Chemistry as a true science, I read, made its first emergence with the work of Robert Boyle in the middle of the seventeenth century. Twenty years Newton’s senior, Boyle was born at a time when the practice of alchemy still held sway, and he still maintained a variety of alchemical beliefs and practices, side by side with his scientific ones. He believed that gold could be created, and that he had succeeded in creating it (Newton, also an alchemist, advised him to keep silent about this). He was a man of immense curiosity (of ‘holy curiosity,’ in Einstein’s phrase), for all the wonders of nature, Boyle felt, proclaimed the glory of God, and this led him to examine a huge range of phenomena.
He examined crystals and their structure, and was the first to discover their cleavage planes. He explored color, and wrote a book on this which influenced Newton. He devised the first chemical indicator, a paper soaked with syrup of violets which would turn red in the presence of acid fluids, green with alkaline ones. He wrote the first book in English on electricity. He prepared hydrogen, without realizing it, by putting iron nails in sulphuric acid. He found that although most fluids contracted when frozen, water expanded. He showed that a gas (later realized to be carbon dioxide) was evolved when he poured vinegar on powdered coral, and that flies would die if kept in this ‘artificial air.’ He investigated the properties of blood and was interested in the possibility of blood transfusion. He experimented with the perception of odors and tastes. He was the first to describe semipermeable membranes. He provided the first case history of acquired achromatopsia, a total loss of color vision following a brain infection.
All these investigations and many others he described in language of great plainness and clarity, utterly different from the arcane and enigmatic language of the alchemists. Anyone could read him and repeat his experiments; he stood for the openness of science, as opposed to the closed, hermetic secrecy of alchemy.
Although his interests were universal, chemistry seemed to hold a very special appeal for him (even as a youth he called his own chemical laboratory ‘a kind of Elysium’). He wished, above all, to understand the nature of matter, and his most famous book, The Sceptical Chymist, was written to debunk the mystical doctrine of the Four Elements, and to unite the enormous, centuries-old empirical knowledge of alchemy and pharmacy with the new, enlightened rationality of his age.
The ancients had thought in terms of four basic principles or elements – Earth, Air, Fire, and Water. I think these were pretty much my own categories as a five-year-old child (though metals may have made a special, fifth category for me), but I found it less easy to imagine the Three Principles of the alchemists, where ‘Sulphur’ and ‘Mercury’ and ‘Salt’ meant not ordinary sulphur and mercury and salt but ‘philosophical’ Sulphur, Mercury, and Salt: Mercury conferring luster and hardness to a substance, Sulphur conferring color and combustibility, Salt conferring solidity and resistance to fire.
Boyle hoped to replace these ancient, mystical notions of Elements and Principles with a rational and empirical one, and provided the first modern definition of an element:
I now mean by Elements [he wrote]…certain Primitive and Simple, or perfectly unmingled bodies; which not being made up of any other bodies, or of one another, are the ingredients of which all those call’d perfectly mixd Bodies are immediately compounded, and into which they are ultimately resolved.
But since he gave no examples of such ‘Elements’ or of how their ‘unmingledness’ was to be demonstrated, his definition seemed too abstract to be useful.
Though I found The Sceptical Chymist unreadable, I was delighted by Boyle’s 1660 New Experiments, where he set out, with an enchanting vividness and a wealth of personal detail, more than forty experiments using his ‘Pneumatical Engine’ (an air pump that his assistant Robert Hooke had invented), with which he could evacuate much of the air from a closed vessel.«13» In these experiments Boyle effectively demolished the ancient belief that air was an ethereal, all-pervading medium by showing that it was a material substance with physical and chemical properties of its own, that it could be compressed or rarefied or even weighed.
Evacuating the air from a closed vessel that contained a lit candle or a glowing coal, Boyle found that these ceased to burn as the air was rarefied, although the coal would begin to glow again if air was reintroduced – thus showing that air was necessary for combustion. He showed, too, that various creatures – insects, birds, or mice – would become distressed or die if the air pressure was reduced, but might revive when air was readmitted to the vessel. He was struck by this similarity between combustion and respiration.
