VAN'T HOFF METHOD.The dissolution enthalpy ( H 0 soln ) of sodium sulfacetamide in water was determined by means of isoperibolic solution calorimetry.It was found that H 0 soln diminishes as the drug concentration increases.Otherwise, the calorimetric values obtained as a function of the drug concentration were significantly different than those predicted by the van't Hoff method.It was demonstrated that the later is not a fully reliable method for the determination of H 0 soln values in the specific case of highly soluble sodium salts.The observed phenomenon could be explained by the presence of strong solute-solute interactions at high salt concentrations, in addition to solute-solvent and solvent-solvent interactions.