Ice keeps things cold because it absorbs energy from its surroundings, melting as it does so. The temperature at which a solid melts, called its melting point, is the same temperature at which the liquid form freezes. For pure water, this is 0° or 32° F. However, if some other substance, such as salt, is added to the water or ice, the freezing/melting point temperature is lowered. Thus, you can use salted ice to freeze liquid water.
Iowa Science Teachers Journal
© Copyright 1994 by the Iowa Academy of Science
"Science Notes - Ice Cream: An Edible Experiment in Thermodynamics,"
Iowa Science Teachers Journal: Vol. 31
, Article 9.
Available at: https://scholarworks.uni.edu/istj/vol31/iss1/9