He investigated whether a bell could be heard through a vacuum (it could not), whether a magnet could exert power through a vacuum (it could), whether insects could fly in a vacuum (this he could not judge, because the insects ‘swooned’ with reduction of air pressure), and he examined the effects of reduced air pressure on the glowing of glowworms (they glowed less brightly).
I loved reading about these experiments and tried repeating some of them for myself – our Hoover was a good substitute for Boyle’s air pump. I loved the playfulness of the whole book, so different from the philosophical dialogues in The Sceptical Chymist. (Indeed, Boyle himself was not unaware of this: ‘I disdain not to take notice even of ludicrous experiments, and think that the plays of boys may sometimes deserve to be the study of philosophers.’)
Boyle’s personality appealed to me greatly, as did his omnivorous curiosity, his fondness for anecdote, and his occasional puns (as when he wrote that he preferred to work on things ‘luciferous rather than lucriferous’). I could imagine him as a person, and a person I would like, despite the gulf of three centuries between us.
Antoine Lavoisier, born almost a century after Boyle, would become known as the real founder, the father, of modern chemistry. There was already a huge amount of chemical knowledge, chemical sophistication, before his time, some of it bequeathed by the alchemists (for it was they who pioneered the apparatus and techniques of distillation and crystallization and a range of chemical procedures), some of it by apothecaries, and much of it, of course, by early metallurgists and miners.
Yet although a multitude of chemical reactions had been explored, there was no systematic weighing or measurement of these reactions. The composition of water was unknown, as was the composition of most other substances. Minerals and salts were classified by their crystalline form, or other physical properties, rather than their constituents. There was no clear notion of elements or compounds.
There was, moreover, no overall theoretical framework in which chemical phenomena could be placed, only the somewhat mystical theory of phlogiston, which was supposed to explain all chemical transformations. Phlogiston was the principle of Fire. Metals were combustible, it was supposed, because they contained some phlogiston, and when they were burned, the phlogiston was released. When their earths were smelted with charcoal, conversely, the charcoal donated its phlogiston and reconstituted the metal. Thus a metal was a sort of composite or ‘compound’ of its earth, its calx, and phlogiston. Every chemical process – not only of smelting and calcination, but the actions of acids and alkalis, and the formation of salts – could be attributed to the addition or removal of phlogiston.
It was true that phlogiston had no visible properties, could not be bottled, demonstrated, or weighed – but after all, was this not equally true of electricity (another great source of mystery and fascination in the eighteenth century)? Phlogiston had an instinctive, poetic, mythic appeal, making fire at once a material and a spirit. But for all its metaphysical roots, the phlogiston theory was the first specifically chemical theory (as opposed to the mechanical, corpuscular one that Boyle had envisaged in the 1660s); it attempted to account for chemical properties and reactions in terms of the presence or absence, or transference, of a specific chemical principle.
It was into this half-metaphysical, half-poetic atmosphere that Lavoisier – hardheaded, keenly analytical and logical, a child of the
Enlightenment and an admirer of the Encyclopedists – came of age in the 1770s. By the age of twenty-five, Lavoisier had already done pioneering geological work, shown great chemical and polemical skill (he had written a prizewinning essay on the best means of illuminating a city at night, as well as a study of the setting and binding of plaster of Paris), and been elected to the Academy.«14» But it was in relation to the theory of phlogiston that his intellect and ambition became sharply focused. The idea of phlogiston seemed to him metaphysical, insubstantial, and the point of attack, he saw at once, lay in meticulous quantitative experiments with combustion. Did substances indeed decrease in weight when they burned, as one would expect if they lost their phlogiston? Common experience, indeed, suggested that this was so, that substances ‘burned away’ – a candle dwindled in size as it burned, organic substances charred and shriveled, sulphur and charcoal vanished completely, but this did not seem to be the case with regard to the burning of metals.
