124 



DRS. L. MOND, W. RAMSAY, AND J. SHIELDS, ON THE 



The fact that the volume energy (PV), or the reduced volume of the gas, except for 

 the first increment of pressure, may be taken as constant, satisfactorily establishes the 

 conclusion that increase of pressure, at least up to 4*6 atmospheres, practically has no 

 effect on the occlusion of hydrogen by palladium black which has already absorbed 

 the maximum quantity of hydrogen at the ordinary temperature. Platinum and 

 palladium black thus behave in precisely the same way as regards the effect of 

 pressure on the occlusion of hydrogen. The first increase of pressure caused the 

 disappearance of several volumes (about ten volumes) of hydrogen, but as this does 

 not continue, it may possibly be due to the presence of moisture, derived from the 

 palladium black, in the gas. 



The influence of pressure on the occlusion of hydrogen by palladium at high 

 temperatures has recently been described by DEWAR ('Proc. Chem. Soc.,' 1897, 

 No. 183, p. 192). 



XI. The Heat of Absorption of Oxygen by Palladium Slack. 



It is fairly certain that, on the absorption of oxygen by palladium black, a definite 

 oxide, or a mixture of definite oxides, is formed. A redetermination of the heats of 

 formation of the different oxides of palladium is outside the scope of this inquiry, but 

 it seemed desirable to determine the heat of absorption of the oxygen actually 

 contained in palladium black, for the purpose of comparing the number so found with 

 the corresponding number for platinum black. Since it was impossible to make the 

 measurement directly, an indirect method was employed, viz., the estimation of the 

 amount of heat absorbed on the removal of the oxygen from palladium black. 



A quantity of palladium black was introduced into the calorimeter, and fully 

 charged with hydrogen. A portion of the hydrogen absorbed was thus really 

 occluded, whilst the remainder removed the oxygen contained in the palladium black 

 as water. After the heat change had been measured, the occluded fraction was easily 

 ascertained by exhausting at a red heat, and from this the volume of oxygen removed 

 from the palladium black was found. 



