Sodium was much cheaper and not quite as violent as potassium, so I decided to look at its action outdoors. I obtained a good-sized lump of it – about three pounds – and made an excursion to the Highgate Ponds in Hampstead Heath with my two closest friends, Eric and Jonathan. When we arrived, we climbed up a little bridge, and then I pulled the sodium out of its oil with tongs and flung it into the water beneath. It took fire instantly and sped around and around on the surface like a demented meteor, with a huge sheet of yellow flame above it. We all exulted – this was chemistry with a vengeance!
There were other members of the alkali metal family even more reactive than sodium and potassium, metals like rubidium and cesium (there was also the lightest and least reactive, lithium). It was fascinating to compare the reactions of all five by putting small lumps of each into water. One had to do this gingerly, with tongs, and to equip oneself and one’s guests with goggles: lithium would move about the surface of the water sedately, reacting with it, emitting hydrogen, until it was all gone; a lump of sodium would move around the surface with an angry buzz, but would not catch fire if a small lump was used; potassium, in contrast, would catch fire the instant it hit the water, burning with a pale mauve flame and shooting globules of itself everywhere; rubidium was still more reactive, spluttering violently with a reddish violet flame; and cesium, I found, exploded when it hit the water, shattering its glass container. One never forgot the properties of the alkali metals after this.
Before Humphry Davy’s discovery of sodium and potassium, metals were thought of as hard and dense and infusible, and here were ones as soft as butter, lighter than water, very easily melted, and with a chemical violence, an avidity to combine beyond anything ever seen. (Davy was so startled by the inflammability of sodium and potassium, and their ability to float on water, that he wondered whether there might not be deposits of these beneath the earth’s crust, which, exploding upon the impact of water, were responsible for volcanic eruptions.) Could the alkali metals, indeed, be seen as true metals? Davy addressed this question just two months later:
The great number of philosophical persons to whom this question has been put have answered in the affirmative. They agree with metals in opacity, lustre, malleability, conducting powers as to heat and electricity, and in their qualities of chemical combination.
After his success in isolating the first alkali metals, Davy turned to the alkaline earths and electrolyzed these, and within a few weeks he had isolated four more metallic elements – calcium, magnesium, strontium, and barium – all highly reactive and all able to burn, like the alkali metals, with brilliantly colored flames. These clearly formed another natural group.
Pure alkali metals do not exist in nature; nor do the elemental alkaline earth metals – they are too reactive and instantly combine with other elements.[23] What one finds instead are simple or complex salts of these elements. While salts tend to be nonconducting when crystalline, they can conduct an electric current well if dissolved in water or melted; and will indeed be decomposed by an electric current, yielding the metallic component of the salt (e.g., sodium) at one pole, and the nonmetallic element (e.g., chlorine) at the other. This implied to Davy that the elements were contained in the salt as charged particles – why else should they be attracted to the electrodes? Why did sodium always go to one electrode and chlorine to the other? His pupil, Faraday, was later to call these charged particles of an element ‘ions’, and further distinguished the positive and negative ones as ‘cations’ and ‘anions.’ Sodium, in its charged state, was a strong cation, and chlorine, in its charged state, one of the strongest anions.
For Davy, electrolysis was a revelation that matter itself was not something inert, held together by ‘gravity’, as Newton had thought, but was charged and held together by electrical forces. Chemical affinity and electrical force, he now speculated, were one and the same. For Newton and Boyle there had been only one force, universal gravity, holding not only the stars and planets together, but the very atoms of which they were composed. Now, for Davy, there was a second cosmic force, a force no less potent than gravity, but operating at the tiny distances between atoms, in the invisible, almost unimaginable, world of chemical atoms. Gravity, he felt, might be the secret of mass, but electricity was the secret of matter.
Davy loved to conduct experiments in public, and his famous lectures, or lecture-demonstrations, were exciting, eloquent, and often literally explosive. His lectures moved from the most intimate details of his experiments to speculation about the universe and about life, delivered in a style and with a richness of language that nobody else could match.[24] He soon became the most famous and influential lecturer in England, drawing huge crowds that blocked the streets whenever he lectured. Even Coleridge, the greatest talker of his age, came to Davy’s lectures, not only to fill his chemical notebooks, but ‘to renew my stock of metaphors.’
