of a solid body, as a grain of sand to a mountain. By the mere
effect of mass,--the force of gravity,--gaseous molecules are
attracted by solids and adhere to their surfaces; and when to this
physical force is added the feeblest chemical affinity, the
liquifiable gases cannot retain their gaseous state. The amount of
air condensed by these forces upon a square inch of surface is
certainly not measurable; but when a solid body, presenting several
hundred square feet of surface within the space of a cubic inch, is
brought into a limited volume of gas, we may understand why that
volume is diminished, why all gases without exception are absorbed.
A cubic inch of charcoal must have, at the lowest computation, a
surface of one hundred square feet. This property of absorbing gases
varies with different kinds of charcoal: it is possessed in a higher
degree by those containing the most pores, i.e. where the pores are
finer; and in a lower degree in the more spongy kinds, i.e. where
the pores are larger.

In this manner every porous body--rocks, stones, the clods of the
fields, &c.,--imbibe air, and therefore oxygen; the smallest solid
molecule is thus surrounded by its own atmosphere of condensed
oxygen; and if in their vicinity other bodies exist which have an
affinity for oxygen, a combination is effected. When, for instance,
carbon and hydrogen are thus present, they are converted into
nourishment for vegetables,--into carbonic acid and water. The
development of heat when air is imbibed, and the production of steam
when the earth is moistened by rain, are acknowledged to be
consequences of this condensation by the action of surfaces.

But the most remarkable and interesting case of this kind of action
is the imbibition of oxygen by metallic platinum. This metal, when