An equation which relates the volume term ( V = M / (~L -p g ) ) of unassociated liquids to pressure P and temperature T has been obtained by the combination of (a) 0 . 3 V ( a l / a V )~, , = T,-T for the effect of temperature on V at low (atmospheric) pressure and (b) -V(aP/a V ) T = P, Vx6/ V"P+O + 9( P -p ) for the effect of pressure on volume at constant temperature. In the equations, p is the vapour pressure; p~ the density of the liquid and pe the vapour density. Often pg can be neglected compared with PL a n d p is small compared with the large pressures required to affect the densities of liquids appreciably. There are three constants: T,, P,, which equals 4.455 x 10" N m-2, and V, which can be calculated by rhe addition of atomic values for all the atoms in the molecule and subtraction of a value (6.56 x m3 mol-1) for each bond. When V approximates to Ilt/pL, the molar volume, the equation can be integrated to give the work and heat of isothermal compression. The viscosity of a liquid is related to the work of compression and solubilities in a liquid to the work required to bring the solute to the compressibility of the liquid. Many relationships can be derived and can be used to estimate properties of unassociated liquids.