ioo MOLECULAR STRUCTURE 



2. Mutual Influence of Different Groups. 



The mutual action of two groups in a molecule may 

 thus show itself in bringing about a combination, and 

 chemical reaction between them ; but without going so far 

 as that it may suffice to change the character of one of the 

 groups under the influence of the other. We may take as 

 instance the acid character due to the group COOH ; this 

 property may be strengthened or weakened, for the reason 

 considered. Since Ostwald's dissociation constant offers 

 a ready measure of the acid character, the principle of 

 determination of constitution has been tested in this 

 direction by the author l named. The dissociation constant 

 K which governs equilibrium between undissociated acid 

 and ions, according to the equation 



and therefore bears the following relation to the concentra- 

 tion of the undissociated acid C a and ions C- (Part I, p. 118), 



n 2 

 IT - * 



"o: 



may easily be determined from the conductivity, since the 

 dissociated part is the same fraction of the total concentra- 

 tion that the molecular conductivity /x for the concentration 

 in question is of its limiting value /x w , i. e. 



Hence C i and C a are calculable for any given concentration, 

 and therefore K is so : 



K -*- = 



whence a expresses the fraction dissociated into ions. 



1 Zeitschr.f. Phys. Chem. 3. 418. 



