Hoping for some help here (just visiting).
According to a BRE Digest:
If you have a closed container,
with a bowl of water,
with an excess of salt (NaCl) in the water,
then the relative humidity at 20 degrees celcius
will be 75% in the container.

There is a balance at 1 atm and 20 degrees:

H20 + (Na+) + (Cl-) <=====> NaCl + AIR(17 grams damp/cubic meter)

If we add damp to one side of the equation, then more salt gets
dissolved until the balance is regained.

Now I understand the result, but not the "whys" of getting there.

Anybody got any links to finding an explanation.
Thanks Gary