424 



Mr. T. Graham on the Occlusion of 



[June 11, 



While hydrogen was absorbed freely by palladium and platinum as 

 negative plates, no oxygen whatever was absorbed by plates of the same 

 metals in the position of positive electrodes. Oxygen gas was disengaged 

 freely on the surface of the latter v/ithout being condensed. A platinum 

 plate which had acted for several hours as a positive electrode, gave after- 

 wards, when submitted to heat v/ith exhaustion, a small trace of carbonic 

 acid but no oxygen. 



The familiar igni ting-power of platinum sponge (or clean plate) upon a 

 jet of hydrogen in the air seems to depend solely upon the influence of the 

 metal upon its occluded hydrogen. The hydrogen appears to be polarized, 

 and to have its attraction for oxygen greatly heightened. T beg to offer 

 the following representation of this phenomenon, with an apology for the 

 purely speculative character of the explanation. The gaseous molecule of 

 hydrogen being assumed to be an association of two atoms, a hydride of 

 hydrogen, it v/ould follow that it is the attraction of platinum for the 

 negative or chlorylous" atom of the hydrogen molecule which attaches 

 the latter to the metal. The tendency, imperfectly satisfied, is to the for- 

 mation of a hydride of platinum. The hydrogen molecule is accordingly 

 polarized, one?i^4 'with its positive or "basylous" side turned outwards, 

 and having its affinity for oxygen greatly enlivened. It is true that the 

 two atoms of a molecule of hydrogen are considered to be inseparable ; but 

 this may not be inconsistent with the replacement of such hydrogen atoms 

 as are withdrawn, on combining with oxygen, by other hydrogen atoms 

 from the adjoining molecules. It is only necessary to suppose that a pair 

 of contiguous hydrogen molecules act together upon a single molecule of 

 the external oxygen. They v/ould form water, and still leave a pair of 

 atoms, or a single molecule of hydrogen, attached to the platinum. 



The oxidation of alcohol, ether, and similar hydrocarbons, through the 

 agency of platinum, likewise appears to be always an immediate conse- 

 quence of a similar polarization of the hydrogen of those substances, or of 

 some other oxidable constituent. 



As has already been rem.arked, it does not follov^ that, because a gas 

 is occluded by a metal, under the pressure of the atmosphere, at a low 

 temperature, the gas will also escape from the metal into a vacuum at 

 the same temperature, a much higher temperature being often required for 

 the expulsion of the gas than for its first absorption. This is particularly 

 true of carbonic oxide occluded by iron. Cast iron is much too porous for 

 such experinients, and allows carbonic oxide, equally with other gases, to 

 pass through abundantly by the agency of gaseous diffusion. Even with 

 malleable iron there is a difficulty in observing, owing to the long time 

 during which that metal continues to discharge carbonic oxide from its 

 own store of that gas. But a malleable iron tube, first thoroughly de- 

 prived of its natural gas, was found to allow carbonic oxide to pass through 



is no doubt penetrated through by hydrogen in the cold, but apparently from the 

 penetrating agency of the acid which is insiuuating itself into the metal at the same 

 time. — Comptes Ee^idus, 4 Mai 1868. 



