Strange Sparks in a Dark Cave
by Annie Shao, age 18
At the end of my Rocks and Ropes class caving field trip, my classmates and I lit up a dark room with candy.
We were led into a large, pitch-black room in Eagle Cave. Our guide gave each of us a Wint-O-Green Life Savers candy, and told us all to bite down at the same time with our mouths open. Blue sparks illuminated our mouths and crackling sounds bounced off the cave walls.
Apparently this only works with this specific Life Savers flavor. To many, this effect is a great unexplained mystery. To a science-nerd life me, it is simple chemistry.
The name of this sparking effect is triboluminescence, light produced by breaking chemical bonds. When you break anything, you break intermolecular forces. These are attractions between molecules that hold them together. Biting the Life Saver breaks intermolecular forces between the sugar molecules of the candy. This mechanical process excites electrons and releases them from the Life Savers to the air. The process gives them enough energy to jump to surrounding nitrogen and oxygen molecules. The extra energy is released in waves of light as the electrons return to their original ground state.
Triboluminescence occurs in any crystal that has an asymmetrical structure or impurities. This actually happens a lot, but we can’t see it because the light emitted is usually in ultraviolet rays. Humans can only see a limited range of energy waves, known as the visible light spectrum. Ultraviolet rays are too high in energy for the eye to see. Impurities in crystals can absorb some of the energy, making the light emission within the visible light spectrum. The wintergreen flavoring agent in Wint-O-Green, methyl salicylate, absorbs the ultraviolet light, so we see blue-green light emitted in sparks.
This phenomenon is nothing new. Four hundred years ago Sir Francis Bacon, the founder of the scientific method, observed that crushing most kinds of sugar produced sparks. In 1753, physicist Giambattista Beccaria confirmed the existence of triboluminescence by having people chew sugar lumps in the dark. In modern times, the “Wint-O-Green Effect” has continued to mesmerize countless people like me and my classmates.
Who knew that a strangely named mint could have such an intriguing science lesson behind it? I thought the “Wint-O-Green Effect” was a pretty sweet phenomenon to learn more about.
[Source: The New York Times]