Sam Kean
Page 25
Ironically, though he did everything to skirt pathological science, Röntgen’s papers show that he couldn’t shake the thought he had gone mad. Moreover, his muttering and his uncharacteristic temper made other people question his sanity. He jokingly said to his wife, Bertha, “I’m doing work that will make people say, ‘Old Röntgen has gone crazy!’ ” He was fifty then, and she must have wondered.
Still, the Crookes tube lit up the barium plates every time, no matter how much he disbelieved. So Röntgen began documenting the phenomenon. Again, unlike the three pathological cases above, he dismissed any fleeting or erratic effects, anything that might be considered subjective. He sought only objective results, like developed photographic plates. At last, slightly more confident, he brought Bertha into the lab one afternoon and exposed her hand to the X-rays. Upon seeing her bones, she freaked out, thinking it a premonition of her death. She refused to go back into his haunted lab after that, but her reaction brought immeasurable relief to Röntgen. Possibly the most loving thing Bertha ever did for him, it proved he hadn’t imagined everything.
At that point, Röntgen emerged, haggard, from his laboratory and informed his colleagues across Europe about “röntgen rays.” Naturally, they doubted him, just as they’d scorned Crookes and later scientists would scorn the megalodon and cold fusion. But Röntgen had been patient and modest, and every time someone objected, he countered by saying he’d already investigated that possibility, until his colleagues had no more objections. And herein lies the uplifting side to the normally severe tales of pathological science.
This early X-ray revealed the bones and impressive ring of Bertha Röntgen, wife of Wilhelm Röntgen. Wilhelm, who feared he’d gone mad, was relieved when his wife also saw the bones of her hand on a barium-coated plate. She, less sanguine, thought it an omen of death.
Scientists can be cruel to new ideas. One can imagine them asking, “What sort of ‘mystery beams’ can fly invisibly through black paper, Wilhelm, and light up the bones in your body? Bah.” But when he fought back with solid proof, with repeatable experiments, most overthrew their old ideas to embrace his. Though a middling professor his whole life, Röntgen became every scientist’s hero. In 1901, he won the inaugural Nobel Prize in Physics. Two decades later, a physicist named Henry Moseley used the same basic X-ray setup to revolutionize the study of the periodic table. And people were still so smitten a century later that in 2004, the largest official element on the periodic table at the time, number 111, long called unununium, became roentgenium.
Part V
ELEMENT SCIENCE TODAY AND TOMORROW
16
Chemistry Way, Way Below Zero
Röntgen not only provided an example of brilliantly meticulous science; he also reminded scientists that the periodic table is never empty of surprises. There’s always something novel to discover about the elements, even today. But with most of the easy pickings already plucked by Röntgen’s time, making new discoveries required drastic measures. Scientists had to interrogate the elements under increasingly severe conditions—especially extreme cold, which hypnotizes them into strange behaviors. Extreme cold doesn’t always portend well for the humans making the discoveries either. While the latter-day heirs of Lewis and Clark had explored much of Antarctica by 1911, no human being had ever reached the South Pole. Inevitably, this led to an epic race among explorers to get there first—which led just as inevitably to a grim cautionary tale about what can go wrong with chemistry at extreme temperatures.
That year was chilly even by Antarctic standards, but a band of pale Englishmen led by Robert Falcon Scott nonetheless determined that they would be the first to reach ninety degrees south latitude. They organized their dogs and supplies, and a caravan set off in November. Much of the caravan was a support team, which cleverly dropped caches of food and fuel on the way out so that the small final team that would dash to the pole could retrieve them on the way back.
Little by little, more of the caravan peeled off, and finally, after slogging along for months on foot, five men, led by Scott, arrived at the pole in January 1912—only to find a brown pup tent, a Norwegian flag, and an annoyingly friendly letter. Scott had lost out to Roald Amundsen, whose team had arrived a month earlier. Scott recorded the moment curtly in his diary: “The worst has happened. All the daydreams must go.” And shortly afterward: “Great God! This is an awful place. Now for the run home and a desperate struggle. I wonder if we can do it.”
