Phosphorus liquid, critical point

T = 7 . above which the liquid and gas phase are no longer distinguishable. Since the liquid can he continuously converted into Ihe gas phase without discontinuous change of properties by any path in the P — T diagram passing above the critical point, there is no definite boundary between liquid and gas. Two liquids ol similar molecules are usually. soluble in all proportions, but very low solubility is sufficiently common to permit the demonstration of as many as seven separate liquid phases in equilibrium at one temperature and pressure (mercury, gallium, phosphorus. perHuoro-kerosene, water, aniline, and heptane at 50 C. I atmosphere). 

While solids can exists in several solid forms, regular, non-mesogenic fluids mainly exists only two forms, namely liquid and gas ones. Obviously, liquids (liquid crystals) with special molecular structure (like disc- or bananashaped molecules) can form different phases, but for regular fluids, most people would not expect more than one liquid form. Surprisingly there are a few liquids (like cesium, selenium, phosphorus), which can exist in more than one liquid forms, like normal ones and dense ones. Being both phases disordered, the transition between the two liquid phases should be very similar to the transition between liquid and vapour phases, i.e. there should be a phase transition line (liquid-liquid line) terminated by a critical point. One of the recent candidate for the membership of the Club for liquids with more than one form is the water in this case the dense liquid phase is hidden in the... 

This triple point is the point of intersection of the three univariant systems solid— vapour (curve FD), liquid— vapour (curve DE), solid— liquid (curve DI). The values of the vapour pressures of solid and of liquid violet phosphorus are given in the tables on pp. 60 and 61. The curve DE will end abruptly at the critical point of liquid phosphorus. The critical temperature was found by W. A. Wahl to lie at 695° C. and from the course of the vapour-pressure curve, Smits and Bokhorst have calculated that at this temperature the pressure (critical pressure) would be 82 2 atm. According to Marckwald and Helmholz, the critical temperature is 720 6 . 

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