Absolute Zero and the Conquest of Cold (24 page)

While overseeing and developing the other sections of the laboratory, Onnes himself relentlessly pursued the liquefaction of gases. His ego did not keep him from adopting whatever innovation was made by another competitor, then improving it greatly—for instance, when he finally set up his own continuous-process hydrogen liquefier, it produced 4 liters per hour, a quantity vastly outstripping what Dewar, Olszewski, or Travers could make from their machinery.

Similarly, Onnes had nurtured an additional strength: in 1901, adjacent to his laboratory building, he had begun the Society for the Promotion of the Training of Instrument-Makers, a workshop and school that supplemented the one he had previously established for machinists and electro-technicians, and he had set these men to work improving his facilities and machinery. Also, the low-temperature laboratory at Leiden was now beyond worries about cost; Onnes enjoyed the confidence of Queen Wilhelmina and the fullest of government support for his work. His equipment was so large and of such good quality, and his attendant assistants were so well trained, that physicists from all over the world vied to spend a sabbatical or a summer at Leiden. Even the young Albert Einstein applied for a position; he never received an answer to his letter to Onnes, and he went on to other pursuits. Later, the two men would develop a friendship.

As Onnes aged, the tubercular weakness in his lungs, evident since childhood, was exacerbated—perhaps by the noxious gases of the laboratory—and he struggled to be well enough to work; his wife's assistance in maintaining his health was widely admired. Onnes lived in Ter Wetering, a beautiful home by the Old Rhine river with a lovely view, but for years was not well-to-do. As he would recall in a letter to van der Waals, he endured decades of poverty, "care-ridden years [with] appalling difficulties." The theorist comforted Onnes with the saw that "time sifts admirably well that which has real value from the other things," suggesting that vindication of the greatness of Onnes's work, as well as of van der Waals's own theories, would eventually arrive.

Some in the Netherlands chided Onnes for being too patient, for taking too many measurements before thrusting ahead in liquefaction. He ignored the cavils, confident of eventual applause, and continued to build his organization, his apparatus, his communications, his network of supporters in other European laboratories, and his storehouse of knowledge.

Dewar's recognition of Onnes's strengths may have been one reason he was always courteous to Onnes, even during the years he was savaging Olszewski and Ramsay. Dewar pleased Onnes by repeatedly referring to van der Waals as a genius underappreciated in countries beyond the Netherlands. For his part, Onnes went out of his way in his publications to pay tribute to Dewar's accomplishments.

The two men were perhaps most alike in being autocratic, old-style masters of laboratories. Dewar refused to give much credit to his assistants, even though both Robert Lennox and James Heath each lost an eye during their long service with him, and he would not permit his assistants to become familiar, rebuking another associate who dared to call him "Sir James" after Dewar had been knighted. Similarly, in later years a top-hatted Onnes would drive with his horse and wagon to pay Sunday social calls on his technicians. During one such visit, an assistant asked for a raise; Onnes refused, saying "Haven't you just bought two nice bicycles?" When an idea occurred to Onnes at home, he would ring a bell on the side of his house, summoning his chief assistant Gerrit Flim, who lived on the opposite bank of the Old Rhine, and who would have to drop what he was doing and row across to discuss the idea with his boss. Although Onnes treated full colleagues with complete deference, there are stories that he was less respectful of doctoral or postdoctoral students and that he seldom shared credit with them on articles; he also required students to donate part of their stipends for the upkeep of the laboratory. One subsequently recalled their master's rules: they should work all day in the lab, taking notes in a little pocket notebook, and in the evening should write up their notes into a neat report. A student could have "a day off for love; I mean when you were engaged. But you could not get a day off really to listen to a theoretical lecture because [Onnes believed that] experimental physics requires the whole man." Other stories, however, paint Kamerlingh Onnes as the perfect colleague, generous of spirit, and the catalog of his publications shows that as he aged, he became progressively more willing to share credit for the work done under his direction.

