An accurate and simple method for the measurement of specific volumes of solid organic compounds under high pressures was proposed. The principle of this method was based on the flotation methods, in which pressure was adjusted to find the floating equilibrium point at isothermal condition. One of the advantages of the proposed method is that the specific volume of solid organic compounds under high pressures can be determined with almost the same accuracy as that of immersion liquids. The specific volumes of naphthalene were measured at 293.15 K and at pressures up to 440 MPa. The immersion liquid used consisted of aqueous NaNO3 solutions. The specific volumes of the aqueous NaNO3 solutions under high pressures were measured with the glass piezometer method proposed in our previous study. Experimental results of the specific volume and also the isothermal compressibility were compared with the literature data. It was found that good agreement was obtained between the present results and the literature data for the volume compressibility.
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