Bunsen’s first love was arsenic. Although element thirty-three has had quite a reputation since ancient times (Roman assassins used to smear it on figs), few law-abiding chemists knew much about arsenic before Bunsen started sloshing it around in test tubes. He worked primarily with arsenic-based cacodyls, chemicals whose name is based on the Greek word for “stinky.” Cacodyls smelled so foul, Bunsen said, they made him hallucinate, “produc[ing] instantaneous tingling of the hands and feet, even giddiness and insensibility.” His tongue became “covered with a black coating.” Perhaps from self-interest, he soon developed what’s still the best antidote to arsenic poisoning, iron oxide hydrate, a chemical related to rust that clamps onto arsenic in the blood and drags it out. Still, he couldn’t shield himself from every danger. The careless explosion of a glass beaker of arsenic nearly blew out his right eye and left him half-blind for the last sixty years of his life.
After the accident, Bunsen put arsenic aside and indulged his passion for natural explosions. Bunsen loved anything that spewed from the ground, and for several years he investigated geysers and volcanoes by hand-collecting their vapors and boiling liquids. He also jury-rigged a faux Old Faithful in his laboratory and discovered how geysers build up pressure and blow. Bunsen settled back into chemistry at the University of Heidelberg in the 1850s and soon ensured himself scientific immortality by inventing the spectroscope, which uses light to study elements. Each element on the periodic table produces sharp, narrow bands of colored light when heated. Hydrogen, for example, always emits one red, one yellowish green, one baby blue, and one indigo band. If you heat some mystery substance and it emits those specific lines, you can bet it contains hydrogen. This was a powerful breakthrough, the first way to peer inside exotic compounds without boiling them down or disintegrating them with acid.
To build the first spectroscope, Bunsen and a student mounted a prism inside a discarded cigar box, to keep out stray light, and attached two broken-off eyepieces from telescopes to peer inside, like a diorama. The only thing limiting spectroscopy at that point was getting flames hot enough to excite elements. So Bunsen duly invented the device that made him a hero to everyone who ever melted a ruler or started a pencil on fire. He took a local technician’s primitive gas burner and added a valve to adjust the oxygen flow. (If you remember fussing around with the knob on the bottom of your Bunsen burner, that’s it.) As a result, the burner’s flame improved from an inefficient, crackling orange to the tidy, hissing blue you see on good stoves today.
Bunsen’s work helped the periodic table develop rapidly. Although he opposed the idea of classifying elements by their spectra, other scientists had fewer qualms, and the spectroscope immediately began identifying new elements. Just as important, it helped sort through spurious claims by finding old elements in disguise in unknown substances. Reliable identification got chemists a long way toward the ultimate goal of understanding matter on a deeper level. Still, beyond finding new elements, scientists needed to organize them into a family tree of some sort. And here we come to Bunsen’s other great contribution to the table—his help in building an intellectual dynasty in science at Heidelberg, where he instructed a number of people responsible for early work in periodic law. This includes our second character, Dmitri Mendeleev, the man generally acclaimed for creating the first periodic table.
Truth be told, like Bunsen and the burner, Mendeleev didn’t conjure up the first periodic table on his own. Six people invented it independently, and all of them built on the “chemical affinities” noted by an earlier generation of chemists. Mendeleev started with a rough idea of how to group elements into small, synonymous sets, then transformed these gestures at a periodic system into scientific law, much like Homer transformed disconnected Greek myths into The Odyssey. Science needs heroes as much as any other field, and Mendeleev became the protagonist of the story of the periodic table for a number of reasons.
For one, he had a hell of a biography. Born in Siberia, the youngest of fourteen children, Mendeleev lost his father in 1847, when the boy was thirteen. Boldly for the time, his mother took over a local glass factory to support the family and managed the male craftsmen working there. Then the factory burned down. Pinning her hopes on her sharp-minded son, she bundled him up on horseback and rode twelve hundred miles across the steppes and steep, snowy Ural Mountains to an elite university in Moscow—which rejected Dmitri because he wasn’t local stock. Undaunted, Mama Mendeleev bundled him back up and rode four hundred miles farther, to his dead father’s alma mater in St. Petersburg. Just after seeing him enrolled, she died.
