Lead Polysulphide

A purple-red polysulphide of lead, having the composition PbS₅, is formed when a solution of calcium polysulphide is added in excess to a dilute solution of lead nitrate cooled to 0° C.; above 10° C. this compound decomposes into lead monosulphide and free sulphur.

It was observed by Hofmann and Wolfl that when lead halides dissolved in dilute sodium thiosulphate solution are exposed to light precipitates are formed which are not lead sulphide, this alone being formed from the solutions in diffused light or in the dark. In the case of the chloride a red precipitate of Pb₄S₆Cl₂ is formed, whereas from the iodide Pb₃S₄I₂ separates as a copper-red powder. The latter compound is also formed by the action of yellow ammonium sulphide solution on lead iodide.