An equation of state that relates the pressure, volume, and temperature of a gas and the gas constant. The Beattie-Bridgman equation uses empirical constants to take into account the reduction in the effective number of molecules due to various types of molecular aggregation. It is given by
where P is the pressure, T is the thermodynamic temperature, V is the volume, R is the gas constant, and A, B, and ϵ are constants related to five empirical constants A0, B0, a, b, and c by: A = A0(1 – a/V), B = B0(1 – b/V), and ϵ = c/VT3. The Beattie–Bridgman equation was proposed by James Beattie and Percy Bridgman in 1928.