ON THE PHYSICAL VIEW OF NATURE. 



165 



The decisive step was taken in 1887 by Arrhenius, 1 who 

 has the merit of having brought together the two inde- 

 pendent courses of research and reasoning, and made 

 them fruitful for each other. He shows 2 " that the dif- 

 ference between active and inert molecules consists in 

 this, that the former are split into their ions, the latter 

 not. Only the free ions take part in the conduction of 

 electricity and in chemical reactions : this is the reason 

 for the proportionality of the two (Faraday's law). The 

 ions behave in solution like independent molecules : this 

 is the reason of the deviation which electrolytic solutions 

 show from the extended gaseous laws (Van't Hoff' s dis- 

 covery)." " What a change has come over our concep- 

 tions," exclaims Victor Meyer, 3 " if we have to accustom 42. 

 ourselves to see in a dilute solution of common salt, no Me ? eron 



change of 



longer the undecomposed molecules of a salt, but separate chemical 



views. 



atoms of chlorine and sodium. For these revolutionary 

 innovations we are indebted to the labours of Van't 

 Hoff, Arrhenius, Ostwald, Planck, Pfeffer, de Vries, but, 

 so far as experiments go, notably to the splendid re- 

 searches of Eaoult, which for years have been prepar- 

 ing the way for this mighty theoretical advance." 



The year 1887, which brought together these two 

 fruitful lines of reasoning and research, can also be con- 

 sidered as the epoch when the new science of physical 

 chemistry was fairly launched into existence. The year 



1 In a communication to the 

 Academy of Stockholm of 8th June 

 and 9th November 1887. 



2 Quoted from Ostwald's ' Allge- 

 meine Chemie,' 2nd ed., vol. ii. 

 part 1, p. 656. 



3 See the highly interesting 



Address by Victor Meyer before 

 the German " Naturforscherver- 

 sammlung " at Heidelberg in 1889, 

 entitled " Chemische Probleme 

 der Gegenwart " (Heidelberg, 

 1890), p. 32. 



