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substance did not give satisfactory results, | resolved to investigate 
systems one of the components of which is a gas at ordinary 
temperature. : } 
According to bicuner’s research *) CO, gives critical end-points 
with several other substances. It was however not closely examined 
whether these systems belonged to the simple case ether-anthraquinone 
or to the type diphenylamine-carbonic acid, discovered by BücHNer. 
The systems naphtalene-carbonic acid and diphenyl-carbonic acid, 
which 1 studied, showed both the first critical end-point. The fact. 
that in both systems the three-phase curve starting from the triple 
point of the solid substance had a steep rise (fig. 1), led to the con- 
clusion, that the systems were analogous to the system diphenylamine- 
carbonic acid. 
K = Critic. point CO, 
p = Critic. endpoint 
diphenyl. 
p, = Critic. endpoint 
naphtalene. 
Biest. 
This made me suppose that other systems with carbonie acid would 
also show a steep three-phase curve and accordingly q at a high 
pressure or no gq at all. So 1 resolved to try systems with ethane. 
Ethane-naphtalene. 
Preliminary experiments showed also this system to have the 
above mentioned property. Because it had proved very difficult to 
find another example of the type ether-anthraquinone and as moreover 
the phenomena suggested that in this system points might be realized 
which had not yet been observed, I still commenced a closer study. 
1) ‚Thesis for the doctorate, Amsterdam 1905. 
oa 
