Absolute Zero and the Conquest of Cold (20 page)

Approaching Christmas 1887, the managers of the Royal Institution told the aged John Tyndall that Dewar, rather than he, would give that year's annual Christmas lecture to children; Tyndall resigned, and the managers appointed Dewar director of the Royal Institution; it was rumored that Dewar insisted the Tyndalls vacate the director's flat by January 1.

A balding, middle-aged man in trim beard, starched collar, and formal black suit, Dewar did magic tricks with liquid oxygen boiling in a tube for the adult Friday Nighters. He extracted a drop of the liquid oxygen and put it on his arm, supposedly to "show that it was in the spheroidal condition," but really to demonstrate that he was not afraid of the cold tiger. He added alcohol to the liquid in the test
tube, and the alcohol instantly froze into a solid within the liquid oxygen. He held a lighted taper over the test tube, and the vapor given off by the liquid ignited the taper into flaring flames. Having startled his audience, he then waxed philosophic, telling the men in evening jackets and the ladies in ball gowns that as science neared the projected temperature of liquefied hydrogen, the world would learn how those temperatures grandly altered many properties of matter. He prophesied that at or below the temperature of liquid hydrogen, "molecular motion would probably cease, and what might be called the death of matter would ensue."

He could make these predictions with some confidence because he had seen indications of astounding transformations from a lengthy and detailed series of experiments he conducted with J. A. Fleming, beginning in the late 1880s and lasting for many years thereafter. Fleming and his assistants made the measurements, while Dewar directed what was to be done and interpreted the results. These experiments accomplished more than any others in delineating many of the contours of the map of Frigor. It was an almost unworldly landscape they painted, one whose features had been etched by the fantastic transformative power of seriously low temperatures.

Scientists had long since established that a bit of chilling made it possible for metals to become better electrical conductors—it lowered the metals' resistance—but Fleming was unprepared for what happened when iron coils were plunged into liquid air: after, the coils registered one-tenth of the "resistivity" they had at room temperature. Dewar and Fleming found that as temperatures dropped drastically, so did resistance. At room temperature, the resistance of iron was 1, and that of copper was much better, at 5.9; but at—197°C, iron was at 8.2 and copper dropped to a breathtaking 34.6. This research moved Dewar to dream that at the absolute zero point, if it could ever be attained, "all pure metals would be perfect conductors of electricity....A current of electricity started in a pure metallic circuit would develop no heat, and therefore undergo no dissipa
tion."
^*
Fleming went so far as to propose a new definition for absolute zero: "the temperature at which perfectly pure metals cease to have any electrical resistance."

As Dewar widened his research, he reached out to other collaborators, including Pierre Curie, with whom he studied the effects of extreme cold on the emanations of radium and on the gases occluded by radium.

At extremely low temperatures, thermometers made of mercury or other liquids were freezing solid. Siemens in Germany had constructed a thermometer based on the curve describing the decline in resistance in a platinum wire, a curve that could by extrapolation give readings for the temperatures of other materials as they became ever colder. Dewar and Fleming began to use such "resistance" thermometers.

The ability to measure low temperatures did not help Dewar and Fleming make sense of the finding that a bath in liquid air made dramatic changes in the insulating capacity of substances that were already good insulators at room temperature. Glass, paraffin, and natural substances such as gutta-percha (a variety of natural rubber) and ebonite (an even harder rubber) did not lose insulating capacity but rather became even better insulators after being immersed in liquid air. The experimenters had no explanation for that. Nor could they come up with reasons for what happened to magnetization under the influence of liquid air or liquid oxygen. Dewar and Fleming were intrigued to find that while most magnets gained strength when subjected to intense cold, some did not; moreover, when pure iron was immersed in liquid oxygen, it afterward required a much greater magnetic field to magnetize it than was needed under normal conditions. Even mercury at very low temperatures could act as a magnet, whereas at room temperature it exhibited virtually no magnetic pull. To help explain that, the experimenters reminded themselves that in the periodic table, mercury was listed as a metal.

