Apparent molar volumes V-phi and apparent molar heat capacities C-p,C-phi of aqueous solutions of L-tartaric acid, mono-sodium L-tartrate, and di-sodium L-tartrate have been measured at molalities 0.006 less than or equal to m/(mol kg(-1)) less than or equal to 1.0, at temperatures 278.15 < T/K less than or equal to 393,15, and at the pressure p 0.35 MPa. Apparent molar volumes were obtained from density measurement using a vibrating-tube densimeter (DMA 512, Anton Paar, Austria). Apparent molar heat capacities were obtained from heat capacity measurements using a twin fixed-cell, differential-output, power-compensation, temperature-scanning calorimeter (NanoDSC model 6100, Calorimetric Sciences Corporation, Spanish Fork, UT, U.S.A.). These results were fit by regression to semi-empirical equations to describe the (m, T, V-phi) and (m, T, C-p,C-phi) surfaces. These results were also used to estimate the change in volume (m, T, Delta(r)V(m)) and the change in heat capacity (in, T, Delta(r)C(p,m)) for the two stepwise proton dissociation reactions of aqueous L-tartaric acid. The (in, T, Delta(r)C(p,m)) surfaces for each proton dissociation reaction were integrated numerically to obtain estimates of the change in enthalpy (m, T, Delta(r)H(m)) and proton dissociation molality quotients (m, T, p Q(a)). These integrated results greatly extend the ranges of m and T over which precise thermodynamic information is available for the two dissociation reactions of aqueous L-tartaric acid.