130 PROGRESS OF SCIENCE IN THE CENTURY. 



many researches, notably, for instance, of those con- 

 cerning the nature of solutions. 



The reader should consult, for instance, the eighth 

 chapter of Professor Tilden's Short History, espe- 

 cially with reference to the theory of ionisation sug- 

 gested by Arrhenius. 



While the early electro-chemical ideas of Berzelius 

 have been abandoned , a new path of enquiry, es- 

 pecially marlced by the work of Svante Arrhenius, 

 continues to be full of promise. Its first milestone 

 bears the date 1884, when Arrhenius proved that def- 

 inite and quantitative relations exist between elec- 

 trical and chemical properties. 



But to this we must add, as suggestive of one of 

 the most significant steps in modern chemical theory, 

 another quotation from Ostwald. " Research based 

 on a well-defined measure of affinity determinable 

 with numerical exactness only became possible, when, 

 by the development of the electrolytic theory of dis- 

 sociation, the formula was found from which a con- 

 stant of a general character and independent of the 

 dilution could be calculated. This constant has a 

 claim to serve as a measure of affinity." 



While the nature of chemical affinity remains ob- 

 scure, a mode of measuring it has been attained. If 

 this step is to be associated with any particular name 

 it should be with Ostwald (1889).' 



