Unstable Endings

In 1896, Henri Becquerel (1852–1908) had discovered, by chance, the phenomenon of radioactivity, after he found that uranium salts left on top of covered photographic plates produced an image on the plates when they were later developed. Soon afterwards, thorium was also found to be radioactive. In 1898 Marie Curie (née Sklodovska) realized that certain minerals were more ‘radioactive’ (a term she first introduced) than could be rationalized by the amount of uranium or thorium that they contained. She guessed that they might contain trace amounts of an even more radioactive element, and during the long purification process, she eventually realized that two such elements were present. The naming of the first of these, discovered in July 1898, is described by her daughter Eve Curie in her biography of her mother: . . . ‘You will have to name it,’ Pierre said to his young wife, in the same tone as if it were a question of choosing a name for little Irène [their first daughter]. The one-time Mlle Sklodovska reflected in silence for a moment. Then, her heart turning toward her own country which had been erased from the map of the world, she wondered vaguely if the scientific event would be published in Russia, Germany and Austria—the oppressor countries—and answered timidly: ‘Could we call it “polonium”?’ . . . Marie Curie named the element after her homeland, Poland, but the country did not exist as a separate entity at that time, and her choice was something of a political statement. The second element discovered by Marie and Pierre Curie was found to be millions of times more radioactive than uranium. This element they called ‘radium’ because of its intense radioactivity. Over three and a half years later, when they finally isolated a tenth of a gram of purified radium salts from tonnes of pitchblende ore, the Curies were delighted to find that the substance was spontaneously luminous. After the discovery that uranium and thorium were radioactive, in September 1899, Ernest Rutherford (1871–1937) made a further discovery: ‘In addition to this ordinary radiation, I have found that thorium compounds continuously emit radio-active particles of some kind, which retain their radio-active powers for several minutes.

The Salt Makers

This chapter looks at the elements from the penultimate group of the periodic table—the halogens (‘salt-formers’). We shall see that the first of these elements was discovered by Scheele during his investigations of the mineral pyrolusite. Lavoisier knew of the element but he failed to recognize it as such since he was convinced the gas had to contain oxygen and so must be a compound. It was left to Davy to prove that this was not so, which led to the English chemist naming this element that had been discovered (but not properly named) over thirty years before by the great Scheele. Davy’s choice was to influence the names given to all the members of this group, including the most recent member named in 2016. There are three common acids known as mineral acids, since they may all be obtained by heating combinations of certain minerals. Their modern names are nitric acid, sulfuric acid, and hydrochloric acid. Of these three, hydrochloric was probably the last to be discovered. Nitric and sulfuric acids were obtained in the thirteenth or early fourteenth centuries, but the earliest unambiguous preparation of relatively pure hydrochloric acid is from a hundred years later, in a manuscript from Bologna which translates as Secrets for Colour. It gives a curious recipe for a water to soften bones: ‘Take common salt and Roman vitriol in equal quantities, and grind them very well together; then distil them through an alembic, and keep the distilled water in a vessel well closed.’ As we saw in Chapter 3, ‘Roman vitriol’ is a hydrated metal sulfate, probably iron or copper sulfate; its mixture with salt, when heated, produces water and hydrogen chloride, which together form the acid solution. Later texts from the sixteenth and seventeenth centuries include similar methods to prepare this so-called spirit of salt, or ‘oyle of salt’. The first mentioned use, to soften bones, is indeed best achieved with hydrochloric acid, which readily dissolves the minerals from bone to leave only the organic matter largely intact. Leave a chicken bone in dilute hydrochloric acid for a few hours, and it may easily be bent without breaking.

