Favourable Condition of the Gases     101
the particles of a body existing in the solid, the liquid, and the
gaseous state; but when we speak of the gaseous state as being
due to the mutual repulsions of the particles or of their atmo-
spheres, although we may err in imagining each particle to be a
little nucleus to an atmosphere of heat, or electricity, or any
other agent, we are still not likely to be in error in considering
the elasticity as dependent on mutuality of action. Now this
mutual relation fails altogether on the side of the gaseous
particles next to the platina, and we might be led to expect
a -priori a deficiency of elastic force there to at least one-half;
for if, as Dalton has shown, the elastic force of the particles of
one gas cannot act against the elastic force of the particles of
another, the two being as vacua to each other, so is it far less
likely that the particles of the platina can exert any influence
on those of the gas against it, such as would be exerted by
gaseous particles of its own kind.
 363.	But the diminution of power to one-half on the side of
the gaseous body towards the metal is only a slight result of
what seems to me to flow as a necessary consequence of the
known constitution of gases.   An atmosphere of one gas or
vapour, however dense or compressed, is in effect as a vacuum
to another; thus, if a little water were put into a vessel contain-
ing a dry gas, as air, of the pressure of one hundred atmospheres,
as much vapour of the water would rise as if it were in a perfect
vacuum.   Here the particles of watery vapour appear to have
no difficulty in approaching within any distance of the particles
of air, being influenced solely by relation to particles of their
own kind;  and if it be so with respect to a body having the
same elastic powers as itself, how much more surely must it be
so with particles, like those of the platina, or other limiting body,
which at the same time that they have not these elastic powers,
are also unlike it in nature.    Hence it would seem to result that
the particles of hydrogen or any other gas or vapour which are
next to the platina, etc., must be in such contact with it as if
they were in the liquid state, and therefore almost infinitely
closer to it than they are to each other, even though the metal
be supposed to exert no attractive influence over them.
 364.	A third and very important consideration in favour of
the mutual action of gases under these circumstances is their
perfect  miscibility.     If  fluid   bodies  capable  of  combining
together are also capable of mixture, they do combine when they
are mingled, not waiting for any other determining circumstance ;
but if two such gases as oxygen and hydrogen are put together,