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Yesterday I heard (or, more precisely, was reminded) that the quinine molecule fluoresces. Fluorescence is what happens when a molecule absorbs electromagnetic radiation--either in the visible light range or elsewhere in the spectrum--and emits light at a different wavelength. Lots of molecules fluoresce. Chlorophyll, for example, is the green molecule that captures the light photons that power the process of photosynthesis. If you shine light at a wavelength of 425 nm (violet) at a tube of chlorophyll, it will fluoresce, or emit light at 680 nm (red).

Here's a DIY video guide to demonstrate the fluorescence of chlorophyll in the comfort of your own home:

Chlorophyll fluorescence

So back to the fizzy beverages. I sing in a choir that has a long tradition of gathering after rehearsals and drinking gin-and-tonics (G&Ts). Tonic water contains quinine, which imparts fizziness and a certain bitterness to the drink. Having re-learned about the fluorescence of quinine, I thought it would be fun to watch the tonic and gin mix under a UV light. We needed a dark place for this experiment, hence the bathroom, the most convenient room that we could completely darken.

Turns out it worked amazingly well. Tonic water is entirely clear under white light, which contains all wavelengths of the visible spectrum; it looks like any other unflavored fizzy water. But under the UV light it glows with a kind of unearthly blue hue:

The quinine in tonic water fluoresces under UV light
The quinine in tonic water fluoresces under UV light

But the real fun is in watching the tonic and gin mix in the glass. We make G&Ts this way: Put a few ice cubes in the glass, squeeze in a bit of lime, pour in two fingers' of gin, then top off with tonic water. So we did everything but pour in the tonic water, then ventured into the bathroom with the UV light, where I recorded this:

Now isn't that cool? Science is great!

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