Boil Water Below Normal Boiling Temperature

As a fun science demonstration, we're going to boil water at about 128F or 53C, significantly below the 212F or 100C that is normally needed, in a syringe.  The water will simply come from a household hot water tap.  The trick is that the boiling temperature of a liquid goes down as the air pressure goes down--water boils when its vapor pressure exceeds the air pressure.

This is a good demonstration to show to kids at home or at a school.



What you need:

• Plastic syringe  (I used a 12mL monoject.  One can buy them cheap in large or small quantities on amazon or ebay.)
• Hot tap water, at around 125F
• Cup for the water
• Optional: Thermometer

Run hot water from the tap, waiting for it to reach full temperature.  Then fill up a cup with the hot water.

Stick a thermometer into it if you like.  But don't take too long, or the water will cool off too much.

Gently fill the syringe a little less than 20% full (I put 2mL of water in a 12mL syringe).  If you want, you can put a little more in, and then eject bubbles by holding the syringe pointing up and pushing the piston up.

Press one finger very tightly over the tip of the syringe.  Hold the syringe horizontally, and pull back the plunger to the full length of the syringe, gently so it doesn't pop out (it'll take some force).  If all goes well, the water should boil for a few seconds along the length of the syringe.  You may also notice the syringe steaming up.  

Then gently release the syringe.  You should notice that everything returns to more or less how it was before the experiment (maybe with a little bit more air, if some leaked in).

It should also boil if you hold the syringe vertically.  But then you or your audience might worry that the bubbling is not boiling, but it's just air leaking in and around the piston.

If it doesn't boil, try using less water.  Or hotter water.  Or alcohol (e.g., heated by putting a small cup of alcohol in a larger cup of hot water).