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James Dewar-More Than a Flask

James Dewar-More Than a Flask

Educator Indian Journal of Chemical Technology Vo l. I 0. July 2003, pp. 424-434

James Dewar-More than a flask

Jaime Wi sniak Department of Chemical Engineering, Ben-Gurion University of the Negev, Beer-Sheva, Israel 841 05

James Dewar (1842-1923) is widely known for his pioneering work i.n , of being the first to achieve the of , by the flask that carries his name, and by his studies about the behaviour of living organisms and materials under conditions of extreme cold. Although he was an excellent experimentalist, he did not leave many significant theoretical contributions.

12 Life and career ' James Dewar (Fig. I) was born on September 20, 1842, in Kinkardine-on-Forth, , the youngest of seven sons of Thomas Dewar and Ann Eadie Dewar. When he was ten years old he went skating and fell through ice in a frozen lake and when rescued walked about in hi s wet clothes until they were dry so that his family would not know about his accident. As a result he contracted rheumatic fever, which crippled him; he had to go on crutches for a couple of years and was left with a damaged heart. During this period he was in much contact with the village carpenter and practiced his hands in making violins. He always regarded th e training he thus received as the most important part of hi s education and the foundation of the great manual dexterity, which he displayed in hi s 1 work and hi s lectures • By the time he was fifteen he had lost both parents and went to li ve with one of hi s brothers who owned a drapery shop in Kincardaine. He stayed with him until he was admitted to the in Clack­ mann shire. At school he was a very distinguished student and was awarded many prizes, one of them in Fig. I- James Dewar ( 1842-1923). By permission of Edgar Fahs Peter Guthrie Tait's (1831-1901) class; with whom he Smith Collection, University of Pennsy lvani a Li brary. would later do research on high . After graduation he went to University demonstrator for Lyon Playfair ( 181 8-1898). where he li ved with hi s brothers Alexander, then professor of from 1867 to 1868. Pl ayfair nearly through hi s medical course. Eventually hi s retired in 1868 (to serve in Parliament, he occupi ed brother was appointed assistant to professor James various positions such as Postmaster General and Syme (1799-1870), and through him James was Lord in Waiting of Queen Victoria) and Dewar was probably in full touch with medicine. appointed assistant to hi s successor, Alexander Crum He graduated from Edinburgh as a in 1861 Brown (1838-1922). Dewar taught the medical and stayed on for almost a decade, first as tutorial class. assistant to James David (1828-1876) and then as In 1869 Dewar was appointc:d Lecturer ( 1869- 1873) and then Professor in the Royal Vererinary E-mail: wisr.iak @bgum ai l.bgu.ac. il College. Between 1873 and I 875 he was appointed Wisniak: James Dewar-More then a flask Educator assistant chemist to the Highland and Agricultural He was appointed Director of the Davy Faraday Society of Scotland and delivered district lectures for Research Laboratory of the ( 1896- this body. He was put in charge of analysing manure, 1923) and was President of the , of foodstuff and fertilizers, lecturing the agricultural the Society of Chemical Industry, and of the British association on chemistry and answering any specific Association. inquiries. He was member of the Royal Institution of Great During the period 1867-1875, he did research on a Britain, honorary member of the Institution of Civil variety of subjects in chemistry, biology and . Engineers, member of the Institution of Electrical He was associated with William Dittmar (1833-1892), Engineers, and member of the British Association. Arthur Gam gee ( 1841-1909) on physiological Dewar was knighted in 1904. chemistry; John Gray McKendrick (1841-1929) on the physiological effect of light on animals; and with Awards Tait on the production of vacuum and in experiments The Royal Society awarded to Dewar its three most with 's (1832-1919) newly invented prestigious medals: Rumford (1894), Davy (1909), radiometer. · and Copley (1916). He received the first Hodgkins In 1875 he was appointed Jacksonian professor of Gold Medal of the (1899); the natural experimental philosophy in the University of Gunning Victoria Jubilee Prize of the Royal Society Cambridge and became the colleague of George of Edinburgh (1904); the first Lavoisier Gold Medal Downing Liveing (1827-1924). Two years later he of the French Academy of Sciences (1904); the also became Fullerian professor of chemistry at the Matteuci Medal of the Societa ltaliana delle Scienze Royal Institution, , replacing John Hall (1906); the Albert Medal of the Gladstone (1827-1902). (1908); the Medal of the Society of Chemical Jndu stry According to Armstrong' "Dewar was not great as ( 1918); and the Franklin Institute Medal (1919). a teacher. His mind was of too original and impatient a type. He never suffered fools gladly and students are Scientific activities too apt to be foolish, even to ape the part of superior Dewar is widely known for his pioneering work in beings. His forte lay in directing competent hands, not cryogenics, the first to achieve the liquefaction of in forming them. He worked himself and through hydrogen, by the flask that carries his name, and hi s skilled assistants, not through pupils. He was violently studies about the behaviour of living organisms and impatient of failure in manipulation, and his work was materials under conditions of extreme cold. Although almost entirely manipulatory. He, therefore, never he was an excellent experimentalist, he did not created a school." distinguish with theoretical contributions. He left us In 1871 Dewar married Helen Rose Banks, the with more than 265 scientific papers in the many daughter of an Edinburgh printer; they had no areas he was active. children. Here are described ~orne of his most important James Dewar died on March 23, 1923, while at contributions. work, at the Royal Institution on Albemarle Street. He was 82 years old. By his express wish his remains The structure of were cremated at Golder's Green. One of the first incursions of Dewar into organic chemistry was related to the oxidation of unsaturated Honours hydrocarbons. He was aware that a common method James Dewar received many honours for his for determining the structure of a compound was by contributions to science and industry. He was oxidation and analysis of the products. In the case of awarded many honorary degrees, among them, M.A., benzene derivatives, although the synthesis and Honoris Causa (1875), Cambridge; honorary LL.D. analysis of its derivatives confirmed each other, the from , St. Andrews, Edinburgh and structure of the principal nucleus remained ; and honorary D.Sc., Victoria, Oxford, and unexplained. For many years Agustin Kekule ( 1829- Dublin. He was nominated Fellow of Peterhouse 1896) had tried to solve the riddle and in 1865 he had College, Fellow of the Royal Society of London, of suggested that benzene consisted of a ring of six the Royal Society of Edinburgh, of the Institute of carbon atoms decorated with six peripheral hydrogen Chemistry, of the Chemical Society, and of the atoms; the carbon atoms were arranged in a closed Society of Chemical Industry. chain with the carbon bonds bound two and one

