http://youtu.be/dfiR1Rde7dI Do not put liquid nitrogen in a sealed container. Without an outlet, the liquid will turn into a gas, pressure will build up extremely quickly, and BOOM! The whole thing will explode. But as you can see in the above video, with a few safety precautions---and 1500 ping-pong balls---Roy Lowry of Plymouth University managed to turn this phenomenon into an unforgettable learning experience.