* Dissolving is about dealing with solids, liquids and gases. You can dissolve solids in liquids until the liquids are saturated. The volume of the liquid always goes up, telling you that the solid is still there even if you can't see it.
* This important subject (which scientists call chemistry) is all about working with things you can't see – solids dissolved in liquids and gases dissolved in liquids, and it's great fun to try to understand how something you can't see works.