Olivia Ash, Age 11, Of St. Albans, W. Va., for her question:

Do solids ever evaporate?

As they become warmer most substances change from the solid state to the liquid state and finally to the gaseous state. Each substance has its own melting and boiling point. Water, for examp1e, is frozen to solid ice at 0 degrees centigrade. This temperature also is the melting point at which ice melts to liquid water. At 100 degrees centigrade, liquid water boils and becomes gaseous water vapor.

Some substances, however, skip the liquid state and pass from the solid state directly to the gaseous state. This trick is called sublimation. As the temperature rises, dry ice changes from the solid state, which is colder than cold, into a common gas that mingles with the air. Dry ice is frozen carbon dioxide, the waste gas we breathe out. When chilled some 80 degrees colder than the freezing point of water, it becomes solid. As the temperature rises above this point, it changes directly into ordinary carbon dioxide.