Wrap the foil around the canister, covering approximately the bottom three-fourths of the canister. Place a 6-inch length of wire onto the foil. Tape the wire and the foil in place. This is the outer conducting plate and lead.
Puncture a hole in the canister's plastic top with the nail. Push the nail three-fourths of the way through the top. Attach one end of a second 6-inch length of wire to the nail head. This is the inner plate's lead.
Pour water into the canister until it is approximately three-quarters full. Add 1 teaspoon of salt. Snap the plastic top, with nail and wire attached, onto the canister. Make sure the nail is immersed in the salt water. The salt water is an electrolyte that serves as the inner plate.
Seal the hole from which the nail protrudes with hot glue. This prevents the salt solution from leaking out and shorting itself against the foil. The Leyden jar capacitor is now ready to be charged through the copper wire leads.