4C30.10 - Reduced Pressure Boiling

See paragraph one in the procedure section
See paragraph two in the procedure section
Code Number:
Demo Title:
Reduced Pressure Boiling
Pressure effects on changes of state
Area of Study:
Heat & Fluids
Water, round bottom flask, ring stand with ring and wire gauze, Bunsen burner, flask stopper, masking tape, crushed ice in a baggie.

Fill the flask half-way with water and boil over the Bunsen burner. Remove from heat, put the stopper in the flask and tape it on. Remove the gauze from the ring and place the inverted flask in the ring. Notice that the water is hot, but not boiling. When the baggie of crushed ice is put on top of the flask, the pressure drop causes the water to boil again.  

The vacuum flask may also be used to show an interesting variation of this demo.  Put ice water with large cubes of ice and not crushed ice in the flask.  Connect this directly to a vacuum pump and evacuate.  Observe the boiling of ice water.

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  • Thomas O, Callaway and Harry D. Downing, "Response", TPT, Vol. 27, # 3, Mar. 1989, p. 136.
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  • H- 260:  "Boiling at Reduced Pressure",  DICK and RAE Physics Demo Notebook.
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  • Julien Clinton Sprott, Physics Demonstrations,  "2.8, Boiling with Ice",  p. 85, ISBN 0-299-21580-6.
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  • Borislaw Bilash II, “ Boiling Cold Water“, A Demo A Day – A Year of Physical Science Demonstrations, p. 96.

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