Mr. T. Graham on the Occlusion of Hydrogen Gas by Metals. 03 



ever, does not resemble the other spectrum of nitrogen, which Pliicker 

 distinguishes as the spectrum of the first order*. 



June 11. — Lieut. -General Sabine, President, in the Chair. 



The following communication was read : — 



" On the Occlusion of Hydrogen Gas by Metals." By Thomas 

 Graham, F.R.S., Master of the Mint. 



In my experiments, already published, on the occlusion of hy- 

 drogen by the metals palladium, platinum, and iron, the absorption 

 of the gas was observed to be of uncertain occurrence at low tempe- 

 ratures, but was ensured by heating the metal, whether in the form 

 of sponge or aggregated by hammering, and allowing it to cool 

 slowly and completely in a hydrogen atmosphere. This fact was 

 referred to the condition of absolute purity of the metallic surface 

 being essential to the first absorbing action, as it is to the action of 

 platinum-foil or wire in determining the combustion of the gaseous 

 mixture of oxygen and hydrogen, as observed by Faraday. A new 

 method of charging the metals with hydrogen at low temperatures 

 has lately presented itself, which is not without interest. 



When a plate of zinc is placed in dilute sulphuric acid, hydrogen 

 is freely evolved from the surface of the metal, but no hydrogen is 

 occluded and retained at the same time. A negative result was 

 indeed to be expected from the crystalline structure of zinc. But 

 a thin plate of palladium immersed in the same acid, and brought 

 into metallic contact with the zinc, soon becomes largely charged 

 with the hydrogen, which is then transferred to its surface. The 

 charge taken up in an hour by a palladium plate, rather thick, at 1 2° 

 amounted to 1 73 times its volume. 



The absorption of hydrogen was still more obvious when the pal- 

 ladium plate was constituted the negative electrode in acidulated water 

 to a Bunsen battery of six cells. The evolution of oxygen gas at 

 the positive electrode continuing copious, the effervescence at the ne- 

 gative electrode was entirely suspended for the first twenty seconds, 

 in consequence of the hydrogen being occluded by the palladium. 

 The final absorption amounted to 200 "4 volumes, and was greater in 

 amount than the volume of hydrogen occluded by the same plate 

 heated and cooled in an atmosphere of the gas, which did not ex- 

 ceed 90 volumes. 



It is worthy of remark that, although the hydrogen enters the 

 palladium and no doubt pervades the whole mass of the metal in 

 such, circumstances, the gas exhibits no disposition to leave the metal 

 and escape into a vacuum, at the temperature of its absorption. 

 Thus a thin plate of palladium, charged with hydrogen in the man- 

 ner described, was washed, dried by a cloth, and then sealed up 

 in an exhausted glass tube. On breaking the tube under mercury 

 after two months, the vacuum was found perfect. No hydrogen had 

 vaporized in the cold (about 12°) ; but on the application afterwards 

 of a heat of 100° and upwards, 333 volumes of gas were evolved from 

 the metal. 



* Philosophical Transactions, 1865, p. 9. 



