The solidification diagram of liquid PbCl2–PbO mixtures was determined for molar fractions of lead oxide smaller than 2/3; three compounds were identified: these are the oxychlorides 3PbCl2,2PbO; PbCl2,PbO, and PbCl2,2PbO. Furthermore, the cryoscopic study of the liquidus of lead chloride led the authors to suggest the existence of the species PbCl2,PbO and the almost complete lack of Cl− ions in the liquid phase.