In 1772 Lavoisier read of the experiments of Guyton de Morveau, who had confirmed in experiments of exceptional precision and care that metals increased in weight when they were roasted in air.«15» How could this be reconciled with the notion that something – phlogiston – was lost in burning? Lavoisier found Guyton’s explanation – that phlogiston had ‘levity’ and buoyed up the metals that contained it – absurd. But Guyton’s impeccable results nonetheless incited Lavoisier as nothing had before. It was, like Newton’s apple, a fact, a phenomenon, that demanded a new theory of the world.
The work before him, he wrote, ‘seemed to me destined to bring about a revolution in physics and in chemistry. I have felt bound to look upon all that has been done before me merely as suggestive…like separate pieces of a great chain.’ It remained for someone, for him, he felt, to join all the links of the chain with ‘an immense series of experiments…in order to lead to a continuous whole’ and to form a theory.
While confiding this grandiose thought to his lab notebook, Lavoisier set to systematic experiments, repeating many of his predecessors’ work, but this time using a closed apparatus and meticulously weighing everything before and after the reaction, a procedure which Boyle, and even the most meticulous chemists of Lavoisier’s own time, had neglected. Heating lead and tin in closed retorts until they were converted to ash, he was able to show that the total weight of his reactants neither increased nor decreased during a reaction. Only when he broke open his retorts, allowing air to rush in, did the weight of the ash increase – and by exactly the same amount as the metals themselves had increased in being calcined. This increase, Lavoisier felt, must be due to the ‘fixation’ of air, or some part of it.
In the summer of 1774, Joseph Priestley, in England, found that when he heated red calx of mercury (mercuric oxide) it gave off an ‘air’ which, to his amazement, seemed even stronger or purer than common air.
A candle burned in this air [he wrote] with an amazing strength of flame; and a bit of red hot wood crackled and burned with a prodigious rapidity, exhibiting an appearance something like that of iron glowing with a white heat, and throwing out sparks in all directions.
Entranced, Priestley had investigated this further, and found that mice could live in this air four or five times longer than in ordinary air. And being thus convinced that his new ‘air’ was benign, he tried it himself:
The feeling of it to my lungs was not sensibly different from that of common air; but I fancied that my breast felt peculiarly light and easy for some time afterwards. Who can tell but that, in time, this pure air may become a fashionable article in luxury. Hitherto only two mice and myself have had the privilege of breathing it.
In October of 1774, Priestley went to Paris and spoke of his new ‘dephlogisticated air’ to Lavoisier. And Lavoisier saw in this what Priestley himself did not: the vital clue to what had perplexed and eluded him, the real nature of what was happening in combustion and calcination.«16» He repeated Priestley’s experiments, amplified, quantified, refined them. Combustion, it was now clear to him, was a process involving not the loss of a substance (phlogiston), but the combination of the combustible material with a part of atmospheric air, a gas, for which he now coined the term oxygen.«11»
Lavoisier’s demonstration that combustion was a chemical process – oxidation, as it could now be called – implied much else, and was for him only a fragment of a much wider vision, the revolution in chemistry that he had envisaged. Roasting metals in closed retorts, showing that there was no ghostly weight gain from ‘particles of fire’ or weight loss from loss of phlogiston, had demonstrated to him that there was neither creation nor loss of matter in such processes. This principle of conservation, moreover, applied not only to the total mass of products and reactants, but to each of the individual elements involved. When one fermented sugar with yeast and water in a closed vessel to yield alcohol, as in one of his experiments, the total amounts of carbon and hydrogen and oxygen always stayed the same. They might be reaggregated chemically, but their amounts were unchanged.
The conservation of mass implied a constancy of composition and decomposition. Thus Lavoisier was led to define an element as a material that could not be decomposed by existing means, and this enabled him (with de Morveau and others) to draw up a list of genuine elements – thirty-three distinct, undecomposable, elementary substances, replacing the four Elements of the ancients.«18» This in turn allowed Lavoisier to draw up a ‘balance sheet,’ as he called it, a precise accounting of each element in a reaction.
