Figure 6 shows a plot of various isotherms of Z ( ρ ρ , T r ) vs ρ ρ r . Also shown are the spinodal and coexistence curves described previously. The subcritical isotherm consists of stable, metastable, and unstable segments, and are identified the same as they were in Fig. 1. Also included are the zero initial slope isotherm and the one corresponding to infinite temperature.