In 1902, the second year Nobel Prizes were given out, the physics award went to H. A. Lorentz, a friend and colleague at Leiden, and to Pieter Zeeman, for whom Onnes had served as thesis advisor; the award was for their discoveries regarding the theoretical basis for the splitting of the spectral lines of sodium in a magnetic field. Onnes
had as yet made no achievements of similar import, though it was widely believed that he would soon do so. In honor of Zeeman and Lorentz, Onnes commissioned his nephew Harm, a noted artist, to make a stained-glass window memorializing their work.

Dewar and Onnes differed in one critically important area: Dewar's continual stream of published papers made very little use of others' theories—including that of van der Waals—and Dewar wrote no theoretical papers of his own. Onnes was continually guided by theory, and he spent much of his time making calculations from theory to predict isotherms that would reveal the critical temperatures of gases to be liquefied, then experimenting to verify the predictions. An exchange of letters in 1904 highlights this difference. When Onnes congratulated his rival on becoming Sir James, Dewar chided him for going overboard, because he, Dewar, was neither a baronet nor a knight, then went on to declare in the same emotional tone, "Exact physical measurements and pioneering work do not go well together. Such refined matters I must leave you to settle." To which Onnes replied, "The determination of the isotherms is the rational way to get data for calculating the critical points ... and exact determination of isotherms is just in my line of accurate measuring work."

In preparation for his assault on absolute zero, Onnes pushed hard to determine the isotherms of hydrogen and helium. Later he would look back and view these efforts as the most crucial to his accomplishments, writing, "Before the determination of the isotherms had been performed I had held a perfectly and different opinion [of the possibility of liquefying helium] in consequence of the failure of Olszewski's and Dewar's attempts" to do so. After determining the isotherms, however, he became convinced he was on the right path.

On the practical front, Onnes—like Dewar—was hampered by the lack of an adequate supply of helium gas. The two had traded letters about helium for some time, and an Onnes assistant, acting as an emissary from Leiden, had even visited Dewar's laboratory. Each scientist complained to the other of bouts of ill health that kept them from their research, and of the "fairly risky business," as Dewar put it, of working with helium. "I have already lost 1 cylinder of helium by the breaking of vacuum vessels during the course of its circulation at liquid air temperatures and I dread any repetition of the disaster," Dewar wrote. Worried he would not be physically well enough to complete the work, he penned a poignant wish to Onnes to possess again "the gift of youth so that I might begin my scientific career after a training in the great Dutch School of Science."

Perhaps the comradely and confessional tone of Dewar's letters encouraged Onnes in mid-1905 to take the extraordinary step of proposing to Dewar that they join forces. Dewar had built a plant to extract helium from the Bath Springs sands; Onnes begged to share that material with him, and he implied that they might jointly work through the "determination of the isotherms of helium at low temperatures as well as the magnetic dispersion of the plane of polarization."

"We both want the same material in quantity from the same place, at the same time, and the supply is not sufficient to great demands," Dewar wrote back, in anguished but firm handwriting. He added, "It is a mistake to suppose the Bath supply is so great.
I have not been able so far to accumulate sufficient for my liquefaction experiments.
If I could make some progress with my own work the time might come when I could give you a helping hand which would give me great pleasure." Then, perhaps remorseful that he had to be so tough with Onnes, Dewar confided that things in London were "in a sad way," that his illness prevented him from doing much work, and that he hoped to get away for a rest. The regretful tone continued in a note a month later, in which he apologized for having not cited Onnes's work in an article.

Dewar's refusal to share the Bath helium probably had more to do
with his ego than with the difficulty of obtaining helium. He was not averse to collaboration, having toiled for many years with various scientists on jointly signed work. But he had been laboring by himself for nearly thirty years on reaching absolute zero, and he was not about to change his solo style when the competitors were on the last lap of the race.

Dewar's decision not to share the Bath Springs helium with Onnes may have prevented a competitor from using that source, but he had no joy of it, because when he transported the Bath Springs helium to the Royal Institution, he found it contaminated with other gases and needing further purification, which slowed his progress. Just when Dewar's disappointment was becoming obvious, Onnes found his own supply of helium.

