( 198 ) 



As to the points a^ and y^, tliey move upward with increase of 

 temperature. 



Tiie result of tliese shiftings must of course be, as lias been just 

 said, that at the maximum temperature of the three phase line (see 

 Fig-, 1) the two three phase pressures become equal, and the points 

 Ci and c\, like e^ and e\, coincide; then the solubility isotherm does 

 not cut the liquid line any longer, but just touches it in the point 

 where c\ and c\ have coincided, after which no three phase pressure 

 is possil)le and the solubility isotherm has got detached from the 

 liquid line. 



Though all this seems very simi)le, the representation of the inter- 

 mediate stages presented some difficulties, which Prof. v. d. Waals 

 was kind enough to renioxe by allowing me to examine some T-x- 

 diagrams corresponding Avi(h pressures respectively smaller, equal 

 and larger than the three phase pressure, in which exactly the same 

 succession of states occurred ^). 



What lias been drawn in accordance with this in the figs. 3, 4 

 and 5, may be brought into words in the following way : 



When the two three phase pressures have dra\vn so near, that 

 the two branches of the solubility isotherm loould touch, intersection 

 takes place, and we get a curve as is indicated by fiC^e\c^c\f\ 

 in Fig. 3. Immediately afterwards, i.e. at somewhat higher temperature 

 a })orlion gels detached, as i-epresented in Fig. 4 and we get two 

 solubility isotherms; one is f c c' f and the other forms a closed 

 curve e e' d, a part of which {e <'') runs through the stable region. 



At the maximum temperature of the three phase line the two 

 three phase pressures e c s and e' c' s have coincided, as is represented 

 in the diagram corresponding with the temperature /g, in Fig. 4, 

 and the solubility isotherm /j Cj /V no longer cuts the liquid curve, 

 but only touches it in the point c^. 



With the exception of this one point it runs therefore wholly 

 through the stable region. The other closed branch no longer cuts 

 the vapour curve, but only touches it in e^ ; further this branch 

 as a whole has contracted through the shifting of d to d^. This 

 second branch of the solubility isotherm lies therefore at the maximum 

 three phase pressure partly in the unstable region, partly in the 

 metastable region. 



At a temperature slightly above the maximum temperature of the 

 three phase curve /., the solubility isotherm ƒƒ' is quite detached 

 from the liquid curve, as is i-epresented in B'ig. 5; in the same 



1) See the foregoing paper by van der Waals. 



