The stoichiometry of the polyanions formed by the action of nitric acid on sodium ortho-vanadate solution has been studied by means of electrometric techniques involving glass electrode and conductometric titrations as well as Job＇s method of continuous variation. The well defined inflections and breaks in the titration curves and maxima from continuous variation study provide cogent evidence for the existence of the anions, pyro-V2O74-, meta-VO3- and poly-H2V10O284- corresponding to the ratios of VO43-:H+ as 1:1, 1:2 and 1:2.6 in the pH ranges (10.1-10.7), (7.0-7.5) and (3.4-3.8), respectively. Similar titrations between alkali and V2O5 solutions also confirm the existence of the same anions,The interaction of lead nitrate with sodium vanadate solutions, at specific pH levels 12.4, 10.5, 7.4 and 3.6 was also studied by pH and conductometric titrations. The end-points obtained from the sharp inflections in the titration curves provide definite evidence for the formation of lead ortho-3PbO . V2O5, pyro-2PbO . V2O5 and meta-PbO . V2O5 vanadates in the vicinity of pH 8.2, 6.5 and 5.6, respectively. (C)2000 Elsevier Science B.V. All rights reserved.