OCCLUSION OF HYDROGEN AND OXYGEN BY PALLADIUM. 



Ill 



platinum black may also best be explained as a superficial oxidation, the chief 

 difference being that the oxide of platinum decomposes or dissociates at a lower 

 temperature than the corresponding oxide of palladium. 



VI. Observations on the Occlusion of Hydrogen by Palladium Black, Sponge, and Foil. 



A series of experiments was next undertaken with the object of comparing the 

 relative occlusive power of palladium in the form of (a) black, (b) sponge, and (c) foil 

 for hydrogen, and investigating the behaviour of the substances produced. This was 

 especially necessary in the case of palladium foil or wire, since the statements of 

 different observers are at considerable variance with each other. Whilst most are 

 agreed that palladium in the compact state readily occludes the maximum quantity 

 of hydrogen when charged electrolytically, there are many cases on record in which 

 the compact metal only occludes a relatively small quantity of hydrogen when it is 

 simply exposed or ignited in the gas. 



a. Palladium Black. 1*619 gram = 0*135 cub. centim. palladium black was 

 charged with pure dry hydrogen in an apparatus similar to that employed for the 

 corresponding experiments with platinum black ('Phil. Trans.,' A, 181)5, vol. 186, 

 pp. 668 and 687). Altogether 152*76 cub. centims. (O c and 760 millims.) = 1131 

 volumes of hydrogen were absorbed, the greater portion of which was taken up 

 almost instantaneously. 



From the experiments already described, it is to be expected that a certain fraction 

 of the total hydrogen absorbed formed water with the oxygen pre-existing in the 

 palladium black. In order to determine the quantity of hydrogen which was really 

 occluded and how much was given off in vacuo at different temperatures, the experi- 

 mental tube was exhausted first at the ordinary temperature, then at higher tempera- 

 tures, and finally at a red heat. The results are given in the following table : 



The difference between the total hydrogen absorbed and that extracted at a dull 



