Absolute Zero and the Conquest of Cold (17 page)

While Andrews had managed to disprove Boyle's law, he had not successfully substituted a new mathematical explanation that took into account Boyle's results, and van Marum's, and his own. Van der Waals determined to craft an explanation that would encompass all their disparate results, an explanation of the interaction of pressure, volume, and temperature that would even settle such lateral matters as the disparity that Joule and Thomson had found between the cooling effect produced by expansion of nitrogen and oxygen and the heating effect of expansion of hydrogen. He did so in his 1873 doctoral thesis,
Over de Continuiteit van den Gasen Vloeistoftoestand
(On the Continuity of the Gaseous and Liquid State), and in a later, follow-up paper.

At the heart of his explanation was the idea of molecular attraction. Van der Waals replaced Boyle's oversimplified equation with a pressure-volume-temperature equation that factored in an additional variable, molecular density. He expressed mathematically the way in which the molecules of a gas were less densely packed than they were in a liquid. The word
gas
originally derived from the Greek word
chaos,
or "disorder," and the notion that the molecules of a gas were less orderly and dense than those of a liquid made intuitive as well as mathematical sense. When graphed, the temperature line described by van der Waals's equation looked very similar to the graphed isotherm line that Andrews had charted, except in the "equilibrium" area where gas and liquid coexisted. In that section, where Andrews's line was straight, van der Waals's line was subtler, curving down, and up, and down again, along the same pressure axis.

Those subtle, reciprocal curves were another way of showing that in the equilibrium area, for any given pressure, a particular temperature could be produced by three different volumes. Van der Waals's work opened up all sorts of possibilities for future research. What would soon prove to be useful was the idea that a gas-liquid mixture contained molecules both of lower density and higher temperature (in the gaseous portion) and of higher density and lower temperature (in the liquid portion). If one could remove from the mixture the higher-temperature, lower-density gas molecules, leaving behind only the lower-temperature, higher-density molecules of the liquid, that liquid would cool off very rapidly—as though by forced evaporation.

An indication of the importance of van der Waals's thesis was that men deeply interested in thermodynamics and the physics of gases, such as James Clerk Maxwell in Great Britain, tried to learn Dutch just to read it.

The stage was now set for a grand assault on the "permanent" gases. Although initially undertaken to accomplish the liquefactions that Faraday had once thought were beyond the capacities of science, this assault had ramifications far beyond that important goal. For it led to a campaign to reach absolute zero, the lowest temperature imaginable, and in doing so revealed new and unexpected aspects of the nature of matter—and, not incidentally, opened up the country of the cold for the extraction of practical applications that would change society in far greater ways than mere refrigeration had already begun to accomplish.

Among the many scientists in Germany, Switzerland, Great Britain, the Netherlands, and France who took up the challenge of liquefying the so-called permanent gases was Louis-Paul Cailletet, a graduate of the school of mines who was employed at a smelting works owned by his father. Occasionally Cailletet would send a communication to the Académie des Sciences, which would sometimes publish a brief item noting what he had done, for example, in tracing the permeability of metals to gases, but would not really comment on it.

Around 1870, Cailletet moved back to his birthplace, Châtillon-sur-Seine, and set up a private laboratory. Châtillon was close to Paris, and the Académie regarded residence in Paris as prerequisite to being elected to membership. Cailletet had been turned down in his first attempts to seek membership. He was in good company. In the fifty years since the Académie had given short shrift to Carnot, it had grown even more encumbered by tradition and drunk with its own scientific importance, which remained considerable. Louis Pasteur spent more than twenty years in unsuccessful attempts to get himself elected to membership before ascending to the pantheon. Joseph Valentin Boussinesq, an expert on the diffusion of heat, had applied unsuccessfully five times between 1868 and 1873. Even political upheaval—the loss of Alsace and Lorraine to Prussia, the end of the empire of Napoleon III, the establishment of the Third Republic, the evisceration of the Paris Commune uprising, the formal adoption of a republican constitution in 1875—in no way undermined the stature of the Académie; rather, these events emphasized its continuity and importance as a pillar of French life. To have a report of one's work read and discussed in the Académies august confines was more than ever essential to establishing a scientific reputation and, not incidentally, a basis on which to claim priority for a patent.

