Heike Kamerlingh Onnes RALPH E. OESPER University of Cincinnati, Cincinnati, Ohio
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N 1913 the Nobel prize for physics was awarded to H. K. Onnes, professor a t the University of Leyden, "in recognition of his investigation into the properties of matter a t low temperatures which led, amongst other things, to the production of liquid helium." This scientific triumph, accomplished on July 10, 1908, was the culmination of years of specialized study and development of the necessary apparatus and technique. The helium was obtained from monazite sand; 160 liters of the total supply (200 liters) were kept in reserve. The compressed gas was cooled by means of evaporating liquid hydrogen to 15O to 16' absolute and then was expanded through a regenerative coil. Most elaborate precautions were taken to prevent the influx of heat. To eliminate any less volatile gases that might freeze and block the tuhes, the helium circuit included a mass of charcoal cooled to the temperature of liquid air. Operations began a t 5 :45 A.M. with the preparation of the necessary liquid hydrogen, of which 20 liters were ready by 1:30 P.M. The circulation of the helium was started a t 4:30 and was continued until the gas had been pumped around the circuit 20 times. Not until 6:30, when the last bottle of hydrogen wasused, was the surface of the liquid helium perceived by reflection of light from below. "Nnt - -~ nnlv had the amaratus been strained to the uttermost, hut the utmost had been demanded from my assistants. But for their perseverance and ardent devotion, every part of the program would never have been attended to with such perfect accuracy as was necessary to render this attack on helium successful. It was a wonderful moment when the liquid, which looked almost immaterial, was seen for the first time. It had not been seen when i t flowed into the glass, its presence was only detected when the receiver had been filled. Its surface stood out sharply defined like the edge of a knife against the glass wall of the vacuum bottle.' I was overjoyed when I could show liquefied helium to my friend-van der Wads, whose theory had been my guide in the liquefaction up to the end." "Onnes was too busy on this memorable day to stop for food; his devoted wife sustained his strength by placing hits of bread in his mouth from time to time." The critical temperature of helium is -267.9"C., its boiling point under atmospheric pressure, is -268.8'C. These figures testify to the extent of his excursion into A A
the realm of ultra-low temperatures. Naturally, Onnes was anxious to accomplish the next stage in this progress toward absolute zero, namely, the solidification of helium. This same day, he made the first of his five unsuccessful attempts. The pressure on the evaporating liquid was reduced to 7 mm., but without result. Later the pressure was carried down to 0.0013 mm., the resulting temperature was calculated to he 0.82O absolute, but "the helium still remained a thin 1 Liquid helium is extremely mobile; no inaease in viscosity can be detected at even the lowest attainable temperatures. liquid." Keesom, his successor as director of the LeyIts index of refraction is very low, likewise its surface tension. den Cryogenic Laboratory, produced solid helium on Consequently it is very difficult to detect the liquefaction because the meniscus is perfectly horizontal against the wall of the con- June 26, 1926, just a few months after the death of his tainer, like that of a liquid in the vicinity of its critical point. revered chief and teacher.=
Liquid helium shows a capillary rise against the glass wall only at messures of about 2 mm. of mercury, that is, at temperatures beiow 2" ahs.
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The melting point of helium is usually given as < -272.2' C. (26atm.).
