# Temperature and pressure for three phase equilibrium of aqueous sodium chloride solutions

I am currently investigating the effect of adding Salt(NaCl) to water on its triple point. Let us assume the mass ratio of water to NaCl is $$1:1$$. I asked a similar question previously. But, I still haven't been able to find the temperature(s) of the triple point(s).

I understand that according to the Gibbs equation $$f = C-P+2$$ Therefore, in my case of Salt water, $$f = 1$$. Thus we have a range of temperatures/presures where the triple point exists.

But how can we find this range of temperature or pressures? IS there an experimental methods?

The range of temperatures is fairly easy. Mix saturated aqueous NaCl (liquid solution, concentration about 5 mol/L) with ice (pure water, solid state), and measure the temperature. It will be about equal to the temperature of a household freezer (no coincident, freezers were using salt/water mixtures in the old days), i.e. -20 $$^\circ$$C. If you keep measuring while the ice melts and the NaCl concentration drops, you will get the temperature ranges, which will have the normal freezing point of water at the high end.