Quick Answer
Principe went into a laboratory and made the recipes work. He holds doctorates in organic chemistry and in the history of science, and he uses both to argue that alchemy was a coherent material practice producing real results, that the obscure language is a decodable code rather than mystical evasion, and that both the occultists and Jung read the texts through frameworks the texts do not support. He is right about the chemistry and unfair about the spiritual dimension he compresses into a single dismissive chapter.
Key Takeaways
- He replicated the experiments. The Philosophical Tree grew in his lab.
- The code is breakable, and once broken the recipes describe real procedures.
- Chymistry, not two fields. The alchemy and chemistry split is retrospective.
- The Jung critique is serious and worth answering rather than waving away.
- The last chapter is the weak one, and it is the chapter about people like his readers.
🕑 16 min read
What This Book Is
The Secrets of Alchemy was published in 2013 by the University of Chicago Press. It is a general history of alchemy from Greco-Egyptian Egypt to the present, running about two hundred and eighty pages, written for readers with no background in either chemistry or the history of science.
It is also an argument, and the argument is combative.
Principe holds that alchemy has been misunderstood by nearly everyone who has written about it. The eighteenth-century chemists dismissed it as superstition. The nineteenth-century occultists claimed it as spiritual allegory. Jung read it as a projection of unconscious contents. Popular writing treats it as either fraud or mysticism.
Against all of these, his position is that alchemists were doing exactly what they said they were doing: attempting to transform matter, on the basis of a theory of matter that was coherent given what was known, using laboratory methods that produced repeatable results.
The thing that makes this book unusual. Historians of science generally cannot run the experiments. Principe can. When he says a recipe works, he means he performed it and observed the outcome, and this changes the evidentiary standing of the claim entirely.
Who Lawrence Principe Is
Principe is a professor at Johns Hopkins with joint appointments in chemistry and in the history of science.
He earned a doctorate in organic chemistry first, worked in that field, and then took a second doctorate in the history of science. That combination is rare and it is the whole basis of the book's method.
A historian without chemistry reads an alchemical recipe and sees obscure language about eagles and dragons. A chemist without history has no reason to open the manuscript. Principe reads the recipe, recognises the substances behind the cover names, and takes it into a lab.
His earlier scholarly work on Robert Boyle established that Boyle, the founder of modern chemistry in the textbook account, pursued transmutation seriously throughout his career, and that the tidy story of chemistry emerging from alchemy by rejection is false.
The Problem He Is Solving
The difficulty with alchemical texts is that they were written not to be understood by casual readers.
They describe procedures using cover names. A substance is called the green lion, or the eagle, or the dragon devouring its tail. Quantities are given in symbols. Steps are given out of order. Some texts state directly that they contain deliberate falsehoods to mislead the unworthy.
Faced with this, the two available readings have been that the texts are nonsense, or that they are not about chemistry at all but about something inner.
Principe proposes a third: that the obscurity is a professional code with conventions, that the conventions can be recovered by cross-reading enough texts, and that the test of a decoding is whether the resulting procedure works in a laboratory.
Chymistry
A terminological point that carries a large historical claim.
In the seventeenth century, the words alchemy and chemistry were used interchangeably and referred to a single field. Principe and his collaborator William Newman revived the period spelling chymistry to name it without importing the modern distinction.
The distinction between a superstitious alchemy and a scientific chemistry was made in the eighteenth century, retrospectively, by chemists constructing a respectable ancestry for their discipline. It was a genealogical decision rather than a description of what earlier practitioners had been doing.
This matters because it dissolves the puzzle of why serious scientists pursued alchemy. There was no separate field to leave. The boundary we assume was drawn after the fact by people with an interest in where it fell.
Breaking the Code
The method, worked out concretely, is the most satisfying part of the book.
Decknamen, cover names, are not arbitrary. They follow patterns. A substance may be named for its appearance, for its behaviour in reaction, for an astrological association, or for a pun in Latin or Greek.
