Constants of Hydrogenium. 339 



calorimeter by the hydride in excess of that of the original 

 palladium. But if a comparison is made between the different 

 hydrides in both series of experiments, then the specific heat is 

 found to exhibit no such regular increase as in the former series. 

 In the bar the extreme values are 3*21 and 3' 77, and the mean 

 of the three results is 3*47. The plate, on the other hand, gives 

 a range of from 2'7 to 3'94, the mean value being 3*31. The 

 amount of variation in the plate is very great as compared with 

 the bar, and is clearly due to some secondary action taking place. 



The increase of specific heat for small charges of hydrogen, 

 when comparison is made with pure palladium, is clearly due to 

 some regular increase of the specific heat of the palladium, or of 

 the hydrogen, or of both individually or conjointly. The mere 

 fact that we have only a very small weight of hydrogen relatively 

 to the amount of palladium does not explain the anomaly, be- 

 cause a small amount of hydrogen by the second mode of com- 

 parison does not yield such high results. The observational 

 errors, although much greater when we are dealing with small 

 quantities, cannot be expected to fall always in the same direc- 

 tion; and thus we are forced to admit there is some regular 

 sequential change taking place in the relations of the hydrogen 

 and palladium. 



The palladium, after use, is not found to have increased in 

 specific heat, but rather the reverse ; so that the explanation can 

 only rest on some altered condition of the bodies when united. 

 So far as my experiments have led me, I am inclined to regard 

 this alteration as a kind of molecular dissociation that increases 

 with diminished charge of hydrogen. I am led to this conclu- 

 sion from observing that the rate at which palladium loses hy- 

 drogen at constant temperature is dependent on the amount 

 present increasing with diminished charge. In conducting these 

 specific-heat experiments, a greater variation in the results has 

 always been observed when small charges were under experi- 

 ment, especially in the first two or three determinations. This 

 increase of dissociation may be explained in part from the for- 

 mation of regular cracks or channels in the mass of palladium, 

 together with the effect of pressure resulting from the contrac- 

 tion of the external layers of palladium from the loss of hydrogen. 

 It is, however, premature to discuss the cause of this increase 

 of dissociation until a more extended series of experiments is 

 made, and the behaviour of the alloy to pressure is investigated. 



Z2 



