OTHER PROPERTIES OF ELECTROLYTIC SOLUTIONS 287 



bonate, and sulphuric acid, exhibit density changes which do not vary 

 as linear functions of the ionization. The cause of the variation in these 

 cases is uncertain, but may be due to the formation of complex ions, to 

 hydrolysis, etc. 



The volume changes of electrolytic solutions in methyl alcohol have 

 likewise been examined. 7 The results obtained correspond very closely 

 with those obtained in the case of aqueous solutions. The density change 

 due to ionization, which is obviously equal to the difference A B, is 

 considerably greater in methyl alcohol solutions than it is in water. This 

 is not surprising, since the dielectric constant of this solvent is much 

 smaller than that of water. We should expect that, if the density change 

 is the result of the action of the field due to the charge on the surrounding 

 solvent molecules, the density change would be the greater the smaller 

 the dielectric constant of the medium. 



In order to finally establish the additive nature of the density changes 

 of electrolytic solutions, it will be necessary to extend the measurements 

 to much lower concentration. Methods exist for measuring the densities 

 of dilute solutions with sufficient precision to make it possible to extend 

 the measurements to concentrations approaching 10~ 3 N. Until this is 

 done, the results of density measurements must remain more or less in 

 doubt. The concordance of the results so far obtained, however, would 

 appear to justify further efforts along these lines. 



Some measurements have been made by Rohrs 8 on the density of 

 solutions in ethyl alcohol and acetone. The interpretation of the results 

 is uncertain owing to the small change in the ionization over the con- 

 centration intervals for which measurements were made. 



3. Velocity of Reactions as Affected by the Presence of Ions. The 

 speed of many reactions, such as the inversion of sugars and the hydroly- 

 sis of esters, for example, is greatly increased on addition of acids. 

 Ostwald 9 showed that the catalytic effect of different acids is the greater 

 the stronger the acid. It appeared, at first, that the catalytic effect of the 

 acids provided an independent method for estimating the concentration 

 of the hydrogen ions in an acid solution. Further investigations, 10 how- 

 ever, showed that the catalytic action is likewise dependent upon other 

 factors, such as the presence of other substances and especially electro- 

 lytes. Thus, the catalytic action due to a strong acid should be reduced 

 on the addition of a salt of this acid. While such a reduction takes place 



7 Ruthenberg, Inaugural Dissertation, Rostock (1913). 



Rohrs, Ann. d, Phys. 57, 289 (1912). 



9 Ostwald. J. prakt. Chem. 28, 449 (1883) ; 29, 385 (1884) ; 31, 307 (1885). 



"Arrhenius, Ztschr. f. phys. CJiem. 5, 1 (1890). 



