823 
In order to apply this rule to fig. 1 we imagine the point D a 
little left from the line CZ; then we obtain a concentration-diagram 
of the type of fig. 1 (II), viz. a convex quintangle. The diagonal 
succession of the phases is then: A-—C—H—b—D—A,;; the succes- 
sion of the curves in the P,7-diagram must be, therefore, (A)—(C)— 
(h)—(B)—(D)—(A) or reversally, we see that this is in accordance 
with fig. 2. 
When we imagine the point D a little right from the line CZ, 
then the concentration-diagram forms a monoconcave quintangle, 
as in fig. 3 (Il). The diagonal succession of the phases is then also: 
A—C— E— B—D, so that the curves have to succeed one another 
as in fig. 2. 
In order to apply the rule to fig. 3 we imagine in this figure 
the point D a little at the right or at the left of the line CE. In 
the first case a biconcave quintangle arises [fig. 5 (I])], in the second 
case a monoconcave quintangle [tig. 3 (ID|. In both cases the dia- 
gonal succession of the phases is: A—C—H—B— DA; the succes- 
sion of the curves in the P,7-diagram must be, therefore: (A)— 
(C)—(E)}-—(B)—(D); this is in accordance with fig. 4. 
In order to apply the rule to fig. 5, we imagine also the point D 
in this figure a little at the right or at the left of CE. In both 
cases a monoconcave quintangle arises [fig. 3 (ID). The diagonal 
succession of the phases is then: A—B—D-—-C—E# or A—b—.b— 
C—D. When we bear in mind that in the P,7-diagram the curves 
(A) and (B) coincide, then we get a succession of the curves as 
in fig. 6. . 
In order to find the succession of the curves in the P,7-diagram 
which belongs to tig. 7, we imagine in fig. 7 the point D to be 
situated again a little at the right or at the left of the line CE; 
then in both cases a biconcave quintangle arises [fig. 5 (ID)|. The 
diagonal succession of the phases is then A—b—D—C—E or 
A—B--H—C—D. As the curves (A) and (B) coincide, a P,T-dia- 
gram as in fig. 8 arises. j 
In out previous considerations we have shifted a little the point 
D in each of the figures 1, 3, 5, and 7; it is evident that we might 
have shifted also the point C or £ a little. 
20. Quaternary systems with two indifferent phases. 
We have seen in communication III that four types of P, 7-dia-. 
gram exist in quaternary systems. When however, 2 indifferent 
phases occur in the invariant point, then, as we shall see further, 
12 types occur. In order to find those types, we might, just as in 
