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





Palladium 

 Positive pole. 



Palladium 

 Negative pole. 



Hydrogenium 

 Positive pole. 



Angles on tangent- 1 

 galvanometer ... j" 



Tangents 



o 



235 



0-4348 



21-5 



0-3939 



40-3 

 0-8541 





The diminution in the intensity of the current during the 

 formation of the hydrogenium arises from the strong current 

 generated in the decomposing-cell by the secondary polarity of 

 the electrodes, acting in the opposite direction, whereas the oxi- 

 dation of the hydrogenium produces a current acting in the 

 same direction as the battery. The intensity of the current 

 during the oxidation of the hydrogenium is nearly doubled ; so 

 that if we consider the resistance in the circuit to remain con- 

 stant, the additional electromotive force added by the oxidation 

 of the hydrogen is equivalent to two cells of Bunsen. The great 

 increase in the intensity of the current during the oxidation of 

 the hydrogenium may be shown in the following manner : — Use 

 two palladium plates in the decomposing-cell with index to show 

 the motion of the plate attached to each, as in the figure former]y 

 given, and include in the circuit a commutator and a fine spiral 

 of platinum wire. During the occlusion of hydrogen the plati- 

 num spiral may be made of such a length as to remain dark, the 

 motion of the index proving the absorption of hydrogen. Re- 

 verse now the direction of the current, and the spiral of platinum 

 will become red-hot, the index moving rapidly back to its original 

 position, while the index of the other plate will begin to move. 

 The oxidation of the occluded hydrogen is the limit to the 

 brightness of the platinum spiral, so that a reversal of the cur- 

 rent produces a renewed brightness. By this arrangement we 

 keep both indices moving along the scale, and the platinum 

 spiral alternately bright and dark. If the electromotive force 

 is really equal to a Bunsen's cell, this arrangement must pro- 

 duce a current far more intense than any similar gas-battery 

 where oxygen and hydrogen are the reacting elements ; but as 

 the resistance in the circuit might vary, several indirect experi- 

 ments were made. When a palladium plate saturated with hy- 

 drogen was associated with a platinum plate in an acid solution 

 of permanganic acid and connected through a voltameter, the 

 arrangement could decompose water. A similar result was ob- 

 tained when a platinum plate coated with platinum -black satu- 

 rated with oxygen was employed; but the action in this case 

 was very slow, and sometimes did not succeed. A platinum 



