If I'm not mistaken
this is more or less the same priciple that George Stephenson used to make it possible to shrink a steam engine to portable size.

Or was it James Watt? Anyway, whoever it was realised that you could get a double hit from a puff of steam - once when it expanded to push a piston, and again by cooling/condensing, making it suck the piston back the other way.
(username failed moderation, Wed 15 Aug 2012, 16:25, 1 reply)

You are not mistaken!
I can never remember who did what when it comes to steam engines...
( TheAlmightyBeev, Wed 15 Aug 2012, 16:34, closed)

And I agree
that is a really good website.

me and the kids are going to destroy some stuff this weekend.
(username failed moderation, Wed 15 Aug 2012, 16:54, closed)

Have fun!
If you want messy, but not particularly destructive demos, you could have a volcanic afternoon:

Flour Volcano - demonstrates how volcanoes form a caldera

Wallpaper Paste Volcano - a great eruption that demonstrates the effect of dissolved gases in volcanoes.
( TheAlmightyBeev, Wed 15 Aug 2012, 17:04, closed)

or the old school dilantant fluid behaviour
with cornflour and water can keep small children entertained for hours.
( the mighty badger Aphrodite, on a bar stool, by your side, Wed 15 Aug 2012, 17:20, closed)