Periodic Tales
Page 34
If all the senses are alert, a vast range of diagnostic information may follow from this apparently crude process. If the user has the breath to sustain the flow of air for ten or fifteen minutes to allow the sampled mineral to come to red heat, the colour of the flame may change repeatedly as different metallic elements are vaporized from it (the reason why the airway is bent is so that the user gets a clear view of the point where the flame strikes the mineral). The smell of the vapours can confirm the presence of non-metal ingredients such as sulphur, selenium and tellurium. Even the sound the mineral makes may be significant, with a crackling noise, for example, being characteristic of chemically bound water being freed from the sample.
The blow-pipe seems to me to express the essence of what Anders describes to me as Sweden’s characteristically ‘boring good chemistry’. Even the scientists may have been bored at times, sweating and puffing in frustration over unreadable minerals, dissolving them up to produce an endless succession of almost indistinguishable salts. It is a world that seems far from the miraculous gold and copper, amber and jewels, that scintillate through the mythology of this land. I wonder what colourful flames of hope must have danced at the back of their minds as these men performed their inexorable experiments. This was science of the green-fingered kind that relies on crafts-manlike skill, immense patience and intimate familiarity with its raw materials. It was these qualities, more than mercurial brilliance or extravagant equipment, that explained the discovery of so many of the elements in this north-eastern extremity of the European continent. These qualities, and of course the prodigal abundance of the soil.
Europium Union
The rare earths are not rare, but they are unsung. This group of elements to which so many of the Swedish discoveries belong populates a row of the periodic table which is usually shown dangling below the rest of the table like a ‘vacancies’ notice slung below a motel sign. Its members are: scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium. And, rare though they are not, you can be easily forgiven for never having heard of a single one of them.
Nor are they really gritty ‘earths’: all are middleweight metals. It is only because they for so long resisted extraction from their oxide ores that they earnt this general label. Recalcitrance may be the rare earths’ main unifying characteristic. In other respects, their properties are finely differentiated; indeed it is a matter of chemical semantics as to whether some of them–scandium and yttrium at the beginning of the sequence, and lutetium at the end–even belong on the list at all.
In almost every case, the isolation of the rare earths–from yttrium in 1794 to promethium in 1945–was a punishing grind. These discoveries do have the distinction, however, that they were made (apart from the anomalous radioactive promethium) by thoroughgoing chemists. They were not dependent upon some unique technology closer to physics as was the case with some other groups of elements–the alkali metals discovered electrolytically by Davy, Ramsay’s inert gases glowing in their discharge tubes, the transuranium elements thrown together in the Berkeley particle accelerator. The separation of the rare earths was chemistry all the way. The typical procedure was to dissolve an ore in acid to form a solution containing a mixture of salts. This was then slowly evaporated so that the salt of each element crystallized out in turn, while the overlying liquid retained others in solution. Careful repetition of this process–sometimes thousands of times–enabled chemists eventually to separate these very similar substances one from another, and from them then to isolate the new elements at their heart. It was, as one chemical historian drily remarks, ‘an enormous undertaking which would have difficulty attracting grant support today’.
Monotonous as it undoubtedly was, this long-running project was heaven to a particular type of experimental mind. The Swede Carl Mosander boasted of his ignorance of chemical theory, and showed exactly how unimportant it was by discovering more rare earths than anybody else by dint of sheer hours spent at the laboratory bench. There is a definite rustle of the anorak about these elements. With the hindsight of established scientific knowledge, it might be easier to crystallize their stories in words than it was to crystallize the elements themselves, but it would quite probably be just as tedious as the original exercise. So I shall not spend time on all of them, but rather single out one or two as representative of the set. The differences between them are slight in any case. They behave in generally similar ways and do similar things. Some of these things are useful–rare earths are widely if sparingly employed in ceramic glazes, fluorescent lamps, television screens, lasers, alloys and refractory materials–but the matter of choosing which one of them to use in many of these applications is, if not entirely inconsequential, then at least somewhat arbitrary. Not always, however. Occasionally, one of these rare earth elements recommends itself for the job above all the others.
If you take a €5 note and hold it under an ultraviolet light, the dull yellow stars that slice through the Classical arch on the front face of the note suddenly glow an intense red. On the reverse, a three-tiered Roman bridge appears to float in a ghostly greenish light above a river of indigo. This light comes from special inks incorporated into the notes in order to make them difficult to counterfeit, which are excited to luminescence by the powerful ultraviolet irradiation.
The exact nature of the chemical compounds used is of course kept secret by the European banks. However, in 2002, just months after the euro went into circulation, a pair of Dutch chemists decided to amuse themselves by performing an unusual spectroscopic analysis. Freek Suijver and Andries Meijerink at the University of Utrecht shone ultraviolet light on to euro notes and recorded the exact colour tones of visible light they emitted as a result. From this they were able to declare that the red light was due to ions of the rare earth element europium bound in a complex with two acetone-like molecules. They were less sure about the other colours, but speculated that the green might be due to even more elaborate ions involving europium combined with strontium, gallium and sulphur, and the blue to a europium complex with barium and aluminium oxides. They suspended their enquiries at this point, warning others who might be tempted to follow them that ‘any further investigation into what causes the luminescence of euro notes would constitute a violation of the law’.
