酢酸ブチルによるクロームの抽出とその定量について

There are a few studies on the extractions of metals from their inorganic salt solutions with immissible organic solvents ; it is familiar to extract Cr as a perchromate from its acidic solution with diethylether or ethylacetate (M. D. Foster , U. S. Geol. Survey Bull., 950. 15 (1946) ). We tried with butylacetate, extracting the perchromate from the solutions which are obtained, oxidizing CrCl_3 solution witn NaOH and Na_2 O_2 or with NH_4 OH and H_2 O_2 in various concentrations of HCl and H_2 O_2.
The extracting power (%) is calculated mediately, measuring the residual Cr in the apueous solution after extraction ; in both cases, the 30% and 8% of Cr are extracted respectively. In the quantitative analysis of the residual solution, it is done by the Mohr' s salt-KMnO_4 method, giving that the end points of titration witn a normal solution of KMnO_4 are not so clear owing to the obscuring by the biproductive substances such as NaCl and Na_2SO_4 or NH_4Cl and (NH_4)_2SO_4, and found that the color change at the end point of titration is puitely sharp, when the original CrCl_3 solutions are treated with NH_4 OH and H_2 O_2 producing (NH_4)_2 CrO_4 and the residual solutions after extraction are evaporated and calcined, rejecting organic solvent and the most part of NH_4Cl and (NH_4)_2SO_4.
Titrations should be done at the temperature not over 30℃, using acidic KMnO_4 solution of 0. 12-N H_2SO_4.