This is the cheap, non-food grade salt that we throw onto icy walkways and use to make ice cream. It doesn't actually go into the ice cream, as some have learned the hard way, but rather into the wooden ice-filled tub that surrounds the bucket of ice cream. The salt lowers the freezing point of the ice, which causes it to melt. As it melts, it absorbs heat from the ice cream, helping it to freeze more quickly. Use a ratio of one part rock salt for every five parts of ice