Dewar, James

(b. Kincardine-on-Forth, Scotland, 20 September 1842; d. London, England, 27 March 1923)

chemistry, physics.

Son of Thomas Dewar, a vintner and innkeeper, and Ann Eadie Dewar, young Dewar attended local schools until he was crippled by rheumatic fever at the age of ten. During his two-year period of convalescence he learned the art of violin making and later said that this was the foundation for his manipulative skills in the laboratory. He entered Edinburgh University in 1858. James David Forbes, professor of natural philosophy, and Lyon Playfair, professor of chemistry, directed his interest to physical science. He was assistant to Playfair (1867–1868) and to Playfair’s successor, Alexander Crum Brown (1868–1873). Dewar became lecturer on chemistry in the Royal Veterinary College of Edinburgh (1869) and assistant chemist to the Highland and Agricultural Society (1873). He was elected Jacksonian professor of natural experimental philosophy in Cambridge (1875) and Fullerian professor of chemistry at the Royal Institution (1877) and held both chairs until his death. The Royal Institution was the chief center of his experimental activity.

In 1871 Dewar married Helen Rose Banks, daughter of an Edinburgh printer; they had no children. He was president of the Society of Chemical Industry (1887), the Chemical Society of London (1897–1899), and the British Association (1902). Dewar was knighted in 1904. He also served as consultant to government and industry. He was a member of the government committee on explosives (1888–1891) and with Sir Frederick Abel invented the smokeless propellant cordite, a gelatinized mixture of nitrocellulose in nitroglycerin (1889).

Dewar’s earliest work (1867–1877) encompassed a wide variety of subjects in physics, chemistry, and physiology. In 1867 he invented a mechanical device to represent Crum Brown’s new graphic notation for organic compounds. Playfair sent the device to Kekulé, and Kekulé invited Dewar to spend the summer in his Ghent laboratory. Dewar suggested seven different structural formulas for benzene, including the diagonal formula

and the formula attributed to Kekulé.

In 1870 he proposed the pyridine ring formula, substituting a nitrogen atom for a CH residue in the benzene ring:

He also suggested that quinoline’s structure consisted of fused benzene and pyridine rings.

Dewar’s early studies included the heats at formation of the oxides of chlorine, the temperature of the sun and of the electric spark, the atomic volume of solids, and the production of high vacua. In 1872 he determined the physical constants of Thomas Graham’s hydrogenium (Graham supposed hydrogen to be the vapor of a volatile metal, “hydrogenium”) and first used a vacuum-jacketed insulating vessel. Interspersed with these physical researches were physiological investigations on the constitution and function of cystine, the physiological action of quinoline and pyridine bases, and the changes in the electrical condition of the eye under the influence of light.

At Cambridge and the Royal Institution, Dewar continued his varied interests. There were studies on the coal-tar bases; atomic and molecular weight determinations; the chemical reactions at the temperature of the electric arc, in which he noted the formation of hydrogen cyanide in the carbon arc burning in air (1879); and the determination of the monatomicity of sodium and potassium vapor from gas density studies (1883).

The first area to be thoroughly explored was spectroscopy. He joined George Downing Liveing, professor of chemistry at Cambridge, in an attempt to correlate line and band spectra with atomic and molecular states. They published seventy-eight papers between 1877 and 1904. Dewar’s interest in spectroscopy stemmed from a fascination with Henri Sainte Claire Deville’s work on dissociation and reversible interactions and Norman Lockyer’s controversial speculations on the dissociation of the elements at high temperatures. He contrasted Deville’s exact experimental methods with Lockyer’s conjectures, which he felt were based on insufficient evidence. Dewar and Liveing accurately determined the absorption spectra of many elements (especially metallic vapors) and compounds. They studied the general conditions affecting the excitation of spectra and, in particular, the ultraviolet emission spectra of many metals. They noted the contrast between single spectral lines, multiplets, and bands, and they attempted to identify the emitting agents for single, multiplet, and band spectra. They classified great, intermediate, and weak intensities with the spectroscopic series as principal, diffuse, and sharp, respectively. Their studies included the differences between the arc, spark, and flame spectra of metals; the emission spectra of gaseous explosions and of the rare gases; and the effect of temperature and concentration on the absorption spectra of rare-earth salts in solution.

