This classic chemistry demo involves the use of toxic metallic mercury, so it’s one of those that is best to just watch on YouTube instead of trying yourself. The pulsing action is caused by surface tension effects–metallic mercury is oxidized at the surface of the drop to form a film of mercury (I) sulfate, which lowers the drop’s surface tension and causes it to flatten under its own weight. The flattening brings the drop into contact with the tip of a carefully-positioned iron nail, which reduces the mercury (I) sulfate back to metallic mercury, which in turn increases the drop’s surface tension and causes it to contract away from the nail. The solution contains an electrolyte and an oxidizing agent, in this case weak sulfuric acid and potassium dichromate, respectively. Thanks to YouTuber sciencevidds for sharing it with us. [via Boing and then some more Boing]

Sean Michael Ragan

Sean Michael Ragan

I am descended from 5,000 generations of tool-using primates. Also, I went to college and stuff. I am a long-time contributor to MAKE magazine and makezine.com. My work has also appeared in ReadyMade, c’t – Magazin für Computertechnik, and The Wall Street Journal.


  • mikheil

    cant we use this process to increase electricity?

    • John Maushammer

      This is a chemical reaction that produces motion that would have to be converted to electricity. There are other chemical reactions that produce electricity directly and are (probably) more efficient because they skip the intermediate step.

      Now, there aren’t a lot of chemical reactions that produce oscillatory motion like this. There has to be a niche for a small machine that can make use of this directly – something where a small electric motor and/or mechanical mechanism wouldn’t make sense… you’re on the right track, I think…

      • mikheil

        thx for the support john but it is looks like i do not have enough understanding to start experimenting with this but the idea may actually work and if it will work it will be reusable clean energy and if it does not work it will work in the near future when we will be able to produce much more precise parts to cause less friction.
        but what is interesting is that how much energy it can generate in theory at max(with max i mean if we do not consider friction at all) ?

  • Lt.Kije

    Evidently work is being done.

    Where does the energy come from? Does it get colder as it runs longer?

    • Sean Michael Ragan

      The oxidizer, in this case potassium dichromate, is consumed over time.

  • Manonymous

    When did everyone start being such pansies with mercury? DO try this, there is no reason not to if the proper safety precautions are followed. Don’t eat it or take a bath in it and you’ll be fine.