81 



The following is apparent from I he direction of (he arrows in 

 fig. J. 



a. In ihe region of tiie liquids rich in water. When a doublesalt 

 is soluble in water withont decomposition, the solution satuiated 

 with this double-salt and with one of its liniit-sul>stances has a 

 smaller vapourpressure than the pure solulion of the (loul>lesalt and 

 also than that of the limit-substance. 



When a double-salt is decomposed by water, the solution saturated 

 with this double-salt and one of its limit-substances has a smaller 

 vapour pressure than the pure solution of the limit-substance. The 

 solution saturated with double-salt aud with the limit-substance, which 

 is not separated, has a smaller vapour-pressure than the solution, 

 saturated with double-salt ami with tiie limit-substance, which is 

 separated. 



h. In the region of the liquids poor in water the opposite takes 

 place. 



As a special case a liquid can be saturated with two substances 

 of such a composition, that one of these may be foi'med from the other 



by addition of watei'. They are 

 represented then by two points F 

 and F' , which are situated with C 

 on a straight line. In fig. 4 this line 

 CFF' does not coincide with one 

 side of the triangle. In this figure 

 a e c f is a satnrationcurve under 

 its own vapourpressure of /^^, cur\'e 

 h e (1/ one of F' ; the ari-ows 

 indicate the direction, in which 

 the pressure increases. Both the 

 curves can be circnni- or exphased 



Fig. 4. 



and they either intersect or they do not. In tig. 4 they intersect 

 in e and ƒ, so that the equilibria F -f- F' -{- Le -j- G and 

 F -\- F' -\- Lf -\- G occnr. Now we can prove that the vapour 

 pressure of those two equilibria is Ihe same, therefore Pe=^ Pf. 

 When we remove viz. the licpdd from both the equilibria, we retain 

 F ^ F' -^ G. As between these three phases the reaction i'^y^'-J-^r 

 is possible, we can consider F -\- F' -|- 6r as a binary system. We 

 then have two components in three phases, so that the equilibrium 

 is monovariant. At each tenq)ei'ature F -\- F' -\- G has, therefore, 

 oidy one definite vapourpressure, from which immediately follows: 



Fe=-Pf- 



6 



Proceedings Royal Acad. Amsterdam. Vol, XVll. 



