Peters — Volumetric Estimation of Copper. 359 



Aet. XXXVI. — The Volumetric Estimation of Copper as the 

 Oxalate, with Separation from Cadmium, Arsenic, Tin, 

 and Zinc ; by Charles A. Peters. 



[Contributions from the Kent Chemical Laboratory of Tale University — XCVIIL] 



It is a well known fact that copper oxalate is insoluble in 

 water and scarcely attacked by moderate amounts of dilute 

 nitric acid.* Upon this fact Bournemannf has recently based 

 a method for the separation of copper from cadmium by pre- 

 cipitating copper as the oxalate in the presence of nitric acid, 

 filtering hot, and estimating the copper after ignition, by any 

 of the well known gravimetric methods. Six to ten grams of 

 copper, as the oxide, were used for a single determination, and 

 the errors were large. Bournemann does not recommend this 

 process as an accurate analytical method. Classen^: describes a 

 method for the separation of metals as oxalates by adding to 

 the solution of the salt of the metals a dilute solution of the 

 potassium oxalate (1 : 6) and concentrated acetic acid to 80 per 

 cent of the total volume. Regarding copper salts in particular, 

 Classen states that precipitation takes place only in dilute solu- 

 tion and then not completely. 



It has been the experience of the writer, that the precipita- 

 tion of copper oxalate from solutions containing at least 0*0128 

 gm. of the oxide and saturated with the oxalic acid is practi- 

 cally complete. The filtrate in such cases gives no blue color 

 with ammonia, looking down on a column of liquid in a test 

 tube, and only a faint brown color is developed when the fil- 

 trate is neutralized, made acid with acetic acid, and tested with 

 potassium ferrocyanide. It is the object of this paper to show 

 that moderate amounts of copper may be determined quantita- 

 tively as the oxalate by precipitation with oxalic acid and titration 

 of the precipitate by potassium permanganate, and also to show 

 that moderate amounts of copper may be separated from other 

 metals in the presence of nitric acid, by the addition of con- 

 siderable amounts of oxalic acid. 



Before attempting the quantitative separation of copper 

 from solution by the addition of oxalic acid a few qualitative 

 experiments upon the precipitation of varying amounts of 

 copper sulphate by varying amounts of oxalic acid were tried 

 at different dilutions. In all the experiments the mixtures 

 stood 16-20 hours, and were filtered from 2 to 1 times through 

 four filters folded together, and the filtrates were tested 



* Storer, Dictionary of Chemical Solubilities, p. 463. 

 f Chem. Ztg., xxiii, 565. 

 JBer., x, b, 1316. 



Am. Jour. Sci. — Fourth Series, Vol. X, No. 59.— November, 1900. 

 24 



