Johnna Echevarria, age 10, of Homedale, Ida., for her question:

Why do we need salt to freeze homemade ice cream?

When we start this wonderful job, the yummy mixture is as warm as the kitchen. It becomes ice cream, Only after it is frozen. A warm substance has more heat than a cold substance. The mixture has more heat than a pail of ice. Heat passes only from a warmer to a cooler substance. The ice takes heat from the creamy mixture and soon becomes warm enough to melt.

The ice chills the ice cream mixture., but ice alone cannot steal enough heat to freeze it. Certain chemicals., however, make it harder for the ice to melt and help it to take up still more heat. Salt and ice together can steal enough heat to freeze the ice cream.