The solubility of potassium carbonate in water at temperatures from 384 to 529 K is reported at the saturation vapor pressure of the solutions. Measurements were made using a visually-accessible apparatus consisting of a platinum cell with sapphire windows and gold seals. The results indicate that potassium carbonate remains prograde-soluble up to 529 K. At approximately 427 K the hydrate form of the solid changes as indicated by visual observation of the solid and a change in the solubility behavior. Solubilities determined at lower temperatures have been compared with literature data and are in good agreement.