An equation of state for a gas of the form

where P is the pressure, V is the volume, T is the thermodynamic temperature, R is the gas constant, and a and b are constants characteristic of the gas. The Dieterici equation is a modification of van der Waals’ equation, which takes account of the pressure gradient at the boundary of the gas. At low pressures the Dieterici equation becomes identical to van der Waals’ equation. The Dieterici equation was proposed by C. Dieterici in 1899.