458 Mr. Graham's Recent Discoveries. 



Heated in air they absorbed 0.2 times their volume of gas, 

 which was principally nitrogen, showing a remarkable indif- 

 ference to oxygen. Silver was also examined, one specimen 

 occluded in successive experiments 8.05 and 7.47 times its 

 volume of oxygen, without any visible tarnish. 



It was with iron that results of the greatest commercial, as 

 well as scientific interest, were obtained. Iron possesses the 

 power to occlude hydrogen, but carbonic oxide is taken up far 

 more largely than hydrogen, by slowly cooling the metal, from 

 a dull red heat. In the process of converting iron into steel 

 by cementation, the bars of malleable iron are imbedded in 

 charcoal, and heated to redness in chests of fire-brick. The 

 cause of the penetration of- carbon into the centre of the mass 

 of iron has always been obscure. 



As Mr. Graham observes, the occlusion of carbonic oxide 

 by the metal at a low red heat appears to be the first and 

 necessary step in the process of " adoration." The gas 

 appears to abandon half its carbon to the iron, when the 

 temperature is afterwards raised to a considerably higher 

 degree. The process of cementation being thus divided into 

 two distinct stages, the first at a low temperature, during 

 which the carbonic oxide is occluded, the second at a higher 

 temperature, in which carbon is separated. 



Lastly, in all these experiments, the metal was first 

 heated in vacuo, in order to remove any gases that might have 

 been occluded in the process of its manufacture. 



The natural gases of commercial wrought iron appear to 

 be a mixture of hydrogen and carbonic oxide. It became, 

 therefore, a point of great interest to examine the natural 

 gases of meteoric iron. A notice of the facts having ap- 

 peared in a late number, it is only necessary to state that the 

 iron of the Lenarto meteorite gave out on heating in vacuo 2.8 

 times its volume of gas; of which eighty-five per cent, was 

 hydrogen. Thus a fall of meteoric iron on the earth brings to us 

 the same gas that has been discovered by Messrs. Huggins 

 and Miller to exist in the atmosphere of many of the fixed stars. 



