OXIDATION BY PERMANGANATE. 189 



f 67*2 or -f 9'6 Cal. per equivalent of oxygen fixed. This 

 figure is hardly higher than that obtained for the transformation 

 of dissolved nitrous acid into dilute nitric acid. N 2 3 dilute 

 + 2 + H 2 = 2HN0 3 dilute + 1815, or 9-25 cal. for each 

 fixed. However, if we regard the two successive oxidations, the 

 calculation shows that the oxidation of the nitrogen trioxide 

 forming nitrous acid liberates a little more heat, viz. 101 per 

 fixed, than that of the nitrous acid changed into nitric acid, viz. 

 9 '25. The change even of one of the salts into the other would 

 liberate, for solid salts of silver 



Hyponitrite changed into nitrite per fixed -f 10'4 

 Nitrite into nitrate -f 8*8. 



For the dissolved salts of potassium the difference is increased, 

 owing to the difference in the heats of neutralisation. 



Hyponitrite changed into nitrite per fixed + 13 '6. 

 Nitrite into nitrate 4- 10'8. 



The relations are always of the same kind. 



7. The oxidation by permanganate, with formation of nitrogen 

 monoxide (deducting the heat due to the reduction of the 

 permanganate) 



N 4 3 dil. + 3 + H 2 = 2HN0 3 dil. + N20 gas liberates + 42 -3. 



The slow decomposition of the hyponitrous acid in contact with 

 the air, and at the expense both of the free oxygen and that 

 dissolved in the water, liberates exactly the same quantity of 

 heat with formation of nitrogen monoxide. The pure and 

 simple separation N 4 3 dil. = 2NO + N 2 gas would liberate 

 -f- 6 '4. The nitrogen monoxide can moreover be formed with- 

 out nitric acid by other methods, which liberate much more 

 heat, and are therefore preferable 



7N 4 3 + water = 7N 2 gas -f 2HN0 3 dil. liberates + 96'6, 

 or -{- 241 for N 4 3 . Combinations of hyponitrous acid present 

 a mobility and complexity of reactions which are explained by 

 their endothermal formation. Many analogous phenomena are 

 known in the series of the lower oxides of sulphur and 

 phosphorus, not to speak of hydroxylamine, which also very 

 easily yields nitrogen and nitrogen monoxide. 



8. The heat of neutralisation of dilute hyponitrous acid by 

 silver oxide has been given above, viz. 



N 4 3 dilute + 2Ag 2 4 = Ag 4 N 4 5 -f 1115 X 4. 

 We have tried also to estimate the heat of neutralisation of 

 hyponitrous acid by the alkalis, by decomposing salts of silver 

 by the alkaline chlorides. The reaction is almost instantaneous. 

 We obtained i(Ag 4 N 4 5 -f 4HC1) dilute at about 14 + 5'50 

 Cal. With barium chloride, BaCl 2 , the liberation of heat has 

 been more considerable, but it seems to be complicated by the 



