380 
phase line jfm,'d for C+ Fel, + L, and so this latter three-phase 
line, which starts from the metastable quadruple point f, becomes 
stable at #, and then after having reached a maximum, it runs to 
the quadruple point d. So the point & is also a quadruple point, 
where besides the two mentioned three-phase lines, two others meet 
viz. the three-phase line for FeC+-FeC,-+-L and that for C-+-FeC-+-FeC,. 
It is clear that the situation could also have been such that the 
ihree-pbase line for C + FeC + L possessed a stable maximum, but 
this does not give rise to essential modifications. If we examine a 
combination of twice the type of fig. 5, the case is less remarkable. 
Anorganic Chemical Laboratory 
Amsterdam, September 8, 1912. of the University. 
Physics. — “On the system ether-water.” By Dr. F.E. C. Scouerer. 
(Communicated by Prof. J. D. van DER WaAAts). 
1. In his Thesis for the doctorate (1912) Dr. Rerprrs described a 
number of experiments which were undertaken with a view to the 
experimental realisation of the phenomenon of double retrograde 
condensation, which had been predicted by Prof. vaN DER WAALS. 
Both the systems which were used for this investigation, carbonic acid 
and urethane, resp. carbonic acid and nitrobenzene exhibited three- 
phase pressures, which at the same temperature, were lower than 
the vapour pressures of the carbonic acid. In neither of the systems 
the direct observation of the said phenomenon has been possible. In 
my opinion Dr. Rrepers justly ascribes the failure of this observation 
to the fact that the difference in volatility of the components of both 
systems is so great that the vapour phase under three-phase pressure 
practically consists of pure carbonic acid, and consequently the 
quantity of the liquid layer, poor in carbonic acid, which is formed 
during the retrograde condensation, is so small that it escapes obser- 
vation. The critical points of the upper layer lie for both systems 
at concentrations which are smaller than 2 mol. percentages of the 
least volatile substance, and hence the concentration which is to 
present the double retrograde condensation contains still less of the 
second component. 
When Dr. Rrrpers told me his results a long time before the 
publication of his Thesis for the Doctorate, it did not seem impossible 
to me that a system, in which the volatility of the components 