But the unravelling of this little secret hardly gets to the nub of the matter. What we would really like to know is how it came to be decided that, of all the many inks that perform this trick, it should be inks based on europium that were chosen. It was, after all, a political decision in the end that a bank note issued in the name of European unity should have its mission slyly reinforced by impregnation with a chemical element named in celebration of the very same idea.
Europium metal is as soft as lead and must be stored under oil to stop it bursting into flame in air. It is the most reactive of the rare earths, and because of its urge to bind strongly to other elements it was among the last of them to be discovered.
In Art Nouveau Paris, Eugène-Anatole Demarçay began to suspect that samples he had acquired of samarium and gadolinium–the future europium’s next-door neighbours in the periodic table, discovered a decade or so before–might not be pure. Demarçay was a gaunt, severe-looking man whose chief glory was his florid moustache. He spent his early career working in the laboratory of a noted Paris perfumer, but soon went freelance and acquired renown as a spectroscopist–he could read the spectrum of a substance like ‘the score of an opera’, according to a contemporary. (The Curies would soon come to him to confirm their discovery of the elements polonium and radium.) Beginning in 1896, Demarçay prepared salts from his samarium and gadolinium samples and, through the exhaustive process of separation by crystallization, was able to isolate a new salt that was progressively richer in an unidentified substance. By 1901, he had amassed sufficient evidence to confirm his suspicion that this was a new element.
&nbs
p; Demarçay named his element for the entire continent of Europe, but he seems to have left no account of why he did so. His choice ran conspicuously against the contemporary trend of naming new elements after nation states. Not long before, Mosander in Stockholm and various others at the University of Uppsala had seen to it that a clutch of new elements were given names after places in Sweden. Gallium was named for France in 1875; germanium for Germany in 1886. Freshest of all in the memory for Demarçay was the Curies’ discovery of polonium in 1898, in which he had assisted. Perhaps all this nationalistic fervour was reason enough to cast an opposing vote.
In the Europe of 1901, prescient souls had long since begun to suspect that nation states might not be everlasting, with Frenchmen taking the boldest line. Victor Hugo was the first to speak of a ‘United States of Europe’, in 1848. The Breton philosopher Ernest Renan dared to ask in a famous lecture given in 1882 at the Sorbonne ‘What is a nation?’ and to imagine that ‘They will be replaced, in all probability, by a European confederation.’ This cosmopolitan spirit was evident at the Paris Universal Exposition of 1900, where more than fifty million people came to see forty nations drawn from all the continents exhibiting their wares–including specimens of the newly discovered rare earths.
Most European citizens, it has to be said, showed no sign of such ideals, and nationalism, having successfully delivered the unified new states of Italy and Germany, set off on a downward spiral based less on liberal highmindedness and more on ethnic and linguistic tribalism. Before long, it seemed that any group of self-asserting Ruritanians, to use the historian Eric Hobsbawm’s term, might suddenly decide to call themselves a nation. For Demarçay, a well-travelled autodidact accustomed to forming his own ideas, it must have been easy to resist the prevailing drift of nationalism and nail his colours to the mast through his chemical discovery. He would have surely welcomed the advent of the European Union and rejoiced to see his metal become part of its economic fabric.
The European Central Bank seems incapable of spreading this joy, however. It wilfully misunderstands my request to know who fought for europium and drearily asks for my ‘understanding that, for security reasons, we cannot comment on the chemical components of the euro banknote security features’. I know what the chemical components are; what I want to know now is who was the wag in the Brussels bureaucracy who made sure it was europium that was used. The bank requires its money to incorporate these security features, including raised print, metallic strips, watermarks and holograms, but does not actually print the stuff itself, and therefore does not specify that europium or any other particular material must be used for the luminescent dyes. So others may have been responsible in any case. However, the leading printers of euro bank notes will tell me nothing either.
I reread Suijver and Meijerink’s paper and see that it contains a clue. Seeking confirmation of their europium revelation, they contacted the Dutch National Bank, and were eventually put in touch with a researcher there. During the course of their conversation, the bank employee accidentally let slip something that jogged a memory in the Utrecht chemists. ‘A few years earlier he and a colleague visited our laboratory,’ Meijerink remembers. ‘During his visit we were able to supply him with a great deal of information about luminescent materials. Not surprisingly, he could not give us much information.’ So were the Utrecht chemists actually responsible for planting the idea of using europium in the first place? Did they simply stage their analytical ‘discovery’ in order to lay a false scent, or did they do it because they couldn’t resist claiming their own paternity, as it were, of the europium dyes in the euro? Or, alternatively, was it the mysterious visiting bankers who had the brainwave, bowing to fate when they heard that an element called europium was one of those that would be suitable for the job? For now, nobody seems to want to claim this inspired decision as their own.
