28 Mr. V. H. Veley. The Conditions of the [June 2, 



stood that the term nitrons acid is applied to that kind of matter 

 which decolorises potassium permanganate, liberates iodine from 

 potassium iodide, and gives various colour reactions with certain 

 organic bases. 



The Formation of Nitrous Acid in Nitric Acid Solution. 



Nitrous acid is generally produced directly by the decomposition or 

 reduction of nitric acid effected (i) by heating the acid, (ii) by pass- 

 ing nitric oxide or nitrous fumes into it, (iii) by electrolysis, or more 

 indirectly (iv) by addition of nitrogen peroxide to water, and (v) by 

 decomposition of metallic nitrites with acids. The nature of these 

 several changes, their conditions, and the composition of the solutions 

 obtained form the main subjects of this investigation. 



The Methods df Analysis. 



The following process was adopted for estimating the respective 

 amounts of nitrous and nitric acids in presence of one another ; the 

 total acidity was determined in the usual manner by means of 

 standard alkali, the nitrous acid by means of potassium permanga- 

 nate ; from the factors thus obtained the amount of acidity due to 

 the nitric acid by itself could be readily calculated. It was found 

 by experience not only in the present but also in previous investiga- 

 tions that nitrous acid could not conveniently be estimated by the 

 addition of the permanganate solution until it is no longer decolor- 

 ised, for the oxidation of the nitrous acid at the end of the operation 

 is gradual and not instantaneous. This point does not seem to have 

 been noticed by the writers on quantitative analysis. Accordingly 

 the method was modified as follows : The solution of the nitrous 

 acid was added to such a quantity of the standard permanganate, 

 acidified with sulphuric acid, which was judged to be in slight excess 

 over that required to complete the oxidation, and the whole mixture 

 allowed to stand in stoppered bottles for half an hour. The pink 

 liquid was then poured into potassium iodide solution, and the 

 amount of iodine liberated by the excess of the permanganate deter- 

 mined, as customary, by standard sodium thiosulphate solution. 

 There was apparently no risk of any of the nitrous acid escaping 

 oxidation, and thus liberating iodine from the potassium iodide, if 

 the method was carried out as described. 



In order to test the accuracy of the process, some purified silver 

 nitrite was recrystallised several times from water, a known quantity 

 of it was weighed out, suspended in water, and decomposed by a 

 slight excess of purified sodium chloride. The amount of nitrous 

 acid calculated as (N0 2 ) WAS determined in the solution, and for a 

 test analysis the following may be cited : 



