At a meeting of the Electrostatics Society of America, electrical engineer Joshua Méndez Harper showed a decades-old science trick: a pickle glowing bright orange at one end. His group at Portland State University in Oregon may now have figured out what causes the glow.
Pickles are usually soaked in salty water. That water contains electrically charged particles, so a pickle can carry an electric current. But people still argue about the glow. One idea is that pickle juice boils at the metal contact, making a pocket of vapor that blocks the current, so sparks jump across the gap. Another idea is electrolysis: the current splits water into hydrogen and oxygen. Heat at the contact might then set off a bright reaction in that mix.
Méndez Harper and his colleagues fitted a pickle with lab tools, including a high-speed camera and a hydrogen sensor. They tested it with two kinds of current. Alternating current, the type from a wall socket, keeps switching direction. Direct current is a steady flow.
Hydrogen showed up in both tests, so some electrolysis does happen. Oddly, the glow appeared only with alternating current. That suggested both effects are at work at once, Méndez Harper said.
The switching of alternating current may help keep the vapor pocket open, so sparks can form and light the hydrogen and oxygen. Direct current, he proposed, may make the vapor pocket unstable, so it collapses. Hydrogen is still produced, but there are no sparks, and therefore no glow.
The team also asked why only one side of the pickle lights up. That part was simpler: it is the juicier side. A pickle stood on end always glowed at the bottom, where the salty juice collects.