Repeatable Reaction by Alchemist Leads to Atomism

Hot silver that has been freshly reduced in a crucible form from the silver carbonate precipitate by heating about 1,000 degrees C. Simple heating of the silver carbonate yields, metallic silver, carbon dioxide and oxygen. photograph by William R. Newman.

For most of the last three centuries, atoms have been considered the smallest bit of matter that can be recognized as an element. From Sir Robert Boyle to Antoine Lavoisier to John Dalton to Dmitri Mendeleev, then into the great discoveries of the 20th century, atoms rule in matter theory.

The path to this central insight begins in Ancient Greece with Democritus. His theory lay dormant for more than a millennia, but beginning in the 1300s, alchemists started to seriously look at the possibility that there was a definable smallest unit of matter.

At the time alchemists were blowing the dust off the ideas of Democritus, Aristotle held full sway in the new and influential universities in Western Europe. The dominant view said matter was a combination of the four elements — earth, air, fire and water — and the four qualities — hot, dry, wet and cold — plus an immaterial form. This form, according to the prevailing theory, did not survive chemical reactions. Sulfur, mercury, and in some views salt, were also thought to be the basis of all metals.

At the beginning of 17th century, Aristotle’s view still held sway in the universities, but experiments by the alchemists were beginning to cast doubt on the dominant view. The discovery of mineral acids allowed alchemists to perform experiments that dramatically showed that original reactants could be recovered in their original form — something that would be difficult to explain using immaterial forms, but made sense if tiny atoms were unchanged by any number of reactions. These repeatable experiments strongly suggested to Boyle that atoms were the smallest particle of matter.

One of the most important of these experiments was conducted by the alchemist Daniel Sennert, who referred to it as “reduction to a pristine state.” The experiment is recorded in color photos in the book “Atoms and Alchemy: Chymistry and the Experimental Origins of the Scientific Revolution” by William R. Newman, Ruth Halls Professor in the Department of the History and Philosophy of Science at Indiana University.

A thin sheet of technical grade silver is cut into small pieces. The silver is then dissolved in nitric acid (Sennert would have said aqua fortis) forming a solution blue in color because of the copper content of technical grade silver. A brown cloud also forms above the liquid as nitrogen dioxide gas leaves the solution. Many experimenters in early chemistry report a blue color in silver salts and solutions, indicating that copper was present in the metal they used. When the silver is fully dissolved the blue liquid is passed through filter paper and it leaves no residue. Then potassium carbonate (salt of tartar) is added to the solution. More brown gas leaves the solution and a precipitate of yellow silver carbonate falls out of the solution. When the yellow mass is heated to 1,000°C in a crucible, the result is silver metal (as well as carbon dioxide and oxygen).

Dissolve the same silver in nitric acid and the result can be repeated endlessly. Boyle used Sennert’s experiment in beginning to formulate a theory of matter based on atoms rather than immaterial forms. That the fluid would pass through the best filter paper and yield silver metal meant the particles of silver in the fluid were smaller than anyone could measure at that time or for more than two hundred years after.

Although Sennert’s work provided Boyle with a major insight in atomism, Sennert himself never accepted that atoms were the fundamental particle of matter. Newman likens the Sennert-Boyle difference of interpretation of experimental results to that of Joseph Priestley and Antoine Lavoisier over the dephlogisticated air/oxygen experiments. Priestley clung to the theory of phlogiston until his death. Lavoisier, on the other hand, correctly deduced that the element he named oxygen was the key to combustion.

Although Sennert did not accept atomism, he and many other alchemists developed and refined laboratory practices that formed part of the foundation of what has become known as the Scientific Revolution. Far from the sudden flowering of reason in a world of superstition, the Scientific Revolution took root in the good soil of the centuries of laboratory experimentation, much of it done by the alchemists.

The popular histories of the Scientific Revolution downplay or omit the contributions of alchemists to early chemistry. The real story is more complicated and more interesting. The beginnings of chemistry include brilliant insights, but these insights are based on long years of laboratory practice developed in very difficult circumstances. Alchemy has its place in the long and rich tradition of experimental chemistry that every chemistry professional shares.

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This article was originally published under the title "We're History" in the April 2007 edition of Chemical Engineering Progress magazine. This article was prepared by Neil Gussman, communications manager for the Chemical Heritage Foundation.