H. L. Ward — Oxalate- Permanganate Process. 431 



The Determination of Copper Associated with Lead. — 

 The oxalate of lead, though fairly soluble in nitric acid, shows 

 a tendency to be included in the precipitation of an oxalate 

 which is insoluble in that acid. For this reason it was found 

 impossible to separate copper from lead as oxalate, even in a 

 solution very strongly acid with nitric acid. It has been shown 

 in a previous paper* that copper oxalate is insoluble in a 10 

 per cent solution of sulphuric acid containing one-half its vol- 

 ume of acetic acid and a large excess of oxalic acid. The 

 method proposed, therefore, is to add to a solution of lead and 

 copper as nitrates an equal volume of acetic acid and then from 

 3 to 5 cm3 of sulphuric acid. Under these conditions the lead is 

 completely precipitated as the sulphate and may be filtered off 

 and weighed as such. The filtrate is then evaporated somewhat, 

 a little more acetic acid added and the copper estimated as 

 the oxalate in the usual manner. The results are shown in 

 Table X. 











Table X. 













The Separation 



of Copper and Lead. Both determined. 













Volume 











>pper 

 esent 



Lead 

 present 



Sul- 

 phuric 

 acid 



Acetic 

 acid 



at pre- 

 cipita- 

 tion 



Oxalic 

 acid 



Copper 

 found 



Error Lead 

 copper found 



Error 

 lead 



grm. 



grm. 



cm 3 . 



cm 3 . 



cm 3 . 



grm. 



grm. 



grm. grm. 



grm. 



0511 



0-0500 



3 



50 



110 



2 



0-0513 



+ 0-0002 0*0499 



—o-oooi 



0511 



0*1000 



5 



50 



100 



2 



0-0508 



— 0-0003 0-0996 



— 0-0004 



0511 



o-iooo 



5 



50 



100 



2 



0-0508 



— 0-0003 0-0997 



— 0-0003 



Since the lead sulphate does not interfere with the perman- 

 ganate titration, it is possible, as shown in Table XI, to estimate 









Table 



XI. 









Determination of Copper 



in Presence of Lead. Lead not determined. 







Sul- 













Copper 



Lead 



phuric 



Acetic 



Dilu- 



Oxalic 



Copper 





present 



present 



acid 



acid 



tion 



acid 



found 



Error 



grm. 



grm. 



cm 3 . 



cm 3 . 



cm 3 . 



grm. 



grm. 



grm. 



0-0511 



o-io 



5 



50 



100 



2 



0*0508 



— 0-0003 



0*1533 



0-20 



5 



50 



100 



2 



0*1527 



— 0-0006 



0-1533 



0-20 



5 



50 



100 



2 



0-1530 



— 0-0003 



0-0511 



0-25 



5 



50 



100 



2 



0-0511 



±0-0000 



0-1086 



0-25 



5 



50 



100 



4 



0-1081 



— 0-0005 



0-0051 



0-30 



5 



50 



100 



4 



0-0052 



+ 0-0001 



0-0511 



0-30 



5 



50 



100 



4 



0*0508 



-0-0003 



0-0543 



0-30 



10 



50 



100 



4 



0-0537 



— 0-0006 



0-1022 



0*30 



10 



50 



100 



o 



0-1018 



— 0-0004 



0-0511 



0*40 



3 



50 



100 



2 



0-0509 



— 0-0002 



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



