Be Excellent To Each Other

At an open day at Oxford Uni I watched a guy pour liquid nitrogen into a beaker, then put it in a bell jar, which is proceeded to evacuate with a fairly powerful pump. As the vapour pressure dropped the nitrogen froze, of course (-210degC, fact fans). Then, he used a compressed air cylinder to really quickly repressurise the bell jar, whipped the lid off, grabbed the beaker, and upended it over the desk. Et voila: a solid lump of nitrogen (it's white) subliming away on the desk. It started off about the size of my fist and lasted two or three seconds before it was all gone, filling the room with dense white mist to about shin level. Awesome demo.

For an encore, he dipped his bare hand into a beaker of liquid nitrogen, which is safer than you think. The warmth of your hand immediately boils a layer of nitrogen, and that layer of gas protects you hand from direct contact with the liquid for a second or so. Then you hand starts to feel cold and your reflexes will snatch it back before any harm befalls you. Well, so he said; I wasn't about to try it.

Oh, and in a total mockery of health&safety rules our physics teacher let us dip our fingers into a beaker of mercury. It's extremely weird, because it's really heavy but not all that visous, and the surface tension is massive so when you pull your fingers out they are quite dry. Impressively weird feeling.

Kalmar, I've heard that potassium trick done as an act of vandalism. You dismantle the u-bend and dry it out really, really well, then superglue a small lump of potassium just under the sink trap. Then you retire to a safe distance and wait for some unsuspecting year 7 kid to wash a beaker out....

During the first Chemistry class in secondary school, the teacher did the whole 'try putting your hand through the yellow flame on the bunsen burner' bit.

I did not.

It's not much of an anecdote, but hey. Don't stick your hand in the fire kids, no matter what the teacher says.