Pulsating Electrochemical Reaction: Mercury Beating Heart
A solution of potassium dichromate in dilute sulfuric acid covers a drop of mercury in a watch glass. An iron nail is positioned so that it nearly touches the mercury. Eventually, the mercury drop starts to beat rhythmically, like a beating heart.
The dichromate oxidizes the mercury to mercury(I) ions, which combine with sulfate ions at the surface of the mercury drop to form a film of insoluble mercury(I) sulfate. This film decreases the surface tension of the mercury, allowing the drop to flatten. Eventually the mercury drop expands to touch the iron nail, at which time electrons flow from the nail to the mercury. The electrons reduce the mercury(I) ions to mercury, destroying the surface film. The surface tension increases and the mercury drop becomes more spherical, pulling back from the nail. When the mercury and the iron nail no longer touch, mercury(I) sulfate again builds up on the surface, and the process repeats.
The size of the movie file is 5.4 MB and its duration is 61 seconds. The name of the movie file is "HGHEART.MOV" and it is located in the folder "MOVIES/HGHEART".
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