Thermogravimetry (TG) and differential thermal analysis (DTA) techniques were used to determine the solid-solution equilibrium curve between certain inorganic salts and water. The rate of evaporation of water through a pin hole of an aluminum pan, containing a small amount of aqueous solution of the salt, was measured by TG and DTA. A slight change in the rate was found to occur when the solution crosses the solubility curve. The composition and temperature at which the vaporization rate changed were determined by differentiating the TG curve with respect to time and then comparing with the literature value. The solubilities of NaCl, KCl, and Na2SO4 crystals into water were determined rapidly with the accuracy of +/-1% for a small amount of sample solution.