RICHARDS AND HEIMROD. — THE IMPROVED VOLTAMETER. 439 



made exactly according to Lord Rayleigh's directions. These are given 

 below, together with the two determinations given in the last paper. 



TABLE XIV. 



Comparison of Porous Cup with Original Ratleigh Voltameteb. 



Tliis is 0.017 per cent more than the average of the preceding series. 

 Probably a mean of the average of the two series, or +0.050 per cent, 

 represents as nearly as possible the correction to be applied to Lord 

 Rayleigh's voltameter. This value is not only an average of averages, 

 involving twenty-three determinations, but is also very nearly the mean 

 between the two extreme results 0.012 and 0.093. It may probably be 

 relied upon to within 0.01 per cent of the total weight of the silver. 



It finds support in some results given in Kahle's * paper. He made a 

 comparison between an ordinary voltameter and one in which the anode 

 solution was constantly siphoned off and thus prevented, more or less 

 perfectly, from reaching the kathode. The solution in both voltameters 

 was strongly acid, but equally so. The siphon voltameter de[)osited, in 

 good agreement with the above results, O.Oo per cent less silver than 

 the ordinary voltameter. 



The fact, however, that the extremes vary from .012 per cent to .093 

 per cent indicates that unless great care is taken in the way in which 

 the anode is wrapped, in the strength of the current and in the size of 

 the anode, the depositions in the ordinary voltameter according to Lord 

 Rayleigh are untrustworthy. 



* Wied. Ann. N. F., 67, 30 (1899). 