Loadstones and Earths

Jöns Jacob Berzelius (1779–1848), discoverer of the elements selenium, thorium, cerium, and silicon and deviser of the chemical symbols we use today, was one of the last in a long list of Swedish mineralogists and chemists active during the eighteenth century. Berzelius himself regarded one of his predecessors, Axel Fredrik Cronstedt (1722–65), as the founder of chemical mineralogy. We met Cronstedt in Chapter 2 as the discoverer of the element nickel, isolated from the ore kupfernickel. But another of Cronstedt’s achievements was perhaps of even greater significance: his development of a classification of minerals based not on their physical appearances, as had been common up to this time, but on their chemical compositions. He first published his scheme anonymously in Swedish in 1758, but it was later translated into English as An Essay towards a System of Mineralogy. Cronstedt recognized four general classes of minerals: earths, bitumens, salts, and metals. As their name suggests, the bitumens were flammable substances that might dissolve in oil but not in water. The main difference between the salts and the earths was that the former, which included the ‘alcaline mineral salt’ natron, could be dissolved in water and recrystallized from it. The earths he defined as ‘those substances which are not ductile, are mostly indissoluble in water or oil, and preserve their constitution in a strong heat’. Cronstedt initially recognized nine different classes of earth. By the time of Torbern Bergman (1735–84), these had been reduced to five which ‘cannot be derived from each other or from anything simpler’. Lavoisier and his collaborators included these five in their great work on nomenclature even though they suspected that, like soda and potash, they were most likely not simple substances, but species that contained new metals. In the 1788 English translation of the nomenclature these were called silice, alumina, barytes, lime, and magnesia. The first two eventually, in the early nineteenth century, yielded the elements silicon and aluminium. The word ‘silicon’ derives from the Latin ‘silex’ (meaning ‘flint’—a form of silicon dioxide), with the ending ‘-on’ reflecting its resemblance to the other non-metals carbon and boron.

Fire and Brimstone

Sulfur has long been associated with the fiery domain of hell, and with its god. In the fifteenth-century poem The Assembly of Gods, after describing Othea, the goddess of wisdom, the anonymous author continues with an account of the god of the underworld: . . . And next to her was god Pluto set Wyth a derke myst envyroned all aboute His clothynge was made of a smoky net His colour was both wythin & wythoute Full derke & dӯme his eyen grete & stoute Of fyre & sulphure all his odour waas That wo was me while I behelde his faas . . . Even more terrifying is the account from the Vatican Mythographers, in which Pluto is described as ‘an intimidating personage sitting on a throne of sulphur, holding the sceptre of his realm in his right hand, and with his left strangling a soul’. This association between sulfur and the fiery underworld is perhaps understandable given that the element is often found in the vicinity of volcanoes. In Mundus Subterraneus, one of many books written by the seventeenth-century polymath Athanasius Kircher (1602–80), the author describes a night-time visit to Vesuvius in the year 1638—just seven years after the great eruption of 1631. He tells us that after arriving at the crater, ‘I saw what is horrible to be expressed, I saw it all over of a light fire, with an horrible combustion, and stench of Sulphur and burning Bitumen. Here forthwith being astonished at the unusual sight of the thing; Methoughts I beheld the habitation of Hell; wherein nothing else seemed to be much wanting, besides the horrid fantasms and apparitions of Devils.’ Kircher believed that the volcanoes were fed by massive fires deep underground, as he tells us in the opening of his book: . . . That there are Subterraneous Conservatories, and Treasuries of Fire (even as well, as there are of Water, and Air, &c.) and vast Abysses, and bottomless Gulphs in the Bowels and very Entrals of the Earth, stored therewith, no sober Philosopher can deny; If he do but consider the prodigious Vulcano’s, or fire-belching Mountains; the eruptions of sulphurous fires not only out of the Earth, but also out of the very Sea; the multitude and variety of hot Baths every where occurring. . . .

‘H Two O’ to ‘O Two H’

