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An examination has been made of the efficiency of the gravimetric reagent hexamethylenetetramine in the separation of thorium from rare earths and in the determination of thorium. Losses to the filtrate, beaker and filter paper are evaluated as well as the extent of rare earth and other contamination of the thorium hydroxide precipitate. When hydroxylamine is used as the reducing agent to keep cerium in the tervalent state, excellent separations are obtained. The efficacy of the reagent is offset by the loss of small amounts of thorium to the precipitation vessel, the scavenging properties of the precipitate for silica and the difficulty in evaluating a true reagent blank.

Methods are proposed for the determination of submicrogram quantities of rare earth and yttrium oxides in thorium oxide by emission spectroscopy, without previous separation or concentration of these oxides in the sample. It is possible to volatilise these refractory materials from the thoria using silver chloride as the carrier. The carrier distillation technique in conjunction with relatively high dispersion spectroscopy (0.8-1.1 A/mm) makes possible analyses at levels which were previously only feasible by preconcentration methods (e.g., La(2)O(3) and Y(2)O(3), 5 ppm; Nd(2)O(3) and Sm(2)O(3) 10 ppm; CeO(2) and Pr(6)O(11), 20 ppm in a 10-mg sample of ThO(2)).