425 Educator Indian J. Chem. Techno!.. Jul y 2003 separately. Now, if the formula was examined graphically, it became evident that benzene had to have three symmetrical groupings, C2H2 (acetylene). Dewar reasoned3 that if Kekule's model was correct then oxiqation would separate the carbon atoms in .. pairs and yield the corresponding oxidized product, ., C2Hc0 4, oxalic acid. He tried oxidizing benzene with ·,..:· potassium permanganate in a sealed tube at 150°C, •:It but no ·reaction occurred; addition of aqueous . potassium permanganate to an aqueous solution of ~a• phenyl alcohol (phenol) resulted in immediate ... decomposition, the solution became alkaline and .•.. • manganese peroxide precipitated. Acidulation of the . I· . liquid phase and addition of calcium acetate .· precipitated calcium oxalate. Dewar believed that by controlled oxidation of phenol several substances might be produced, such as oxalic and fumaric acids. He added that if the resisting nucleus in benzene was C4H2, then he would expect that mellitic (C4H 20 4) acid would be formed.

3 In this publication Dewar did not present any J • . significant experimental results that helped nail down \~::/ (/ . / ·. . . the chemical structure of benzene. But his paper has ..... ·~ ... an especial feature that illustrated his understanding .. of the problem as well as his manual skills. He described the construction a simple mechanical arrangement adapted to illustrate the structure in non­ saturated hydrocarbons. His device consisted of a seri es of narrow thin bars of brass of equal length, where it was possible to join every two of the bars in Fig. 2-Structures of benzene as sugg:!sted by Dewar th e centre by a nut. This primary structure represented using hi s kit. a single carbon atom with its four places of attachment. In order to make the combination look The chemical action of light like an atom, Dewar added a thin round disk of Dewar did work on the chemical action of li ght on blackened brass under the central nut. When a number plants and its physiological effects on the retina and 45 of carbon atoms were now joined together, all the the optical nerve · . joints and arms were moveable and it was easy to According to him, the chemical actions generally show saturation in a closed or open chain and the induced by light were of the trigger or relay many arrangements corresponding to the same description; they were not necessarily related to the formula. power evolved by the transformation. Plants, for example, stored large amounts of energy in th e form Dewar illustrated the use of his device showing of combustible matter under the influence of solar seven different ways of associating six carbon atoms, light. It was not yet possible to show that th ere existed ;.unong them being the well-known arrangement often an accurate equivalent proportion between the power referred to as Dewar's benzene formula, although he of energy of the solar rays, which was absorbed by th e did not single it out in particular (Fig. 2). green leaves of the plants, and the energy which was Professor Playfair was so impressed by Dewar's stored up in the form of chemical force in the interi or ingenuity th at he sent a copy of the paper to Kekule at of plants. It was known that under the influence of the University of Ghent; Kekule responded by solar energy a square foot of land producing corn or inviting Dewar to spend with him the summer of trees was able to manufacture 0.036 lb of carbon per 1867. year. Burning of an equivalent amount of carbon

