Mercury Beating Heart: Classical Demonstration


Miniature mercury pool in a watch glass is covered with aqueous solution of sulfuric acid and hydrogen peroxide. When iron nail touches the mercury surface with the tip mercury starts to beat like a heart.

Watch glass (with diameter 8 or 10 cm), Petri dish with diameter 6 or 8 cm, plastic pipets, plastic tray, iron nail, patafix, white sheet of paper.

Mercury, sulfuric acid (c = 2 mol/L), hydrogen peroxide (w = 10 %), sulfur


  • Work in a plastic tray. Place the chemicals in the tray.
  • Place a white sheet of paper in the tray.
  • Place the Petri dish on the paper sheet and on top of it the watch glass.
  • Use the plastic pipet to add 1-2 mL of mercury in the watch glass.
  • Use the patafix to fix the iron nail on the watch glass with the tip 1-3 mm from the mercury.
  • Add sulfuric acid to the watch glass to cover the mercury pool and few drops of hydrogen peroxide (Fig. 1).
  • Move the watch glass to provide contact (just a gentle touch) of the nail to the mercury
  • Observe the shape changes of the mercury.
After the demonstration collect the liquid in a bottle with heavy metal waste

Fig. 1. Set up

Fig. 2. Equilateral triangle shape of mercury

Observation and Discussion

When the mercury pool is touched with a tip of an iron nail, oscillations start. The oscillations create different shapes (Fig. 2) of the mercury pool (oval, equilateral triangle, pentagon etc.), depending on the experimental conditions . Redox reactions and surface tension changes take place during the oscillations. The system oscillates between two states. One, when the system is with high contracted mercury pool and it has high surface tension and high surface electron density. In this system consisting of an aqueous solution of sulfuric acid and hydrogen peroxide as an oxidizing agent, touching the mercury surface with the tip of the iron nail provides electrons and causes the following redox reactions:
Fe(s) = Fe3+(aq) + 3e–

When this contact breaks due to the mercury pool contraction another reaction takes place:

H2O2(aq) + 2H3O+(aq) + 2e– = 4H2O(l)

This reaction shows how electrons are spent on reduction. This causes decrease in surface tension, the mercury pool flattens and the contact with the nail is archived again. Electrons are generated again and they provide high surface tension of the mercury which causes contraction of the mercury pool and the mercury is detached from the nail again.

Safety Tips
Mercury and its compounds are highly poisonous. Spilled mercury should be collected and saved in a closed labeled container. Sulfur powder may also be used onto the spilled droplets of mercury. In order to prevent mercury spill one should work in a plastic tray. Mercury vapor is especially dangerous, thus in badly ventilated laboratories the spilled mercury may induce chronic mercury poisoning.