Reflux is a technique used in chemistry to heat a reaction mixture for a specific amount of time while continually cooling the vapors produced back into liquid form using a condenser/01%3A_General_Techniques/1.04%3A_Heating_and_Cooling_Methods/1.4K%3A_Reflux). The purpose of refluxing a solution is to heat it in a controlled manner at a constant temperature/01%3A_General_Techniques/1.04%3A_Heating_and_Cooling_Methods/1.4K%3A_Reflux). Organic chemical reactions often take a long time to complete, and heat is applied to speed up these reactions. However, organic compounds are usually volatile with high vapor pressure, and if heated, they will evaporate and be lost. Refluxing allows the reaction mixture to boil indefinitely without loss of solvent, reactant, or product, as the vapors condense in the condensing tube and trickle back down into the reaction vessel. The reactants for reflux experiments can be solid and liquid, or both liquids. The temperature at which the reaction is heated depends on the boiling points of the solvents and also the reflux ring, which is the boundary between the portion of the solvent that travels up the condenser tube before condensing back into the flask and the portion that flows back into the flask/01%3A_General_Techniques/1.04%3A_Heating_and_Cooling_Methods/1.4K%3A_Reflux). The temperature of the reaction must be set so that the reflux ring should only be one-third to half way up the condenser/01%3A_General_Techniques/1.04%3A_Heating_and_Cooling_Methods/1.4K%3A_Reflux). Refluxing is often used in conjunction with distillation, which separates compounds based on differences in boiling points.