. Peters — Volumetric Estimation of Copper. 367 



of nitric acid when the larger amounts of ferric nitrate are 

 present. 



For a practical application of the above separation of copper 

 from iron a convenient amount of finely ground chalcopyrite 

 (05 gm.) was roasted 2-3 hours in a porcelain crucible until 

 all sulphur was driven off, washed into a beaker, strong nitric 

 acid about 5 cm3 was added and, with the beaker covered, 

 allowed to evaporate slowly on a hot plate, nearly to dryness. 

 A little dilute nitric acid was added, the solution was filtered, 

 the residue was washed with water containing dilute nitric 

 acid, the filtrate, about 50 cm3 in volume, was precipitated with 

 2*0 gms. oxalic acid, and the precipitate was estimated after 

 standing 12-16 hours, as previously described. The washing 

 with water acidified with nitric acid is important because the 

 finely ground ferric oxide remaining undissolved passes through 

 the filter when washed with water alone, but gives no trouble 

 if the water be acidic. The results of two estimations are here 

 given. 



ilcopyrite. 

 gms. 



Copper found 

 by battery. 



Copper found by 

 oxalate method. 



Difference. 



0-5000 



31-00^ 



30-92$ 



— 0-08$ 



1-0000 



a 



31-25 



+ 0-25 



Separation of Copper from Zinc. 



The separation of copper from zinc was not altogether suc- 

 cessful owing to the tendency of the zinc oxalate to come 

 down with the copper oxalate. Some experiments are given 

 in section M of the table. 



The separations of copper from bismuth and antimony were 

 unsuccessful. 



The work maybe briefly summarized as follows: Copper 

 exceeding in amount the equivalent of O0128 gm. of the 

 oxide to 50 cm3 of solution as the sulphate may be separated 

 completely, even in the presence of a moderate amount of 

 strong nitric, by the addition of sufficient amount of oxalic 

 acid. 



Copper may be separated from cadmium, arsenic, iron, and 

 small amounts of tin, when precipitated by oxalic acid in a 

 volume of 5O0 cm3 containing 5 cm3 strong nitric acid. Inasmuch 

 as the completeness of precipitation of the copper depends 

 upon the presence of a certain minimum amount of the cop- 

 per salt this method is not applicable when the amount of 

 copper falls below - 0128 gm. of the oxide to 50 cmS of solution. 



The author wishes to thank Professor F. A. Grooch for much 

 kind help given in the preparation of this paper. 