In the grip of Frigor, iron, copper, and zinc exhibited enhanced rigidity and greater strength: a coil that at room temperature could support only a pound or two of weight could support three times as much after immersion in liquid oxygen. When balls of various metals taken from the bath were dropped on an anvil, they bounced higher than they normally did, leading the researchers to conclude that lowered temperature produced greater elasticity in metals, and to guess that this might be traceable to increased molecular density of the supercooled metals.

It was a good guess, and its likelihood was spectacularly bolstered by the work of Dewar and Fleming on chemical affinities at the temperature of liquid oxygen. Generations of science students had been startled and delighted by demonstrations involving the violent reactions of some chemicals when brought into the presence of oxygen at room temperature, watching as these substances instantly formed oxides, a process that generated a great deal of chemical heat, sometimes accompanied by sparks and burnings. But when such usually volatile substances as phosphorus, sodium, and potassium were plunged into liquid oxygen, nothing happened. The ability of chemicals to combine, the researchers discovered, was all but abolished in the extreme cold. Not only that, but compounds that at room temperature would always generate electricity failed to do so at the temperature of liquid oxygen.

The most curious and unexpected of the experimental findings had to do with the optical properties of materials. Under the extreme cold, substances such as mercuric oxide, normally bright scarlet, faded to light orange, while white-colored substances intensified their whiteness, and blue-colored substances did not change their color at all. Reaching for explanations, Dewar and Fleming thought the changes in color corresponded to changes in the substances' specific absorption of light, but they could not be certain. Rounding a corner of the optical-properties valley, the researchers discovered the presence of something they recognized but had not suspected of existing in these latitudes: phosphorescence. All sorts of materials that in the normal-temperature world did not even give off the faintest of shines began to glow with their own bluish-colored light in the extreme cold—substances such as gelatin, paraffin, celluloid, rubber, ivory, and bone. Sulfuric and hydrochloric acids gleamed brightly. An egg immersed in liquid oxygen and then stimulated by an electric lamp radiated as a globe of blue light. Feathers glowed, too, as did cotton, wool, tortoiseshell, leather, linen, even sponges. Perhaps the ability to become phosphorescent had to do with the internal oxygen content of the material, but the experimenters couldn't prove that either. As with geographical explorers encountering strange flora and fauna in a country never before traversed, Dewar and Fleming, in their forays in the temperature region of liquid oxygen, simply captured the beasts, collected the flowers, and carried the samples back home to await further testing and eventual explanation.

"The prosecution of research at low temperatures approaching the zero of absolute temperature is attended with difficulties and dangers of no ordinary kind," Dewar wrote. There existed "no recorded experience to guide us...[in] storing and manipulating exceedingly volatile liquids like liquid oxygen and liquid air," which exploded ordinary glass vessels, caused metals to freeze and shatter, and exceeded the measuring capacities of instruments. His rather exalted language couched the difficult though ordinary problem of figuring out how to store low-temperature liquefied gases, and it reflected Dewar's increasingly heroic view of himself as engaged in a great struggle for knowledge.

The solution to the storage problem came to him in 1892, and it harked back to experiments he had begun twenty years earlier, on making vacuums. "Exhausting" the air between the outer and inner walls of a container, he found that the inner vessel could then readily
contain the corrosive and volatile liquefied oxygen and could hold it in quantities large enough for a series of experiments. Perfecting this device took him a year and innumerable tries, during which he determined that coating the inside of the flask with a thin layer of silver or mercury reduced loss by radiation by a factor of 13. Dewar presented the first perfected flask to the Prince of Wales at a public meeting at the Royal Institution. The "cryostatic devices" that Dewar produced for his low-temperature work were avidly sought and adopted by everyone else in the field and became known as "dewars." A "magnificent invention," Kamerlingh Onnes called the dewar, "the most important appliance for operating at extremely low temperatures."

The commercial version came about almost by accident: Dewar was having difficulty obtaining proper glass for his cryostats and commissioned a glass blower in Germany to make some for him; that man put his baby's milk in one of the flasks overnight and found that the milk was still warm in the morning. He took the idea of a "Thermos Flasche" to a manufacturer, and an everyday item was born.

