Georg Ernst Stahl

German chemist and physician

• Born: October 21, 1660
• Birthplace: Ansbach, Franconia (now in Germany)
• Died: May 14, 1734
• Place of death: Berlin, Prussia (now in Germany)

Stahl was a physician who developed the phlogiston theory, modern chemistry’s first great explanatory system. The theory provided chemists with a framework for understanding reactions such as combustion and the smelting of metal ores, and it guided research into productive discoveries such as new gases and the composition of chemical molecules.

Early Life

Georg Ernst Stahl (gay-AWRK ehrnst shtahl) was born in St. John’s parish in Ansbach, then part of Franconia, a duchy in southern Germany. His father was a Protestant minister, and he grew up heavily influenced by Pietism, a seventeenth century movement in the Lutheran Church to infuse new spirit into an increasingly dogmatic Protestantism. Pietism stressed the moral, devotional, and mystical aspects of Christianity, and this doctrine helped to shape Stahl’s view of the world, which was sensitive to the presence of the spiritual.

As an adolescent, he developed an interest in chemistry through reading a manuscript of lectures given by Jacob Barner, a professor of medicine at Padua. In the same period, he read a study of metals and minerals by Johann Kunckel von Löwenstjern, a court alchemist and apothecary who would later help to instigate Stahl’s development of the phlogiston theory. Stahl once said that he knew these works by Barner and Kunckel von Löwenstjern practically by heart. They stimulated him, under the practical guidance of an enameler, to begin doing chemical experiments.

In the late 1670’s, Stahl traveled to Thuringia in central Germany to study medicine at the University of Jena. One of his teachers, Georg Wolfgang Wedel, was a proponent of iatrochemistry, a discipline that held that diseases originate in the imbalance of chemical elements in the body and that the physician’s task is to restore the body’s chemical equilibrium. Stahl later wrote against the iatrochemists, for he could not understand how such a great variety of human illnesses could be attributed to such a small range of chemical causes, for example, acidity and alkalinity. Although he disagreed with the iatrochemists, some of their ideas, such as explaining physiological processes in terms of chemical composition, did inform his medical theory and practice. During his years of study at Jena, Stahl formed a close friendship with Friedrich Hoffman, a fellow student who shared Stahl’s fascination with chemistry and medicine. Even while he was a medical student, Stahl showed great ability as a chemist, and in 1683, around the time that he received his M.D. degree, he began to teach chemistry at Jena.

As a young teacher, he wrestled with many of the ideas that had fashioned the classical and modern doctrines of chemistry and medicine. He studied alchemy, and in 1684 he expressed his belief in the possibility of transmuting such metals as lead into gold (his mature attitude toward transmutation was much more cautious). He read the works of natural philosophers such as René Descartes and Robert Boyle, and he grew skeptical of their claim that all chemical phenomena could be explained in terms of mechanical interactions between variously shaped particles of homogeneous matter (this mechanical view of nature also conflicted with his Pietism). The courses that Stahl taught at Jena in chemistry and medicine gained for him such renown that in 1687 he was invited to become personal physician to Duke Johann Ernst of Sachsen-Weimar, a position he accepted and held for seven years.

In 1693, the elector of Brandenburg, Frederick III (who later became King Frederick I of Prussia), founded a new university at Halle. He gave Hoffmann the duty of establishing the faculty of medicine, and Hoffmann invited his friend Stahl to join him. Halle was a center of the Pietist movement, and when Stahl found that he would be able to teach medicine and chemistry in association with his friend, he agreed to go. In 1694, the year the University of Halle was officially inaugurated, Stahl took his post, one he would hold for twenty-two years.

Life’s Work

As second professor in medicine at Halle, Stahl lectured on theoretical medicine, physiology, pathology, pharmacology, and botany, whereas Hoffmann, as first professor, lectured on practical medicine, anatomy, physics, and chemistry. Through the efforts of these talented and hardworking professors, Halle became a leading medical school. Unfortunately, as time went on, Stahl and Hoffmann became rivals instead of friends. Temperamentally, they had always been different, though there is little evidence to support the traditional contrast of Stahl as misanthropic and intolerant, and Hoffmann as congenial and open-minded; however, there is evidence that their differences were the result of increasingly divergent views on intellectual issues. In particular, Hoffmann became a dedicated iatrochemist who saw living organisms as machines, whereas Stahl, though he interpreted physiological processes through chemical changes, insisted that neither mechanical nor chemical laws were able to account fully for the mystery of life.

