Cold finger

Cold fingers.

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 as is a type of cold trap.

Typically a cold finger is used in a sublimation apparatus, or can be used as compact version of a condenser in either reflux reaction or distillation apparatus.

The device usually consists of a chamber in which a coolant fluid (cold tap water, or perhaps something colder) can enter and leave. Another version involves filling the device with a cold material (examples: ice, dry ice or a mixture such as dry ice/acetone or ice/water).

Media

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  Cold finger used in sublimation. The raw product (6) is in the bottom of the outer tube (4) which is heated (7) while under vacuum (through side-arm 3). The sublimated material collects (5) on the cold finger proper, cooled by a coolant (blue) circulated through ports 1 and 2.

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  Camphor being sublimed. The crude product in the bottom is dark brown; the white purified product on the bottom of the cold finger above is hard to see against the light background.

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  Dark green crystals of nickelocene, freshly sublimed on a cold finger.

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  A cold finger which includes a vacuum outlet.