Gee Whiz Facts About Ice
Most kinds of matter contract as they freeze, but when water freezes its molecules move apart taking up more space and become locked together making it less dense than water. That's why ice floats in a glass of water. Salt water is even denser than fresh water, so giant icebergs, which are composed of fresh water float in the ocean.
Some chemicals like salt lower the freezing temperature of water and can make ice melt. This chemical reaction keeps the temperature of water at about 28ºF, lower that the freezing point for water. This is what happens when making ophie's easy homemade ice cream When salt and ice are added around the out side of the ice cream "freezer" or in this example ophie's coffee can, the resulting water provides a uniform chilling effect around the ice cream, but will not freeze it. Without salt, the ice would melt, and the water temperature would rise preventing the ice cream from freezing.
The effects of pressure on ice explains how big masses of glaciers can slide downhill. Storglaciaren in Sweden has been clocked moving at 3 inches a day and Rinks Ibrae, a glacier in Greenland, has been recorded moving about 90 feet a day!
More Gee Whiz Facts
Sandra Markle,Oddball Ice,Creative Classroom(Jan/Feb 2001), 67.