(c) Anthony K. Grafton 2003

Easy as Ice Cream

You can make ice cream in your kitchen in only about fifteen minutes. You’ll need ice, milk, sugar, vanilla extract, rock salt, a one-gallon zip-lock bag, and a one-pint zip-lock bag. Once you have all these things handy, follow these instructions:

1. Get permission from your mom or dad, and ask one of them to help you.

2. Pour one cup of milk, two tablespoons of sugar, and one-half tablespoon of vanilla extract into the one-pint bag and then zip it closed.

3. Fill the one-gallon bag half way with ice and add one-half cup of rock salt. Put the sealed small bag inside the large bag, then zip the large bag closed.

4. Shake the bag for about ten minutes.

5. Unzip the large bag, take out and open the small bag, and enjoy your homemade ice cream!

Why does this kitchen experiment work? The rock salt dissolves into the water and ice causing more ice to melt. It does this in two ways. Dissolved salt lowers the melting point of the ice, and causing ice to melt is an endothermic (meaning requiring heat) process. The heat used to melt more ice comes from the water, making the water even colder. In the end, the temperature of the mixture in the bag will drop to about –15 ^oC. This is the same process that occurs when people put salt on icy roads and sidewalks to help melt the ice in winter.