A simple approximate relation is derived for the temperature of the maximum occurring in the vapour-pressure lines of saturated solutions of a number of non-volatile substances of high melting point in a volatile solvent. T h e derivation is analogous to that for saturated solutions of one dissolved substance 1).This formula, although derived only for ideal mixtures, is found to give reasonably satisfactory results for a series of vapour-pressure curves determined in this laboratory in non-ideal systems. 4 1. The composition of solutions saturated with respect to two substances.In a system of two components of high melting point and one of low melting point in which the other two are soluble there is a very simple relation between the solubility and the temperature, provided the solution behaves as an ideal mixture and the heats of solution do not change with the temperature. Let x, and x2 represent the concentrations as mole fractions of the high-melting components 1 and 2, and Q, and Q, their heats of fusion.