J.G. Fairchild F.S. Crimaldi 1949 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. application/pdf 10.3133/70094925 en U.S. Geological Survey The U.S.G.S. phosphate-fluoride-iodate method for the determination of very small amounts of thorium in naturally occurring materials reports