Dejected as Scott’s men were, their return trip would have been difficult anyway, but Antarctica threw up everything it could to punish and harass them. They were marooned for weeks in a monsoon of snow flurries, and their journals (discovered later) showed that they faced starvation, scurvy, dehydration, hypothermia, and gangrene. Most devastating was the lack of heating fuel. Scott had trekked through the Arctic the year before and had found that the leather seals on his canisters of kerosene leaked badly. He’d routinely lost half of his fuel. For the South Pole run, his team had experimented with tin-enriched and pure tin solders. But when his bedraggled men reached the canisters awaiting them on the return trip, they found many of them empty. In a double blow, the fuel had often leaked onto foodstuffs.
Without kerosene, the men couldn’t cook food or melt ice to drink. One of them took ill and died; another went insane in the cold and wandered off. The last three, including Scott, pushed on. They officially died of exposure in late March 1912, eleven miles wide of the British base, unable to get through the last nights.
In his day, Scott had been as popular as Neil Armstrong—Britons received news of his plight with gnashing of teeth, and one church even installed stained-glass windows in his honor in 1915. As a result, people have always sought an excuse to absolve him of blame, and the periodic table provided a convenient villain. Tin, which Scott used as solder, has been a prized metal since biblical times because it’s so easy to shape. Ironically, the better metallurgists got at refining tin and purifying it, the worse it became for everyday use. Whenever pure tin tools or tin coins or tin toys got cold, a whitish rust began to creep over them like hoarfrost on a window in winter. The white rust would break out into pustules, then weaken and corrode the tin, until it crumbled and eroded away.
Unlike iron rust, this was not a chemical reaction. As scientists now know, this happens because tin atoms can arrange themselves inside a solid in two different ways, and when they get cold, they shift from their strong “beta” form to the crumbly, powdery “alpha” form. To visualize the difference, imagine stacking atoms in a huge crate like oranges. The bottom of the crate is lined with a single layer of spheres touching only tangentially. To fill the second, third, and fourth layers, you might balance each atom right on top of one in the first layer. That’s one form, or crystal structure. Or you might nestle the second layer of atoms into the spaces between the atoms in the first layer, then the third layer into the spaces between the atoms in the second layer, and so on. That makes a second crystal structure with a different density and different properties. These are just two of the many ways to pack atoms together.
What Scott’s men (perhaps) found out the hard way is that an element’s atoms can spontaneously shift from a weak crystal to a strong one, or vice versa. Usually it takes extreme conditions to promote rearrangement, like the subterranean heat and pressure that turn carbon from graphite into diamonds. Tin becomes protean at 56°F. Even a sweater evening in October can start the pustules rising and the hoarfrost creeping, and colder temperatures accelerate the process. Any abusive treatment or deformation (such as dents from canisters being tossed onto hard-packed ice) can catalyze the reaction, too, even in tin that is otherwise immune. Nor is this merely a topical defect, a surface scar. The condition is sometimes called tin leprosy because it burrows deep inside like a disease. The alpha–beta shift can even release enough energy to cause audible groaning—vividly called tin scream, although it sounds more like stereo static.
The alpha–beta shift of tin has be
en a convenient chemical scapegoat throughout history. Various European cities with harsh winters (e.g., St. Petersburg) have legends about expensive tin pipes on new church organs exploding into ash the instant the organist blasted his first chord. (Some pious citizens were more apt to blame the Devil.) Of more world historical consequence, when Napoleon stupidly attacked Russia during the winter of 1812, the tin clasps on his men’s jackets reportedly (many historians dispute this) cracked apart and left the Frenchmen’s inner garments exposed every time the wind kicked up. As with the horrible circumstances faced by Scott’s little band, the French army faced long odds in Russia anyway. But element fifty’s changeling ways perhaps made things tougher, and impartial chemistry proved an easier thing to blame* than a hero’s bad judgment.