Dewar’s coming to the Royal Institution in 1877 marked the beginning of his work in cryogenics, his major field of study. In that year Louis Cailletet and Raoul Pictet liquefied small amounts of oxygen and nitrogen. This achievement interested Dewar because hitherto almost all the work on liquefaction of gases had been done at the Royal Institution, especially by Michael Faraday, who by 1845 had liquefied all the known gases except the six permanent ones (oxygen, nitrogen, hydrogen, nitric oxide, carbon monoxide, and methane). During a Royal Institution lecture in 1878 Dewar gave the first demonstration in Great Britain of the liquefaction of oxygen. His principal interest was not the liquefaction of gases but the investigation of the properties of matter in the hitherto uninvestigated vicinity of the absolute zero of temperature.

In 1884 the Polish physicists Florenty von Wroblewski and Karol Olszewski improved the refrigerating apparatus, prepared moderate amounts of liquid air and oxygen, and measured their physical properties and critical constants. Dewar further improved the apparatus and methods of the Polish scientists and in 1885 prepared large quantities of liquid air and oxygen by compressing the gases at the temperature of liquid ethylene. In 1891 he discovered that both liquid oxygen and ozone were magnetic.

Dewar hoped to liquefy hydrogen; after a decade of work he had not succeeded. The critical temperature of hydrogen is –241° C. The lowest temperature attainable with liquid air as a refrigerant is about –200°C. His attempts to reach lower temperatures were unsuccessful until 1895, when he took advantage of the Joule-Thomson effect whereby the temperature of a compressed gas decreases with expansion into a vacuum because of the internal work done to overcome molecular attraction. Hydrogen was an exception; its temperature increased slightly. But Dewar showed that hydrogen had a normal Joule-Thomson effect if it was first cooled to –80°C. He cooled hydrogen by means of liquid air at –200°C. and 200 atmospheres pressure and forced it through a fine nozzle. He obtained a jet of gas mixed with a liquid that he could not collect. The temperature of the hydrogen jet was very low, and by spraying it on liquid air or oxygen he transformed them into solids. Dewar was convinced that he could reach still lower temperatures, and he spent a year making a large liquid-air machine. In 1898 his endeavor ended in success. Cooled, compressed hydrogen liquefied on escaping from a nozzle into a vacuum vessel. With liquid hydrogen he reached the lowest temperature then known. Liquid hydrogen boils at –252.5°C. at ordinary pressure. By reducing the pressure he lowered the temperature to –258°C. and solidified the hydrogen. He cooled the solid to –260°C. With liquid hydrogen, every gas except helium could in turn be both liquefied and solidified.

The lowest temperature attainable with hydrogen was still 13° above absolute zero. Could Dewar close this gap? He turned to the recently discovered helium and predicted that if the critical temperature was not below 8°K., then it should be possible to liquefy helium by methods similar to those for hydrogen. As a source of helium he used the gas bubbling from the springs at Bath, which Lord Rayleigh had found to contain the element. He failed in his liquefaction attempts because the Bath spring gas also contained neon, and in the cooling process the neon solidified, blocking the tubes and valves of the apparatus. In 1908 Heike Kamerlingh Onnes at Leiden, using Dewar’s methods, succeeded in liquefying the helium isolated from the mineral monazite. Dewar presented Kamerlingh Onnes’s work at a British Association meeting and showed that by boiling helium at reduced pressure he could reach a temperature less than 1° from absolute zero.

Dewar’s study of the properties of matter at very low temperatures was made possible by his invention in 1892 of the vacuum-jacketed flask, the most important device for preserving and handling materials at low temperatures. The insulating property of the vacuum was well known, and Dewar had used a vacuum flask in 1872 in making specific heat determinations of Graham’s hydrogenium. When he wanted to investigate the properties of liquefied gases, the idea of using a vacuum-jacketed vessel suggested itself to him.

