that
osmosis establishes itself in the way which best equalizes the
surface-tensions of the liquids on both sides of the partition.
Solutions possessing the same surface-tension, though not in molecular
equilibrium, would thus be always in osmotic equilibrium. We must not
conceal from ourselves that this result would be in contradiction with
the kinetic theory.

Sec. 3. APPLICATION TO THE THEORY OF SOLUTION

If there really exist partitions permeable to one body and impermeable
to another, it may be imagined that the homogeneous mixture of these
two bodies might be effected in the converse way. It can be easily
conceived, in fact, that by the aid of osmotic pressure it would be
possible, for example, to dilute or concentrate a solution by driving
through the partition in one direction or another a certain quantity
of the solvent by means of a pressure kept equal to the osmotic
pressure. This is the important fact which Professor Van t' Hoff
perceived. The existence of such a wall in all possible cases
evidently remains only a very legitimate hypothesis,--a fact which
ought not to be concealed.

Relying solely on this postulate, Professor Van t' Hoff easily
established, by the most correct method, certain properties of the
solutions of gases in a volatile liquid, or of non-volatile bodies in
a volatile liquid. To state precisely the other relations, we must
admit, in addition, the experimental laws discovered by Pfeffer. But
without any hypothesis it becomes possible to demonstrate the laws of
Raoult on the lowering of the vapour-tension and of the freezing point
of solutions, and also the ratio which connects the heat of fusion
with this decrease.

These considerable results can evidently be invoked as _a posteriori_
proofs of the exactitude of the experimental laws of osmosis. They are
not, however, the only ones that Professor Van t' Hoff has obtained by
the same method. This illustrious scholar was thus able to find anew
Guldberg and Waage's law on chemical equilibrium at a constant
temperature, and to show how the position of the equilibrium changes
when the temperature happens to change.

If now we state, in conformity with the laws of Pfeffer, that the
product of the osmotic pressure by the volume of the solution is equal
to the absolute temperature multiplied by a coefficient, and then look
for the numerical figure of this latter in a solution of sugar, for
instance, we find that this value is the same a