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.[17]
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.
14
In his biography of Lavoisier, Douglas McKie includes an exhaustive list of Lavoisier’s scientific activities which paints a vivid picture of his times, no less than his own remarkable range of mind: ‘Lavoisier took part,’ McKie writes,
… in the preparation of reports on the water supply of Paris, prisons, mesmerism, the adulteration of cider, the site of the public abattoirs, the newly-invented ‘aerostatic machines of Montgolfier’ (balloons), bleaching, tables of specific gravity, hydrometers, the theory of colors, lamps, meteorites, smokeless grates, tapestry making, the engraving of coats-of-arms, paper, fossils, an invalid chair, a water-driven bellows, tartar, sulphur springs, the cultivation of cabbage and rape seed and the oils extracted thence, a tobacco grater, the working of coal mines, white soap, the decomposition of nitre, the manufacture of starch… the storage of fresh water on ships, fixed air, a reported occurrence of oil in spring water… the removal of oil and grease from silks and woollens, the preparation of nitrous ether by distillation, ethers, a reverberatory hearth, a new ink and inkpot to which it was only necessary to add water in order to maintain the supply of ink…, the estimation of alkali in mineral waters, a powder magazine for the Paris Arsenal, the mineralogy of the Pyrenees, wheat and flour, cesspools and the air arising from them, the alleged occurrence of gold in the ashes of plants, arsenic acid, the parting of gold and silver, the base of Epsom salt, the winding of silk, the solution of tin used in dyeing, volcanoes, putrefaction, fire-extinguishing liquids, alloys, the rusting of iron, a proposal to use ‘inflammable air’ in a public firework display (this at the request of the police), coal measures, dephlogisticated marine acid, lamp wicks, the natural history of Corsica, the mephitis of the Paris wells, the alleged solution of gold in nitric acid, the hygrometric properties of soda, the iron and salt works of the Pyrenees, argentiferous lead mines, a new kind of barrel, the manufacture of plate glass, fuels, the conversion of peat into charcoal, the construction of corn mills, the manufacture of sugar, the extraordinary effects of a thunder bolt, the retting of flax, the mineral deposits of France, plated cooking vessels, the formation of water, the coinage, barometers, the respiration of insects, the nutrition of vegetables, the proportion of the components in chemical compounds, vegetation, and many other subjects, far too many to be described here, even in the briefest terms.
15
Boyle had experimented with the burning of metals a hundred years before, and was well aware that these increased in weight when burned, forming a calx or ash that was heavier than the original. But his explanations of the increase of weight were mechanical, not chemicaclass="underline" he saw it as the absorption of ‘particles of fire.’ Similarly, he saw air itself not in chemical terms, but rather as an elastic fluid of a peculiar sort, used in a sort of mechanical ventilation, to wash the impurities out of the lungs. Findings were not consistent in the century that followed Boyle, partly because the gigantic ‘burning glasses’ used were of such power as to cause some metallic oxides to partly vaporize or sublime, causing losses rather than increases in weight. But even more frequently there was no weighing at all, for analytical chemistry, at this point, was still largely qualitative.
16
In this same month, Lavoisier got a letter from Scheele describing the preparation of what Scheele called Fire Air (oxygen) admixed with Fixed Air (carbon dioxide), from heating silver carbonate; Scheele had obtained pure Fire Air from mercuric oxide, even before Priestley had. But in the event, Lavoisier claimed the discovery of oxygen for himself and scarcely acknowledged the discoveries of his predecessors, feeling that they did not realize what it was that they had observed.
All this, and the question of what constitutes ‘discovery,’ is explored in the play
17
Replacing the concept of phlogiston with that of oxidation had immediate practical effects. It was now clear, for example, that a burning fuel needed as much air as possible for complete combustion. François-Pierre Argand, a contemporary of Lavoisier’s, was quick to exploit the new theory of combustion, designing a lamp with a flat ribbon wick, bent to fit inside a cylinder, so that air could reach it from both the inside and the outside, and a chimney which produced an updraft. The Argand burner was well established by 1783; there had been no lamp so efficient or so brilliant before.