Dewar realized that the insulating capacity of the vacuum flask depended on the state of exhaustion of the space between the inner and outer vessels. In 1905 he discovered that charcoal’s adsorptive power for gases was enormously increased at –185°C. By putting a small quantity of charcoal in the evacuated space and filling the flask with liquid air, the cooled charcoal adsorbed the remaining traces of air in the space, producing a vacuum of greater tenuity. Furthermore, the charcoal-containing flasks enabled Dewar to substitute metal vessels for glass ones. Metals gave off small quantities of occluded gas, which would impair the vacuum. Since charcoal would adsorb the gas, metal vacuum vessels became feasible. They could be made both larger and stronger than glass ones. (Such vessels are now called Dewar flasks or vessels.)

Dewar used the different condensability of gases on charcoal to separate or concentrate the constituents of a gas mixture. Charcoal preferentially adsorbed oxygen from air passed over it at –185°C. Collecting the liberated gas in fractions as the temperature rose, he obtained air containing eighty-four percent oxygen. Dewar also separated the rare gases from air by this method. In 1908 he used the carbon-adsorption technique in making the first direct measurement of the rate of production of helium from radium.

Dewar examined a wide range of properties in pioneering explorations on the effect of extreme cold on substances. He determined the properties of all the liquefied gases. He measured the decreased chemical reactivity of substances at low temperatures. He studied the effects of extreme cold on phosphorescence, color, strength of materials, the behavior of metal carbonyl compounds, the emanations of radium (with William Crookes), and the gases occluded by radium (with Pierre Curie).

Dewar established that many vigorous chemical reactions did not take place at all at very low temperatures; oxygen, for example, did not react with sodium or potassium. He wanted to test the effect of cold on fluorine, the most reactive element, and in an 1897 collaboration with Henri Moissan, who had isolated the element in 1886, he liquefied fluorine and examined its properties. After Dewar had liquefied hydrogen, they resumed their investigation and solidified fluorine at –233°C. Even when the temperature was reduced to –252.5°C., solid fluorine and liquid hydrogen violently exploded.

Dewar intended to explore the whole field of cryogenics. Between 1892 and 1895 he joined with John A. Fleming, professor of electrical engineering at University College, London, in an investigation of the electrical and magnetic properties of metals and alloys. Their aim was to determine the electrical resistance from 200°C. to the lowest attainable temperature. They obtained temperature-resistance curves and found that the resistance for all pure metals converged downward in such a manner that electrical resistance would vanish at absolute zero. They gathered accurate information on conduction, thermoelectricity, magnetic permeability, and dielectric constants of metals and alloys from 200°C. to –200°C.

Another area of extensive investigation was lowtemperature calorimetry (1904–1913). Dewar devised a calorimeter to measure specific and latent heats at low temperatures. He determined the atomic heats of the elements and the molecular heats of compounds between 80°K. and 20°K. He discovered in 1913 that the atomic heats of the solid elements at a mean temperature of 50°K. were a periodic function of the atomic weights.

World War I prohibited continuation of Dewar’s costly cryogenic research. He turned to thin films and bubbles, which had been the subject of the first of his nine courses of Christmas lectures for children at the Royal Institution (1878–1879). He studied both solid films, produced by the evaporation of the solvent from amyl acetate solutions of nitrated cotton, and liquid films from soap. He investigated the conditions for the production of long-lived bubbles and of flat films of great size, the distortions in films produced by sound, and the patterns formed by the impact of an air jet on films.

At the time of his death Dewar was engaged in studies with a delicate charcoal-gas thermoscope that he constructed in order to measure infrared radiation. From a skylight in the Royal Institution he measured the radiation from the sky by day and night and under varying weather conditions. Dewar was a superb experimentalist; he published no theoretical papers.

BIBLIOGRAPHY

I. Original Works. Dewar’s papers were reprinted in Collected Papers of Sir James Dewar, 2 vols., Lady Dewar, J. D. Hamilton Dickson, H. Munro Ross, and E. C. Scott Dickson, eds. (Cambridge, 1927); and in George Downing Liveing and James Dewar, Collected Papers on Spectroscopy (Cambridge, 1915).