There’s no doubt Scott’s men found empty canisters—that’s in his diary—but whether the disintegration of the tin solder caused the leaks is disputed. Tin leprosy makes so much sense, yet canisters from other teams discovered decades later retained their solder seals. Scott did use purer tin—although it would have to have been extremely pure for leprosy to take hold. Yet no other good explanation besides sabotage exists, and there’s no evidence of foul play. Regardless, Scott’s little band perished on the ice, victims at least in part of the periodic table.
Quirky things happen when matter gets very cold and shifts from one state to another. Schoolchildren learn about just three interchangeable states of matter—solid, liquid, and gas. High school teachers often toss in a fourth state, plasma, a superheated condition in stars in which electrons detach from their nucleic moorings and go roaming.* In college, students get exposed to superconductors and superfluid helium. In graduate school, professors sometimes challenge students with states such as quark-gluon plasma or degenerate matter. And along the way, a few wiseacres always ask why Jell-O doesn’t count as its own special state. (The answer? Colloids like Jell-O are blends of two states.* The water and gelatin mixture can either be thought of as a highly flexible solid or a very sluggish liquid.)
The point is that the universe can accommodate far more states of matter—different micro-arrangements of particles—than are dreamed of in our provincial categories of solid, liquid, and gas. And these new states aren’t hybrids like Jell-O. In some cases, the very distinction between mass and energy breaks down. Albert Einstein uncovered one such state while fiddling around with a few quantum mechanics equations in 1924—then dismissed his calculations and disavowed his theoretical discovery as too bizarre to ever exist. It remained impossible, in fact, until someone made it in 1995.
In some ways, solids are the most basic state of matter. (To be scrupulous, the vast majority of every atom sits empty, but the ultra-quick hurry of electrons gives atoms, to our dull senses, the persistent illusion of solidity.) In solids, atoms line up in a repetitive, three-dimensional array, though even the most blasé solids can usually form more than one type of crystal. Scientists can now coax ice into forming fifteen distinctly shaped crystals by using high-pressure chambers. Some ices sink rather than float in water, and others form not six-sided snowflakes, but shapes like palm leaves or heads of cauliflower. One alien ice, Ice X, doesn’t melt until it reaches 3,700°F. Even chemicals as impure and complicated as chocolate form quasi-crystals that can shift shapes. Ever opened an old Hershey’s Kiss and found it an unappetizing tan? We might call that chocolate leprosy, caused by the same alpha–beta shifts that doomed Scott in Antarctica.
Crystalline solids form most readily at low temperatures, and depending on how low the temperature gets, elements you thought you knew can become almost unrecognizable. Even the aloof noble gases, when forced into solid form, decide that huddling together with other elements isn’t such a bad idea. Violating decades of dogma, Canadian-based chemist Neil Bartlett created the first noble gas compound, a solid orange crystal, with xenon in 1962.* Admittedly, this took place at room temperature, but only with platinum hexafluoride, a chemical about as caustic as a superacid. Plus xenon, the largest stable inert gas, reacts far more easily than the others because its electrons are only loosely bound to its nucleus. To get smaller, closed-rank noble gases to react, chemists had to drastically screw down the temperature and basically anesthetize them. Krypton put up a good fight until about −240°F, at which point super-reactive fluorine can latch onto it.
Getting krypton to react, though, was like mixing baking soda and vinegar compared with the struggle to graft something onto argon. After Bartlett’s xenon solid in 1962 and the first krypton solid in 1963, it took thirty-seven frustrating years until Finnish scientists finally pieced together the right procedure for argon in 2000. It was an experiment of Fabergé delicacy, requiring solid argon; hydrogen gas; fluorine gas; a highly reactive starter compound, cesium iodide, to get the reaction going; and well-timed bursts of ultraviolet light, all set to bake at a frigid −445°F. When things got a little warmer, the argon compound collapsed.
Nevertheless, below that temperature argon fluorohydride was a durable crystal. The Finnish scientists announced the feat in a paper with a refreshingly accessible title for a scientific work, “A Stable Argon Compound.” Simply announcing what they’d done was bragging enough. Scientists are confident that even in the coldest regions of space, tiny helium and neon have never bonded with another element. So for now, argon wears the title belt for the single hardest element humans have forced into a compound.
