In the Alchemist’s Den

In​ 1770 a new perfume shop opened in the centre of Paris on the rue du Bourg-l’Abbé, a fragrant oasis adjoining a district that was, according to one contemporary, ‘by far the worst-smelling place in the world’. This stretch of the Right Bank was home to an abattoir, a fish market, a butcher, an overcrowded prison and a mortuary, whose combined effluvia flowed through open sewers directly into the Seine. Blaise Laugier’s new store in a side street off the open market of Les Halles, sandwiched between a florist and a seller of scented fans, took its place among a cluster of fashionable boutiques catering to an expanding metropolitan class for whom perfume had become an essential part of daily life.

The 18th century’s ‘new calculus of olfactory pleasure’, as Alain Corbin called it in his classic study from 1982, Le Miasme et la jonquille (published in English as The Foul and the Fragrant), created an opportunity both for Laugier and for his home town of Grasse in Provence, which had long been renowned for the production of floral essences, waters and perfumes. Musk, civet and ambergris, the high-status scents of the 17th century, were too pungent and excremental for the new bourgeois sensibility. The fields around Grasse bloomed from spring to autumn with successive waves of violets, orange blossom, roses and jasmine, which provided the scented waters demanded by the new morning fashion of the toilette. Wholesome natural scents were seen as a protection against infectious disease and the pervasive miasma of the fetid city. As well as being applied to the skin, they were widely used for scenting gloves and other garments, and had great medical value as fumigants, topical antiseptics, breath fresheners and digestive aids.

Grasse was the first town to manufacture floral essences on an industrial scale. The local population was employed throughout the long growing season in the labour-intensive gathering of petals and blossom – jasmine at dawn, roses in late afternoon – which were hauled back to town by the sackload for processing. Some essences, such as citrus, could be extracted by simple pressing and squeezing, but over the centuries other techniques had been developed. Robust herbs such as rosemary, cloves and juniper might be steam-distilled: heated over a boiler, cooled in a condenser and separated into oil and water. More delicate plants required enfleurage, in which the scent was captured in fat. In ‘enfleurage à chaud’, or maceration, flowers would be gently heated in liquefied fat using the old alchemical device of a bain-marie. But flowers such as jasmine and tuberose couldn’t stand any heat, and Grasse became known for its use of ‘enfleurage à froid’, in which petals were carefully layered on fat-impregnated cloth sheets. The goal of every method was to separate the ‘spirit’ of the plant – the aromatic essence – from the ‘phlegm’, the base vegetable matter in which it was held.

The language used to describe these processes was comprehensively reformed in the 1780s by Antoine Lavoisier, whose ‘new chemistry’ reconceived matter on the basis of the smallest constituent parts into which it could be decomposed, which could then be quantified by weight. The alchemical ‘principles’ of salt, sulphur and mercury were replaced by ‘elements’ and their ‘compounds’. ‘Sugar of lead’ became lead acetate, ‘oil of vitriol’ became sulphuric acid, aqua fortis became nitric acid, and for aqua ardens or ‘spirit’ Lavoisier claimed the Arabic term ‘alcohol’. This last was a substance, or class of substances, that particularly fascinated him, as he puzzled over the chemistry of traditional processes such as brewing, fermenting, distilling and vinegar-making. In fermentation, it was clear that sugars were turned into alcohol, but he was never able to make this occur as a simple chemical reaction.

Lavoisier’s realm was the laboratory. It was here that he proved water was not an element but a compound, which could be created in a bell jar by burning jets of hydrogen and oxygen. The chemistry of living things, however, presented complexities that he struggled to resolve. Most plant compounds, when broken down into their fundamental constituents, turned out to be disarmingly simple: all were essentially combinations of carbon, hydrogen and oxygen, with a few admixtures. What, then, accounted for the teeming variety of living forms, and the vast differences between substances with apparently similar chemical formulae? Some contended that living organisms contained a vital principle that was lost after death, rendering it invisible to chemical analysis of their oils and essences; others suggested that there was a further principle, yet to be discovered, that determined how these basic elements combined. In Elixir, Theresa Levitt tells the entwined stories of the Laugier family and the development of perfume in the first decades of what in the early 19th century would come to be called ‘organic chemistry’. The long tradition of isolating plant essences, she argues, played an underappreciated role in these discoveries. Smell has always been a crucial diagnostic sense, the one that brings us closest to the fundamental properties of matter, and the evolution of perfume follows an unbroken narrative thread that extends from alchemy to modern industrial chemistry.

