54 Formation and Decomposition of Nitrous Acid. [June 2, 



(i.) The formation of the impurity of nitrogen peroxide in nitric 

 acid, imparting to it the well-known yellow tint, takes place in the 

 case of the more concentrated acid, even at a temperature of 30, and 

 of the less concentrated acids at from 100 150, even when the 

 acid is not unduly exposed to sunlight. 



(ii.) The reaction between nitric oxide and nitric acid may be 

 regarded as reversible, thus : 



provided that the acid be sufficiently dilute, and the temperature 

 sufficiently low. Under these conditions equilibrium is established 

 between the masses of nitric acids when the ratio of the former to 

 the latter is, roughly speaking, as 9 : 1. The actual ratio varies 

 slightly on the one side or the other, according to the conditions of 

 the experiments. With more concentrated acids and at higher 

 temperatures the chemical changes taking place are more compli- 

 cated, and the decomposition of the acid more profound. 



(iii.) The decomposition of solutions containing both nitric and 

 nitrous acids is also investigated ; the rate of the change is shown to 

 be proportional to the mass of the nitrous acid undergoing change. 

 The curve representing the amount of chemical decomposition in 

 terms of the mass present is shown to be hyperbolic, and illustrative 

 of the law 



(I)^-- C2 

 * } dT~ M ' 



This holds good, whatever be the method employed for the produc- 

 tion of the nitrous-nitric acid solution. 



The observed values for C or the concentration of the nitrous acid 

 are concordant with those calculated according to the above differ- 

 ential equation within the limits of experimental error. 



The rate is dependent upon the ratio of the masses of the nitrous 

 and nitric acid, being the more rapid, the greater the proportion of 

 the former to that of the latter. 



In the particular case of the liquid prepared from nitric oxide and 

 nitric acid, wherein the reproduction of solutions of similar concen- 

 tration presents less difficulty, it is shown that as the temperature 

 increases in arithmetical the rate of change increases in geometrical 

 proportion, in accordance with the equation 



(IT.) v t = v,k-V, 

 the value for Is being 0-0158. 



Finally, though the nitrous-nitric acid solutions behave in a similar 

 manner as regards the diminution of the mass of the nitrous acid, 

 yar, in other respects, such as evolution of gases and the action upon 

 nietals, they are dissimilar. 



