Laboratory funnels, adapted into different forms to suit numerous specialized needs, including filtration, are ubiquitous in the lab. Funnels fitted with filter paper, as well as Buchner and Hirsch funnels, can remove fine particles from a liquid, although a sintered glass frit is suggested for more demanding filtering applications. Funnels and filtration methods are available made from plastic, glass, metal or porcelain to fit any laboratory needs. Plastic funnels that do not come into contact with solvents are generally used for transferring powders, while polyethylene funnels are used for aqueous solution transfers. Glass funnels are noted for their inertness compared to metal and plastic, while metal funnels won't chip, break or corrode.
A variety of laboratory funnels are available. Made from glass, metal, plastic, or porcelain, they are designed for general and specific purposes. Glass reusable funnels are suitable for most uses that involve chemicals.
The standard funnel shape is conical with the sides at an approximate 60 degree angle. Glass and polypropylene powder funnels may have a larger diameter stem, or no stem at all. If liquids are being filtered using filter paper, ribs on the surface of the bowl can help prevent vapor lock.
Other types of funnels include:
- Weighing Funnels: Function as weighing dishes for solid materials; can be used to transfer the weighed solid to another vessel
- Thistle Tube Funnels: Have a reservoir attached to a long narrow neck; typically used to transfer a small amount of liquid to another vessel, sometimes to a specific location
- Filtering Funnels: Include both Hirsch (conical) and Buchner (cylindrical) funnels with integral filtering surfaces or frits; used to remove particulates from a liquid mixture or for filtrations where filter paper use is not an option
- Separatory Funnels: Cylindrical or globe-shaped vessels with an upper opening and a stopcock-controlled bottom opening; used with liquid-liquid extractions to facilitate the removal of the lower (typically aqueous) layer
- Filling Funnels: Standard conical shape; used to transfer liquids or more easily add liquids to containers with narrow openings
- Special Purpose Funnels: Includes safety or air vent funnels; used to safely transfer solvents, thinners, oils, paint wastes, and other hazardous materials to storage or disposal containers
- Dropping Funnels: Small, graduated reservoirs with a stopcock exit opening; for dropwise or measured liquid dispensing