4) Add 1/2 to 3/4 cup salt (sodium chloride) to the bag of ice.

5) Place the sealed quart bag inside the gallon bag of ice and salt. Seal the gallon bag securely.

6) Gently rock the gallon bag from side to side. It's best to hold it by the top seal or to have gloves or a cloth between the bag and your hands because the bag will be cold enough to damage your skin.