The natural freezing point of pure water is 0 degrees Celsius or 32 degrees Fahrenheit. If you add salt to water, however, its freezing point lowers significantly. Water saturated with salt--holding as much salt as it can--has a freezing point of -21 degrees Celsius or -6 degrees Fahrenheit. This task is easy to perform at home with a bit of salt and water. The most common applications for water with a lowered freezing point are making ice cream and de-icing roads.
Fill a container with one quart of room temperature water.
Add 3.8 tbsp. or 58.45 grams of salt to the water for every 1.8 degree Celsius you want the freezing point to decrease.
Stir until the salt dissolves into the solution. When the salt stops dissolving, the water is fully saturated.