88 PROPERTIES OF ELECTRICALLY CONDUCTING SYSTEMS 



ance or of the ion concentration. The equation obviously approaches in 

 form that which follows from the mass-action law which is: 



' K 



If the mass-action law holds, the ratio of the ionized to the un-ionized 

 fraction is inversely proportional to the ion concentration. If, therefore, 



v 

 we were to plot the values of the ratio = - against values of the ion 



concentration Cy, we should obtain a rectangular hyperbola. When the 

 constant ra equals unity, the equation is of the same form, except that 

 the entire curve is raised by an amount equal to D. In this case, there- 



Y 



fore, the curve is again a rectangular hyperbola asymptotic to the 



1-Y 



axis on one side and asymptotic to the horizontal line y - = D on the 



other. 



In very concentrated solutions, in the case of substances for which the 

 value of ra does not differ too greatly from unity, the equivalent con- 

 ductance at a given concentration for different electrolytes is roughly 

 proportional to the value of D. The value of this constant, as has already 

 been pointed out, is in a large measure a distinctive property of the 

 electrolyte and varies only little as a function of the solvent. For the 

 strongest electrolytes the value of D is always of the same order. 



As we shall see later, the conductance of an electrolyte is a function 

 of the temperature. At very high and very low concentrations the con- 

 ductance invariably increases with increasing temperature, while, at in- 

 termediate concentrations, the conductance in many cases decreases with 

 increasing temperature, and always decreases at high temperatures. As 

 we shall see, this behavior is due to the fact that the value of D remains 

 constant and independent of the temperature, while the constant ra 

 varies, increasing with increasing temperature. At intermediate concen- 

 trations, therefore, the ionization decreases with increasing temperatures 

 whereas at very high and very low concentrations the ionization remains 

 practically fixed. 



3. Relation between the Properties of Solvents and Their Ionizing 

 Power. Various attempts have been made to connect the power of a 

 solvent to ionize dissolved substances with the properties of this solvent. 

 So, for example, it has been suggested that those solvents which are 

 normally associated are capable of dissociating substances dissolved in 

 them. This relation, however, is not a general one for it is now known 



