300 J. Dewar — Thermal Evolution of Gases. 



The mean composition of the 6 liters is again 56 per cent 

 oxygen. From the above experiments it follows that one of 

 the most rapid means of extracting a high percentage of oxygen 

 from atmospheric air is to absorb it in charcoal at low tempera- 

 tures, and then to expel it either rapidly or slowly by heating 

 the mass of charcoal to the ordinary temperature. 



A few experiments have been made using, instead of air, 

 special mixtures of oxygen and nitrogen. Thus it was found 

 that a gas containing 6*5 per cent of oxygen used in the same 

 manner as in the air occlusion experiments, gave, on heating up 

 the charcoal rapidly to 15° C, 5 liters of gas having the com- 

 position of 23 per cent, of oxygen. A repetition of the same 

 process with the 23 per cent of oxygen would have raised 

 the percentage about 60 per cent, or a stronger concentration 

 could have been reached by fractionating the gas as it slowly 

 leaves the charcoal on gradually increasing the temperature. 



This preliminary investigation suggests many fields for fur- 

 ture inquiry, and some of these I hope to deal with in future 

 papers. 



