Have
you ever kept icy cold liquids in a thermos? They stay colder a lot
longer than they would in an ordinary bottle.
Even
better, have you ever kept hot coffee or cocoa piping hot in a
thermos?
A
thermos of hot cocoa or coffee can be a beautiful thing at a
nighttime football game or concert under-the-stars—and we have
James Dewar to thank for it!
Dewar
(born on this date in 1842) was a Scottish chemist and physicist who
studied atomic and molecular spectroscopy and the liquefaction of
gases. He needed something to store liquid gases—something that
would keep heat out—and the idea occurred to him to build a double
bottle—a bottle inside a bottle—with a vacuum between the two. We
call this invention a Dewar flask.
A
Dewar flask has very reflective surfaces (mirrors) facing each other
to prevent heat from being transmitted by radiation. In other words,
the inner surface of the outer bottle has a reflective surface, and
the outer surface of the inner bottle also has a reflective surface.
In between these two reflective surfaces is...nothing at all! A
vacuum is a space with almost no atoms at all—no air, nothing. The
vacuum prevents heat being transmitted by conduction.
This
great idea was exploited for commercial use by the Thermos company.
By the way, Dewar didn't get any money from this commercial use of
his idea because he failed to file a patent on it.
Learn
more about a Dewar flask or Thermos from How Stuff Works.
Learn
more about heat from Science Kids
and neoK12.
Also
on this date:
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