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



The Separation of Copper from Iron as the Oxalate. 



To secure the complete precipitation of copper in the pres- 

 ence of iron the first method tried was evaporation to dryness, 

 carried out exactly as in the case of arsenic. No nitric acid 

 was used on precipitation and the residue was extracted with 

 very dilute acid, after the addition in most cases of crystallized 

 oxalic acid other than that nsed in the precipitation. The 

 results of experiments appear in Table VI. It is plain that 

 when only a moderate amount of iron is present the copper 

 may be estimated with a fair degree of accuracy, but when the 

 iron much exceeds 0*16 grm., the figures show, not an increase 

 due to the inclusion of the oxalate of iron, as would be ex- 

 pected, but a loss in copper due to incomplete precipitation. 

 The filtrate also gives a test for copper. The method, there- 

 fore only gives satisfactory results when not more than - l 

 grm. of iron is present. 



Table VI. 

 Separation of Copper from Iron by Desiccation and Extraction. 

 Oxalic Diki- Nitric Oxalic 





Volume 



acid 



tion 



acid 



acid 











at 



on 



on 



on 



on 







Copper 

 pre- 

 sent 



Iron 

 pre- 

 sent 



preci- 

 pita- 

 tion 



preci- 

 pita- 

 tion 



ex- 

 trac- 

 tion 



ex- 

 trac- 

 tion 



ex- 

 trac- 

 tion 



Copper 

 found 



Error 



grm. 



grm. 



cm 3 



grm. 



cm 3 



cm 3 



grm. 



grm. 



grm. 



0-0504 



0-0393 



50 



1 



50 



q 



2 



0-0500 



— 0-0004 



0-0504 



0-0393 



50 



1 



50 



2 



2 



0-0501 



— 0-0003 



0-0504 



0-0393 



50 



1 



50 



2 



2 



0-0499 



-0-0005 



0-0504 



0-0786 



50 



1 



50 



2 



2 



0-0499 



— 0-0005 



0-0511 



o-iooo 



50 



1 



50 



5 



3 



0-0506 



— 0-0005 



0-1533 



o-iooo 



50 



1 



50 



5 



3 



0-1527 



— 0-0006 



0-0051 



0-1572 



50 



2 



50 



5 



2 



0*0036 



— 0-0015 



0-0504 



0-1572 



50 



1 



50 



2 



2 



0-0497 



— 0-0007 



0-0504 



0-1572 



50 



1 



50 



2 



2 



0-0597 



— 0-0007 



0-1542 



0-1572 



50 



4 



50 



5 



4 



0-1524 



— 0-0018 



0-0511 



0-2000 



50 



1 



50 



5 



3 



0-0475 



— 00036 



0-0511 



0-2000 



50 



1 



50 



5 



3 



0-0475 



— 0-0036 



0-0511 



0-2000 



50 



3 



50 



5 



3 



0-0491 



— 0-0020 



0-0511 



0-3404 



50 



4 



50 



5 



4 



0*0482 



-0-0029 



The effect of precipitation in a solution containing one-half 

 its volume of glacial acetic acid is shown in Table VII. 



It appears that when no nitric acid is present, the errors 

 are positive, indicating that some of the iron comes down 

 with the copper. When, however, the solution contains much 

 free nitric acid, losses appear and these losses increase with 

 the amount of nitric acid present. It is evident, therefore, 

 that the solution should not be strongly acid with both these 

 acids at precipitation. 



