1096 
in an air-bath. If the first critical end-point was observed, the pres- 
sure and temperature of p were determined oy the Cam.Lerer-method 
and g was also sought for. 
The binary systems which | examined are the following: 
Ether-alizarine. 
A preliminary investigation by Smirs ') had already shown that 
the three-phase line intersects the plaitpoint line. The meltingpoint 
of alizarine (290°) is about as high as that of anthraquinone (284.6°) 
and much above the critical point of ether (77, 193.9°, P;, 36.1 atm.). 
I observed the first critical end-point p at 196.4° and 37.5 atm. 
So the solubility of alizarine in ether proves to be so small, that 
the critical temperature of ether is only increased by 2.5°. This in- 
crement is much smaller than in the case of the ether-anthraquinone 
system, where p lies at 203° and 43 atm. 
For the determination of g a mixture of higher concentration of 
alizarine was required. The large quantity of alizarine caused however 
the observation to be extremely difficult; the vapour-phase and the 
liquid-phase were both dark black-red, so that the meniscus was no 
more to be distinguished. On this account it could only approxi- 
mately be established, that qg lies about 258°; the system was im- 
proper for an exact investigation. 
Ether-hexachlorobenzene. 
The melting-point of hexachlorobenzene lies at 224°; the difference 
with the critical temperature of ether being much smaller than in 
the former case. The solubility appeared to be so great, that the 
three-phase curve does not meet the plaitpoint line. 
Ether-isophtalic acid. 
Isophtalic acid having a high melting-point (880°) dissolves so 
slightly in ether, that the critical line starting from ether is already 
intersected at 196.1° and 36.8 atm. Since the isophtalic acid is decom- 
posed by heating a long time at high temperatures, q could not be 
determined. 
Hexane-anthraquinone. 
This system does not show critical end-points. 
As the combination of either ether or anthraquinone with another 
) Z. Phys. Chem. 51. p. 214. 
