1S91.] 



117 



[Warwick. 



Copper from Cadmium. 



Copper 

 taken. 



Grams. 

 .1074 



Cadmium 



taken. 



Grams. 



.0984 



Metal 



deposited. 



Grams. 



.2061 



Free 

 acid, 

 c.c. 

 10 



H 2 0. 



c.c. 



100 



OH gas 



per miu. 



c.c. 



Time. 



Difference 

 from theory 

 Hours. Percentage. 

 17 



This result was not unexpected, considering what we have already 

 learned in regard to the behavior of these metals. The deposit was very 

 dark and spongy. Both metals were completely precipitated. Two sub- 

 sequent experiments were equally unsatisfactory ; in one the current was 

 reduced to .3 c.c. OH gas per minute ; in the other, 25 c.c. of formic acid 

 was added. No separation was effected. 



Copper from Iron. 



Although free acid was present in considerable quantity (25 c.c), the 

 formate of iron in the solution was decomposed with the formation of 

 ferric hydrate, which separated as a light yellow froth on the surface of 

 the solution. It also formed crusts at the edge of the copper deposit, 

 which adhered to the dish with such tenacity that all attempts at removal 

 by mechanical means were failures. Mere washing was without avail, 

 and more energetic measures resulted in a loss of copper, (1) and (4). 

 Dilute hydrochloric acid was added to (2) ; but, while it dissolved traces 

 of copper, it failed to remove the deposit of iron hydrate. Dilute sul- 

 phuric acid was also tried without success (3). In the final determina- 

 tion 20 c.c. of concentrated oxalic acid was added at the end of seventeen 

 hours and the current allowed to act one hour longer. The froth floating 

 on the surface was dissolved, but the deposit on the copper was not 

 appreciably affected. Except at the periphery the copper had a bright 

 metallic lustre and was firm and adherent. 



Cadmium from Iron. 



The same trouble was experienced here. Similar attempts were made 

 to remove the iron, but without success. In the first of the above deter- 

 minations 10 c.c. of oxalic acid solution was added before the conclusion 

 of the experiment ; in the latter, 20 c c. of the same solution. 



