1892.] Formation and Decomposition of Nitrous Acid. 43 



which the nitrous acid is retained by solutions containing the prod acts 

 of the reaction between nitric acid and metals. It also seemed 

 possible that such a line of inquiry might throw some light upon the 

 nature of an acid intermediate between nitrous and nitric acids, in 

 whose existence certain writers believe, though the facts adduced at 

 present are perhaps hardly sufficient to warrant such a belief. 



The apparatus and method of experiment finally adopted were as 

 follows : The nitrous acid solution was placed in a cylindrical tube 

 containing 100 c.c. up to a certain mark ; at its upper end were two 

 apertures, into one of which was sealed a glass delivery tube, while 

 the other could be wholly or partially closed by a small rubber plug 

 through which passed a pipette of exactly 2 c.c. capacity. The 

 former, which served for the passage of a stream of carbonic acid, 

 was sealed off at its lower end, the gas passing through a small pin- 

 hole at the side, and thus not directly impinging upon the liquid ; 

 the space between the loosely-fitting plug and the glass wall serving 

 for its exit. At the end of certain intervals of time the plug was 

 rammed in, whereby the pressure of the gas forced the liquid up the 

 pipette ; when this was filled up to the graduation mark the sample 

 was removed for analysis, while the aperture of the cylindrical tube 

 was partly closed meanwhile by a duplicate plug. The cylinder was 

 immersed in a water-bath, the temperature of which was kept 

 constant to within one- tenth of a degree on either side of that 

 required. Before any observations were made the ratio of nitrous to 

 nitric acid present was determined. 



Nitrous Acid from, Silver Nitrite and Hydrochloric Acid. 



The solution of nitrous acid was prepared in the usual manner by 

 the decomposition of recrystallised silver nitrite with a slight defi- 

 ciency of hydrochloric acid, and the liquid filtered from the precipi- 

 tated silver chloride into the decomposition flask. The amount of 

 nitrous acid was determined at the end of fixed intervals of time, 

 generally half an hour, and the results calculated on the hypothesis 

 that the volume of the liquid was maintained constant throughout 

 the course of the experiment. 



In the following table the results obtained are set forth, in which 

 T is the time from start, and C the concentration of the solution. 



