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Vanadium(lV) and vanadium(V) in the presence of 2-hydroxyacetophenone oxime were extracted quantitatively into chloroform in the pH ranges 3.6-4.5 and 2.7-4.1, respectively. The organic layer showed absorbance maxima at 345 and 350 nm for V I V and VV, respectively. Studies of the behaviour of V'V were also carried out a t a wavelength of 350 nm. Vanadium(V) absorbed considerably beyond 380 nm whereas Viv had negligible absorbance in this region. The absorbance of the organic layer, for both VIV and VV, was unaltered, even after 4 d. The composition of the complexes formed was established to be 1 : 2 (metal : ligand) by Job's method. Interference studies were carried out for both V i V and VV and methods are suggested for eliminating interference by foreign ions. Both VIV and VV are extracted quantitatively at pH 4; this extraction was exploited successfully for the simultaneous determination of VIV in the range 1-3 pg ml-1 and VV in the range 1-6 pg ml-1 by measuring the absorbances at 350 and 400 nm, respectively.

A second-derivative spectrophotometric method has been developed for the simultaneous determination of uranium and thorium using 4-(2'-thiazolylazo)resacetophenone oxime as the spectrophotometric reagent. The method allows the determination of uranium and thorium in the range 0-10.0 ppm. The relative error is less than 4%. Common anions and cations do not interfere in the determination even when present in large amounts. However, for transition metal ions, viz., Cu, Ni, Pd and Pt, the tolerance limit is less than 100 ppm.

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