78 



vapour pressure the pressure is tlie same in all points and equal to 

 the pressure of sublimation of the ice. 



Now we shall consider the boiliugpointcurves ; in general tlie 

 same applies to them as to the saturationcurves under their own 

 vapourpressure, which we have considered above. 



Now we assume that the curves in fig. 1 repj'esent boilingpoiuf- 

 curves; ihe |)oint H no longer represents a point of maximum 

 temperature, but a point of maximum pressure; consequently it is 

 always silnated l)etween 6' and /•. This point of maximumpressure 

 H is always situated ch)ser to C than the point of maximum tem- 

 |)erature /7 ; the same applies to the points //' and H" in the figs. 

 2 and 3. Wishing to indicate by arrows the direction in which the 

 temperature increases, we must give the opposite direction to the 

 arrows in the tigs. 1 — 3. 



We saw before that on the side CB of fig. 2 a point of maxi- 

 mumtemperatnre H' may either occur or not; on this side, however, 

 always a })oint of maximumpressure is situated. The same applies 

 to the side CA. We now liiid the following. 



a) of all solutions satni-ated under constant P with a binai-y or 

 ternary hydrate, the pure solution rich in water has the lowest — 

 and the i)ui-c solution poor in watei- the highest boiling-point. There- 

 fore, the boilingpoini im-reases along the boilingpointcurve from the 

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

 When the solid substance is a ternary hydrate, the highest boiling- 

 point is at the same time a maximum- and the lowest at tlie same 

 time a minimumboilingpoint. 



b) along the boilingpointcurve of a component or of an anhydric 

 double-salt the boilingpoint increases from the pure solution. When 

 the solid substance is an anhydric double-salt, the boilingpoint of 

 the pure solntion is at the same time a minimum. 



c) along the curve of the S(jlu(ions saturated with ice nnder a 

 constant pressure the boilingpoint is the same in all the points and 

 it is equal to the sublimationpoint of the ice. 



The icecurve under its own vapourpressure of the temperature 

 T and the boilingpointcurve of the ice under the pressure P coincide, 

 therefore, when P is the pressure of sublimation of the ice at the 

 temperature 7. 



The following is amongst others apparent from what precedes. 

 We take a pure solution of a solid substance (component, binary or 

 ternary compound). Through this solution pass a saturationcurve 



