An Equation of State Applicable to Gases at Densities Near that of the Solid and Temperatures Far above the Critical

It is suggested that, at high pressures and temperatures far above the critical, the intermolecular interaction is predominantly repulsive. The effect on a molecule of its neighbours is therefore replaced by an infinitely steep potential well of volume related to the molecular volume. This concept is used to write down the equation of state for such a gas. It is shown that this equation is likely to hold in the range of density and temperature characteristic of the detonation wave in condensed explosives. The equations of the hydrodynamic theory of detonation are developed in terms of this equation of state, and applied to pentaerythritol tetranitrate. The calculated dependence of detonation velocity on loading density is in very good agreement with experiment; the temperature shows a sharp decrease with increased loading density. This is a consequence of the intermolecular repulsive energy characteristic of the model chosen.