Potential of Electrodes in Stationary Liquids. 2o 



use of according to dottrell's method, and at the same time 

 to indicate the nature and the scope of the conclusions that 

 can be drawn from the results obtained. 



Description of Apparatus and Electrical Arrangements. 



It was necessary that the apparatus should fulfil the 

 following conditions : — 



(1) The electrode under examination must be placed hori- 

 zontally either at the top or at the bottom of the apparatus. 

 It should be readily interchangeable and accessible to obser- 

 vation during an experiment, and allow the current to have 

 uniform density. 



(2) The electrode not under examination should be as 

 non-polarizable as possible, and no gases must be evolved 

 which might stir the liquid. 



(3) The difference of potential between the electrode and 

 the layer of electrolyte in contact with it must be capable of 

 continuous measurement during the course of an experiment. 



(4) It was found desirable to have the apparatus arranged 

 so that several successive determinations could be carried 

 out without taking it to pieces. 



Figs. 1 and 2 serve to illustrate the apparatus that was 

 designed to meet these requirements. For the sake of 

 brevity we shall call the electrode under observation the 

 cathode, the other electrode through which the working 

 current enters or leaves the liquid the anode, although there 

 is no reason why our cathode should not be used as anode 

 and dee versa. Making use of these abbreviations, fig. 1 

 shows the apparatus with the cathode at the top, that is for 

 liquids that become specifically lighter during electrolysis. 

 In fig. 2 the cathode is at the bottom as used for liquids that 

 become specifically heavier during electrolysis. The positions 

 of the anode arc indicated in both figures by A. The current 

 passes up the wide tube B, and then enters the long straight 

 tube < ! of about 1 cm. bore. The cathode is approached 

 through a hole d in the glass plate D, as shown in fig. 1. 

 The electromotive force between the cathode and the part of 

 the electrolyte on the other side of the glass plate D is 

 determined, a liquid connexion being tapped off here through 

 the annular space E and the tubes F to the non-polarizable 

 standard electrode G. We shall indicate by T the place in 

 the electrolyte between the glass plate D and the tube C 

 where the liquid connexion is tapped off to the standard 

 electrode. The electromotive force actually measured on the 



