RICHARDS AMD HEIMROD. — THE IMPROVED VOLTAMETER. 



427 



from the oxide, it probably contains Ag 2 0, and may be assumed to have 

 the formula already given, Ag 3 + . Thus the preceding interpretation 

 is confirmed. 



The next question which arises concerns the permanence of this com- 

 plex in the presence of acid. In order to test this, a solution of argentic 

 nitrate was saturated with argentic oxide, and then treated with a slight 

 excess of nitric acid. After a short time, perhaps an hour, electrolyses 

 were made with this solution in series with the standard, as usual. 



TABLE VI. 

 Standard vs. Standard saturated with Ag 2 0, but afterwards acidified. 



The results are somewhat less regular than usual, but clearly most if 

 not all of the oxide-complex had been removed by the acid. Thus, while 

 the complex is capable of existence in a neutral solution, the speed of its 

 reaction with acid results in its decomposition in a short time, as would 

 be expected. 



It is possible that this oxide-complex is not the only one capable of 

 being formed at the anode. Kahle, Sulc,* Mulder and Heringaf and 

 others, present evidence showing that with a small anode, where both 

 silver and nitrate ions would be less available for transferring electricity, 

 a highly oxidized compound having some such formula as Ag 7 NO n may 

 be formed. This compound is capable of dissolving in acids, forming a 

 brown solution ; and it may be responsible for the colored rings which 

 Kahle has noticed from old acid solutions. The fact that after boiling 

 with metallic silver such solutions cease to yield colored rings is evidence 

 that the foreign compound is a highly oxidized substance. 



In spite of the fact that the nitrite, the oxide-complex, and the per- 



* Sulc, Z. anorg. Cliem., 12, 89, 180 (1896) ; 24, 305 (1900). 

 t Mulder and Heringa, Ber d. d. ch. Ges., 29<, 583 (189G). 



