Science party trick results from mini explosions triggered by sparks, experiments suggest
A pickle skewered by electrodes emits an orange glow at one end when plugged in. Researchers have new insights into the science behind this spectacle.
Joshua Méndez Harper and Benjamin Crall
COCOA BEACH, Fla. — Here’s what happens when you plug in a pickle.
At an otherwise formal meeting of the Electrostatics Society of America, electrical engineer Joshua Méndez Harper pulled out a jar of pickles, a power strip, and some electrodes. “I hope the fire alarm doesn’t go off,” he said.
He skewered each end of a pickle with an electrode and flipped the switch. The pickle sizzled in protest, then turned bright orange at one end. As an aroma of roasted pickle wafted over the audience, he cut the power. It’s a decades-old scientific trick, and now Méndez Harper’s group at Portland State University in Oregon may have discovered what dill is.
Pickles are usually soaked in a salty brine. Since salt water is made up of ions – electrically charged atoms – pickles are able to conduct electricity. But the cause of this glow is debated. One idea is that the pickle juice boils at the electrode, creating a pocket of vapor that blocks the flow of current, causing sparks to pass through the gap. Another idea involves electrolysisa process by which an electric current transforms water into a mixture of hydrogen and oxygen. This mixture is explosive, so the heat from the electrode can trigger small explosions of light.
Méndez Harper and his colleagues outfitted a pickle with monitoring equipment in their lab, including a high-speed camera and a hydrogen sensor. Then they zapped it with alternating or direct current. (Méndez Harper is a professional – don’t try this at home.) AC current is the type that comes from a wall outlet, in which the flow of charge changes direction periodically, while DC current is a constant flow.
Hydrogen was produced in both cases, indicating that some electrolysis is taking place. But oddly enough, the glow only appeared with alternating current. This suggested the mechanism actually involves both effects at once, Méndez Harper said at a conference on June 16.
The oscillating nature of alternating current could help keep the vapor pocket open, allowing sparks to form that ignite the hydrogen and oxygen, Méndez Harper explained. Direct current, he proposed, could make the vapor pocket unstable, so that it would collapse, producing hydrogen but no sparks, and therefore no ignition or glow.
The team also wanted to understand why only one side of the pickle glows. It was less complicated: that’s the juicier side. A vertically placed pickle always glows at its lower end, where brine accumulates, the team discovered.
After the demo, the pickle went in the trash. Taste testing was not on the menu.
