>I'm trying to think of some other cool things one can do in a modestly
>equipped lab that impress first graders.  Without maiming any of the little
>rugbiters.

have you actually had a balloon with enough air in it to make it pop when
you pump down the chamber?

One that always intrigues me, but is really related to boiling water from
your point of view. Part of our procedures for doing things like using epoxy
for staking large components, or mixing the conformal coating for PCB's
requires outgassing after mixing. This is done in a vacuum chamber, and for
a typical mix that is an 1/8 inch thick clear layer in the bottom of a 250ml
beaker, during outgassing becomes a "boiling" mass that almost overflows the
beaker, while looking like a blancmange. Never fails to impress me.

Another trick you may be able to do, but it will take some organising to
work in an impressive way. If you can organise a container with a one way
valve that will let the air out. Put it in the chamber, and pump down. Now
ask the kids what will happen when you let the air back in the chamber. Off
course now the container has a vacuum inside and the valve will not let the
air in so it crushes. I had a teacher do something similar with a gallon can
when I was at primary school, except he had some water in the bottom, I
guess an inch or so, and had it boiling on a stove. Turned stove off, then
put cap on and put can in cold water, making sure he did them in the right
order.

Another trick you could do is break the glass on a torch bulb so the
filament is exposed. If necessary demonstrate that one will burn out in air.
Put the bulb in the vacuum chamber and pump down. Now turn on the bulb :)
Problem with this one is to organise power into the chamber if you do not
happen to have suitable connections available.

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