Heike Kamerlingh Onnes

Heike Kamerlingh Onnes

Heike Kamerlingh Onnes (1853-1926) won the Nobel Prize in physics for his work with liquefied helium.

Heike Kamerlingh Onnes was a Dutch experimental physicist distinguished for his work in the field of low-temperature physics. He was the first scientist to succeed in liquefying helium, a breakthrough which yielded a previously unattainable degree of cold. This accomplishment won him the 1913 Nobel Prize in physics, in addition to numerous other awards. He is also credited with the discovery of superconductivity—that is, the complete disappearance of electrical resistance in various metals at temperatures approaching absolute zero.

Kamerlingh Onnes was born in Groningen, the Netherlands, on September 21, 1853. His father owned a tile factory, and both his parents were strict, imbuing Kamerlingh Onnes and his brothers with an understanding of the value of hard work and perseverance. He was initially educated at Groningen High School under J. M. van Bemmelan, and in 1870 he enrolled in the physics program at the University of Groningen. The following year he submitted an essay on vapor density and won first prize in a contest sponsored by the University of Utrecht. In October 1871, Kamerlingh Onnes transferred to the University of Heidelberg in Germany, where he was taught by the eminent German chemist Robert Wilhelm Bunsen . He was one of only two students allowed to work in the private laboratory of German physicist Gustav Robert Kirchhoff. In April 1873, he returned to the University of Groningen, where he spent the next five years studying for his doctorate.

In 1878, Kamerlingh Onnes moved to Delft Polytechnic where he became an assistant to the professor of physics there. In 1879 he travelled to Groningen to defend his thesis, entitled "New Proof of the Earth's Rotation." He was awarded his physics doctorate magna cum laude. At Delft Polytechnic, Kamerlingh Onnes composed a paper on the general theory of fluids from the perspective of kinetic theory. He soon realized though that such a general theory of the nature of fluids required accurate measurements of volume, pressure, and temperature over as wide a range of values as possible. To this end, he turned his attention to the problem of attaining and maintaining very low temperatures.

In 1882, at the age of twenty-nine, Kamerlingh Onnes accepted Holland's first chair in experimental physics at Leiden University. He also became the director of the laboratory there, where he was able to pursue his interest in low-temperature physics, also known as cryogenics. A dedicated experimentalist, Kamerlingh Onnes declared in his inaugural address: "I should like to write 'through measuring is knowing' as a motto above each physics laboratory." He would spend the rest of his career at Leiden. During the next forty-two years, he established it as the undisputed world headquarters of low-temperature research.

When Kamerlingh Onnes began his pioneering work, cryogenic physics was a relatively unknown science. Before him, the liquefaction of gases at very low temperatures was considered an end in itself, but Kamerlingh Onnes was interested in low-temperature physics in order to gather experimental evidence about the atomic nature of matter. When he set out to cool gases such as oxygen, hydrogen, and helium to extremely low temperatures, there were three means at his disposal. A cooling effect due to the rapid evaporation of a liquid had been discovered in 1877 by the Swiss physicist R. P. Pictet. That same year, the French physicist L. P. Cailletet had achieved low temperatures when he was able to cool oxygen by the application of intense pressure. The final method was based on the 1850 discovery by J. P. Joules and W. Thomson (Lord Kelvin) that when a gas under pressure is released through very small openings, its temperature is lowered by an amount that depends on the nature of the gas. In Munich in 1895, Carl Linde constructed an apparatus that made use of the so-called Joule-Thomson effect; gas was put under pressure and repeatedly forced into a coil of tubes that also acted as a heat exchanger. This was known as the regenerative process. The amount of liquid gas produced by all of these means was, however, negligible.

In trying to achieve very low temperatures, Kamerlingh Onnes employed a combination of Pictet's and Linde's methods. His first objective was to liquefy oxygen—the creation of a bath of liquid oxygen being necessary for the liquefaction of other gases, particularly hydrogen. Kamerlingh Onnes vaporized oxygen, then liquefied it, and then forced it under pressure into a closed, circulating system. The system was bathed in gases that had achieved progressively lower temperatures than the circulating oxygen. This methodology proved successful and Kamerlingh Onnes was able to produce about fourteen liters of liquid air an hour.

The production of liquid helium and liquid hydrogen proved more difficult than the production of liquid air. Kamerlingh Onnes theorized that if he could begin from a point of normal pressure and liquefy oxygen by the application of immense pressure, then it would be possible to liquefy hydrogen, starting with the temperature of liquid oxygen. In 1892, he was midway through this painstaking process when the Scottish chemist and physicist James Dewar succeeded in liquefying oxygen using a modified form of Pictet's cascade method. The process yielded about a pint of liquid oxygen.

