James Dewar

James Dewar (1842-1923), British chemist and physicist, best known for his researches in low-temperature physics and the invention of the vacuum flask. A noted experimenter, he ascribed his acquired manipulative skills to making fiddles during an extended bout of rheumatic fever caused by a fall though the ice when aged ten.

Dewar was born in Kincardine, Scotland, on September 20, 1842. Tragically, he lost both parents by the age of 15 and went to live with one of his brothers. After graduating from the University of Edinburgh, he stayed as the demonstrator of the professor of chemistry, Lyon Playfair (1818-1898). In 1869 he was appointed lecturer at the Royal Veterinary College, in Edinburgh, where he started his lifelong study of low-temperature physics. This was briefly interrupted during his years (1873-1875) as assistant chemist to the Highland and Agricultural Society of Scotland, where he analysed manure and fertilizers, and became involved in what he called “peripatetic lecturing”. In 1875 he was elected Jacksonian Professor of Natural Experimental Philosophy and Chemistry at the University of Cambridge, and two years later to the Fullerian Professorship at the Royal Institution, in London, both posts he held until his death. Most of his researches were carried out in the better-equipped laboratory in London.

His research was wide-ranging. He studied the structure of benzene, including the ring-structure proposed by Friedrich August Kekulé von Stradonitz, and spent the summer of 1867 with Kekulé in Ghent, Belgium. Dewar also worked on the specific heat of hydrogen, on the temperature of the Sun and of the electric spark, on the physiological action of light, and with his Cambridge colleague G. D. Liveing (1827-1924) he began in 1878 a long series of spectroscopic investigations over a 25-year period, the later of which were concerned with the spectroscopic observation of the gaseous constituents of atmospheric air separated at very low temperatures. With J. A. Fleming of University College, London, he investigated the electrical resistance of substances cooled to a very low temperature, predicting that resistance would disappear at absolute zero (-273.15° C/-459.67° F, or 0° K on the Kelvin scale). In 1889 he was the co-inventor with Sir Frederick Abel (1826-1902) of cordite, which is a smokeless gunpowder, and in 1904 he worked with Pierre Curie on the effects of very low temperatures on the decay of radium to helium. In 1905 he discovered that the gas-absorbing powers of charcoal increased at very low temperature, and applied this to the production of high vacua.

The work on the liquefaction of gases, on which Dewar’s fame rests, was started in 1877. In that year, French physicist Louis Cailletet (1832-1913) and Swiss physicist Raoul Pierre Pictet (1846-1929) liquefied a small amount of oxygen. Dewar demonstrated their apparatus before the Royal Institution in 1878, and from then on tried to reach lower and lower temperatures, in particular to liquefy hydrogen, and later helium. In 1895 he achieved the liquefaction of hydrogen by utilizing the Joule-Thomson effect: hydrogen was cooled to –200^o C (-328^o F), then compressed to 200 atmospheres of pressure, and next expanded through a nozzle. Liquid hydrogen could be seen but not collected, but by 1898 he managed by means of a much larger machine to produce liquid hydrogen in quantity. He was the first person to liquefy hydrogen and then to solidify it (in 1899). He used a similar technique to liquefy naturally occurring helium, but was unsuccessful as it contained neon as an impurity. The Dutch physicist Heike Kamerlingh Onnes was the first to achieve this in 1908. See also Cryogenics.

In the course of his low-temperature work, Dewar invented his vacuum flask. His original vessel of 1892 was made of glass and was un-silvered. In 1904 the “Dewar flask” went into commercial production for domestic use by the German glass-blower Reinhold Burger and was given the name of “thermos” (Greek for “hot”, as the vessel can, of course, keep things hot as well as cold), which then became a protected brand name.

Dewar was knighted in 1904. He died in London on March 27, 1923.