From David Deming at RealClearScience:
After a grand beginning, the academic study of the history of science has largely degenerated into a caricature of itself. It is not that it is merely bad. No, it is far worse than that. The scholarship being produced by most historians of science today is not good enough to be bad. Consider a quote from a recent paper by two historians of chemistry. “We find that efforts to differentiate alchemy from chemistry prove to be anachronistic, arbitrary, or presentist.” In other words, there is no difference between alchemy and chemistry. This thesis would not only shock a modern chemist, it would be rejected by any intelligent person with no special knowledge of these subjects.
In fact there is a chasm between chemistry and alchemy. Alchemy contributed apparatus and procedures to chemistry, but it also mixed chemical technology with religion, philosophy, magic, metaphysics, and astrology. Naturalism is essential to science but alchemy incorporated supernaturalism. Alchemists sought to obscure their methods and knowledge whereas chemists seek to reveal and clarify. Robert Boyle and Antoine Lavoisier, men who struggled to free chemistry from metaphysics and define it as an exact science, would be outraged at the claim that chemistry and alchemy were indistinguishable. More.

First, the history shows that alchemy shaded into what we now call chemistry by degrees. There was no sharp divide, nor any reason to expect one. People learned by doing; it was the only way.
See, for example: Mediaeval alchemists were real scientists, it turns out.
and
The fuss over Isaac Newton’s more eccentric beliefs says more about the fussers than about him
Second, Dr. Deming’s* assertion that naturalism is essential to science is tragically wrong. Naturalism, as a metaphysical project, is undermining science today.
It’s no better to make science a project for seeking support for naturalism (nature is all there is) than to make it a project for seeking support for Marxism or democracy or Noah’s Flood. When any such trend dominates without free discussion, inconvenient evidence becomes hostage to politics.
Naturalism, for example, sponsors the view that we did not evolve so as to grasp reality, that our brains were shaped for fitness, not for truth, and even that we evolved to need coercion.
All of these claims provide justifications for the enforcement of dogma over evidence, for expediency. Where they are widely held, we should not be surprised if chronic problems multiply over science claims that are not evidence-based but find their way into law and custom. And are hard to undo.
For that matter, the quest to make the fabled multiverse some kind of a science fact—without any evidence at all— exists principally to avoid honest discussions of evidence for fine-tuning of the universe. Down that route lies a return to something that will make alchemy look reasonable.
See also: Cosmic coincidences?: New Scientist says a multiverse is best explanation!
* David Deming (ddeming@ou.edu) is Professor of Arts & Sciences at the University of Oklahoma, and the author of Science and Technology in World History (McFarland, 2010, 2012, 2016), a history of science in four volumes.
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