If you try to mix water and sand, the sand will mix around and eventually fall to the bottom. Sand and water can't make a solution, so they separate. However salt and water can make a solution, and they don't separate. If air is a mixture, why don't the gases separate? 1) So, pretty much what i'm asking is, is there a term for a solution of gases? 2) Is it just called a solution? 3) Or am i completely off track and is it something totally unrelated? 4) I was also thinking, why don't they separate because of density?