ACTION OF SPONGY PLATINUM. 185 



creasing with its temperature, combination proceeds at an 

 accelerated rate, till the platinum becoming red hot, may cause 

 the combination to extend to a distance from it, by kindling 

 the gaseous mixture. Platinum acts in this manner with 

 greatest energy when in a highly divided state, as in the form 

 of spongy platinum, owing to the greater surface exposed and 

 the rapidity with which it is heated. The metal itself contri- 

 butes no element to the water formed, and is in no respect 

 altered. It is an action of the metallic surface, which must be 

 perfectly clean, and is retarded or altogether prevented by the 

 presence of oily vapours and many other combustible gases, 

 which soil the metallic surface. Mr. Faraday is disposed to 

 refer the action to an adhesive attraction of the gases for the 

 metal, under the influence of which they are condensed and 

 their particles approximated within the sphere of their mutual 

 attraction, so as to combine. This opinion is favoured by the 

 circumstance that the property is not peculiar to platinum, 

 but appears also in other metals, in charcoal, pounded glass, 

 and all other solid bodies ; although all of them, except the 

 metals, act only when their temperature is above the boiling 

 point of mercury. But on the other hand, at low tempera- 

 tures^ the property appears to be confined to a few metals only 

 which resemble platinum in their chemical characters, namely 

 in having little or no disposition to combine with oxygen gas, 

 and in not undergoing oxidation in the air. The action of 

 platinum may, therefore, be connected with its chemical pro- 

 perties, although in a way which is quite unknown to us. The 

 same metal disposes carbonic oxide gas to combine with oxygen, 

 but much more slowly than hydrogen; and it is remarkable 

 that if the most minute quantity of carbonic oxide be mixed 

 with hydrogen, the oxidation of the latter under the influence 

 of the platinum is arrested, and not resumed till after the car- 

 bonic oxide has been slowly oxidated and consumed, which 

 thus takes the precedence of the hydrogen in combining with 

 oxygen. This extraordinary interference of a minute quantity 

 of carbonic oxide gas, which cannot from its nature be supposed 

 to soil the surface of the platinum like a liquefiable vapour, 

 seems to point to a chemical, perhaps to an electrical explana- 

 tion of the action of the platinum, rather than to the adhesive 

 attraction of the metal. The oxidation of alcohol at the tem- 

 perature of the air, and also at a low red heat^ is promoted in 

 the same manner by contact with platinum. 



