Based on our own and some literature results, we have carried out a detailed analysis of concentration regions of the aqueous-organic mixture in which the temperature dependences of both excess molar heat capacity, , and apparent molar heat capacity of each component, , are intersected. It is established that the and derivatives (W is water) for the {(W + hexamethylphosphoramide (HMPA)} and {(W + tert‑butanol (t-BuOH)} mixtures intersect in a rather narrow concentration interval between (0.30 and 0.35) and (0.35 and 0.40) mole fractions of the organic component, respectively. This fact we have interpreted as evidence that the decisive role in the mutually overlapping heat-capacity contributions to resulting in such a situation plays the abnormal change in the isobaric molar heat capacity of W (), which has a minimum at T≈ 308 K, when the temperature increases.
