J. Dewar— Thermal Evolution of Gases. 297 



The apparatus was further improved into the form illustrated 

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

 Substances Radio-Actives," 2d 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 (fig. 1) containing from 

 0*5-1 gram of charcoal has a long narrow tube C 1 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 experiment's, 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 condition 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 containing 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 distills 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 is about 14*5 c.c. per calory), we get the actual 

 thermal evolution together with the volume of gas absorbed. 



The heat correction for the rush of gas into the same 

 exhausted glass bulb without charcoal is small in proportion 

 to the total heat evolved, and the same may be said of the 

 volume correction on account of the cooling of the space 

 external to the charcoal. With a variable material like cocoa- 

 nut charcoal I have in the calori metric experiments used the 

 same sample in all cases. The following table embodies the 

 general results per cubic centimeter of charcoal. The gas 

 absorption is given at 0° and 760 mra . If the volume of gas 

 absorbed had been measured under the same conditions of 

 pressure at —185° C, then the numbers in Column II would 

 all have to be divided by three. 



