A short history of freezing salt water

In 1718 ice cream was made with salted ice, and in 1724 Fahrenheit marked the zero of his thermometer with a salt and ice mixture. Today's eutectic plate uses the same physics in a sealed body.

15 April 2026Updated 28 September 2026

Short answer

Salt melts ice, and because melting ice draws heat from its surroundings, the mixture falls below zero. The effect was used in 18th-century ice cream making and in Fahrenheit's thermometer scale. With sodium chloride and water the limit is about -21.2 °C, and salt-solution eutectic plates work on the physics of that limit.

Add salt to ice and the ice melts, drawing the heat it needs from its surroundings, so the mixture falls below zero. The effect was in use in kitchens and laboratories long before mechanical refrigeration.

Year	Record	What was done
1718	Mary Eales's book of receipts	Pots of cream buried in ice and bay salt and frozen in a cellar
1724	Fahrenheit, Philosophical Transactions	Zero on the thermometer marked with ice, water and sal ammoniac or sea salt

However much salt is added, the temperature does not fall below a certain limit. For sodium chloride and water that limit is the eutectic point: about -21.2 °C at 23.2 percent salt by weight. GEBHARDT's salt-solution eutectic plates come in several melting points including -21 °C; the measured mixture sits in a sealed body, and the user only freezes the plate.