An emf cell technique was used to measure the thermodynamic properties of Pb-Na solutions at temperatures ranging from 245 ~ to 500~ and compositions between 2.35 and 16.79 atomic per cent (a/o) Pb. The results, while in general agreement with earlier work, reveal that the deviations from ideal solution behavior cross over from negative to positive at low Pb concentrations. This property has not been previously reported for the Pb-Na system. Sodium activity measurements, which were made as a function of decreasing temperature, display a marked change in slope upon transition to a two-phase region. The resulting liquidus-line is in agreement with the published phase diagram. A study of the change in sodium activity as a function of temperature was also made for saturated solutions of Ge in Na. The results show that the solubility of Ge in Na is represented by the equation