226 Scientific Intelligence. 



The paper contains some attempts to explain the extraordinary- 

 behavior 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 

 occlusion of hydrogen by platinum black, thereby avoiding errors 

 due to the preexistence 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 -j-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 +11*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, con- 

 sidering 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 conjunc- 

 tion with the behavior 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 

 experiments 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 pal- 

 ladium exists as black, sponge, foil, wire, or compact metal, or 

 whether it is charged by direct exposure to hydrogen gas (the 

 proper conditions being observed), or charged electrolytically, 

 the amount of hydrogen occluded in each case is approximately 

 the same, the atomic ratio varying between 1*37 and 1*47. 



Hoitsema has shown that Troost and Hautefeuille's deduction 

 that a compound exists having the formula Pd 2 H is not warranted. 

 The constancy of the heat of occlusion over the whole range of 

 absorption is also opposed to the view that such a compound is 

 formed. 



The composition of fully charged palladium hydrogen corre- 

 sponds closely with the formula Pd s II 2 first suggested by Dewar. 

 The principal and almost only evidence, up to the present, in 

 favor of the formation of such a definite chemical compound is to 

 be found in the approximation of the above atomic ratios to the 



