Warwick. ] 



116 



[Nov. 6, 



Cadmium from Zinc. 



The first seven determinations were made in a platinum dish weighing 

 about 67 grams; the remainder in a much larger dish weighing 117 

 grams. The results obtained with the latter were not as satisfactory as 

 with the smaller dish (2) (3) (5), although a qualitative examination of 

 the deposit and solution proved that the separation was complete (9) (12- 

 19). The distance between the poles materially influences the results. 

 In (6) the positive pole was in close contact with the dish ; the cadmium 

 contained zinc. In (9) the conditions were similar in all respects to the 

 preceding, except that the distance between the poles was 2.5 cm. ; the 

 deposit was free from zinc. With .2 c.c. OH gas per minute, only a 

 small quantity of the cadmium was separated (1), the greater portion re- 

 maining in solution. With 1.25 c.c, on the other hand, the zinc was 

 deposited as a dark -gray coating upon the cadmium (7), even in the pres- 

 ence of 35 c.c. of free acid (10). In solutions containing .10 grams of 

 each metal a current of .8-1 c.c. HO gas per minute sufficed to secure a 

 satisfactory deposit in the presence of 25 c.c. formic acid (12-19). "With 

 smaller quantities of metal (9) 15 c.c. of free acid was sufficient. The 

 deposits in the above experiments were adherent and compact. There was 

 no tendency to sponginess even in deposits containing large quantities of 

 zinc. 



