1140 



(^r-^,H) quant, of /:„+(//— V) (inant. •)\: F+i^—i/) quant, of F =0 (22) 

 in which always one of the coefficients is negative. This reaction 

 represents, according- to tiie sign of the coefficients : 



1. a congruent melting or soliditication of i^ -f" ^"^ "^'iz. the reaction 

 F-^F':^L,. 



2. an incongruent melting or soliditication of F -\- F' viz. the 

 reaction F:^F' -f L„ or F'-^ F -\- L,. 



Consequently the incongruent melting or solidification of F -\- F' 

 means: the inversion of F in F' or reversally, by the side of liquid 

 and vapour. 



From (18) and (20) it follows that Vx represents the change of 

 volume and i/, the change of entropy, when one (|uantity of vapour 

 is formed at this reaction. Therefore, Vx is the increase of volume, 

 Hx the increase of entropy at the congruent or incongruent melting 

 of i^+i^'. 



Between the three phases F, F' and G^, the reaction : 

 (,?' — (?) quant, of G^ -f {y ^ — {i') quant, of F -\- {S—y) quant, of F' =0 (23) 

 may take place. From (19) and (21) it follows that V\.x represents 

 the increase of \o\nn\e, H\,x the increase of entropy when one ciuantity 

 of vapour is formed at the reaction (23). V\.x is, therefore, the 

 increase of volume, H\x the increase of entropy at the congruent or 

 incongruent sublimation of F -\- F' . 



If we call Wx the (congruent or incongruent) heat of melting, and 

 W\,x the (congruent or incongruent) heat of sublimation of F~\-F', 



then Br =^ and Hi , = . Further we put tor the sake of 



abbreviation 



Fix. Wx-Vx. Wi,r = K (24) 



When Vx, the change of volume on melting of i^ -j- ^' Js positive, 

 K is certainly positive; when, iiowevei* Vx is negative, this form 

 will nevertheless still be also positive, by reason of the great value 

 of V\,x with respect to Vx- For this we shall assume K positive. 



When we put further -. 



AF= Fl, - T'M Vx and Air=. TFi., - (^A W,. . (25) 



it follows : 



(IP hW dP RT dT RT' 



T — = ; — = .AW ; — = LV . (26) 



dT AV dx K d.v K ^ ' 



— 1 is ihe ratio of the quantity ot A in the vapour to that in the 



liquid when we add a little A to the binary equilibrium /"-[- ^' + 



