80 



Let us now contemplate the solution m of fig. 3 saturated with 

 the liydrales F -\- F' ; it is apparent from the figure that solution w< 

 has a smaller vapourpressure than / or ii. When we talve however 



Fig. 3. 



the solution h, saturated wiili these hydrates, this has a larger 

 vapourpressure than the solutions a and c. 



Curve !>(/ represents the solutions of the e(|uililirinni F-{-F'-\- L-\-G; 

 point H is the point of maxinuimteniperatuve of this curve. In 

 accordance with our pi-evions definitions we call the liquids of bi-anch 

 pH rich in water and those of branch Nq poor in v^rater. We then 

 may express what precedes in this way: 



the solution saturated with two components or with their hydrates 

 has in the region rich in water always a smaller vapoui-pressui-e, 

 in I'ne region poor in water ahvays a greater vapourpressure than 

 the pure solution of each of the substances separately. 



Let us now take a liquid saturated with a double salt and one 

 of its limit-substances. [In fig. 1 the series of solutions saturated 

 with F of curx-e bed is limited in /; by the occurrence of F' and 

 in d by the occurrence of F". Therefore we shall call F' and F" 

 the limit-substancep of the double-salt F]. Curve po represents the 

 solutions of the equilibrium F -\- F' -\- L -\- G, curve oc/ those of 

 the equilibrium F' -}- F -\- L -[- G and curve oi those of the equili- 

 brium F" -\- F -\- L ^ G. ^f and M' are points of maximum- 

 temperature of these curves, in accordance with previous definitions 

 we call solutions of oM and oM' rich in water and tiiose of M(/ 

 and M'i poor in water. 



