cohesion induced by heat.

The power of cohesion exists between the particles of liquids as well as
those of solids, the only difference being that in solids the particles
are relatively fixed, while in liquids they move freely about one
another, unless indeed when they are attracted to the surface of a
solid--a fact we are familiar with when we dip our finger into a vessel
of water. The cohesive power of liquids is overcome by heat as well as
that of solids, only to a much greater degree, for under it they assume
a new form, acquire new properties, and expand immensely in volume. They
pass into the form of vapour, occupy a thousand times larger area, and
possess an elasticity of compressibility and expansibility they were
destitute of before.

There is a beautiful phenomenon which accompanies the expansion of ether
under the influence of heat. Placed in a flask to which heat is applied,
the ether will go off in vapour; and as the heat increases, the vapour
will gradually light up into a lovely flame. The expansibility of air,
which is vapour in a permanent form, can be shown by experiment. If we
tie up an empty or collapsed bladder, and place it in a vessel over an
air-pump, we may see, as we withdraw the air from the vessel, and so
diminish its pressure, the bladder gradually expand and swell as it does
under inflation.

The cohesive power of water is beautifully illustrated. Have a small
barrel or bucket so constructed as to be fitted with gauze at the top;
immerse it exactly, so that the water may form a film between the
meshes, and then open the tap at the bottom: the water will not flow
till the meshes at the top are broken by blowing on their surface. The
adhesion of the particles in a soap-bubble is another illustration, no
less beautiful, as well as more familiar; for the soap, which might be
supposed to be the cause of the phenomenon, serves only to prevent the
intrusion of dust between the particles, but by no means to intensify
their attractive power.

There are some liquids the adhesiveness of whose particles is so perfect
as to bar out the access of air when we strew them on the surface of
other liquids; and on the Continent it is not uncommon to protect wines
against the action of the atmosphere by, instead of corking the bottle,
simply pouring in a few drops of oil, which, being lighter than the
wine, floats on the surface. It is parallel to the instance of the
barrel with the gauze-wire top mention