﻿during the Formation of Graham's Hydrogenium. 429 



platinum electrode. The amount of chemical action effected by 

 the unit-surface of the electrode, and its distribution, depend 

 upon the position of the plate relatively to the lines of force 

 emanating from the poles. Now, of the two surfaces of the pal- 

 ladium plate, the surface next to the positive pole has the greatest 

 concentration of the lines of force ; and therefore the greatest 

 evolution of hydrogen takes place on this surface, so that the 

 quantity of alloy formed in the first instance is in excess of the 

 amount produced on the other side. The plate, from the great 

 expansion on the outer side, becomes convex, until the progres- 

 sion of the action on the other side is able to compensate this 

 flexure by a corresponding expansion, thereby bringing the plate 

 to its original form. But I have already explained how this 

 backward motion goes beyond the original position, producing 

 a flexure in the opposite direction, only in some cases returning 

 to its normal shape. This, in all probability, arises from the 

 combined effect of expansion and compression. Graham has 

 shown that the tenacity of the alloy is considerably diminished 

 as compared with that of the palladium, so that in the first 

 flexure of the plate the expansion has to compress the rigid pal- 

 ladium, whereas, when it begins to return, the compression is 

 effected on the less rigid hydrogenium already formed on the 

 other side, the elasticity of form being also probably relatively 

 small. This is the general explanation of the motion of the 

 plate ; but it must be remembered that the smaller flexures 

 produced by different forms and positions of the electrodes are 

 the result of non-homogeneity or excessive strain. There is one 

 position, at least, of the palladium relatively to the other elec- 

 trode, where the plate should have no lateral motion — that is, 

 when it is at right angles to the surface of the positive plate; 

 but all the attempts made with the small palladium plate at 

 my disposal failed to prevent lateral motion, probably from 

 want of uniformity of surface producing different rates of pene- 

 tration. 



Effect on the Current during the Formation of the Hydrogenium, 



In order to determine the effect on the current during the oc- 

 clusion of the hydrogen and its reoxidation, two Bunsen's cells 

 were connected, through a tangent-galvanometer, with a plate of 

 palladium and platinum as poles in a cell containing acidulated 

 water. The intensity of the current was determined, first, during 

 the decomposition of the water when the palladium pole evolved 

 oxygen, then during the absorption of hydrogen (when the cur- 

 rent was reversed), and lastly when the oxidation of the occluded 

 hydrogen was taking place. 