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Heike Kamerlingh Onnes was horn on September 21, 1853, in the university town of Groningen. He and his brothers were raised in a home where "all was made subservient to one central purpose: to become men." His father, owner of a tile factory, had little of the usual businessman's limited outlook. He led the family conversations on a high plane, philosophizing on subjects of all kinds. The family was an independent unit not much given to social life. They preferred to stay a t home, reading widely and intensively. Long walks into the country were enjoyed together. The importance of neat dress was stressed. Diligence, as a cardinal virtue, was taught by example, and often when Heike arose at five in the summer to prepare his school assignments he found his mother busy in the garden. He entered the local high school in 1865. The principal was van Bemmelen, who later became professor of chemistry at Leyden. He doubtless fostered Heike's natural inclinations toward science. The boy matriculated at the University of Groningen in 1870, and the next year submitted the winning essay in a contest sponsored by the University of Utrecht. The title was: "A critical examination of the methods of determining vapor density and of the results obtained thereby, with respect to the relation of the nature of the chemical compounds and the density of their vapors." Not yet 18, he had every reason to exhibit his gold medal with pride. Deeply interested in both chemistry and physics, Onnes was naturally attracted by a man who had done outstanding work in both fields. Bunsen was a t the height of career, and a t his side was the great physicist Kircbhoff, his associate in the invention of spectrum analysis. Onnes was a t Heidelherg from 1871 to 1873 and soon made such a good impression that he was one of the two students permitted to work in Kirchhoff's private laboratory. Foucault's pendulum occupied most of his attention, and his results were later incorporated in the doctoral dissertation that he submitted to the faculty a t Groningen. This university awarded him a silver medal in 1872 for the essay he entered in competition. It bore the title: "A critical survey of the methods of determining the quantity of heat liberated by chemical reactions and dissociations, and of the results ohtained by different investigators." The judges commented that the discussion "contained some serious chemical and physical errors hut the writer often exhibits great ingenuity and resourcefulness." On his return to Holland, Onnes ohtained a post in the physics department a t Delft. Here he began his career as teacher and also made an excellent record as an independent experimenter. The final stage toward his doctorate was his defense, in 1879, of his thesis, "New proof of the earth's rotation." The examiners burst into applause, and, without asking the candidate to retire, voted him the degree magm cum laude. In 1882, Onnes was appointed to the chair of experimental physics a t Leyden. He spent the rest of his life
there, and developed the field in which he became the preeminent authority. His choice was quite logical. Van der Waals had received his doctor's degree a t this same university in 1873 for his thesis: "On the continuity of the gaseous and liquid states," and in 1880 he published his famous paper on "The law of corresponding states." Stimulated by these magnificent publications, Onnes became interested in the equations of state and the general thermodynamic properties of gases and liquids. However, he had the conviction that there was greater need for accurate measurements than for fresh theoretical developments. Precise measurements at low temperatures became the core of the work in his laboratory. A great celebration was held in November, 1908, a t Amsterdam to honor these two great physicists. They were close friends and each was glad to extol the achievements of the other.3 The modest quarters available a t first were soon outgrown and the Cryogenic Laboratory of Leyden came into being.' It soon became a research center and students came from many countries to learn low-temperature techniques. The constant need for the construction of new types of special equipment led Onnes to found, in 1901, the Society for the Promotion of the Training of Instrument Makers. Skilled workers from this school became invaluable in laboratories throughout the scientific world. There was nothing of the flashy showman about Onnes; the liquefaction of helium was not a superstunt but the capstone of years of painstaking intelligent preparati~n.~In the course of his work he developed gages for high pressures, methods of measuring low temperatures and of determining the boiling points of liquefied gases. The optical, magnetic, and magneto-optical properties of materials a t extremely low temperatures were of special interest to him. His discovery of the superconductivity of metals, that is, the sudden disappearance of measurable resistance, was of particular importance because of its hearing on the theory of electrical conduction in solids. The industrial significance of low temperatures increased steadily and Onnes, as founder of the "Institut international du Froid," did much to further the bonds between theory and practice. Honors came to him in wel-deserved measure, hut his greatest joy was derived from the appreciative gratitude of his students and coworkers. Of all his titles he liked best the respectful appellation bestowed by his intimate friends "the gentleman of absolute zero." This master of experimental physics died on February 21, 1926. a Van der Waals received the Nobel prize in 1910 for his work in connection with the equation of state for gases and liquids. The well-known periodical, Communicatwns from ihePhysicn1 Laboratory at the University of Leiden, in which many of his papers appeared was renamed (1935) Communicalions from thc Komerlingh Onnes Labomlory of the Uniwrsity of Leiden. Unsuccessful attempts to liquefy helium had been made by Dewar (1901). Travers (1903). Olszewski (1905).
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