Absolute Zero and the Conquest of Cold

by Tom Shachtman

  Gorrie and Twining were shortly eclipsed by the French entrepreneur Ferdinand Carré. Twenty years after Faraday's ammonia-absorption experiments, Carré adapted them to make an "absorption" refrigeration machine. It began the procedure by applying heat and pressure to aqua ammonia, which separated the ammonia gas from the water. The gas then passed into a condenser of pipes containing cold water; in this cooler environment, a second application of pressure liquefied the ammonia gas. The liquefied gas then flowed into the actual refrigerating chamber, also known as the evaporating chamber because this was where the liquid ammonia was forced to evaporate—to become a gas again, and to expand as it did so, absorbing heat and producing the "cold effect" that turned water in an adjoining chamber into ice. After the gas had done all of this, it was reabsorbed into the first batch of water, becoming, once again, aqua ammonia.

  A Marseilles brewery installed Carrés prototype machine in 1859, and in 1860 he won patents in France and in the United States. Then came his big break—the onset of the Civil War in the United States. Because the Gorrie process had languished after its inventor died, and because Twining was a Northerner whose machinery was not welcome in the South, the Civil War provided an opportunity for Carré. Several of his machines were shipped past Union blockades into Southern ports and set up to produce ice, where the Northeast natural-ice traders were no longer supplying ice. Southerners used Carré-process ice principally in hospitals but occasionally to provide ice-cooled delicacies that permitted some households to maintain the illusion that the war had not affected their lifestyles.

  The wartime success of the Carré plants proved the efficacy of artificial icemaking and set the stage for the spread of ice-based refrigeration throughout the world. But to achieve further mastery of the cold would require more precise understanding of its basic processes—and the search for them had been under way, by a group of unlikely scientists, for some time.

  5. The Confraternity of the Overlooked

  THE EARLY NINETEENTH CENTURY WAS a hectic and confused time in science, and research into the nature and uses of cold suffered from science's inadequacies. Some of the confusion stemmed from societies having to deal with the upheavals of the French and American revolutions; scientists also had to struggle against a deeply entrenched, mechanistic conception of the world that had solidified 150 years earlier. It had been articulated by Robert Boyle and his generation, for instance in Boyle's characterization of the universe as "nothing but ... a machine whose workings are in principle understandable by human reason...[like] a rare clock ... where all things are so skillfully contrived, that the engine being once set a-moving, all things proceed according to the Artificer's first design." In that clockwork universe, light was considered an invisible substance composed of corpuscles, and chemicals were attracted to or repulsed by one another because of natural affinities and molecular forces, one of them being the "subtle fluid" called caloric, believed responsible for heat and cold by combining with other substances in unfathomable ways. These mistaken notions had to be overcome before scientists could make progress in basic understandings of how the universe actually works.

  But in the years around 1800, science had not yet entirely disentangled itself from either magic or philosophy. Audiences filled popular lecture halls to see and hear chemists, partly because they provided spectacular demonstrations and explosions, and partly in the hope that chemistry would confirm or refute the philosophic doctrine of materialism, which insisted that man had no immortal soul, and matter was just matter. Coleridge attended such lectures. Goethe wrote a novel using a chemistry-based metaphor, Elective Affinities.

  Physicists, who considered chemists no more than apothecaries, disdained the study of heat and cold as belonging to chemistry, since heat was believed to be a product of chemical reactions connected to oxygen burning. Chemists believed that oxygen burning and the theory of caloric had explained everything necessary to know about heat. With both physicists and chemists unwilling to investigate the phenomena further, heat and cold became the least desirable field of inquiry for scientists just at the very moment when heat, in the form of steam engines, was revolutionizing the labors of humanity.

