SVANTE AERHENIUS WALKER 725 



In August, 1884, Ostwald visited Arrhenius in Upsala, and his 

 visit had a marked effect on Arrhenius's future. Ostwald undertook 

 to get Arrhenius appointed as a docent in Riga, and the offer no 

 doubt led to the favorable reception of an application by Arrhenius 

 for a similar post in physical chemistry at Upsala. The two men 

 had, while together, projected a scheme of research on physical 

 chemistry to be undertaken in Ostwald's laboratory in Riga, but 

 the illness and subsequent death of Arrhenius's father kept him in 

 Upsala. Through Edlund's influence he received in December, 1885, 

 a valuable traveling scholarship from the Academy of Sciences which 

 enabled him to work in continental laboratories at discretion. The 

 next five years were Wander] ahre. In 1886 he was with Ostwald in 

 Riga, and Kohlrausch in Wiirzburg, during 1887 with Boltzmann in 

 Graz, during 1888 with van 't Hoff in Amsterdam and again with 

 Ostwald, now in Leipzig. In 1889 and 1890 he worked in the 

 laboratories of Ostwald and Boltzmann. When in Sweden he lec- 

 tured on physical chemistry in Upsala or worked in Edlund's labo- 

 ratory in Stockholm. It was during this journeyman's period of his 

 life that the theory of electrolytic dissociation was finally developed. 



His original papers left the nature of the difference between the 

 active and the inactive portions of the electrolyte unsettled, and 

 the absolute value of the dissociation vague. As I have said, the 

 theory was still in solution. The nucleus which determined its crys- 

 tallization came through van 't Hoff's theoretical work on osmotic 

 pressure and his interpretation of Raoult's experimental results. 



Van 't Hoff, in a memoir presented to the Swedish Academy on 

 October 14, 1885, showed that it was possible to write for solutions 

 an equation PV=R'T^ analogous to the gas equation, where P, 

 however, is the osmotic pressure instead of the gaseous pressure. 

 The constant R' was in many cases equal to the gas constant, but 

 in many others differed from it. Van 't Hoff then wrote the general 

 equation for dissolved substances in the form of PV = iRT, where R 

 is the gas constant and i a coefficient sometime.s equal to unity, 

 but sometimes assuming values much greater, in particular for 

 aqueous salt solutions when the results are calculated from Raoult's 

 experiments. For example, i is 1.98 for hydrochloric acid, 1.82 

 for sodium nitrate, and 1.T8 for potassium chlorate. Van 't Hoff 

 contented himself with these empirical values and made no attempt 

 at an explanation. His paper was published in 1886, but Arrhenius 

 did not receive a copy until March, 1887. On the 30th of that month 

 he wrote to van 't Hoff from Wiirzburg : " Your paper has cleared 

 up for me to a remarkable degree the constitution of solutions. If, 

 for example, sodium chloride were normal in its behavior, i. e., if it 

 consisted of simple molecules, its coefficient i would be equal to unity. 



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