Dialytic Separation of Gases by Colloid Septa, 527 



given off amounted to 



5*56 cub. centims. in fifteen minutes. 



0-30 



5-86 

 Of this gas 5-56 cub. centims., or nearly the whole, proved to 

 be oxygen gas ; or the silver held occluded 0*545 volume of 

 oxygen. This silver had been purified from the chloride, and it 

 contained no trace of copper. 



When silver, of British standard (that is, containing 7'5 per 

 cent, of copper) , is exposed to air or oxygen at a low red heat, 

 the silver becomes almost black on the surface from oxidation of 

 the copper. Silver wire in this blackened state gave off several 

 volumes of oxygen under the action of heat and a vacuum. 

 Much of the superficial oxide disappeared at the same time. It 

 appeared as if the operation tended to the reduction of the super- 

 ficial oxide of copper, oxygen being liberated, and the copper 

 absorbed by the mass of silver. 



5. A specimen of silver reduced from the oxide, in the form 

 of sponge, which was considered pure, but was not analyzed, oc- 

 cluded 6-15, 8-05, and 7'47 volumes of oxygen, in successive ex- 

 periments, without any visible tarnish of the surface. Can the 

 attraction 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 ? 



6. The same specimen of fritted silver was found to occlude, 

 in successive experiments, 



0*907 vol. Hydrogen. 



0-938 „ 



0*486 „ Carbonic acid. 



0545 



>} 



)) 



0*156 „ Carbonic oxide. 



Hydrogen and carbonic acid, as well as oxygen, appear to be 

 taken up in larger proportion 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 vol- 

 ume 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 

 connected with the observed capacity of the colloid metal, soft- 

 ened by heat, to absorb the same gas, although to a less extent. 