One practical advantage of Dewar's achievement was that Kamerlingh Onnes now had a source of cold with which to attempt to liquefy helium. He believed that if he started out from the freezing point of hydrogen—the lowest temperature to which it was possible to cool it—he could thereby liquefy helium using Linde's regenerative process. Kamerlingh Onnes constructed a system with a jacket of liquid hydrogen; the liquid hydrogen evaporated, which cooled the helium, and then the helium was forced under pressure through a small aperture which cooled it further, liquefying some of it. He then compressed the helium in a refrigerator, where it passed through an elaborate circuit surrounded by circuits of liquid hydrogen, which were themselves surrounded by liquid air, which were in turn surrounded by a flask in which warmed alcohol circulated.

In 1908, Kamerlingh Onnes finally succeeded in the long-elusive goal of liquefying helium. At first, he and his colleagues did not even notice what they had achieved: the liquid helium was colorless, and it was not until the circuit was almost full that they realized what had finally appeared before them. The accomplishment meant that a previously unattainable degree of cold was now at their disposal. Liquid helium was found to have a temperature of -268.8 degrees Celsius, only about four degrees above absolute zero—absolute zero being a hypothetical temperature characterized by a complete absence of heat and equivalent to about -273.15 degrees Celsius or -459.67 degrees Fahrenheit. Kamerlingh Onnes now set out to solidify the liquid helium in order to reach even lower temperatures, and in 1910, by boiling liquid helium under reduced pressure, he reached just over one degree above absolute zero.

Kamerlingh Onnes used these temperatures to extend the range of his research into the properties of substances at low temperatures, and the results of these investigations were published regularly in English as "Communications from the Physical Laboratory at Leiden." In 1911, Kamerlingh Onnes made yet another breakthrough when he discovered superconductivity, the complete disappearance of electrical resistance in various metals at temperatures approaching absolute zero. He also discovered that the superconductor effect can be negated without changing the temperature by the application of a magnetic field.

Kamerlingh Onnes and his team remained preoccupied with the challenge of crystallizing helium. Their experiments yielded some intriguing if baffling results. In 1911, they found that the density of liquid helium peaked at a temperature of 2.2 degrees Kelvin. When the various physical properties of liquid helium were measured, Kamerlingh Onnes discovered strange behavior in the helium in and around this temperature. Above 2.2 Kelvin it was violently agitated, but at or below this temperature it seemed to lose its dynamic qualities. Kamerlingh Onnes was unable to explain this phenomenon. This was because he was attempting to understand it in terms of the classical laws of physics, but the behavior of liquid helium at these temperatures, unbeknownst to him, obeys the laws of quantum mechanics. Kamerlingh Onnes simply did not have the tools at his disposal to account for his findings. In the end, he and his colleagues put them down to some fault in their methodology and published only "definite and reliable" values for temperatures above 2.2 Kelvin, the position of the inexplicable maximum of the density of liquid helium.

Although he had yet to achieve absolute zero, in 1913 Kamerlingh Onnes was awarded the Nobel Prize for physics for his investigations into the properties of matter at low temperatures leading to the discovery of liquid helium. By 1921, Kamerlingh Onnes came within a degree of reaching absolute zero, and for the next three years he relentlessly pursued his quest. In 1926, he came across further peculiarities in the behavior of helium at 2.2 degrees Kelvin. This time Kamerlingh Onnes did not dismiss his findings as due to technical faults but began to seriously consider the possibility that some kind of fundamental change in helium occurred at this temperature. Unfortunately, although he was on the right track, Kamerlingh Onnes did not live long enough to resolve the mystery. His successor at Leiden, W.H. Keesom, came to the conclusion that helium above and below 2.2 degrees Kelvin is in fact two separate liquids, differing in fundamental ways. Keesom also completed another aspect of Kamerlingh Onnes' work: he succeeded in obtaining solid helium by cooling the liquid to about -272 degrees Celsius under pressure.

Kamerlingh Onnes was widely recognized for his work in low-temperature physics, and he received a number of awards in addition to the Nobel Prize. In 1904, he received the first of many distinctions when he was created Chevalier of the Order of the Netherlands Lion. In that same year, which was the twenty-fifth anniversary of his doctorate, his students and colleagues at Leiden issued a Gedenkboek, a survey of the work carried out at the laboratory from 1882 to 1904. A second Gedenkboek was issued in 1922, commemorating Kamerlingh Onnes' forty-year tenure as professor of experimental physics at Leiden. In 1912, he was awarded the Royal Society of London's Rumford Medal, and four years later the society made him a foreign member. In 1923, he was elevated from Chevalier to Commander of the Netherlands Lion. Despite being known by his friends as "the gentleman of absolute zero," Kamerlingh Onnes died at Leiden on February 21, 1926, without ever having achieved it (German chemist Walther Nernst proved it was impossible to reach absolute zero in an experimental setting when he articulated the Third Law of Thermodynamics in 1905). That same year, he was posthumously elected a Corresponding Member of the Prussian Academy of Sciences in Berlin.

Further Reading

Klein, Martin J., Paul Ehrenfest: The Making of a Theoretical Physicist, North-Holland Publishing Co., 1970.

Livanova, Anna Landau, A Great Physicist and Teacher, Pergamon Press, 1980. □