Important papers include “On the Oxidation of Phenyl Alcohol, and a Mechanical Arrangement Adopted to Illustrate Structure in Non-Saturated Hydrocarbons,” in Proceedings of the Royal Society of Edinburgh, 6 (1866–1869), 82–86; “On the Oxidation Products of Picoline,” in Transactions of the Royal Society of Edinburgh, 26 (1872), 189– 196; “On the Liquefaction of Oxygen and the Critical Volumes of Fluids,” in Philosophical Magazine, 5th ser., 18 (1884), 210–216; “The Electrical Resistance of Metals and Alloys at Temperatures Approaching the Absolute Zero,”ibid., 36 (1893), 271–299; and “Thermoelectric Powers of Metals and Alloys Between the Temperatures of the Boiling-Point of Water and the Boiling-Point of Liquid Air,” ibid., 40 (1895), 95–119, written with J. A. Fleming.

See also “The Liquefaction of Air and Research at Low Temperatures,” in Proceedings of the Chemical Society, 11 (1896), 221–234; “Sur la liquefaction du fluor,” in Comptes rendus hebdomadaires des séances de l’Académie des sciences, 124 (1897), 1202–1205; “Nouvelles expériences sur la liquéfaction du fluor,” ibid., 125 (1897), 505–511; “Sur La solidification du fluor et sur la combinaison à –252.5° du fluor solide et de l’hydrogéne liquide,” ibid., 136 (1903), 641–643, written with Henri Moissan; “New Researches on Liquid Air,”: in Notices of the Proceedings of the Royal Institution of Great Britain, 15 (1899), 133–146; “Liquid Hydrogen,” ibid., 16 (1902), 1–14, 212–217; “Solid Hydrogen,” ibid.,16 (1902), 473–480; “Liquid Hydrogen Calorimetry,” ibid., 17 (1904), 581–596; “Studies With the Liquid Hydrogen and Air Calorimeters,” in Proceedings of the Royal Society, 76 (1905), 325–340; “The Rate of Production of Helium From Radium” ibid., 81 (1908), 280–286; “Atomic Specific Heats Between the Boiling Points of Liquid Nitrogen and Hydrogen,” ibid., 89 (1913), 158–169;“Studies on Liquid Films,” in Proceedings of the Royal Institution, 22 (1918), 359–405; and “Soap Films as Detectors: Stream Lines and Sound,” ibid., 24 (1923), 197–259.

II. Secondary Literature. A bibliography of Dewar’s works was compiled by Henry Young, A Record of the Scientific Work of Sir James Dewar (London, 1933). Two detailed studies of his accomplishments are Henry E. Armstrong, James Dewar (London, 1924) and Alexander Findlay, in Findlay and William Hobson Mills, eds., British Chemists (London, 1947), pp. 30–57. Informative accounts include Henry E. Armstrong, “Sir James Dewar, 1842–1923,” in Journal of the Chemical Society, 131 (1928), 1066–1706, and Proceedings of the Royal Society, 111A (1926), xiii-xxiii; Ralph Cory, “Fifty Years at the Royal Institution,” in Nature, 166 (1950), 1049–1053, which has many personal remembrances of Dewar by the librarian of the Royal Institution; Sir James Crichton-Browne, “Sir James Dewar, LL.D., F.R.S.,” in Proceedings of the Royal Society of Edinburgh, 43 (1922–1923), 255–260; and Hugh Munro Ross, in Dictionary of National Biography, 1922–1930 (London, 1937), pp. 255–257.

Dewar’s cryogenic research was analyzed in “Low-Temperature Research at the Royal Institution” by Agnes M. Clerke, in Proceedings of the Royal Institution, 16 (1901), 699–718, and Henry E. Armstrong, ibid., 19 (1909), 354–412, and 21 (1916), 735–785. A more recent study is K. Mendelssohn, “Dewar at the Royal Institution,” ibid., 41 (1966), 212–233.

Albert B. Costa

Dewar, James

BRITISH CHEMIST AND PHYSICIST
1842–1923

Sir James Dewar was born in Kincardine, Scotland, on September 20, 1842, the son of an innkeeper. He attended local schools until he was ten when he suffered a serious case of rheumatic fever lasting two years. During this period he built a violin, and music remained a lifelong interest of his. In 1858 he entered the University of Edinburgh. There he studied physics and chemistry. Dewar, in an early display of his dexterity, developed a mechanical model of Alexander Crum Brown's graphic notation for organic compounds. This was sent to Friedrich Kekulé in Ghent who then invited Dewar to spend some time in his laboratory.

