Relation of Liquid and Vaporous Particles 109
ing it through the agency of a stronger attraction than that of
the hydrogen, or otherwise, remains to be decided by more
extended experiments.
 392.	The theory of action which I have given for the original
phenomena appears to me quite sufficient to account for all the
effects by reference to known properties, and dispenses with the
assumption of any new power of matter.    I have pursued this
subject at some length, as one of great consequence, because I
am convinced that the superficial actions of matter, whether
between two bodies, or of one piece of the same body, and the
actions of particles not directly or strongly in combination, are
becoming daily more and more important to our theories of
chemical as well as mechanical philosophy.1   In all ordinary
cases of combustion it is evident that an action of the kind con-
sidered, occurring upon the surface of the carbon in the fire,
and also in the bright part of a flame, must have great influence
over the combinations there taking place.
 393.	The condition of elasticity upon the exterior of the
gaseous or vaporous mass already referred to (362, 363) must    .
be connected directly with the action of solid bodies, as nuclei,
on vapours, causing condensation upon them in preference to
any condensation in the vapours themselves; and in the well-
known effect of nuclei on solutions a similar condition may have
existence (359), for an analogy in condition exists between the
parts of a body in solution, and those of a body in the vaporous
or gaseous state. This thought leads us to the consideration
of what are the respective conditions at the surfaces of contact
of two portions of the same substance at the same temperature,
one in the solid or liquid, and the other in the vaporous state;
as, for instance, steam and water. It would seem that the
particles of vapour next to the particles of liquid are in a different
relation to the latter to what they would be with respect to any
other liquid or solid substance; as, for instance, mercury or
1 As a curious illustration of the influence of mechanical forces over
chemical affinity, I will quote the refusal of certain substances to effloresce
when their surfaces are perfect, which yield immediately upon the surface
being broken. If crystals of carbonate of soda, or phosphate of soda, or
sulphate of soda, having no part of their surfaces broken, be preserved from
external violence, they will not effloresce. I have thus retained crystals
of carbonate of soda perfectly transparent and unchanged from September
1827 to January 1833; and crystals of sulphate of soda from May 1832
to the present time, November 1833. If any part of the surface were
scratched or broken, then efflorescence began at that part, and covered the
whole. The crystals were merely placed in evaporating basins and
covered with paper.