Water substance along the melting line

TABLE 2-357 Thermodynamic Properties of Water Substance along the Melting Line... 

If you move to the left (at constant pressure) along the line EF, you will find a temperature at which the liquid freezes. The line AC shows the temperatures and pressures along which solid and liquid are in equilibrium but no vapor is present. If the temperature is decreased further, all of the liquid freezes. Therefore, only solid is present to the left of AC. Water is an unusual substance the solid is less dense than the liquid. If the pressure is increased at point F, at constant temperature, water will melt. The line AC has a slightly negative slope, which is very rare in phase diagrams of other substances. If the pressure on this system is increased and you move up the line AC, you can see that pressure has very little effect on the melting point, so the decrease in temperature is very small. 

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