ON THE SILVER VOLTA.M! II l: 595 



i in I nitrite increasing the value by about one part in 10,000 and hyponitrite by about 

 one part in -_'<K)0. Occasionally, however, abnormally low values are obtained, as, for 

 instance, in the case of the commercial sample W,, which gave the mean value 

 1"11818, and in a large number of the earlier porous pot exjxiriments 1 '11786 (4a), 

 1-11810 (5a), T11818 (Ca), M1815 (76), &c.* 



These low values we were able to associate in most cases with the presence of acid, 

 but if acid was responsible for the low values the quantity required to lower the 

 electrochemical equivalent by one part in 10,000 appeared to be very small and could 

 not easily be detected by litmus and other indicators. The commercial sample W, 

 had admittedly been crystallised from an acid solution and showed a trace of acid 

 when carefully tested with blue litmus paper. Finally it was found that the porous 

 pots which had been cleaned with nitric acid but soaked in water for a fortnight until 

 all the acid had apparently been removed, gave up acid to the solutions when 

 a current was passed through them, and this in sufficient quantity to be detected by 

 litmus. It was thought, however, to be desirable to make direct experiments on the 

 influence of acids. 



Our own experiments have shown that the addition of nitric acid to silver nitrate 

 solutions produces very irregular results. The normal effect appears to be a small 

 decrease in the electrochemical equivalent, but this never exceeds about two parts in 

 10,000, and there is very little difference in the effect produced by a mere trace of 

 acid which can only be detected with difficulty by means of litmus and that produced 

 by the addition of acid corresponding to 1 per cent, of the silver nitrate present in the 

 solution. On the other hand we have found that addition of diluted nitric acid may 

 produce an increase in the electrochemical equivalent ; this we attribute to the 

 presence in the nitric acid of oxides of nitrogen or other substances which, like the 

 hyponitrite, may raise the electrochemical equivalent to such an extent as to mask 

 completely the small decrease due to the acid. 



The irregular effects obtained may be seen from the following summaryt : 



I. Normal solution ril830(65b). II. Normal solution 1-11826(666). 



0-1 per cent. HNO 8 1-11841 (G5c). O'l per cent. HNO, 1-11860 (66c). 



1-0 per cent. HNO, 1*11836 (65d). 1*0 per cent. HNO, 1 '11840 (66ci). 



III. Normal solution T11830 (46c). IV. Normal solution 1 '11827. 



0-2 per cent. HNO, 1-11812 (736). I'O per cent. HNO, M1814( 58c). 



1-0 per cent. HNO, 1-11814 (73c). 1-0 per cent. HNO, 1-11810 (75c). 



Ilia. 1-0 per cent. HNO, 1-11829 (73d). TO per cent. HNO, 1-11819 (7Sl>). 



0-1 per cent. HNO, 1-1 1822 (78c). 



* There was, however, a considerable quantity of loose silver in most of the early determinations, 

 t One scries, No. 53, has been omitted, as the unacidified solution (53c) gave a high value and the nitrate 

 was therefore not pun 1 . 



4 o 2 



