at the Contact of Solids and Gases. 7 



tinued to rise, but only slightly. Accordingly 

 Pd | Pd, C1=076L>. 



The attempt to polarise palladium with chlorine by electro- 

 lysis of hydrochloric acid had to be given up as useless. Even 

 chlorine gas introduced from without into the gag element 

 attacked the palladium and browned both the metal and the 

 liquid after a time ; while in the electrolysis the attack com- 

 menced immediately and with violence, and a coating of pal- 

 ladium-black was at once driven off. 



Ethylene and carbonic oxide gas, into which the tube con- 

 taining a palladium plate was introduced, polarized it positively: 

 indeed, after introducing the ethylene, I found the values 



1-22, 1-24, 1-23, 

 Mean ... Zn | Pd, C 2 H 4 =P23D; 



and after the introduction of the carbonic oxide, 

 1-05, 1-06, 



Mean ... Zn [ Pd, 00=1*05 D. 

 Therefore 



Pd, 2 4 | Pd=0-05D, 



Pd,CO | Pd = 0-23D. 



When sulphuretted hydrogen was brought into the tube, I 

 obtained immediately after the appearance of the first bubble 

 the tension-difference 



Zn | Pd,H 2 S=088D. 



On continually agitating the liquid with fresh quantities of 

 gas until it was saturated, the above difference was scarcely 

 altered ; after two successive fresh saturations I obtained 



0-87 and 0-87; 

 so that we have 



Pd,H 2 S | Pd=0'41D. 



The carbons with which I have experimented were four- 

 edged rods of retort-carbon, such as are used for electric lamps. 

 They are of great hardness and very close structure. They were 

 purified by boiling in nitric acid, in water, and lastly in dilute 

 sulphuric acid, in which they were then left to cool. If they 

 were to be used in dilute hydrochloric instead of sulphuric 

 acid, this liquid was then the last in which they were boiled. 

 Through this treatment the rods were pretty homogeneous. 

 Introducing them into dilute sulphuric acid, and uniting this 

 by the siphon with the zinc-cell, I obtained the following elec- 



