James Dewar

James Dewar was born in Kincardine-on-Forth on 20 September 1842, the youngest of six sons of a vintner. At ten he fell through the ice of the village pond and spent two years recovering from rheumatic fever; during the convalescence a local joiner taught him to make fiddles, and Dewar credited that work with the manual dexterity that later made him a formidable experimentalist. He studied at Edinburgh under Lyon Playfair, and in 1877 took the Jacksonian Professorship at Cambridge and the Fullerian Professorship at the Royal Institution in London, where he stayed for forty-six years.

His central obsession was cold. He built a research programme aimed at the last unliquefied gases and, in 1892, produced the invention that made the whole field possible: a double-walled glass vessel with the space between the walls evacuated and both facing surfaces silvered. The vacuum defeats conduction and convection; the silver reflects radiation. A cryogenic liquid could now be stored and worked with rather than merely glimpsed. Every technique in cryogenics since presupposes the Dewar flask.

In 1898 he liquefied hydrogen at 20 K, and in 1899 froze it solid at 14 K — the coldest temperature reached by anyone to that point. Hydrogen warms rather than cools on Joule–Thomson throttling at room temperature, so he had to pre-cool it below its 205 K inversion temperature with liquid air first, then throttle it in a regenerative cycle and catch the product in his own flasks. He tried for helium next and was beaten to it in 1908 by Kamerlingh Onnes in Leiden, partly for want of a supply of helium gas, of which Britain then had almost none.

He never patented the vacuum flask. When the German firm Thermos GmbH commercialised it in 1904, Dewar sued and lost: he had published the design freely and could claim no priority. He was, by all accounts, permanently embittered, and he was already difficult — he feuded with Ramsay over the noble gases and with Liveing's successors over spectroscopy, and he refused to allow women in his laboratory. He was knighted in 1904 and died in London on 27 March 1923, still holding his Royal Institution chair. His flask is in every schoolbag in the world.