sciencegeekgirl: If a boy pees on the floor and there’s nobody there to see it

The boys’ urinals were often surrounded by a puddle of “liquid.” Were the urinals weeping water? Or were the boys purposely urinating on the floor (as the janitor believed)? And, most importantly, how can we use our good friend SCIENCE to solve this mystery, the teacher asked?

Is there a powder I can sprinkle on the floor that will turn a particular color?
A UV light to shine on the puddles that will fluoresce?

It turns out that, yes, there is such a device!

Note that I have not deigned to confirm this effect with my own UV light.

However, I had read about the etched fly “targeting system” discussed; I had charged a friend of my brother’s with the task of finding one of these when he was in Europe. I had read they had been installed in the Amsterdam airport, but he didn’t see any there. This was taken at a restaurant in Berlin