Page:Outlines of Physical Chemistry - 1899.djvu/239

 of attraction will no longer have' a common part, and the mutual attraction of a and a' will bo reduced to a minimum. This takes place as it the dissolved molecules tended to separate from each other as far as they- would if they were gaseous. — But it does not suffice to consider two molecules swamped in an excess of solvent, similar to two gaseous molecules in an indefinite vacuous space ; for in a solution, the molecules a and a' are surrounded on all sides

by a", a"', a", and the condition of equilibrium in such

a system is the mutual and equal penetration of the spheres of attraction.

If we now represent an osmotic experiment diagram - statically as in fig. 62, we find on one side of the semi- permeable wall an excess of the solvent (b), and on the other side the solution (a) the dissolved molecules of whioh are equidistant

Before starting the ex- periment the semiperme- able walls are moistened and the pores filled with pure water. If we admit that there is a great am- nity between the molecules

of water and the material particles of the wall, then there must exist a disjunctive influence, quite similar to that which exists between the dissolved molecules (a), which makes itself felt between these molecules and the wall. The dissolved molecules are thus kept at a distance, and above all will not be allowed to enter any of the capillary canals of the wall, On the other hand, a molecule of water (b) which has already entered one of these capillaries is in equilibrium if

1 The structure of the semipermeable membrane being quite unknown, the diagram only very vaguely represents i(s inner surface.

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