A flask is a common piece of laboratory glassware. They are used for storing, mixing and measuring liquids, a similar role to beakers and graduated cylinders. Flasks are available in various shapes but what makes them a distinct from other laboratory containers is that they have a wider body with a narrower neck extending to an opening at the top. The next is almost always cylindrical, while the body differs in shape between different types of flask. A common use of flasks is for mixing solutions since the narrow neck and larger body facilitates swirling of the contents without spillage. They may also be used for boiling where the narrow neck reduces evaporative loss.
Some common types of flask include:
- The Erlenmeyer flask, conical flask, or titration flask is one of the most common designs of flask. It has a flat base so it can sit unsupported on a laboratory bench surface. The body is conical extending upwards to a cylindrical neck. Erlenmeyer flasks are often graduated for approximate measurement. The are available in a wide range of volumes and plastic or glass materials. The neck may have an axisymmetric rolled lip, which allows a flat cover or rubber bung to seal it. They may also have a ground glass neck for a better seal.
- A Florence flask, boiling flask, or has a spherical body with a single relatively long neck. The base may follow the spherical contour of the body, requiring some form of stand, or the base may be flattened to allow it to sit on a bench. This design of flask is particularly well suited to uniform heating, boiling and swirling. These flasks are usually made from borosilicate glass due to the need for heat resistance.
- A round-bottom flask has a spherical body with one or more necks. A Florence flask is therefore a type of round-bottom flask.
- Volumetric flasks are calibrated for one specific volume, with the bulbous body and very much narrower graduated neck giving greater precision. This is the same principle as the way that volumetric pipettes work, but the accuracy is generally lower for volumetric flasks.
- Retorts are a specialized from of flask used for distillation. The body is spherical and the neck is conical, tapering to a narrow opening, and also bends downwards. The neck functions as a condenser, with vapor exiting the body at the top of the body, condensing on the walls of the neck, and then running down the walls to exit the next at a downward facing opening.
- Büchner flasks, vacuum flasks or side-arm flasks are shaped like a Erlenmeyer flask but with a narrow tube protruding from the side of the neck. This narrow tube is typically fitted with barbs to fit a rubber hose. They are often used for filtration, with a filter fitted to the larger opening at the top of the neck, and a vacuum pump attached via the side tube used to accelerate the filtration.