The enthalpy increments of four liquid solutions Li0.8Na0.2F, Li0.6Na0.4F, Li0.4Na0.6F, and Li0.2Na0.8F were measured in the temperature range (1230 to 1470) K by drop calorimetry. The liquid phases of the LiF and NaF end-members were also measured, in the temperature range (1230 to 1470) K and (1320 to 1540) K, respectively. From the obtained results the molar heat capacity was derived and the data for pure LiF and NaF were correlated with the literature. In order to overcome problems related with the corrosive nature of alkali metal fluoride vapours at high temperature, a novel encapsulation technique is presented in this study. Small nickel crucibles were developed for this purpose which are sealed by laser welding. (C) 2009 Elsevier Ltd. All rights reserved.