Mr. T. Graham on the Occlusion of Hydrogen Gas by Metals. G5 



While hydrogen was absorhed 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 without being con- 

 densed. A platinum plate which had acted for several hours as a 

 positive electrode, gave afterwards, when submitted to heat with ex- 

 haustion, a small trace of carbonic acid but no oxygen. 



The familiar igniting-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. I beg to offer the following representation of this phe- 

 nomenon, 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 would fol- 

 low that it is the attraction of platinum for the negative or " chlo- 

 rylous" atom of the hydrogen molecule which attaches the latter to 

 the metal. The tendency, imperfectly satisfied, is to the formation 

 of a hydride of platinum. The hydrogen molecule is accordingly 

 polarized, oriente, with its positive or " basylous" side turned out- 

 wards, 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 replace- 

 ment of such hydrogen atoms as are withdrawn, on combining with 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 would 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 

 consequence of a similar polarization of the hydrogen of those sub- 

 stances, or of some other oxidable constituent. 



As has already been remarked, it does not follow 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 experiments, 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 deprived of 

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

 into a vacuum very slowly compared with hydrogen, although the 

 volume of carbonic oxide which the metal is capable of absorbing is 

 very sensible, amounting to 4 volumes, and more considerable than 

 the volume of hydrogen which the same metal can occlude. Car- 



Phil. Mag. S. 4. Vol. 3G. No. 240. July 1868. F 