The green lion, for instance, resolves to a specific substance once you notice which properties the texts consistently attribute to it and which reactions it appears in. Cross-reading across many texts constrains the possibilities until one candidate fits every occurrence.
Principe walks through several such decodings step by step, showing the reasoning and the dead ends.
The check is empirical. A correct decoding produces a procedure that yields the described observations. A wrong one produces nothing or produces something else, and the recipes contain enough specific detail about colour changes, timing and residues that the match is not easy to fake.
The Philosophical Tree
The showpiece, and worth describing because it does more argumentative work than any amount of textual analysis.
Alchemical texts describe the growth of a metallic tree, a branching structure said to arise in the flask, and this has generally been read as pure symbolism: the tree of life, the world tree, an image of organic growth applied to matter.
Principe decoded the relevant recipe and ran it. A branching crystalline structure of silver grew in the vessel, visible, physical, matching the descriptions and the illustrations.
The phenomenon is now understood in ordinary terms as a form of crystal growth. That is not the point. The point is that the alchemists were describing something they had seen, and that generations of interpreters treating the tree as symbol were reading past a laboratory observation.
What this demonstration establishes is narrower than it first appears and more damaging for it. It does not show that alchemy had no symbolic dimension. It shows that at least some images long read as purely symbolic were reports of observed phenomena, which means the interpreter who assumes symbolism has no way of knowing when they are wrong. Every image in the corpus now carries the question: did somebody see this? That question was not being asked.
Why Transmutation Was Reasonable
Principe is careful to reconstruct the theory rather than mock the goal.
The dominant matter theory held that metals were composed of shared principles, commonly sulphur and mercury in the Arabic tradition, combined in different proportions and degrees of purity. Lead and gold differed as a poor mixture differs from a perfect one.
Given that theory, transmutation is not fantasy. It is the obvious application. If gold is lead with the proportions corrected, then correcting the proportions is a technical problem, and technical problems are what laboratories exist to solve.
The theory was wrong, and it was wrong in a way that could not have been detected with the available means. Nothing observable in a seventeenth-century laboratory distinguishes elements from compounds in the relevant respect, and metals do behave as though they share something.
Principe's insistence on this point is the ethical core of the book. The alchemists were reasoning correctly from premises that were false and unfalsifiable at the time, which is a different situation from being credulous.
The Historical Arc
The narrative runs in four stages and is efficiently told.
Greco-Egyptian origins in the first centuries of the common era, where the earliest surviving texts concern the working of metals and the production of imitation gold and purple dye, with the theoretical framework already present.
The Arabic period, where the work was systematised, the sulphur-mercury theory developed, and the corpus expanded considerably. Principe stresses that the medieval Latin West inherited a mature science rather than fragments.
The Latin Middle Ages and the transmission through translation, with the appearance of the great pseudonymous corpora and the beginning of the interpretive problem, since attributing a text to a famous name was standard practice.
The early modern flourishing, the seventeenth century, where the material is richest and where the figures we now file under science were working.
Starkey and Boyle
The case study Principe knows best and the one that carries the argument about the seventeenth century.
George Starkey was an American-born chymist working in London, who published under the pseudonym Eirenaeus Philalethes and whose texts became among the most influential in the tradition. His laboratory notebooks survive.
The notebooks allow something almost unique: the published obscure text and the private working record of the same procedures can be compared directly. The cover names in the publications correspond to identifiable substances in the notebooks.
This is the strongest possible evidence for Principe's method, because it removes the need for inference. The code is not being guessed at; it is being read off a key the author left behind.
Boyle knew Starkey, learned laboratory technique from him, and pursued transmutation for decades. The founder of modern chemistry, in the standard account, was doing the thing the standard account says modern chemistry was founded by rejecting.
The Newton Problem
Newton left roughly a million words of alchemical manuscript. Not marginal notes, not youthful indiscretion: sustained work over decades, running in parallel with the optics and the mechanics.
