﻿The Action of Ultra-violet Light on Chlorine. 757 



The superiority of the above method will be realized when 

 it is compared with the proofs of the equivalent relations by 

 the authors named. 



In the application of the second law to mixtures similar 

 transformations of the differential equation are often useful. 

 In that case the equation has to be supplemented by terms 

 containing quantities which determine the amounts of the 

 various components of the mixture. These terms may be 

 of the form fidm, equal in number to the number p of 

 the components, where m stands for the quantity (e. g. mass 

 or number of gramme-molecules) of each component, and //. 

 is called the potential (Gibbs). In many cases it is more 

 appropriate to refer the equation to a definite quantity 

 (<?. g. unit mass or one molecule), and introduce variables 

 which determine the composition of the mixture, e. g. the 

 ratios x, y, ... of the amounts of the 2nd, 3rd, . . . component 

 to the whole ; the equation then assumes the form 



du = Tds + S Ad* + S Xdx. 



The total number of forms into which this equation may be 

 put by the subtraction of expressions like d(Ti), d(Aa). or 

 d(X#), is obviously 2 n+p , giving rise to the introduction of the 

 same number of thermodynamical functions (including u 

 itself) and allowing the deduction of (n+p)(n-\-p — V)2 n +P— 1 

 thermodynamical relations of the special simple form under 

 consideration. A further discussion of these relations or of 

 the application of the functions e. g. for the construction of 

 thermodynamical surfaces would be out of place here *. 



LXXIV. The Action of Ultra-violet Light on Chlorine. 

 By E. B. Ludlam, D.Sc.^ 



THE action of ultra-violet light upon many elements 

 causes them to eject electrons, and the more electro- 

 positive the element the more easily is the electron ejected. 

 Thus, the alkali metals are the most sensitive to ultra-violet 

 light and less positive metals less so; nevertheless, an 

 element so electronegative as oxygen gas appears to be 

 ionized by ultra-violet light, presumably by the detachment 

 of an electron, as in the case of metals. It was therefore a 

 matter of interest to ascertain whether chlorine, the most 



* Compare H. Kamerlingh Chines and W. H. Keesom, Encyklopadie der 



Math. Wiss. v., which is to appear shortly, 

 t Communicated by the Author. 



