Small values of this quantity can be measured by the Knudsen method of molecular effusion.  
Two equations giving the temperature dependence of this quantity in terms of three constants are the Kirchhoff relation and the Antoine equation.  Small values of this quantity can be measured by the Knudsen method of molecular effusion.  Another equation relates its logarithmic temperature dependence to the associated latent heat, and by definition its total value is equal to the sum of its values for pure components times the mole fraction of each component in an ideal solution, according to Raoult's law.  The Clausius- Clapeyron equation gives the temperature dependence of, FTP, this quantity which equals one atmosphere at the normal boiling point of a liquid.
Two equations giving the temperature dependence of this quantity in terms of three constants are the Kirchhoff relation and the Antoine equation.  
{vapor pressure}