( 182 ) 
Physics. — “On the phenomena which occur when, in a ternary 
system the plaitpoint surface meets the two sheet three-phase 
surface .” *) By Prof. A. Smits and E. C. Witsknburg. (Com¬ 
municated by Prof. J. D. van der Waals.) 
(First communication). 
(Communicated in the meeting of June 26, 1909). 
From the behaviour of the system ether-anthraquinone it may be 
be readily deduced that (very peculiar phenomena must occur when 
to that system is added a third substance which differs from ether 
in so far that it does not give critical phenomena with anthraquinone 
in saturated solutions or in other words does not give the critical 
terminal points p and q. 
In this case the peculiar phenomenon of the occurrence of the 
two critical terminal points p and q, will still at first be noticed on 
addition of that third substance, but on addition of large quantities of 
the same it entirely disappears, because the points p and q gradually 
approach each other and finally coincide. 
In order to elucidate the matter in the most simple manner we 
will make use of the representation in space as given in Fig. 1. 
On the posterior plane is drawn the P, ^-projection of the system 
ether-anthraquinone and on the anterior plane that of the system 
alcohol-anthraquinone so that alcohol is here our third substance 
which, as shown by the research, complies with the above demands. 
This was already anticipated as the critical temperature of alcohol 
is 243°,1 and the melting point of anthraquinone 284°, whereas the 
solubility of anthraquinone in alcohol is relatively large. Owing to 
this it is difficult for the plaitpoint curve of this system to come 
into conflict with the three-phase line. 
From the representation in space it will be plainly seen that 
jjvithin the space between the posterior and anterior planes t e 
behaviour of all possible mixtures of ether-alcohol with excess o 
anthraquinone. may be indicated.. 
For we should remember that between the interrupted three-phase 
line epqd. and the continuous three-phase line ed extends a two sheet 
three-phase surface because, in a ternary system, a three-phase eqm 1 
brium is a bivariant system in consequence of which three phases 
may coexist over a series of pressures at a constant temperature. 
*) We wish to take this opportunity 
University Union for kindly enabling i 
pump with accessories, thus rendering it 
upress 
i procu 
sible to 
our thanks to the Amsterdam 
re a Schaffer and Bodknbkrc 
carry out this research. 
