436 MB. T. GRAHAM ON THE ABSOKPTION AND 



or affinity of silver for oxygen, which enables the pure metal to occlude that gas, be 

 enhanced by the presence of a mere trace of some positive metal like copper 1 



6. The same specimen of fritted silver was found to occlude, in successive experi- 

 ments, 



0"907 vol. Hydrogen. 



0-938 „ 



0'486 „ Carbonic acid. 



0-545 „ 



0'156 „ Carbonic oxide. 



Hydrogen and carbonic acid, as well as oxygen, appear to be taken up in larger pro- 

 portion by this silver than by the former specimen of the same metal. 



7- Of pure silver highly laminated, 500 leaves, weighing 12*5 grms., were exposed to 

 air at a red heat, and thereafter exhausted at the same temperature. The silver (1 vol.) 

 gave up 1'37 volume of oxygen, 0-20 volume of nitrogen, and 0-04 volume of carbonic 

 acid. 



It appears that silver has a relation to oxygen similar to that exhibited by platinum, 

 palladium, and iron to hydrogen. The power of silver and of litharge in a state of 

 fusion to absorb oxygen, and to allow that gas to escape on solidification, may be con- 

 nected with the observed capacity of the colloid metal, softened by heat, to absorb the 

 same gas, although to a less extent. 



Iron. 



The penetration of iron by hydrogen is demonstrated as clearly by MM. Deville and 

 Teoost as that of platinum. A thin tube of cast steel, 3 or 4 millims. in thickness, 

 already enclosing hydrogen gas in its cavity, was surrounded by air or by nitrogen gas 

 circulating in an annular space between the steel tube mentioned and a wider external 

 porcelain tube. In the absence of any visible pores in the steel, hydrogen made its 

 way through the substance of the metal, and escaped into the annular space as soon as the 

 system of tubes was exposed to a red heat. A nearly if not entirely complete vacuum 

 was formed within the iron tube*. In another modification of the experiment, car- 

 bonic oxide from an uncertain source appeared within the iron tube, particularly when 

 the temperature was most elevatedf. 



Wrought iron, in the form of thin wire (No. 23), about 0*4 millim. in diameter, first 

 carefully cleaned with caustic alkali and water, was heated alone in the porcelain tube 

 exhausted of air, for the purpose of eliminating any natural gases. 



1. Of the iron wire referred to, 46 grms., with a volume of 5*9 cub. centims., the 

 specific gravity of the metal being taken at 7 "8, were heated by the open combustion- 

 furnace. Gas came ofi" freely at a red heat, — 



(1) In fifteen minutes, 15*6 cub. centims., containing 3*5 cub. centims. carbonic acid, 

 or 22-4 per cent. 



* Comptes Rendus, t. Ivii. p. 965 (1863). t lb. t lix. p. 102 (1864). 



