Salt:
* Dissolves: Salt (sodium chloride) is highly soluble in water. When mixed, the salt crystals break down into individual ions (sodium and chloride) and disperse evenly throughout the water. You can't see the salt anymore.
* Creates a saline solution: The water becomes a saltwater solution, which has a higher density and a slightly different taste than pure water.
Sand:
* Suspends: Sand grains are much larger than salt ions and are insoluble in water. They will mostly sink to the bottom of the container. However, you might see some fine sand particles briefly suspended in the water, especially if you stir the mixture vigorously.
* Settles: Over time, the suspended sand will settle to the bottom, leaving a clear salt solution above it.
The Result:
You'll end up with a clear saltwater solution with a layer of sand settled at the bottom. If you let the water evaporate, you'll be left with the sand and the salt crystals will form again.
Important Note: This assumes you're using a small amount of salt and sand. If you use a large amount of salt, you might reach a point where the water can't dissolve any more, and you'll have undissolved salt crystals at the bottom, along with the sand.
