( 176 ) 



point p. T mentioned this here because for tlie 



same reason lOgf is generally negative at the 



second critical end-point q. 



/ \ So when no other complications had made 



/ K their appearance, the melting-point line of 



/ / Na,SO^ would have had a sliaoe as has been 



/ / ' 



T I / given schematically in fig. 2. 



/ / The found melting-point line, however, de- 



viates from this, for before the point B.^ has 

 been reached the rhombic modification of NajSO^ 

 has changed into the monoclinic one, in conse- 

 quence of which a very interesting part of the 

 melting-point line disappears and already below 

 ^ the point R^ a new melting point line Joins 



Fig. 2. the first ; the new line immediately runs back, 



which proves that lOs/Vgi is already stronger positive than ?<;^L2;,y for 

 the new modification. 



If we now proceed to discuss the second critical end-point q, 



where also: 



\dTJsLG y^^^JsG ^^/" 



we see at once that if — as is the case for ether-anthraquinone — the 

 expression T(^ ) in ^ is negative, ?ty will have to be negative, 



\dTjsLG 



because is/ is undoubtedly positive in that point. So it follows from 

 this circumstance, w4iich is the normal one in my opinion, that the 

 positive value of v../ in the point q does not suffice to make also 

 Wsf positive ; so the locus id,/ = seems already to ha\e retreated 

 inside the liquid branch of the connodal line at q. 



So somewhat above the point q the numerator of the second 

 member of equation (3) is positive, the denominator also being 

 positive, so : 



7 — =: positive 

 dT ^ 



Rise of temperature does not bring about any change in tliis; 

 when the temperature falls to the second critical end-point q 



dxi 

 T — becomes = -^ go . 

 dT 



So if also the point q had lain on the ascending branch of the 

 three-phase line, so that in this case T-— would have been positive 



