Tonic blues
Question: Last night my husband poured me a wonderful large gin and tonic but
we were both rather concerned to notice that our tonic water had a curious
bluish colour to it. What was going on here, or had I had one too many?
Answer: You hadn’t had one too many—tonic water always fluoresces
slightly blue. The reason for this is that it contains around 75 parts per
million of quinine, which is what makes it bitter.
Quinine absorbs light at the ultraviolet end of the spectrum and re-emits it
at a slightly longer wavelength—so it appears…
