The Fabric of the Globe: Chemistry and Geology in Enlightenment Edinburgh

Boulders from the River Tilt, Tayside. Engraving based on a drawing by John Clerk. Reproduced with the permission of Sir Robert Clerk, Penicuik House, Penicuik, Midlothian, Scotland.

By Matthew D. Eddy

During the 18th century, geology was closely linked to chemistry via medical and industrial experiments that sought to identify the composition of stones that formed the surface and foundations of the globe. Over the past two centuries this connection has been largely overshadowed as historians have sought to identify how early modern notions of geological strata led to 19th-century evolutionary ideas. However, if one digs into the dusty articles and dissertations of Enlightenment chemistry, it becomes quite evident that the practice of “chemical mineralogy,” a forerunner of geology, was pursued in most universities across Europe. In Britain the leading center during this time was the University of Edinburgh. Its professors were keenly interested in geological matters, and this article explains how their chemical knowledge framed the emergence of the discipline of geology in Scotland.

Chemical Principles

In 18th-century Scotland the leading chemists taught in the University of Edinburgh’s medical school. Chemistry had played a central role in the curriculum ever since the school had been founded in 1726 by students who had trained in Leiden with the renowned Dutch chemist Hermann Boerhaave. Although chemistry was also taught in Glasgow and Aberdeen throughout the century, by 1750 the professors of Edinburgh’s medical school set the standard in Scotland for chemical experimentation and patronage. For the next 50 years it was predominantly University of Edinburgh students who lectured in the city’s Royal College of Physicians and edited Scotland’s internationally acclaimed Essays Physical and Literary, the Scottish Pharmacopoeia, and, later, the Transactions of the Royal Society of Edinburgh. Edinburgh’s medical school also had an impact abroad. Its students held positions in the Russian court, traveled on British naval vessels, obtained professorships in America, and maintained lucrative practices in London.

As in most Enlightenment chemical communities, when creating the smells and bangs of their experiments, Edinburgh’s professors and students used a form of chemical nomenclature based on six basic types of matter: Earths, Salts, Metals, Inflammables, Airs, and Water. Each of these categories was called a “principle,” and each was treated as both a primary substance and (save for Metals and Earths) an agent of material change. Using these principles, chemists performed experiments both on the human body and in vitro in the laboratory. To generate extra money for themselves, chemistry students were taught how to apply their knowledge to pharmaceutical production or to the industries of mining, bleaching, brewing, ceramics, and metallurgy. Some students met with considerable success. John Roebuck, for example, founded the first sulfuric acid plant in Scotland and became a captain of industry, and the agriculturalist James Anderson went on to write successful books that addressed the chemical foundations of farming.

Such an interest in practical application made Edinburgh’s chemists less interested in the armchair speculation offered by more gentlemanly institutions like the Royal Society of London or even the early theories offered by the chemical reformer Antoine-Laurent Lavoisier during the 1780s. From the 1750s until around 1800 the Scottish canon of chemistry textbooks drew heavily from authors who lived in Germany and Scandinavia. William Cullen (1710–1790), Edinburgh’s professor of chemistry during the 1750s and 1760s, strongly recommended the work of the Dutch Boerhaave, the German Georg Ernst Stahl, and the Swede Axel Cronstedt. His successor, Joseph Black (1728–1799), promoted these authors and added the names of two more Swedes: Torbern Bergman and Johan Gottschalk Wallerius. Key to almost every single one of the chemical experiments explained by Cullen, Black, and the books they promoted were minerals. This was mainly because mineralogy supplied the raw material for the acidic and alkaline Salts that they used as solvents in most of their experiments. Additionally, Scotland was by no means lush country, and if its physicians wanted indigenous sources for drugs, they had to turn to minerals rather than plants. These minerals usually came from the Salts, Earths, and Metals extracted from Scotland’s many moors, mines, and mineral wells.

