1 ()(> 



The last reaction of .4 being the same as the tirst of .^i, the 

 reaction series AA^ consists of tive reactions, two of which are 

 three-phased. The same applies to the series i>/>\ and CC^. In the 

 cases marked 7 — 10 each series consists of seven reactions of which 

 three are three-phased; in the cases marked 10 — 12 each series 

 consists of nine reactions, four of which are three-phased. 



From the above table we also notice that if the liquidum point 

 L and the vapour point G appear in direct succession (type 1 — 6) 

 the reaction series consists of 5 reactions; if the points L and G 

 are separated from each other by a solid phase the reaction series 

 consists of 7 reactions (type 7 — JO) and if L and G are separated 

 from each other by both solid phases (type 11 — 12) it consists of 

 9 reactions. 



The reaction series appertaining»; to a definite type may be readily 

 deduced ft-oni a diagram in which the points F, F', S and D^ are 

 situated according to that assumed type. In fig. 1 they lie accord- 

 ing to type 1 or FLGF', in fig. 2 according to type 7 or FLF'G, 

 in fig. 3 according to type 11 or GFF'L. We now allow the four- 

 phase equilibrium in these figures to move in a positive direction, 

 starting from a point just before the mininium melting point, to a 

 point just behind the maximum sublimation point. The liquid then 

 traverses curve a c from a point close to S and situated between 

 S and a to a point close to D and situated between D and c. The 

 vapour then traverses curve a^c^ from a point situated close to S^ 

 and situated between >S'i and a^ to a point close to D^ and situated 

 between D^ and Cj, 



If now we consider the situation of the four points F, F, L and G 

 in regard to each other and the changes occurring in this system 

 owing to the moving of the system, we notice that in fig. 1 occurs 

 the reaction series 1 or AA^ in fig. 2 the reaction series 7 and in 

 fig. 3 the reaction series 11. 



The three-phase reactions F'^L -\- G ov F' "^L -\- G, which we 

 find in the series 7 — 12 can only appear in exceptional circumstances; 

 we shall see later that in this case the four-phase curve of the com- 

 plex F 4" F' comes into contact with the three-phase curve of the 

 compound F or F' . 



We wdl now consider more closely the P,2^-curve of the four- 

 phase equilibrium F + F' -\- L -\- G and for this take the relation 



dP A W 

 T — = . 



(IT LV 



As noticed previously this curve meets in the minimum melting 