After holding a number of chemical posts in Scotland, Dewar was appointed Jacksonian Professor of Natural Philosophy at the University of Cambridge in 1873, and four years later he was appointed Fullerian Professor of Chemistry at the Royal Institution. He held both chairs concurrently, but spent most of his time in London. At Cambridge he collaborated with George Downing Liveing on an extensive spectroscopic study linking spectra with atomic and molecular states. This led to a very public disagreement with Norman Lockyer about the dissociation of matter in the Sun and stars. One of Dewar's chief characteristics was his ability to engage, at times, in quite vitriolic arguments with other scientists; Robert John Strutt, the fourth Lord Rayleigh wrote that to argue with Dewar was akin to being a fly in molasses.

At the Royal Institution, Dewar found himself at the intersection of major scientific networks involving the government and industry. He thus collaborated in the late 1880s with Frederick Abel on the invention of the explosive cordite. Nevertheless, at the Royal Institution Dewar focused almost entirely on cryogenics. In 1877 oxygen had been liquefied in France, and the following year Dewar demonstrated this for the first time in England at a lecture at the Royal Institution. New methods for obtaining low temperatures were developed in the 1880s, but Dewar's ability to take advantage of these methods was restricted by his not being fully in charge of the Royal Institution. However, after forcing John Tyndall's retirement in 1887, Dewar became the director of its laboratory. He improved low-temperature methods, especially by the application of the Joule–Thomson effect that produced much lower temperatures. Dewar had now turned his attention to hydrogen, which he could not liquefy even at the low temperatures obtainable.

In the mid-1890s Dewar was responsible for one of the most important developments in the history of the Royal Institution: the establishment and endowment of the Davy–Faraday Research Laboratory of the Royal Institution. This not only entailed the acquisition of a new building, but also the direct support of Dewar's cryogenic research. Success came in 1898 when he finally liquefied hydrogen. However, in the race with Heike Kamerlingh Onnes at the University of Leiden to liquefy helium, Dewar lost and the Nobel Prize went to Kamerlingh Onnes. Although Dewar was nominated several times, he never won the coveted prize.

One of the consequences of Dewar's work was his invention of the vacuum flask to minimize heat loss. It was expensive and time-consuming to liquefy gases; hence, Dewar designed a container where, once liquefied, gases could be kept for as long as possible. Still known as the Dewar flask among chemists, it is more widely known as the Thermos, named after the company that obtained the patent for the flask and to whom Dewar lost an ensuing court case.

Dewar's later work involved investigating the chemical and physical properties of substances at low temperatures, including low-temperature calorimetry. With the outbreak of the Great War (or World War I, 1914–1918), the laboratory at the Royal Institution lost most of its staff and Dewar turned his attention to soap bubbles. By the end of the war Dewar, now in his late seventies, did not have the energy to restart the laboratory, nor would he retire. He died on March 27, 1923, and his funeral service was held in the director's flat at the Royal Institution.

see also KekulÉ, Friedrich August.

Frank A. J. L. James

Bibliography

Armstrong, H. E. (1924). James Dewar 1842–1923. London: Ernest Benn.

Brock, William H. (2002). "Exploring the Hyperarctic: James Dewar at the Royal Institution." In "The Common Purposes of Life": Science and Society at the Royal Institution of Great Britain, ed. Frank A. J. L. James. Aldershot, U.K.: Ashgate, pp. 169–190.

Gavroglu, K. (1994). "James Dewar's Nemesis: The Liquefaction of Helium." Proceedings of the Royal Institution 65:169–185.

Gavroglu, K. (1994). "On Some Myths Regarding the Liquefaction of Hydrogen and Helium." European Journal of Physics 15:9–15.

Mendelssohn, K. (1966). "Dewar at the Royal Institution." Proceedings of the Royal Institution 41:212–233.