Chemistry and Physics. 225 



water produced. 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 . 0-72 " 



On heating in an atmosphere of oxygen, palladium black goes 

 on absorbing oxygen at least up to a read heat, with the forma- 

 tion of a brownish-black substance, which does not again lose its 

 oxygen at a dull red heat in vacuo. The amount of oxygen 

 absorbed (nearly 1000 volumes) was about one and a half times 

 as much as corresponds with the formula Pd 2 0, and if the igni- 

 tion had been sufficiently 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 

 originally contained in the black, which is in good agreement 

 with the direct gravimetric estimation. 



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

 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 

 probably oxidized and then again reduced at a still higher tem- 

 perature, it was introduced once more into the experimental tube. 

 It immediately occluded a considerable quantity of hydrogen, and 

 by maintaining 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 to have taken up 846 volumes, i. e. approxi- 

 mately 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°. 



Am. Jour. Sci. — Fourth Series, Yol. Y, No. 27. — March, 1898. 



15 



