A retort flask is a laboratory glassware used for distillation or refluxing. It is a pear-shaped or round-bottomed flask with a long, narrow neck and a side arm. The side arm is angled downward at a 45-degree angle and is usually attached to a water-cooled condenser. The retort flask is designed to hold and heat a liquid mixture and separate it into its components based on their boiling points. During distillation, the mixture in the retort flask is heated to the boiling point of the component with the lowest boiling point. This component vaporizes and rises up the neck of the flask into the condenser, where it is cooled and condensed back into a liquid. The liquid is then collected in a separate container. This process is repeated for each component in the mixture, resulting in a separation of the components based on their boiling points. In refluxing, the side arm is used to allow the vapor to condense back into the flask, which creates a reflux of the condensed liquid back into the mixture. This process allows for a more complete reaction of the mixture and can be used for chemical reactions that require a longer time to proceed. Retort flasks are made of borosilicate glass, which is resistant to heat and chemical corrosion. They come in various sizes, with the most common size being 500 mL or 1000 mL. The side arm can be connected to a variety of condensers, including Graham condensers, Liebig condensers, and Allihn condensers. Retort flasks are commonly used in chemistry and biochemistry labs for a variety of applications, including distillation, refluxing, and chemical reactions.