4-22 Properties of liquid-vapor mixtures The so-called steam or water vapor that is usually seen rising from boiling water is not vapor at all but small drops of liquid that are entrained in the vapor. Because individual molecules are far too small to be seen, the capor itself is not visible. Dry saturated vapor is the term commonly used to describe a saturated vapor that is completely free of liquid particles, whereas the term wet vapor is used to denote vapor that has liquid in mixture with it. The quality of a vapor, designated as the X component, is an expresaion of the percent by weight vapor in any mixture of liquid and vapor, whereas the moisture content, designated as the y component, is an expression of the percent by weight liquid in the mixture. Keeping in mind that any wet vapor (liquid-vapor mixture) must, of necessary, be saturated, it follows that the temperature of any mixture will always be the saturation temperature corresponding to the pressure of the mixture. Other properties of the mixture can be determined by taking the appropriate values from the saturated vapor table and combining them in proportion to the percentages of liquid and vapor in the mixture, as follows: