1106 
So when with this mixture the upper limit of the P-7' loop is 
determined, the intersection of this curve with the three-phase line 
will give approximately the point q. 
The first mixture, that I studied, corresponds to 2, in fig. 9. 
Determining the upper limit of the P-7’ loop, I saw the meniscus 
always disappear in the top of the tube, so that 4r must lie at a 
temperature higher than 71.4°. (see fig. 6, fig. 2 line ZF and table 1). 
The composition of this mixture was between 25 and 26 mol. °/, 
naphthalene. As I did not succeed in observing q directly with this 
mixture, although I sometimes saw a fluid phase in contact with 
solid, I resolved to proceed along the previously described way. 
The second mixture contained 24.75 mol. °/, naphtalene; it might 
therefore lie on the left or on the right of g, or it might happen 
to have exactly the composition of x, itself. 
On determining the P-7' loop the meniscus also here always disap- 
peared in the top of the tube, indicating, that the mixture contained 
more napbtalene than «a, (see table 1 and fig. 2 line GH). Three 
points could be found on the metastable part of the curve. The 
pressure of the point at 52.4° and 122.27 atm. is high, which can 
be explained by assuming that perhaps some solid has got under 
the mercury. 
With this mixture the composition of point 1 from fig. 10 was 
experimentally sought. From the intersection of the two end-conden- 
sation lines with the three-phase curve I might conclude, that g lay 
at about 57°. I chose 59.9° as temperature of the experiment, also 
2.9° higher than the assumed 7. The above mentioned method 
gave at 59.9° a pressure maximum of 126.64 atm. 
With this mixture, showing Ar at 59.9° and 126.64 atm. another 
point of the P7' loop was determined at a temperature lower than 
kr. The meniscus disappeared a little below the middle of the tube 
at 55.5° and 123.81 atm. (metastable point). The intersection of the 
curve, which joins those two points, with the three-phase curve 
offers a value for g, which is very near the true one. This shows 
the second critical end-point to lie at 57.4° and 124.8 atm. and the 
composition to be between 20 and 25 mol. °/,. 
Finally I wish to express my thanks to Dr. F. E. C. SCHEFFER 
for his help and advice. 
Amsterdam, January 1915. Inorg. Chem. Laboratory 
of the University. 
