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Metal corrosion is a chemical reaction between a metal surface and its environment. Corrosion can occur in a gaseous (dry) environment or a damp (wet) environment. The second type of corrosion is probably the more familiar to you.  Most people are aware that when iron metal gets wet it rusts.  Rust is simply a common name for metal corrosion.
Corrosion in a gaseous environment is also familiar to you but probably not as well recognized by you.  Anyone who owns any silver jewelry is probably aware that if you just leave it sitting in your jewelry box it most often turns black.  This is a form of corrosion produced by exposure of the metal to the gaseous environment, more specifically exposure to the oxygen in the air. Corrosion in a gaseous environment produces a surface layer of converted metal. In the case of silver a compound called silver oxide (Ag₂O) is produced on the surface of the silver.
Corrosion in a wet environment attacks the metal by removing the atoms on the metal surface. The metal atoms at the surface lose electrons and become actively charged ions that leave the metal and enter the ‘wet’ electrolyte. The metal ions join with oppositely charged ions from another chemical and form a new, stable compound.  The leaving of these atoms is what causes rusted cars to become brittle and form holes.
In both cases, corrosion produces physical evidence of its presence. The form it takes depends on the mechanism of the corrosion.

In today’s experiment you will be exposing several different metals to different types of corrodents and making observations regarding their effects.  You will also be presented with examples of the same corrodents and metals that have been in contact with each other over a long period of time.  In addition to the bare metals, you will also be provided with some treated metals.  These “treated” metals have been coated so that they will resist corrosion.  It will be your job to determine the efficiency of these coatings.