426 Wi sni ak: James Dewar-More then a flask Educator allowed heating 291 1b of water by 1° C. Since the -190°C for twenty-four hours without any noticeabl e total amount of solar energy reaching the earth could impairment of their growth or functional activity. heat by 430,000 lb of water by 1° C the numerical Phosphorescent microorganisms supplied a striking relation between these two phenomena was so high illustration of the alternate suspension and renewal of that it was impossible to determine the quantity of vital processes by freezing and thawing. Under solar heat so accurately so as to be able to detect the normal conditions their cells emitted light as a result loss of such a small fraction as absorbed by the plants. of chemical processes of intra cellular oxidation, and Anyhow, Dewar's first estimate of the mean the phenomenon ceased with the cessation of their agricultural efficiency of a given piece of land activity. Surprisingly, when cooled down in liquid air cultivated as forest was about 1/600 of the total they became non-luminous, but the intracellular energy of sunlight. oxidation producing the phosphorescence recom­ Afterwards, Dewar used the experimental results of menced with full vigour when the temperature was Jean-Baptiste Boussingault' s (1802-1877) on the raised. The sudden cessation and rapid renewal of th e amount of carbon dioxide recomposed by a given area shinning faculty of the cells, despite extreme changes of green leaf and Edward Frankland's (1825-1899) of temperature, were very instructive. The same determination of the thermal value of grape sugar to results were observed when the microorgarisms were improve his estimate of the efficiency conserved exposed to the temperature of liquid hydrog~n. On th e putting it now at 1/238 of the total incident energy of basis of these results, Macfadyen remarked "that the 4 sunlight • fact that life can continue to exist at a temperature at Dewar worked with McKendrick in measuring the which, according to our present conception, mol ecular effect of light on the electromotive force of the retina activities with which we are acquainted, either ceases and the optic nerve. Their results indicated that the or enters on an entirely new phase, affords new alteration was 3 to 10 percent of the total amount of ground for reflection as to whether life, after all , is the natural current, the action on the compound eye of dependent for its continuance on chemical reactions." the crustacean being the same as that on the simple eye. The change of the electrical effect with luminous Liquefaction ofgases •intensity was found to vary according to Gustav At the end of 1877 the scientific community Theodor Fechner's (180 1-1887) law that the learned that Louis Cailletet (1832-1913) in France and difference in sensation was proportional to the Raoul Pictet (1846-1929) in Geneva had indepen­ logarithm of the luminous intensities by which they dently and simultaneously achieved what was were provoked. Dewar also showed that yellow light, believed impossible: the liquefaction of . On which was known to have the greatest luminous hearing this news Dewar promptly obtained a effect, was also the most effective in producing the Cailletet expansion apparatus, quickly set to work and electrical alteration. Warm and cold-blooded animals developed his own appliances. Simultaneously, two 5 were shown to behave alike . Polish scientists, Zygmunt von Wroblewski ( 1845- 1888) and (1846-1915) al so set Effect of low temperature on vital phenomena about to modify Cailletet's apparatus and within two Low temperature research is of extreme importance months they were able to produce a reasonable for the study of vital phenomena. Warm-blooded amount of . To do so they resorted to animals will die when subjected to extreme cold. cooling Cailletet's thick walled tube down to Samples of blood, meat, and milk, sealed in glass - 130°C using pumped ethylene rather than ethylene at tubes, will undergo putrefaction after prolonged atmospheric . Obtention of a significant immersion in liquid oxygen. The power of resistance, amount of liquid oxygen by Wroblewski and however, increases with simplicity of organization, Olszewski was considered to be a major sci entific and bacteria are able to survive an indefinite amount achievement. It demolished the concept of a and degree of freezing. The germinating power of permanent gas and established that the concept of seeds is also not impaired by subjection to high cold. critical isotherm developed by Thomas Andrews Macfadyen and Dewar6 studied the effect of very low (1813-1885) for carbon dioxide was applicable to all temperatures on a typical series of bacteria possessing gases. various degrees of resistance to exiernal agents. They In 1878 Dewar succeeded in producing liquid were first simultaneously exposed to oxygen in for the first time. He performed

427 Educator Indian J. Chern. Techno!., July 2003 many experiments with the liquid and in 1891 he temperature level. One year after being able to liquefy 8 showed that it was magnetic. He was the first person hydrogen he succeeded in achieving its solidification . to obtain solid oxygen. His first attempts at obtaining the solid phase, made He constantly improved his equipment until he was by pumping hydrogen vapour over the liquid, failed able to produce routinely large quantities of liquid and he immediately realized that the stray heat influx oxygen and liquid air materials, which would be a into his was too large to be counterbalanced major help factor in his following achievements. His by the cold he could obtain in evaporating the liquid. next major goal was to try to liquefy hydrogen. The This finding lead to further improvements in the difficulty of the problem can be appreciated from the design and !building of what would eventually become fact that the critical temperature of hydrogen is 33.3 K known as the Dewar flask, for storing liquefied gases whereas the lowest temperature obtainable by (see below). pumping liquid air (the coolest medium available at At about that time it was realized that . that time) is in the neighbourhood of 70 K. Dewar's which had recently been found (1884) to also exist in experiments on the liquefaction of hydrogen were the earth, had an even lower boiling point. This performed at the Royal Institution in London. On May discovery set the three personalities, Dewar. I 0, 1898, after several runs, which were hampered by Olszewski and ( 1853-1926) the presence on impurities in the air and in the on independent programs to achieve the liquefacti on equipment, he finally succeeded in liquefying of the gas having the lowest boiling point. hydrogen. According to his Laboratory Notebooks: After Kamerlingh Onnes succeeded in liquefy in g 9 "Shortly after starting the nozzle plugged but it got helium in 1908 , Dewar lost interest in low free by good luck and almost immediately drops of temperature research and this topic became neglected liquid began to fall. .. and soon accumulated 20 cc. in England for many years. The hydrogen was a clear transparent liquid well­ defined meniscus ... " When Dewar immersed a Fluorine sealed tube contained helium into the Dewar collaborated with Henri Moissan ( 1852- he "could see liquid formed. This tube gave nothing 1907; 1906 Nobel Prize for Chemistry) in achieving when placed in liquid air." He repeated the the liquefaction and solidification of fluorine and experiment several days later and found liquid studying the properties of the element in these two 10 13 hydrogen appear "more brilliant than liquid air". states - . For this purpose Moissan travell ed to Dewar presented hi s results to the Royal Society on England and took with him h1s apparatus for May 12, 1898, and asserted that he was able to liquefy producing nuorine. both hydrogen and helium; only by mid-June did he The liquefaction of fluorine was realized one year stop mentioning the liquefaction of helium after he before that of hydrogen and was achieved initially at understood that what he took to be condensed helium about -185°C using liquid oxygen as the cooling 7 were traces of impurities . medium, and afterwards at -190°C using liquid . 10- 12 Liquefaction of hydrogen was regarded at the time as alr a major technological achievement and was fraught Moissan and Dewar proceeded then to determine with dangerous experimentation, as can be the physical and chemical properties of liquid appreciated by the fact that during the course of this lluorine. They reported that it was a clear yell ow liquefaction study two of Dewar's assistants, J. W. liquid of great mobility, boiling in open vessels at Heath and Robert Lennox, both lost an eye, as a result -187°C and refusing to solidify at -210"C. It was of explosions. soluble in liquid air and oxygen, had a density 1.14 Some authors 1 claim that Dewar never gave a times that of water and a capillarity smaller th an that detailed account of his apparatus, although it was of liquid hydrogen; examined with the spectroscope 7 based on the Joule-Thomson effect. Gravroglu has through a thickness of about 0.5 em showed no pointed out that although this claim is nominally specific absorption bands in the visible spectrum and correct, the full details of his equipment do appear in put between the poles of a powerful electromagnet did Dewar's Laboratory Notebooks. not show any magnetic phenomena. The energetic Dewar, after succeeding in liquefying hydrogen, chemical affinities characteristics of the gas were did much research studying its properties, as well as almost entirely suppressed by th e extreme cold the behaviour of substances at this new low- needed for its condensation. The liquid could be

