

On the Occurrence of Gallium in Clay-ironstone. 403 



reduce the iron to the ferrous state. This operation was unsuccessful, 

 a quantity of iron remaining in the ferric state. The solution N 

 was, therefore, added and the mixture evaporated that the moro 

 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. Bat, to avoid inaccuracy, the best although more 

 troublesome process seemed to be the precipitation of the phos- 

 phates 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 filtrate, the pre- 

 cipitate R being slightly darker than P. Filtrate Q, 



Small quantities of the three residues, 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 S, small in 

 quantity and of a dark green colour, was removed by nitration. It 

 contained only a trace of gallium. 



The precipitates and S, containing a much larger proportion of 

 iron than P and R, were dissolved in hydrochloric acid, and the 