In addition to his problems with Hoffmann, Stahl encountered troubles in his personal life. He had married after he had come to Halle, but in 1696 his wife died of puerperal fever, which, despite his best medical efforts, he failed to cure. In 1706, his second wife died of the same disease, and in 1708 a daughter died. Although Stahl married a total of four times, little else is known of his family life. He did have a son who became interested in chemistry and who popularized a method of making silver sulfate from silver nitrate and potassium sulfate.

Despite these misfortunes in his personal and professional relationships, Stahl’s years at Halle were extremely productive. He worked prodigiously. His lectures in medicine and chemistry were very popular, and they became the bases of the books that issued from his pen in a steady stream, many of them in Latin, some in German, and some in a mixture of Latin and German. His subjects were wide-ranging: medical theory, pharmacology, physiological chemistry, chemical theory, experimental chemistry, fermentation, metallurgy, and many others. His style was convoluted and confusing, and many scholars believe that he wrote both too much and too quickly and that his awkward sentences indicate not complexity of thought but a lack of clear thinking.

His greatest medical work was Theoria medica vera (1708; the true theory of medicine), which presents in massive detail his doctrines of physiology and pathology as well as his animistic medical philosophy. Paramount among Stahl’s basic ideas, in his medicine and in his chemistry, is a sharp distinction between the living and nonliving. Stahl was influenced in his views about this distinction by Johann Joachim Becher, who would also influence his ideas on phlogiston. Like Stahl, Becher was the son of a Protestant pastor, and he also went on to become a university professor of medicine, though, unlike Stahl, he converted to Roman Catholicism rather than Pietism. Like Becher, Stahl argued that living things cannot be reduced to a conglomerate of mechanical effects. He did not deny that nonliving things functioned mechanically or that living things, in certain activities, could be interpreted mechanically (for example, the arm as a lever in lifting an object), but the mechanism is always an instrument in the control of a directing agent or anima. Stahl used the Latin word anima, usually translated—though with loss of meaning—as soul or spirit, to capture his belief that every bodily response was rooted in an indivisible vital principle, but anima was not a mystical idea for him, since he arrived at it through rational analysis.

Some scholars have misunderstood Stahl’s animism and antimechanism. He was not a reactionary, trying to revive a defunct religious or ancient Greek worldview. In fact, he was extremely critical of Aristotle’s and Galen’s theories, which he found conflicted with experience. The mechanical philosophy, too, had failed to produce much medical progress because mechanists failed to grasp that it was the soul, not physics and chemistry, that rules the body. The mind clearly acts on the body through voluntary actions, but even involuntary bodily effects have psychic causes. For example, mental perturbations such as anger and fear can change the pulse rate and upset the digestion. Therefore, mental changes do regulate the materials of the body according to certain goals.

In contrast to Stahl’s medical ideas, which did little to advance the field, his chemical ideas had great influence. His best work in chemistry was done during his Halle professorship, and this work was as antimechanist as his medical work. He deeply believed that simple machine models could not adequately explain chemical phenomena. Although he accepted the existence of atoms, he regarded the corpuscularian viewpoint as deficient, since, as he put it, atomic theories scratch the surface of things and leave their kernel untouched. He could not see how arranging and moving inert and homogeneous particles around could generate such qualities as color and reactivity.

Stahl defined chemistry as the art of resolving compound bodies into their principles and recombining them. Since, in his view, atoms never exist by themselves, elements are formed when these indivisible particles join chemically to form what he called “mixts,” and these mixts unite with other mixts in a hierarchy of increasing complexity. Though the highly reactive original elements could never be isolated, they could leave one mixt and enter another. Stahl believed that, for chemists to do meaningful work, they had to assume chemically distinct kinds of matter. For example, he defined metals in terms of their visual and tactile properties, more specifically, their luster and malleability. He defined acids in terms of their reactions with color indicators such as the syrup of violets. Mechanistic explanations of these qualities were clever but speculative and untestable, whereas Stahl preferred to take a direct, empirical approach to the practical problems of chemistry.

