OCCLUSION OF HYDROGEN AND OXYGEN BY PALLADIUM. 119 



It is evident from the last column of the table that the heat evolved per gram of 

 hydrogen occluded remains the same for the different fractions. 



The mean of the four experiments is 4672 K, and if we exclude the last, in 

 which experimental errors have a greater influence owing to the smallness of the 

 quantity of hydrogen occluded, the mean of the three principal results is + 46-44 K., 

 and the deviation from this mean in the case of the fourth result is only 0'6 percent. 



The value -f 46'44 K. for the heat evolved per gram of hydrogen occluded may 

 safely be taken as correct within 1 per cent. 



In Experiment V. a portion of the hydrogen which had been occluded was 

 exhausted by means of the pump, giving the number 45'5 K. absorbed per gram of 

 hydrogen removed. The hydrogen comes off so slowly at C. that the experiment 

 could not be continued. The result does not differ very much from those already 

 obtained, and no doubt the conditions under which the experiment was made account 

 largely for the difference. In experimenting with the ice calorimeter it is essential, 

 in order to obtain an accurate measurement of the deflection, that the normal 

 creepage of the instrument should be in the same direction as the deflection to be 

 measured. In this case, however, the two were opposed to each other. In the 

 particular instrument with which we have worked, there was generally a slow 

 creepage inwards, due to the slow melting of the ice. In any serious attempt, 

 therefore, to measure the amount of heat absorbed, it would be advisable to alter 

 the melting point of the ice in the interior of the calorimeter by increasing or 

 diminishing the pressure at the open end of the capillary tube until the creepage 

 was either entirely suspended, or, at least, in the same sense as the deflection to be 

 measured. 



FAVRE, by means of his mercury calorimeter (' Comptes Rend.,' vol. 78, p. 12G2), 

 determined the heat evolved on the occlusion of hydrogen by palladium sponge, and 

 obtained numbers varying from 202'7 K. to 38'9 K. The results which exceed 

 60 K., however, were only obtained for the first fractions of hydrogen admitted, and 

 were obviously due, as FAVRE himself recognised, to the simultaneous occurrence of 

 a second reaction, viz., the formation of water from oxide of palladium. 



If we exclude four* of FAVRE'S experiments, in which the result is greater than 

 60 K., then the general mean of the twenty-five remaining experiments, varying 

 between 60 K. and 38 '9 K., is 48'6 K. per gram of hydrogen occluded, a result 

 which is approximately the same as that found by us, viz., 46'4 K. In another 

 independent series of experiments ('Comptes Rend.,' vol. 68, p. 1306) FAVRE 

 estimated the heat of occlusion of hydrogen at 41 '6 K. from the difference between 

 the quantities of heat evolved when an ordinary Smee cell was placed in the calori- 

 meter (i.e., when the hydrogen was allowed to escape) and when in the same cell 



* Three of the four are the first members in a series of seventeen experiments, whilst the fourth is 

 the first of another series of eleven experiments. 



