1904.] 



on Liquid Hydrogen Gfflorimetrt/. 



oSf) 



cool gaseous nitrogen and be condensed. Hence nitroo-en would not 

 be a convenient calorimetric substance. h\ any case, the boiling 

 points of nitrogen, air, and oxygen being so close together, it is 

 obvious that liquid air is the most convenient substance in the 

 neighbourhood of -180° to -200° C. 



The calorimeter has been described in mv paper "On the 

 Scientific Uses of Liquid Air,"* and later an improved form in 

 " Recherches sur les Substances Radio-Actives," by Madame Curie,;t 

 further a sketch of it is given in the paper on'" The Absorption 

 and Thermal Evolution of Gases occluded in Charcoal at Low 

 Temperatures." % The annexed diagram shows its construction. It 



consists essentially of a large vacuum vessel A, capable of holding 

 two or three litres, into which is inserted the calorimeter, a smaller 

 vacuum vessel B, of 25 to 50 c.c. capacity, which has been sealed on 

 to a long narrow tube G, projecting above the mouth of A, and held 

 in its place by some loosely packed cotton wool. From the side of 

 this narrow tube, either before or after passing out of K, a branch 

 tube, E, is taken off to enable the volatilised gas from the calorimeter 

 to be collected in the receiver F, over water, oil, or other suitable 

 liquid. To the extremity of the projecting tube G, a small test-tube 

 G, to contain the portions of material experimented on, is attached by 

 a piece of flexible rubber-tubing D, thus forming a movable joint, 



* Roy. Inst. Proc. 1894, vol. xiv., p. 398. 



t 2nd Edition, p. 100. 



X Roy. Soc. Proc. 1904, vol. Ixxiv., p. 123. 



