1893.] 



Platinum Electrodes in Sulphuric Acid, 



81 



deflection positive, and then the experiment was continued as below. 

 When the positive deflection was obtained its amount was noted, and 

 the slider was moved so as to increase the steady deflection nearly up 

 to the point on the scale reached by the impulsive one, and another 

 trial then made. In this way, by watching the point reached by each 

 impulsive deflection, and then increasing the steady one almost up to 

 that point, the latter was increased until the former vanished, that is, 

 until the potential of the quadrants was that of polarisation. The 

 magnitude of this deflection was then noted, and the polarisation 

 calculated from it. In these trials the key Jc was kept down only for 

 about two seconds, just sufficient time to allow the extent of the 

 deflection to be seen, and at least two minutes were allowed to elapse 

 between one trial and the next. 



After the maximum deflection had been reached, a considerable 

 interval of time was allowed to elapse, and then the key &' raised 

 and k simultaneously lowered and kept down, and the rate of fall of 

 the deflection noted. The above motion of the keys threw the slider 

 off and put the electrode on to the quadrants, at the same time 

 stopping the current. The deflection was therefore due to polarisa- 

 tion alone, and its rate of fall was therefore the rate of fall of the 

 polarisation. 



The results of one series of experiments are given in the accom- 

 panying table. 



All the results point to the polarisation being constant with large 

 electrodes, being independent of the strength of the solution and the 

 intensity of the current. The variations in the figures do not occur 



Mean polarisation = 2"09 volts. 



VOL. LIV. 



