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To lower the temperature in the lab, there are a number of good experiments to be done with liquid nitrogen. Freeze flowers, bananas and an egg in a frying pan. Fantastic contraction and expansion can be shown with balloons in a more spectacular way than the old faithful ball and ring. If you have the equipment, show magnetic levitation with the Meisner effect or use a safe coil arrangement to show how resistance drops at low temperatures. Pierce a small hole in two sides of a ping pong ball and submerge it in liquid nitrogen. Taking it out to allow the nitrogen to boil, the ball spins round in a similar fashion to Heron of Alexandria's aeolipile or "steam ball". See www.mlahanas.deGreeksHeronAlexandria.htm

for details of the early steam engine.

* A note of caution with all these experiments - do follow safety precautions and use appropriate gloves and protective equipment. Be aware also that regulations for transporting liquid nitrogen have recently changed so check, or ask your local university to lay this on for you.

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