Venues of Experimentation

Although chemistry was taught primarily n the medical school, chemically related subjects were frequently discussed in other venues in and around the city of Edinburgh. Overall, there were three types of places where experiments were discussed. The first and most obvious venue was the laboratory, which was then less rigorously defined than the modern concept. In Edinburgh one sees the word applied to rooms in the university, the Royal Infirmary, or even a professor’s home.

Second, chemical discourse was also conducted in polite society. The university not only allowed its own students to sign up for courses outside their official degree program but also permitted professionals, merchants, and gentlemen to audit classes. Thus a variety of people could attend medical school courses on chemistry and mineralogy, and many of them aspired to be naturalists—whether professional or amateur. Moreover, between 1750 and 1800 a wide range of clubs and societies were founded in Edinburgh. Many of them focused on “natural philosophy” and were therefore attended not only by university professors but also by students who had audited the chemistry course. The associations that most frequently discussed chemistry were the Philosophical Society (renamed the Royal Society of Edinburgh in the 1780s), the Medical Society, the Highland Society, the Society of Antiquaries, and the student-run Chemistry Society. As with other European clubs and societies (in London and Paris, for example), chemistry played a central role in their discussions, not only in relation to medicine, but also in reference to topics like agriculture, mining, industry, weather, and—inevitably—the structure and composition of the globe. For the most part, a paper as read at each meeting and then debate ensued. Discussion often spilled over into coffeehouses, pubs, and private homes. If the topic proved especially interesting, members wrote letters to each other, or even to other experts, on the subject. For the benefit of the public, summaries of some of their papers were often printed in the Caledonian Mercury and the Scots Magazine.

A third chemical venue was the natural world itself. Many of Edinburgh’s students went on to pursue careers that took them to various corners of Scotland and to posts in the British colonies. This created a network of chemically trained naturalists interested in collecting a wide variety of minerals and plants that could be used to make drugs. Most of these objects could be obtained only in rural areas or in the wilderness. Since traveling naturalists did not have the space to carry back items that might prove useless, they performed their own chemical tests in situ to determine whether the object was worth taking back to Edinburgh. Their observations can be found in the letters written back to Edinburgh’s Philosophical Society and in articles printed in the city’s magazines and newspapers. Many of these travelers went on to write about their experiments in essays and treatises on mining, alkali production, and mineral-well analysis.

From Chemistry to Mineralogy

In Enlightenment Europe there were primarily two ways to classify minerals. The first was to use physical characters like shape, color, and texture. The main promoter of this approach was the Swede Carl Linnaeus. Trained as a physician, he originally developed the method to classify plants, but he then used the same characters to classify minerals. His method spread quickly among the 18th-century dilettantes, gentlemen, and professionals who maintained their own collections of natural “curiosityes.” There was, however, another way to classify minerals, one based on chemical characters like Salts, Earths, and Metals. Although numerous early modern chemists had proposed chemically founded mineralogical arrangements, it was the Berlin chemist Johann Heinrich Pott who eventually argued that stones were made up of different types of Earth. He performed hundreds of experiments in which he used water, fire, and acids to reduce stones to what he thought to be the most basic “primary” Earths: Vitrescible, Calcareous, Argillaceous, and Talky. He published his results in Lithogéonosie (1745) and so laid the foundation for a chemical understanding of stones. Thus when Cullen began to teach chemistry at Edinburgh in the 1750s, he taught his students to base their systems on the four Earths of Pott.

After Pott, the chemical classification of minerals was dominated by the medically and industrially orientated experiments of Cronstedt, Wallerius, and Bergman, each of whom proposed a different number of primary Earths. All these men published their thoughts in books, and the Scots followed their publications with great interest—so much so that, when Cullen found out about Cronstedt’s new mineralogical system, he immediately commissioned a translation of the classification categories so that he could give copies to his students. The Scots, however, being proficient chemists themselves, did not accept these systems blindly, and their independence engendered a wide variety of personalized arrangements influenced by the experiments or mineralogical collections of the chemists creating them.