426 ME. T. GEAHAM ON THE ABSOEPTION AND 



sphere of the same gas for several hours. A second glass tube receiver, to which the 

 platinum-foil was transferred, was exhausted, as usual, at 20° C. without any sensible 

 evolution of gas. With a red heat superadded, gas came off in twenty minutes (but 

 nearly all in the first seven minutes) to the extent of 075 cub. centim., of which 0-56 

 cub. centim. proved to be hydrogen. The volume of 8-3 grms. of platinum is 0-385 cub. 

 centim. Hence one volume of platinum foU appears to take up, in three hours, 



1-45 vol. hydrogen at 230° C. 



9. The same portion of platinum-foil was again charged with hydrogen at a still lower 

 temperature, namely between 97° and 100°, for three hours. Submitted to exhaustion 

 at red heat, the platinum now gave off 0-5 cub. centim. of gas in thirty-five minutes, of 

 which about 0-3 cub. centim. were hydrogen. One volume of platinum-foil has taken up 



0-76 vol. hydrogen at 100°. 



By this property platinum is connected with palladium, which of all metals appears 

 to possess the power of absorbing hydrogen in the highest degree. 



Palladium. 



Of late years palladium has become comparatively uncommon ; and some difficulty was 

 experienced at first in procuring more than a gramme or two of the metal, in the form of 

 thin foil. The palladium-foil first employed weighed 1*58 grm., and measured 0"133 

 cub. centim., taking the specific gravity of the metal at 11*86, and had a surface of 

 0"00902 square metre. It gave off, when heated in vacuo for one hour, 1-50 cub. centim. 

 of natural gas, containing no compound of carbon, but consisting of hydrogen and air. 



1. As it appeared from preliminary experiments that the occlusion of hydrogen by 

 palladium was likely to be a phenomenon exhibited at a comparatively low range of 

 temperature, the metal was heated in hydrogen no higher than 245° C, by an oil-bath, 

 and allowed to cool very slowly, so as to pass through still lower ranges of temperature 

 which might be favourable to the absorption of hydrogen. The metal, when afterwards 

 transferred to the distillatory glass tube, appeared to give out nothing to a vacuum at 

 17°8 C. and barom. 759 millims. But the moment the combustion-furnace was lighted 

 under the tube, gas come off" most freely. Of the first portion collected, ll-77cub. centims. 

 contained H'74 cub. centims. hydrogen. The gas ceased to be evolved in fifteen minutes, 

 when 69'92 cub. centims. were collected, of which the greater part came over in the 

 first ten minutes. Hence palladium has taken up a large volume of gas when the tem- 

 perature of the metal never exceeded 245° C. 



1 vol. palladium held 526 vols, hydi-ogen. 



2. In a similar experiment the temperature of absorption was still further lowered 

 with good effect. The palladium was exposed to hydrogen between 90° and 97° C. for 

 three hours, and then allowed to cool in the gas for one hour and a half Now placed 

 in a glass tube, exhausted, and heated by a gas-flame, the palladium gave off gas in a 



