849 



point of maxiniiun pressure Q of (he eqiiilibritiiii B -\- L -\- (I and 

 the uri-ows in opposite direction, then \ve liave : on increase of P 

 the boilingpoint curve disappears in Q [fig. 5 (XI)J, when the con- 

 centration of the new substance is greater in the liquid than in the 

 vapour; it does not disappear in Q [tig. 6 (XT)], when the concen- 

 tration of the new substance is smaller in the liquid than in the vapour. 



Of course we have meant above with concenti'ation the perspective 

 concentration. 



From the m^-aning of the perspective concentrations aS and >Si of 

 a new substance, it follows immediate!}' : 



for equilibria in the vicinity of the side BC {x = 0) : 



when aS^aSi then also i/i'- y'^ x^: x and reversally, 

 when>S<AS, „ „ in:y<^-r.,:x „ 



for equilibria in the vicinity of the side BA {y = 0) : 



when >S^ *Si then also x^ : x ^ y^ -. y and reversally, 

 when S < *S\ „ „ X, : x > y, : y „ 



On increase of pressure the boilingpointcurve hn of fig. 2 changes 

 its position and form in order to disappear at last. This may take 

 place in different ways which we shall consider now. We have seen 

 at the deduction of the boilingpointcurves of the binary compound F, 

 that the point of maximum pressure Q of the binary system F-\- L -f- (r 

 takes a prominent position, it is evident that this is also the case 

 with the boilingpoint curves of the substance B. 



We saw before that we may distinguish the three cases men- 

 tioned sub 1", 2", and 3" with regard to the movement of the 

 region LG on decrease of F or increase of T. In the case mentioned 

 sub 1" as well the solvent C as A is more volatile than the solid 

 substance B. Therefore a point of maximum pressure of the binary 

 equilibrium B -\- L -\- G can be" situated either on BC or not; the 

 same applies to the side BA. 



In the case sub 2" both the solvents A and C are less volatile 

 than the substance B; therefore neither on BA nor on BC can a 

 point of maximum pressure be situated. 



In the case mentioned sub 3° C is more volatile, A however less 

 volatile than the substance B ; therefore on j5C either a point of maxi- 

 mum pressure occurs or it does not; this is however not possible on BA. 



With regard to the occurrence of a point of maximum pressure in 

 both the binary systems B -{- L -\- G, we may, therefore, distinguish 

 three cases : 



a. no point of maximum pressure occurs. 



fj- one 



c. two points „ „ „ occur. 



