Glowing Pickle or Electric Pickle Experiment

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Glowing or Electric Pickle Experiment
The glowing pickle or electric pickle experiment illustrates ionic conduction and atomic emission.

The glowing pickle experiment is a fun, easy, and dramatic demonstration of ion conduction and atomic emission spectra. Other names for the project are the electric pickle, frankenpickle, and the pickle lamp. Here’s how you make a glowing pickle and a look at how it works.

Make a Glowing Pickle

Basically, you need a large pickle, a couple of pieces of metal, a lamp cord with plug, and either a variac or outlet (sources of AC or alternating current). If you’re using wall current, please plug the lamp cord into a power strip with an on/off switch. This gives you an easy way of cutting the power and improves safety. Because this project involves electricity and exposed wires, it is an “adults only” experiment.

  • Pickle
  • 2 Nails or metal forks
  • Lamp cord with plug
  • Power strip with on/off switch and outlet for wall current OR a variac

There are few ways of setting up the glowing pickle. In one version, hammer the nails through a piece of wood so they support the pickle (or whatever you’re testing). Otherwise:

  1. Set the pickle on top of a glass jar. Glass is an insulator, so it’s a good choice for supporting the pickle.
  2. Insert two forks or two nails into the pickle, one at either end. Make sure the two metal pieces don’t touch each other.
  3. Separate the lamp wire far enough that you have two wires long enough to reach the nails or forks. Either wrap the exposed wire around the nail or else clip the wire to the metal using alligator clips.
  4. Plug the lamp plug into either a variac (variable power supply) or else into a power strip (in the “off” position), which is in turn plugged into the wall.
  5. When you turn on the power, the pickle initially drips. It then glows and may smoke. Be sure to turn off the power and disconnect it before examining the pickle.

How the Glowing Pickle Experiment Works

While it’s easy making a pickle glow, explaining exactly what’s going on has challenged scientists for decades.

The first part is simple. Pickling liquid contains salt. Salt solutions conduct electricity because salt is an electrolyte. Salt (NaCl) dissolves in water and dissociates into its ions (Na+, Cl–). Applying an electric current makes these ions move.

The yellow glow comes from the emission spectrum of sodium. You see the same phenomenon in candle flames and the flame test in chemistry. The energy from the electric current excites the sodium ions. Electrons enter an excited state and return to a more stable state, emitting photons with a characteristic wavelength (yellow).

The chemistry likely involves chlorine (Cl2) and sodium hydroxide (NaOH) production and hydrogen combustion. The nails or forks act as electrodes for electrolysis, plus you can see gas bubbling from the metal. Electrocuting a pickle changes its composition, making it unsafe to eat.

There’s nothing particularly special about using a cucumber. Other pickled produce, such as pickled tomatoes, also work.

Make the Pickle Glow Other Colors

The salt in normal pickling solution is sodium chloride, but if you pickle cucumbers or other foods in other chemicals the pickle glows other colors. For the best results, first bleach the green color from cucumbers by soaking them in a hydrogen peroxide solution. Then, pickle your produce in a solution of 10% salt in vinegar. Here are some salts and their characteristic emission colors:

  • lithium chloride – pink
  • potassium chloride – purple
  • strontium chloride – red
  • barium chloride – yellow

Practical Applications

The first published mention of the glowing pickle experiment was a 1989 report by Digital Equipment Corporation. While the publication date of April Fool’s Day sets the report up as a fun science project, it also describes some serious science. At its heart, the glowing pickle is an example of an organic light emitting diode (OLED). You see similar technology at work in televisions, monitors, and other displays.

References

  • Appling, Jeffrey R.; Yonke, Fredrick J.; Edgington, Richard A.; Jacobs, Steve (1993). “Sodium D line emission from pickles.” J. Chem. Ed. 70(3): 250. doi:10.1021/ed070p250
  • Gardner, Martin (2012). Martin Gardner’s Science Magic: Tricks and Puzzles. Courier Corporation. ISBN 978-0486152905.
  • Hamburgen, Bill; Mogul, Jeff; et al. (April 1989) “Characterization of Organic Illumination Systems.” WRL Technical Note TN-13. Digital Western Research Laboratory.
  • Rizzo, Michelle M.; Halmi, Tracy A.; et al. (2005). “Revisiting the Electric Pickle Demonstration.” J. Chem. Ed. 82(4): 545. doi:10.1021/ed082p545
  • Vollmer, M.; Möllmann, K.-P. (2014). “Light-emitting pickles.” Phys. Ed. 50(1): 94. doi:10.1088/0031-9120/50/1/94