Levitt’s story, which unfolds almost entirely in France, takes in successive political as well as chemical revolutions, and shows how Lavoisier’s triumph in the latter led directly to his downfall in the former. He had become fabulously wealthy as a tax collector on behalf of the ancien régime, not least by devising a method of measuring precisely whether a distilled spirit was an esprit de vin, the strongest grade, or a weaker eau de vie, taxed at a lower rate. He created and enforced a system of ‘proof’ marks, using a hydrometer to test alcohol levels, which produced a huge boost in tax revenue. Among those squeezed by the new system was Blaise Laugier, whose high-grade perfumes were taxed at the top rate. When revolution came, the many grievances against Lavoisier were taken up by the mob, and in 1793 he was included in a mass arrest of former tax collectors. He was convicted of embezzlement and, in May 1794, guillotined along with 27 of his colleagues.

The perfume industry got a boost from Napoleon, who as first consul led the fashion for ever more elaborate toilettes, getting through sixty bottles of scent a month: he poured it in his bath, added it to wine and insisted it imbued him with the spirit of health and vitality. The signature product of the new era was eau de Cologne, a sharp, intensely fresh formulation of citrus and bergamot essences. Laugier developed an eau de Paris along similar lines, and in 1812 applied for a patent from Napoleon’s Commission of Secret Remedies, newly established to regulate the trade in patent medicines. His application, along with almost all the others, was rejected: Lavoisier’s former colleague Claude Berthollet admitted that ‘chemistry does not give the means of perfectly recognising the elements which compose it.’

By this time, however, some underlying principles of plant essences were becoming clearer. In 1804 the young German chemist Friedrich Sertürner isolated morphine from opium, the first time that a plant had given up not merely an extract or tincture but a pure chemical substance. To Sertürner’s surprise, it wasn’t an acid but a base, therefore alkaline. The isolation of further ‘alkaloid’ compounds followed swiftly: caffeine from coffee and tea, nicotine from tobacco, quinine from cinchona. This transformed the pharmacy trade, launching new plant-derived remedies such as camphor, distilled from the bark of laurel trees, which became a household staple during Paris’s cholera epidemic of 1832. Further progress was made by the German chemist Justus von Liebig, who, working from his state-of-the-art laboratory in Giessen, designed a glass device he called a Kaliapparat, which allowed him to burn substances and measure precisely the mass of carbon they contained.

These discoveries drew the next generation of Laugier Père et Fils, as it was now known, into the world of experimental chemistry. At the age of nineteen, Édouard Laugier became a teaching assistant at the École Polytechnique, which brought him into proximity with an increasingly well-organised network of pioneering chemists, including Liebig and the young Swiss prodigy Jean-Baptiste Dumas. Laugier wrote the entry on perfumery for a prestigious new encyclopedia, the Technological Dictionary, and turned his experiments to use in the family trade, perfecting a transparent, mild soap to rival the latest sensation from Britain, the glycerine-based Pears soap. After the July Revolution of 1830 finally forced the family shop out of business by making it impossible to collect on foreign debts, Édouard took up residence on the bohemian Left Bank, where he joined a group of utopian socialists and formed a partnership with another disaffected young chemist, Antoine Laurent.

In 1832, Liebig, working in his Giessen laboratory with the essential oil of bitter almonds, claimed to have identified a stable grouping of carbons, hydrogen and oxygen in the ratio 7:5:1 that formed the root of a huge family of organic chemicals. He named it the ‘benzoyl radical’ and, by reacting it with chlorine, bromine and ammonia, created a succession of novel compounds. Together, Laugier and Laurent set up a laboratory in the back of the shuttered perfume shop and began their own work on reactions with bitter almonds, a material that Laugier knew well as a source of soap fragrances, and which was equally familiar to pharmacists as a deadly toxin.

It was here, in 1835, that the pair made their breakthrough. By distilling the bitter almonds in a new apparatus constructed by Laugier, they produced a viscous resin, which they dissolved and filtered several times to separate it into its constituents. When they passed a stream of chlorine over one of these substances, then dissolved it in alcohol and crystallised it, not only did the crystals’ chemical composition match that of the benzoyl radical, but they formed in ‘beautiful prisms’, regular geometrical shapes quite different from those formed by synthetic chemicals. They proposed that Lavoisier’s reduction of all substances to the elements that composed them concealed a fundamental characteristic of organic chemicals: the molecules had a distinctive spatial arrangement, which could be as important as its composition in determining its properties.

