mercury element experiment

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Experimental physics i & ii "junior lab", the franck-hertz experiment, description.

The Franck-Hertz experiment equipment.

These experiments measure two phenomena encountered in collisions between electrons and atoms: quantized excitation due to inelastic scattering, and ionization. The excitation potential and ionization potential of the mercury atom are determined from measurements of the critical accelerating potentials at which electrons lose energy by inelastic scattering in mercury vapor.

The Franck-Hertz Experiment Lab Guide (PDF)

Franck-Hertz Experiment References

Bohm, David. “Square Potential Solutions.” In Quantum Theory. Upper Saddle River, NJ: Prentice Hall, 1951, pp. 229-263.

Bleuler, Ernst, and George J. Goldsmith. “Charged Particle Spectra.” In Experimental Nucleonics. New York, NY: Rinehart, 1952, pp. 342-346.

Melissinos, Adrian C. “The Franck-Hertz Experiment.” In Experiments in Modern Physics. San Diego, CA: Academic Press, 1966, pp. 8-17.

———. “Thermionic Emissions of Electrons from Metals.” In Experiments in Modern Physics. San Diego, CA: Academic Press, 1966, pp. 65-80.

Schiff, Leonard I. “Ramsauer-Townsend Effect.” In Quantum Mechanics. 3rd ed. New York, NY: McGraw-Hill, 1968, pp. 108-110.

Harnwell, Gaylord P., and J. J. Livinwood. “Experiments on Excitation Potentials,” and “Experiments in Ionization Potentials.” In Experimental Atomic Physics. Huntington, NY: R. E. Krieger, 1978, pp. 314-320. ISBN: 9780882756004.

Rapior, G., K. Sengstock, and V. Baeva. “ New Features of the Franck-Hertz Experiment .” American Journal of Physics 74 (2006): 423-428.

Ramsauer-Townsend Effect Experiment References

Bohm, David. “Ramsauer-Townsend.” In Quantum Theory. Upper Saddle River, NJ: Prentice Hall, 1951, pp. 564-573.

Richtmyer, F. K., E. H. Kennard, and T. Lauritsen. Introduction to Modern Physics. 5th ed. New York, NY: McGraw-Hill, 1955, pp. 274-279.

Mott, N. F., and H. S. W. Massey. “Ramsauer-Townsend.” In The Theory of Atomic Collisions. 3rd ed. Oxford: Clarendon Press, 1965, pp. 562-579. ISBN: 9780198512424.

Kukolich, Stephen G. “ Demonstration of the Ramsauer-Townsend Effect in a Xenon Thyratron .” American Journal of Physics 36, no. 8 (1968): 701-703.

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Mercury Beating Heart Chemistry Demonstration Recently updated !

The mercury beating heart is a popular chemistry demonstration based on an an electrochemical redox reaction that causes a blob of mercury to oscillate, resembling a beating heart. Here’s how the mercury beating heart works and how you can perform this chemistry demonstration yourself.

Mercury Beating Heart Overview

A drop of mercury is placed in a watch glass. The mercury is covered with a solution of an oxidizing compound in sulfuric acid. The oxidizer usually is potassium dichromate, hydrogen peroxide, or potassium permanganate. An iron nail or wire is placed such that the tip of the nail is almost touching the mercury. The mercury will begin to pulsate rhythmically, like a beating heart.

Perform the Mercury Beating Heart Demo

Place a drop of mercury in a watch glass, petri dish or saucer.
Pour sulfuric acid over the drop to cover it. The exact concentration of sulfuric acid is not critical. Car battery acid works for this demo.
Add a small amount of oxidizer, such as potassium permanganate, hydrogen peroxide or potassium dichlorate. Aqueous solution or a few crystals are fine.
When you are ready to start the beating heart, approach the drop of mercury with the tip of the iron wire or nail. The heart starts to beat when the iron is close to the mercury, but not quite touching it. The mercury heart will beat for about 20 seconds before stopping.

How the Mercury Beating Heart Works

The mechanism for this reaction is not clearly understood, but it likely involves oxidation of the iron. The permanganate, peroxide, or dichromate oxidizes the mercury and produces mercury(I) ions. These ions combine with sulfate ions from the sulfuric acid and form a thin layer of mercury(I) sulfate on the surface of the drop of mercury. The formation of the layer reduces the surface tension of the drop, causing it to flatten out. When the flattened drops contacts the iron wire or nail, the mercury sulfate oxidizes the iron to form the iron(II) ion while reducing the mercury to its normal metallic form. The mercury has a higher surface tension, so the drop becomes rounded again. As contact with the iron ceases, the oxide coating starts to form again, repeating the process. When all of the oxidizer has been reduced, the reaction stops. There is some debate about the mechanism because weaker oscillations have been observed even without the presence of oxidizer.

Less Toxic Alternative to Mercury

Mercury is very toxic, so you may wish to perform this demonstration with another material. It turns out molten gallium works in place of the drop of mercury. Gallium melts at a low temperature and is much less toxic and easily contained than mercury. To perform the demonstration with gallium, melt a pellet of gallium and immerse it in sulfuric acid. Add a small amount of an oxidizer, such as potassium permanganate, to the sulfuric acid. The gallium heart beats more slowly than the mercury heart.

Watch the Mercury Beating Heart in Action

It’s much safer to watch a video of this demonstration than to do it yourself. Here’s what happens…

Avnir, David (1989). “Chemically induced pulsations of interfaces: the mercury beating heart.” J. Chem. Educ . 66 (3): 211. doi: 10.1021/ed066p211
Demiri, Sani; Najdoski, M.; et al. (2007). “Mercury Beating Heart: Modifications to the Classical Demonstration.” J. Chem. Educ . 84 (8): 1292. doi: 10.1021/ed084p1292
Shu-Wai Lin; Joel Keizer; Peter A. Rock; Herbert Stenschke (1974). “On the Mechanism of Oscillations in the Beating Mercury Heart.” Proceedings of the National Academy of Sciences of the United States of America . 71 (11): 4477–4481. doi: 10.1073/pnas.71.11.4477