Cox chart: The chart, known as the Cox chart, uses a logarithmic scale for the vapor pressure and an entirely arbitrary scale for the temperature in °F. The vapor pressure curve for any particular component, as shown in Figure 15-1, can be defined as the dividing line between the area where vapor and liquid exists. If the system pressure exists at its vapor pressure, two phases can coexist in equilibrium. Systems represented by points located below that vapor pressure curve are composed only of the vapor phase. Similarly, points above the curve represent systems that exist in the liquid phase. These statements can be conveniently summarized by the following expressions: • p < pv → system is entirely in the vapor phase • p > pv → system is entirely in the liquid phase • p = pv → vapor and liquid coexist in equilibrium where p is the pressure exerted on the pure component. Note that the above expressions are valid only if the system temperature T is below the critical temperature Tc of the substance. The vapor pressure chart allows a quick determination of pv of a pure component at a specific temperature. For computer and spreadsheet applications, however, an equation is more convenient. 1) A straight-line graph of the logarithm of vapor pressure against a special nonuniform temperature scale; vapor pressure-temperature lines for many substances intersect at a common point on the Cox chart. 2) Cox chart Molecular formula : CAS : nature : Linear said the liquid vapor pressure and temperature of a map. If elected to vapor pressure and temperature on a straight line, said the coordinates, then it is by a minority of the data, it is easy to figure out a wide range of vapor pressure values. The plan by E. R. Cox in the 1923's, its longitudinal coordinates of the vapor pressure values, and the abscissa used by the water vapor pressure (on 1 The coordinates of the other liquid vapor pressure (on numerical). Continue as in 3 and 4 until the vertical scale is established over the desired range for the Temperature 2 . namely water.numerical) and the temperature linear drawing from the special temperature calibration. 200 degrees. that covers the range of T that is to be marked on the vertical axis 3. say 100⁰F. say 45 ⁰. 100.9487 psia on the horizontal axis. and then horizontally to the vertical axis.525 psia. the relationship between temperature and become straight. 50. Mark the scale at the intersection at 100⁰F 4. for the index tic mark for the first integer. Then proceed horizontally left until you hit the vertical axis. you look up a vapor pressure of water at 100⁰ F in the steam tables. you use a reference substance. to get 0. Locate 0. on integers such as 25.9487 psia. and proceed vertically until you hit the 45 ⁰ straight line.525 psia on the horizontal axis proceed vertically to the 45⁰ straight line. From 11. Mark on the horizontal scale values of log p* so as to cover the desired range of p* for the compound of interest 2. Cox called this straight line Making a Cox chart: 1. Mark the scale at the intersection with the vertical axis at 200⁰F 5. and so on. say 200⁰F. To calibrate the vertical axis in comm. for which the vapor pressure of water 11. Next draw a straight line on the plot at a suitable angle. or calculate it from the Antoine equation. Pick the next temperature. Here are two possible forms of the Antoine's equation: 3 .