Garrels and Gucker have discussed the deviation of the behaviour of lead chloride solutions from that of a strong electrolyte in terms of both of the Gronwall-La Mer-Sandved extension of the Dbye-Huckel theory and of incomplete dissociation. They conclude that the postulate of incomplete dissociation leads to the more satisfactory treatment of the data but reveal that the various methods of determining the degree of dissociation of the intermediate ion PbCl+ are not in agreement. We here report an extensive investigation of the absorption spectra of lead halides in a range of water methanol mixtures form which we derive dissociation constants for the species Pbcl+, PbBr+, PbI+ in water and mixed solvent at 18°C. We will review the methods which have been used and will later discuss their validity in some detail. Having established the presence of intermediate ions in solution w will discuss the nature of these ions, particularly as regards their bond type and stability in solution. We will also discuss the nature of the absorption process and will attempt a correlation of observed absorption spectra in the crystalline and liquid phases, in terms of a proposed mechanism for the absorption process, and of a proposed absorption spectrum criterion for the nature of complex ions in solution.