Near-criticality in dilute binary mixtures: distribution of azulene between coexisting liquid and vapor carbon dioxide

The equilibrium distribution of dilute solutes between vapor and liquid coexisting phases of near-critical solvents exhibits a simple dependence on the solvent's liquid density which extends over a wide temperature range; however, theory predicts this dependence only as an asymptotic limit. In order to test quantitatively the extension of this behavior and compare it with the value predicted from the asymptotic relationship, a novel high-pressure apparatus with a sampling manifold, which avoids perturbing the system during sampling, was used to measure the equilibrium concentrations of azulene in coexisting liquid and vapor carbon dioxide contained in a high pressure sapphire cell.