Water and ice baths
A bath of ice and water will maintain a temperature 0 °C since the freezing point of water is 0 °C. However, adding a salt such as sodium chloride will lower the temperature through the property of freezing-point depression. Although the exact temperature can be hard to control, the weight ratio of salt to ice influences the temperature:
−10 °C can be achieved with a 1 to 2.5 ratio by weight of calcium chloride hexahydrate to ice.
−20 °C can be achieved with a 1 to 3 ratio by weight of sodium chloride to ice.
−40 °C can be achieved with a 1 to 0.8 ratio by weight of calcium chloride hexahydrate to ice.