- Shattered stuff with liquid nitrogen: PB&J sandwich, bouncy balls, etc.
- Melted various metals in crucibles over Fisher burners. Got burned a few times when I didn't realize the crucible lids were still hot.
- Made ferrofluid. Not particularly dangerous, but very cool stuff. Search for it on Youtube.
- Thermite reactions. These were fun. You had to start them with sparklers (or a lit magnesium strip).
- Lit hydrogen bubbles (we used to have "fire Friday")
- Chlorine and sodium reaction to make salt
- Nitrogen triiodide (an explosive; can be detonated with one alpha particle)
- Aluminum sulfur reaction: This one was interesting; the science lab book specified a small zinc sulfur reaction. I wanted to up the ante with aluminum and sulfur. Per the Wikipedia page which I read after the experiment:
"This reaction is extremely exothermic and it is not necessary or desirable to heat the whole mass of the sulfur-aluminium mixture; (except possibly for very small amounts of reactants). The product will be created in a fused form; it reaches a temperature greater than 1100 °C and may melt its way through steel. The cooled product is very hard."
Yeah, my friend and I finely ground up a HUGE batch of that aluminum and sulfer in a mortar and lit it in the fume hood. It looked like a rocket was going off. What we also didn't realize was that the product, aluminum sulfide, should NOT go in water, and water is exactly where I dumped the stuff. It stunk up the lab with hydrogen sulfide. I wonder how many brain cells I killed with that.
- Burned some chromium compound. Can't remember what it was, but when I showed the instructor the product, he got really upset. He began scooping it out of the sink because apparently I'd created a carcinogen.
- Found a container of mercuric (II) nitrate. It was the one thing the instructor wouldn't let us play with.
That was all in high school. Mostly in the fume hood. College was a lot more boring (we had to wear goggles and gloves to handle Kool-aid), although I did accidentally spill a container of concentrated sulfuric acid all over the place in organic synth lab.