'52 



Professor Sir James Dewar 



[June 7, 



0*06172 mm.). This shows how different the occlusion volatiHty of 

 hydrogen is at the temperature of Uquid air as compared with that of 

 nitrogen for equal concentration. In a corresponding manner the 

 concentrations, for the same pressure, vary greatly with the tempera- 

 ture. The following table exemplifies this, even although the pressures 

 are not quite constant. 



The temperatures employed were the boiling-points of hydrogen^ 

 oxygen, and carbon dioxide. 



The Heat of Occlusion for Different Gases in Charcoal. 



Accompanying the condensation of all gases to the liquid state 

 there is evolution of heat, and we know that during the absorption 

 of a gas in charcoal, or any other occluding body ; as for instance, the 

 occlusion of hydrogen in palladium ; the amount generated exceeds 

 that of direct liquefaction. From the relation between occlusion 

 pressure and temperature at the same concentration, the reaction being 

 reversible, we are able to calculate this heat-evolution. Thus, if the 

 concentration in the charcoal for each of the following gases has the 

 values given in the table, then the following mean molecular latent 

 heats of occlusion result from my experiments. 



The concentrations of the occluded gases were so regulated as to 

 start with an initial pressure not exceeding 8 mm. at the respective 

 boiling-points of hydrogen, nitrogen, oxygen, or carbonic acid. 



