1 141 



-\- />„ -|- ^/'„ ; we may call lliis müü the liiiiitratio of .1 in /''-|--^''' + 



+ ^^0 + (Ar 



Considering the cases ( ^ M <C i ^^"<^' ( ) ^ ^ i'^ connection with 



tlie valnes ofFi.,,, Vx, U^ii andlT,. ( T^, can also be negative) it follows : 

 The F,T curve of the ternary e(|nilibrinm 7''-)- 7^'' -)- L + ^^ ends 

 in the quadruplepoint F -\- F' -\- L,,-\- <r„ ; it is a curve ascendant 

 with the temperature, when the limitratio of A is smaller or only 

 a little larger than 1 ; it may have a point of maximumpressure 

 when the limitratio of A is much greater than 1 ; it may have, 

 besides the point of maximumpressure, also a point of maximum- 

 temperature, when the limitratio of .4 is \'ery large (e. g. larger than 

 40000) and when the volume increases at the congruent or incon- 

 gruent melting of F -\- F' . 



We may express the previous also in the following way : 

 The congruent or incongruent melting-point of two substances 

 [F -\- F') is always lowered by addition of a new substance, when 

 we take the pressure constant; generally this is also the case when 

 this addition takes place under its own vapourpressure. In the latter 

 case the temperature may however, before it decreases, yet first 

 rise a little. This can take place however onl}' in the case that the 



imitratio ( — ) of the new substance in F -\- F' + L,, -\- 6r„ is YQry 



large and when the volume increases at the formation of liquid 

 from F-\- F'. 



The vapourpressure of the congruent or incongruent meltingpoint, 

 can by addition of the new substance according to the value of 



— , either decrease immediatelv oi-, before it decreases, firstly in- 



crease. This latter is certainly the case when the temperature increases 

 also firstly, but it may also take place then, when the tem[>erature 

 decreases immediately. 



Let us now consider the case that ( — 1 is exceedingly small or 



approaches to zero. This will be the case when the quantity of A 



is exceedingly small in the vai)oiir, therefore, e.g. when .4 is a salt, 



very little or not volatile. From (25) and (26) then follows : 



ilP U'l^. dP RT dT RT' 



dT Vi,a, dx K •' dx K ^ ^ 



As W\.x represents the (congruent or incongruent) heat of subli- 



