1912] 



on Heat Problems. 



581 



The lowest tenipemtures which can bo attained with various 

 coohng agents are of considerable interest. Gray Lussac showed that 

 it was possible to freeze mercury by the evaporation of ice, and the 

 experiment, arranged for projection on a screen, can be performed 

 in the following manner (Fig. 2). A flat glass bulb, A, contain- 



FlG. 



ing the mercury, is supported on a quill tube in the flask C, con- 

 taining snlphuricacid. This vessel is connected through a side tube 

 in the neck by means of a 3-way cock D to an exhaust pump, and a 

 bulb of charcoal E. At each end of A some strands of wet cotton 

 wool are fastened. The charcoal having been cooled in liquid 

 air, the exhaust pump is turned on to C for a short time ; and the 



2 Q 2 