Given argon’s reluctance to change its habits, forming an argon compound was a major feat. Still, scientists don’t consider noble gas compounds, or even alpha–beta shifts in tin, truly different states of matter. Different states require appreciably different energies, in which atoms interact in appreciably different ways. That’s why solids, where atoms are (mostly) fixed in place; liquids, where particles can flow around each other; and gases, where particles have the freedom to carom about, are distinct states of matter.
Still, solids, liquids, and gases have lots in common. For one, their particles are well-defined and discrete. But that sovereignty gives way to anarchy when you heat things up to the plasma state and atoms start to disintegrate, or when you cool things down enough and collectivist states of matter emerge, where the particles begin to overlap and combine in fascinating ways.
Take superconductors. Electricity consists of an easy flow of electrons in a circuit. Inside a copper wire, the electrons flow between and around the copper atoms, and the wire loses energy as heat when the electrons crash into the atoms. Obviously, something suppresses that process in superconductors, since the electrons flowing through them never flag. In fact, the current can flow forever as long as the superconductor remains chilled, a property first detected in mercury at −450°F in 1911. For decades, most scientists assumed that superconducting electrons simply had more space to maneuver: atoms in superconductors have much less energy to vibrate back and forth, giving electrons a wider shoulder to slip by and avoid crashes. That explanation’s true as far as it goes. But really, as three scientists figured out in 1957, it’s electrons themselves that metamorphose at low temperatures.
When zooming past atoms in a superconductor, electrons tug at the atoms’ nuclei. The positive nuclei drift slightly toward the electrons, and this leaves a wake of higher-density positive charge. The higher-density charge attracts other electrons, which in a sense become paired with the first. It’s not a strong coupling between electrons, more like the weak bond between argon and fluorine; that’s why the coupling emerges only at low temperatures, when atoms aren’t vibrating too much and knocking the electrons apart. At those low temperatures, you cannot think of electrons as isolated; they’re stuck together and work in teams. And during their circuit, if one electron gets gummed up or knocks into an atom, its partners yank it through before it slows down. It’s like that old illegal football formation where helmetless players locked arms and stormed down the field—a flying electron wedge. This microscopic state translates to superconductivity when billions of billions of pairs all do the same
thing.
Incidentally, this explanation is known as the BCS theory of superconductivity, after the last names of the men who developed it: John Bardeen, Leon Cooper (the electron partners are called Cooper pairs), and Robert Schrieffer.* That’s the same John Bardeen who coinvented the germanium transistor, won a Nobel Prize for it, and dropped his scrambled eggs on the floor when he heard the news. Bardeen dedicated himself to superconductivity after leaving Bell Labs for Illinois in 1951, and the BCS trio came up with the full theory six years on. It proved so good, so accurate, they shared the 1972 Nobel Prize in Physics for their work. This time, Bardeen commemorated the occasion by missing a press conference at his university because he couldn’t figure out how to get his new (transistor-powered) electric garage door open. But when he visited Stockholm for the second time, he presented his two adult sons to the king of Sweden, just as he’d promised he would back in the fifties.
If elements are cooled below even superconducting temperatures, the atoms grow so loopy that they overlap and swallow each other up, a state called coherence. Coherence is crucial to understanding that impossible Einsteinian state of matter promised earlier in this chapter. Understanding coherence requires a short but thankfully element-rich detour into the nature of light and another once impossible innovation, lasers.
Few things delight the odd aesthetic sense of a physicist as much as the ambiguity, the two-in-oneness, of light. We normally think of light as waves. In fact, Einstein formulated his special theory of relativity in part by thinking about how the universe would appear to him—what space would look like, how time would (or wouldn’t) pass—if he rode sidesaddle on one of those waves. (Don’t ask me how he imagined this.) At the same time, Einstein proved (he’s ubiquitous in this arena) that light sometimes acts like particle BBs called photons. Combining the wave and particle views (called wave-particle duality), he correctly deduced that light is not only the fastest thing in the universe, it’s the fastest possible thing, at 186,000 miles per second, in a vacuum. Whether you detect light as a wave or photons depends on how you measure it, since light is neither wholly one nor the other.