598 



These regions may arise either any- 

 where within the triangle, or on one 

 of the sides or in one of the angular- 

 (3oints ; in tig. 1 we may tliink them 

 arisen in the angular-point C/ Also two 

 or more of these regions may be formed 

 in different points of the triangle and 

 they may come together later in diffe- 

 rent ways. 

 ^j\ We will distinguish now three prin- 

 Fig. 1. cipal cases according to the phenomena 



in the binary system BC. 



I. The equilibrium liquid-gas of the binary system BC shows 

 neither a maximum- nor a minimumpoint of pressure. The pressure 

 of every liquid consisting of B and C is situated, therefore, between 

 the pressure of the pure substances B and 6'. 



II and III. The equilibrium liquid-gas of the binary system BC 

 shows a maximum- or a minimumpoint of pressure. 



We take at first the case mentioned sub I; we assume, for fixing 

 the ideas, that the pressure decreases from C to B. The result of 

 this is that every heterogeneous region L — G, at every temperature 

 and under every pressure, intersects only once the side BC (fig. 1) 

 and that this region on 'decrease of P with its liquid-line ahead 

 moves along BC from CtoB. Of course it is indifferent, where the 

 gasregion and the region L — G arise, on condition that this does 

 not occur in a point of the side 5C (excepted in 6' itself). Decreasing 

 the pressure, a pressure Fm, occurs, under which the liquidcurve of the 

 reo-ion LG and the saturationcurve of F obtain at first a common 

 point; we shall call this point M. Pm, therefore, is the highest 

 pressure, under which the system F -\- L -\- G occurs. 



When M is situated within the triangle, then, as was formerly 

 deduced, M is a point of contact of the two curves and F, M and 

 the corresponding vapourpoint M^ are situated on a straight line. 

 The point M then is a point of maximum pressure of the saturation- 

 curve under its own vapourpressure. 



When M is situated on the side BC of the triangle, e.g. in the 

 point p of figure 1, the points F, p, and the corresponding vapour- 

 point on the side BC are, therefore, also situated on a straight line ; 

 then usually the two curves do not come in contact with one another. If 

 we imagine in fig. 1 the liquidcurve drawn through p, the two curves 

 will come in contact with one another in p only exceptionally. The 

 pressure Pp is then the highest pressure under which the system 



