212 PROFESSOR THOMAS GRAHAm's SCIENTIFIC WORK. 



short of reduess. Coiucideutly, at temperatures even below those 

 requisite for trausmission, palladium was found capable of absorbing 

 many hundred times its volume of hydrogen. Thus apiece of palladium- 

 foil maintained at a temperature of 90O-97° for three hours, and then 

 allowed to cool down during an hour and a half, while surrounded by a 

 continuous current of hydrogen gas, gave off, on being afterward heated 

 w vacuo, 04:3 times its volume of the gas, measured cold ; and even at 

 ordinai-y temperatures, it absorbed 370 times its volume of the gas, pro- 

 vided it had first been recently ignited in vacuo. In another experi- 

 ment, palladium sponge, heated to 200° in a current of hydrogen and 

 allowed to cool slowly therein, afterward yielded 080 times its volume 

 of the gas ; while a piece of electrolytically deposited palladium heated 

 only to 100c> in hydrogen, afterward yielded, upon ignition in vacuo, no 

 less than 082 times its volume of the gas. The lowness of the tempera- 

 ture at which, under favorable circumstances, the absorption of hydro- 

 gen by palladium could thus be effected, soon suggested other means of 

 bringing about the result. For example, a piece of palladium-foil was 

 placed in contact with a quantity of zinc undergoing solution in dilute 

 sulphuric acid; and, on subsequent examination, was found to have 

 absorbed 173 times its volume of hydrogen. Again, palladium, in the 

 forms of wire and foil, was made to act as the negative pole of a Bun- 

 sen's battery effecting the electrolysis of acidulated water ; and in this 

 ; manner was found to absorb from 800 to 950 times its volume of hydr»- 

 geu in different experiments. 



Palladium being thus chargeable with hydrogen in three different 

 ways — namely, by being heated and cooled in an atmosphere of the gas ; 

 by being placed in contact with zinc dissolving in acid, i. e., with hydro- 

 gen in the act of evolution ; and, lastly, by being made the negative 

 electrode of a battery — correlativelj', the charged metal could be freed 

 from its occluded hydrogen by exposing it to an increase of temperature 

 in air or vacuo ; by acting on it with different feebly oxidizing mixtures; 

 and by making it the positive electrode of a battery. 



The palladium, when charged to its maximum, was frequently found 

 to give off a small proportion of its hydrogen, though with extreme 

 slowness, at ordinarj- temperatures, both into the atmosjdiere and into 

 a vacuum. But not until the temperature approached 100° was there 

 any appreciable gas-evolution ; which, above that point, took place with 

 a facility increasing with the temperature, so as to be both rapid and 

 complete at about 300°. Since, however, the transmission of hydrogen 

 through heated palladium is a phenomenon of simultaneous absorption 

 and evolution, it follows that the property of palladium to absorb hydro- 

 gen does not cease at 300", or indeed at close upon the melting-point of 

 gold — the highest temperature at Mhich Mr. Graham's experiments on 

 transmission were conducted ; but whereas the maximum absorption of 

 hydrogen by i)alladium takes place at comparatively low temperatures, 

 the velocity of transmission was observed to increase, in a rapid ratio, 

 with the increase of temperature, indefinitely. 