Laurent and Laugier’s insight would be confirmed over the following years by other chemists, including Jean-Baptiste Biot, who demonstrated that organic crystals rotated the plane of polarised light where synthetic ones did not. But evidence of this sort did nothing to convince the leading figures of the new chemistry, who were committed to describing organic compounds exclusively in Lavoisierian terms and regarded Laurent and Laugier’s theory as an attempt to smuggle alchemical and vitalist notions of an intangible life force into a science that had only recently rid itself of them. In Paris, Jean-Baptiste Dumas was building up a cadre of laboratory scientists in the École Polytechnique to rival Liebig’s in Giessen, and in 1837 he froze Laurent out of his programme with a manifesto that focused entirely on chemical formulae and excluded any consideration of the shapes of molecules or the prismatic properties of crystals. Édouard Laugier returned to the rue Bourg-l’Abbé to work as a distiller, and Laurent continued his researches on a shoestring, creating strange substances from coal tar and bitter almonds in a ramshackle laboratory that reminded his colleagues of an alchemist’s den. He reported that, day and night, visions of endlessly transmuting molecular structures danced before his eyes.

After the Revolution of 1848, the restored French republic became a powerhouse of industrial chemistry. Coal tar, previously considered a malodorous waste product, could be made to yield a yellowish compound, aniline, which smelled of rotting fish but could also be used to produce a range of vibrant synthetic pigments, including a purple that rivalled costly natural indigo and was given the name ‘mauve’. In the process, evidence continued to mount that there was more to organic chemistry than Lavoisier’s formulae. Oil of wintergreen, for example, could now be manufactured synthetically; it proved identical to the natural oil, except that it was inactive under polarised light, and some perfumers claimed its smell was slightly different. Even more mysterious, it was discovered that caraway and spearmint, despite their strikingly different aromas, shared the same chemical formula.

Many of these puzzles were eventually solved by the generation of scientists who succeeded the perfumers. Louis Pasteur began his career peering through Laurent’s microscope at geometrical crystals, and subsequently spent years trying and failing to create a synthetic chemical that was optically active. Along the way, he resolved the problem of fermentation by showing that it was not, as Lavoisier had believed, a simple chemical reaction: a living ‘germ’ was required to activate the process. In 1860 Pasteur finally succeeded in demonstrating that there was indeed a fundamental difference between the chemistry of life and substances created in the laboratory. Some molecules display a particular sort of asymmetry whereby they cannot be superimposed on their mirror image. Such molecules would come to be described as chiral, from the Greek for ‘hand’, since left and right hands have a similar relation to each other. Many organic molecules contain chiral groups, so exist in two forms – called enantiomers – which are identical in every respect but their ‘handedness’. In nature, however, a substance will often occur not as an equal mixture of the two enantiomers but predominantly in one form or the other. Caraway and spearmint, it turns out, are the two enantiomeric forms of the same compound, called carvone, which smell different from each other. Not all pairs of enantiomers have dramatically different odours, but they do all rotate plane-polarised light in opposite directions. Natural wintergreen comprises more of one of its enantiomers than the other, so is optically active; synthetic wintergreen contains both enantiomers in equal amounts, so is optically inactive.

Just a couple of years after Pasteur’s revelation, August Kekulé, a graduate of Liebig’s laboratory at Giessen, resolved the mystery of the ‘benzoyl radical’ by showing that the compound from which it derived, by this time known as benzene, took the structural form of a hexagonal ring. Kekulé said that he had been dozing and saw in his mind’s eye a chain of molecules looping on itself, like a snake eating its tail. This was a story he volunteered only decades later, at a commemoration of his great achievement, and Levitt suggests it may have been an attempt to conceal his influences, ‘particularly if they came from so despised a source as Laurent’. In any case, Kekulé became a master of ‘a new kind of structural chemistry’, in which organic molecules could be understood as arrangements in space, and modelled accordingly with coloured balls for atoms and thin rods for the bonds between them. With this, science had finally acquired the tools to match the perfumer’s nose, and set the table for the synthetic organic chemistry to come.