428 Wi sni ak: James Dewar-More then a flask Educator stored harmlessly in glass bulbs and did not react with remained underdeveloped until 1904 when Dewar oxygen and water. There was no reaction either when made experiments with finely divided platinum and silicon, selenium, boron, carbon, sulphur, red , which were known to occlude gases, in phosphorus, arsenic, iodides, and reduced iron were particular hydrogen and oxygen, even at ordinary first cooled in liquid oxygen and then put in an temperatures and to take up larger quantities when atmosphere of fluorine, It did though react with heated. Finding that their absorptive power was little hydrogen and hydrocarbons with incandescence. affected by cooling, he remembered his results about Turpentine in the solid state was attacked by liquid charcoal and proceeded to compare its behaviour with fluorine; combination took place with explosive force, that of the two mentioned. A surprising finding a brilliant flash of light and deposition of carbon. It was the extraordinary absorption power that charcoal would thus seem that the powerful affinity of fluorine presented when cooled by liquid air. Further ex peri­ for hydrogen was the last to di sappear. mentation showed that the absorption power of If a current of liquid oxygen was directed to the charcoal depended on the way in which it was surface of liquid oxygen at about -190°C, the fluorine prepared and that the power was enhanced by di ssolved in all proportions, imparting a yellowish carbonising the coconut shell slowly while gradually colour, giving th e liquid a graded tint from the upper increasing the temperature; "whereas the specimens at 3 to the lower part. If on the contrary, fluorine gas was first used absorbed only about 150 cm of air per introduced at the bottom of liquid oxygen, the yellow gram, at -185°C those prepared subsequently with colour was produced at the bottom and diffused these precautions absorbed from 350 to 400 cm3 per slowly to the upper layers. This phenomenon gram." Porous materials other than charcoal, such as indicated that the densities of liquid fluorine and alumina, meerschaum (sepiolite), and sili ca, also oxygen are very near each other. absorbed an increased proportion of gases at low Liquefaction of fluorine was now followed by temperatures but their retention power was much achi evement of its solidification using liquid inferior to that of charcoal. hydrogen. The yellow liquid was converted into a It was also found that pressure has but relatively white solid (solid chlorine is also solid, bromine little influence in increasing the amount of gas becomes somewhat paler in colour) melting at about absorbed. 40 K, a temperature a little below that at which solid One of the most interesting series of observations oxygen melts. When the point of a tube containing made was related to the equilibria established when solid fluorine plunged in liquid hydrogen was broken saturating charcoal at low temperatures with a mi xture off by means of steel pincers a violent explosion took of gases. Charcoal that has been heated, exhausted, pl ace. and then allowed to absorb atmospheric air at -185°C, presumably contained within its pores a mi xture having about 80 percent and 20 percent The use of charcoal in the production of high oxygen. If, at the same low temperatures, a stream of vacuum air was passed slowly and continuously over th e 14 Tait and Dewar were the first to realize that charcoal charcoal, initially almost pure nitrogen escaped, had a strong power for retaining gases even under showing that the system had preference for oxygen; very low : "The method we have devised to after several hours, however, the occluded gas had a absorb traces of gases is based on the remarkable new and apparently definite composttt on. power of absorption of cocoa-nut charcoal for gaseous Displacement of the whole of the gas absorbed, bodies generally ... We need hardly say that this easy produced a mixture containing on the average about means of obtaining vacua will be of importance in 60 percent of oxygen. If charcoal saturated with such observations ... " a mixture was subjected in a similar manner to the The method developed by Tait and Dewar action of a slow current of hydrogen, then about one consisted of heating charcoal to low red heat in a tube out of every five molecules of oxygen and nitrogen during exhaustion with a mercury pump and then were displaced by hydrogen, giving ri se to a sealing the vessel when it was completed. When the composition of about two nitrogen molecules and two charcoal was cold the vacuum was found to be so oxygen molecules per molecule of hydrogen. Other complete that even when a powerful coil was used, no experiments led to the conclusion that the more spark would pass between platinum wires sealed into volatile or less condensable the gas was, the less it the tube one-fourth of an inch apart. The method was absorbed and retained in the charcoal.

