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Scientific Apparatus
Glass Dewar

Set of glass dewars named after its inventor Sir James Dewar (1842-1923). Like the thermos bottle (a more common use of this technology) a dewar is an evacuated doubled walled cylinder. By using cryogenic fluids in a dewar temperatures down to 1 K (-272 °C, -458 °F) can be attained for use in laboratory experiments.

The set shown here consists of two nested cylindrical glass dewars: in use the outer one is filled with liquid nitrogen and the inner with liquid helium and the experiment under investigation. The inner surfaces of the glass walls are silvered to block thermal radiation apart from a small strip that is left un-coated to allow the user to view the contents and liquid level.

This dewar was made here at Caltech by the glassblower of the Low Temperature Group, Fred A. Wild, probably in the 1960's. Among the many experiments done at Caltech in dewars like this one was an (unsuccessful but famous) attempt by Professor John Pelham to test Richard Feynman's prediction of quantized vorticity using a fly's wing as an airfoil. Feynman took a keen interest in experiments and often visited the low temperature laboratory to watch them being done.

Glass dewars have been largely phased out of laboratory use (replaced by sturdier metal dewars) mainly due to their fragile construction - there are few mistakes more spectacular than breaking a glass dewar while it is full of cryogenic fluids; hence the protective perspex screen.

Facts:
Water boils at: 373 K, 100 °C, 212 °F
Liquid nitrogen boils at: 77 K, -196 °C, -321 °F
Liquid helium boils at: 4 K, -269 °C, -452 °F


ID: 2004-00082

Creation Jan. 1, 1960 through Dec. 31, 1969

MEDIUM: Glass, Wood

Topics: Physics

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