It is shown, that liquid two-phase (liquid alloy + intermetallic compound) alloys of praseodymium and neodymium with indium or bismuth can be used as trusty reference electrodes, allowing to study the processes of alloy formation between the mentioned above 4f-elements and individual low-melting metals or their metallic compositions. The dependencies of potential differences between metal electrode (Pr and Nd) and the two-phase alloy, formed by the corresponding rare earth metal and indium or bismuth, are given in the wide temperature range between 573-1073 K. Partial thermodynamic functions (ДH AS, AG) of praseodymium and neodymium in the two-phase alloys were calculated.