296 



J. Dewar — Thermal Evolution of Gases. 



the vapor even at atmospheric pressure could be made into a 

 fairly high vacuum showing very wide strise. When the char- 

 coal was heated the bromine vapor was again expelled, and on 

 allowing it to cool, all stages in the appearance of the electric 

 discharge as the vacuum is reached could be conveniently 

 observed without the use of any form of air-pump. 



When in the course of low temperature investigations the 

 perfection of the vacuum vessels for the storage and manipula- 

 tion of liquid air and hydrogen came to be important, the 

 effect of charcoal on heat isolation in such utensils was fully 



investigated and confirmed in a paper entitled " Liquid Air as 

 an Analytic Agent."* Still no systematic experiments on the 

 absorptive power of charcoal at low temperatures were made 

 either at this time or subsequently. 



It is the object of the present preliminary paper to contrib- 

 ute some definite quantitative data regarding gas absorption 

 and thermal evolution in charcoal at the temperature of liquid 

 air. The mode in which liquid gases like oxygen or air could 

 be used as calori metric agents was described in my paper on 

 the " Scientific Uses of Liquid Air."f 



*Proc. Boy. Inst., 1898. 



