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



the copper as oxalate by precipitation and titration without 

 first filtering off the sulphate of lead. In this case the sulphate 

 is precipitated as before, the solution heated to boiling and 

 oxalic acid added. The sulphate and oxalate are then filtered 

 off together, heated to boiling with dilute sulphuric acid and 

 the oxalate titrated with permanganate. 



Summary. 



It has been shown in this paper that copper may be 

 estimated in the presence of cadmium by precipitation as 

 oxalate, in the presence of nitric acid and subsequent evapo- 

 ration to dryness, the residue then being extracted with nitric 

 acid, and the oxalate filtered off and titrated with potassium 

 permanganate. A still more accurate determination is obtained 

 by precipitation of the oxalate in the presence of a large 

 amount of free acetic acid and small amounts of free nitric 

 acid. 



Copper may be separated from arsenic in the higher condi- 

 tion by the same methods as are applicable in the presence 

 of cadmium. 



Copper may be separated from small amounts of iron by 

 desiccation of the oxalate in the presence of nitric acid and 

 extraction with dilute nitric acid. A better method and one 

 more universally applicable is to precipitate the copper by 

 adding oxalic acid to the water solution of the salts of 

 iron and copper and adding two volumes of acetic acid to 

 separate the small amount of copper remaining in solution. 



Copper associated with lead may be estimated by first pre- 

 cipitating the latter metal with sulphuric acid in a solution 

 containing a large amount of free acetic acid and then throwing 

 out the copper by oxalic acid (either before or after filtration), 

 and determining the copper by titration in the usual manner. 



