422 



Mr. T. Graham on the Occlusion of 



[June 11, 



Sulphurous anhydride 32*0 



Chlorine , 35*5 



Mercury lOO'O 



It is obvious that the above results have a very direct bearing upon the 

 views now generally held regarding the constitution of the sun, stars, and 

 nebulae ; but I refrain from making any such application of them until I 

 have the honour of laying before the Royal Society a complete account of 

 these experiments. 



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

 Graham, F.R.S., Master of the Mint. Received May 22, 1868. 



In my experiments, already published, on the occlusion of hydrogen by 

 the metals palladium, platinum, and iron, the absorption of the gas was 

 observed to be of uncertain occurrence at low temperatures, but was 

 ensured by heating the metal, whether in the form of sponge or aggre- 

 gated 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 combus- 

 tion of the gaseous mixture of oxygen and hydrogen, as observed by Fara- 

 day. A new method of charging the metals with hydrogen at low tem- 

 peratures 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 ex- 

 pected from the crystalline structure of zinc. But a thin plate of palla- 

 dium 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 12° amounted to 173 times its volume. 



The absorption of hydrogen was still more obvious when the palladium 

 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 negative 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 exceed 90 volumes. 



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

 dium and no doubt pervades the whole mass of the metal in such circum- 

 stances, 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 pal- 

 ladium, charged with hydrogen in the manner described, was washed, 

 dried by a cloth, and then sealed up in an exhausted glass tube. On 



