Scientific Reason for Salt Solution Gaining Volume A little background to this question: my mom placed a glass with salt and enough water to just cover the salt in a room to "absorb negative energy" out of the room at her office. It obviously "worked". So when I arrive home from university she asked me if salt water draws moisture out of the air — and explains to me what happened.

The scientist part of me is curious, because you cannot "absorb negative energy" using salt water. So I placed salt in a glass, covered it with enough water and left it overnight. To my surprise, the volume of water increased by around 20-25%, the glass is significantly more fill. 

My question is this: why?

I have 2 thoughts:


Somehow the ions in the solution as the salt dissolved have charges that repel other molecules making more space in between molecules and therefore increasing the apparent volume.  
Because it is a salt solution some form of osmosis occurs to actually absorb moisture out of the air.


My next idea is to redo this later today but weigh the glass and solution first to see if it gains mass. That would support 2. If no mass gain, then I assume something similar to 1 is happening.

Thoughts?

P. S. I am an applied mathematician so I have no background in the specifics of chemistry and how molecules and ions etc. etc. interact. 

P. S. S.: I also couldn't find an answer to this on the internet. IN FACT salt added to water appears to reduce the volume in a lot of information I read.
The vapour tension over the saturated table salt solution { the best  with the solid salt excess) is equivalent to the relative humidity about 75 %. 

If the rel. humidity is lower than 75%, the solution evaporates and the salt crystallizes.

If the rel. humidity is higher than 75%, the solution absorbs the air moisture and the salt is dissolving.

Such systems may be informally called "relative humidity buffers". They are useful for hygrometer calibration or for making a constant humidity aerial baths for long term weathering of devices or materials.

See the articles with tables of relative humidity above saturated solutions of various salts:


Researchgate.net
PDF on NIST  
PDF on Omega.com