Mendeleev proved to be a brilliant student. After graduation, he studied in Paris and Heidelberg, where the eminent Bunsen supervised him for a spell (the two clashed personally, partly because Mendeleev was moody and partly because of Bunsen’s notoriously loud and foul-fumed lab). Mendeleev returned to St. Petersburg as a professor in the 1860s and there began to think about the nature of elements, work that culminated in his famous periodic table of 1869.
Many others were working on the problem of how to organize elements, and some even solved it, however haltingly, with the same approach as Mendeleev. In England, a thirty-something chemist named John Newlands presented his makeshift table to a chemistry society in 1865. But a rhetorical blunder doomed Newlands. At the time, no one knew about the noble gases (helium through radon), so the top rows of his periodic table contained only seven units. Newlands whimsically compared the seven columns to the do-re-mi-fa-sol-la-ti-do of the musical scale. Unfortunately, the Chemical Society of London was not the most whimsical audience, and they ridiculed Newlands’s nickelodeon chemistry.
The more serious rival to Mendeleev was Julius Lothar Meyer, a German chemist with an unruly white beard and neatly oiled black hair. Meyer had also worked under Bunsen at Heidelberg and had serious professional credentials. Among other things, he’d figured out that red blood cells transport oxygen by binding it to hemoglobin. Meyer published his table at practically the same time as Mendeleev, and the two even split a prestigious pre–Nobel Prize called the Davy Medal in 1882 for codiscovering the “periodic law.” (It was an English prize, but Newlands was shut out until 1887, when he earned his own Davy Medal.) While Meyer continued to do great work that added to his reputation—he helped popularize a number of radical theories that turned out correct—Mendeleev turned cranky, a queer fish who, incredibly, refused to believe in the reality of atoms.* (He would later also reject other things he couldn’t see, such as electrons and radioactivity.) If you had sized up the two men around 1880 and judged which was the greater theoretical chemist, you might have picked Meyer. So what separated Mendeleev from Meyer and the four other chemists who published tables before them, at least in history’s judgment?*
First, more than any other chemist, Mendeleev understood that certain traits about elements persist, even if others don’t. He realized a compound like mercuric oxide (an orange solid) doesn’t somehow “contain” a gas, oxygen, and a liquid metal, mercury, as others believed. Rather, mercuric oxide contains two elements that happen to form a gas and a metal when separate. What stays constant is each element’s atomic weight, which Mendeleev considered its defining trait, very close to the modern view.
Second, unlike others who had dabbled in arranging elements into columns and rows, Mendeleev had worked in chemistry labs his whole life and had acquired a deep, deep knowledge of how elements felt and smelled and reacted, especially metals, the most ambiguous and knotty elements to place on the table. This allowed him to incorporate all sixty-two known elements into his columns and rows. Mendeleev also revised his table obsessively, at one point writing elements on index cards and playing a sort of chemical solitaire in his office. Most important of all, while both Mendeleev and Meyer left gaps on their table where no known elements fit, Mendeleev, unlike the squeamish Meyer, had balls enough to predict that new elements would be dug up. Look harder, you chemists and geologists, he seemed to taunt, and you’ll find them. By trac
ing the traits of known elements down each column, Mendeleev even predicted the densities and atomic weights of hidden elements, and when some predictions proved correct, people were mesmerized. Furthermore, when scientists discovered noble gases in the 1890s, Mendeleev’s table passed a crucial test, since it easily incorporated the gases by adding one new column. (Mendeleev denied that noble gases existed at first, but by then the periodic table was no longer just his.)
Then there was Mendeleev’s outsized character. Like his Russian contemporary Dostoevsky—who wrote his entire novel The Gambler in three weeks to pay off desperate gambling debts—Mendeleev threw together his first table to meet a textbook publisher’s deadline. He’d already written volume one of the textbook, a five-hundred-page tome, but had got through just eight elements. That meant he had to fit all the rest into volume two. After six weeks of procrastinating, he decided in one inspired moment that the most concise way to present the information was in a table. Excited, he blew off his side job as a chemistry consultant for local cheese factories to compile the table. When the book appeared in print, Mendeleev not only predicted that new elements would fit into empty boxes beneath the likes of silicon and boron, but he also provisionally named them. It couldn’t have hurt his reputation (people seek gurus during uncertain times) that he used an exotic, mystical language to create those names, using the Sanskrit word for beyond: eka-silicon, eka-boron, and so on.
