1904] occluded in Charcoal at Low Temperatures. 123 



When the charcoal was heated the bromine vapour 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 manipulation 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 contribute 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 calorimetric 

 agents was described in my paper on the " Scientific Uses of Liquid 

 Air."f 



The apparatus was further improved into the form illustrated and 

 described in Madame Curie's Work, "Recherches sur les Substances 

 Radio Actives," 2nd edition, p. 100, as used for the determination 

 of the heat evolved by radium bromide either in liquid oxygen or 

 hydrogen. Such calorimeters are easily adapted to the simultaneous 

 observation of the volume of any gas absorbed by charcoal, and of 

 the concomitant heat evolution. 



For this purpose a small glass bulb C containing from 0*5 1 gramme 

 of charcoal has a long narrow tube C attached, so that it can be 

 immersed in the liquid oxygen or air in the calorimeter A B, while 

 still allowing a part of the tube to project above the cork A. In 

 order to dry and cool the 40 c.c. of gas, which represents the largest 

 volume taken in by the charcoal in my experiments, a little annular 

 space is arranged at D into which liquid air is poured immediately 

 before the experiment is made. 



The charcoal, after being placed in the tube C, is heated to a low 

 red heat and simultaneously exhausted by a good air-pump, and after 

 all the gas has been removed the stop-cock E is closed. In this con- 

 dition it is placed in the calorimeter. 



The experiment is conducted by connecting the end of the tube at 

 E by means of an india-rubber tube with a graduated vessel F con- 

 taining the gas. When all is ready the stop-cock E is opened, so that 

 the gas may rush into the charcoal, and the heat evolved by its 

 absorption distils off the equivalent quantity of liquid air from the 

 calorimeter, which is measured in the vessel G. 



The constant of the calorimeter being known (which with liquid air 



* ' Roy. In st. Proc.,' 1898. 

 t ' Roy. Inst. Proc.,' 1894. 



