I wasn't an eyewitness to this one, although I wish I had been. I pass it on secondhard from a former colleague of mine, on which it made an understandable impression.
Bromine's an odd element. The two lighter halogens leading up to it are nasty gases. Fluorine, the first one, is actually beyond merely nasty, being a hazard to life from several different directions. Chlorine is something you can handle,although it was still nice enough to be used on the battlefield in World War I. But bromine is the first one of the series that makes the grade as a liquid at room temperature and pressure.
All the halogens have colors - for example, I'm told that liquid fluorine is green, not that I hope to see any of the damned stuff, and liquid chlorine is supposed to be yellow. Iodine is notoriously purple, and For its part bromine is a deep, almost opaque red-orange. It's one of those liquids that hasn't forgotten its gaseous heritage, and you always see it with a red haze of vapor above it. It's unmistakeable.
You'd think. Our story begins, as do so many fine lab disaster tales, with the phrase "There was this summer student. . ." In this case, there was this summer student whose grad-student supervisor thought he was ready for a spot of bromine work. They'd ordered a fresh bottle, which had come in from Aldrich the day before, and everything was ready for a good old-fashioned bromination reaction. As the chemists here know well, if you add bromine to a compound with an exposed carbon-carbon double bond, it'll react with the alkene, breaking it down to a single bond with a bromine on each carbon. Sometimes it's fast enough that you can see the red color disappear as the stuff drops into the reaction, and you can just go until the color persists, but sometimes it hangs around as an orange solution for a while.
So, our grad student leaves for lunch, entrusting this small-scale bromination to his ready-to-solo summer undergrad. And he wanders back presently to check out the reaction, but there's something wrong. The flask has no color to it, for one thing. For another, there are chunks of floating crud whirling around in the clear solution, and that's not right, either. He turns to the summer student and asks him if that's the bromination.
"Sure is!" Hmmm. Did he, in fact, use. . .bromine in this reaction? Oh yes, indeed. The bromine that just came in? Absolutely! What's that stuff floating around in the flask? Well. . .the bromine, right? Show me this bromine, then, by all means. And the summer student goes over to the opened shipment and lifts out the vermiculite packing material that's in there to keep the bottle from breaking during shipment. Behold the bromine!
No, you cannot make anything foolproof. Fools are too tricky. Needless to say, anyone who can't tell the difference between bromine and box-filler is someone that you don't want within a hundred yards of a working research lab. My colleague had not recorded the reaction of the grad student to this revealing answer, but I'm sure it involved raised voices and plenty of adjectives.