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Liquid Nitrogen Bomb

One thing you should never do to liquid nitrogen is to seal it in a pressure vessel.... so we had a go.

If you cool down air in liquid nitrogen it will condense to form a liquid and shrink by a factor of about 600.

In this video you can see the air in the balloon shrinking as it cools down, and you should be able to just see the liquid air that it condenses into.

This is because as you cool down the gas you are sucking energy out of its molecules, until eventually they don't have enough energy to overcome the weak attraction between one another and they stick together in the form of a liquid.

This liquid takes up only about a 600th of the original volume of the gas you started with. Nitrogen is the largest component of air, so if you heat liquid nitrogen up above its boiling point it will expand again by a factor of about 600.

So if you try sealing the liquid nitrogen in a container the pressure will build up and up until something fails. If the container is strong this failure will happen at a very high pressure and it will be very violent.

A lemonade bottle is a remarkably well designed device which will not fail until the pressure reaches at least 10 atmospheres so the failure is very very violent.

This is dangerous, so do not do this at home!

This film has been speeded up by about a factor of 10 before the explosion, but sloweddown by a factor of 10 during the explosion.

Written by Dave Ansell

Your Comments

You can do a less dangerous version of this experiment using a plastic (polythene) supermarket milk bottle. It bursts at rather lower pressure, so is safer.
Indoors (in the lab) it still makes a very satisfactory bang however!

I wondered whether you should have made a warning about the amount of nitrogen to use (you said about 2inch depth (50mm) on the podcast): too much and you risk it exploding too soon (and freezing your hand while putting the cap on), too little and it may build up dangerous pressure but fail to explode (then what???).

- techmind - 8th Apr 09

It's very dangerous and should be carefull

- raghavendra - 9th Apr 09

Unless you really fill the bottle to the top it is going to take a while to explode, as a lot of nitrogen has to boil off before it goes bang. The first part of the video was slowed down a lot - it took about 4 minutes to go off.

But yes this is very dangerous, don't do it...

- daveshorts - 14th Apr 09

It is so funny you can watch the cap flying toward you...

- Robb - 31st May 09

Potentially this situation could happen in many places in a plant designed to make and handle cryogenic liquids - like liquid nitrogen. Try the experiment again but put a "thermal relief valve"(PSV) in the cap - this is how engineering makes science practical. The PSV could be a baloon (or paper etc) held over the mouth with an elastic band in place of the plastic top... Or it could be a 'real' thermal PSV (pressure safety valve).

- Ray Sacks - 14th Jul 09

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