292 On the Occlusion of Hydrogen and Oxygen by Palladium, 



to have taken up 846 volumes, i.e., approximately the same quantity 

 as the black or sponge. 



The hydrogen occluded by palladium foil is given off again very 

 slowly at the ordinary temperature in vacuo, but rapidly and almost 

 completely at 100°. 



The paper contains some attempts to explain the extraordinary 

 behaviour of palladium foil. 



The heat evolved on the occlusion of hydrogen by palladium black 

 was measured in an ice calorimeter (temperature of the room 

 20 — 24°) in nearly the same way as the corresponding heat of occlu- 

 sion of hydrogen by platinum black, thereby avoiding errors due to 

 the pre-existence of oxygen in the substance. 



Favre's statement that the heat of occlusion remains constant for 

 the different fractions of hydrogen occluded was confirmed, and it 

 was found that -f-46'4 K (4640 g. cal.) were evolved per gram of 

 hydrogen occluded. 



The authors consider that this number may be taken as correct 

 within 1 per cent., and compare it with the different values found by 

 Favre and those calculated by Moutier and Dewar. 



If the external work done by the atmosphere be eliminated, the 

 heat evolved per gram of hydrogen occluded becomes +43*7 K. 



The heat evolved per gram of oxygen absorbed was also deter- 

 mined in an indirect manner, and found to be -fll'2 K (1120 g. 

 cal.). 



This number, referred to 16 grams of oxygen, lies intermediate 

 between the values given by Thomsen for the heat of formation of 

 palladious and palladic hydroxides, and may be consistent, consider- 

 ing the accuracy of such measurements, with the formation of either 

 of these hydroxides or with a mixture of both. In any case it is of 

 the same order of magnitude, and taken in conjunction with the 

 behaviour of palladium black when heated in an atmosphere of 

 oxygen, is undoubtedly in harmony with the view that the absorption 

 of oxygen by palladium black (and probably also by platinum black) 

 is a true phenomenon of oxidation. 



The authors have also investigated the atomic ratio — palladium : 

 hydrogen for fully charged palladium black, sponge, and foil, and 

 give in tabular form the corresponding ratios deduced from experi- 

 ments by Graham and Dewar in which wire and block palladium 

 were charged with hydrogen electrolytically. They have arrived at 

 the conclusion that no matter whether the palladium exists as black, 

 sponge, foil, wire, or compact metal, or whether it is charged by 

 direct exposure to hydrogen gas (the proper conditions being ob- 

 served), or charged electrolytically, the amount of hydrogen occluded 

 in each case is approximately the same, the atomic- ratio varying 

 between 137 and 147. 



