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The 1.0 to 2.5 per cent of sulfur normally present in rubber products is oxidized with concentrated nitric acid-bromine reagent, followed by perchloric acid in the presence of excess lead nitrate. Sulfur as lead sulfate is precipitated and washed with acetone. The lead sulfate is dissolved in 50 per cent hydrochloric acid, and absorbance of the lead chloride complex is recorded at 270 mµ. Sulfur is calculated on the basis of the measured lead content of the precipitate. The high sensitivity puts the method in the micro-range. An experienced analyst can analyze 40 to 50 samples a day. Precision and accuracy are comparable to those of the conventional barium sulfate gravimetric method at the low sulfur concentrations normally found in rubber products.

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