Summary 1. A method of separation of isomeric acids by utilizing the differences in their solubilities and ionization constants is described. The method is applied satisfactorily to the separation of 8-(2-naphthoyl)-propionic acid and p-(l-naphthoy1)-propionic acid. 2. Values are given for the solubilities, the ionization constants and the per cent. ionization of these acids in saturated solution at 25'.
