text: If V is the molar volume and T the critical temperature of a liquid the surface tension γ is given by
  where k is a constant valid for all liquids, with a value of 2.1×10 J/(K·mol).
  More precise values can be gained when considering that the line normally passes the temperature axis 6 K before the critical point:
  The molar volume V is given by the molar mass M and the density ρ
  The term  is also referred to as the "molar surface tension" γ :
  A useful representation that prevents the use of the unit mol is given by the Avogadro constant N :
  As John Lennard-Jones and Corner showed in 1940 by means of the statistical mechanics the constant k&prime; is nearly equal to the Boltzmann constant.