See my blog for a writeup of this experiment: [ Ссылка ]
In this experiment, a drop of mercury metal is immersed in dilute sulfuric acid and a few drops of potassium permanganate solution. An iron wire is placed near the drop, which then begins to oscillate. This was actually very hard to get right, as the wire placement is extremely sensitive and it must be at exactly the right spot.
The explanation: The permanganate oxidizes the mercury to mercury (I) ions, which combine with sulfate ions from the sulfuric acid to form a thin layer of mercury (I) sulfate on the surface of the drop. The film reduces the surface tension of the drop, causing it to flatten out slightly. When the drop touches the iron wire because of this effect, electrons can flow from the iron to the mercury. This reduces the mercury (I) back to mercury metal, causing the drop to regain its normal surface tension and pull away from the wire. When the contact is broken, the film forms again and the cycle repeats.
