  We study the slow dynamics of salol by varying both temperature and pressure
using photon correlation spectroscopy and pressure-volume-temperature
measurements, and compare the behavior of the structural relaxation time with
equations derived within the Adam-Gibbs entropy theory and the Cohen-Grest free
volume theory. We find that pressure dependent data are crucial to assess the
validity of these model equations. Our analysis supports the entropy-based
equation, and estimates the configurational entropy of salol at ambient
pressure ? 70% of the excess entropy. Finally, we investigate the evolution of
the shape of the structural relaxation process, and find that a
time-temperature-pressure superposition principle holds over the range
investigated.