429 Educator Indian J. Chern . Techno!. . Jul y 2003

Dewar concluded that charcoal could be used for elimination of convection currents and minimizing separating the constituents of a mixture of gases of conduction, for several years. However, Dewar was different degrees of volatility. the first person to apply vacuum in sulation for One great advantage attached to the use of charcoal studying the properties of liquid gases. was that it allowed the maintenance of a very high The next step was replacemem of the metalli c vacuum during any required period of time. In the chambers by others made of glass. Dewar performed a pre-charcoal period, this was impossible due to the large number of experiments searching for an leakage of gas into the exhausted vessel either as a improved vessel and by 1893 he had improved the consequence of the mechanical imperfections of the time storage of by a factor of 5 1.'. glass vessel or because of the existence of air Other experiments demonstrated that heat losses imprisoned in bubbles or tubules within the glass. could be significantly cut by introducing into the Such leakage may now be counteracted by means of vacuum space powders such as charcoal, lamp bl ack. charcoal. Metallic vacuum vessels could not be made silica, alumina, and bismuth oxide. Addition of a formerly for a similar reason, the gas occluded within smaii amoJUnt of charcoal in the vacuum space served the escaping gradually and spoiling the vacuum to improve the vacuum by cryoabsorption. These in the vessel. By enclosing a quantity of charcoal in a experiments were foiJowed by the finding th at coating globular space so that is cooled by the liquid air in the the glass with a thin layer of or mercury 16 inner vessel, this difficulty is entirely obviated. Such reduced radiation losses by a factor of 13 • Dewar metallic vessels are now made of nickel, brass, or also found that using three turns of sheet copper. These vessels are as effective as chemically was not as good as using silvered surfaces. As stated 7 17 silvered glass vacuum vessels . by Scurlock , had Dewar gone on to appl y further turns of aluminium, he would have di scovered the principle of multi-layer insulation, which is superior The Dewar flask to silvering. His final version, wh1ch is virtually the During his experiments on the same as the thermos of today, was first Louis Paul Cailletet (1832-1913) found that demonstrated in a lecture at the Royal Institution early observations were hampered by the frost, which in 1893. fo rmed on the outside of the of his Dewar had substantial difficulty in finding apparatus. To eliminate this problem he surrounded competent glass blowers to undertake the construction this tube by a second one, fitted on to the inner tube of his double-walled vessels and was forced to make wi th stoppers and filled at the bottom with calcium them in Germany; by 1898, a ready supply became chloride, as a drying agent. This arrangement kept the available. However, it was said that the di scovery by a internal tube surrounded by a dry atmosphere so that German glassblower, Muiier of Coburn, that a no condensation could take place. Further improve­ silvered vacuum flask could also be used for keeping ments were achieved by researchers trying to liquefy milk hot overnight for feeding hi s baby, lead to a oxygen usi ng liquid ethylene as the cooling medium: major commercial development, namely the Th er111os 17 18 Cold ethylene vapor was drawn over the outer wall of Flashe for keeping liquid hot ' • The flask was not the glass vessel containing the liquid ethylene, which manufactured for commercial or domestic use unti I in turn shielded the liquid oxygen from inflowing 1904, however, when two German glass blowers heat. This was the system adopted at the same time by formed Thermos GmbH. They held a contest to Karol Olszewski (1846-1915) in Poland and Dewar in rename the vacuum flask and a resident of Munich England. The specially designed container in which submitted "Thermos", which came from the Greek the liquefied gas was kept for observation became word "Therme" meaning "hot." In 1907, Thermos known as a cryostat and the art of producing cold was GmbH sold the Thermos trademark rights to three called cryogenics. independent companies: The American Thermos The heart of Dewar's apparatus was a double-waiJ Bottle Company of Brooklyn, NY: Thermos Limited made from an inner brass chamber of Tottenham, England; and Canadian Thermos Bottle surrounded by an external brass chamber. To improve Co. Ltd. of Montreal, Canada. (Thermos is a the of the instrument Dewar proprietary name or trademark applied to a type of evacuated the volume between the two chambers. Dewar flask protected by a metal casing. Scientists had known the insulating properties of Foiiowing Dewar's invention in 1892, the design of vacuum in preventing the influx of heat, by the virtual Dewar vessels for containing cryogenic liquids did

