( 469 )- 
rapidly, we should therefore undoubtedly get from the liquid mixtures 
solid pyridine (m.p. —50 ) and solid methyl iodide (m.p. below —80°). 
Moreover, all those liquid mixtures in which no compound has 
formed as yet are homogeneous. 
If, however, the liquid mixtures are kept for some time, the 
compound is formed with a considerable evolution of heat and it 
separates at the ordinary temperature in the solid condition, the 
amount depending on the temperature and the proportion of the 
mixture. At higher temperatures, however, it may cause the formation 
of two liquid layers. The peculiar behaviour shown is elucidated in 
the annexed figure in which the composition of the mixtures is 
expressed in molecule-percents of pyridine. 
Let us first glance at the 
7/20 5 : D 
Ee right side of the figure. In this 
‚ 1 is the melting- or solubility- 
4 4 L /00 
line of the compound, commen- 
cing with the melting point of 
the compound (117°) and ex- 
tending to a _ eutectic point 
very close to the melting point 
of pyridine, because at lower 
temperatures the compound is 
but little soluble in pyridine. 
ar. AY 61° from dS Dm ol 
oe, eee L go° 
go" 
zo" 
bo 
JY of pyridine, the line 1 is however 
a interrupted as no homogeneous 
-10° 
liquid can exist between the 
-20° two concentrations. The line 2 
ineloses with its two branches, 
-49 which meet in M, an immisci- 
-§°° bility-region which becomes 
|S! —t 20" ‘ 10° » 1: HAR 
0 0 20 go 40 0 60 ~ 90, 92,100 enlarged at higher temperatures. 
EC The fused compound is therefore 
miscible with pyridine toa limited extent only. The point M, however, 
ean only be reached when there is no separation of solid compound 
which may be easily prevented for some time. 
At the left side of the figure we meet with nearly the same 
series of phenomena: 3 is here the solubility line, 4 the two branches 
of the immiscibility line. The immiscibility region is here very great, 
at 88° from about 0.5 to 41 mol.°/, of pyridine, whilst no change 
could be observed at higher temperatures and consequently no 
critical mixing point is known. 
