1891.] 107 [Warwick. 



aside for some time until it had acquired the temperature of the room and 

 weighed. The solutions failed to give any indication, except the merest 

 traces, of copper when tested with ferrocyanide of potassium. The 

 time varied from sixteen to forty-six hours without materially affecting 

 the result. No perceptible oxidation took place during drying, although 

 the deposit was somewhat dark. It came out as a compact adherent coat- 

 ing, readily dissolving in nitric acid. 



A comparison between the results obtained shows conclusively not only 

 that the deposition of copper from its formate solution can be accom- 

 plished, but that it is fully as accurate as the ordinary gravimetric method. 



ZINC (DETERMINED AS ZNO). 



Zinc formate taken, Zinc by theory, Zinc in zinc Difference in percentage 

 in grams. in grams. oxide found. from theoretical. 



(1) .5508 .1875 .1870 .26$ 



.(2) " " .1876 +.05 



(3) " " .1869 .31 



(4) .1872 .16 



The four determinations made by the usual gravimetric method were 

 estimated finally as zinc oxide which, for purposes of comparison, have 

 been converted into metal. 



ZINC (DETERMINED ELECTROLYTICALLY). 



The foregoing determinations of zinc formate were performed under a 

 variety of conditions. (1), (2), (3), (4) were made with the dish as cathode, 

 and the wire spiral as the positive pole ; the results both with and without 

 free acid were unsatisfactory, the deposit being very spongy and failing 

 to come out completely, as proved by testing the solution with potassium 

 ferrocyanide. The dish was then made the anode and the zinc was 

 allowed to separate on the platinum crucible which was made the negative 

 pole. The amount of free acid varied from 10 to 25 c.c. The deposit was 



PROC. AMER. PHILOS. SOC. XXIX. 136. O. PRINTED DEC. 14, 1891. 



