Rock salt forces the ice surrounding the can of ice cream mix to melt.
If there were no salt added to the ice, it would melt at 32 degrees Fahrenheit and eventually the ice water and mix would come to equilibrium at 32 degrees. The ice cream mix, however, does not begin to freeze until its temperature falls below 27 degrees. Therefore, in order to freeze the mix, we need a salt concentration, or a ratio of 5 cups of ice to 1 cups of salt. This will give the rapid cooling and freezing that is essential to making smooth creamy ice cream. Bethesda, Maryland For ice to melt into liquid water it must absorb a lot of heat energy.