The language of chemistry, Lavoisier now felt, had to be transformed to go with his new theory, and he undertook a revolution of nomenclature, too, replacing the old, picturesque but uninformative terms – like butter of antimony, jovial bezoar, blue vitriol, sugar of lead, fuming liquor of Libavius, flowers of zinc – with precise, analytic, self-explanatory ones. If an element was compounded with nitrogen, phosphorus, or sulphur, it became a nitride, a phosphide, a sulphide. If acids were formed, through the addition of oxygen, one might speak of nitric acid, phosphoric acid, sulphuric acid; and of the salts of these as nitrates, phosphates, and sulphates. If smaller amounts of oxygen were present, one might speak of nitrites or phosphites instead of nitrates and phosphates, and so on. Every substance, elementary or compound, would have its true name, denoting its composition and chemical character, and such names, manipulated as in an algebra, would instantly indicate how they might interact or behave in different circumstances. (Although I was keenly conscious of the advantages of the new names, I missed the old ones, too, for they had a poetry, a strong feeling of their sensory qualities or hermetic antecedents, which was entirely missing from the new, systematic and scentless chemical names.)
Lavoisier did not provide symbols for the elements, nor did he use chemical equations, but he provided the essential background to these, and I was thrilled by his notion of a balance sheet, this algebra of reality, for chemical reactions. It was like seeing language, or music, written down for the first time. Given this algebraic language, one might not need an actual afternoon in the lab – one could in effect do chemistry on a blackboard, or in one’s head.
All of Lavoisier’s enterprises – the algebraic language, the nomenclature, the conversation of mass, the definition of an element, the formation of a true theory of combustion – were organically interlinked, formed a single marvelous structure, a revolutionary refounding of chemistry such as he had dreamed of, so ambitiously, in 1773. The path to his revolution was not easy or direct, even though he presents it as obvious in the Elements of Chemistry; it required fifteen years of genius time, fighting his way through labyrinths of presupposition, fighting his own blindnesses as he fought everyone else’s.
There had been violent disputes and conflicts during the years in which Lavoisier was slowly gathering his ammunition, but when the Elements was finally published – in 1789, just three months before the French Revolution – it took the scientific world by storm. It was an architecture of thought of an entirely new so
rt, comparable only to Newton’s Principia. There were a few holdouts – Cavendish and Priestley were the most eminent of these – but by 1791 Lavoisier could say, ‘all young chemists adopt the theory and from that I conclude that the revolution in chemistry has come to pass.’
Three years later Lavoisier’s life was ended, at the height of his powers, on the guillotine. The great mathematician Lagrange, lamenting the death of his colleague and friend, said: ‘It required only a moment to sever his head, and one hundred years, perhaps, may not suffice to produce another like it.’
Reading of Lavoisier and the ‘pneumatic’ chemists who preceded him stimulated me to experiment more with heating metals and making oxygen, too. I wanted to make it by heating mercuric oxide – the way Priestley had first made it in 1774 – but I was afraid, until the fume cupboard was installed, of toxic mercury fumes. Yet it was easy to prepare simply by heating an oxygen-rich substance such as hydrogen peroxide or potassium permanganate. I remember thrusting a glowing wood chip into a test tube full of oxygen and seeing how it flared up, flamed with an intense brilliance.
I made other gases, too. I decomposed water, using electrolysis; and then I recomposed it, sparking hydrogen and oxygen together. There were many other ways of making hydrogen with acids or alkalis – with zinc and sulphuric acid or aluminium bottle caps and caustic soda. It seemed a shame to have this hydrogen just bubble off and go to waste, so to stopper my flasks, I got tight-fitting rubber bungs and corks, some with holes in the middle for glass tubes. One of the things I had learned in Uncle Dave’s lab was how to soften glass tubing in a gas flame and gently bend it to an angle (and, more excitingly, to blow glass as well, gently puffing into the molten glass to make thin-walled globes and shapes of all sorts). Now, using glass tubing, I could light the hydrogen as it emerged from the stoppered flask. It had a colorless flame – not yellow and smoky like the flames of gas jets or the kitchen stove. Or I could feed the hydrogen, with a gracefully curved piece of glass tubing, into a soap solution to make soap bubbles filled with hydrogen; the bubbles, far lighter than air, would rush up to the ceiling and burst.