CARRIERS IN ELECTROLYTIC SOLUTIONS 215 



Solutions of complex selenides and tellurides have been obtained in 

 liquid ammonia by the action of the normal salts on the free elements. 24 

 Solutions of the complex tellurides in liquid ammonia are the only ones 

 which so far have been extensively investigated. The normal telluride, 

 which is only slightly soluble in ammonia, is formed by the direct action 

 of the metal on sodium in ammonia solution. The telluride so formed 

 is a white substance, apparently somewhat crystalline in character. In 

 the presence of excess tellurium the normal telluride reacts with the metal, 

 forming a complex tellurium salt which is very soluble in ammonia. The 

 composition of the solution in equilibrium with a normal telluride Na 2 Te 

 is Na 2 Te 2 . 25 Apparently the following reaction takes place: 



Na * Te solid + Te solid = Na 2 Te * solution- 



This solution exhibits an intense violet blue color. When the normal 

 telluride Na 2 Te has disappeared, the complex Na 2 Te 2 in solution reacts 

 with free tellurium to form another complex. In concentrated solutions 

 the composition of the ammonia solution corresponds very nearly with 

 Na 2 Te 4 . The exact value of the composition, however, is a function of 

 the concentration, the amount of tellurium in solution decreasing at lower 

 concentrations. 26 The color of the solution in equilibrium with metallic 

 tellurium is deep red. 



The molecular weight of the telluride in equilibrium with metallic 

 tellurium has been determined and found to correspond with the formula 

 Xu 2 Te.Te x ; that is, sodium is associated with a divalent complex tel- 

 lurium anion. 27 



While the normal telluride is a white substance exhibiting only non- 

 metallic characteristics, the product resulting on evaporating a solution 

 containing larger amounts of tellurium is metallic in appearance, indicat- 

 ing that the salts of the complex tellurides are metallic substances. This 

 behavior of the complex tellurides in the free state is particularly im- 

 portant when we come to consider similar complex anions of metals of 

 the fourth and fifth groups. 



Whereas our knowledge of the complex anions of this type has pre- 

 viously been restricted chiefly to elements of the sixth and seventh 

 groups, in recent years, through a study of solutions in liquid ammonia, 

 evidence has come to light which indicates that the elements of the 

 fourth and fifth groups form complex anions similar in character to the 

 complex sulphide and iodide ions. In the case of the salts of these com- 



"Hugot, Compt. rend., 129, 299 and 388 (1899). 



85 Chiu, Dissertation, Clark University (1920). 



* E.g. Chiu, loc. cit. 



87 E. H. Zeitfuchs, Dissertation, Clark University (1921). 



