548 Professor Sir James Dewar [Jan. 22, 



obtained with liquid air, some 9 degrees higher. The approximation 

 of Xo. 2 to No. 3 as the higher concentrations are reached is due to 

 the rapidly increasing tension of neon and hydrogen in charcoal 

 containing relatiyely large amounts of occluded nitrogen and 

 oxygen. The disturbance in the equilibrium of the condensed con- 

 stituents under these conditions is beginning to be appreciable. To 

 illustrate the problems resulting from such a condition the following 

 experiment is instructiye : Two similar U-shaped bulbs charged with 

 10 grms. of charcoal and proyided with inlet and outlet stopcocks are 

 cooled in liquid air and opened to the atmosphere of the room. One 

 is simply allowed to saturate itself from the air, while the second has 

 a slow current of dry air passed through it for some time after 

 saturation. This haying been done, both bulbs are warmed up by 

 immersion in tepid water, and the gases so expelled are roughly 

 tested by inserting a glowing splint of cedar-wood ; the gas issuing 

 from the first bulb at once extinguishes the sphnt, whereas that 

 coming from the second excites a brilliant combustion. Nitrogen 

 is giyen off from the bulb which has been saturated by atmospheric 

 air ; whereas oxygen principally results after the air current to which 

 the second charcoal was subjected. In the latter case the less volatile 

 and more condensable oxygen has accumulated in the charcoal to a 

 greater extent to that of nitrogen. The slow current of dry air has 

 proyided the opportunity for the equilibrium of the two gases 

 occluded in the charcoal to be established ; but when air rushes in at 

 atmospheric pressure, filling the pores of the charcoal in a small limited 

 ^pace, the proportions of each gas present in the charcoal must haye 

 substantially the composition of the ordinary air. Thus, on warming 

 up each of these samples of charcoal which haye been treated as aboye 

 described, it is to be anticipated that the one sample of charcoal would 

 giye gas containing excessiye nitrogen and the other excessive oxygen. 

 The alteration of the proportions of helium, neon and hydrogen 

 in air when it has been equilibriated in charcoal at liquid air 

 temperature is given in the following table : — 



Gas occluded in charcoal after air current at\! 



85-Abs / 



Above repeated with compressed air from steeli 



bottles f , 



1-64 6-1 



1-53 9-8 