Dewar's reticence to patent his own invention has been attributed by some historians to his mingling with the upper crust of London society, whom he might have believed likely to frown on any attempt at commercialism by a serious scientific researcher. But Lord Kelvin was not above obtaining patents for his work, and no scientist was held in greater respect by the elite. Perhaps Dewar did not realize that something designed for use at—200°C would be useful outside the land of Frigor.

In any event, with dewars in hand, their inventor could almost taste the triumph that lay ahead, the true liquefaction of hydrogen; by 1894, it seemed just inches from his grasp.

Seventeen years after Cailletet and Pictet had announced the first, fractional liquefactions of nitrogen and oxygen, Dewar in 1894 stood at the brink of the great mountain range he and everyone else in the field thought was the most important barrier between them and the cold pole of absolute zero. That mountain was the challenge of liquefying hydrogen in quantity. Dewar was working to remove the last kinks and problems from his materials and machinery, since every speck of impurity in the gas supply or minute defect in the seals of the apparatus, or in its ability to maintain pressure, or in the vacuum insulation of the cryostats, could spoil the experiment and result in failure. Although he was not the sort of man who shared his frustrations, the entire scientific community of Great Britain knew that he was on the verge of his greatest triumph and that it might be only a few months before he reached his goal of 20 cubic centimeters of hydrogen boiling quietly in a vacuum vessel, at a mere two dozen degrees above absolute zero.

Repeatedly during the 1880s and early 1890s, while proceeding with his scientific inquiries in the low-temperature region, Dewar would extract from them effects that delighted lecture audiences. The pressure he put on himself to invent better and more startling demonstrations multiplied as the geographic explorers returned from their quests to give popular lectures at other institutions. The Royal Institution's Friday Nighters were treated to having the amphitheater darkened and watching Dewar rub a cotton-wool sponge soaked in liquid air over a large vacuum vessel containing mercury or iodine vapor; just a touch produced luminous glows in the vessel, or bright flashes of light that enabled the audience to see its shape. A bath in liquid oxygen turned oxides and sulfides bright orange, chrome yellow, or metallic white, or made them lose their color. A multicolored soap film, suspended above a flask of liquid air, froze in the dense gas given off, preserving its sequence of colors. Tracing a line of liquid air on a band of India rubber, Dewar made the rubber alternately contract and expand in response to his drawing. He accompanied such magical demonstrations with erudite patter—the changed colors of the oxides and sulfides revealing "that the specific absorption of many substances undergoes great changes at the temperature of minus one hundred and ninety degrees centi
grade"—but it was the visual displays that stayed in the minds of audience members.

As a connoisseur of Dewar's lectures later wrote, the showy demonstrations were of interest to "those in his audience who knew what they were witnessing, whilst the rest of his audience was interested much as it might have been by conjuring tricks." Magic shows were at the height of their popularity in Victorian music halls just then. Though the Friday Nighters loved Dewar's showmanship, the more scientifically learned in the audience did not, in general, approve: the theatrics smacked overmuch of magic and illusion, drew attention to the experimenter instead of to the advance of science, and strongly and adversely altered the expectation of lecture audiences for other scientists' reports of their work. Worse, the grandstanding became intertwined with Dewar's growing sense of the importance of his own position and research, his autocratic behavior, and his unwillingness to put enough effort into maintaining good relations with colleagues among the scientific elite.

When Dewar was awarded the Royal Society's Rumford Medal in 1894 for his dewars, most English scientists applauded, but a few grumbled under their breath at the unfairness of it—could not the committee have also included Fleming in the citation? In Krakow, Olszewski seethed at the announcement. It seemed to him that Dewar had simply copied the metal apparatus he had perfected in 1889 to 1890. Olszewski based his belief on having published a report of the work in a French-language journal in 1890, a copy of which he had sent to Dewar. A long illness in 1892 had made it difficult for Olszewski to leave his laboratory building, and he had simply moved into it his bed and belongings; since he was wifeless and childless, the change in accommodations isolated him all the more and induced in him a touch too much contemplation of his own successes, failures, slights, and annoyances.