When two dissimiliar metals are in contact without
a protective barrier between them and they are in
the presence of liquid, an electrolytic cell is
created. The degree of corrosion is dependent on
the area in contact and the electro-potential
voltage of the metals concerned. The less noble of
the metals is liable to be attacked, i.e. zinc will act
as a protector of steel in sea water whereas copper
or brass will attack the steel in the same
environment.