19U] on The Coming of Age of the Vacuum Flask 247 



on the structure of the atom, discussing vortices of electrons, 

 central positive charges, and so forth. It was remarkable, in view of 

 these experiments, that some of them had predicted that the atomic 

 heats must be chiefly determined by the atomic volumes and the 

 elastic constants. 



Atomic Specific Heats hetween the Boiling Points of Liquid 

 Nitrogen and Hydrogen. 



The Mean Atomic Specific Heats at 50' Absolute of the 

 Elements, a Periodic Function of the Atomic Weights. 



A method of determining the specific heat of substances at low 

 temperatures was described in a paper on " Studies with the Liquid 

 Hydrogen and Air Calorimeter," * also in the abstract of a Friday 

 Evening DisccTurse in 1904 on "Liquid Hydrogen Calorimetry," f 

 where the apparatus then used is illustrated. 



Continuing the use of the same method, but with some modifica- 

 tion of the apparatus, the investigation has been extended to a large 

 number of inorganic and organic bodies. In this later series of 

 experiments, the measurements of the specific heats of materials by 

 the liquid hydrogen calorimeter were made over a range of tempera- 

 ture from boiling nitrogen to boiling hydrogen, a fall of temperature 

 of some ST"" Absolute. 



Weighed pieces of the material are cooled to the temperature of 

 boiling nitrogen in a quartz cooling vessel of special design. By a 

 simple mechanical device they are then released from this vessel, and 

 drop into liquid hydrogen in the calorimeter below. The resulting 

 volumes of hydrogen evaporated are measured. From this value and 

 a knowledge of the latent heat of the liquid hydrogen and the mass 

 of the substance, the specific heat can be calculated as follows : — 



If y is volume of hydrogen at N.T.P. evaporated by the fall of 

 1 grm. of the substance through T degrees above the temperature of 

 boiling hydrogen, and s its specific heat, L being the volume of 

 hydrogen evaporated by 1 calorie, then 



.T = ^, i.e. . = ^. 



The latent heat of liquid hydrogen is taken as 115 calories, and 

 therefore L = 97*05 c.c. ; also in these experiments T is constant 

 (57' '5) therefore 



s =y X 0-0001792. 



* Roy. Soc. Proc, A, Ixxvi. p. 325. 

 t Eoy. Inst. Proc, xvii. p. 581. 



