Examination of the hexamethylenetetramine procedure for separation of thorium from rare earths and for determination of thorium.
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.
Photochemical precipitation of thorium and cerium and their separation from other ions in aqueous solution.
Thorium was precipitated from homogeneous solution by exposing solutions of thorium and periodate in dilute perchloric acid to 253.7 nm radiation from a low-pressure mercury lamp. Periodate is reduced photochemically to iodate which causes the formation of a dense precipitate of the basic iodate of thorium(IV). The precipitate was redissolved, the iodate reduced, the thorium precipitated first as the hydroxide, then as the oxalate and ignited to the dioxide for weighing. Thorium(IV) solutions containing 8-200 mg of ThO(2) gave quantitative results with a standard deviation (s) of 0.2 mg. Separations from 25 mg each of iron, calcium, magnesium, 50 mg of yttrium and up to 500 mg of uranium(VI) were quantitative (s = 0.25 mg). Separations from rare earths, except cerium, were accomplished by using hexamethylenetetramine rather than ammonia for the precipitation of the hydroxide. Cerium(III) was similarly precipitated and converted into CeO(2) for weighing. Quantitative results were obtained for 13-150 mg of CeO(2) with a standard deviation of 0.2 mg. Separations from 200 mg of uranium were quantitative. Other rare earths and yttrium interfered seriously. The precipitates of the basic cerium(IV) and thorium iodates obtained are more compact than those obtained by direct precipitation and can be handled easily. Attempts to duplicate Suzuki's method for separating cerium from neodymium and yttrium were not successful.
Stigmatic Plane Grating Spectrograph with Order Sorter
A new plane-grating spectrograph has been developed to give in a compact mounting a stigmatic image, a nearly flat focal curve, and resolving powers greater than 300 000 at dispersions up to 0.2 A/mm. The performance of the instrument in the low orders is at least as good as that of a Wadsworth concave grating spectrograph of the same focal length. However, the upper wavelength limit is increased to 40 000 A or even 60 000 A, in the first order of a 7500-line/inch grating. At such settings the many overlapping orders are separated by an “order sorter,” a prism predispersor crossed with the grating dispersion. This makes it possible to obtain in a single exposure on 30 in. of plate the continuous wavelength range 2140 A to 6340 A at dispersions ranging from 0.44 A/mm to 1.1 A/mm.