CLEAR ICE CUBES
This article, written by the American Ground Water Trust was originally published in
THE AMERICAN WELL OWNER, 2000, Number 3]
How does one match the sparkling clarity of the ice seen in all the beverage advertisements? The opaque nature of most homemade ice occurs because of trapped air bubbles. It can be difficult to make clear ice because of the dissolved gases in most tap water. For those that want to try making clear ice at home we provide the following information and suggestions.
Water holds about 0.003 percent dissolved oxygen at 32°F. As water is warmed its ability to dissolve oxygen decreases to zero at the boiling point. Dissolved oxygen atoms (O) are "trapped" by surrounding water molecules (H2O). To enter and leave the structure of water molecules, dissolved oxygen atoms must “push" their way past the water molecules to the water/ air surface. This can take some time, so if the water freezes too fast, the oxygen atoms can’t escape an ice crystal before it becomes solid, thus forming a tiny bubble in the ice cube.
The first step for clear ice cubes is to heat the water to almost boiling. This helps remove gases. Gently pour the hot water into a metal ice cube tray (a plastic tray may melt or deform) so that no splashing or agitation of the water occurs. Turn the temperature on the freezer up (less cold) so that the ice cubes will form slowly and allow oxygen to diffuse out of the water before it freezes. A freezer temperature set just below freezing (32°F) may work the best. Once the ice cubes are formed you should return the freezer temperature back to a lower setting.
For pictures of water molecules and the structure of ice and water you can click onto the following web site developed by NY University: http://www.nyu.edu/pages/mathmol/library/
[© American Ground Water Trust. This article may be reprinted for non-commercial educational purposes provided it is used in its entirety and that reference is made to its source as an article in THE AMERICAN WELL OWNER, 2000, Number 3]