ADHESION - is the molecular attraction exerted between bodies
in contact. It occurs between solids and solids, liquids and
solids, liquids and liquids, gases and solids, gases and gases, and gases
and liquids. The adhesion between two plates of the same material is the same as
that between; one of the plates and any material which possesses a less adhesive
property. Adhesion is supposed to manifest itself at an appreciable distance
before actual contact of bodies. The ascent of liquids in capillary tubes is a result
of adhesion, as well as the spreading out of liquids between two surfaces kept in
close proximity. The chain-pump, in which the water is carried up by a simple
chain in a tube, is a practical example of adhesion of liquids to solids. The
adhesion of gases and solids, is illustrated by the adhesion of air around a piece of
solid iron, which causes it to float on melted iron. In the Giffard injector a blast
of steam is used to carry water by its adhesion to it into the boiler against its own
pressure.
The adhesive force on railroads may be estimated approximately by multiplying
the weight of the locomotive in tons which rests on the driving-wheels by a
coefficient of adhesive for said wheels. This coefficient is with dry rails 670; very dry
rails 560; under ordinary circumstances 450; wet rails 314; in snowy. or frosty
weather 225. On horse-railroads the coefficient varies from 300 to 400 in snow and frost.
Your Comments Welcomed! Copyright © 1995 Roger Corrie