where n$_{i}$, i = liq, gas are the values in the corresponding phases, n$_{c}$, T$_{c}$ are the critical density and the temperature. The second fact is another linear law which was derived by Batchinsky [4] long ago from the classical vdW equation: The curve defined by the equation Z = P/ ( n T ) = 1 for the compressibility factor Z as it directly follows from Eq. (3) is a straight line: where T (vdW) B = a/b is the Boyle temperature determined by the vdW constants in accor- dance with the virial expansion for Eq. (3). In work of Ben-Amotz and Herschbach [5] the line Z = 1 is called by the Zeno-line. Both relations (2) and (5) are approximate and have phenomenological character. But surprisingly they are observed for a wide variety of fluids. As was noted in [6] the law (2) is fulfilled in rather broad temperature interval of the vapor-liquid phase coexistence region 0 . 65 ≲ T/T$_{c}$ ≲ 1. In the vicinity of the CP the deviations from the linearity become noticeable [7, 8]. In series of works [9–13] the performed analysis of the data for both the real fluids and the systems with model potentials discovered a number of interesting relations between coordinates of the CP, the law of the rectilinear diameter (2) and the Zeno-line: Here T$_{B}$ is the Boyle temperature and for n$_{b}$ the following equation followed from the virial expansion was proposed in [14]: The phenomenological concept of the “Triangle of Liquid-Gas States“ has been formulated in [11]. It is heavily based on the cute observation that the Zeno-line is the tangent to the binodal extrapolated to low temperature region. Then the liquid-vapor binodal is inscribed into triangle formed by the straight lines: the coordinate axes n and T and the Zeno-line. Obviously, the thermodynamic states which satisfy the equation Z = 1 include the trivial states with negligible density n → 0. This is nothing but the coordinate axis on the ther- modynamic n − T plane. Thus the set of the Zeno states is formed by the union of two lines P = n T 1 − n b − a n $^{2}$. (3) n 1 /b + T T (vdW) B = 1 . (4) n n$_{b}$ + T T$_{B}$ = 1 . (5) T$_{B}$ = n$_{b}$ B$_{3}$ ( T$_{B}$ ) B ′ $_{2}$( T$_{B}$ ) . (6) 3