reduce the iron to the ferrous state. This operation was unsuccessful, a quantity of iron remaining in the ferric state. The N was, therefore, added and the mixture evaporated that the more volatile acids might be expelled by the sulphuric acid. On adding water to the residue a small quantity of matter remains undissolved ; it was removed by filtration. Residue M.
Up to this stage no reagent had been used which was likely to contain gallium, and we had to consider which of the processes known to separate gallium would be suitable under the conditions of our analysis. The simplest would have been to boil with iron or zinc, but gallium is found associated with both of these metals, and it was decided not to use them. Precipitation by barium carbonate would have been easily effected if sulphuric acid had not been present in such quantity. But, to avoid inaccuracy, the best—although more troublesome process—seemed to be the precipitation of the phosphates of the sesquioxide metals in an acetic acid solution, there being phosphoric acid already in the liquid. The precipitates should contain all the gallium, chromium, and aluminium as phosphates and some phosphate of iron. The gallium is easily separated from chromium and iron by fusion with caustic soda, and from phosphoric acid, aluminium, and chromium by precipitation with potassium ferrocyanide.
The iron was first reduced by passing sulphur dioxide into the solution until it became strongly charged, and heating to boiling, with addition of ammonia, to neutralise the excess of free acid. The addition of ammonia was continued until the white precipitate which formed remained undissolved after boiling for two or three minutes. Boiling water was then added to make the volume of the solution about four litres; this dilution caused a large quantity of light coloured precipitate to form. Ammonium acetate was added, and the liquid, after boiling for several minutes, filtered.
Residue 0 .—The filtrate was boiled and ammonium carbonate added until a quantity of pale, greenish-coloured precipitate was deposited. More ammonium acetate was added, and the liquid, still acid with acetic acid, was filtered. Residue P.
The process just described was repeated with the , the precipitate R being slightly darker than P. Filtrate Q.
Small quantities of the three r, 0 , P, R, were examined spectrographicaily. The gallium lines are strongest in R. The filtrate Q was again boiled with addition of ammonium carbonate to neutralise some of the excess of acid, and the precipitate , small in quantity and of a dark green colour, was removed by filtration. It contained only a trace of gallium.
The precipitates 0 and S, containing a much larger proportion of iron than P and P, were dissolved in hydrochloric acid, and the
