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lity. The layer of ferrocyancopper in the porous pot will generally stop 
the wide pores. The pores through which neither coppersulfate nor 
potassium ferrocyanide can pass, remain open, but we may expect 
that between the ferrocyancopper formed and the wall of the porous 
pot holes narrow enough will remain and moreover that in the layer 
of ferrocyancopper there will remain narrow holes fit for the 
semipermeability. Where this layer is formed, the concentration 
of the two solutions locally decreases considerably, so that probably 
the layer will not be continuous, leaving holes narrow enough 
for semipermeability. 
Also when the concentration of the solution near the wall is not 
zero, or when the pores are somewhat too wide osmotic phenomena 
may occur. Then, however, the simple law will no longer be valid ; 
the semipermeability will not be perfect and by pressing the solution 
we shall not obtain the pure solvent through the pores, but a solution, 
though perhaps of lower concentration than the one under the 
pressure. . 
The decrease of the melting point may illustrate the above 
considerations, also because we have indications here, that at a solid 
wall the concentration of a solution can be zero. Let us consider 
the solution at such a temperature that there is also ice present in 
the sugar solution. The ice is separated from the solution by a layer 
of pure water, in which the pressure close to the wall is p,. When 
the solution is frozen, generally pure water on the surface of the ice 
is frozen. This indicates that probably in the layer surrounding the 
vee the solved substance does not occur. Now when under constant 
pressure the concentration «, is increased by de,, the pressure p, 
changes by such an amount that vdp, = — MRTde,, where v is 
therefore the specific volume of the water next to the ice. Now the 
solid wall is a wall of ice, which must be in thermodynamic equi- 
librium with the water. When however the equilibrium is destroyed 
not directly between the ice and the solution, but between the ice 
and the layer of pure water surrounding the ice, in which layer 
the pressure p, along the ice surface and therefore also the difference 
in pressure p,-—p, is changed, only a change of temperature can 
restore the equilibrium, can cause that the two phases in contact 
regain their coexisting equilibrium. A change of the temperature dt, 
will change the potentials of the water and of the ice by —1, dt 
and —y dt. As —nydt is at the same time the total change of the 
thermodynamic potential of the ice, we shall have 
— Hi; dt = — Nw dt + v dp 
