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



but a wide unglazed tube, about 431 millims. (17 inches) long 

 and 19 millims, (0*75 inch) in internal diameter. It was required 

 to place so wide a tube in a vertical position, and to admit the 

 air by the upper and draw it off by the lower extremity of the 

 tube. The proportion of oxygen in the half-litre of air collected 

 was as follows : — 





Oxygen per cent. 



Experiment 1. 



Experiment 2. 



Mean. 



When collected in 1 minute ...... 



When collected in 13 minutes ... 

 When collected in 75 minutes ... 

 When collected in 120 minutes ... 

 When collected in 304 minutes ... 



2100 

 22-33 

 2277 

 23-25 

 23-54 



22-25 

 2302 

 23-22 

 23-51 



22-29 

 22-89 

 23-23 

 23-53 



The proportion of oxygen in the air circulated appears thus to 

 increase with the slowness of its passage through the tube atmo- 

 lyser. The proportion of air drawn into the air-pump vacuum 

 must be very large when the time is protracted ; but the addi- 

 tional concentration of oxygen appears small. 



The preceding observations being made by means of a porous 

 tube which may be considered wide and of considerable capacity 

 with reference to its internal surface, the experiment was varied 

 by substituting a porous tube about eight times as long, very 

 narrow, and therefore of small internal capacity. This second 

 atmolyser was composed of twelve ordinary tobacco-pipe stems, 

 each about 10 inches in length and of 1*9 millim. internal dia- 

 meter, connected together by vulcanized caoutchouc adapters so 

 as to form a single tube. Having flexible joints, the tube was 

 folded up and placed within a glass cylinder that could be ex- 

 hausted. Air was then circulated through this atmolyser by the 

 pressure of several inches of water. The instrument appeared 

 to work with most advantage when the air delivered at the exit- 

 tube amounted to about one-fourth of a litre per hour. A 

 volume of 268 cubic centimetres, which had circulated in one 

 hour, was found to contain 24*37 per cent, of oxygen. The 

 current was then made slower, so that only 108 cub. centims. of 

 gas passed and were collected in one hour, but with little further 

 concentration of the oxygen. The result, however, is interesting 

 as being the highest concentration of oxygen yet obtained by an 

 instrument of this kind. The air collected was composed of 



Oxygen 

 Nitrogen 



24-52 

 75-48 



10000 



