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XVIII. On the Absorption and Dialytic Separation of Gases hy Colloid Septa. 

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



Received June 20,— K«ad June 21, 1866. 



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 destitute 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 ; 

 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 discovered a power in gases to 

 penetrate india-rubber in a thin sheet, or in the form of the little transparent balloons 

 which Dr. Mitchell was the first to prepare from that substance. He remarked in 

 particular that such balloons collapse sooner when inflated with hydrogen than with 

 atmospheric air, and still sooner when filled with carbonic acid ; and he connected the 

 latter fact with the observation that a solid piece of india-rubber is capable of absorbing 

 its own volume of carbonic acid when left long enough in the pure gas. By means of a 

 proper arrangement. Dr. Mitchell found that various gases passed spontaneously 

 through the caoutchouc membrane, when there was air on the other side, with different 

 degrees of velocity. "Ammonia transmitted in 1 minute as much as sulphuretted 

 hydrogen in 2\ minutes, cyanogen in Z\ minutes, carbonic acid in 5^ minutes, nitrous 

 oxide in 6^ minutes, arsenietted hydrogen in 27^ minutes, olefiant gas in 28 minutes, 

 hydrogen in 37^ minutes, oxygen in 1 hour and 53 minutes, carbonic oxide in 2 hours 



MDCCCLXVI. 3 K 



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