﻿228 Mr. Bernard Oavanagh on 



The same difficulty arose when a dynamical explanation of 

 the law of mass-action was attempted, the essential continuity 

 of action of u physical " forces * standing in the way, and 

 Boltzmann had to assume — with conscious artifici;tlity — dis- 

 continuity in a field of force in order to arrive at the desired 

 result. 



It seems indeed that, besides the more obvious and less 

 peculiar properties of shortness of range, " specificity," and 

 saturability, there is a quality of discontinuity of action (in 

 time or in space or in both) which distinguishes "chemical 

 forces '• from " physical," the distinction being sharp so far 

 as we can yet see. 



We find then an absence of direct dependence of 

 dissociation upon the thermal motion closely connected with 

 the possibility of accounting for the law of mass-action 

 dynamically. 



The parallel with our " rider " and its indispensability as a 

 basis for the deductions of molecular thermodynamics is 

 significant. 



The transitory orbital system which was the older 

 " physical " conception of a molecule, and which quite 

 probably occurs in all dense gases and liquids f, is clearly 

 quite directly dependent on the thermal motion, is, in fact, 

 itself merely an u episode " in that motion, and cannot in 

 any sense be regarded as fulfilling the requirement of out- 

 rider. We cannot, therefore, predict from thermodynamics 

 the " mass-action " equilibrium law for the " reactions " of 

 such " molecules " under any circumstances, for we cannot 

 treat them 'as molecules for the purposes of molecular 

 thermodynamics. And, in parallel, we find that dynamical 

 theory is unable to predict the law of mass-action for such 

 " molecules." 



The electrolyte question provides an important application 

 of these considerations. 



It has frequently been supposed that a pair of ions, closely 

 linked by their electrostatic fields alone, must be regarded as 

 a molecule, and should behave thermodynamically as such. 

 Electrostatic forces as we know them, however, are typical 



* That is, " forces " within the conception of the older physics. It 

 seems convenient to use, in contradistinction, the term u chemical forces " 

 for the " forces " or means by which a molecule is formed or /' hound " 

 [see end of this section] and held together, and the expression may 

 find some further justification in the fact that in the nature of these 

 latter '' forces " lies, probably, the key to all the facts and phenomena of 

 chemistry. 



t Compare here Cantor's objection, mentioned above. 