Auerlicht
The girl is naked from the waist up; and from there down she is draped only in the lightest gauze. She is kneeling, with her head cocked to one side, and smiles naughtily out from beneath her brunette curls. In her right hand she appears to hold a dazzling halo of white light, at the centre of which an even brighter light shines out–‘appears’ because the light has no obvious source or connection; it is pure illumination. She grips the stem of a large sunflower for support and is framed by vigorous tendrils of other growth. Set to one side in front of the plane of the picture–it would be anachronistic within it–is a standard gas street lamp. The message becomes clear. This vestal virgin is holding forth the promise of a new light, like the light of the sun, that will brighten the world.
Giovanni Mataloni’s 1895 poster advertised the improved gas lighting of the Brevetto Auer company of Rome (‘guardarsi dalli contraffazioni’–beware of imitations). It was one of hundreds of similar images that appeared in cities across Europe and America around the turn of the century. Full-colour illustrated posters were the latest fashion in advertising, and no field of commerce was more assiduous in seeking the public’s favour than the fast-expanding domestic lighting industry, where gas and electricity vied ceaselessly with rival innovations.
The breakthrough that enabled gas to maintain its advantage over the newfangled electric lighting for a little longer during the closing years of the nineteenth century was made by Carl Auer, later the Baron von Welsbach, a Viennese who had completed his studies in Heidelberg with Robert Bunsen, long the guru of European chemists. On his arrival in Heidelberg in 1880, Auer showed the great man a modest collection of rare earth mineral specimens that he had amassed, and Bunsen set him to work analysing them, laughing off Auer’s protests that the quantities were insufficient. This project set the course of his career; and the rare earths would make his fortune. Auer’s annus mirabilis came in 1885 back in Vienna, when he succeeded in separating the supposed element didymium into two true elements, which were duly named praseodymium and neodymium. Their green and pink compounds make them attractive for use in ceramic wares and in tinted glass for protective eyewear.
Auer was not content merely to add to the number of the rare earths. In his Heidelberg days, he had marvelled at Bunsen’s already famous burner, with its tunable flame that could be adjusted to simmer or roast. He had noticed how, when turned up high, the bunsen burner flame would cause his rare earth ores to glow brightly with their own light. He began to explore this phenomenon with different combinations of metal oxides. It was well known that a flame set against a piece of lime (calcium oxide) will produce the incandescence known as limelight. Auer’s investigation included the oxides of magnesium and beryllium, both closely related to lime, as well as those of his rare earths and other elements.
Gas lighting was well established in streets and homes by the mid nineteenth century, but the light it shed was limited by the luminosity of the flame it produced, which depended in turn on the mixture of hydrocarbons being burnt. Candles and oil lamps gave a brighter light than gas, but only gas could be supplied continuously. Auer believed that a lamp design in which his rare earth oxides were positioned close to the gas flame might yield a brighter light. Over a period of several years, he soaked sleeves of cotton mesh in different mixtures of rare earth and other salts. Once dried, these sleeves or mantles, now stiff with encrusted oxide, were placed around the flame, which burnt away the fabric to leave a brittle lace of the refractory oxide. This would then glow brightly in the heat of the flame.
Little was known about the properties of many of the oxides, and still less about how they behaved in combination, so there was no way of predicting which composition would produce a white incandescence. Auer first patented a gas light with a mantle made of a mixture of magnesium, lanthanum and yttrium oxides in 1885, but its fragility and sickly green light meant that it remained unpopular. However, by 1891, he found that thorium and cerium oxides mixed in the proportions of ninety-nine to one gave a satisfactory white light (thorium is not a rare earth but is the heavier–and, unknown then, radioactive–cousin of cerium). Mantle
s made of this material were more sturdy and quickly caught on. Unusually for a scientist, Auer was an astute businessman, and his name soon became more widely known even than Bunsen’s. For while the bunsen burner had its place in the laboratory, the bright new Auerlicht, as it was known, was of utility to all, and was rapidly distributed across a grateful continent by various Auer companies. Some 90,000 Auer mantles were sold in Vienna and Budapest alone in 1892; twenty years later, annual production stood at 300 million units.
It can have done no harm to the inventor’s prospects that Auer, a variant of the prefix Ur-, is an archaic German word for the dawn. At the exact moment when the first of Auer’s bright gas lamps was lit outside the Opern Café in Vienna on 4 November 1891, Auer’s countryman Gustav Mahler, no stranger to the place, was composing a song that would be incorporated into his second symphony, called ‘Urlicht’–primordial light.
Auer clearly acquired a taste for appending his name to his inventions. He followed up the success of the gas mantle with an osmium electric filament, the Auer-Oslight–even as he perfected his gas mantle, Auer was hedging his technological bets by experimenting with materials for the electric lamps that he already suspected might one day replace them. In 1903, he patented an alloy of cerium and iron–he called it Auermetall No. 1–that produced sparks when struck. ‘Flints’ of this material are still used in cigarette lighters today. Everything Auer touched seemed to turn to light. No wonder that on the occasion of his ennoblement he chose for his coat of arms the motto ‘Plus Lucis’–more light.