In a tincture, the solvent is alcohol. The solvation process is the method by which solvents dissolve solutes. This leaves a positively charged Sodium atom exposed to the water. The negatively charged end of a water molecule will attach to this Sodium atom and pluck it from the lattice. The process continues and dissolves away the salt crystals.
Solvents can only hold so much solute.
When a solvent has dissolved all the solute it can it is said to be saturated. At this point it cannot hold any more solute. You may have witnessed this condition by noticing the sugary ooze that is left in the bottom of a bowl when you put too much sugar on the cereal. Actually, some solvents can dissolve more solute than they are theoretically supposed to. In this case the solution is said to be supersaturated.