In his attempts to find convincing chemical explanations of phenomena, Stahl relied heavily on the doctrines of Becher. In 1703, he brought out an edition of Becher’s Physica subterranea (1669; geological physics), and in the same year he wrote an analysis of Becher’s ideas. Stahl disagreed with Becher’s contention that metals grow like plants in the earth and that lead changes into gold with time, but he found much to admire in Becher’s ideas about minerals. Germany was then the center of a thriving mining industry, and many studies were being done on metallurgical processes. In Physica subterranea, Becher stated that the world’s nonliving substances were composed of three different types of earth: a glasslike earth (terra lapidea), endowed with substantiality that rendered bodies solid and difficult to change; an oily earth (terra pinguis) was primarily responsible for combustibility, but it also accounted for odor, taste, and color; and a fluid or mercurial earth (terra mercurialis) supplied ductility, fusibility, and volatility. Stahl took Becher’s second earth and gave it the name “phlogiston.” The word had been used earlier, in different contexts and in different senses, and the idea of combustibility as a general principle had been used since antiquity (in the medieval period it surfaced as the alchemical principle sulfur). Stahl’s great accomplishment was to take phlogiston and make it into the organizing idea for chemistry. Becher gave almost no experimental support for his theories, whereas Stahl collected numerous observations and experimental facts to confirm his views. His theory also stimulated chemists to do many new experiments.

The explanation of combustion was a central feature of the phlogiston theory. When a substance burned, phlogiston was expelled, and so burning was a decomposition. Stahl saw phlogiston as the principle of fire but not fire itself. Other chemists called phlogiston the food of fire or the inflammable principle. Since phlogiston was an elementary principle, its nature could be known only from its effects. Like the elementary atoms, phlogiston was impossible to isolate, and like the reactions of the mixts, phlogiston could be transferred only from one substance to another. In combustion, phlogiston went out of the flame to combine with the air, but since air had only a limited capacity to absorb phlogiston, this transfer reaction eventually lessened. Furthermore, Stahl noted that a flame could blacken a pane of glass, and this showed that phlogiston was responsible for color.

In an important extension of the phlogiston theory, Stahl recognized that the rusting of metals was similar to the burning of wood, since phlogiston was emitted in both processes. When Stahl heated a metal strongly, the process of rusting was accelerated and what he called an ash appeared (later phlogistonists called this a calx, and the process of making this powdery material from the metal was called calcination). More poetically, the calx was the dead body of the metal, from which the soul of phlogiston had been removed by fire. From his studies, Stahl deduced that a metal was really a compound of a calx and phlogiston. He could reverse the process by heating the calx with charcoal, a rich source of phlogiston. This brought about a transfer of phlogiston from the charcoal to the calx, re-creating the metal.

One thing that troubled later chemists about the phlogiston theory was an observation, known to the medieval Arabs and to many chemists of the sixteenth and seventeenth centuries, that calcined metals actually increased in weight. At first glance, this observation contradicts the phlogiston theory’s analysis of calcination as a decomposition. Therefore, metals should lose weight when they are calcined (because they lose phlogiston), and the calx should gain weight when reconverted to the metal. In fact, the reverse is true, as Stahl knew. Nevertheless, this did not shake his confidence in his theory, because he thought of phlogiston not as an isolable substance but as a weightless, perhaps buoyant, fluidlike heat that could flow from one body to another. Since phlogiston was like light and electricity rather than like air and water, it made no more sense to weigh metals and ores to discover the loss or gain of phlogiston than it would to weigh a piece of paper to measure its whiteness.

Stahl first conceived the phlogiston theory at the end of the seventeenth century, and he developed its implications for combustion, calcination, and the smelting of ores during the first decade of the eighteenth century, when he also applied his theory to such biological phenomena as fermentation and respiration. The theory’s spread throughout Europe augmented Stahl’s fame, but it aggravated rather than improved his relationship with Hoffmann. The atmosphere between them was so poisoned that Stahl welcomed an invitation in 1716 to become personal physician to the king of Prussia, Frederick William I, in Berlin. While at the Prussian court, Stahl continued to write, do research, and teach students. Among his most important publications during this period was Fundamenta chymiae dogmaticae et experimentalis (1723; the fundamentals of dogmatic and experimental chemistry), a work prepared for publication by Johann Samuel Carl, whom Stahl regarded as his best pupil. Depictions of Stahl from this period show a man in a large dark-haired wig surrounding a face with strong features and a melancholic bearing. Stahl, contented with his new life in Berlin, never returned to Halle but held his court appointment until his death on May 14, 1734.

