216 PROPERTIES OF ELECTRICALLY CONDUCTING SYSTEMS 



plex anions, however, the non-metallic characteristics have disappeared, 

 and these substances in the solid state are metals. In solution, how- 

 ever, they exhibit properties similar to those of tellurium. A charac- 

 teristic property of such solutions is the existence of anions of distinctly 

 metallic elements. Thus, lead is precipitated on the anode when the 

 current is passed through a solution containing the complex Na 4 Pb.Pb x . 28 

 A similar result has been obtained in the case of the antimony complex 

 Na 3 Sb . Sb x . 29 In a solution of the lead complex in equilibrium with lead, 

 2.25 atoms of lead are precipitated on the anode per equivalent of elec- 

 tricity. 30 This corresponds with the mean composition of the solution. 

 The proportion of lead to sodium in the presence of excess lead is inde- 

 pendent of the concentration of the solution. In the case of the anti- 

 mony complex, the mean composition of the solution is a function of 

 the concentration. The maximum lies in the neighborhood of 0.4 N 

 sodium. 31 At lower concentrations, the mean composition falls off 

 sharply from the value 2.33 at the maximum to 1.2 at a concentration of 

 0.005 N. Bismuth and tin likewise form complexes of a similar nature 

 which have not thus far been studied in detail. 



The solutions of these complexes, except possibly at the highest con- 

 centrations, are purely electrolytic in character. 32 While the number of 

 charges associated with the negative complex has not been definitely 

 determined in the case of lead and antimony, it is probable that the 

 charges are respectively 4 and 3, corresponding with the position of these 

 elements in the periodic system. It is evident that many metallic ele- 

 ments are capable of forming complex anions similar to the complex 

 sulphur and iodide ions. The compounds which are left behind on 

 evaporation of ammonia are metallic. In view of the electrolytic prop- 

 erties of these compounds when in solution, it appears probable that the 

 solid compounds themselves are, in fact, salt-like in character, the more 

 electronegative element carrying a negative charge. The existence of a 

 large number of compounds in binary systems, such as those of sodium 

 and lead, is probably due to the formation of negative ionic complexes. 

 In all likelihood, this property is not confined to the metals whose com- 

 pounds are soluble in ammonia. It is probable that the constitution of 

 the compounds formed between the strongly electropositive elements and 

 such elements as thallium and mercury is similar to those of lead. 



9. Other Complex Ions. Complex anions are formed by many salts 

 of metallic and non-metallic elements on interaction with salts of the 



M Kraus, J. Am. Chem. Soc. 29, 1557 (1907) ; Smyth, ibid.. 39, 1299 (1919). 



"Peck, J. Am. Chem. Soc. 40, 335 (1918). 



Smyth, loc. cit. 



81 Peck, loc. cit. 



"Kraus, J. Am. Chem. Soc. #, 752 (1921). 



