1904.] occluded in Char coal at Low Temperatures. 125 



In all cases, it will be observed, the amount of gas occluded has been 

 greatly increased at the low temperature, and the degree of condensa- 

 tion is generally such as we should anticipate from the known physical 

 constants of the gases. The amount of heat evolved is so great as to 

 be in excess of that required for liquefaction in the case of gases like 

 hydrogen, nitrogen, and oxygen. The heat produced when successive 

 fractions of the volume of gas required for saturation are absorbed has 

 yet to be determined. In the time required for the absorption no 

 measurable amount of chemical combination was effected between 

 mixtures of hydrogen and oxygen or carbonic oxide and oxygen in the 

 pores of the charcoal. 



Such experiments must be extended to the use of platinised charcoal 

 and other catalytic agents. 



Perhaps the most striking result is the great difference in properties 

 exhibited by helium. While resembling the other gases in showing 

 increased absorption at the temperature of liquid air, the absolute 

 amount occluded per unit volume of charcoal is about one-tenth that 

 of the other gases at the same temperature. There can be little doubt 

 that when the relative absorption of helium in charcoal is measured 

 at the temperature of liquid hydrogen, the increased absorption will 

 be so marked as to make it comparable to that of hydrogen in the 

 present set of experiments. In this case charcoal at the boiling point 

 of hydrogen will become an efficient condensing agent for helium, and 

 this property will have important applications in future research. 



Separation of Highly Concentrated Oxygen from Air. 



In order to examine the changes taking place in a mixed gas like air 

 during the absorption, a quantity of about 50 grammes of charcoal was 

 after heating and exhaustion saturated at - 185 in a current of pure 

 dry air ; got by passing the air current through a U-tube immersed in 

 liquid air. 



For a time the air rushed into the charcoal with great rapidity, and 

 in about 10 minutes between 5 and 6 litres were taken in. A mano- 

 meter attached to the vessel containing the charcoal showed, on shutting 

 off the air current, that during the early part of the saturation the 

 absorption was so effective as to give practically no measurable 

 mercury pressure. As soon as the absorption was ended, and a current 

 began to pass slowly over the charcoal, the composition of the air 

 leaving the charcoal showed 98 per cent, nitrogen. After the current 

 of air had passed for half an hour, the total gas occluded in the 

 charcoal was expelled by taking the vessel in which it had been treated 

 out of the liquid air, and allowing the temperature to rise to 15 C. 



The gas, which was rapidly expelled, measured 5 '7 litres, and 

 contained 56 per cent, of oxygen. If the saturated charcoal before 



