Some organic reaction take place by a method called reflux. During reflux, the reaction mixture is dissolved in boiling solvent. To prevent the solvent from boiling away, a condenser is attached to the reaction flask.   The condenser contains an inner tube which is surrounded by an outer jacket that is cooled by running cold water.  The vapors travel part-way up the inner tube, condense, and then return to the flask. The start time of a reflux begins when the condensed vapors dripping from the bottom of the condenser drip back into the reaction solution in the round bottom flask.

        When using the condenser, it is important to have water running through it the entire time; otherwise, the solvent will evaporate.  The water should enter through the bottom of the condenser and flow out through the top.  This will allow for the condenser to be cooled the entire time.  You do not need to have the water running like a fire hose but a steady flow rate is sufficient.  The water should be flowing through the condenser to cool before the reaction is heated.

   

        To prevent the reaction mixture from bumping, boiling stones or chips may be added to the reaction flask.  This will allow for even boiling throughout the reflux. In addition, a magnetic stir bar may be added to constantly stir the reaction mixture.  For this, you will need to use a stir plate underneath the heating mantle.  Remember to grease the condenser before attaching it to the reaction flask.  Forgetting to do so will cause the two pieces of glass to become stuck together and it will be difficult to remove them.