Ammonium Tri-Iodide was good fun, too.

We used to drop it around the lab floors and let it dry out in blobs.
Frightened the kecks off a few cleaners sweeping up the next morning.
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®óñ© © ²°¹°-°³

Yes, fond memories of the stuff. When doing "A" level chemistry I made some
and it ended up all over the benches. My chemistry partner came in and
tossed her book onto the bench "BANG" and a small black hole in her book!
The chemistry lecturer came trotting to the back of the lab, and thinking
fast I exclaimed - "Sir - there was a big bang when she put her book down!".
"Yes!" said the lecturer, "Some idiot has made ammonium tri-iodide" and
looked at me suspiciously. Got away with it though.

Also had fun with the stuff at the paint factory. A little blob on the power
button of a big machine. The bloke came to start up to his machine and
pushed the 'ON' button - 'BANG' - He got the site electrician looking at his
machine for ages and was baffled how he got such a big "electrical" shock!

David.