On the Occlusion of Hydrogen and Oxygen by Palladium. 291 



inasmuch as the oxygen cannot be removed in vacuo at a dull red 

 heat, and consequently had to be determined in the ignited sub- 

 stance by passing hydrogen over it and weighing the water pro- 

 duced. Palladium black dried at 100° contains 0"72 per cent, of 

 water, and hence, on the assumption that the oxygen exists as PdO, 

 we have for the analysis of palladium black — 



Pd 86-59 per cent. 



PdO 12-69 „ = 1-65 per cent. 2 



H 2 072 „ 



On heating in an atmosphere of oxygen, palladium black goes on 

 absorbing oxygen at least up to a red heat, with the formation of a 

 brownish-black substance, which does not again lose its oxygen at a 

 dull red heat in vac?io. The amount of oxygen absorbed (nearly 

 1000 volumes) was about one and a half times as much as corre- 

 sponds with the formula Pd 2 0, and if the ignition had been suffi- 

 ciently prolonged, the whole of the palladium would probably have 

 been converted into the oxide PdO. 



Palladium black, when exposed to hydrogen gas, absorbed over 

 1100 volumes, but of this only 873 volumes were really occluded, the 

 remainder having formed water with 139 volumes of oxygen origin- 

 ally contained in the black, which is in good agreement with the 

 direct gravimetric estimation. 



Of the hydrogen occluded, about 92 per cent, was pumped ofE 

 slowly at the ordinary temperature, and almost the whole of the 

 remainder at 444°. Increase of pressure of the hydrogen from one 

 atmosphere up to 4'6 atmospheres had no influence on the quantity 

 occluded at the ordinary temperature. 



The pure palladium sponge remaining in the experimental tube 

 after the above experiment was over occluded 852 volumes of 

 hydrogen, and about 98 per cent, of this was extracted in vacuo at 

 the ordinary temperature. 



New palladium foil behaved in a very peculiar fashion. At first 

 it scarcely occluded any hydrogen even after ignition in the gas and 

 subsequently cooling down. It was therefore charged and discharged 

 several times electrolytically with hydrogen, but still it persistently 

 refused to occlude any appreciable quantity when replaced in an 

 atmosphere of hydrogen. 



After powerful ignition in the blowpipe flame, when it was proba- 

 bly oxidised and then again reduced at a still higher temperature, it 

 was introduced once more into the experimental tube. It imme- 

 diately occluded a considerable quantity of hydrogen, and by main- 

 taining the temperature between 100° and 130°, a large additional 

 quantity was slowly absorbed. On cooling down to the ordinary 

 temperature, hydrogen was again occluded, and it was finally found 



