wrote in message
...
On Thursday, December 1, 2016 at 9:43:07 AM UTC-5,
wrote:
For this to work there must be an electron pathway between the anode
and the metal to be protected (e.g., a wire or direct contact) and
an ion pathway between both the oxidizing agent (e.g., water or
moist soil) and the anode, and the oxidizing agent and the metal to
be protected, thus forming a closed circuit; therefore simply
bolting a piece of active metal such as zinc to a less active metal,
such as mild steel, in air (a poor conductor and therefore no closed
circuit) will not furnish any protection.

First, the issue is protection in a wet environment, so there is an
"ion pathway" (electrolyte). Plain, pure water is not much of an
electrolyte -- but neither is it a severe corrosion problem. Salt in
the water, or even many contaminants, produce more of a corrosion
problem AND a better ion pathway.

The direct contact with the metal surface being protected usually is
enough of a conducting path. Many protective electrodes used in marine
environments are just screwed onto the metal being protected, and they
work quite well.

--
Ed Huntress

===============

There is a sacrificial anode in your electric water heater. Home Depot
now carries replacements.