120 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



TABLE XIX. 



The simplest way to decide what effect the concentration of the re- 

 versible ion, if 1 may use such a phrase, has on the electromotive force, 

 would be to make a series of measurements on reversible electrodes by 

 the dropping mercury method. I have not been in a position to do 

 this, and I have had to find an easier, though less satisfactory, manner 

 of settling the question. Suppose we have electrodes of zinc and 

 copper in a mixture of zinc and copper sulphates, one solution. In- 

 creasing the concentration of the zinc sulphate or decreasing the con- 

 centration of the copper sulphate must diminish the electromotive 

 force of the cell, and vice versa if the reverse operations be performed. 

 Through the courtesy of Professors Trowbridge and Peirce of the 

 Physical Laboratory, I have been able to make the few experiments 

 necessary. As it was only required to find out whether there was any 

 change at all, there was no need of determining the absolute value of 

 the electromotive force. This made the experimental pait very easy. 

 I connected the cell with a large external resistance and a galvanome- 

 ter. I changed the ratio of the two components in the solution, and 

 noted the position of the galvanometer needle. I made measurements 

 with the electrodes in pure zinc sulphate solutions, in pure copper sul- 

 phate solutions, and in mixtures of the two in varying proportions. 

 Under all these different conditions I obtained the same electromotive 

 force, showing that it is a function neither of the relative nor of the 

 absolute concentrations.* Althoucrh one obtains the same value from 



* This applies only to electrodes reversible in respect to the kation. I hope 

 to make tiie case of electrocles reversible in respect to the anion the subject of a 



