360 



Peters — Volumetric Estimation of Copper. 



both with ammonia and with potassium ferrocyanide. In cases 

 where the filtrate gave no blue color with ammonia and only 

 a slight precipitate with ferrocyanide the precipitation was con- 

 sidered practically complete and the conditions were regarded 

 suitable for the trial of the method quantitatively. In the fol- 

 lowing table is recorded the work upon the precipitation of 

 copper sulphate by 0*5 gm., 1*0 gm., and 2*0 gms. of oxalic 

 acid in 50 cm3 of solution. 



Table I. 

 Dilution 50 cm3 . 



Oxalic acid added in 

 solution. 



Oxalic acid added in 

 crystalline form. 



CuO 

 taken as 



CuS0 4 

 gms. 



2-0 gms. f 0-018 



Filtrate 



treated 



with 



NH 4 OH 



blue color 



oxalic 



acid 



present. 



1*0 gm. 



oxalic 



acid 



present. 



0'5 gm. 

 oxalic 

 acid, 

 present. 



0-031 trace 



blue color 



] 0-051 

 L 0-064 



r o-ois 



I 0-081 

 051 trace " 

 0-064 



0-094 



0-018 blue color 

 0-031 " 



0-051 trace " 



0-064 



0-094 



Filtrate 



treated 



with 



K 4 FeC 6 N 6 



abundant ppt. 



evident " 

 trace " 



abundant ppt. 



evident " 



trace " 

 abundant ppt. 



it u 



u u 



evident " 



trace " 



Filtrated 



with 

 NH 4 OE 



blue color 

 trace " 



blue color 

 trace " 



blue color 

 trace " 



Filtrate 



treated 



with 



K 4 FeC 6 N 6 



abundant ppt. 

 evident " 



it a 



trace " 



abundant ppt. 

 evident " 



trace " 



abundant ppt. 



evident 

 trace 



It will be seen readily by comparison of the right and left 

 band sides of the table above that somewhat smaller amounts 

 of copper may be precipitated completely by the addition of 

 crystallized oxalic acid than by the same amount of oxalic acid 

 already in solution. Thus, when dissolved oxalic acid is added 

 to the solution of 50 cm3 amounts of copper sulphate less than 

 0-040-0-050 gm. are not precipitated completely, while under 

 conditions otherwise the same excepting that the oxalic acid is 

 added in crystalline form, the precipitation of amounts as 

 small as 030 gm. is practically complete. The amount of 

 oxalic acid in solution necessary for the complete precipitation 

 (after 16 to 20 hours) of this minimum amount of copper, 

 0*031 gm. of copper oxide taken as the sulphate, appears, as 

 shown in Table II, A, which follows, to be about 3 - 5 gms. in 

 50'0 cm3 . If the amount of oxalic acid is increased to 5 gms., 

 making the solution saturated for that substance, using the 



