The phase rule and its applications . ven a diagrammatic representation of thetwo kinds of pressure-concentration curves which have so far been obtained. In the onecase, the vapour pressureof the invariant system (atconstant temperature) lieshigher than the vapourpressure of either of thepure components; a phe-nomenon which is verygenerally found in thecase of partially miscibleliquids, ether Accordingly, bythe addition of water toether, or of ether towater, there is an increase in the total vapour pressure of thesystem. With regard to the second type, the vapour pressure ofthe
The phase rule and its applications . ven a diagrammatic representation of thetwo kinds of pressure-concentration curves which have so far been obtained. In the onecase, the vapour pressureof the invariant system (atconstant temperature) lieshigher than the vapourpressure of either of thepure components; a phe-nomenon which is verygenerally found in thecase of partially miscibleliquids, ether Accordingly, bythe addition of water toether, or of ether towater, there is an increase in the total vapour pressure of thesystem. With regard to the second type, the vapour pressure ofthe systems with two liquid phases lies between that of thetwo single components. An example of this is found insulphur dioxide and On adding sulphur dioxide towater there is an increase of the total vapour pressure; buton adding water to liquid sulphur dioxide, the total vapourpressure is diminished. The case that the vapour pressure of the system with twoliquid phases is less than that of each of the components is Concentration Fig. 25. 1 Konowaloff, toe. cit. 2 Roozeboom, Zeitschr. physikal. Chem. I, 8. 526 ; Rec. Trav. Chim. , 1884, 3. 38. SOLUTIONS 107 With regard to the partial pressure of the components, thebehaviour is more uniform. The partial pressure of onecomponent is in all cases lowered by the addition of the othercomponent, the diminution being approximately proportionalto the amount added. If two liquid phases are present, thepartial pressure of the components, as well as the total pressure,is constant, and is the same for both phases. That is to say,in the case of the two liquids, saturated solution of water inether, and of ether in water, the partial pressure of the ether inthe vapour in contact with the one solution is the same as thatin the vapour over the other Complete Miscibility.—Although the phenomena of com-plete miscibility are here treated under a separate heading, itmust not be thought that there is any essen
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