Correlation of the critical parameters of the gas-liquid phase transition and the density of the crystal at zero absolute temperature

The empirical formula of Timmermanns connecting the density of the crystal at zero absolute temperature with the parameters of the critical point of the gas-liquid phase transition is derived theoretically from the Van der Waals equation of state using the conditions of phase equilibrium. Two equations of state with three parameters describing the critical point of any pure substance are considered. The formula is derived approximately from the first equation and exactly from the second one.