Diffusion and dissolution of the hydroxybenzoic acids in water

Abstract

Abstract Single spheres of o ‐, m ‐ and p ‐hydroxybenzoic acid have been dissolved into a water stream ( Re range 100—1000) and the data are correlated by a relationship of the form equation image The meta ‐isomer (ϕ = 0.80) behaves differently from the ortho ‐ and para ‐isomers (ϕ = 0.71) and it is suggested that this is due to the influence of surface effects on the dissolution process. A quantity termed the ‘work of replacement’, which can be calculated from surface tensions and wetting angles, has been defined to give a measure of the influence of these effects. Solubility, density, viscosity and diffusivity data are presented for saturated aqueous solutions of the three hydroxybenzoic acids. Differences in diffusivity of the isomers are explained by considering the effects of dimerisation due to hydrogen bonding.