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Abstract
A method to derive experimentally the configurational entropy that governs the structural relaxation process in supercooled (supercompressed) liquids is presented. Light scattering, dielectric, calorimetric and dilatometric measure-ments are used to test the method in o-terphenyl. The combined analysis of relaxation data as a function of temperature and pressure is found to be essential to quantify a realistic value of the non-structural thermal expansion and the configurational entropy of the system. The latter is estimated as a fraction of the excess entropy of the liquid over its stable crystalline phase. Our results indicate that the number of configurations connected to the structural relaxation contributes approximately 70% to the excess entropy.