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DIALTTIC SEPAEATION OF GASES BY COLLOID SEPTA. 439 



carbon (in the form either of diamond or charcoal) upon iron is allowed to produce cast 

 iron and not steel. It appears that the diffused action of carbonic oxide is the proper 

 means of distributing the carbon throughout the mass of iron. The blistering of the 

 bar appears to testify to the necessary production and evolution of carbonic acid, owing 

 to the decomposition of the carbonic oxide in the interior of the bar. 



The inquirj' suggests itself whether acieration would not be promoted by alternation 

 of temperature frequently repeated. The lowest red heat, or a temperature even lower, 

 appears to be most favourable to the absorption of carbonic oxide by iron, or for impreg- 

 nating the metal with that gas ; while a much higher temperature appears to be 

 required to enable the metal to decompose carbonic oxide, to appropriate the carbon, 

 and become steel. The action of a high temperature is made very clear by M. Mar- 

 GUEEITTE. The process of acieration, it seems then, should be divided into two distinct 

 stages, conducted at very different temperatures, — the first to introduce carbonic oxide 

 into the iron, and the second to decompose the carbonic oxide so introduced. The 

 carbonic oxide once safely occluded by the iron, the metal might even be cooled and 

 preserved in the air, the second heating being postponed for any length of time. Such 

 alternations of temperature are not unlikely to occur by accident during the usual long 

 process of cementation ; but they might be properly regulated with advantage, and the 

 process may admit of being abridged in point of time. 



Antimony, as a highly crystallizable metal, was exposed to hydrogen gas both above 

 and below the point of fusion of the metal, and afterwards submitted to exhaustion in 

 the usual manner. No hydrogen was extricated. 



MDCCCLXVI. 8 P 



