OCCLUSION Of HYDROGEN AND OXYGKN BY PALLADIUM. 



117 



VII. The Heat of Occlusion of Hydrogen by Palladium Black. 



The determination of the heat of occlusion of hydrogen by palladium black was made 

 in the ice calorimeter already described by us (' Phil. Trans.,' A, 1897, vol. 1 90, p. 131), 

 and it may be interesting to note that during the course of these investigations the 

 temperature of the room in which the calorimeter was placed varied between 

 20-24 C. The experiments were made in a manner precisely similar to the 

 corresponding series with platinum black, the only essential difference being that a 

 constant volume manometer was attached to the experimental tube. 



To pump 



To experimental tube. 



A constant volume manometer was constructed, as shown in the accompanying 

 figure. This form was chosen for two reasons. In the first place, it obviated the 

 necessity of calibration. The capacity of the capillary tubing between the two taps 

 and the mark at the point A was determined once for all and added to that of the 

 experimental tube. During the course of the experiments the mercury in the right 

 limb was always kept near the mark A, and during an actual measurement of 

 pressure exactly at the mark. The second and chief reason for selecting this form of 

 manometer, however, was that the main bulk of the gas in the experimental tube 

 was at 0., whilst the projecting portion was at atmospheric temperature, and in 

 the case of an ordinary manometer it would have been very difficult to estimate the 

 average temperature of the projecting volume of gas, which would have been consider- 

 able, since capillary manometers are unreliable. 



