at the Contact of Solids and Gases. 5 



The plate enveloped in oxygen exhibited not the slightest 

 alteration in its electromotive quality, neither immediately 

 nor after a longer-continued action of the oxygen. The dif- 

 ference of tension Zn | Pd, was invariably the same as 

 Zn | Pd. The hydrogen gas, on the contrary, exerted a 

 powerful influence from the first moment onwards : at the 

 appearance of the first gas-bubble the palladium became at 

 once positive ; and after gas had been absorbed for some time 

 by the metal the force Zn | Pd, H was found, in different ex- 

 periments made with plates or wires, to be 



0-64, 0*69, 0-71, 0-70, 069. 

 Mean ... Zn | Pd, H=0 69 D. 



At this height it remained even when hydrogen had been in- 

 troduced from without (or evolved on the plate itself) so long 

 that the palladium could absorb no more, but free hydrogen 

 enveloped its upper surface. According to this, the tension- 

 difference would be 



Pd,H | Pd = l-28-069 = 059D, 



while I had previously found 



Pt,H | Pt=081D. 



Whether the palladium was employed bright, or coated with 

 palladium-black, made no difference. 



Further, palladium plates were used as the electrodes of a 

 Grove's pile of three or four couples, or a Meidinger's pile of 

 six couples. These electrodes were also enclosed in glass 

 tubes, to enable me to continue the electrolysis until the hy- 

 drogen was no longer absorbed by the palladium. The mea- 

 surement of the polarization present was, as before, effected 

 by means of the universal compensator ; with some practice 

 the simple discharge obtained at it furnished very constant 

 results, even though, like all similar contrivances, it was not 

 entirely free from the inconvenience that the polarization- 

 current was not closed till some, although a very short, time 

 after the interruption of the polarizing current. To distin- 

 guish it from the electromotive force Zn | Pd, H, which was 

 excited by merely enveloping a palladium plate in hydrogen, 

 I denote by Zn | Pd H the force excited by the galvanic polari- 

 zation of hydrogen. This was found to be 

 0-69, 0-71, 0-67, 

 Mean ... Zn | Pd H = 0'69D,— 



that is, exactly equal to Zn [ Pd, H. In this case, therefore, 

 no more hydrogen could be pressed into the palladium plate ; 

 the plate was already saturated with hydrogen. 





