James Dewar Biography (1842-1923)

chemist and physicist

Born on September 20, 1852, in Kincardine, Fife, Scotland, James Dewar becamefamous for his work in cryogenics--the study of objects at extremely low temperatures. He was educated at the University of Edinburgh and obtained professorial posts at both Cambridge and the Royal Institution in London. Dewar's interests covered a variety of fields. He was involved with spectroscopy, organic chemistry, the effect of light upon the retina, electricity, and the measurement of high temperatures. Dewar is best known for his work with the liquification of gases at extremely low temperatures.

In 1877, Louis Cailletet and Raoul Pictet independently were able to create small amounts of oxygen and nitrogen in liquid form at temperatures less than80° above absolute zero, a feat even Michael Faraday, who had liquified most of the known gases by 1845, had been unable to carry out. Dewar decided to pursue this line of research beginning in the late 1870s. However, Dewar was not so much concerned with the mechanism of liquefying the gases as he waswith studying their properties as they approached absolute zero.

The greatest stumbling block he encountered in his work with liquification was keeping the gases cold long enough to study them. Liquid oxygen kept in a flask absorbed heat from the surrounding air and returned to its gaseous phase. To eliminate the effect of the warm air, Dewar put the flask of liquid gasinside a larger flask and created a vacuum between them. A vacuum would prevent the transfer of energy that occurred through conduction or convection; heat would not penetrate and cold would not escape. To eliminate the transfer ofradiant energy, Dewar silvered the walls of the flasks so they would reflect, rather than absorb, energy. He also invented a technique to create a more efficient vacuum. In 1902, Dewar discovered that when charcoal was cooled, itbecame very efficient at absorbing molecules. He was able to create a bettervacuum by using charcoal to absorb any molecules that had not been pumped outwhen the vacuum was created. The final result of Dewar's efforts was the vacuum bottle or Dewar flask which, strangely, Dewar did not bother to patent. Since a vacuum prevented the transmission of both heat and cold, the Dewar flask was found to be an excellent device for storing hot and cold liquids. It is best known for its use as in insulated beverage container, better known as a Thermos TM brand bottle.

Dewar was the first person to produce a large quantity of liquid oxygen in 1885 but it was not until 1898 that he managed to liquify hydrogen gas. In further efforts he developed methods of lowering the temperature as low as -258°C (13 ° above absolute zero). At this temperature, every gas but helium could be cooled to a liquid or a solid. Although Dewar attempted to liquifyhelium he failed because his helium source was contaminated with neon gas which froze at a higher temperature, plugging his apparatus with ice. Itwas left to another cryogenics specialist, Heike Kamerlingh Onnes (1853-1926), to accomplish the task in 1908 using Dewar's methods.

Dewar also collaborated with two inventors famous in their own right. The first of these collaborations landed Dewar in the midst of a major controversy.While on a government committee studying explosives at the end of the 1880s,Dewar and a colleague Frederick Abel invented a smokeless gunpowder called cordite and were granted a patent for it. Unfortunately, the invention had comefollowing long discussions with Alfred Nobel, who was the creator of TNT, and Nobel sued to overturn the patent. The court ruled against Nobel, allowingDewar and Abel to keep their lucrative patent. Dewar also worked with John Ambrose Fleming (who later invented the vacuum tube) from 1892 to 1895 to conduct a study of the electrical properties of supercooled gases.

Dewar was knighted in 1904. While many of his discoveries came about throughthe collaboration of colleagues, Dewar did not work well in a team situation;he could be brusque and individualistic at times. He was indifferent as a teacher, but excellent as a public lecturer. At the time of his death, on March27, 1923, the 80-year-old was still experimenting, using a charcoal-gas thermoscope to measure infrared radiation from the sky.

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