Don't try this at home kids!

In the excerpt from the video: A World Without Disorder: Absolute Zero Temperature Bob Richardson makes a toast with liquid nitrogen. This is a low temperature physicist's parlor trick akin to fire breathing or sword swallowing. It is dangerous - don't do it.

Liquid nitrogen is very cold. It is 77 Kelvin or -196 C or -321 F. So why wasn't Bob Richardson injured? There are three reasons. First, he didn't stay in contact with the liquid nitrogen for very long. The cup had an insulated base to protect his hand. He never touched his lips to the bowl of the cup which is why there was a slurping sound to the toast. And he spit out the liquid almost immediately. Second, liquid nitrogen has a relatively small heat capacity and a relatively small heat of vaporization. That means that when it comes briefly into contact with people it doesn't have much cooling power. Instead, it tends to get boiled off very rapidly. That is not to say that you can't freeze your tonsils, just that you have to gag briefly to do so. Thirdly, the rapid boiling of the liquid nitrogen tends to create a vapor layer between your skin (or tonsils) and the liquid nitrogen. The vapor layer serves as insulation for a short time.

If you have ever sprinkled a few drops of water on a hot skillet and seen the droplets dance across the surface as they boil away, then you have seen the behavior of a few drops liquid nitrogen in contact with a body at room temperature. By analogy, if you were to pour a cup or so of water on a hot skillet, or a similar quantity of liquid nitrogen into a room temperature skillet, then there would be enough liquid to cool the skillet, and it would only dance on the surface for a short time.

The real danger of toasting with liquid nitrogen is the danger that you might swallow a bit by accident. If this were to happen, then the valve at the top of your stomach might close, trapping some liquid nitrogen inside you. Then two very bad things would happen:

  1. The liquid nitrogen would be held in contact with your tissues for long enough to cause damage, possibly destroying the valve at the top of your stomach or another part of your throat or stomach.
  2. Second, the rapidly boiling liquid would generate a huge amount of vapor inside you. You probably wouldn't explode, but it would be extremely unpleasant.
So please, never, ever toast with liquid nitrogen! (Unless you have a Ph.D. in experimental low temperature physics, and have won or have a good chance of winning a Nobel prize in Physics. You still shouldn't do it, but....)

Last modified: Wednesday, October 14, 1996.