REPRESENTATION BY ZETA FUNCTION 319 



situated as in Fig. 14 or as in Fig. 16. We shall now deduce 

 that the equilibria resulting from Fig. 14 may be represented 

 by Fig. 15, and those resulting from Fig. 16 by Fig. 17. 



19. AtT = T(a) three points of the line (TF)a'(i/) of Fig. 14 

 represent stable phases. So at T = T(a) the reaction 



solid X + solid H ^ L{a) (27) 



can occur. We represent L{a) in Fig. 15 by the point a. At a 

 temperature a little higher than T{a) the f-curve intersects the 

 line {W){H)', we may now draw tangents from {W) and (//), 

 the points of contact representing liquids saturated with 

 respect to W and H respectively. At a temperature a little 

 lower than T{a) the f -curve lies above {W){H), so that only 

 solid W and solid H exist as stable states. The tangents drawn 

 from {W) and (H) now represent metastable systems only. 

 From Fig. 14 we may therefore make the following deductions 

 regarding Fig. 15. A field, solid W + solid H, must be situated 

 below point a (Field I) ; two saturation curves, namely those of 

 W and H, must run through the point a, their parts proceeding 

 towards higher temperatures representing stable liquids, whilst 

 the parts situated in Field I represent metastable liquids. 

 In a corresponding manner it is apparent that at T = T(b) 

 the reaction 



solid H + solid X ^ L(6) (28) 



can occur. If in Fig. 15 we represent L(6) by point 6, we find 

 that the saturation curves running through h must be situated 

 as shown, whilst Field II represents solid H + solid X. 



Since we have already proved that the saturation curve of H 

 must have a maximum at T = T{H) in point m, it follows that 

 we can represent by Fig. 15 all the equilibria resulting from 

 Fig. 14. 



20. ki T = T{a) in Fig. 16 the same obtains for the line 

 {W)a'{H) as in Fig. 14. ki T = T{h), however, in Fig. 16 the 

 point (H) is situated between b' and (X). Instead of reaction 

 (28) we must now have 



sohd H ^ L(6) + solid X. (29) 