A few years later, Mendeleev, now famous, divorced his wife and wanted to remarry. Although the conservative local church said he had to wait seven years, he bribed a priest and got on with the nuptials. This technically made him a bigamist, but no one dared arrest him. When a local bureaucrat complained to the tsar about the double standard applied to the case—the priest was defrocked—the tsar primly replied, “I admit, Mendeleev has two wives, but I have only one Mendeleev.” Still, the tsar’s patience wasn’t infinite. In 1890, Mendeleev, a self-professed anarchist, was booted out of his academic post for sympathizing with violent leftist student groups.
It’s easy to see why historians and scientists grew attached to Mendeleev’s life’s tale. Of course, no one would remember his biography today had he not constructed his periodic table. Overall, Mendeleev’s work is comparable to that of Darwin in evolution and Einstein in relativity. None of those men did all the work, but they did the most work, and they did it more elegantly than others. They saw how far the consequences extended, and they backed up their findings with reams of evidence. And like Darwin, Mendeleev made lasting enemies for his work. Naming elements he’d never seen was presumptuous, and doing so infuriated the intellectual successor of Robert Bunsen—the man who discovered “eka-aluminium” and justifiably felt that he, not the rabid Russian, deserved credit and naming rights.
* * *
The discovery of eka-aluminium, now known as gallium, raises the question of what really drives science forward—theories, which frame how people view the world, or experiments, the simplest of which can destroy elegant theories. After a dustup with the theorist Mendeleev, the experimentalist who discovered gallium had a definite answer. Paul Emile François Lecoq de Boisbaudran was born into a winemaking family in the Cognac region of France in 1838. Handsome, with sinuous hair and a curled mustache, prone to wearing stylish cravats, he moved to Paris as an adult, mastered Bunsen’s spectroscope, and became the best spectroscopic surgeon in the world.
Lecoq de Boisbaudran grew so adroit that in 1875, after spotting never-before-seen color bands in a mineral, he concluded, instantly and correctly, he’d discovered a new element. He named it gallium, after Gallia, the Latin name for France. (Conspiracy mongers accused him of slyly naming the element after himself, since Lecoq, or “the rooster,” is gallus in Latin.) Lecoq de Boisbaudran decided he wanted to hold and feel his new prize, so he set about purifying a sample of it. It took a few years, but by 1878 the Frenchman finally had a nice, pure hunk of gallium. Though solid at moderate room temperature, gallium melts at 84°F, meaning that if you hold it in the palm of your hand (because body temperature is about 98°F), it will melt into a grainy, thick puddle of pseudoquicksilver. It’s one of the few liquid metals you can touch without boiling your finger to the bone. As a result, gallium has been a staple of practical jokes among the chemistry cognoscenti ever since, a definite step up from Bunsen-burner humor. One popular trick, since gallium molds easily and looks like aluminium, is to fashion gallium spoons, serve them with tea, and watch as your guests recoil when their Earl Grey “eats” their utensils.*
Lecoq de Boisbaudran reported his findings in scientific journals, rightfully proud of his capricious metal. Gallium was the first new element discovered since Mendeleev’s 1869 table, and when the theorist Mendeleev read about Lecoq de Boisbaudran’s work, he tried to cut in line and claim credit for gallium based on his prediction of eka-aluminium. Lecoq de Boisbaudran responded tersely that, no, he had done the real work. Mendeleev demurred, and the Frenchman and Russian began debating the matter in scientific journals, like a serialized novel with different characters narrating each chapter. Before long, the discussion turned acrimonious. Annoyed at Mendeleev’s crowing, Lecoq de Boisbaudran claimed an obscure Frenchman had developed the periodic table before Mendeleev and that the Russian had usurped this man’s ideas—a scientific sin second only to forging data. (Mendeleev was never so good about sharing credit. Meyer, in contrast, cited Mendeleev’s table in his own work in the 1870s, which may have made it seem to later generations that Meyer’s work was derivative.)
