Well, since I'm not sure, quite simply: Is there a possible way (apart from running a current through in the presence of a perpendicular $\mathbf{B}$ field) to make a small mixture of mercury magnetic so that it would respond to an applied magnetic field, like from a permanent magnet?

  • $\begingroup$ Now I know why this rang a bell: physics.stackexchange.com/q/490107 . $\endgroup$
    – Ed V
    Commented Sep 2, 2019 at 12:39
  • 2
    $\begingroup$ Mercury, being a liquid metal - is magnetic. But, since it is a liquid, it cannot hold a static magnetization. So, you can certainly perturb it - but it will relax. You must use an alternating magnetic field, if set up correctly, you will have a permanent displacement. $\endgroup$
    – Stian
    Commented Sep 2, 2019 at 18:47

1 Answer 1


Don't use a mixture, just use pure Hg. Chill to 4.2 K, conveniently reached with liquid He, and all magnetic fields are excluded. Levitate on a magnet, sans yogi.

Mercury in a static magnetic field, with direct current, forms a simple homopolar electric motor, creating a vortex. A safer way (sans neurotoxic Hg) to demonstrate a homopolar motor requires just some copper wire, a magnet and a cell. Or make a linear motor. A nice explanation of the demonstration is also available. [Sorry, this discursion might be better in Electrical Engineering StackExchang].

But if you insist on using Hg at standard temperature and pressure, just use a varying magnetic field and induced current - no direct electrical connection required.

N.B. Mercury is volatile, and its vapor is extremely toxic and hard to remove completely. A building in Massachusetts, USA, was recently condemned and a number of animals died due to Hg contamination. Use gallium, instead, currently available for ~US$15 for 50 grams, and you can also demonstrate gallium attacking the crystal structure of aluminum, or make a Ga mirror. Gallium is also a superconductor, though it needs to be colder than Hg. To liquefy, just warm to ~30 °C in your hand or in warm water.

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    $\begingroup$ well pardon my language , I meant using pure Hg not a mixture with other metals or substances. In my apparatus I already will have a convection type mhd pump where current will pass through the mercury in the presence of an applied perpendicular B field, I was just thinking that maybe that will not be enough to keep it steady given that the channel into which the mercury will be itself will be rotating. Like a reverse mhd pump where the liquid metal needs to stay steady in a single position with respect to the pump walls moving. $\endgroup$
    – Girts
    Commented Sep 2, 2019 at 6:48
  • $\begingroup$ PS. what was in the video link the other person is referring to? $\endgroup$
    – Girts
    Commented Sep 2, 2019 at 6:51
  • $\begingroup$ The last link is region-restricted. $\endgroup$ Commented Sep 2, 2019 at 9:50
  • $\begingroup$ @PeterTaylor Unsurprisingly, many companies outside Europe take the attitude of "Eff GDPR; we'll just block access from the EU instead of complying with it." $\endgroup$ Commented Sep 2, 2019 at 11:08
  • $\begingroup$ @DrMoishe Pippik Could you please repost the YouTube link you originally had? As per the Physics.SE post by the OP (see the link in my comment to the OP), direct electrical contact with the mercury was desired, though the question here is about using a permanent magnet, no direct electrical Hg contact, etc. Thanks! $\endgroup$
    – Ed V
    Commented Sep 2, 2019 at 13:22

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