Measurement of Electrolytic Conductivity. 



21 



used a long trough of known section with two fixed non- 

 polarizable electrodes at the ends (Cu electrodes in CuS0 4 ) 

 and one movable electrode between them. A resistance in 

 series with the shorter column of liquid was adjusted to 

 balance the bridge. The resistances so measured were of the 

 order of 12 ohms or less. For many purposes the use of non- 

 polarizable electrodes is impossible or inconvenient. 



The method to be described is in many respects similar to 

 those of Tollinger and Elsas, but it differs from them in the 

 form of electrolytic cell employed, and especially in a very 

 material point, viz. : — the employment of high voltages and 

 high resistances so as to effectually drown any residual error 

 arising from differential polarization. 



Fig. 1 will make the arrangement clear, rr are equal re- 

 sistances, C c are two similar electrolytic cells equal in all 



Fig. 1. 



respects, except that in C the electrolytic conductor is very 

 long, in c very short. The resistance-box R is adjusted till 

 there is a balance, when, of course, the resistance in the box 

 is equal to the difference in the resistances between the two 

 cells C and c. Since the resistances rr are equal it will be 

 clear that when approximate balance has been obtained equal 

 currents will be traversing both electrolytic cells, and therefore 

 there should be the same polarization in each cell, and these 

 polarizations are clearly opposed and are in theory eliminated. 

 Instead of the arrangement shown in fig. 1, in which the 

 cells are arranged in parallel, we have also tried the effect of 

 interchanging the battery and galvanometer so as to arrange 

 the cells in series. In the first case the polarization of one 

 cell is opposed to that of the second, so that the polarization 

 of each cell is much more persistent ; in the other case the 

 cells are joined in series, so that the polarization falls as soon 



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