410 B. B. Biggs — Separation of Chromium from Iron, etc. 



until oxidation seemed* complete. This required from five to 

 fifteen minutes : the more dilute the solution the longer the 

 operation. 5 CCS - of the peroxide was sufficient for the oxida- 

 tion. 



The availability of hydrogen peroxide, as an oxidizing agent, 

 having been determined, the influence of its presence on the 

 iron and the effect of dilution, on the solubility of aluminium 

 hydroxide in sodium hydroxide solutions, remained to be ascer- 

 tained. Filtrates from ferric hydroxide, which had been 

 digested in sodium hydroxide solutions containing hydrogen 

 peroxide, gave no sign of the presence of iron except to the 

 sulphocyanide test, showing the influence to be rather favor- 

 able than otherwise. 



In determining the effect of dilution on the solubility of 

 alumina, quantities of the hydroxide, equivalent to 0*05 grm. 

 of the element, were severally treated with 0*5 grm. of sodium 

 hydroxide in solutions varying in volume from 50 to 500 c-cs * 

 In every case solution was effected within five minutes. The 

 influence of dilution was however appreciable. 



Experiments, made, to test the practical workings of the 

 method, on mixtures of the three substances, confirmed the 

 observations made in connection with their separate treatments, 

 except that the presence of large quantities of iron hinders 

 somewhat both the oxidation of the chromium and the solu- 

 tion of the aluminium. As to the limits of the method the 

 impurities, of even the best of available reagents, render the 

 detection of very small amounts of either iron or alumina 

 uncertain. In mixtures, containing the equivalents of 0'2 

 m.grm. each of iron and chromium, and 0*5 m.grm. of alu- 

 minium, separations were made and the several constituents 



* In a majority of the experiments, in the more concentrated solutions, the 

 precipitates disappeared quickly and completely. Where it was necessary to con- 

 tinue the heating for more than ten minutes, there remained an unoxidizable 

 residual which increased rather than diminished on further heating. In all cases 

 prolonged digestion resulted in a precipitation of what proved to be silica. The 

 amount of this precipitate was found to be proportionate to the quantity of per- 

 oxide added and the following experiments showed that it came from the corro- 

 sive action of an alkaline solution of the peroxide on the glass. 50 C-C8- of water, 

 containing 1 grm. of sodium hydroxide, digested for an hour in glass, remained 

 clear to the end. 50 C-C8- of hydrogen peroxide, similarly heated, remained clear, 

 evaporating quietly. 50 c-cs- of the peroxide, containing - 5 grm. of sodium 

 hydroxide, was also similarly digested (the alkaline solution effervesces energet- 

 ically on being heated). In fifteen minutes the solution had become perceptibly 

 clouded. At the end of an hour, the effervescence having ceased, a considerable 

 precipitate had formed. From 200 c - c8- of the peroxide, containing 2 grm. of 

 sodium hydroxide, 4 m.grm. of silica (carrying a trace of iron) were obtained. 

 500 C-C8- of the peroxide, containing 5 grm. of sodium hydroxide, heated in plati- 

 num for an hour, remained perfectly clear. 



The reagents used were Roseugarten's 15 per cent hydrogen peroxide. 500 e '" - 

 of which gave, on evaporation, a residue of - 2908 grm. (silica 0-1067 grm.,. 

 alumina 02 grm.,) and sodium hydroxide made from sodium. 



