CARRIERS IN ELECTROLYTIC SOLUTIONS 217 



more electropositive elements. Many such complex anions have been 

 investigated in which mercury, tin, lead, platinum, silicon and other ele- 

 ments appear in the anion complex in association with strongly electro- 

 negative elements such as chlorine, fluorine, etc. The constitution of 

 these complex anions is accounted for by Werner's theory which has 

 already been briefly outlined. 



Complex or, preferably, intermediate ions, both positive and negative, 

 may be formed when salts of higher type ionize in stages. Such ions 

 have many representatives among the higher types of weak acids and 

 bases when the ionization constants of the different ions have different 

 values. This is the case, for example, with phosphoric acid. 



Whether similar complex ions are commonly formed in solutions of 

 salts of higher type is uncertain. The cation transference number of 

 cadmium iodide at high concentrations is greater than unity, which 

 clearly indicates the existence of an intermediate cadmium ion. In the 

 case of other salts, the existence of intermediate ions is not definitely 

 established although, as we shall see below, the existence of such ions in 

 mixtures may be inferred from solubility data. There are no data 

 available relative to the existence of similar ions in non-aqueous solu- 

 tions. It is possible, also, that binary electrolytes may associate and 

 dissociate with the formation of complex ions. Their existence has not 

 been established. 



