  Ultrasonic experiments allow one to measure the elastic modulus of bulk solid
or fluid samples. Recently such experiments have been carried out on
fluid-saturated nanoporous glass to probe the modulus of a confined fluid. In
our previous work [J. Chem. Phys., (2015) 143, 194506], using Monte Carlo
simulations we showed that the elastic modulus $K$ of a fluid confined in a
mesopore is a function of the pore size. Here we focus on modulus-pressure
dependence $K(P)$, which is linear for bulk materials, a relation known as the
Tait-Murnaghan equation. Using transition-matrix Monte Carlo simulations we
calculated the elastic modulus of bulk argon as a function of pressure and
argon confined in silica mesopores as a function of Laplace pressure. Our
calculations show that while the elastic modulus is strongly affected by
confinement and temperature, the slope of the modulus versus pressure is not.
Moreover, the calculated slope is in a good agreement with the reference data
for bulk argon and experimental data for confined argon derived from ultrasonic
experiments. We propose to use the value of the slope of $K(P)$ to estimate the
elastic moduli of an unknown porous medium.
