73 



In fig. 1 different satnt-alioncurves are completely or partly di-awn ; 

 the pressure increases along tlieni in the direction of the arrows. 

 Further it is apparent that along the saturationcnrve of Z^^the pressiii'e 

 is maximum or minimum in its points of intersection with the line 

 C F; the point of maximumpressure is situated closest to C. On 

 the curve bcdi/ig of fig. 1, which is only partly drawn, c is, 

 therefore, a point of maximum-, h a point of minimuinpressure. 



The pressure along a saturationcurve of the binary hydrate F' 

 (or F") is highest in the one and lowest in the other end, without 

 being however in these terminating points maximum or minimum. 

 On the curve ahgf of fig. i which is onlj^ partly drawn, the 

 pressure in a is the highest and in ƒ the lowest. 



This is also in accordance with the rule, formerly deduced, that 

 the pressure is maximum or minimum, when the phases 7*^, L, and (r 

 are situated on a straight line, but that this is no more the case 

 when this line coincides with a side of the triangle. 



As the vapour has always the composition C here the point of 

 maximum- and that of minimumpressure of the saturationcurve of F 

 are, tiierefore, always situated on the line CF; the saturationcurves 

 of F' and F" can, however, not have a point of maximum- or 

 niinimum-pressure. 



As we may obtain all solutions of the line Ch [C B and C A) 

 by adding water to F {F' and F'') or removing water from F {F' 

 and F"), we shall call the solutions of Ch {C B and .C A) pure 

 solutions of F {F' and F"). Further we call the solutions of C H 

 {CH' and C E") rich in water and those of Hh {H' B and H" A) 

 solutions poor in water. Consequently in fig. 1 a, c and e represent 

 pure solutions rich in water and ƒ, It and k pure solutions poor in 

 watei'. We may express now the above in the following way -. 



Of all solutions saturated at constant T with a binary or ternary 

 hydrate, the pure solution r-ich in water has the greatest and the 

 pure solution poor in water the lowest vapourjiressure. Therefore, 

 the pressure increases along the saturationcurve from the pure solution 

 poor in water towards the pure solution rich in water. When the 

 solid substance is a ternary hydrate, the highest pressure is at the 

 same time a maximum- and the lowest pressure also a minimum 

 pressure. 



We see that this is in accordance with the direction of the arrows 

 in fig. 1. 



/;) The solid substance is the component .4 or B or a binary com- 

 pound of A and B ; therefore, it docs not contain the volatile com- 

 ponent C, 



