564 Professor Suante Arrhenius [June 3, 



By heljD of the gaseous laws it is also possible to determine the 

 heat evolved at the dissociation of a weak acid or base, and in this 

 way I was able to calculate the heat of neutralisation of acids and 

 bases in a general manner. In an analogous way, Fanjung calculated 

 the changes of volume at dissociation of a weak acid or base and at 

 the neutralisation of these bodies. All these calculations gave values 

 very nearly agreeing with the observed ones. 



An important role is played by the water, which may be regarded 

 as a weak acid or base. By its electrolytical dissociation, it 

 causes the hydrolysis of salts of weak acids and bases. By observa- 

 tion of the hydrolysis, it was possible to calculate the electrolytic 

 dissociation of water, and this quantity was soon after determined by 

 electrical measurements by Kohlrausch and Heydweiller in perfect 

 agreement with the previous calculations. For physiological 

 chemistry this question is of the greatest importance, as is confirmed 

 by the experimental results of 8j6gvist and others. Also for the 

 explanation of volcanic phenomena, the concurrence between water 

 and silicic acid at different temperatures has found an applica- 

 tion. 



The catalytic phenomena in which acids and bases are the chief 

 agents, have been investigated by many observers, and it has been 

 found that the catalytic action depends on the quantity of free 

 hydrogen or hydroxyl ions that are present in the solution. To this 

 review, that makes no pretension to be complete, may also be added 

 the wide-reaching researches of van't Hoff, Ostwald, and especially 

 Nernst, on the electromotive forces produced by the ions. By these 

 investigations we have now acquired an explanation of the old problem 

 of the manner in which electromotive forces in hydro-electric com- 

 binations are excited. 



I have now traced the manner in which the idea of electrolytic 

 dissociation grew out of our old conception of atoms and molecules. 

 Sometimes we hear the objection that this idea may not be true, but 

 only a good working hypothesis. This objection, however, is in 

 reality no objection at all, for we can never be certain that we have 

 found the ultimate truth. The conception of molecules and atoms 

 is sometimes refuted on philosophical grounds, but till he has got a 

 better and more convenient representation of chemical phenomena, the 

 chemist will no doubt continue to use the atomic theory without 

 scruple. Exactly the same is the case for the electrolytic dissocia- 

 tion theory. 



This theory has shown us that in the chemical world the most 

 important role is j^layed by atoms or complexes of atoms, that are 

 charged with electricity. The common tendency of scientific inves- 

 tigation seems to give an even more prej^onderating position to 

 electricity, the mightiest agent of Nature. This development is now 

 jiroceeding very rapidly. Already we see not only how the theory 

 of electrons of J. J. Thomson, in which matter is reduced to a very 

 insignificant part, is developing, but also how efforts are made with 