For his part, Mendeleev scanned Lecoq de Boisbaudran’s data on gallium and told the experimentalist, with no justification, that he must have measured something wrong, because the density and weight of gallium differed from Mendeleev’s predictions. This betrays a flabbergasting amount of gall, but as science philosopher-historian Eric Scerri put it, Mendeleev always “was willing to bend nature to fit his grand philosophical scheme.” The only difference between Mendeleev and crackpottery is that Mendeleev was right: Lecoq de Boisbaudran soon retracted his data and published results that corroborated Mendeleev’s predictions. According to Scerri, “The scientific world was astounded to note that Mendeleev, the theorist, had seen the properties of a new element more clearly than the chemist who had discovered it.” A literature teacher once told me that what makes a story great—and the construction of the periodic table is a great story—is a climax that’s “surprising yet inevitable.” I suspect that upon discovering his grand scheme of the periodic table, Mendeleev felt astonished—yet also convinced of its truth because of its elegant, inescapable simplicity. No wonder he sometimes grew intoxicated at the power he felt.
Leaving aside scientific machismo, the real debate here centered on theory versus experiment. Had theory tuned Lecoq de Boisbaudran’s senses to help him see something new? Or had experiment provided the real evidence, and Mendeleev’s theory just happened to fit? Mendeleev might as well have predicted cheese on Mars before Lecoq de Boisbaudran found evidence for his table in gallium. Then again, the Frenchman had to retract his data and issue new results that supported what Mendeleev had predicted. Although Lecoq de Boisbaudran denied he had ever seen Mendeleev’s table, it’s possible he had heard of others or that the tables had gotten the scientific community talking and had indirectly primed scientists to keep an eye peeled for new elements. As no less a genius than Albert Einstein once said, “It is theory that decides what we can observe.”
In the end, it’s probably impossible to tease out whether the heads or tails of science, the theory or the experiment, has done more to push science ahead. That’s especially true when you consider that Mendeleev made many wrong predictions. He was lucky, really, that a good scientist like Lecoq de Boisbaudran discovered eka-aluminium first. If someone had poked around for one of his mistakes—Mendeleev predicted there were many elements before hydrogen and swore the sun’s halo contained a unique element called coronium—the Russian might have died in obscurity. But just as people forgave ancient
astrologers who spun false, even contradictory, horoscopes and fixated instead on the one brilliant comet they predicted exactly, people tend to remember only Mendeleev’s triumphs. Moreover, when simplifying history it’s tempting to give Mendeleev, as well as Meyer and others, too much credit. They did the important work in building the trellis on which to nail the elements; but by 1869, only two-thirds of all elements had been discovered, and for years some of them sat in the wrong columns and rows on even the best tables.
Loads of work separates a modern textbook from Mendeleev, especially regarding the mess of elements now quarantined at the bottom of the table, the lanthanides. The lanthanides start with lanthanum, element fifty-seven, and their proper home on the table baffled and bedeviled chemists well into the twentieth century. Their buried electrons cause the lanthanides to clump together in frustrating ways; sorting them out was like unknotting kudzu or ivy. Spectroscopy also stumbled with lanthanides, since even if scientists detected dozens of new bands of color, they had no idea how many new elements that translated to. Even Mendeleev, who wasn’t shy about predictions, decided the lanthanides were too vexed to make guesses about. Few elements beyond cerium, the second lanthanide, were known in 1869. But instead of chiseling in more “ekas,” Mendeleev admitted his helplessness. After cerium, he dotted his table with row after row of frustrating blanks. And later, while filling in new lanthanides after cerium, he often bungled their placement, partly because many “new” elements turned out to be combinations of known ones. It’s as if cerium was the edge of the known world to Mendeleev’s circle, just like Gibraltar was to ancient mariners, and after cerium they risked falling into a whirlpool or draining off the edge of the earth.
Sam Kean Page 5
