RICHARDS AND HEIMROD. — THE IMPROVED VOLTAMETER. 419 



irregularity of Lord Rayleigh's voltameter is probably a heavy complex 

 ion ; hence it is not surprising that both the migration-rate and the 

 diffusion-rate of the impurity is small. On the other hand, when the 

 porous cup is too coarse-grained or too large, or when the anode solution 

 is allowed to rise too high and thus filter through, the effect of the diffu- 

 sion begins to be manifest. The same error begins to show itself when 

 the viscosity of the solution is diminished by increasing temperature, as 

 we showed in the preceding paper. 



If now the formation of ionized silver at the anode is attended by such 

 disturbing side reactions, it is reasonable to assume that a remedy may 

 be found in the use of an anode of some other metal. For this purpose 

 zinc seemed to offer peculiar advantages ; it possesses only one degree of 

 quantivalence, and has so great a solution-tension as to avoid the possi- 

 bility of contaminating the deposit of silver at the kathode. 



A zinc rod (so-called " C. P.") served as the anode in the following 

 two experiments, and it was surrounded by a ten per cent solution of 

 zincic nitrate prepared from the same material by solution in nitric acid 

 (standing for a week over zinc), filtration, and crystallization. The 

 kathode solution consisted of a ten per cent solution of argentic nitrate, 

 as usual. 



TABLE II. 



The Effect of a Zinc Anode. 



A peculiar reaction was observed during this electrolysis. The zinc 

 rod was covered with a copious white flaky precipitate, and a marked 

 test for nitrite was observed in the supernatant solution.* Thus the 

 ionization of the zinc is attended with the formation of basic salt and 



* See also Senderens, Comp. Rend., 104, 504 ; also Ber. d. d. oh. Ges., 20, 197 R 



(1887). 



