A convenient field test has been developed in the Geological Survey for the detection and semi-quantitative estimation of phosphate in phosphate rocks. The basis of the test is the yellow phosphovanadomolybdate color which has been used for the determination of phosphorus in a variety of materials (Mission 1908). Materials containing wavellite or pseudowavellite must first be decomposed in boiling sulfuric and nitric acids to make the test, but tests for apatite may be made by merely shaking the finely ground sample with the nitric acid solution of the reagent. Although the test was devised to distinguish between samples containing 5, 15 and 30 per cent P2O6, it was found capable of giving results to the nearest 5 per cent. Interfering ions such as arsenic are not normally present in sufficient quantity to need consideration. Occasionally the samples must be ignited to remove organic matter.

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