RICHARDS AND HEIMROD. 



THE IMPROVED VOLTAMETER. 



421 



second lo.st 0.72 milligram, while the two crucible deposits lost respec- 

 tively 0.20 and 0.24 milligram. These losses, accompanied by audible 

 decrepitation, must have been due to retained electrolyte. 



lu the table the weights of the ignited precipitates are given. 



TABLE IIL 

 Comparison of Porous Cup Voltameter with Wire Gauze Voltameter. 



The gauze kathode thus showed an average surplus of less than a 

 tenth of a milligram. But even this slight error is explicable, for it is 

 clear that the argentic nitrate held by the electrolyte must have left silver 

 nitrite or silver behind on heating. If we assume that the temperature 

 of ignition was enough wholly to decompose the electrolyte, the average 

 loss of 0.57 milligram would correspond to a residue of about 0.1 milli- 

 gram, while the corresponding residue from the weaker solution used in 

 the porous cup voltameter could not have exceeded 0.02 milligram. The 

 difference between these two figures is exactly equal to the observed 

 difference between the gauze voltameter and the porous cup voltameter, 

 so that the two may be said to give precisely identical results. 



An important point connected with this experiment is the f\xct that 

 the kathode surface available for deposition on the gauze had an area of 

 less than half that on the inside of the large crucible. Hence the current 

 density in the gauze voltameter must have been over twice that in the 

 standard. 



There has thus been accumulated a convincing array of evidence indi- 

 cating that the porous cup A^oltameter affords a means of depositing the 

 amount of silver which really corresponds to the quantity of electricity 

 sent through it. The numerical averages may be summed up in a brief 

 table as follows : — > 



