Mr. T. Graham on the Molecular Mobility of Gases. 429 



tube, should be coated with a 

 resinous varnish, to render them 

 impermeable to air. Now, a 

 good vacuum being obtained 

 within the outer tube, and sus- 

 tained by the action of an air- 

 pump, the mixed gas is made to 

 enter and traverse the clay tube. 

 More or less of gas is drained 

 off through the porous walls and 

 pumped away, while a portion 

 courses on and escapes by the 

 other extremity of the clay tube, 

 where it may be collected. The 

 stream of gas diminishes as it 

 proceeds, like a river flowing 

 over a pervious bed. The lighter 

 and more diffusive constituent 

 of the mixed gases is drawn 

 most largely into the vacuum, 

 leaving the denser constituent, 

 in a more concentrated condi- 

 tion, to escape by the exit end 

 of the clay tube. The more 

 slowly the mixed gas is moved 

 through that tube, the larger 

 the proportion of light gas that 

 is drained off into the vacuum, 

 and the more concentrated does 

 the heavy gas become. The 

 rate of flow of the mixed gas 

 can be commanded by either 

 discharging it from a gas-holder, 

 or drawing it into a gas-receiver, 

 in either case by a regulated 

 pressure. 



To observe the effect of a more 

 or less rapid passage through 

 the tube atmolyser, the impell- 

 ing pressure was varied so as to 

 allow a constant volume of half 

 a litre of atmospheric air to pass 

 through and be collected in dif- 

 ferent periods of time. The clay 

 tube used in these particular ex- 

 periments wasnot a tobacco-pipe, 



