( 588 ) 



evidently also for the general case that b ^ 0). Comparison with 



tig. 4 teaches us, that tlie point M, where the three phase pressure 

 begins, lies at a temperature lower than that of R.^. If the three 

 phase pressure lies between the vapour pressures of the two com- 

 ponents (the full-traced curves starting from Cj and (7, represent the 

 vapour tension lines), in other words if «i^.»,,, then fig. 6 holds; 

 if on the other hand x, ^ x^ and the three phase pressure always 

 higher than the vapour pressure of the two components, then fig. 6a 

 holds. The line C^R shows then a minimum. (In the figure the three 

 phase pressure line is always denoted by AAA). 



b. Principal tijpe IF. 



After what has been discussed above, the relations for this type 

 may be made sutficiently clear even without diagrams. At a tem- 

 perature somewhat lower than that of li^, where the spinodal line 

 again touches the plaitpoint line (now C\A) a three phase equilibrium 

 again prevails. Now the gas phase 3 does not split up into 3 and 

 1, as with type I, but the liquid phase 2 into two liquid phases 2 

 and 1. Just as with type I the plaitpoints from M (between R^ and 

 Ci) to A were unrealizable (cf. also fig. 6), those from M (now between 

 7?3 and C») to A are now also unrealizable. Tlie three phase equi- 

 librium formed continues to exist down to the lowest temperatures. 

 Here the same phenomenon of the minimum critical temperature in 

 the neighbourhood of C^ is met with as with type I. At tempera- 

 tures lower than 2'=: 0,96 1\ the two liquid pliases 1 and 2 are 

 no longer to be mixed to one homogeneous phase by pressure, 

 however great. 



The successive y^ .;,'-lines are again omitted. 



Finally we find in fig. 7 the />, 7 -representation. The three phase 

 pressure line lies here between the two vapour pressure lines, so 

 that .I'j <^ .fj on the border near x = 0. 



c. Principal ti/pe III. 



The possibility of this type for mixtures of Mt»/'»ia/ substances will 

 be examined separately afterwards. Wlien it occurs (inter alia for 

 mixtures of C.,II„ with C5H5OH3, etc,, for triethylamine and water), 

 then the plaitpoint line C\C.2 has the shape drawn in fig. 8. 



If we pass downward from the higher critical temperature at Cj, 

 a (l()ul>le plaitpoint will again occur at A^ at the temperature indi- 

 cated liy /,, hence t'oniialioii of an i^cihiknl coinioilal line as in tig. 3, 

 at soniewiuil lower temiieraliire. This li'oes on till at I (he closed 



