H. L. Ward — Oxalate- Permanganate Process. 423 



Art. XXXV. — The Oxalate -Permanganate Process for the 

 Determination of Copper Associated with Cadmium, 

 Arsenic, Iron, or Lead ; by H. L. Ward. 



[Contributions from the Kent Chemical Laboratory of Yale Univ. — ccxxx.] 



It has been shown by Peters* in a paper from this labora- 

 tory that copper oxalate may be precipitated by oxalic acid 

 with practical completeness from solutions of a copper salt, 

 provided the volume of the liquid is not too great and that 

 the amount of copper present exceeds a minimum value, some- 

 what dependent on conditions. Still more recently, it has been 

 shown f that the condition of supersaturation, which is respon- 

 sible for failure in the precipitation of minimum amounts of 

 copper oxalate, may be easily overcome by freezing the solu- 

 tion, by addition of alcohol to the amount of 50 per cent of the 

 solution, and, in a higher degree, by evaporation to dryness or 

 by the addition of large amounts of acetic acid. The best and 

 most convenient procedure for the precipitation of large as 

 well as small amounts of copper oxalate ideal in composition, con- 

 sists in adding 2 grms. of oxalic acid to 50 cm3 or 4grms. to 100 cm3 

 of the 50 per cent acetic acid solution of the copper salt con- 

 taining 5 to 10 per cent of nitric acid. The permanganate 

 titration of the washed oxalate, in the presence of sulphuric 

 acid, gives a very accurate determination of the copper. 



The present paper is an account of attempts to apply the 

 latter two processes in separations of copper from cadmium, 

 arsenic, and iron, and in the determination of copper after sep- 

 arating the lead as sulphate. 



In the experiments of the first part of Table I a standard 

 solution of copper sulphate was treated with one gram of oxalic 

 acid, added in the solid form to the boiling solution of about 

 50 cm3 volume, and the liquid was then evaporated on the steam 

 bath. Extraction was made with the amounts of nitric acid 

 indicated and water to make up a volume of 50 cm3 . The liquid 

 was then boiled for 10 minutes in contact with the precipi- 

 tate and allowed to cool. The oxalate was collected upon 

 asbestos in a perforated crucible and washed carefully with 

 small amounts of water. The crucible with its contents was 

 placed in a beaker and covered with about 200 cm3 of hot water, 

 containing 25 cm3 of dilute sulphuric acid (1 : 4), and approxi- 

 mately N/10 potassium permanganate of known standard 

 added to coloration. 



* This Journal [4], x, 359. 



f Gooch and Ward, ibid. [4], xxvii, 448. 



