Janice Nussbaum, age    , 13, of East Lansing, Mich., for their questions:

Why does salt melt ice?

Every substance has its own melting point and boiling point, the two temperatures at which it turns from a liquid into a solid or from a liquid into a gas. And plain water is a different substance from water which contains a quantity of dissolved salt, One of the differences is in the melting point. Salty water needs to be a few degrees colder than plain water before it can freeze into solid ice.

When we sprinkle salt on an icy sidewalk, it forms a mixture which needs a few more degrees of cold before it can freeze solid. It dissolves in the cracks and trickles down to turn more and more ice into water, If the weather is cold enough, however, it will freeze even a strong solution of salt and water into solid ice.