Picric acid
Look it up in wiki.

Shouldn't (and now probably isn't) let anywhere near A level chemistry students, but at the time it was thought of as a mildly dangerous reagent.

This stuff is potentially lethal. We had a small bottle of it in the locked fume cupboard in the lab, and were told NEVER to touch it.

Well. You know what that means to schoolkids.

This stuff has to be kept wet as when it dries it crystallises into a violent explosive. That's why, when on the one occasion we were allowed to use it, we had to smear the top and neck of the bottle with Vaseline.

One bright spark (scuse the pun) thought "It can't be that bad, can it?" , undid the bottle (all inside the fume cupboard thank god), poured a bit out and hit the small puddle with another bottle.

Cue evacuation, and 1 new fume cupboard.
(Dr Teeth Who asked you, you fuckin' hobbit?, Mon 28 Jul 2008, 5:47, 2 replies)

I have done similar experiments
with ammonium triiodide, in my time. It makes a reasonably big bang, but unfortunately it leaves obvious iodine stains everywhere, which are especially visible on nice white fume cupboard walls...
( K2k6 has a proper job these days, Mon 28 Jul 2008, 9:07, closed)

@K2k6
Yeah, ammonium triiodide is fun but I work with some really nasty explosives. I had a bit of an accident with tetraselenium tetranitride a couple of months back. I've only just recovered a stirrer bar that had wedged itself into a very tight spot at the top of my fume cupboard!
( Raindance Work is inversely proportional to post-count, Mon 28 Jul 2008, 13:45, closed)