You probably know it already, but with this experiment you can prove it. Dissolve two spoons of salt in a glass of water. Attach a piece of copper wire to both poles of a torch battery. Let the two wires hang into the salt water (they must not meet!) and watch what happens! At the negative wire, bubbles will form. The positive wire will be covered by a greenish-yellow coat.  Using the electrical current you have, in fact, separated salt into its constituents. The sodium in the salt immediately reacts with the water to form liquid caustic soda.  Hydrogen gas is then released and forms the bubbles that you can see. The chloride in the salt reacts with the copper of the positive wire and forms copper chloride – that is the greenish-yellow dust. This whole process is called "electrolysis".