RICHARDS, COLLINS, AND HEIMROD. — COPPER AND SILVER. 133 



sufficiently explains the arrangement. At the close of an experiment 

 the cathodes were immediately immersed in water, and after a thorough 

 washing in pure water and alcohol were dried as usual. The electrolyte 

 contained 100 grams of crystallized cupric sulphate in a litre. 



The silver cells were essen- 

 tially similar to those used by 

 Lord Rayleigh, except that the 

 cathodes consisted of large light 

 platinum crucibles instead of 

 bowls. These crucibles weighed 

 only 60 grams, although they 

 were capable of holding 120 

 cubic centimeters ; they were 

 provided with lips. A crucible 

 exposes a smaller surface to the 

 impurities of the atmosphere 

 and gave in our experiments a 

 more evenly distributed deposit 

 than a bowl. The anode con- 

 sisted of a lump of pure silver, 

 wrapped in pure filter paper, 

 and the electrolyte contained 

 ten per cent of argentic nitrate. 

 When the current was stopped 

 the argentic nitrate was decant- 

 ed through a weighed Gooch 

 crucible, and, after standing 

 main' hours with several lilliiiirs 

 of pure water, the crucibles 



were washed with pure water and alcohol, and dried at 130°. The 

 decantates were filtered, in order to be sure that no silver had been 

 lost; if the Gooch crucible was found to contain any of the deposit, its 

 weight was added to that of the greater part clinging to the cathode. 

 In one or two of the earlier determinations, plates were used instead of 

 crucibles as cathodes ; but since the results thus obtained showed no sys- 

 tematic variation from those with the crucibles, the table is not compli- 

 cated by calling attention to this inessential fact. The danger of losing 

 silver mechanically from the corners of a plate is so great that this form 

 of cathode was soon abandoned. 



Figure 5. — Common Silver Volta- 

 meter (| natural size; section). 



A, >ilver anode. B, filter paper covering. 

 C, lip of platinum vessel forming cathode. 