  It was the genius of an engineer, Nicolas Léonard Sadi Carnot, to unite the study of steam engines and the study of the fundamental physics of heat and, in the process, to lead the way to understanding what cold is and how it is produced. His single published work, Réflexions sur la puissance motrice du feu (Reflections on the Motive Power of Fire), a study of an ideal steam engine published in 1824, would eventually be praised as among the most original works ever written in the physical sciences, with a core of abstraction comparable to the best of Galileo. It would greatly influence the study of what came to be called thermodynamics, and in the twentieth century it would form the basis for constructing apparatus to reach within a few billionths of a degree of absolute zero. But during Carnot's lifetime, the book was virtually ignored.

  In the 1870s, when Hippolyte Carnot found some old notes of his long-dead brother and convinced the Académie des Sciences to print them, he began his accompanying biographical sketch of his brother by writing that "the existence of Sadi Carnot was not marked by any notable events." But he also provided tantalizing descriptions of a man of "extreme sensibility, extreme energy ... sometimes reserved, sometimes savage," who studied such diverse things as boxing, music, crime, and botany. Among the maxims that Hippolyte extracted from Sadi's notebooks was this mordant gem: "It is surely sometimes necessary to abandon your reason; but how do you go about retrieving it when you have need of it?"

  One school of scientific biography contends that a scientist's accomplishments can only be understood by reference to his times; another school, by reference to his personality. In the case of Sadi Carnot, both his era and his personality were deeply influenced by his father. A mathematician, engineer, and soldier, Lazare Carnot published in 1783 an essay that discussed the dynamics of machines in terms of the "work" they did, rather than in terms of forces, à la Newton. Crossing into politics, by 1793 Lazare had risen to share with Robespierre and others of the Committee for Public Safety the responsibility of establishing fourteen armies for the revolution, as well as for condemning people to the guillotine. Exiled for opposing a coup, he came back to power with Napoleon in 1799, lost his positions in 1807, was recalled to service in 1814, and after Waterloo was once again exiled.

  A founder of the École Polytechnique, Lazare helped arrange for the acceptance there of his eldest son, Sadi, as a pupil-cadet in 1812, at the age of sixteen. Sadi won a first prize in artillery, and after taking part with classmates in the siege of Paris, he transferred to the École du Génie, the school for artillery and engineering, where he wrote a paper on an astronomical instrument and toiled on fortifications through the remainder of the last Napoleonic War. Denied promotion in the army, he was seldom employed in the specialty for which he had trained. "Fatigued with the life of the garrison," as Hippolyte put it, Sadi transferred to the general staff in Paris in 1818, then retired at half pay into "voluntary obscurity."

  He gravitated to the Conservatoire des Arts et Métiers, a recently founded technological museum that scandalized establishment scientists by offering lectures to the general public. In addition to being a temple of the practical, the Conservatoire was a hotbed of liberal, antiroyalist sentiments, which Sadi shared. Among its stalwarts were two men who came from the same region as Carnot, Nicolas Clément and Charles Bernard Desormes, brothers-in-law who did joint research on the physics of steam engines. All three felt keenly France's military loss to England, understood that French industry needed a boost to prevent England's burgeoning mills and factories from eclipsing France's own, and believed that the way to improve industry was to better understand the principles behind the operation of machines.

  Sadi Carnot devoted the years from 1820 to 1824 to the 118-page Réflexions, which he self-published in an edition of 600 copies. The book remained obscure until well after his de
ath. Among the reasons for its being ignored during his lifetime: it was not written by an Académie-certified expert, was not published in an establishment periodical, and did not contain original experimental results. Pointing out that the steam engine had become more important for the economic health of England than its navy, Carnot set out to explain why the newer steam engines were more efficient than James Watt's original, to establish the maximum efficiency of an engine under ideal conditions, and to deduce from that inquiry the general relationship between heat and mechanical work. His thesis was that the action in the steam engine was a function of temperatures and that the power of the engine had to do with the fall in temperature from hotter to colder. He drew on earlier attempts—by his father, among others—to improve the water-wheel engine, in which power derived from the volume of water and the length of time it was in contact with the wheel, during which the water was carried from high point (entry) to low point (exit). The action in the steam engine, he insisted, was analogous, the "motive power" of its heat depending "on what we shall call the height of its fall, that is, on the temperature difference of the bodies between which the caloric flows."

