How to make a devil diver (Cartesian diver)
Find a tall glass jar with a quite wide mouth. Wrap a few turns of copper wire about the thin part of the rubber bulb from a medicine dropper. Fill the jar brim full of water. Put a little water in the bulb and float it in the jar of water. The bulb should have enough water to bring it nearly to the point of sinking. At this point approximately all the rubber will be under water. Considerable adjustment will be needed. Remove air from the bulb a bubble at a time by pinching the bulb.