Warning: High Voltage Ahead. This Instructable shows you how to make an old-school high voltage capacitor, a Leyden jar, out of a jar of salt water. Even though this shows you how to make a small-jar capacitor, so the voltage is probably not lethal, it’ll still pack a wallop, so not something to be undertaken if you don’t know what you’re doing.
This project is done by Plasmana, the same Instructable member who did the World’s Smallest Electronic Shocker and the Marx Generator. We have a really sweet story in The Best of Instructables about a regular MAKE/Instructables reader who didn’t know that Plasmana was the handle for a kid he knows and whose projects he’s admired and thought about building. And they both ended up in the book!