August 29, 1901] 



NATURE 



429 



attempted a slight resistance. . . . All the uneasiness 

 connected unavoidably with important revolutions had 

 been directed against a second idea, which, appearing 

 somewhat later, removed a fundamental difficulty in the 

 theory of solutions, which had until that time made its 

 acceptance impossible for me. This idea has neverthe- 

 less shown itself as an aid to investigation to be of 

 unparalleled sweep and value ; it is the theory of electro- 

 lytic dissociation of Arrhenius. . . . No scientific idea pro- 

 duced in my time has helped me in such measure as these 

 two theories. ... In particular the extraordinarily mani- 

 fold and severe test, which lies in the numberless 

 numerical consequences of the theories in all possible 

 fields; has yielded such a number of confirmations that 

 the relatively rare cases where the unprejudiced decision 

 was insufficient entirely vanish." 



In 1867 Guldeberg and Waage published their investi- 



previous series of experiments, as a comparison of the 

 numbers in the subjoined table shows : — 



Hydrochloric 



Nitric 



Sulphuric 



Oxalic 



Orthophosphoric . 

 Monochloracetic . 

 Tartaric 

 Acetic 



In 1887 came the theory of electrolytic dissociation ; 

 it explained at once the relationship which had been 

 observed both by Arrhenius and by Ostwald between 

 the affinity coefficients and electric conductivities ; the 



Fig. 2.— Ostw.ild an J Arrhen 



gations on the subject of mass action, and enunciated 

 the law that the intensity of the interaction of two sub- 

 stances was proportional to the product of their active 

 masses, and to a coefficient which depended on the 

 nature of the substance, temperature, &c. 



This induced Ostwald, in 1877, to carry out a long 

 series of experiments with the object of determining, by 

 volumetric and optical methods, the manner of distribu- 

 tion of a base among different acids present in excess, 

 and hence calculate the "specific affinity coefficients" 

 of the latter. 



In 1SS4 he suggested another method for the deter- 

 mination of these coefficients : it consisted in measuring 

 the velocities of reactions induced by them, such as the 

 inversion of cane sugar, the decomposition of acetamide, 

 methyl acetate, &c. The results he obtained in this way 

 were found to confirm generally those obtained in the 



NO. 1 66 1, VOL. 64] 



degree of dissociation of an acid being a measure of its 

 strength, and the conductivity being due principally to 

 the hydrogen ions, it would follow from theoretical con- 

 siderations that the conductivities of solutions of different 

 acids would be proportional to the number of hydrogen 

 ions in the solution, and so to the relative strength of 

 the acid. Ostwald pointed out that the application of 

 Guldeberg and Waage's law to electrolytes should enable 

 us to obtain a "dissociation constant" for each electro- 

 lyte, the determination being made by means of conduc- 

 tivity measurements. 



He then proceeded to trace the relationships between 

 the "dissociation constants" of organic acids and the 

 structure or constitution of the radicals. He showed 

 that they varied with the nature of the acid radical, 

 and that an increase of the negative group such as O, 

 CI, Br, I, CN, &c., increased the tendency of the hydrogen 