In the fall of 1877, there had been no deaths of full members, and so there was no possibility of the forty-five-year-old Cailletet being selected to succeed anyone. The prospect of becoming a corresponding member, a junior position, was held out to him. Determined to obtain it, he would do nothing to jeopardize the delicate process of accumulating enough positive votes in committee to recommend him. This meant not showing off, or scheduling the report of an important discovery at a time when it might be viewed as attempting to influence the committee's decision. There were the requisite rounds of calls to make to senior members, who would, of course, be certain not to give any hints of their approval or disapproval of the applicant. There were also alliances whose aid must be enlisted or their enmity avoided—the group of students of a single influential teacher, the graduates of a school such as the École Polytechnique (whose members made up 25 percent of the academicians), the adherents of a particular theory, or those who disliked researchers who worked on practical problems or for industrial concerns.

As with many researchers, Cailletet had been captivated by the challenge of doing what Faraday had not had the tools to accomplish and was spurred to action by the observations of Andrews and the theory of van der Waals. It had become clear that the right combination of pressure and lowered temperatures ought to be able to liquefy almost any gas, and the task had devolved to the technological problem of finding or making the right apparatus. Cailletet bought turbines to build up pressure, rigged tubing and glass vessels, and with an assistant set to work in November 1877 on liquefying acetylene. He chose this hydrocarbon, which was not a permanent gas, because its molecular weight predicted that it could be liquefied with 60 atmospheres of pressure—and in recent years it had become possible to generate considerably more pressure than that under controlled laboratory conditions.

In a manner reminiscent of Faraday's work with ammonia, Cailletet's first try resulted in an accident whose products showed him that he had succeeded in his liquefaction attempt. The cooling-to-liquid stage had occurred as the pressure on the compressed gas had been accidentally released. He did another test with a purer batch of the gas and at a critical temperature of 308 K—that is, above the freezing point of water—and with a "critical pressure" of 61.6 atmospheres, he liquefied acetylene. But this gas was not one of the permanent gases, two of which were major components of air. To really get the Académies attention, Cailletet would have to liquefy oxygen.

To do so, he combined recent pressure technology—he needed 300 atmospheres—with refrigerating processes that had been evolving in laboratories since the experiments of William Cullen in 1748. Cailletet surrounded a glass tube holding gaseous oxygen with another that contained sulfur dioxide evaporating into a stream of dry air, which reduced the temperature of the inner vessel to—29°C, while he maintained great pressure on the apparatus. When he suddenly released the pressure, a mysterious mist and then droplets formed inside the tube containing the oxygen, and slid down its walls, indicating that some of the oxygen had been liquefied. The few drops did not remain long in the liquid state, but the event had occurred. Cailletet guessed that the sudden fall in pressure had pushed the temperature down to about—200°C.

This happened on Sunday, December 2, 1877. Cailletet immediately wrote a letter describing his success and his methods to Henri Sainte-Claire Deville, a friend and a full member of the Académie. Then he turned crafty. The Académie's weekly meeting took place at three o'clock on a Monday afternoon; in December, that meant on the 3rd, 10th, 17th, and 24th. Cailletet's potential election as corresponding member was scheduled for December 17. He determined to win election on that date and to announce the liquefaction of oxygen on Christmas Eve. Toward that end, he organized a demonstration of his liquefaction of oxygen at the École Normale on the 16th. His assistant knew assistants in other laboratories, and word spread quickly about the demonstration. It went off as planned and may well have tipped the balance, for on the 17th, Cailletet was elected as a corresponding member of the Académie des Sciences by a vote of 33 to 19. Only after that did he send in his "communication," with the expectation of having it read on the 24th.

Christmas Eve in Paris was always a festive yet solemn time, with an air of anticipation of the next day's celebration. At three in the afternoon, the academicians gathered in the chapel under the gilded dome of the former Collège des Quatre Nations, opposite the Louvre, on the left bank of the Seine. Many wore their distinctive black uniforms with the green embroidery. There was Victor Regnault, who was very ill and expected to die shortly. There were the former students of Jean-Baptiste Dumas: Deville, Charles-Adolphe Wurtz, Auguste Cahors. Each member sat in his designated place, the seats arranged in an ellipsoid form surrounding the central lectern, and each having a view of the area that had once been the altar of a chapel and was now the site of the desks of the officers and permanent secretary. Beyond, on three sides, were rows of benches for the public, with some reserved for journalists. The desk of the permanent secretary was piled high with letters, articles, and books addressed to the Académie by dozens of applicants, many of whom were unknown to the academicians. On a December afternoon, the chamber would have been illuminated by gas lighting, which had replaced candlelight only two years earlier. Heating columns in the four corners of the room supported busts of a few scientists such as Laplace, and on the upper part of the back wall hung portraits of others, including Lavoisier.

