The term saturation defines a condition in whicha mixture of vapor and liquid can exist togetherat a given temperature and pressure. Thetemperature at which vaporization (boiling) startsto occur for a given pressure is called thesaturation temperature or boiling point. Thepressure at which vaporization (boiling) starts tooccur for a given temperature is called thesaturation pressure. For water at 212°F, thesaturation pressure is 14.7 psia and, for water at14.7 psia, the saturation temperature is 212°F.For a pure substance there is a definiterelationship between saturation pressure andsaturation temperature. The higher the pressure,the higher the saturation temperature. Thegraphical representation of this relationshipbetween temperature and pressure at saturatedconditions is called the vapor pressure curve. Atypical vapor pressure curve is shown in Figure 5. The vapor/liquid mixture is at saturation whenthe conditions of pressure and temperature fall on the curve.