﻿Elements of the Higher Groups. 1133 



parts, — , of their respective surfaces. Boltzmann was 



of opinion that for the formation of diatomic molecules ' n ' 

 varies directly as the maximum valency of the element (viz. 

 2 for Ca, 7 for I, and so on) ». 



In recent years the "steric factor" has been introduced 

 into thermodynamics by Stern f in a new theory of the 

 dissociation of 1 2 vapour. 



Stern considered the case from the standpoint of both 

 thermodynamics and the kinetic theory, and came to the 

 conclusion that ' n ' lay between 6 and 7 in case of combi- 

 nation of two I-atoms to form an I 2 -molecule, thus lending 

 colour to Boltzmann's belief. The kinetic theory is not 

 very convincing, for the following reasons. According to 

 dynamical principles, two particles A and B approaching 

 each other from infinity cannot form a closed system until 

 and unless they lose a certain fraction of their energy, 

 presumably by radiation. Similarly, a molecule AB cannot 

 be dissociated into A and B if the system does not absorb 

 energy from the outside. 



Thus a complete theory of ionization is incomplete without 

 a consideration of the mutual action between radiation and 

 matter, and we are beset with the same difficulties which 

 have confronted all investigators on the subject since the 

 days of Boltzmann. 



Proceeding to the thermodynamical theory, the funda- 

 mental equation was derived from the equation 



S +S 6 -S„ 6 =U/T, ..... (A) 



where U = heat evolved, S a , S&, S a 6 were calculated from the 

 quantum theory involving certain assumptions. (Here 'a' 

 is Ca + , b is ' <?,' S a & is Ca.) The above equations are derived 

 on the assumption that the steric factor n = l. Taking the 

 " steric factor " into account, the probability that a and b 



would simultaneously present the definite portions, — , — , of 

 their surfaces to each other is given by 



w=(i.l) N , 



where X = total number of particles of each species. 



* Boltzmann,. Gastheorie, Band ii. pp. 175-177. Jeans, ' The Dynamical 

 Theory of Gases,' pages 209 to 217, 2nd edition, 

 t Stern, Ann. der Physik. vol. xliv. 



