STUDIES ON THE METAL COMPLEXES OF HYDROXAMIC ACIDS. PART II. COLOURED COMPLEXES OF IRON, VANADIUM AND MOLYBDENUM WITH NICOTINOHYDROXAMIC ACID AND THEIR ANALYTICAL USES

Traces of iron (whether present initially as ferrous or ferric) has been determined spectrophotometrically by measuring the optical density of the golden yellow colour formed between the metal and nicotinohydroxamic acid at pH 4.5 to 6 o at 440 mμ. (Sandell sensitivity 0.014 \(\gamma\)). The empirical compositions of the violet, red and the golden yellow coloured complexes of ferric iron have been determined by job's method of continued variation, giving metal­ ligand ratio of I : I, I :2 and I : 3 respectively. Vanadium has been determined by measuring the optical density of the golden yellow complex formed between the metal and the reagent in 50% ethanol over the pH range 3.3 to 4.5 at 440 mμ (Sandell sensitivity 0.014 \(\gamma\)). A solvent extraction procedure for its determination has also been described. The empirical compositions of a variety of coloured products formed between the metal and the reagent in aqueous and also in 33% ethanol medium have been determined (Job's method). The metal-ligand ratio for all is given. by I : 3. Molybdenum has been estimated by measuring the intensity of its yellow coloured complex with the reagent at 380 mµ or at 390 mµ over the pH range 6.3 to 9 cr. The composition of the complex has also been determined (job's method). It gives a metal-ligand ratio of I : 2