504 UNIVERSITY OF VIRGINIA PUBLICATIONS 



Discussion of some of the probable factors involved. 



For our case as the temperature was held constant and the iodine 

 content (free) was also constant, the only independent variable was the 

 concentration of the KI. It is not so easy however to be sure that we have 

 under consideration all of the dependent variables, and even if so it is in some 

 cases difficult to determine what function such variables are of the con- 

 centration. The following factors will be discussed. 



1. Density. 



2. Fluidity (or reciprocal viscosity). 



3. Dissociation of the KI3 molecule into ions. 



4. Effect of the common ion (K). 



These factors will be taken up and discussed separately, and so far as 

 possible the relation existing between them and the concentration of the 

 KI will be determined. 



Density and concentration. A glance at the density curve for KI 

 solutions (Plates I and II) will show how exactly density and concen- 

 tration go together for this salt. A careful scrutiny of table VII will show 

 the same. Density curves for some other solutions will be found on plate 

 II. While these curves are approximately straight lines, all have some 

 perceptible curve except that for KI, which is a straight line exactly, at least 

 so far as our measurements show. 



All curves on Plate II are drawn on the same scale as those on Plate I, 

 and therefore are fairly comparable. The data was obtained from Van 

 Nostrand's Annual, Biedermann's Chemiker-Kalender, Landold-Born- 

 stein-Roth's Tabeln, or from original sources. In most cases laborious 

 computations had to be made to transform by interpolation values given 

 in percent, into values for normal or molar solutions. This suggests the 

 need for a set of tables giving the various physical properties of solution 

 for normal and molar concentrations instead of the usual percent concen- 

 trations. Such tables should cover the fullest possible range, and not 

 merely values below and up to normal, as is the case for those few tables 

 that use normality as the concentration unit. 



The previously noted fact, that the density of KI solutions is directly 

 proportional to the concentration of the KI prevents density from having 

 any distinct or separate value as a variable; that is, we can not distinguish 

 between the effects of density, as such, and of concentration as such. 



Fluidity and concentration. By fluidity is meant the reciprocal 

 viscosity. For our purpose it matters little what unit be used, but for 

 convenience I have always taken the viscosity of pure water at 25° as 1, 



