Inventors
Sir
James Dewar
By
Mary
Bellis
Sir
James Dewar, (1842-1923) was a chemist and physicist, best known for his
work with low-temperature phenomena. Dewar was born in Kincardine, Scotland,
and educated at the University of Edinburgh. He was professor of experimental
natural philosophy at the University of Cambridge, England, in 1875 and
professor of chemistry at the Royal Institution of Great Britain in 1877,
where he was appointed director of the Davy-Faraday Research Laboratory.
Dewar
developed structural formulas for benzene (1867). He studied the specific
heat of hydrogen and was the first person to produce hydrogen in liquid
form (1898) and to solidify it (1899). He constructed a machine for
producing liquid oxygen in quantity (1891). He invented the Dewar flask
or thermos (1892) and co-invented cordite (1889), a smokeless gunpowder,
with Sir Frederick Abel. His discovery (1905) that cooled charcoal can
be used to help create high vacuums later proved useful in atomic physics.
Dewar was knighted in 1904.
The
Dewar flask or vacuum flask/bottle is a container for storing hot or cold
substances, i.e. liquid air. It consists of two flasks, one inside the
other, separated by a vacuum. The vacuum greatly reduces the transfer of
heat, preventing a temperature change. The walls are usually made of glass
because it is a poor conductor of heat; its surfaces are usually lined
with a reflective metal to reduce the transfer of heat by radiation. Dewar
used silver. The whole fragile flask rests on a shock-absorbing spring
within a metal or plastic container, and the air between the flask and
the container provides further insulation. The common thermos bottle is
an adaptation of the Dewar flask. Dewar invented the Dewar flask in 1892
to aid him in his work with liquid gases.
The
vacuum flask was not manufactured for commercial/home use until 1904, when
two German glass blowers formed Thermos GmbH. They held a contest to rename
the vacuum flask and a resident of Munich submitted "Thermos", which came
from the Greek word "Therme" meaning "hot."
In
1907, Thermos GmbH sold the Thermos trademark rights to three independent
companies: The American Thermos Bottle Company of Brooklyn, NY; Thermos
Limited of Tottenham, England; and Canadian Thermos Bottle Co. Ltd. of
Montreal, Canada.
(Thermos
is a proprietary name or trademark applied to a type of Dewar flask protected
by a metal casing.)
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