  Carnot's central tenet was that mechanical work was produced in proportion to the fall (of caloric) between higher- and lower-temperature bodies. He undermined his argument somewhat by relying on the theory of caloric. Antoine Lavoisier, the father of French chemistry, had died on the guillotine in 1794, but his theory of caloric had lived on. Carnot was actually uneasy with caloric; acknowledging critics of caloric such as Count von Rumford and Humphry Davy, he wrote that the basic principles of the caloric theory of heat needed "close attention" because "many experimental results would seem to be nearly inexplicable according to the present state of the theory." But he also balanced their criticism by citing a series of prizewinning French experiments done in 1812 on the specific heat of gases in relation to their density, the results of which seemed to shore up the notion of caloric.

  Unknown to Carnot, the figures obtained in the 1812 experiments were wrong, an error that the historian of caloric, Robert Fox, calls "one of the most influential in the whole history of the study of heat. Backed by the prestige associated with victory in [an official] competition, the result quickly became standard and ... misled many calorists."

  With hindsight, we can see that Carnot's discovery did not depend on caloric: he asserted that mechanical work would not be produced unless heat was transferred from a body at a high temperature to a body at a lower temperature, and that the greater the temperature difference between those two bodies, the more work done. Carnot's four-stage ideal engine required, for backward operation, the same input of work as the output when run forward. This alternation was crucial to his contention that the maximum amount of work possible was done in an engine with reversible processes. But while the processes might be reversible, the temperature direction of the flow emphatically was not. Donald Cardwell, a modern historian of thermodynamics, points out that only Carnot, of all who wrote about engines in this era, recognized that "the vast majority of thermal and thermomechanical changes are ... irreversible." A quarter century later, after the theory of caloric had been disproved, that irreversibility led Rudolf Clausius and Lord Kelvin (William Thomson) to formulate the second law of thermodynamics; in the late twentieth century, Carnot's understandings of the working of the ideal steam engine led to many advances in the generation of ever lower temperatures achieved by means of a "Carnot cycle" used to produce cold close to absolute zero.

  Among the reasons Carnot could not accept all the implications of the irreversibility he postulated was that he agreed with a pillar of the mechanistic universe, the notion of the conservation of all matter and forces. This idea contended that everything in the universe was already in existence, and nothing could be created or destroyed. It was a belief with religious origins, and Carnot could not afford emotionally to accept the damage to it that his own insight would bring. The idea that matter could indeed be irrevocably destroyed or changed in some not-yet-understood way was a frightening concept to this otherwise clear-eyed scientist.

  Carnot presented Réflexions before the Académie. There was a long and appreciative review of it in one journal, a brief notice in another, and an encomium by Clément recommending it to students, but the book brought the author no renown. After the publication, Carnot was briefly activated again in the army, then returned to Paris, where he described himself in 1828 as a "constructor of steam engines." His studies, now more specifically dealing with the physics of gases, were interrupted by the revolution of 1830, which toppled Charles X, restored a degree of popular sovereignty, and established a new king. Carnot became part of a cohort of École Polytechnique graduates who supported the new order. In the spring of 1832 an inflammation of the gorge confined him to his bed; by summer he was so weak that he could not fight off cholera, and he died in August. That Carnot died at Charenton, a hospital associated with the insane, occasioned some historians to say he went mad; but Charenton was used for cholera patients in 1832 because other hospitals were overcrowded, and in the hope that isolating those with cholera would halt the progress of the disease through the population.

