James Dewar was born in Kincardine, Scotland, on 20 September 1842.
The youngest of six children and orphaned at the age of 15, Dewar attended Kincardine Parish School and Dollar Academy. He was subsequently educated at Edinburgh University where he studied chemistry under Lyon Playfair, to whom he was to become assistant.
His early scientific work covered topics such as organic chemistry, hydrogen and its physical constants, high-temperature research, the temperature of the sun and the electric spark, spectrophotometry, and the chemistry of the electric arc. Thus, in 1867, Dewar described several chemical formulae for benzene.
In 1869 he was elected a Fellow of the Royal Society of Edinburgh at the suggestion of his mentor Playfair.
Dewer took up the post of professor of natural experimental philosophy at Cambridge University in 1875 and two years later became professor of chemistry at the Royal Institution (Great Britain).
With Professor J. G. McKendrick, of the University of Glasgow, he investigated the physiological action of light and examined the changes that take place in the electrical condition of the retina under its influence. With Professor G. D. Liveing, of Cambridge University, he began in 1878 a long series of spectroscopic observations, the last of which was devoted to the spectroscopic examination of various gaseous elements separated from atmospheric air with the aid of low temperatures. He was joined by Professor J. A. Fleming of University College London in investigating the electrical behavior of substances cooled to very low temperatures.
In 1889, together with the British chemist Frederick Abel, he invented smokeless gunpowder, a mixture of nitroglycerine and nitrocellulose.
In 1891 he built a machine to produce liquid oxygen in large quantities. A year later, he invented the Dewar glass vessel (a glass container with silvered, double walls between which the vacuum has been made), capable of storing liquefied gases at temperatures close to absolute zero and whose industrial versions are called thermos flasks. He was the first scientist to liquefy hydrogen (1898) and solidify it (1899).
In 1905, he began investigating the gas-absorbing powers of charcoal when cooled to low temperatures and applied his research to the creation of the high vacuum, which was used for further experiments in atomic physics. His research during and after World War I consisted mainly of investigating the surface tension of soap bubbles, rather than further work on the properties of matter at low temperatures.
James Dewar died in London on 30 June 1923.