430 Wisniak: James Dewar-More then a flask Educator not change for over 60 years, until the growing resistivity of all pure metals decreased with increase availability of in the 1950s gave rise to of cold, but many abnormalities and peculiarities were its use in open without liquid hydrogen brought to light. The various metals did not, in all shielding. From the 1960's on there have been cases, maintain the same relative places on the scal e. significant improvements in the economy of storage At -200°C copper was a better conductor than sil ver. of cryogenic fluids. In 1955 a charge would last for iron than zinc, aluminium than gold. The about 6 hours and the evaporation rate per day was extraordinary reduction in resistance of some of th e 400%. In 1975 it was 100 days and 1 percent, and in metals at the boiling point of hydrogen was very 1995 it went down to 1000 days and 0.1 %. All these remarkable. Thus copper has only 1/105, gold 1/30. dramatic improvements were achieved by modified platinum 1135 to 1117, silver 1124 the resistance at the shield of the flask, the design of the neck, use of melting ice, whereas iron was only reduced to I /8 of 20 multiple radiative reflectors of aluminium foil or the same initial resistance . aluminised film, etc. Scurlock has described It was left to Kamerlingh Onnes to perform very 17 them in detail • delicate experiments on the electrically conductivity at very low temperatures of highly purified mercury Low temperature physics and prove definitely the phenomenon of Between 1892 and 1895 Dewar and John Ambrose superconductivity. Kamerlingh Onnes found th at at all Fleming ( 1849-1945, the inventor of the thermoionic measured temperatures the expected regular decrease valve) of University College, London, collaborated in in resistance. At liquid-helium temperatures still the study of the behaviour of materials at low measurably higher than , however, th e temperature. Their work covered a wide variety of resistance already appeared to have completely subjects, such as heat conduction, thermoelectricity, vanished. Kamerlingh Onnes published his findings in the temperature dependence of the electrical November 1911 in a paper entitled "On the Sudden Change in the Rate at Which the Resistance of resistance of several materials and elements, the 2 1 thermopower of some 24 metals and alloys, the Mercury Disappears" . Subsequent tests of tin and dielectric constant of metals, alloys, and inorganic lead showed that superconductivity was a property of materials, and the magnetic behaviour of steel, liquid many metals, if they were cooled sufficiently. oxygen, and liquid air at low temperatures. Dewar and Fleming were unable to offer an The study of electrical resistance was the most explanation for many of their experimental findings. interesting because resolution of a theoretical For example, cooling substances such as glass. controversy was at stake. It was well known by this paraffin, gutta-percha, and ebonite that were good time that the electrical resistance in a metal decreased insulators at room temperature turned them into better with temperature. Exactly what would happen to insulators after being immersed in liquid air. Most resistance at temperatures approaching absolute zero, magnets gained strength when subjected to intense however, was hotly debated. Lord Kelvin believed cold, some did not; moreover, when pure iron was that the flow of electrons, which seemingly improved immersed in liquid oxygen, it afterwards required a with decreasing temperatures as the lower resistance much greater magnetic field to magnetize it th an was indicated, might actually stop altogether, the electrons needed under normal conditions. Even 'mercury at becoming frozen in place. The resistance at absolute very low temperature became a good magnet, whereas zero would then be infinitely high. Others, including at room temperature if exhibited virtually no magneti c Kamerlingh Onnes and Dewar, assumed that the power. Mechanical strength was al so changed decrease in resistance with falling temperature would significantly: Iron, copper, and zinc exhibited continue in an orderly fashion, ultimately reaching enhanced rigidity and greater strength: a co il th at at zero at the zero temperature point. room temperature could support only a pound or so of Accordingly, in 1896 Dewar and Fleming studied weight could support three times as much aft er the resistance of mercury 19 and confirmed that there immersion in liquid oxygen. When balls of vari ous was a large decrease in the resistance at roughly 230 metals taken from the bath were dropped on an an vil. 22 K as the liquid froze, and noted further that the they bounced higher than they normally did . resistance continued to drop as the temperature These results led Dewar and Fleming to test th e decreased. They found that all metals behaved flow of a metal into wire about the temperature of similarly to mercury below its freezing point. The liquid air. The only metal that could be examined in

43 1 Educator Indian J. Chem. Techno!.. July 2003 this way was lead. At the ordinary temperature in the voltaic combinations brought down to its temperature apparatu s used, lead flowed into wire under a pressure ceased to give electric cunents. Photographi c film. of 7.5 tons, but at - 170°C, it was necessary to apply however, retain about one-fifth of their ordin ary the pressure of 67.5 tons, or nine times the pressure, sensitiveness to light, nor does it wholl y disappear to cause flow. In the same manner solder flowed into even through the agency of liquid hydrogen. Dewar wire at the ordi nary temperature when 35 tons and Flem]ng speculated that possibly the decom­ pressure was appli ed, but at the temperature of - posing force which came into play under these 170°C the appl icati on of 125 tons pressure caused no circumstances was not chemical but mechanical. motion of the all oy through the aperture. This was the An elaborate course of experiments on thermal greatest pressure that any of the dies used in the transparency, canied out in 1897-1898, completely experiments would stand without rupture. negated Raoul Pictet's (1846-1929) conclusion that at Perhaps the most striking case of alteration in a given degree of cold, non-conducting substances 23 24 properties resulting from extreme cold was afforded lose their faculty of insul ati on · . Pictet after an by natural rubber, whi ch is one of the most elastic of elaborate in vesti gation had concluded that below a substances at ordinary temperature. When cooled in certain temperature all substances had practically th e liquid air, however, it became so rigid and brittle that same thermal transparency and that a non-conducting it was easily pulverized. One of the most interesting body became ineffective at low temperatures in illustrations of the increased strength and elasticity of shielding a vessel from the influx of heat. Dewar and a body at the lowest temperatures was to take a very Fleming proved that the substances tested by Picret thin transparent film of natural rubber, to stretch one remained unimpai red at the boiling point of liquid air. end its ends over a and the insert and seal the the abnormal transferences of heat observed by Pictet other one in a long nan-ow tube. The test tube end was were not so much due to the materi als themselves, but immersed in liquid air while the other end was placed to the air contained in their interstices. in a vessel containing mercury to observe the The comparative absorption of X-rays by vari ous diminution in pressure, which was between 9 to 10 frigid bodies was used to determine that the atomic inches of mercury. The film thus treated was shown to weight of argon is double its density relative to be impermeable to gaseous oxygen by molecular hydrogen, obtained confirmation from the diffusion. Repeating the experiment with liquid approximately equal opacities found for th at hydrogen in stead of liquid oxygen produced a substance in the liquid state, for liquid chlorine and pressure drop of almost 29 inches of mercury, the film for potassium. This was the first use of X-rays for being known impermeable to hydrogen diffusion. In determining atomic weight. the cooled state such films struck with a hammer gave out a clear metallic ring; repeating the striking Phosphorescence and photographic action while th e film heats back to room temperature, 22 Phosphorescence may be regarded as a kind of produced a gamut of notes by the varying elasticity . fluorescence which lasts a long time after the A most curious and unexpected result was related excitation has ceased, and may be bri efly defined as to the optical properties of materials. Under the the phenomena observed when certain substances extreme cold, substances such as mercuric oxide, give out light through the transformation of absorbed normally bright scarlet, faded to light orange, while vibrations of shorter period. Temperature was known white-coloured substances intensified their whiteness, to play an important part in the phenomena of and blue coloured substances did not change their phosphorescence and Pictet had shown that at ve ry colour at all. Dewar and Fleming thought that changes low temperatures it might inhibit the phenomena in colour corresponded to changes in the substances' totaiil3 He had first exposed a powder of a specific absorption of light, but they could not be phosphorescent substance such as calcium sulphide, certain. barium sulphide, and strontium sulphide to sunlight Chemical affinity was almost completely abolished and then suddenly. inserted it in a double wall glass by cold and chemical combinations that at room cylinder full of nitrogen monoxide at -140°C. The temperature would always generate electricity failed tube was cooled to about - 100 °C and then transferred to do so at the temperature of liquid oxygen. For to a dark environment. Pictet observed that under exampl e, phosphorus, sodium, and potassium these conditions the material did not emit li ght but as remained in ert in liquid oxygen and failed to react;

