542 Capt. H. R. Sankey. [Apr. 4, 



fore, taken to obtain the fall of the C.E.M.F. on breaking the circuit, 

 so as to obtain the correction to be applied to the reading. This 

 correction was found to vary considerably according to the electrodes 

 and the electrolytes'; with acidulated CuS0 4 solutions and electro- 

 type copper electrodes it varied from 3 to 15 per cent. 



A variety of tests were made to ascertain wliat degree of depend- 

 ence could be placed on these measurements of C.E.M.F., because, of 

 course, on them the whole matter rests. Probably the most con- 

 clusive of these tests was the measurement of the resistance (by the 

 method employed in these experiments) of an arrangement, consist- 

 ing of a box of coils and of an electrolytic cell of very large area, 

 whose resistance might be neglected, but which supplied a C.E.M..F. 

 The measured resistances agreed, within 2 per cent., of the resistance 

 unplugged in the box. 



The conclusion come to is that the C.E.M.F. was determined with 

 a fair degree of accuracy, sufficient to show the existence of a transfer 

 resistance. 



The resistance of the electrolyte itself was measured in some cases 

 by finding the P.D. across two cross-sections of the liquid, by means 

 of fine wires dipping into the liquid at a known distance apart. This 

 resistance was found to be (as might be expected) independent of 

 the current density. 



Deducting the resistance of the electrolyte as thus obtained from 

 the resistance of the cell gave the " transfer " resistance. 



In commencing each trial a current of about 2*7 milliamperes was 

 passed through the cell for some time, which was found to increase 

 the resistance of the cell up to a limit depending on the previous 

 history of the electrodes. 



The current was then increased by approximately doubling it each 

 time until it reached about 370 millia-mperes. It was found that as 

 the current increased the resistance diminished, rapidly at first, more 

 slowly afterwards (set A). 



After applying the 370 milliamperes current, the current was 

 again suddenly reduced to about 2*7 milKamperes, and it was found 

 that the resistance had become much smaller, but that it immediately 

 began to increase again, somewhat rapidly at first (set B). 



A few minutes afterwards the current was again increased, as in 

 set A, and the resistance was found to diminish as the current 

 increased, but more slow]y than in set A (set C). When a current 

 of 370 milliamperes was reached, the resistance in both set A and 

 set C were practically equal, and the transfer resistance was small. 



The figure shows one of the trials with acidulated CuS0 4 solution 

 and lead electrodes. The sudden rise in the resistance (set A) 

 occurred at the moment the cathode became covered with copper. In 

 this figure the thick line, shows set A, the thin line set C, and the 



