441 
Br and the I. For the melting diagram has a form which is twice 
that of a system as discussed in the preceding paragraph (see the 
lower half of Fig. 4) so that both the combinations Br—IBr and 
IBr—I are comparable therewith. We may thus expect that this 
system is described by a spacial figure which is a doubling of our 
Fig. 2. 
Here, however, it must be borne in mind that the doubling is not 
a perfect one because the mixture of 50 atom percent Br and 50 | 
does not melt sharply, but has a melting range of 1° ; in the melting 
diagram only narrowing takes place at about the concentration «= 0.50. 
The same applies to the equilibrium L—G. Hence, as no disconti- 
nuity occurs” at that concentration the two semispacial figures will 
pass continuously into each other. 
Each of the semidiagrams will have to exhibit, in regard to the 
three-phase tension GLS, a maximum; between those two maxima 
a minimum must, therefore, be expected. 
3. An experimental investigation as to the three-phase pressure 
GLS in the system Br—I has been started by one of us some years 
ago; owing to particular circumstances it was postponed but has 
now been resumed in a somewhat different manner. *) 
The purification of the materials used took place in the same 
manner as with Meerum Terwoert. Pure Bromine from KAHLBAUM 
was first shaken for a few hours with water and then a KBr solution 
and ZnO were added. This mixture was distilled, the bromine layer 
distilled again and collected over P,O,. After remaining over night 
it was distilled off, it passed over entirely at 58°.3 (corrected) at 
751.6 m.m. pressure; nevertheless the first and the last portions of 
the distillate were not used. The thus made preparation had a sharp 
melting point at — 7°.4. The purification of the Iodine took place 
by subliming Zodium resublimatum with addition of KI and then 
drying over H,SO,. 
The modus operandi is represented in Fig. 3. In flask A was 
contained the mixture of Br and J. BC is a tensimeter containing 
strong sulphuric acid. The further arrangement E to M serves to 
compensate the vapour tension of the halogens as much as possible 
1) The investigation in 1912 took place with JAcKson’s glass manometer. There 
has only been made one preliminary measurement with the mixture of the com- 
position 1Br at 400,6. A three-phase pressure of 47.6 mm. of mercury was found. 
Now a pressure of 48.2 mm. has been found in two independent determinations at 
409.4, As the three-phase tension between 40.49 and 40.6° is indeed falling (see 
4 and fig. 4) the agreement is very satisfactory. 
