IJ 49 



F^ F' + />+ O, tlien /"-f F' remains. Therefore, in fig. 1 curve 

 F -\- F' -\- L -\- (i inusl coincide willi r h ; it will, however, only 

 partly cover tiiis curve. It is re[)rcsented in fig. 1 by luo, wherein 

 u and ID are the points of intersection of mKFM and m' K' F' M' . 



In order to see this we take any point x of the curve F-\-F'-\-L-\-G. 

 When we remove F' and when we keep further the (piantity of 

 vapour always exceedingly small, tlie liquid L of the remaining 

 equilibrium I~\-L-\-(t traces at change of temperature a solutionpath 

 of F under its own vapourpressure. The P, 7-curve of this path is 

 represented in fig, 1 by y ^c F. When we remove i'^ and when we 

 keep again the quantity of vapour exceedingly small, the liquid L 

 traces a solutionpath of F' on change of temperature ; this is indi- 

 cated in fig. 1 by y' x F' . 



Only the part yx of the first solutionpath, only the part x F' of 

 the second represent stable conditions. Restricting ourselves to stable 

 conditions, we may sa}- therefore : from each point of the modifi- 

 cationcurve F -\- F' ^ L -\- (r one solutionpath of i^^ proceeds towards 

 lower temperatures, and one of F' towards higher temperatures. 

 From this it follows that the one extremity of the modificationcurve 

 must be situated in u, and the other in w. 



In order to deduce the modificationcurve and its corresponding 

 vapourcurve in the concentrationdiagram, we may act in a similar 

 way as e.g. at the deduction of the saturationcnrves under (heir own 

 vapourpressure. When we take a definite T and P and when at 

 this T and under this P a saturalioncurve of F exists, this is 

 circumphased ; the same applies to that of F' . When at the assumed 

 T and P the modification F is the stable one, its saturationcurve 

 sui-rounds that of F' ; when F' is the stable form, the saturation- 

 curve of F' surrounds that of F. 



The two saturationcnrves can never intersect each other, they can 

 completely coincide. This is the case when we choose P and T in 

 such a way that they are in accordance with a point of curve r h 

 in fig. 1, so that the two modifications F and F' may exist by the 

 side of one another. Tijen these two coinciding curves form the modifi- 

 cationcurve under a constant P and at a constant 7'; it represents 

 the liquid L of the equilibrium F -r F' -\- L. 



Now we change not only the T or the P, but both together and 

 in such a way that they are always in accordance with a point of 

 the curve r k in fig. 1 ; also we consider the vapourregion and the 

 heterogeneous region L — G. Tlien we find easily that the modifi- 

 cationcurve under its own vapourpressure and its corresponding 

 vapourcurve are circumphased. 