It was not until the late eighteenth century—over a hundred years after the discovery of phosphorus—that it was appreciated that both phosphorus and sulfur were actually elements. Prior to this time, it was thought that all matter was made up of four so-called elements: earth, air, fire, and water. The realization that this was not so centred on understanding that the air is actually composed of a number of different gases, and in particular, understanding what happens when things burn. The discovery that water could be broken down into, or indeed synthesized from, two simpler elementary substances started a chemical revolution in France. The fruits of this revolution are embodied in the very names we now use for these two components, hydrogen and oxygen. However, the path to enlightenment was tortuous, lasting over 200 years. At its peak at the end of the eighteenth century, chemists fell into two distinct camps—those for the new French chemistry, and those against it. Several different names were given to the gases before ‘hydrogen’ and ‘oxygen’ triumphed. As it turns out, one of these names is still based on an incorrect theory, and it might have been more appropriate if the names hydrogen and oxygen had been swapped around. From the sixth century BC, the ancient Greek philosopher Thales taught that water was the primary matter from which all other substances were formed. Perhaps this idea came from water’s ready ability to form solid ice, ‘earth’, or vapours and mists, ‘airs’. Other philosophers thought the primary substance was air; others still, fire. It was less common for earth to be thought of in this way, possibly, as Aristotle later wrote, because it was too coarse-grained to make up these fluids. In the fifth century BC Empedokles brought the four ‘elements’ together—earth, air, fire, and water—and for many centuries it was thought that these made up everything around us.

Goblins and Demons

The belief that there were no more than seven metals persisted for hundreds of years, and it was not until the seventeenth century that the inconvenient, inescapable realization came that there were probably many more. I’ve already mentioned Barba’s report from 1640 about the new metal bismuth; it was one of a number of metals or metal-like species that began to be noticed in the sixteenth and seventeenth centuries. In his History of Metals from 1671, Webster begins Chapter 27: ‘Having now ended our Collections and Discourse of the seven Metals, vulgarly accounted so; we now come to some others, that many do also repute for Metals; and if they be not so, at least they are semi-Metals, and some of them accounted new Metals or Minerals, of that sort that were not known to the Ancients.’ In the chapter Webster speaks of antimony, arsenic, bismuth, cobalt, and zinc. While we now understand these as distinct elements, earlier on there was great confusion, with the names being used for compounds rather than the elements themselves—and, furthermore, the different compounds and elements often being mistaken for each other. This makes unravelling their history all the more complicated. We’ll start with Barba’s ‘Mettal between Tin and Lead, and yet distinct from them both’: bismuth. The first mention of bismuth predates Barba’s reference by more than one hundred years. The name appears in its variant spelling, ‘wissmad’, in what is probably the very first book on mining geology. This was published around the turn of the sixteenth century and attributed to one Ulrich Rülein von Calw, the son of a miller who entered the University of Leipzig in 1485. Ulrich mentions in passing that bismuth ore can be an aid to finding silver, since the latter is often found beneath it. Consequently, miners called bismuth ‘the roof of silver’. As Webster later put it in his History of Metals, ‘The ore from whence it is drawn . . . is also more black, and of a leaden colour, which sometimes containeth Silver in it, from whence in the places where it is digged up, they gather that Silver is underneath, and the Miners call it the Cooping, or Covering of Silver.’

Heavenly Bodies

We don’t know for sure where the names of the longest-known elements come from, but a connection was made early on between the most ancient metals and bodies visible in the heavens. Figure 1 shows an engraving from a seventeenth-century text with the title ‘The Seven Metals’ (translated from the Latin). It isn’t immediately obvious how the image is meant to depict seven metals until we explore the connections between alchemy and astronomy. However strange such associations seem to us now, we shall see that new elements named in the eighteenth, nineteenth, twentieth, and twenty-first centuries have had astronomical origins. We can’t properly understand why some of the more recent elements were named as they were without first understanding these earlier historical connections. As we look into the night sky, the distant stars remain in their same relative positions and seem to move gracefully together through the heavens. Of course, we now know that it is the spinning Earth that gives this illusion of movement. The imaginations of our ancestors joined the bright dots to pick out fanciful patterns such as the Dragon, the Dolphin, or the Great Bear—the latter being more often known today (with rather less imagination) as the Big Dipper, the Plough, or even the Big Saucepan. But, while these patterns, the constellations, remained unchanging over time, there were seven objects, or ‘heavenly bodies’, that seemed to move across the skies with a life of their own. They were given the name ‘planet’, which derives from the Greek word for ‘wanderer’ (‘planetes asteres’, ‘πλάνητες ἀστέρες’, meaning ‘wandering stars’). These seven bodies were the Sun, the Moon, Mercury, Venus, Mars, Jupiter, and Saturn, all of which were documented by the Babylonians over three thousand years ago. Until the sixteenth century, the most commonly held view was that the Earth was at the centre of the Universe and that the seven bodies revolved around the Earth, with the relative orbits shown schematically in Figure 2.

