We have determined the solubility, s, of indium oxide in the liquid mixture isobutyric acid + water along the critical isopleth at temperatures above the upper critical solution temperature near 299 K. When plotted in van't Hoff form with In s vs 1/T, the measurements of solubility lie on a straight line for values of the absolute temperature, T, which are sufficiently in excess of the critical solution temperature, T,. The sign of the slope, (partial derivative In s/partial derivative(1/T)), indicates that the enthalpy of dissolution is endothermic. When the temperature is within 1 K of T(c), however, the slope departs from its constant value and appears to diverge toward negative infinity. The principle of critical point universality predicts that a divergence in (partial derivative In s/partial derivative(1/T)) is to be expected for T near Tc in those cases where the stoichiometry of the dissolution reaction involves both components ofthe solvent; moreover, the Gibbs-Helmholtz equation predicts that if the enthalpy of solution is endothermic, the sign of the divergence should be negative. Both of these predictions are confirmed by the experimental data.