105 



From all this it follows Ihal in (lie system F -\- F' -\- L -{- G 

 many reactions are possible as a rule; in (he vieiuity of the minimum 

 melting point, however, always one of the reaction series A, B oi' 

 C occurs and iji (he vicinity of llie maximum sublimation point 

 one of the series .l^, i>\ or 6\. 



Let us now consider the four points F, F' , S and D^ situated 

 on a straight line. In fig. 1 tliese lie in the order FSD^F' or in 

 the reverse order F'B.SF ; in fig. 2 the order is FSF' D, or D.F'SF, 

 in tig. 3 it is D.FF'S or SF'FD,. 



In all, we can distinguish 24 cases; as, however, each succession 

 from the right to tlie left corresponds with a succession from the 

 left to the riglit, there are only twelve types. If we replace the 

 point S of the liquidum curve by L and the point i)i of the vapour 

 curve by (t we find : 



FF'LG, FF'GL, F'FLG, F' FGL, FLGF', 

 FGLF', FLF'G. FGF L, FLFG, F'GFL, 

 LFF'G end LF'FG. 



We now allow the four-phase equilibrium to move in a positive 

 direction staiting from a point just before the minimum melting- 

 point, to a ])oint just behind the maximum sublimation point. 

 To this movement belongs a definite reaction series which however, 

 is dependent on the situation of the points F, F', S and D^, in 

 regard to each other, so that to each type belongs a definite reaction 

 series. Each of these series commences of course, with one of the 

 series A, B or C and terminates with one of the series /Ij, ^j or C'l, 



From a consideration of the difterent cases we can deduce the 

 following table in which the different types and their correlated 

 reaction series are united. 



Type : Reaction series : 



1) FLGF' A; A, 



2) FGLF' A; A, 



3) FF'LG B; B, 



4) FF'GL B-B, 



5) F'FLG 6; 6, 



6) F'FGL C; C, 



7j FLF'G A; F':^L^ G; B, 



8) F'LFG A; F:^L + G; C, 



9) FG'FL B; F':^L-\- G; A, 



10) F'GFL C; L:^L-^G; A, 



11 ) LF'FG B; F':^L -f G-, F + F' -^L^G- F:^L-^ G- 6\ 

 n) LFF'G C;F:^L-^G; F -^ F' :^ L -{- G-, F'-^L^G;B, 



