184 Professor Sir James Deivar [Jan. 20, 



As the relation between volume and temperature is nearly lineal 

 at the lowest portions of either the hydrogen or helium absorption, 

 we may infer that at the temperature of from 5° to 6 ° helium would 

 be as freely absorbed by charcoal as hydrogen is at its boiling 

 point, and that in all probability the boiling point of helium is not 

 below 5° abs. This inference is quite legitimate, because good 

 charcoal at the respective boiling points of liquid hydrogen, nitrogen 

 or oxygen, absorbs at atmospheric pressure nearly the same volume 

 of each gas, viz., 260 c.c. per gramme. 



It is to be noted that the rate of increase of the helium absorp- 

 tion is three times that of the hydrogen, so tliat a degree or two 

 makes a large increase in the volume condensed. From these results 

 it seems highly probable that the boiling point of helium is about a 

 fourth that of hydrogen, just as the latter is about one-fourth that 

 of nitrogen. 



In column IV. we get the heat evolved by each gas. These 

 values provide us with still further striking results, for the heat 

 developed is, generally, greatly in excess of that required for lique- 

 faction. Thus, for hydrogen, whose latent heat at the boihng point 

 I have recently determined by this calorimeter and found to be 120 

 gramme calories, the liquefaction of 185 c.c. of this gas would only 

 evolve about 1|- calories, or ^th of that evolved by occlusion in 

 charcoal at the boiling point of air. Similarly, if we take 51 gramme 

 calories as the latent heat of oxygen, the liquefaction of 230 c.c. of 

 this gas would produce some 17 calories, or about half of that evolved 

 during occlusion. 



Separation of Highly Concentrated Oxygen from Air ly Charcoal 

 at Loiv Temperatures. 



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

 air during the absorption, a quantity of about 50 grammes of char- 

 coal was after heating and absorption 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 w^ere taken in. A 

 manometer attached to the vessel containing the charcoal showed, on 

 shutting off the air current, that during the early part of the satura- 

 tion the absorption was so effective as to give practically no measure- 

 able 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 OS 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. 



