438 MB. T. GRAHAM ON THE ABSORPTION AND 



2*3 cub. centims. Hydrogen. 



0*2 „ „ Carbonic oxide, &c. 



2i 



The iron appears therefore to be capable of holding 0*46 volume of hydrogen. The 

 wire became white, like galvanized iron. This was confirmed in a second observation, 

 a thicker wire holding 0*42 vol. hydrogen. 



5. The same specimen of iron was now charged with carbonic oxide gas, in the manner 

 it had previously been charged with hydrogen. It was also freely exposed to air. The 

 iron wire remained soft, was not capable of becoming hard when heated red-hot and 

 suddenly cooled, and was not altered in aspect or in solubility in acids. The gas extri- 

 cated by the air-exhauster amounted to 



9"45 cub. centims. in 13 minutes. 



Of this gas 20-76 cub. centims. proved to be carbonic oxide. Pure iron, then, is capable 

 of taking np at a low red heat, and holding when cold, 4-15 volumes of carbonic oxide gas. 

 This fact was confirmed in various other experiments. It explains partly, if not 

 entirely, the abundance of carbonic oxide observed among the natural gases of iron in 

 experiinents 1, 2, and 3. In the course of its preparation wrought iron may be supposed 

 to occlude six or eight times its volume of carbonic oxide gas, which is carried about 

 ever after. How the qualities of iron are affected by the presence of such a substance, 

 no way metallic in its characters, locked up in so strange a way, but capable of reappear- 

 ing, under the influence of heat, at any time, with the elastic tension of a gas, is a subject 

 which metallurgists may find worthy of investigation. 



The relations of the metal iron to carbonic oxide gas appear to be altogether peculiar. 

 They cannot fail to have a bearing upon the important process of acieration. The inter- 

 vention of carbonic oxide in the usual process of tlie cementation of iron ^vith charcoal, 

 long recognized by accurate observers, may be said now to be placed beyond all doubt 

 by the recent beautiful research of M. Margueritte *. Hitherto the decomposing 

 action of the iron upon carbonic oxide has been supposed to be exercised only at the 

 external surface of the metal. A surface-particle of the iron has been supposed to 

 assume one half of the carbon belonging to an equivalent of carbonic oxide (C2 Oj), while 

 the remaining elements diffused away into the air as carbonic acid (C Og), to reacquire 

 carbon from the charcoal placed near, and to become capable of repeating the original 

 action. It is now seen that such a process need not be confined to the surface of the 

 iron bar, but may occur throughout the substance of the metal, in consequence of the 

 prior penetration of the metal by carbonic oxide. The direct contact and action of 



* Anaales de Chimie, &c., 4 ser, t. vi., 1865. 



