238 J. Ohen — Investigation into the Existence of 



This coefficient would be one for " ideal" solutions and greater 

 than one for the acids, bases and salts. ' . 



Arrhenius^ showed, also in 1887, how these exceptions 

 might be explained ; and thus the law hold for all substances. 

 The osmotic pressure, other things being equal, depends upon 

 the number of particles present in a given volume of the solu- 

 tion, in the same way as the pressure of a gas depends upon 

 the number of its particles. If then the osmotic pressure is 

 too great, there must be more particles present than were put 

 in. These substances must therefoj*e be dissociated, i. e., the 

 molecules split up into two or more parts. Arrhenius rea- 

 soned in this manner. 



This same assumption had been made use of to explain the 

 abnormal pressures of some gases ; but on account of the 

 chemical objections had not before been applied to solutions. 

 Arrhenius accordingly brought forth again the electrolytic 

 theory of Clausius, and established it, seemingly, by showing 

 how to calculate the amount of dissociation. 



Clausius had believed that " some of the molecules of an 

 electrolyte are dissociated into their ions, which move about 

 independent of each other." During electrolysis these mo- 

 mentarily free ions would be guided to their respective poles. 

 According to this theory there is no direct decomposition of 

 the electrolyte by the current, as was held by Grotthiiss in his 

 theory. It has been shown since the time of Grotthiiss that 

 electricity moves with the same ease in electrolytes as in 

 metals, so there is no place for such work as decomposition. 



From the activity coefficient (a), which he considers the ratio 

 of the actual molecular conductivity to the maximum con- 

 ductivity, i. e., the conductivity at infinite dilution, Arrlienius 

 proceeds to show how to determine the coefficient i of the 

 formula, and thus test the theory. By a comparison of the 

 lowering of the freezing point of a liter of water, in which a 

 gram molecule of the substance is dissolved, and i as calcu- 

 lated from the conductivity method, he found the agreement 

 to within tile limits of experimental error. 



The theory has since been tested b}' a great many men, by 

 the method of the lowering of the freezing point, the rise of the 

 boiling point, osmotic pressure, conductivity, etc. There are 

 seemingly some exceptions as shown by Kahlenbergf and 

 others, but the preponderance of evidence is certainly in its 

 favor so far. Some of these exceptions may be due to the 

 somewhat limited knowledge we have of the true composition 

 of some substances. And the law has its limitations, in the 

 same way as the gas laws, and holds only for dilute solutions. 

 The theory, at least, explains a great many phenomena that 

 cannot be explained, at present, by -any other means. 



*Ibid., i, 631, 1887. f Am. Jour. Phys. Chem., June, 1901. 