Through the auspices of his brother Onno, who was in charge of the Dutch government's Office of Commercial Intelligence, in 1905 Onnes arranged to import large quantities of monazite sand from gravel pits in North Carolina, sand known to contain significant amounts of rare-earth metals and helium. After that, as Onnes later wrote, "the preparation of pure helium in large quantities became chiefly a matter of perseverance and care." That was an understatement, since the process of extracting helium gas from the sand was complex, involving exploding the sand with oxygen, using liquid hydrogen to freeze out certain gases, and compressing the helium gas until it was absorbed by a charcoal filter, from which it could be recovered. Four chemists, working continuously over the next three years, were able to produce barely enough helium for experimental purposes.

During that period, Onnes remained uncertain that his attempt to liquefy helium would succeed, because scientists believed that at very low temperatures the Joule-Thomson effect might not further lower the temperature of a gas but might actually raise it. More perplexing was the unknown temperature at which the gas would become a liquid. All three laboratories had used a test devised by Dewar to measure how much helium a charcoal filter would absorb at the temperature of liquid hydrogen, but the results differed. Based on this test and others, Olszewski guessed that the critical temperature of helium might be less than 2 degrees above absolute zero, Dewar now thought it would be closer to 8 degrees above, and Onnes's own best estimate was 5 to 6 degrees.

Onnes recognized that the differences between 8, 5, and 2 degrees were highly significant, and he wrote that the results of the various laboratories' charcoal tests not only "left room for doubt" in his mind; far worse, they begat "ample room for fear that helium should deviate from the law of corresponding states." For a quarter century, Onnes had been conducting low-temperature research to experimentally verify the theory of corresponding states articulated by van der Waals. If the critical temperature of helium was really significantly lower or higher than the 5 K predicted by van der Waals's law, then that law of corresponding states would not apply to all elements, which would mean it was not universal, and his friend's theory might have to be junked. Moreover, in practical terms, a 2 K critical temperature would also mean that even the most advanced state-of-the-art apparatus would not be able to force the gas to become a liquid. "So it remained a very exciting question what the critical temperature of helium would be. And in every direction ... we were confronted by great difficulties."

It was at this moment that Kamerlingh Onnes's determination of the isotherms rescued him from paralyzing doubt, because the mathematical calculations showed that the temperature at which helium ought to liquefy was between 4 and 5 degrees above absolute zero—not, as he had feared, significantly higher or lower than that. Dewar now began to agree with him that the critical temperature was more likely to be nearer 5 K than 8 K.

Onnes pored over the details of the work of Hampson and Olszewski, trying to figure out whether his adaptations of their machinery would do the job. Once, in March 1908, he thought that
he had accomplished the task, but in an odd way—that he had compressed helium into becoming a solid, without its ever having stopped at the liquid state. He dashed off a telegram to Dewar to this effect, and received a congratulatory telegram in return, before having to retract his claim because the solid he had produced was composed not of helium but of impurities in the gas.

Before the retraction reached the Royal Institution, Dewar had written a letter to the London
Times
noting the feat. The letter was published, and then Dewar had to apologize for it to Onnes: "I felt a duty to inform the world ... that you had succeeded where I failed. Considering the enormous difficulty of such experiments we can all be mislead." In this letter to Onnes of April 15,1908, Dewar all but conceded that Onnes would shortly win the race. He expressed admiration for Onnes's ability to admit mistakes, to identify the problem that caused them, and to move ahead. As for himself, he wrote, his health was improving, though only slowly; more to the point, "the Royal Institution has no money to prosecute such many extensive experiments...[and] has no endowment to draw on." What Dewar did not inform Onnes directly about was a near catastrophe in his lab: during an attempt at lowering the temperature of helium, the impurities in the gas froze and clogged a capillary tube; in a too-quick reaction, one of Dewar's assistants turned a vent the wrong way, and many months' supply of hard-won helium gas escaped into the upper atmosphere. This, Dewar recognized, was fatal to his chances to win the race.