561 
that line is tangent therefore in /’ to the three-phasé line and # is 
justly called the minimum melting point. Also in G wG—as, hence 
mp OF Qos eat ; 
Hig = —— and the sublimation curve of the compound is tangent 
here to the three-phase line. “And in M ay, —aq, hence 
p oF Sas Us Var 
ds, Vas Vis Qar 
which involves the meeting of the three-phase line and the “line 
of the minima on the GZ surface”. 
By these tangential contacts the P7-section at the composition of the 
compound gets the simple form of tig. 4") LG FK is a continuous curve 
although LG is the quasi-unary subli- 
mation curve, GH part of the three- 
phase line, and /’A’ the quasi-unary 
melting line of the compound. /’P and 
GP are demarcations for the complete 
T condensation and evaporation, respec- 
tively. From a purely unary diagram, 
Fig. 4. this figure is distinguished only by the 
fact that the triplepoint has grown to a range G/ and the pheno- 
mena of the condensation and evaporation take place not at a single 
limit value, but also over an interval. 
With a system of the type Br-[ the difference with unary behaviour 
is much greater still. Beeanse two phases nowhere attain the same 
composition, we miss the tangents at the three-phase line, in 
fact all lines for quasi-unary equilibrium 
get doubled to two streak limits. In 
Fig. 5 we notice the P7-section for 
v= 0.50. Fig. 5 therefore indicates the P7- 
condition diagram for the compound IBr 
and it may be readily deduced from the 
spacial figure (compare Fig. 5 of the third 
communication) or from our Fig. 3. It is 
Fig. 5. only one possible configuration; at the 
deduction it will be noticed that the mutual relations of the concen- 
trations of coexisting phases decide the form of a figure such as Fig. 5. 
When following the section up from lower temperature we intersect 
first the region S+G. In point 1 the section for the first time 
meets the three-phase region, namely in the line indicating the 
composition of the mixed crystals. In point 2 the liquid branch 
1) Wuire, Dissert Amsterdam 1909 p. 19. 
26 
JD 
Proceedings Royal Acad. Amsterdam. Vol XIX 
