112 DRS. L. MOND, W. RAMSAY, AND J, SHIELDS, ON THE 



red heat in vacuo corresponds to the presence of 1877 cub. centinis., or 139*1 volumes, 

 of oxygen in the palladium black. Since this volumetric estimation of the amount of 

 absorbed oxygen is in good agreement with the direct gravimetric determination, viz., 

 138 volumes, we are justified in concluding that 115'22 cub. centims., or 853*6 volumes, 

 is the quantity of hydrogen really occluded. 



It will be observed that practically the whole of the occluded hydrogen was extracted 

 at 444, and that about 92 per cent, of it can be pumped off at the ordinary tempera- 

 ture. The last traces of the hydrogen given off at the ordinary temperature come off 

 very slowly, so that the pumping requires to be continued for a day, or longer. 



It was noticed that the palladium black contracts and passes into sponge above 

 184 C. 



This result, viz., that palladium black occludes about 854* volumes of hydrogen, 

 was confirmed by additional experiments (v. Table, p, 125), in which 860*, 868*, aud 

 868* volumes were occluded. 



b. Palladium Sponge. The pure palladium sponge remaining behind in the experi- 

 mental tube after the preceding experiment was completed was charged with hydrogen. 

 112*4 cub. centims. = 833""" volumes were occluded. Of this 111'5 cub. centims., or 

 826'1 volumes, representing about 99 per cent, of the whole, were pumped off at the 

 ordinary temperature, whilst on heating to redness 1*4 cub. centim., or 10*4 volumes, 

 were extracted. It would appear, therefore, from this experiment that more hydrogen 

 can be removed from palladium sponge than from palladium black at the ordinary 

 temperature. 



This does not agree with GRAHAM'S observation (' Researches,' p. 287) that "in 

 the pulverulent spongy state palladium took up 655 volumes of hydrogen, and so 

 charged, it gave off no gas in vacuo at the ordinary temperature, nor till its tempera- 

 ture was raised to nearly 100." 



c. Palladium Foil. The palladium foil employed weighed 1'333 gram, and was 

 about 0*025 millim. thick. It had been prepared by rolling out sponge, and was said 

 to contain over 99 per cent, of palladium. 



Before being introduced into the experimental tube it was boiled in caustic potash 

 solution, washed, and dried between filter paper. 



On ignition in vacuo a small quantity of gas, which was not examined, was given 

 oft. After cooling down to the ordinary temperature again, hydrogen was admitted, 

 but apparently none was occluded. The palladium was therefore ignited in the 

 hydrogen and allowed to cool down slowly. Next day it was found that only 

 29 volumes had been occluded. Practically none of this could be extracted in vacuo 

 at the ordinary temperature, but on ignition 28 volumes were pumped out. 



The result of this experiment, therefore, goes to show that the occlusion of hydrogen 

 by new compact palladium foil is thus either (l) very small,, or (2) very slow. 



* A slight correction must be applied to these numbers, the nature of which is explained on p. 120, 

 and the corrected values will be found in the Table on p. 121. 



