Abstract
An improved method is proposed for the determination of silica, magnesium oxide, R 2O 3, ferric oxide, calcium oxide, and aluminium oxide in high-purity talc. In the method for silica and magnesium oxide, the sample is fused with sodium carbonate and the cooled melt is dissolved with perchloric acid in such a manner that it floats free from the crucible (in previous schemes for the analysis of talc there are frequently mechanical losses due to the difficulty of removing the magnesium silicate melt from the crucible). The solution is then evaporated to fumes of perchloric acid and the silica is filtered off and ignited. The magnesium oxide is determined in the filtrate by precipitation as magnesium ammonium phosphate and a correction is made for the calcium which is precipitated along with the magnesium ammonium phosphate. R 2O 3 is determined after treatment of the sample with nitric and hydrofluoric acids and evaporation to fumes of perchloric acid. Iron oxide and calcium oxide are determined by atomic absorption, after treatment with nitric and hydrofluoric acids and evaporation to fumes of perchloric acid. Al 2O 3 is calculated by difference.
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