Recheck the temperature every few minutes. Next, add a tablespoon of table salt to the water. Stir the ice, salt and water together. Here is why. The salt dissolves in the water.
Salt water freezes at lower temperatures, depending on how much salt is in the water.
As the ice turns to water, the change from solid to liquid requires heat. This is just like when water changes from liquid to gas, for example when evaporating sweat cools your skin. As ice melts, the heat is taken from the ice and water around it. Both get colder. For directions on how to make ice cream in a plastic bag, click here .