362 



Peters — Volumetric Estimation of Cojyper. 



phate in 50 cm3 of water was thrown down by the addition of 

 dry oxalic acid to the hot solution, and, after standing over 

 night, the precipitate was filtered on asbestos, washed two or 

 three times with small amounts of cold water. The precipi- 

 tate, still in the crucible, was returned to the beaker in which 

 precipitation took place, 5 or 10 cm3 of dilute sulphuric acid 

 (1 : 1) were then added together with a convenient amount of 

 water, and, after heating the liquid to boiling, the oxalic acid 

 was titrated with permanganate, the oxalate of copper dissolv- 

 ing readily as fast as the excess of oxalic acid is removed by 

 the permanganate. The precipitate may also be dissolved in 

 10 cm3 of strong hydrochloric acid,* 0*5 gm. manganous chloride 

 added and titrated at 30°-50°. Experiments 4 and 5 were con- 

 ducted after this manner. In Table III, A, which follows, are 

 recorded results of the quantitative tests of the method. 









Table III. 









CuO 





Volume 









taken as 



Oxalic 



at precipi- 



CuO 







0uSO 4 . 



acid. 



tation. 



found. 



Error. 





gms. 



gms. 



cm 3 . 

 A 



gms. 



gms. 



1 



0-0372 



0-15 



100 



0-0286 



— 0-0086 



2 



0-1860 



0-50 



125 



0-1831 



— 0-0029 



3 



0-0398 



a 



50 



0-0376 



— 0-0022 



4 



0-1860 



1-0 



150 



0-1834 



— 0-0026 



5 



(i 



0-5 



50 



0-1864 



+ 0-0004 



6 



a 



a 



a 



0-1866 



+ 0-0006 



7 



a 



u 



(« 



0-1866 



+ 0-0006 



8 



(i 



1-0 



a 



0-1866 



+ 0006 



9 



0-0398 



a 



a 



0-0391 



— 0-0007 



In experiments 1-4, deficiencies are found in the amounts 

 of oxalate precipitated at different degrees of dilution and 

 by different amounts of the precipitant which are in agree- 

 ment with the results obtained in the preliminary work ; 

 the results of experiments 5-9, in which 0*5 grm. and 1-0 grm. 

 of oxalic acid act in a total volume of 50 cm3 , show the precipi- 

 tation to be essentially complete under these conditions. 

 - To study the insolubility of the copper oxalate in nitric acid 

 the experiments in Section B of the table were made. 



In experiments 10-13 amounts of oxalic acid varying from 

 0*5 gra. to 3'0 gms. appear to precipitate the copper completely 

 in the presence of 5 cm3 of strong nitric acid. In experiment 14 

 the amount of oxalic acid used was not sufficient to throw 

 down all the copper in the presence of 10 cm3 of nitric acid, but 



* Goocb and Peters, this Journal, vii, 461, 1899. 