432 Wisniak: James Dewar-More then a fl ask Educator the tube started to warm up the material regained its accompanied by formation, indicating th e normal brilliancy, without the help of external light simultaneous progress of molecular change. The and without having received any significant influence effect was completely stopped by the presence of of diffuse light. In other words, the material kept a hydrogen, or by the least trace of organic matter. At latent store of light energy that was again evolved on the temperature of liquid hydrogen, phosph orescent allowing the sulfide to ri se to ordinary temperature. action was further intensified. These results were common to all the substances The electric stimulation of crystals by coolin g studied. He also determined that the temperature limit brought about actual discharges between the for the extinction of visible gleam was between -60° molecules. In some platinocyanides and nitrate of to -70°C. Pictet concluded that the production of uranium, the temperature of liquid air suffices to luminescent phosphorescence required a certain develop marked electrical and luminous phenomena. movement of the particles that constituted the bodies. which are intensified and expanded through th e Cooling to a sufficiently low temperature cancelled agency of liquid hydrogen. Some crystals when the oscill ating caloric movements, prevented the pl aced in liquid hydrogen became for a time self­ generation of light waves, and phosphorescence luminous, on account of the hi gh electric stimulati on di sappeared. brought about by the cooling causi ng actual electric di scharges between the crystal molecules. This was Dewar extended Pictet's results to materials that 25 26 very marked with some platinocyanides and nitrate of showed little or no phosphorescence · . He found, in uranium. Even cooling such crystals to the general , that th e great majority of substances temperature of liquid air is sufficient to develop exhibiting weak phosphorescence at ordinary tem­ marked electrical and luminous effects. perature would become markedly more active at very Considering that both liquid hydrogen and air are low temperatures. Thus gelatin, celluloid, paraffin, highly insulating liquids, the fact that electric ivory, horn , and natural rubber all of which are not di scharges took place under such conditions proved phosphorescent, become di stinctly luminous, with that the electric potential generated by cooling mu st bluish or greeni sh phosphorescence, after cooling to be very high. When the cooled crystal were taken out - l 80°C with liquid air and being stimulated by the of the either liquid and allowed to heat, luminosity electric li ght. All alkaloids forming fluorescent and electric discharge took place again during th e solutions invariably became phosphorescent at low return to the normal temperature. A crystal of nitrate temperatures. Glycerine, sulphuric acid, hydrogen of uranium got so highly charged that, although its chloride, and strong ammonia, were also very bright, density is 2.8 and that of liquid air about l , it refused as well as most substances containing a ketone group. to sink, sticking to the side of the vacuum vessel and Milk was highly phosphorescent; water when pure requiring a marked pull on a silk thread, to whi ch it was only feebly phosphorescent, but remarkably so was attached, to di splace it. Such a crystal rapidl y when impure. Colored salts generally showed little removed cloudiness from liquid air by removing all activity, but a large number of colorless salts were the suspended particles onto its surface. very luminous. Remarkable results were obtained Along with these experiments on phosphorescence. with an eggshell and a feather, respectively. The egg a number of photographs were taken at -1 80°C, usin g shone brilliantly as a globe of blue light and the various sensitive plates and films, and compared with feather was equally brilliant, its outline showing similar photographs taken at the same time under clearly in the darkened room. The white of egg was similar conditions at room temperature. It was found more phosphorescent than the yolk, white substances that the photographic action was reduced by 80% at generall y being superior in thi s respect to the colored 26 ones. Other organic substances giving good results the temperature of - 180°C . were cotton wool paper, leather, linen, tortoise shell, 27 29 milk, and sponge. Complexity of structure was Hydrogenium " inferred to be one of the main conditions upon which Thomas Graham (1805-1869) studied diffusion of the possession of this quality depended. several gases in metals and found that pallad ium An unexpected result was that only oxygen among adsorbed large amounts of hydrogen gas upon heating the simple gases showed this ability. A current of and cooling. Graham believed that hydrogen was th e oxygen fl owing into an exhausted tube, after exposure vapour of a very volatile metal, hydrogenium, whi ch to an electric spark, emitted hazy white light had alloyed with the palladium. Others held to an

