Hitherto the zinc sulphide material required for luminescent phosphors has usually been obtained by the reaction between a zinc salt and hydrogen sulphide. In this paper we report a new method of preparation of zinc sulphide by the reaction between thiourea and a zinc salt in an alkaline medium, at optimum conditions of pH. The zinc sulphide precipitate obtained under varying conditions of pH has been characterized by the methods of X-ray diffraction, electron microscopy and diffraction, optical microscopy, magnetic susceptibility, diffuse reflectance and density. A very important point which came out of these investigations is that with varying pH for the precipitating conditions, varying degrees of non-stoichiometry have been obtained. All these aspects have been discussed in terms of interstitial zinc atoms or Zn + ions and electrons in anion vacancies.

A method for the assay of thiourea in acidic solution by titration with standard permanganate solution is described.

A method for the determination of thiourea in acidic solution by titration with permanganate in the presence of a known amount of oxalic acid is described. The reaction is a four-equivalent oxidation of thiourea by permanganate. The oxalic acid in the solution effects a change in the mechanism such that thiourea becomes a four-electron reductant in its reaction with permanganate.