The significance of this particular occasion was pointed out by Dumas, the permanent secretary and the principal champion of restoring the reputation of Antoine Lavoisier. After Lavoisier had lost his head to the guillotine in 1794, there had been a concerted effort by some academicians to retroactively disparage his work, an effort that gained currency when the theory of caloric was disproved. Through the efforts of Dumas and others, the reputation of the father of French chemistry had been somewhat restored. Now Dumas found it appropriate to silence any lingering doubts about Lavoisier, and to link in the minds of his audience the report to come with the great traditions of French chemistry, by reading from the work of the master a speculative rumination as to what might occur if the earth were suddenly transported into "the very cold regions" of the solar system; there, Lavoisier fantasized,

the water of our rivers and oceans would be changed into solid mountains. The air, or at least some of its constituents, would cease to remain an invisible gas and would turn into the liquid state. A transformation of this kind would thus produce new liquids of which we as yet have no idea.

Only after this prologue was Cailletet's "communication" read. As expected, there was considerable excitement. The most important caveat was voiced by a member who argued that the real breakthrough would occur when one could create a larger quantity of liquefied oxygen and maintain it as a liquid for more than a second or two.

Then, just as Cailletet was basking in the glory, the secretary announced that a telegram had been received two days earlier from Raoul Pictet, the Swiss-born physicist who was already a pioneer in commercial refrigeration. The telegram said: "Oxygen liquefied today under 320 atmospheres and 140 degrees of cold by combined use of sulfurous and carbonic acid."

Cailletet was aghast, and even more so when a Pictet letter—prepared earlier, anticipating the result—was read that detailed Pictet's quite different approach to the liquefaction of oxygen.

Henri Sainte-Claire Deville came to the rescue. As a former student of Dumas's, he had no difficulty being recognized by the chair. Deville insisted that Cailletet had priority, revealing that on December 3, when he had received Cailletet's letter, he had immediately taken it to the permanent secretary, who had signed, dated, and sealed it. The letter was found and examined, and Cailletet was awarded the laurel of being the first to liquefy oxygen.

A week later, on New Year's Eve, Cailletet was back at the Monday afternoon session with the news that while others had been busy celebrating Christmas, he had returned to his laboratory and liquefied the other major component of air, nitrogen.

In a single week, giant steps had been taken inside a far region of the cold, and closer than anyone had ever come to absolute zero.

N
EWS OF THE DECEMBER
1877 Cailletet and Pictet liquefactions of nitrogen and oxygen excited the scientific world, opening up vast possibilities of research in the extreme regions of the cold. Individuals and teams of scientists began drives toward achieving the absolute zero of temperature as well as investigations into the properties of matter that might be revealed by very low temperatures.

For the next thirty-five years, during the Gilded Age at the end of the nineteenth century, and in the early part of the twentieth, a set of scientific rivals explored the contours and characteristics of what they frequently referred to as "the map of Frigor." They used such terminology because they believed themselves embarked on voyages of exploration, with all of the danger, sense of the unknown, and fervid romanticism summoned up by that metaphor. Geographic explorers were thrusting toward the North and South Poles; this band of physicists and chemists were on a similar adventure, aiming toward their own "cold pole," or "Ultima Thule," the absolute zero of temperature. "The arctic regions in physics incite the experimenter as the extreme north and south incite the discoverer," the director of the Dutch laboratory pursuing ultra-low temperatures, Heike Kamerlingh Onnes, said in a speech. James Dewar of the Royal Institution in London, another leading laboratory in the race toward absolute zero, lamented in a lecture that while the geo graphic quests had enormous appeal to the popular imagination, the scientific quest for absolute zero had much less, but on the other hand (as the London
Times
paraphrased his main point), "the approach to the zero of temperature will open out fields of investigation where matter and energy can be examined under new conditions....In both cases, success may be said to depend upon equipment, persistency, and the selection of the right road." While there was no inherent reason why the North Pole could not be attained, there were "strong grounds for belief that the zero can never be reached, [and] the nearer we get to it the more important physical problems become." Kamerlingh Onnes also pointed out that because it was so difficult to make progress, every step toward absolute zero would yield extremely important scientific data; the more so, the closer the experimenters came to their goal.