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A cold finger is a piece of laboratory equipment that is used to generate a localized cold surface. It is named for its resemblance to a finger and is a type of cold trap.
The device consists of an elongated chamber where a coolant lowers the temperature of the glass item. There are two models:
- First model uses a continuous stream of cooling fluid, such as cold tap water, or something colder
- Another model is a simple glass tube where a cold material, such as dry ice or dry ice/acetone is added
Cold fingers have a ground glass joint, which allows them to be fitted to a specially designed vacuum flask, which is then connected to a LN2 trap and a vacuum pump.
Cold fingers can be purchased from lab suppliers. Good quality cold fingers are a bit pricey, but since you need good quality glassware when working under vacuum, it's a good idea to avoid using cheap types and go for something better.
- Purify air-sensitive compounds