604 



Deducing the boilingpointcurves for different pressures we refind 

 again the figures 2, 3, and 4 and figures 5 and 6 deduced from 

 these. The arrows must tlien be drawn however in opposite direction 

 so thai in the figs. 2, 3, and 4 Ti, is the lowest and T„ the highest 

 temperature at which the equilibrium F-\-L-\-G occurs. 



We must still contemplate the cases II and III namely that the 

 vapourpressurecurve of the binary system BC shows a point of 

 maximum, or a point of minimum pressure. After the previous 

 general considerations on the occurrence of ternary points of maximum- 

 aud of minimum-pressure, this need not to be considered here. 



Now we shall contemplate some points more in detail. When F 

 is a binary compound of the composition 0, |i, 1 — ^ (therefore « = 0} 

 Ixr + {y-M dx + {xs + {y-m dy = 0. . . . (1) 

 applies to its saturationcurve at a constant T and P. 

 The liquid cur\'e of the region LG is fixed by : 



[{x—.x)r + {y,-y)s] d.v 4- [{w~.v)s + {y,-y)t] dy = 0. . (2) 



We now imagine in fig. 1 that the liquid curve of the region LG 



dy 

 is drawn through the point p or q; we now contemplate — in this 



point p or q for both the curves. Because in this point x = and 

 Lim. ,rr ^ Rl it follows for the saturation curve that: 



^dy\ _ Rr+{y~^> (3^ 



and for the liquid curve of the region LG that : 



(^^^-.\^RT + {y,-y)s 



\dxJx=Q 



.... (4) 



{y-yy 



From (3) and (4) it follows that the tangents on both the curves 

 in the point p have usually a different position, so that the two 

 curves do not come in contact with one another. When (3) is 

 accidentally equal to (4), the two curves touch one another in j) or 

 q. This will be the case when : 



,„_, = g _,)„_,) 0. '^J^. ... (5) 



Later we shall see that in this case their point of contact p or q 

 is then also a point of maximum- or of minimumpressure of a 

 saturationcurve under its own vapour pressure or of a boiling point 

 curve. 