433 Educator Indian J. Chern . Techno!.. July 2003 alternative hypothesis, which was simply that the References hydrogen had been absorbed without chemical I Armstrong H E, James Dewar ( 1842- 1923) (E Be nn Ltd. reaction. Graham measured the specific gravity of the London), 1924. 2 Crichton-Browne J, Sci Prog, I 8 (1923) 126. occluded hydrogen by observing the increase in 3 Dewar J, Proc Roy Soc Ed, 6 ( 1867) 82. length of palladium wire after being fully charged 4 Dewar J, Proc Roy Soc Ed, 7 (1872) 751. with hydrogen and estimated the density of the 5 Dewar J & McKendrick J G, Proc Roy Soc Ed. 8 ( 1873) I 00. absorbed hydrogen to be 0.733. Dewar measured the 110, 179. 6 Macfadyen A & Dewar J, Proc Roy Sue, 66 ( 1900) 180. specific gravity, specific heat of hydrogen and the 7 Gavrouglu K, Eur 1 Phys, 15 (1994) 9. coefficient of expansion of hydrogen in palladium, as 8 Dewar J, Pruc Roy lnst, 16 ( 1900) 473. 27 29 well as its absorption in the metal at red heat . . On 9 Kamerlingh Onnes, H, Proc Kon Akad We/en\clwppen the basis of Regnault' s findings that the specific heat Amsterdam, II (1908) 168, 1908, Lei den Comm. No I 08. of an alloy was equal to the sum of its constituents30 I 0 Moissan H & Dewar J, Proc Chem Soc, 13 ( 1897) 175. 186. II Moissan H & Dewar J, Compt Rendu, 124 ( 1897) 1202. he calculated the specific heat of absorbed hydrogen 12 Moissan H & Dewar J, Compt Rendu , 125 ( 1897) 505. as 3.1 cal per atom weight, nearly identical to that of 13 Moissan H & Dewar J, Compt Rendu, 136 ( 1903) 64 1. gaseous hydrogen. He then measured the specific 14 Tail P G & Dewar J, Proc Roy Soc Ed. 8 ( 1875). 348. 628. gravity of the absorbed hydrogen in palladium during 15 Dewar J, Proc Roy lnst, 16 ( 1899) I, 2 12. 16 Dewar J, Proc Roy lnst, 14 (1893) I. the saturation process and obtained a constant value 17 Scurlock R G, Proc Roy lnst, 65 (1994) 145. of 0.620, which meant that the atomic volume of 18 Soulen R, Phys Today, 49(1996) 32. hydrogen was 1.6. The coefficient of expansion of 19 Dewar 1 & Fleming J A, Proc Roy Soc, 60 ( 1896) 76. hydrogen was found to be 0.000246, a value about 20 Dewar J, Proc Roy Soc, 68 (1901 ) 360. one and a half larger than that of liquid mercury. 2 1 Kamerlingh Onnes H, Proc Kon Akad We1enschappen AmsTerdam, 14 ( 1911) 113, 799,81 8. All these results led Dewar to conclude that 22 Dewar J, Proc Roy lnst, 17 ( 1903) 61 8. hydrogen was present as an absorbed gas and not 23 Pictet R, Campi Rendu, 119 (1894) 527. forming an alloy, as claimed by Graham. 24 Pic tel R, Compt Rendu, 119 (1894) 1202. 25 Dewar J, Proc Roy Soc, 15 (1894) 340. 26 Dewar J, Proc Roy lnst, 14 (1895) 665. 27 Dewar J, Phil Mag, 44 ( 1872) 400. Dewar was appointed to the Government 28 Dewar J, Trans RoySoc Ed, 27 (187.3) 167. Committee on Explosives (1888-1891) and with Sir 29 Dewar J, Phil Mag, 47 (1874) 334. Frederick Augustus Abel (1827 -1902), a chemist and 30 Regnault H, Ann Chim Phys [3], I ( 1841) 129. military explosives speciali st, invented cordite (1889), a type of smokeless . Before the invention Notes of cordite, battles could not be fought without the !.The Dewar nask or vacuum nask/bottle is a container for storing hot or cold substances, i.e. liquid air. It co nsists of two obscuring smoke clouds of gunpowder weapons. flasks, one inside the other, separated by vacuum. The vacuum Cordite was mixed from purified ingredients of greatly reduces the transfer of heat, preve nting a temperature nitroglycerine, nitrocellulose and petroleum jelly then change. The walls are usually made of glass because it is a poor extruded as cords. When dried, this explosive could conductor of heat; its surfaces are usually lined with a re llecti ve metal to reduce the transfer of heat by radiation. The who le fragil e be measured more precisely and handled more safely flask rests on a shock-absorbing spring ithin metal or pl astic than gunpowder. Cordite was later adopted as the container, and the air between the llask and the container provides standard explosive of the British army, and proved further insulation. The common thermos bottle is an adaptati on o f vital in wwr. the Dewar f.lask .

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