<Table> <Tr> <Td> </Td> <Td> This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (November 2011) (Learn how and when to remove this template message) </Td> </Tr> </Table> <Tr> <Td> </Td> <Td> This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (November 2011) (Learn how and when to remove this template message) </Td> </Tr> <P> A vacuum flask (also known as a Dewar flask, Dewar bottle or thermos) is an insulating storage vessel that greatly lengthens the time over which its contents remain hotter or cooler than the flask's surroundings . Invented by Sir James Dewar in 1892, the vacuum flask consists of two flasks, placed one within the other and joined at the neck . The gap between the two flasks is partially evacuated of air, creating a near - vacuum which significantly reduces heat transfer by conduction or convection . </P> <P> Vacuum flasks are used domestically to keep beverages hot or cold for extended periods of time and for many purposes in industry . </P>

What is a thermos flask and how does it work
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