Significance

Georg Ernst Stahl’s life bridged two ages, and his phlogiston theory is often seen as a bridge from alchemy to modern chemistry. His personality, which many have interpreted as a combination of opposites, suited him for this linking role. He was deeply attracted to the devotional and penitential rigors of Pietism, but his penetrating intelligence also found satisfaction in constructing a highly rational system of chemistry. In his youth, he had been fascinated by alchemy, and he continued to use alchemical symbols throughout his career, but in his developed theories these symbols stood for a new explanation of the composition of chemical substances.

Today, most people associate Stahl with the phlogiston theory that dominated chemistry for nearly a century, and many scientists have the impression that this domination retarded chemical progress; however, modern historians of science, though they recognize Stahl’s theory as false, find much to praise in it. Some even see it as a great landmark in the history of chemistry, because it was the first logical theory to encompass most important chemical transformations. It rejected the confusing ideas of alchemy, established chemistry as an independent discipline, and constituted a paradigm within which experimental work could be planned, practiced, and related to other discoveries.

Through the eyes of an early eighteenth century chemist, the phlogiston theory was a liberation from enervating scientific concepts of the past, and the most intelligent and creative chemists of the period accepted Stahl’s theory with enthusiasm. In England, Joseph Priestley, Henry Cavendish, and Joseph Black were phlogistonists; in Germany, Caspar Neumann, Johann Pott, and Andreas Sigismund Marggraf; in Sweden, Torbern Bergman and Carl Wilhelm Scheele; in Russia, Mikhail Vasilyevich Lomonosov; and in France, Pierre-Joseph Macquer and even Antoine-Laurent Lavoisier, until he developed his oxygen theory. These scientists found Stahl’s ideas extraordinarily useful in making important discoveries, including those of new gases and inorganic solids.

Bibliography

Crosland, Maurice P. Historical Studies in the Language of Chemistry. Cambridge, Mass.: Harvard University Press, 1962. This book, which derives from Crossland’s doctoral dissertation for the University of London, traces the evolution of chemistry from the period of alchemy to the end of the nineteenth century. Though intended for scientists and historians of science, the book should lead the general reader to a better appreciation of the history of chemistry, including Stahl’s contributions.

Donovan, Arthur, ed. “The Chemical Revolution: Essays in Reinterpretation.” Special issue. Osiris 4 (1988). The entire issue of this journal centers on new views of the chemical revolution. Though intended for historians of science, the essays deal with a time period and subject matter that make the material accessible to a wider audience.

Duncan, Alistair. Laws and Order in Eighteenth-Century Chemistry. New York: Oxford University Press, 1996. Chronicles scientific discoveries in the eighteenth century that enabled chemistry to establish itself as a discipline. Includes information on how scientists attempted to explain chemical combustion.

Greenberg, Arthur. A Chemical History Tour: Picturing Chemistry from Alchemy to Modern Molecular Science. New York: John Wiley & Sons, 2000. This illustrated overview of chemical history includes a brief discussion of Stahl and the phlogiston theory.

Ihde, Aaron J. The Development of Modern Chemistry. Reprint. Mineola, N.Y.: Dover, 1983. Though the book’s emphasis is on the period of chemistry since the chemical revolution, Stahl’s work is discussed in the initial section on the foundations of chemistry. Contains useful bibliographic notes.

Leicester, Henry M. The Historical Background of Chemistry. New York: John Wiley & Sons, 1956. Although he discusses how some important chemical ideas have influenced world history, Leicester’s emphasis is on the evolution and interrelations of chemical concepts within the history of science. Unlike Aaron Ihde, he devotes considerable attention to the earlier periods of chemistry, including a good discussion of Stahl’s views. Accessible to readers with little or no chemical background.

Levere, Trevor H. Transforming Matter: A History of Chemistry from Alchemy to the Bucky Ball. Baltimore: Johns Hopkins University Press, 2001. This popular history of chemistry includes a chapter, “A German Story: What Burns and How?” containing information on Stahl’s theory.

Partington, J. R. A History of Chemistry. Vol. 2. London: Macmillan, 1961. This volume of Partington’s monumental history of chemistry (he died before its completion) contains two chapters on the phlogiston theory, one devoted to Becher, the other to Stahl. Contains a selected bibliography of Stahl’s writings.

Weeks, Mary Elvira. Discovery of the Elements. 7th ed. Easton, Pa.: Journal of Chemical Education, 1968. Because the phlogiston theory was important in the discovery of elemental gases such as hydrogen, oxygen, and nitrogen, this book has many references to Stahl’s work. The book was originally intended to acquaint chemists with the great achievements of their science, but there is much in these densely packed pages to interest general readers.