MadSci Network: Earth Sciences

Re: Is it possible for non-salt water to be below 32 degrees without freezing.

Date: Mon Sep 13 19:17:06 1999
Posted By: Everett Rubel, MadSci Admin
Area of science: Earth Sciences
ID: 936573469.Es


Thanks for the question.  The answer is definitely yes, water that is not salty 
can be colder than 32 degrees F or 0 degrees Celsius and not freeze.

One way this could happen is if there is something besides salt dissolved in the 
water.  Many different substances will lower or depress the freezing point. 
Gases like the carbon dioxide in soda pop could do it, liquids like ethylene 
glycol (antifreeze) could do it, or solids that dissolve like sugar could do it.

Another way this could happen is by super cooling.  If the water is very clean 
and is not agitated or disturbed it can cool well below the normal freezing 
point without freezing.  However, if the water is disturbed or if particles like 
 dust or sand is added to the water then it rapidly freezes.  Super cooled water 
 can occur as small floating droplets in clouds and will turn to ice when 
disturbed by an airplane flying through the clouds.  This causes dangerous icing 
to occur on the airplane's wings.

Atmospheric pressure will have little or no noticeable affect on the freezing 
point of water.  It takes pressures hundreds or thousands of times greater than 
atmospheric pressure to make a significant change in the freezing/melting point 
of water/ice.


Everett Rubel

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