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the lines 0—10 have also been drawn, these lines representing the 
vapour pressures of water and of solutions containing 10, 20...100 
mol. per cent of salt, so that 10 represents the vapour pressure of 
the fused salt. 
On the line AB, the evaporation of the saturated solution takes 
place when heat is supplied. If we disregard the small quantity 
of salt in the vapour the following process takes place: 
Saturated solution — solid salt + water vapour. 
As long as the solution is very rich in water, the evaporation 
of the water absorbs more heat than is yielded by the solidification 
of the salt dissolved therein. Consequently the vapour pressure increases 
with the elevation of the temperature. With the elevation of the 
temperature, however, the concentration of the solution is increased 
and a point B will be reached where these two quantities of heat 
become equal; here the thermic effect becomes nil and this point 
is the maximum. 
At still higher temperatures and still more concentrated solutions 
on the part BC of the curve, the evaporation of the small quantity 
of water would on the other hand absorb less heat than that yielded 
by the crystallisation of the large amount of salt dissolved therein, 
consequently the evaporation of the saturated solution would evolve 
heat; therefore the vapour pressure now decreases. 
If the evaporation of the salt is disregarded the line BC ought 
to end vertically in CU). 
Up to now this peculiar course of the line ABC was only observed 
by me in the case of solutions saturated with Ca Cl,.6 H,O°). 
Although quantitative agreement was found with the course calculated 
from the quantities of heat, the pressures were here so small that 
the example was little suited to bring out the great significance of 
the matter. 
As other phenomena outside the region of salts with water could 
only find their explanation in the course indicated by the vapour 
curve, I thought it desirable to further examine this curve and the 
phenomena connected with it by means of other examples. 
Dr. Sirs, to whom I wish to express here my thanks, at my 
request took charge of the experiments. Our choice fell on some 
") Van *t Horr. Vorlesungen I, 35 (1898). 
2) Recueil trav. Chim. Pays-Bas. 8. 100 (1889). 
