559 
second maximum 7, the crossing at M and the appearance of a 
minimum pressure in the Pe-seetions of the system is, therefore, 
a necessity. *) 
4. Now in the system Br-I also appear two maxima and one 
minimum, but in this system neither «gs becomes = a, nor ag— «Gq, 
nor «r— vg at any temperature, as has been proved by the deter- 
minations of the melting and boiling curves by Mrrrum Terwoer ®). 
Only, the differences #s—aqG and «#s— ay, show and approach to 
O and this is sufficient to cause the 
appearance of the three marked points. 
Os For this we have only to examine 
Fig. 3, which indicates sketchily the 
proportions in the system Br-I in P7 
and Te figure. 
P 
Starting in O 4 the value of the con- 
centration fraction will at first 
UIT UL 
again increase and the value may become 
Qs 
equal to ——, thus causing the maximum 7'to appear. As the nume- 
CLS 
rator in equation (2) here becomes negative, the three-phase line will 
fall. This fall will be very pronounced, for the denominator of the 
concentration fraction decreases very strongly. For at about «= 0.5 
the narrowing on the melting curve is very strong; it is, however, 
conceivable that the denominator in the second member of equation 
(2) will not turn to zero, for then the concentration fraction should 
assume the value 10000. 
Meanwhile, not only the denominator of the concentration fraction 
assumes a small value, but the numerator will also decline particu- 
larly after the temperature has been passed at which the narrowing 
on the melting curve occurs. It is well known that vapour pressure *) 
or boilingdiagrams of systems with a compound present a narrowing 
all the stronger when the dissociation is less. The boiling diagram *) 
of the system Br—I also exhibits such a narrowing, even at a tem- 
perature about 100° above that of the three-phase line. This narrowing 
1) It is meanwhile evident that this relation is not necessarily decisive. For 
beyond H the concentration fraction must a/so attaintheratio of the caloric values 
(Consult the papers cited), 
*) Diss. A'dam 1904 and Zeitschr. f. anorgan. Chem. 47, 205 (1905). 
3) In this connexion see J. J. vAN LAAR, Zeitschr f. physik. Chem. 47, 129 (19C4). 
4) P, C. E. MEerum Terwoert, loc. cit. 
