(178) 



In order to be able to apply this equation, we must know the 

 sign of the ditferent quantities in the point where the line solid- fluid 

 intersects the vapour branch of the border-line, both for the same 

 \alue of X. 



If we apply the equation 



\dT,f)r v,f 



to the line for solid-fluid ^Fig. 1) and the analogous relation: 



to the vapour-branch of tiie border-line (Fig. 2) as far as the plait- 

 point K, the quantities ivi^ , Vf,f, iv^f SiWÓ. vir, have the sign indicated 

 ill the figs. (1) and (2) in different places. 



T T 



Fig. 1. Fig. 2. 



Let us suppose we begin with a temperature far removed from 

 a plaitpoint. Then the liquid branch of the border-line will be inter- 

 sected by the upmost branch of the line solid-fluid, and the vapour 

 branch of the bordei'-line will be intersected bj tlie downmost 

 branch of the curve for solid-fluid. 



The first intersection, now, yields a point of the already discussed 

 melting-point line under the vapour pressure, the second intersection 

 on the other hand indicates a point of the vapour-line to which our 

 equation (3) refers. 



So, as this latter intersection takes place between the lower branches 

 of the two lines, the quantities mentioned above all have the negative 

 sign in the point of intersection. 



[f we write down the second term of the righthand member of 

 equation (3j once more separately with the signs over resp. under 

 the different quantities, we get : 



if^lg • Vsf — tVsf . Vlg 



{Xs Wg) Vlg 



{.VI Wg) Vsf 



+ 



(-i) 



