280 Scientific Proceedings, Royal Dublin Society. 



The voltage between the cell terminals was measured by a "Weston 

 voltmeter. 



This instrument is almost dead-beat and very suitable for measuring with 

 fair accuracy a varying voltage. By estimation readings could be made to 

 0-01 volt, 



The initial value of the voltage on open circuit was taken. The circuit 

 was then closed, and the voltage on closed circuit was read at intervals for 

 10 minutes, during which the current was maintained at the constant value 

 of 0"2 ampere. The circuit was then opened and the recovery of the cell 

 from polarisation noted until it had almost recovered its initial value. 



It is unnecessary to give the observations. A typical curve is given in 

 Fig, 1. This series of observations was repeated several times, during which 

 the initial value of the E.M.F. fell from 1-52 to 1"41 volts. In spite of this 

 alteration in the cell, the recovery in each case was represented by the same 

 curve, as was shown by the coincidence of the curves plotted on transparent 

 paper. The cell was allowed to stand for three weeks, and the experiment 

 repeated. Practically the same recovery curve was obtained. The same 

 regularity was not shown in the growth of polarisation when the current was 

 passing through the cell which was represented by slightly varying curves. 

 The polarisation was therefore studied by the recovery curve in all the 

 subsequent work. 



(2) The two Types of Polarisation shown by the Recovery Curve. 



The recovery curve may be described, in general terms, as rising very 

 rapidly, and becoming almost parallel to the axis of time after about 

 10 minutes. In the set of observations represented in fig. 1, the voltage 

 rose - 63 volt during the first 10 minutes to T43 volts. In another 

 60 minutes the recovery was 0"04 volt. The initial value T50 volts was 

 registered 30 hours afterwards. We are, therefore, led to divide the period 

 of recovery into two sections : (1) the first part, characterized by a rapid rise, 

 and practically completed within an hour, (2) the second, a slow creep going 

 on for several hours, and perhaps not entirely completed for several days. 

 On the ionic theory the polarisation occurs at the carbon-manganese-dioxide 

 electrode due to the arrival of positive ions which are not discharged 

 instantaneously. A surplus of positive ions thus accumulates at the electrode 

 in the electrolyte, and a corresponding negative charge appears on the 

 electrode. The process is analogous to the charging of a condenser which 

 has a faulty insulation, and so discharges itself when the charging current is 



