CONTRIBUTIONS FROM THE CHEMICAL LABORATORY OF 

 HARVARD COLLEGE. 



ON THE ACCURACY OF THE IMPROVED VOLTAMETER. 



By Theodore William Richards and George William Heimrod. 



Presented February 12, 1902. Received January 29, 1902. 



Introduction. 



In a recent preliminary paper * it was shown that the disturbing in- 

 fluences in the common silver " voltameter " (or better, coulometer f) are 

 due to the concentrated liquid which falls from the anode. In order to 

 avoid the inaccuracy thus caused, it was suggested that the anode be 

 surrounded by a fine-grained porous cup, which is capable of preventing 

 this heavy liquid from reaching the kathode. 



The weight of silver deposited by a given current in such a voltameter 

 was found to correspond very closely to the amount of copper deposited 

 at the same time in a copper voltameter shielded as much as possible 

 from all discoverable sources of error ; hence it seemed probable that the 

 new voltameter gives the true value of the electrochemical equivalent of 

 silver. 



In a matter so important as this, however, it seemed advisable to ob- 

 tain much more information concerning the constancy and trustworthiness 

 of the new instrument, as well as to discover if possible the mechanism 

 of the phenomena which rendered the older form untrustworthy. The 

 investigation described below was undertaken with these objects. 



I. The Constancy of the Porous Cup Voltameter. 

 The first problem was to determine if two instruments in series would 

 always give identical results; in other words, to find if the new voltam- 

 eter is always consistent with itself. 



* Richards, Collins, and Heimrod, These Proceedings, 35, 123 (1899). 



f The word " voltameter " was devised before electrical dimensions were 

 understood. It is moreover too much like the universally used and suitable word 

 " voltmeter." Now that the former instrument is placed upon a firm basis of 

 accuracy, it may appropriately receive also an accurate name ; and it is hoped that 

 the new word "coulometer" may replace wholly the anachronism. 



