# Will the addition of salt further cool down ice that is already at -30 °C?

I know that ice gets colder when salt is added. But how big is the effect if it is already −30 °C?

Can it cool it down more or does it just work with −1 °C cold ice?

Another question: If I have a water cooling circuit, does adding salt help it cool down?

• (1) At -30°C, common table salt ($\ce{NaCl}$) wouldn't do anything to ice; $\ce{CaCl2}$ probably would. (2) No. Apr 8 '16 at 9:38

If you add salt to icy water, it's the water that gets colder. Pure water under atmospheric pressures will be $0~\mathrm{^\circ C}$ - even when the ice melting in it is colder (for example if it's just out of the fridge). When you then add salt to that water, it lowers the freezing point of your water-salt solution, all the way down to $-21~\mathrm{^\circ C}$ once it contains $5.2\ \mathrm{mol}$ of NaCl per kg of water. That's the maximum amount of salt this solution can contain at that temperature. (Find the thermophysical data at NIST (page 30).