This paper describes how calorimetry may be used to obtain two sets of information, namely, (i) the internal energy of a material’s polymorphs by measuring their heat of solution as well as the effect of structural relaxation on this energy, and (ii) the amount of intergranular liquid (or a second solid phase) in polycrystalline solids. Experiments have confirmed the usefulness of the two methods, and have shown that a substantial amount of liquid at thermodynamic equilibrium is present at the grain junctions in a polycrystalline solid, or that such solids premelt significantly. The formalism and concepts developed here are expected to apply equally well to polycrystalline solids, which undergo order-disorder phase transformation, and where the more disordered phase remains at the grain junctions of the ordered phase.