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The advantage of this equation, which so far as I am aware 
is deduced here for the first time, is, from the practical point of 
view, that it is possible to determine the displacement of the trans- 
ition temperature by external pressure by means of electrical mea- 
surements, if the specific gravities of the two modifications forming 
the electrodes have been determined. 
For the electrical determinations of the temperature coefficients 
of the two electrodes of the transition element in the neighbourhood of 
the transition point quite small quantities of the electrode material (1 or 
2 grams) suffice, whilst for calorimetric determinations, which in the 
nature of things are less accurate, considerable quantities are required. 
The result of the measurements will be communicated as soon as 
the specifie gravity of the grey tin has been determined in a com- 
pletely satisfactory way. 
Amsterdam, Chem. Lab. of the University, September 1899. 
Chemistry. — Prof. H. W. BakHurs RoozeBooM in presenting 
the dissertation of Dr. D. J. Hissink: “On mixed Crystals 
of Sodiua nitrate with Potassium nitrate and of Sodium nitrate 
with Silver nitrate’, makes the following communication with 
respect to it. 
This research is a third contribution to our knowledge of the 
phenomena observed in the solidification of fused mixtures of two 
substances which form mixed crystals and in the transformation of 
the mixed crystals into another modification. 
With respect to the system KNOs + Na NOs the fact is mentioned 
that mixed crystals are formed on solidification ; the limits within which 
these can exist are, however, so narrow that it did not appear to be 
worth while to investigate the exact connection hetween the phenomena. 
The solidification of the system NaNO; + Ag NO; belongs to a 
type of which no example was known. The meltingpoint line rises 
continually trom the meltingpoint of AgNO, (208,°6) to that of 
NaNO, (308°). It consists, however, of two branches, AC and CB, 