  Unknown at the time of Carnot's death, but of importance to our story, was that around 1830 he had come to the realization that the caloric theory was wrong. The corpuscular theory of the transmission of light had been disproved, and experiments were demonstrating the likelihood that electricity, light, and magnetism were not the products of separate "forces" but were interrelated. In terms of heat and caloric, Carnot asked, "How can one conceive of the forces agitating the molecules, if they are never in contact with one another, if each [molecule] is perfectly isolated? Supposing that there is a subtle fluid interposed doesn't reconcile the difficulties, because that fluid would necessarily be composed of molecules." This reasoning led to an important conclusion:

  Heat is nothing other than motive power, or perhaps motive power that has had a change of form. If there is a destruction in the particles of a body, there is at the same time heat production in a quantity precisely proportional to the quantity of motive power that is destroyed; reciprocally, in every configuration, if there is destruction of heat, there is production of motive power.

  This understanding of how heat was transformed into motive power pushed Carnot to boldly state a modification of the everything-in-nature-is-preserved notion that he had been unwilling to make in 1824 but that he could no longer avoid:

  that the quantity of motive power in nature is invariable, that it is never properly speaking produced nor destroyed. Truly it changes form, sometimes manifesting itself as one kind of movement, sometimes as another, but it is never annihilated.

  Carnot was reaching here for a concept that he could not elucidate and that would take another quarter century to be defined and understood: energy. It is energy that is never annihilated, merely manifested as one or another kind of movement. Carnot didn't quite get the concept right, but he came close. In 1830 it would have been shocking to contend publicly that heat was not conserved, because it would call into question all of French science based on the work of Lavoisier and Marquis Pierre Simon de Laplace, considered France's greatest mathematician. Equally disturbing would have been Carnot's new contention that matter could be completely transformed into motive force, which countermanded the idea that the Artificer of the universe would permit some aspect of His creation to vanish into thin air. Cardwell suggests that Carnot's most compelling reason for not publishing these notes during his lifetime, though, was that to do so he would have had to revise his major work in the light of his new understandings, and that task was beyond the capacity of a single individual; the complete revision and integration of his new ideas would required the combined talents of some of the century's most ingenious thinkers. *

  The French engineer Émile Clapeyron was a contemporary of Sadi Carnot, having passed through the École Polytechnique a few years after him, and having possibly been in touch
with him during the 1830 uprising. Two years after Carnot's death, Clapeyron published an exegesis of Carnot that did what Carnot had been at pains not to do: it used mathematical formulas, graphs, and diagrams, for instance, to extrapolate from Carnot's analysis "Clapeyron's equation," which holds that the maximum amount of work a unit of heat can perform when it vaporizes a liquid cannot be larger than the amount it would perform if it were doing another task. Clapeyron also proved mathematically Carnot's contention that the amount of work done during the course of a one-degree fall of a unit of heat decreases as the temperature increases. More widely circulated than Carnot's book, Clapeyron's paper was also translated into English and German, which made it accessible to those doing research in what would become known as thermodynamics, the study of the transformations of energy, leading to its further influence on the exploration of the cold.

  As pointed out in the previous chapter, during the 1820s and 1830s science's growing ability to produce cold was ignored. In the same year as Clapeyron's publication, 1834, and also in France, an amateur scientist of independent means used electricity to directly produce heat and cold in a way that in the twentieth century would become quite important. Jean-Charles-Athanase Peltier, who had retired from clockmaking when the death of his wife's mother resulted in a small inheritance that allowed him to follow his scientific interests, had been intrigued by the research of an earlier Estonian-born German physicist, Thomas Johann Seebeck. Peltier passed a continuous current along a circuit of two conductors, made from different metals and connected by two junctions, and found that the temperature of one junction rose and the temperature of the other junction fell.* In other words, electricity could be used either to cool or to heat: Seebeck and Peltier had discovered an entirely new field, thermoelectricity. In 1838, using Peltier's thermoelectric method, the German scientist H. F. E. Lenz froze a drop of water. He, too, was ignored. In other words, by 1838 the technical means of providing cold to those who might need or want it had been demonstrated in several scientific laboratories, but neither the pure scientists, nor the technologists, nor the few would-be entrepreneurs of refrigeration seemed interested in the process or the goal.