1891.] 



115 



[Warwick. 



the anode, the platinum crucible serving as the negative electrode. In 

 (1) and (2) the cadmium was not completely deposited. Traces of cad- 

 mium were found in (6) and (7). More or less manganese was found in 

 all the deposits, but only in traces in the presence of more than 20 c.c. of 

 free acid ; (4) and (7) were very spongy ; the others were slightly so at 

 the periphery of the crucible, but adherent. The best results were 

 obtained by fulfilling the conditions described in (3), (4) and (8) ; but to 

 obtain a compact deposit of cadmium free from all traces of manganese, 

 it is evident that the amount of free acid must be increased and the poles 

 separated. Under these conditions, a stronger current must be employed 

 than that furnished by the battery of "crowfoot" cells, with which my 

 experiments were carried on. 



ZINC FROM MANGANESE. 



Zinc taken. 



Grams. 

 (I) .0562 



Zinc 

 found. 



Grams. 

 .0554 



Free 



acid. 



c.c. 



30 



20 



TT n OH gas TJ Difference 



H2 - per min. Time " from theory. 



c.c. 



90 



100 



c.c. 

 2.9 



Hours. 

 17 

 16 



Percentage. 



The dish served as anode, the crucible as kathode. Both were failures 

 the zinc being spongy and containing MnO 2 and not entirely precipitated. 



COPPER FROM ZINC. 



As will be seen from the above, it was possible to separate copper free 

 from zinc, except the slightest traces, by using a weak current in solutions 

 to which 15-20 c.c. of free formic acid had been added. By employing 

 stronger currents, or diminishing the amount of free acid, the copper was 

 deposited admixed w t ith considerable quantities of zinc. If the necessary 

 precautions are observed no zinc will be deposited, and the copper will 

 be compact and adherent. 



PKOC. AMER. PHILOS. SOC. XXIX. 136. P. PRINTED DEC. 21, 1891. 



