Total mass is unchanged. It is conserved (unchanged) no matter what you do (unless you are interested in the extremely small changes in mass that are associated with any reaction that gives off heat or takes up heat, in the vein of E=mc^2).
For volume, it's actually very complicated and much more interesting. It also depends on what "volume" you mean. For the dry salt, do you mean just the actual volume of particles, or the bulk volume which includes air down in the dry salt mix?
Backing up to a simpler, but interesting example, suppose you mix 100 mL of pure ethanol and 100 mL of pure water, you do not get 200 ml of final liquid. You get less (about 192 mL).
This site describes why:
https://www.carolina.com/teacher-re...hemistry-lost-volume-demonstration/tr10785.tr
Bonding models of liquids
Bonding models for liquids are more difficult to predict due to their significant molecular motion and strong intermolecular forces. Bonding models for liquid water, although extensively studied, are still not fully understood. Recent studies suggest that some regions of pure water may temporarily resemble the solid structure of ice, which has a very open structure to maximize hydrogen bonding. The open structure of solid ice is the reason ice floats in water.
When water and ethyl alcohol mix, several forces come into play. First, between the water and ethyl alcohol is strong hydrogen bonding that draws the different molecules close together. Second, open spaces in the liquid are much less likely because the ethyl alcohol interferes with any temporary open structures that are similar to those of solid water. The 2 different molecules pack closer together than in pure solution, resulting in a reduction of volume.
This has more:
http://mathscinotes.com/2016/07/volume-reduction-in-ethanol-water-mixtures/
and
https://www.quora.com/Thermodynamic...ion-have-less-volume-than-the-pure-components
