The thermodynamic properties of solutions of lanthanum or gadolinium chlorides in mixed molten LiCl-KCl were determined-by electromagnetic force (emf) measurements of LaCl3 or GdCl3 formation cells. The temperature dependence of the emf between 380 and 590 degrees C was used to calculate the Gibbs energy and the enthalpy of formation of dissolved LaCl3 or GdCl3. The electrode process es of La(III) and Gd(III) reduced on a tungsten electrode were investigated by cyclic voltammetry and chronopotentiometry.