Peters — Volumetric Estimation of Copper. 



361 



same volume of liquid, the minimum amount completely pre- 

 cipitable is reduced to 0*0128 gms. but not to one-half that 

 amount. 



Table II. 



Oxalic A 

 CuO acid Volume Filtrate Filtrate 



taken as added in at precipi- treated treated 



CuS0 4 solution. tation. with with 



gms. gms. cm 3 . NH 4 OH. K 4 FeC 6 N 6 . 



0031 0*5 50 blue color abundant ppt. 



(C T.Q it U U (( 



" 2-0 " trace " " " 



" 3-0 " slight " " " " 



" 3-5 " evident « 



0-0128 5-0 " no blue trace " 



0-0064 5-0 " blue color abundant " 



B 

 0-0064 0-5 20 faint blue abundant ppt. 



" " 10 " faint " 



" " 5 trace " 



0-0003 0-5 5* 



" 0-1 If 



It appears from the experiments of Table II, B, that the 

 volume of liquid in which precipitation takes place influences 

 the complete precipitation of the copper oxalate. Thus the 

 precipitation of 0*0064 gm. of copper oxide taken as the sul- 

 phate by 0*5 gm. of oxalic acid is complete in 5 cm3 of liquid. 

 The precipitate which falls from 0*0003 gm. of the oxide 

 taken as the sulphate dissolves in 5 cm3 of liquid, but remains 

 visible in l cm3 . 



As a result of the preliminary experiments, it may be said 

 that the presence of a certain minimum amount of copper, 

 varying with the conditions, is essential to complete precipita- 

 tion. Thus, at a dilution of 50 cm3 a saturated solution of oxalic 

 acid will precipitate with practical completeness copper taken as 

 the sulphate in amounts exceeding the equivalent of 0*0128 gm. 

 of copper oxide ; that 2*0 gms. of oxalic acid will precipitate 

 almost completely for the same volume of solution the equiva- 

 lent of 0*03 gm. of copper oxide ; and that 1*0 gm. or 0*5 

 gm. of oxalic acid will precipitate the equivalent of 0*064 gm. 

 of the oxide. 



In the quantitative separation of copper as the oxalate the 

 method of treatment was in general as follows. Copper sul- 



* Precipitate redissolved. 

 f Precipitate remained. 



