H. L. Ward — Oxalate-Permanganate Process. 425 



The first process used for the separation of copper and cad- 

 mium is as follows : To the boiling concentrated solution of 

 the nitrates or sulphates of copper and cadmium, containing 

 5 0m3 of strong nitric acid, is added 4 grms. of crystallized oxalic 

 acid. The solution is evaporated to dryness on the steam bath 

 and the residue is taken up with cold water containing nitric 

 acid, it being unnecessary to heat the acid to bring about the 

 solution of the cadmium. The precipitate is transferred to 

 the perforated crucible by means of the filtrate and washing 

 is done with small amounts of water. The crucible is then 

 placed in a beaker containing about 25 cm3 of dilute (1:4) sulphu- 

 ric acid and 20Q cm3 of water heated to boiling, and the dissolved 

 oxalate is titrated with permanganate. It is necessary to use 

 a large excess of oxalic acid in the precipitatiou, for some of 

 it is destroyed by the nitric acid on evaporation to dryness. 

 It will be seen from Table II that when 10 per cent nitric acid 

 is used in extraction, the errors, while all negative, are within 

 permissible limits. On using 20 per cent acid, however, a 

 considerably greater amount of oxalate goes into solution. 

 This process, at best, is not extremely accurate. 











Table II. 











Separation of Copper from Cadmium 



by Desiccation and Extraction. 





Copper 

 >resent 



Cad- 

 mium 

 present 



Nitric 

 acid on 

 precipi- 

 tation 



Volume 



at 

 precipi- 

 tation 



Oxalic 

 acid 



Liquid 

 used in 

 extrac- 

 tion 



Nitric acid 

 used in 



extrac- Copper 

 tion found 



Error 



grm. 



grm v 



cm 3 



cm 3 



grm. 



cm 3 



cm 3 



grm. 



grm. 



)'0514 



0*01 



5 



50 



4 



50 



5 



0-0507 



— 0-0007 



)-0514 



0-06 



5 



50 



4 



50 



5 



0-0506 



— 0-0008 



)-0051 



o-io 



5 



50 



4 



50 



5 



0-0048 



— 0-0003 



)*0504 



o-io 



5 



50 



4 



50 



5 



0-0502 



— 0-0002 



)*0514 



o-io 



5 



50 



4 



50 



5 



0-0508 



— 0-0006 



)'0514 



0-20 



5 



50 



4 



50 



5 



0-0508 



— 0-0006 



)'1542 



0-20 



5 



50 



4 



50 



5 



0-1537 



-0-0005 



)'0516 



0-30 



5 



50 



4 



50 



5 



0-0507 



-0-0009 



)'0504 



o-io 



5 



50 



2 



50 



10 



0-0488 



— 0-0016 



)-0504 



o-io 



5 



50 



4 



50 



10 



0-0494 



—o-ooio 



)-0514 



0-20 



5 



50 



4 



50 



10 



0-0500 



— 0-0014 



It has been shown in the previous paper* that copper may 

 be precipitated very completely from solutions of its salts by 

 oxalic acid, provided one-half the volume of the solution con- 

 sists of glacial acetic acid, and that considerable amounts of 

 nitric acid may be present without causing appreciable error. 

 In separating copper from cadmium by this second process, pre- 

 cipitation is brought about by oxalic acid in a solution one-half 



* This Journal [4], xxvii, 448, 1909. 



