751 



a small distance, must point vcrticallj^ upwards, so tliat it lias there 

 a vertical tangent. Considering the satnrationcurvcs under their own 

 vapourpressure, we see that FZ^ intersects only curves of tempe- 

 ratures lower than Tn, so that the temperature decreases along 

 FZ, from F. 



Considering the boilingpointcurvcs, we see that the same still 

 applies to these as to a solutionpath, situated between FE and FZ^. 

 The pressure, therefore, increases at first from F and after that it 

 decreases. From all this it follows that the /^.y^-curve has, therefore, 

 a form as curve bF in fig. 2. 



Let us now take a solutionpath between FZ^ and FZ,. Tt is easy 

 to see that the P, 7^-curve retains a form as FZ^ in fig. 2, with 

 this ditlference, however, that the tangent in F stands no longer 

 vertically. The curve proceeds viz. from F immediately towards 

 higher pressures and lower temperatures. According as the solution- 

 path in fig. 1 comes closer to FZ^, in fig. 2 the point of maxi- 

 mumpressure Q" approaches closer to F. When the solutionpath 

 coincides with FZ^, Q" coincides with F, and in figure 2 the 

 P,T-cnvve obtains a form as Z^F with a horizontal tangent in F. 



Jn order to see this, we consider the solutionpath FZ^ which 

 touches the boilingpointcurve FK in F. {Cig. 1). Going from P along 

 an infinitely small distance along curve FK and, therefore, also 

 along the tangent FZ^, the temperature decreases, while the pres- 

 sure remains constant. As (IT, therefore, is negative and dP is zevo, 

 the P, T-curve must, therefore, from F over a small distance point 

 horizontally towards the left; consequently it has a horizontal tangent 

 in F. 



We now^ take a solutionpath FZ, situated between FLJ and 

 F Z^. It follows from a consideration of the saturationcurves under 

 their own vapourpressure and the boilingpointcurves in the vicinit}' 

 of F, that pressure and temperature decrease from F. The /-*, 7- 

 curve is represented in fig. 2 by F Z, it proceeds from F towards 

 lower temperatures and pressures. 



At the deduction of fig. 2 it is assumed that the saturationcurves 

 under their own vapourpressure and the boilingpointcurves have a 

 form as in fig. 1. Curve Fs and Fk are drawn herein in the 

 vicinity of F, concave towards H. When in AMhey turn their convex 

 side towards H, then curve Fs will intersect its tangent FZ^ still 

 in another point and curve FK its tangent FZ^. Although then in 

 fig. 2 the tangent in F to Z^ F remains horizontal and the tangent 

 to Z^F vertical, all curves will obtain a somewhat ditferent 

 form in the vicinity of F (we may also con)pare the previously 



