Vacuum kettle

Try out cool boiling!

10 minutes


  • Carefully review the general safety advice on the back of the box cover before starting the experiment.
  • Observe safety precautions when working with boiling water.
  • Disassemble the setup after the experiment.


  • Dispose of solid waste together with household garbage.

Scientific description

Liquid water  in an open vessel  gradually turns into gas  and flies away in a process known as evaporation. Hot liquid  evaporates more quickly than cold liquid , which is why you can even observe the steam  rising from hot drinks  with the unaided eye.

Typically, steam  rises from water  because evaporating  into the air  is easier than into the liquid  or the vessel in which it is located. But if you heat  water  to a certain point, it begins to evaporate  so intensely that it starts to evaporate  inside itself—to boil. The bubbles  in boiling water  are made of steam .

How intense the evaporation  must be for the water  to boil depends on air  pressure . By lowering the pressure , you make it easier for water  to boil, and it begins to do so at a lower temperature than it does at atmospheric pressure.