Differential scanning calorimetry, thermogravimetric-differential thermal analysis, and X-ray diffraction measurements were performed on single crystals of L(+)-tartaric, D(-)-tartaric, and monohydrate racemic (MDL-) tartaric acid. The exact crystal structures of the three acids, including the positions of all hydrogen atoms, were determined at room temperature. It was pointed out that one of O-H-O hydrogen bonds in MDL-tartaric acid has an asymmetric double-minimum potential well along the coordinate of proton motion. The weight losses due to thermal decomposition of L-and D-tartaric acid were observed to occur at 443.0 and 443.2 K, respectively, and at 306.1 and 480.6 K for MDL-tartaric acid. The weight losses for L-and D-tartaric acid during decomposition were probably caused by the evolution of 3H 2 O and 3CO gases. By considering proton transfer between two possible sites in the hydrogen bond, we concluded that the weight losses at 306.1 and 480.6 K for MDL-tartaric acid were caused by the evaporation of half the bound water molecules in the sample, and by the evaporation of the remaining water molecules and the evolution of 3H 2 O and 3CO gases, respectively.

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Binary phase diagrams have been determined for solution-crystallized samples of two long-chain symmetrical ketones (Kn) and n-alkanes (Cn) with the same carbon numbers of n ) 25 and 39 from differential scanning calorimetry (DSC) measurements. Toluene was used as the solvent for crystallization of K39/C39 samples and hexane for K25/C25. They are found to form a solid solution which exhibits the solid-solid phase transition behaviors characteristic of a crystal of the pure n-alkane component, when the molar fraction f m of Kn is lower than a critical value f m,c , being dependent on n. For f m > f m,c , K39/C39 samples have formed another type of solid solution which melts after a rather broad solid-liquid equilibrium at elevated temperatures. On the other hand, K25/C25 samples have given eutectic mixtures for f m > f m,c , and the phase diagram is found to agree with that of the same samples crystallized from melt. We apply the Flory-Huggins theory for reproducing the phase diagrams using the interaction parameter 12 between Kn and Cn molecules and discuss effects of solvent which gave rise to these anomalous phase behaviors in terms of 12 and 0i (i ) 1, 2) between solvent and Kn (or Cn) estimated from their solubility curves.