Equipment:
5 iron nails
1 piece of aluminium kitchen foil
2 lengths of stripped copper electrical wire (4" 12cm in length)
2 lengths of silver solder (as used in circuitry or plumbing)
Small piece of wire wool or fine sandpaper
Shallow glass/ceramic dish (I used a Pyrex dish) large enough to contain all the nails
Salt

Method:
Clean each of the nails with wire wool or fine sandpaper. Gently clean the silver solder and copper in the same way. Wrap the aluminium foil around the head of one nail, the copper wire around the head of another, and the silver solder around a third (ensure that the wrapping is tight and that there is a good bond between the two metals).
The fourth nail is not joined to anything. Then wrap a piece of copper wire around the other length of silver solder.
Fill the dish with warm water, add a teaspoon of salt and stir until it is dissolved. Carefully place the bowl somewhere that it can remain undisturbed for 24 hours, and so that you can easily observe it without having to move it.

Carefully add each of the metal items you prepared to the water - make sure that they are not touching each other. The experiment should look like the picture below :

Observe the mixture after a few hours; take notes of what you can see. Observe after 12-15 hours; take notes of what you see. Which items have corroded? Have some corroded faster than others? If you see corrosion, what is the colour of the corrosion that you see? Rate the level of corrosion of each of the nails from 0 to 5 (0 being no corrosion, 5 being very corroded).