 at least throughout the duration of the experiment, as is shown 

 by the agreement of the estimations of bromine effected before 

 and after the action of the hydrochloric acid. 



This being established, the reaction 



2HC1 -f Ag 2 = 2AgCl 4- H 2 liberates + 201 ; 

 whence it follows that 

 N 4 3 dilute 4- 2 Ag 2 = Ag 4 N 4 5 liberates + 40'2-17'9 = +22-3, 



or 4- 1215 for each equivalent of oxide combined. Hence we 

 have N 4 4- 3 4- water = N 4 3 dilute 38*6 Cal. Hyponitrous 

 acid is therefore formed from its elements with absorption of 

 heat, as would be supposed from the instability of the acid itself. 

 Its transformation into nitric acid, by oxidation (by means of 

 bromine), liberates N 4 3 dilute 4- 7 4- 2H 2 = 4HM) 3 dilute 



