Dialytic Separation of Gases by Colloid Septa. 415 



The same bag, left exhausted for eighteen hours, was found 

 afterwards to yield at once 41*6 cub. centims. of air, containing 

 40*3 per cent, of oxygen, which had accumulated in the cavity of 

 the bag; therm, about 20° C. 



From a larger bag of similar thin sheet rubber, having a sur- 

 face of 640. square inches, distended by teD or twelve ounces of 

 sawdust, 21*35 cub. centims. of dialyzed air were obtained in one 

 hour; barom. 761 millims., therm. 19°*5 C. This dialyzed air 

 appeared to consist of 



Oxygen 41*80 



Carbonic acid . . . 0*94 

 Nitrogen 57*26 



100*00 



It does not appear, then, that the increased thickness of the 

 rubber septum tends to increase the proportion of oxygen in the 

 dialyzed air, while this thickness causes the passage to be pro- 

 portionally slower. The oxygen appears to attain, but never to 

 exceed, at 20° C, the proportion of 41*6 to 58*4 nitrogen. 



The thick rubber brings notably into view the carbonic acid of 

 the air. The small proportion of this gas in air is probably in- 

 creased in all experiments with the rubber septum, however thin. 

 It was observed to rise so high in a small crowded room, as to 

 negative the inflaming action of the oxygen on smouldering 

 wood. But rubber appears to have a power to charge itself gra- 

 dually from atmospheric air with about half per cent, of its vo- 

 lume of carbonic acid. This carbonic acid, accumulated in thick 

 sheet rubber, appears again to be carried on by the other gases 

 imbibed in a dialytic experiment. 



4. Thin Balloons of india-rubber. 



These little balloons were made available for the dialytic pas- 

 sage of air into a vacuum by filling them with sifted sawdust 

 through a funnel, an operation which requires some address. 

 The balloon collapsed upon the sawdust, which formed an inte- 

 rior ball, the sides of rubber still retaining a thickness of about 

 one-fiftieth of a millimetre. The rubber is not vulcanized. Such 

 a ball, of which the original rubber weighed 0*76 grm., still re- 

 mained 95 millims. in diameter after the air was exhausted. It 

 was found, when exhausted, to admit 19*6 cub. centims. of dia- 

 lyzed air in forty-one minutes (barom. 579 millims., and therm. 

 19° C.) . The same air possessed 41*32 per cent, of oxygen. The 

 ball had a surface of 0*0283 square metre, and it dialyzed 0*48 

 cub. centim. of air in one minute. For a square metre of surface 

 this is a passage of 16'9 cub. centims. per minute. The passage 

 therefore is about fifty times as fast as through a sheet of rubber 



