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With a system of three components, four variables are possible; the pressure, temperatureand two concentration terms (the concentration of the third component will be automaticallyfixed).Under such conditions, the phase properties are best defined by using the triangular diagram.This contention is borne out by the fact that in an equilateral triangle the sum of Pa

PbPc (also for any point other than P) is always equal to the length of any one side (comesponding to a total of 100%).If components A, B and C are completely miscible with each other at all proportions, then any point inside the triangle represents a system of three components and one phase, therefore F, the number of degrees of freedom, is 2, which means that the concentrations of any two components can be varied with respect to one another while that of the third component is maintained constant.If componentA is gradually added to the above mixture, the composition, will vary following points on theline AX. If A is completely miscible with both B and C, it will distribute itself between the twolayers and eventually a composition corresponding to point Mis reached where complete miscibility is observed.On an equilateral triangle (as shown in figure below) the apexes A, B and C represent pure components (100% each).

With a system of three components, four variables are possible; the pressure, temperatureand two concentration terms (the concentration of the third component will be automaticallyfixed). To simplify the study of the phase properties, the system is treated as a condensed one at a constant temperature, in which case the pressure and temperature as variables, are dispensed with. The phase rule expression reduces hence to: FCP. Under such conditions, the phase properties are best defined by using the triangular diagram. On an equilateral triangle (as shown in figure below) the apexes A, B and C represent pure components (100% each). A point on any one side represents a mixture of two components only. A point P inside the triangle represents the composition of a mixture of A, B and C of percentages respectivelyproportional to the lengths of the lines Pa, Pb and Pc drawn parallel to the sides of the triangle. This contention is borne out by the fact that in an equilateral triangle the sum of Pa

PbPc (also for any point other than P) is always equal to the length of any one side (comesponding to a total of 100%).If components A, B and C are completely miscible with each other at all proportions, then any point inside the triangle represents a system of three components and one phase, therefore F, the number of degrees of freedom, is 2, which means that the concentrations of any two components can be varied with respect to one another while that of the third component is maintained constant. if components B and C form a pair of partially miscible liquids, a mixture of the two composition X (as shown in the figure) will separate into two layers having the composition determined by points b and a (compare the phenol-water system). If componentA is gradually added to the above mixture, the composition, will vary following points on theline AX. If A is completely miscible with both B and C, it will distribute itself between the twolayers and eventually a composition corresponding to point Mis reached where complete miscibility is observed. Similarly, for any other mixture of A and B of composition between a and b, a point is reached where there is complete miscibility. The line connecting the various points is the bimodal curve b M a. Within this curve (immiscibility region) any point represents a system with C = 3 and P = 2; therefore: F = I, which means that changing the concentration of one component, the concentrations of both other components must change Outside the curve, is the region of complete miscibility and is treated as explained before