THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FOURTH SERIES.] 



DECEMBER 1866. 



LV. On the Absorption andDialytic Separation of Gases by Colloid 

 Septa. By Thomas Graham, F.R.S., Master of the Mint*. 



Part I. — Action of a Septum of Caoutchouc. 



MIXED gases must differ considerably in diffusibility and 

 specific gravity, in order to separate from one another to 

 any great extent in their molecular passage into a vacuum 

 through a porous septum, such as the plate of graphite or the 

 walls of an unglazed earthenware tube. The agency of atmolysis 

 is therefore very limited in parting the oxygen and nitrogen of 

 atmospheric air — gases which differ so little in density from 

 each other. 



Substances existing in the liquid condition often admit of 

 being separated much more fully than gases, by the proper use 

 of dialytic septa in addition to the agency of liquid diffusion. 



Evidently there cannot be anything like the dialysis of gases; 

 for dialysis involves the passage of a substance through a septum 

 composed of soft colloid matter, such as must be wholly desti- 

 tute of open channels, and therefore be impermeable to gas as 

 such. Still liquid dialysis may be imported into the treatment 

 of gases, in consequence of the general assumption of liquidity 

 by gases when absorbed by actual liquids or by soft colloids. 

 Water when charged with air holds liquid oxygen and nitrogen 

 in solution j and the latter substances then become amenable to 

 liquid diffusion and dialysis, and so penetrate animal membrane 

 in the act of respiration. 



A considerable time ago Dr. Mitchell of Philadelphia disco- 



* From the Philosophical Transactions for 186G, part 2. Communicated 

 by the Author. 



Phil. Mag. S. 4. Vol. 32. No, 218, Dec. 1866. 2 D 



