Wiktionary
n. (context chemistry English) A piece of laboratory equipment used for creating a cold spot on a surface.
Wikipedia
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 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).
Typically a cold finger is used in a sublimation apparatus, or can be used as a compact version of a condenser in either reflux reaction or distillation apparatus. Many commercially available rotary evaporators can be purchased with a cold finger in place of a Dimroth condenser, for example. When used as a condenser in a rotary evaporator, cold fingers can be cooled to a lower temperature of −78 °C (dry ice), compared with water condensers that can be cooled to −40 °C ( ethylene glycol/water mixture). The lower temperature achieved reduces the quantity of volatile material exhausted into the air.
Usage examples of "cold finger".
The metal arms were half outstretched before it and a sudden, icy premonition ran a cold finger up his spine.
The cold finger that had touched John's spine repeatedly during the past few minutes left his whole body chilled this time.
The rain caught him in the dark by surprise, a cold finger at his cheek, tapping him awake to night and storm and the confusions of consciousness.
A cold finger ran up Haven's backbone, and something molten clutched in his gut.
I felt the fractional grip, like gentle sandpaper, as it took, and then a long cold finger leapt down past my collar bone and deep into my chest.