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the solution, which deposition at. first increases, viz. to + 125°. 
Above this temperature the deposited quantity of solid substance dis¬ 
solves more and more, and vanishes again entirely at 208° in v. We 
have then got into the liquid region for the second time, and so 
have observed the phenomenon of retrograde solidification. 
If we now continue heating, another change takes place, and 
monoclinic anhydric Na 2 S0 4 deposits from the solution at 241° in 
the point w. 
The series of observable phenomena is not exhausted yet, the most 
interesting one is still coming, for if we raise the temperature still 
more, we see the critical phenomenon, appear at 365°, in consequence 
of the liquid becoming identical with the vapour in the presence of 
solid Na 2 S0 4 . 
We must, however, point out here that this latter phenomenon 
requires another volume than the preceding ones; for it is necessary 
for the points m, n, v , and w, that the quantity of vapour is very 
small, because we want the known total concentration to be equal 
in these points to the concentration of the liquid, the three-phase 
pressure yet prevailing. 
For the critical phenomenon, however, the volume of the liquid 
must be equal to that of the vapour at the critical temperature, and 
so it is clear that for the observation of the critical phenomenon a 
new filling is required. 
As it appeared in this determination that the critical temperature 
of the saturated solution did hot lie sensibly higher than that which 
was observed for pure water, viz. 365° *); we concluded from this 
that the solubility of Na 2 S0 4 in water at the critical temperature is 
very slight. 
Now the question naturally rises what we get at higher tempe¬ 
rature. If decomposition were excluded, a point q would have to 
appear below the melting point of Na 2 S0 4 , so below + 885°, where 
the same liquid as for p or in case of non-miscibility another, reached 
its critical point, and we should then get a T, ,x -figure which would 
closely resemble that for ether-anthraquinone. But as it is highly 
*) For the critical temperature of water other investigators found the following : 
Nadejdine 358,1° 
Batelu 364,3° 
Cailletet and Colardeau 200,5° 
Kohnstamm and Keesing 364—365 c 
Suns 365° 