From under the Nose

This chapter looks at the elements in the final group of the periodic table—those elements known as the rare or noble gases. We shall see how their discovery in the atmosphere in the 1890s dates back to an observation first made by the meticulous Henry Cavendish over one hundred years earlier. This led to the unexpected discovery of an entire group of elements that needed to be added to the earliest periodic tables; and remarkably, one man was to dominate all these discoveries. One of Isaac Newton’s classic experiments was using a glass prism to split a beam of sunlight into a spectrum to show that white light is actually a mixture of all the colours of the rainbow. In 1802, William Hyde Wollaston (1766–1828), discoverer of the elements palladium and rhodium, modified the experiment by using a thin slit to admit the sunlight instead of the circular hole that Newton used. He subsequently discovered that the solar spectrum was not completely seamless, but actually contained a number of fine dark lines, now known as Fraunhofer lines. They get their name from Joseph Fraunhofer (1787–1826), who became the most skilled worker of glass and producer of lenses of the time. Using his highest-quality optical lenses, Fraunhofer observed that the solar spectrum had many dark lines; he mapped out over five hundred of these and designated the most distinct ones with the capitals letters A to H, with A and B being in the red region of the spectrum, and G and H in the violet. He used these as calibration lines in the development of better glasses for his optical instruments, and to demonstrate the superiority of his products compared with those of his competitors. The nature of the dark lines was not properly understood until the work of the German physicist Gustav Kirchhoff (1824–1997), who, in a beautiful collaboration with his colleague the chemist Robert Bunsen (1811–99), developed one of the most important analytical techniques still used in chemistry. It was with this technique that they discovered two new elements, and paved the way for others to discover many more.

Of Ashes and Alkalis

The name azote, proposed by Lavoisier and his colleagues, did not gain wide acceptance; nitrogen, meaning ‘nitre-former’, is the name now familiar to us. Modern chemists understand ‘nitre’ to mean ‘potassium nitrate’, one of the key ingredients of gunpowder, containing the elements potassium, oxygen, and nitrogen. However, although it dates back to antiquity, the name nitre initially referred to a completely different compound containing no nitrogen at all. It is the Latinized name, natrium, derived from this original use, that gives us the modern chemical symbol Na, for the element Humphry Davy named sodium. Travellers to modern-day northern Egypt may find themselves in a region known as the Nitrian Desert, or the Natron Valley—Wadi El Natrun. Here, ancient Egyptians would collect crude salt mixtures from certain lakes and use them for a variety of purposes, such as cleaning, making glass, embalming, and the preparation of medicines. The Egyptian word for the salt may be written ‘nṭry’ or ‘ntr’ (‘neter’), and it has survived for over three thousand years through variations including ‘neter’ (Hebrew), ‘nitron’ (Greek), ‘nitrum’(Latin), and more modern modifications ‘nether’, ‘niter’, ‘nitre’, ‘natrun’, and ‘natron’. Bartholomeus Anglicus, the thirteenth-century monk and author of De proprietatibus rerum (‘On the Properties of Things’), quotes Isidore of Seville from five hundred years earlier saying: ‘Nitrum hath ye name of the countrey of Nitria that is in Aegypt. Thereof is medicine made, & there with bodies and clothes be cleansed and washed.’ Whether the salt was actually named after the region or vice versa is not clear. Although its composition varied enormously, what distinguished nitre from common salt was the presence of significant proportions of sodium carbonate and sodium bicarbonate (sodium hydrogen carbonate). In addition to these carbonates, analyses of ancient samples, including that used in the embalming of the pharaoh Tutankhamun, who died in 1352 BC, also reveal large proportions of common salt (sodium chloride), sodium sulfate, and silica (silicon dioxide), with smaller proportions of calcium and magnesium carbonates and other minor impurities.