In the method previously described for the determination of trace amounts of beryllium in silicates, a double fusion of the sample with sodium hydroxide was made and beryllium was then determined Auorimetrically in the filtrates with morin as reagent'. This procedure gives satisfactory results when applied to silicic rocks such as granites, but, as already pointed opt, it is not suitable for basic rocks because of the retention of beryllium by iron, magnesium, and calcium in the fusion residue.
The method has now been improved so that it can be applied to basic rocks. The essential feature of the modified method is the elimination of iron, magnesium, calcium, and manganese in the following way. After the sample has been decomposed with hydrofluoric and sulphuric acids and brought into hydrochloric acid solution, mercaptoacetic (thioglycolic) acid is added, and an ammonium hydroxide precipitation is made. Aluminum and titanium, together with beryllium are thus precipitated, whereas the metals mentioned remain in solution. Ferrous iron forms a complex with mercaptoacetate which gives no precipitate with ammonia, and a separation of aluminum from iron based on this behavior has already been proposed by MAYR AND GDBAUIZR~.
The ammonia precipitate is then subjected to double fusion with sodium hydroxide to bring beryllium into solution. Good recoveries of beryllium are thus obtained since the residue consists essentially only of titanium oxide and such amounts of iron as may have been coprecipitated. The results obtained in applying the proposed method to subsilicic rocks as represented by two diabases and to a synthetic solution simulating a basic rock, containing from 2 to 8 p.p.m. of added beryllium, are uniformly slightly low, the worst result corresponding to 80% recovery of beryllium. The average recovery in these samples corresponds to approximately go%. Therefore, it seems reasonable to suppose that the method will give substantially correct values when applied to typical basic rocks in which the natural beryllium content is of the order of I p.p.m. as indicated by results of the analyses of composites. Although the method was developed with basic rocks especially in mind, it is believed to be more satisfactory than the previously described method for silicic rocks when results of the best accuracy are sought.