Abstract
THE polarographic reduction of niobium in concentrated hydrochloric acid1, and in oxalate and tartrate solutions (ref. 2 and Mrs. B. Lamb, private communication), has been shown to be due to reduction of Nb(V) to Nb(IV). Reductions in these media are, however, irreversible. Recent studies on the precipitation of niobium with tannic acid from various complexing solutions (G. W. C. Milner, G. A. Barnett and A. A. Smales, unpublished work) in this laboratory have indicated that niobium forms complexes with malic, citric, lactic and ethylenediamine-tetra-acetic acids. We have found polarographic steps corresponding to the reduction of these complexes.
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