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difference of these volumes will be intimately connected with the 
dimensions of the molecule. Moreover, except with regard to the 
attraction, a solid wali impenetrable for the particles is quite difte- 
rent from a fluid wall formed by the particles themselves. 
Let us consider avery much diluted solution e. g. a solution of sugar 
in water, the vapour phase of which does therefore not contain the 
solved substance. The concentration zw will then decrease in the 
passage layer from w, in the homogeneous solution to zero at the 
vapour -side. In the passage layer near the solid wall too the concen- 
tration will change and in very different cases a similar change of 
the concentration must occur as in the passage of fluid to vapour, 
viz. from wz, to zero in the layer next to the solid body. Now 
it is important to consider what will happen to the pressure 
p, (in the direction of the surface layer) especially in the layer 
next to the solid wall in which the concentration will be regarded 
as zero, when the concentration within the solution is increased 
from wz, to 2,-+dzx,. Here therefore we have not to do with 
the change in the total surface tension of the solution when 
in contact with the solid wall fi, —p,) dh, but only with the change 
of p, in the layer next to the wall. When the concentration is 
increased by de,, the potential of the solvent decreases. For when 
we have the solution under the pressure of the saturated vapour, 
the thermodynamic potential of the vapour decreases by va dp, when 
dp is written for the decrease of the vapour pressure and va for the 
specific vapour volume. In the uppermost layer of the passage layer next 
to the vapour the decrease of the thermodynamic potential is 
vadp, =vadp, as here too dp, —=dp. Also in the layer next to 
the solid wall the thermodynamic potential will decrease by the 
same amount. This decrease may be due for the greater part to 
a decrease of p, in the immediate neighbourhood of this wall, 
where just as in the vapour no dissolved matter is- present, so 
that a change of w can have no influence, as here x is zero. 
This is a tempting supposition, as in this case vadp would be equal 
to vdp,, when v represents the specifie fluid volume of the pure 
solvent near the wall. However this may be, it is certain that p, 
will change at the wall when the concentration is altered. 
Let us consider two glass vessels, both filled with the same diluted 
solution of sugar in water of exactly the same concentration. The 
vessels should be connected by a tube part of which is so narrow that 
no sugar molecules can pass through it, as their distance from the 
