Distillation separates a liquid from a mixture by boiling it and condensing the vapour. In organic synthesis it is used to remove a volatile product from a reaction mixture, or to separate liquids with different boiling points.The mixture is heated in a round-bottomed flask containing anti-bumping granules, which give smooth boiling. A still head holds a thermometer with its bulb level with the side arm, so it reads the temperature of the vapour leaving the flask. The vapour passes into a Liebig condenser, cooled by water that enters at the bottom and leaves at the top so the jacket stays full of cold water. The condensed liquid, the distillate, drips into a collecting flask.