The U.S.G.S. phosphate-fluoride-iodate method for the determination of very small amounts of thorium in naturally occurring materials

Detailed procedures are presented for the determination of very small percentages of thorium. The methods are designed to determine 0.001% of thorium oxide as the lower limit and are applicable to nearly all types of rocks. For quantities below a milligram of ThO₂, the thorium is determined nephelometrically as the iodate or photemetrically with p-dimethylamineasephenylarsonic acid. For quantities of thorium above one milligram of ThO₂, the thorium is determined gravimetrically. A discussion of the important feature of the methods and a summary of the more important experimental work that lead to the adoption of the procedures.