( 462 ) 



only occurs between those two and, Uiei-efore, the tangeiit HM to 

 the three-pliase line must be the line indicating the j) ,t values for 

 tiie series of liquids and Aajtours having equal composition. 



Just as in F occurs as tangent to the three phase line the mel- 

 ting point line FK, which is the extreme limitation of the equilibria 

 betAveen solid and liquid, and in G the subliming line GL, which 

 is the extreme limitation for the equilibria solid and vapour, the 

 tangent in H is the line HM, which is the boiling point line of the 

 liquids with a constant boiling point, and also the extreme limitation 

 for the equilibria liquid-vapour ^). 



The points F G and H are, therefore, points of strictly related 

 significance; tlie^' are tlie points where the order of the phases sud- 

 denly changes. 



Let us now further considei- braiudi HI). In lig. 3 occurs a point 

 of maximum pressure T„ and of minimum pressure T^. The first 

 point is quite comparable with the maximum 7' \n the branch Cl'F, 

 the part Dl\ is again Ih on which, on heating, the transformation 

 L-^ S-\- G takes place, the part 7', 1\ is branch f<(, to which 

 belongs the reverse transformation, whilst in 1\ itself ti»e iieat of 

 transformation passes tiu-ougli zero. 



Owing to the continuous connection of D 7\, 7\ to IT(j, we 

 necessarily get a small i-ising part 7\ H of branch 1, after the line 

 has passed through a minimum 7'. The i)ossil)iiity of this minimum 

 may be exj)lained as follows : 



Just beyond 7'„, the amount of heat necessary to convert S -\- G 

 into L can at first increase, because L and G both approach in 

 composition to S, so that the quantity of (r concerned in the said 

 transformation diminishes with regard (o S. But as Ave approacii on 

 the three-phase line the ])oi]it H, L and G approach each other 

 more than they apju-oach ^' (for point //, where L^:iG, is reached 

 sooner than G, where >S' = G)\ consequently the i-atio of the phases 

 GjS, which transform themselves in L. becomes again larger and 

 the heat required for this again smaller until it liiially becomes zero 

 at T^ and beyond this point negative, in other words the trans- 

 formation again becomes Fj —^ !■> -\- G \ the small i)art 7\ If again 

 represents //> and kee|)s on doing so up to the point // wdiei-e the 

 transformation in branch 3 takes place. 



As the minimum 7\ does not coincide with the point H where 

 L=G, a small modification must be made in the /; ,.ivprqjection ot 



1) 111 llif liguie Hie liiK-'s HM and LG intersect. In the spacial figure this is 

 however, a crossing. 



