( 175 ) 



the introdnc'tioii, and tlie melting point line must approach the plail 

 {G ^=z L) with rise of temperature. P>ut we know that t».,/- passes 

 through zero at this a|)proacii and becomes greater and greater 

 positive, which has tlie consequence that also vr,/- can |)ass through 

 zero, after which it continually increases in ptjsitive value. 



Now it follows from equation (4) that in_^f becomes zero for a 

 positive value of Vgf. So if ?',ƒ = 0, iv^f has still a negative value; 

 so at that moment numerator and denominator are still posiiive. 

 This is also still the case when Vsf is posiiive and ?/;,/• still negative, 

 but on approach to the pïaitpoint iv/ continually increases in positive 

 value, in consequence of which ?/;.,ƒ also becomes positive, and then 

 for a certain positive value of v,,f and corresponding positive value 

 of lu^f, the numerator will become = zero, in consequence of which 

 the melting point line gets a vertical tangent for the second time. 



Above this point Wsf . VfjL begins to exceed more and more the 

 first term ?r^/^ . Vgf, the denominator becoming smaller, so that 



7'—— becomes larger and larger negative, and the melting point line 

 dT 



becomes more retrograde, till the plaitpoint has been reached, at 



which numerator and denominator become = 0. But as then also 



(Lvi 

 T -—- will be = — 00 . 

 dT 



It is of importance to point out here, that the positive sign of 

 lUsf at the critical end-point p also follows from the circumstance 

 that for a critical end-point, for which : 



Xj—.VL a^g — A'L 



follows from equations (1) and (2), 



t'^ =Tf^ ^ =^ 

 dTsig XdTsfJx Vsf 



or in words, that the line for the equilibrium between solid-fluid at 



constant x touches the three-phase line just in the plaitpoint /;. 



„, dTsifj 

 As now I - — - IS positive in this point, while v,f is also positive, 



dp J r ^ 



it follows from this that also id,/ must have a positive value in the 



12* 



