﻿426 Mr. J. Dewar on the Motion of a Palladium Plate 



shifted the evolution of gas only on the same side on which it 

 was firmly pressed. In order to examine the action of mixed 

 electrodes, the palladium plate was welded with a similar plati- 

 num plate into a V-shaped electrode, when the apex of the com- 

 bination could be placed in or out of the liquid. If the platino- 

 palladium electrode is made the negative pole, hydrogen makes 

 its appearance immediately on the platinum plate; no gas is 

 evolved by the palladium for some time. If, after saturation, 

 by reversing the poles oxygen is thrown on the mixed electrode, 

 no gas is evolved from the platinum ; and when the gas began to 

 be evolved, it appeared simultaneously on both plates. The 

 same result is observed whatever may be the position of the com- 

 pound plate relatively to the other pole in the liquid, relative 

 distance from the other pole having no effect. This proves that 

 the whole of the oxygen that ought to be evolved on the platinum 

 is transferred by a polar chain through the liquid on to the pal- 

 ladium plate, so long as this plate contains occluded hydrogen. 

 The presence of the strong electric current is shown by connect- 

 ing the hydrogenized palladium with a platinum plate in an acid 

 liquid, the circuit containing a galvanometer. If the apex of 

 the V electrode is placed in the acid liquid, additional phenomena 

 are witnessed, depending upon which side of the compound elec- 

 trode is next to the other electrode. If the platinum side of the 

 V electrode is firmly clipped in a stand, a glass rod keeping the 

 apex in the same position in the liquid, and if the palladium 

 plate is next to the positive electrode, we observe the following 

 change during the course of the hydrogenation. The angle of 

 the V continually diminishes by the motion of the palladium 

 towards the perpendicular, the hydrogen evolved coming only 

 from the outer surface of the compound plate. After some time 

 the plate returns to its original position, and would curve beyond 

 it if the action were continued. If oxygen is now evolved on the 

 compound plates the first effect of the oxygen is to curve it be- 

 yond its first position, or to diminish the angle of the V. If the 

 palladium plate is furthest from the positive electrode, the first 

 effect of the hydrogenation is to increase the angle of the com- 

 pound plate by the palladium moving outwards ; after some time 

 it returns. Similar observations with the palladium clipped 

 in a stand, but made with the junction out of the liquid, showed 

 a decided movement depending on the relative position of the 

 plates. Seeing the palladium moved, although firmly clipped in 

 a socket out of the liquid, it was evident the motion could be 

 examined without the use of compound plates. 



After devising several arrangements in order to examine with 

 ease the motion of the plate, the following plan was found to be 

 the best in practice :— 



