th 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
massive, is of a lustrous white colour, but it may be brought, by
separating it from its solutions, into so finely divided a state,
that its particles no longer reflect light, and it forms a powder as
black as soot. In this condition it absorbs eight hundred times its
volume of oxygen gas, and this oxygen must be contained within it in
a state of condensation very like that of fluid water.

When gases are thus condensed, i.e. their particles made to
approximate in this extraordinary manner, their properties can be
palpably shown. Their chemical actions become apparent as their
physical characteristic disappears. The latter consists in the
continual tendency of their particles to separate from each other;
and it is easy to imagine that this elasticity of gaseous bodies is
the principal impediment to the operation of their chemical force;
for this becomes more energetic as their particles approximate. In
that state in which they exist within the pores or upon the surface
of solid bodies, their repulsion ceases, and their whole chemical
action is exerted. Thus combinations which oxygen cannot enter into,
decompositions which it cannot effect while in the state of gas,
take place with the greatest facility in the pores of platinum
containing condensed oxygen. When a jet of hydrogen gas, for
instance, is thrown upon spongy platinum, it combines with the
oxygen condensed in the interior of the mass; at their point of
contact water is formed, and as the immediate consequence heat is
evolved; the platinum becomes red hot and the gas is inflamed. If we
interrupt the current of the gas, the pores of the platinum become
instantaneously filled again with oxygen; and the same phenomenon
can be repeated a second time, and so on interminably.

In finely pulverised platinum, and even in spongy platinum, we
therefore possess a perpetuum mobile--a mechanism like a watch which
runs out and winds itself up--a force which is never
exhausted--competent to produce effects of the most powerful kind,
and self-renewed ad infinitum.

Many phenomena, formerly inexplicable, are satisfactorily explained
by these recently discovered properties of porous bodies. The
metamorphosis of alcohol into acetic aci