There still existed, in the early nineteenth century, a union of literary and scientific cultures – there was not the dissociation of sensibility that was so soon to come – and Davy’s period at Bristol saw the start of a close friendship with Coleridge and the Romantic poets. Davy himself was writing (and sometimes publishing) a good deal of poetry at the time; his notebooks mix details of chemical experiments, poems, and philosophical reflections all together; and these did not seem to exist in separate compartments in his mind.[25]
There was an extraordinary appetite for science, especially chemistry, in these early, palmy days of the Industrial Revolution; it seemed a new and powerful (and not irreverent) way not only of understanding the world but of moving it to a better state. Davy himself seemed to embody this new optimism, to be at the crest of a vast new wave of scientific and technological power, a power that promised, or threatened, to transform the world. He had discovered half a dozen elements, as a start, suggested new forms of lighting, made important innovations in agriculture, and developed an electrical theory of chemical combination, of matter, of the universe itself – all before the age of thirty.
In 1812, Davy, the son of a wood-carver, was knighted for his services to the empire – the first scientist so honored since Isaac Newton. In the same year he married, but this did not seem to distract him from his chemical researches in the least. When he set out for an extended honeymoon on the Continent, determined to do experiments and meet other chemists wherever he went, he brought along a good deal of chemical apparatus and various materials (‘an airpump, an electrical machine, a voltaic battery… a blow-pipe apparatus, a bellows and forge, a mercurial and water gas apparatus, cups and basins of platinum and glass, and the common reagents of chemistry’) – as well as his young research assistant, Michael Faraday. (Faraday, then in his early twenties, had followed Davy’s lectures raptly, and wooed Davy by presenting him with a brilliantly transcribed and annotated version of them.) In Paris, Davy had a visit from Ampere and Gay-Lussac, who brought with them, for his opinion, a sample of a shiny black substance obtained from seaweed, with the remarkable property that when heated, it did not melt, but turned at once into a vapor of a deep violet color. A year earlier, Davy had identified Scheele’s greenish yellow ‘muriatic acid air’ as a new element, chlorine. Now, with his enormous feeling for the concrete[26] and his genius for analogy, Davy sensed that this odoriferous, volatile, highly reactive black solid might be another new element, an analog of chlorine, and soon confirmed that it was. He had already tried, unsuccessfully, to isolate Lavoisier’s ‘fluoric radical’, realizing that the element it contained, fluorine, would be a lighter and even more active analog of chlorine. But he also felt that the gap in physical and chemical properties between chlorine and iodine was so great as to suggest the existence of an intermediate element, as yet undiscovered, between them. (There was indeed such an element, bromine, but it fell not to Davy to discover it, but to a young French chemist, Balard, in 1826. Liebig himself, it turned out, had actually prepared the fuming brown liquid element before this, but misidentified it as ‘liquid iodine chloride’; after hearing of Balard’s discovery, Liebig put the bottle in his ‘cupboard of mistakes.’)
23
The enormous chemical reactivity of potassium made it a powerful new instrument in isolating other elements. Davy used it himself, only a year after he discovered it, to obtain the element boron from boric acid, and he tried to obtain silicon by the same method (Berzelius succeeded here, in 1824). Aluminium and beryllium, a few years later, were also isolated through the use of potassium.
24
Mary Shelley, as a child, was enthralled by Davy’s inaugural lecture at the Royal Institution, and years later, in
25
David Knight, in his brilliant biography of Davy, speaks of the passionate parallelism, the almost mystical sense of affinity and rapport, that Coleridge and Davy felt, and how the two planned, at one point, to set up a chemical laboratory together. In his book
Water and flame, the diamond, the charcoal… are convoked and fraternized by the theory of the chemist… It is the sense of a principle of connection given by the mind, and sanctioned by the correspondency of nature… If in a
Coleridge was not the only writer to ‘renew his stock of metaphors’ with images from chemistry. The chemical term
26
The great chemist Justus von Liebig wrote powerfully about this feeling in his autobiography:
[Chemistry] developed in me the faculty, which is peculiar to chemists more than to other natural philosophers, of thinking in terms of phenomena; it is not very easy to give a clear idea of phenomena to anyone who cannot recall in his imagination a mental picture of what he sees and hears, like the poet and artist, for example… There is in the chemist a form of thought by which all ideas become visible in the mind as the strains of an imagined piece of music…
The faculty of thinking in phenomena can only be cultivated if the mind is constantly trained, and this was effected in my case by my endeavouring to perform, so far as my means would allow me, all the experiments whose description I read in the books… I repeated such experiments… a countless number of times,… till I knew thoroughly every aspect of the phenomenon which presented itself… a memory of the sense, that is to say of the sight, a clear perception of the resemblance or differences of things or of phenomena, which afterwards stood me in good stead.