Warwick.] 



106 



[Nov. 6, 



and tin were not prepared, as they were not considered available for 

 various reasons. 



In order to ascertain the comparative accuracy of the results obtained 

 by means of the ordinary gravimetric methods, as compared with those 

 obtained by means of the current, a series of experiments was made with 

 the metals chosen for particular study. The gravimetric method adopted 

 was the same for all three, namely, estimation as oxide, conducted in the 

 ordinary way. 



COPPER (DETERMINED AS CuO). 



Copper formate Copper by theory, Copper in Difference in percentage 

 taken, in grams. in grams. CuO formed. from theoretical. 



(1) .8024 



(2) .7924 



(3) .7063 



(4) .7063 



.2252 

 .2226 



.1984 

 .1984 



.2261 

 .2232 



.1982 

 .1979 



-J-.39 per cent. 

 +.27 

 .10 

 .25 



The first two determinations were high, due perhaps to the efflorescence 

 of the salt. All subsequent weighings were done in a covered watch- 

 glass, and the results obtained corresponded closely with the theoretical. 



In the following electrolytic depositions of copper, solutions of copper 

 formate of known strength were used. 



COPPER (DETERMINED ELECTROLYTICALLY). 



Copper present 

 in solution. 



Copper 

 found. 



Free formic 

 acid. 



C.c. H 2 O. 



125 



(1) .1434 grams. 



(2) .1074 " 



(3) .0987 " 



(4) .0987 " 



(5) .1074 " 



(6) .1057 " 



(7) .1057 " 



(8) .1101 " 



In the above experiments a platinum dish was used at the negative 

 pole, and the wire spiral as the anode. A current of 0.8 1.60 c.c. HO 

 gas per minute was allowed to run over night. The poles were separated 

 2.5 cm. Before cutting off the current, the level of the liquid in the dish 

 was raised by the addition of water, and the current allowed to act for an 

 additional half hour. No further deposit of copper took place on the 

 clean surface of the dish, indicating that the metal was completely pre- 

 cipitated. The current was then discontinued, the liquid quickly poured 

 off, and the dish washed with hot water, being finally dried on a warm 

 iron plate at a temperature not exceeding 100 C. The dish was then set 



