104 PROPERTIES OF ELECTRICALLY CONDUCTING SYSTEMS 



elusion that in the case of solutions of the formates in formic acid, 

 likewise, the approximately linear form of the curve over a limited con- 

 centration interval is due to the existence of an inflection point and that 

 the causes underlying the course of the curve are the same as those in 

 solutions of sodium acetate in water. It appears probable, therefore, 

 that solutions of the formates in formic acid do not constitute an excep- 

 tion to the well-known behavior of strong electrolytes in solvents of high 

 dielectric constant. From this point of view these solutions are normal 

 in their behavior. 



6. The Behavior of Salts of Higher Type. Up to this point, the 

 electrolytes considered have been of the binary type. In the case of 

 salts of higher type the interpretation of conductance measurements 

 becomes much more difficult and uncertain, since it is possible, and even 

 probable, that ionization may take place in several stages, as indeed it 

 does in the case of weak acids and bases. For example, a salt of the 

 type MX 2 may ionize according to the equations: 



MX 2 = MX + + X- 



MX + = M ++ + X- 

 MX 2 = M ++ + 2X-. 



If ionization takes place only according to the last equation, then the 

 degree of ionization may be calculated from conductance measurements. 

 But if ionization takes place according to the first two equations, then it 

 is not possible to determine the number of carriers in the solution at a 

 given concentration. In the case of weak dibasic acids, ionization often 

 takes place according to the first two equations, the constants of the 

 two reactions being such that one reaction is practically completed before 

 the other reaction has begun. With salts this does not appear to be 

 the case. 



In any case, if the concentration is sufficiently low, we should expect 

 that, ultimately, there would be present in the solution only the ions M ++ 

 and X-. Since the ion M ++ carries two charges, its carrying capacity 

 will be approximately twice as great as that of an ion carrying only a 

 single charge. The molecular conductance of such an electrolyte should 

 therefore approach a value approximately twice that of a binary electro- 

 lyte, or its equivalent conductance should approach a value of the same 

 order as that of binary electrolytes. An examination of the conductances 

 given in Table III indicates that this is the case. The limiting value 

 of the equivalent conductance for salts of different type is throughout 

 of the same order, and we may conclude, therefore, that at low concen- 



