In my opinion, the simplest way to make relatively pure Cl2 gas is to obtain MnO2 from a zinc-carbon battery (its that brown-black paste-like stuff between the outer shell and the carbon electrode), pour in a little hydrochloric acid, and set up a simple apparatus in order to bubble the Cl2 gas produced through some water into a test tube. Voila. Isolated chlorine gas.
The chemical equation of this reaction is: 4 HCl + MnO2 → MnCl2 + 2 H2O + Cl2
For those of you who are curious, this method of creating chlorine gas was actually how chlorine was discovered. It was discovered in 1774 by Carl Wilhelm Scheele.
