Abstract Association in organophosphoric acids due to hydrogen bonding appears to be stronger than that in monocar☐ylic acids. Molecular weights obtained by freezing-point studies show that the following monobasic phosphoric acids are dimeric in benzene and naphthalene: bis-(2-ethylhexyl), bis-(phenyl), bis-(2,6-dimethylheptyl-4), bis-[p-(1,1,3,3-tetramethylbutyl). The dibasic phosphoric acids, mono-(2-ethylhexyl) and mono-[p-(1,1,3,3-tetramethylbutyl) phenyl] were found to be polymeric in these solvents. Distribution studies of these acids between immiscible organic phases gave additional information as to their states of aggregation, and in addition indicated the strong interaction between these acids and a hydrogen bonding solvent, such as ethylene glycol. Infra-red studies of these acids in carbon tetrachloride show that no non-associated OH spectra appear in the fundamental and overtone regions.