THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[SIXTH SERIES.] 

 JANUARY 1920. 



I. Note on the Determination of Chemical Constants. 

 By Alfred C. Egerton *. 



Introduction. 



UP till recently, the value of the integration constant of 

 the vapour-pressure formula, known as the "chemical 

 constant," has generally been considered to he about 3 (in 

 absolute units). From affinity measurements, hydrogen 

 appeared, however, to have a lower value (given in Nernst's 

 6th edition Theoretical Chem. as 1*6) while other substances 

 such as iodine had a higher value about 4*0. The point arose 

 whether the constant depended on the nature of the element ; 

 Sackur {Ann. d. Phys. xl. p. 67, 1913) and Tetrode (ibid. 

 xxxviii. p. 434, and xxxix. p. 255, 1912) developed an 



expression, i= In— — -h , wherein the constant is con- 

 sidered to be related to the atomic weight. Lindemann 

 (Phil. Mag. vol. xxxviii. p. 177, 1919) has shown also from 

 dimensional considerations that the integration constant of a 

 monatomic substance should be equal to a universal constant 

 plus one and half times the logarithm of the atomic weight. 

 It is of importance, therefore, to determine as accurately 

 as possible the chemical constants of several monatomic 

 elements. For this purpose, a careful calculation of the 

 chemical constant of mercury has been made and the vapour 



* Communicated by Prof. F. A. Lindemann, 

 Phil. Mag. S. 6. Vol. 39. No. 229. Jan. 1920. B 



