  A microscopic description is given for the behavior of the fluid system in an
immediate vicinity of its critical point, where theoretical and experimental
researches are difficult to carry out. For the temperatures $T<T_c$, the
regions of chemical potential and density variations are singled out and
analyzed. The equation of state of the cell fluid model in terms of
temperature-chemical potential is written using the Heaviside functions. This
equation is also given in terms of the temperature and density variables. As a
result of the study of the relationship between the density and the chemical
potential, an equation for the binodal curve is obtained in a narrow
neighborhood of the critical point.
