( 459 ) 



and in this waj' retrograde phenomena by variation in pressure 

 become possible. 



On the branches 2 and 3 a reversal of the direction of the trans- 

 formation caused by heat siipplv is as a rule not probable, as this 

 always consists in the evaporation of the solid matter, coupled with 

 melting of the same, or evaporation of the licpiid, processes which 

 generally want a supply of heat ^). The readiness of the reversal on 

 branch 1 is, therefore, closely connected with the fact that the liquid 

 phase is here the middle body. 



If we consider in an analogous manner the character of the three- 

 phase line on which the most volatile component A occurs as solid 

 phase, the order of the phases is here SGL, therefore the line AC 

 represents branch 3 ; in the point A, G and L become simultaneously 

 equal to S; consequently, there exists no branch corresponding with 

 branch 2 of the compound. On the three-phase line DB where the 

 least volatile compound B is the solid phase, the order is GLS, 

 therefore DB corresponds with branch 1. 



In the previously studied binary compounds the volatility of the 

 one component was so much smaller than that of the other, that on 

 the three-phase line only the branches 1 and 2 were noticed ; if 

 the second constituent is sufficiently volatile branch 3 may be met'^ 

 with as in the case of JCl and JOl^. 



Such is the state of affairs in the case that the vapour tension of 

 the liquid mixtures gradually decreases from 100% -4 to 100 "/„ ^. 



If now, however, a minimum or a maximum occurs in the vapour 

 tensions the possibility may arise that, somewhere on the three-phase 

 line of a compound, the liquid and vapour phases, wich coexist 

 with the solid phase, become equal in comi)Osition ; and the question 

 arises what significance this fact possesses foi- the division of the 

 three-phase line. 



In his communication cited Dr. Smits has for the first time o-iven 

 the three-phase lines for both cases and also the p , ./'-projections of 

 the appertaining spacial figure but has not further investigated the 

 character of the different parts of the three-phase line. 



Let us first take the case that a minimum occurs in the p-,v-\h\es 

 foi- liquid-vapoTU'. If (he compound in liquid and gaseous state was 



^) The special cases where reversal might take place will not be considered here. 



-) If branch 3 is wanting because on branch 2, S nowhere becomes equal to G, 

 there is still a possibility tlial this occurs somewhere on the three-phase line 

 vvhich the compound with the least volatile component as solid phase and vapour 

 gives below the point D. This we cannot further enter into. 



32 



Proceedings Royal Acad. Arasterdam. Vol. VIII. 



