The chemical revolution

 The chemical revolution

The new research on “airs” attracted the attention of the young French aristocrat Antoine-Laurent Lavoisier. Lavoisier commanded both the wealth and the scientific brilliance to enable him to construct elaborate apparatuses to carry out his numerous ingenious experiments. In the course of just a few years in the 1770s, Lavoisier developed a radical new system of chemistry, based on Black’s methods and Priestley’s dephlogisticated air.

Lavoisier first determined that certain metals and nonmetals absorb a gaseous substance from the air in undergoing calcination or combustion and, in the process, increase in weight. Initially, he thought that this gas must be Black’s fixed air, for he knew of no other chemical species present in ordinary air; moreover, fixed air was known to be produced in smelting, so it seemed reasonable to think that it was present in the calx that was smelted. At this point (October 1774), Priestley communicated to Lavoisier his discovery of dephlogisticated air. Further experiments led Lavoisier to continuously modify his ideas, until it finally became clear to him that it was this new gas, and not fixed air, that was the active entity in combustion, calcination, and respiration. Moreover, he determined (or so he thought, at least) that this gas was contained in all acids. He renamed it oxygen, Greek for “acid producer.”

Lavoisier’s oxygen was in some respects the inverse of phlogiston. Rather than releasing anything, the combustible or metal absorbed (more precisely, chemically combined with) oxygen in the process that Lavoisier now called oxidation. He showed that atmospheric air was a mixture of two principal components, oxygen and a physiologically inert gas (known to Priestley) that he called azote or nitrogen. He also showed that water is a chemical compound of two substances, oxygen and what Cavendish had called “inflammable air.” The latter gas was now renamed hydrogen (“water producer”). Black’s fixed air proved to be a gaseous form of oxidized carbon, or carbon dioxide. The various parts of Lavoisier’s new system were beginning to fit together beautifully.

The keys to Lavoisier’s success were twofold. First, he carefully accounted for all the substances, including gases, entering into and emerging from the chemical reactions he studied by tracking their weights with the greatest possible precision. He knew to do this partly from Black’s example, but he proceeded with a mastery that the science had never before seen. Second, he established a simple operational definition of a chemical element—namely, a substance that could not be reduced in weight as the result of any chemical reaction that it undergoes. Oxygen, carbon, iron, and sulfur were now regarded as elements, along with close to 30 other substances. Lavoisier wrote a textbook to promote the new oxygenist chemistry, Traité élémentaire de chimie (1789), which appeared in the same year the French Revolution began. He and his associates also developed a new nomenclature—essentially the one used today for inorganic compounds—along with a new journal. As an aristocrat of the ancien régime and an investor in a tax-collection agency, Lavoisier was executed in the Reign of Terror, but by that time (1794) the chemical revolution that he had started had largely succeeded in replacing phlogistonist chemistry.

Alchemy

 Alchemy

Three different sets of ideas and skills fed into the origin of alchemy. First was the empirical sophistication of jewelers, gold- and silversmiths, and other artisans who had learned how to fashion precious and semiprecious materials. Among their skills were smelting, assaying, alloying, gilding, amalgamating, distilling, sublimating, painting, and lacquering. The second component was the early Greek theory of matter, especially Aristotelian philosophy, which suggested the possibility of unlimited transformability of one kind of matter into another. The third of alchemy’s roots consisted of a complex combination of ideas derived from Asian philosophies and religions, Hellenistic mystery religions, and what became known as the Hermetic writings (a body of pseudonymous Greek writings on magic, astrology, and alchemy ascribed to the Egyptian god Thoth or his Greek counterpart Hermes Trismegistos). It is important to note, however, that Hellenistic Egypt is only one of several candidates for the homeland of alchemy; at about the same time, similar ideas were developing in Persia, China, and elsewhere.

In general, alchemists sought to manipulate the properties of matter in order to prepare more valuable substances. Their most familiar quest was to find the philosopher’s stone, a magical substance that would transmute ordinary metals such as copper, tin, iron, or lead into silver or gold. Important materials in this craft included sulfur, mercury, and electrum (a gold-silver alloy). However, many other alchemists spurned alchemical transmutation (aurifaction), devoting their efforts instead to a pharmaceutical preparation known as the “elixir of life” that would cure any disease, including the ultimate disease, death. The philosopher’s stone and the elixir of life could be considered parallel quests, for each would “cure” metallic or human bodies, respectively, yielding immortal perfection. There was a parallel religious dimension to all this as well. Finally, some alchemists spurned material manipulations entirely, devoting themselves to meditation with the goal of achieving spiritual purity and ultimate redemption.

After the rise of Islam, Arabic-speaking scholars of the 9th century translated Greek scientific and philosophical works into their own language. Thereafter, philosophers in the Islamic world pursued chemical and alchemical ideas with enthusiasm and success. The sizable number of modern chemical words derived from Arabic—alcohol, alkali, alchemy, zircon, elixir, natron, and others—suggests the importance of this period for the history of chemistry. One of the leading ideas of medieval Arabic alchemy was the theory that all metals were formed of sulfur and mercury in various proportions and that altering those proportions could transform the metal under study—even to produce silver or gold from lead or iron. Not every alchemist, however, believed in the possibility of such transmutations.

Later, scholars in Christian western Europe learned of ancient Greek and early medieval Arabic philosophy by translating these books into Latin. Thus, the alchemical tradition, along with the rest of the Greco-Arabic philosophical and scientific corpus, passed to the West in the course of the 12th century. Well-known Scholastic philosophers of the 13th century, such as Roger Bacon in England and Albertus Magnus in Germany and France, wrote on alchemy. Alongside this learned literature, the empirical chemical arts continued to flourish and comprised a largely separate realm of expertise among artisans, engineers, and mechanics.

An important Western alchemist of the late 13th century was the pseudonymous Latin writer who called himself Geber in homage to the 8th-century Arab alchemist Jābir ibn Ḥayyān. Geber was the first to record methods for the preparation and use of sulfuric acid, nitric acid, and hydrochloric acid; the earliest clear evidence for widespread familiarity with distilled alcohol also does not much predate his day. These substances could only have been produced by novel stills that were more robust and efficient than their predecessors, and the appearance of these remarkable new materials produced dramatic changes in the repertoire of chemists.

The Renaissance saw even stronger interest in the science. The German-Swiss physician Paracelsus practiced alchemy, Kabbala, astrology, and magic, and in the first half of the 16th century he championed the role of mineral rather than herbal remedies. His emphasis on chemicals in pharmacy and medicine was influential on later figures, and lively controversies over the Paracelsian approach raged around the turn of the 17th century. Gradually the Hermetic influence declined in Europe, however, as certain celebrated feats of putative aurifaction were revealed as frauds.