A calorimeter for enthalpy of solution measurement has been constructed. It is of an isoperibol type, using a quartz thermometer for temperature sensing, and equipped with a special solution mechanism of solid sample. The performance of the calorimeter has been tested by enthalpy of solution of KCl in water at 298.15K. The result was discussed by comparing with literature values.
Enthalpies of solution of Biuret in various aqueous electrolyte solutions and in Urea solution were measured at 298.15K, using this calorimeter. The result was discussed in terms of the solute-solute-solvent interactions.

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In principle we can expect the dependence of heat capacity on time or frequency in every materials. However, owing to the limitation of the experimental technique only a few phenomena, e. g., the logarithmic decay in amorphous, the frequency dispersion near glass transition, etc., have been reported. Recently a new method, which can measure a thermodynamical quantity related to heat capacity, has been developed by applying ac calorimetry. In this review article, we introduce the method and its application to glass transition; Using the method thermal effusivity given by the product of cκ (c is heat capacity and κ is thermal conductivity) is obtainable; The measurement of frequency dependence of cκ has been performed at the glass transition of glycerol and others in the frequency range over the low to high frequency limit; The detailed analysis of the results has been carried out and the mechanism of the glass transition has been discussed. Furthermore, it is pointed out that combining cκ with the thermal diffusivity measured by the extension to the above method we can determine the heat capacity, the thermal conductivity and the thermal diffusivity at the same time. The recent development of ac calorimetry will be applied to the study of heat capacity spectroscopy in variety of phenomena including protein denaturation process.

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Clathrate hydrates are rare inclusion compounds which have orientational disorders of both guest and host water molecules. Focusing attention on their molecular motions and ordering phenomena, experimental (mainly heat capacity) studies are reviewed based on 65 references. The contents are as follows:
1. Introduction
2. Kinds and structures of clathrate hydrates
3. Molecular motions of the guest and the host observed by dielectric and NMR studies
4. Guest ordering transition in TMO str. I hydrate
5. Freezing of orientational motion of water molecules
6. Glass and phase transitions in some KOH-doped hydrates
7. Interrelation between the guest and the host in their molecular reorientational motions
8. Concluding remarks

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