426 SCIENCE PROGRESS. 



this case of dissociation in solution, Ostwald has been able 

 to calculate a constant from the conductivities of the 

 weaker acids at different dilutions, which he regards as a 

 good expression of the affinity of the acid. The dissocia- 

 tion constant, or affinity constant, determined in this way 

 is independent of the amount of water in which the acid is 

 dissolved. 



For bases we have methods corresponding to those 

 employed for acids. First of all we have one acceleration 

 process — the conversion of hyoscyamine into the isomeric 

 alkaloid atropine. Under the influence of strong bases this 

 transformation occurs at a rate depending on the strength 

 of the base, other things being equal. Then we have a 

 class of reactions in which the base participates directly, 

 namely the saponification of ethereal salts. The rate at 

 which ethyl acetate, for example, is converted by a base 

 into the acetate of that base and ethyl alcohol is a measure 

 of the strength of the base. Again, it is found that the 

 electrical conductivity of aqueous solutions of the various 

 bases is proportioned to their strength as determined by 

 any of the above methods. The explanation given by the 

 theory of electrolytic dissociation is that the specific activity 

 of bases is due to the hydroxyl ions which they produce 

 when dissolved in water, and that the strengths of the bases, 

 together with their electric conductivities, are closely pro- 

 portional to the number of these ions produced when the 

 bases are in equivalent solution. A dissociation or affinity 

 constant for bases can also be calculated in a manner 

 precisely similar to that adopted for the dissociation con- 

 stants of acids. 



The proximate problem of chemical affinity then is to 

 determine as many of these characteristic dissociation 

 constants for acids and bases as possible, for they can be 

 used in solving very many problems of the speed of 

 reactions and the equilibrium of opposed reactions in 

 aqueous solutions, with which the chemist is mostly con- 

 cerned. 



The methods detailed above are well suited for the 

 investigation of all but the weakest acids and bases, but 



