516 Mr. T. Graham on the Absorption and 



The volume of 8*3 grms. of platinum is 0-385 cub. centim. 

 Hence one volume of platinum-foil 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 a red heat, 

 the platinum now gave off 05 cub. centim. of gas in thirty-five 

 minutes, of which about 0*3 cub. centim. were hydrogen. One 

 volume of platinum-foil had taken up 



076 vol. hydrogen at 1Q0°. 



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 mea- 

 sured 0*133 cub. centim. (taking the specific gravity of the metal 

 at 11*86), and had a surface of 000902 square metre. It gave 

 off, when heated in vacuo for one hour, 1*50 cub. centim. of na- 

 tural gas, containing no compound of carbon, but consisting of 

 hydrogen and air. 



1 . As it appeared from preliminary experiments that the oc- 

 clusion 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 absorp- 

 tion of hydrogen. The metal, when afterwards transferred to 

 the distillatory glass tube, appeared to give out nothing to a va- 

 cuum at 17°*8 C. and barom. 759 millims. But the moment 

 the combustion-furnace was lighted under the tube, gas came off 

 most freely. Of the first portion collected, 11*77 cub. centims. 

 contained 11*74 cub. centims. hydrogen. The gas ceased to be 

 evolved in fifteen minutes, when 69*92 cub. centims. were col- 

 lected, of which the greater part came over in the first ten mi- 

 nutes. Hence palladium had taken up a large volume of gas 

 when the temperature of the metal never exceeded 245° C. 



1 vol. palladium held 526 vols, hydrogen. 



2. In a similar experiment the temperature of absorption was 

 still further lowered with good effect. The palladium was ex- 



