Pressure dependence of the isothermal compressibility and a modified form of the Tait equation

The pressure dependence at low pressures of the isothermal compressibility βT of liquids has been computed via a van der Waals type model of the liquid state for the temperature range 1 ? T/Tt ? 1.4 (where Tt denotes the triple point temperature). The results are in good agreement with the scarce experimental data: for most organic solvents, the quantity −(∂βT/∂P)T/βT2 ranges from 9–11. For water, the theory correctly predicts a much lower value. In the indicated range, the variation with temperature is small, in agreement with experiment and suggested by a modified Tait equation.