Spectrophotometric determination of silicon in ferrophosphorus

A method is described for the spectrophotometric determination of 0-4% silicon in ferrophosphorus, following fusion with sodium peroxide in a zirconium crucible. Silicomolybdic acid is formed with sodium molybdate. The acidity is increased to 2N and the solution stood for 10 min to destroy phosphomolybdic and arsenomolybdic acids. The silicomolybdic acid is reduced with ascorbic acid and the absorbance measured at 810 nm. The colour is stable, and a standard deviation of 0.006% was achieved for 0.7% silicon. Results obtained for three samples with alternative procedures are compared.