4:48 Gooc/i and Ward — Copper Oxalate in Analysis. 



Art. XXXIX. — The Precipitation of Copper Oxalate in 

 Analysis / by F. A. Gooch and H. L. Ward. 



[Contributions from the Kent Chemical Laboratory of Yale Univ. — cxcix.] 



It has been shown by Peters, in a paper from this laboratory 

 on the volumetric estimation of copper as the oxalate,* that 

 copper oxalate may be precipitated by oxalic acid with practical 

 completeness from solutions of copper sulphate, provided the 

 volume of the liquid is not too great and that the amount of 

 copper present in solution exceeds a certain minimum value. 

 It was shown that when the amount of copper present falls 

 below a certain minimum either precipitation does not take 

 place or it is incomplete. It was noted that the minimum was 

 variable with the concentration of the precipitant, oxalic acid, 

 and to some extent dependent upon the condition of the pre- 

 cipitant, the minimum being smaller when the oxalic acid was 

 added in crystalline form rather than in solution to the liquid 

 containing the copper salt. Peters' observations in respect to 

 the effect, concentration and condition of the oxalic acid in 

 solution of 50 cm3 are summarized in the following statement : 



Minimum amount 



of copper, taken as 



the sulphate, which 



must be present in 



order that nearly 



complete precipitation 



may take place Ci 



grm. 



Amount of oxalic 

 acid used. In 

 ;ystalline solution 

 grm. grm. 



Volume of 



liquid 



cm 3 . 



o-oio 



5 



6f 



50 



0-025 



2 



3-5 



50 



0-040 



1 





50 



0-050 



0-5 



._ 



50 



f Saturated solution poured upon the copper salt dissolved in the least 

 amount of water. 



It was also noted that when a saturated solution of oxalic 

 acid, containing 0*1 grm. of oxalic acid to l cm3 , was slowly added 

 to a drop of the copper solution containing 0*0003 grm. of cop- 

 per the precipitated oxalate first formed dissolved completely 

 in a volume of 5 cm3 of the precipitant. 



In the procedure for the quantitative determination of cop- 

 per by precipitation as the oxalate, Peters recommends a volume 

 of 50 cm3 , with 0*5 grm. to 2 grm. of crystallized oxalic acid as the 

 precipitant for 0*15 grm. of copper. An increase of the oxalic 

 acid beyond this degree up to the point of saturation of the 

 solution is apparently without effect. In subsequent work 



* This Journal, x, 359, 1900. 