The material was suppressed for two centuries and became widely known only after it was sold at auction in 1936, at which point it caused considerable discomfort.
The response was to treat it as an aberration, a private eccentricity separate from the real work. Principe rejects this and places Newton's chymical work in the ordinary intellectual life of the period, where investigating the transformation of matter was a normal thing for a natural philosopher to do.
He is more cautious than some scholars about claiming direct influence on the physics. The claim he makes is the weaker and better supported one: that there is no boundary to cross here, because the boundary did not yet exist.
The Case Against Jung
The confrontation many readers come for, and it should be presented at full strength before it is assessed.
Principe's charges are four.
The framework came from outside. Jung arrived at the alchemical corpus with a theory of the unconscious already formed and found the theory confirmed, which is a pattern that should raise the question of whether any other reading was available to him.
The sample was narrow. The texts Jung worked with most closely, particularly the Rosarium Philosophorum, are unrepresentative of a corpus that is overwhelmingly technical. A reader who took the whole body of material would encounter far more instruction on furnace construction than on symbolic marriage.
Procedure was read as symbol. The Philosophical Tree is the exhibit. Passages describing observable laboratory events were treated as projections because the interpreter did not know the events were observable.
The intermediaries distorted. Jung worked substantially through nineteenth-century occultist editions and translations, which had already been shaped by an interpretive tradition invested in the spiritual reading.
What Can Be Said for Jung
The critique lands and it is not the end of the matter.
Jung was not primarily making a historical claim. His interest was in what the images do in the mind of a person who encounters them, and the value of his work on alchemical imagery does not depend on the alchemists having intended what he found.
An image can be an accurate report of a laboratory event and also carry the significance a later reader finds in it. Principe's demonstration shows Jung was wrong about what the alchemists were describing. It does not show he was wrong about what the descriptions evoke.
There is also a real question about the corpus that Principe passes over quickly. Some alchemical writing is explicitly and unambiguously religious, concerned with the purification of the soul in language that no laboratory reading accommodates. He acknowledges this and does not give it much room.
The fairest summary is that Jung's historical claims about alchemy are largely indefensible and the psychological material he built is a separate structure that stands or falls on separate grounds.
The Chapter That Fails
The final chapter covers alchemy from the eighteenth century to the present: the occult revival, the Theosophical reading, Jung, and contemporary spiritual practice.
It is the weakest part of the book and the weakness is one of temperament.
Principe's tone shifts. Where he has been scrupulous about reconstructing the internal logic of positions he does not hold, giving the sulphur-mercury theory its due as reasonable given its premises, he becomes brisk and dismissive when he reaches people who use alchemical language now.
The methodological generosity that makes the earlier chapters excellent is withdrawn. The esoteric reception is described but not reconstructed, and the question of why alchemical imagery has been so productive for later readers is not asked.
A historian who has spent two hundred pages showing that a discredited framework was reasonable in context might have extended the same courtesy for twenty more pages. He does not, and the book ends less well than it deserves.
What the Book Gives You
Three things, and they are worth the price on their own.
The historical control. Anyone reading the stages of the work or the prima materia symbolically now has a way to check what the terms meant to the people who used them.
A working method. The decoding procedure is transferable and it changes how you read any deliberately obscure text.
Rehabilitation without romance. The alchemists come out of this as competent investigators working from a wrong theory, which is more respect than either the debunkers or the enthusiasts have extended them.
What It Does Not Settle
Two questions remain open after the book and it is worth naming them.
Whether the explicitly religious strand of alchemical writing can be accommodated by the laboratory reading. Principe says the two coexisted. The texts where the religious language dominates entirely are not examined closely enough to know whether that is right.
Whether a later reader's use of alchemical imagery requires historical warrant at all. Principe writes as though misreading a text is a straightforward error. Traditions have always worked by productive misreading, and the question of when that is legitimate is a real one he does not engage.
How to Use It on the Texts
A practical note, because the book is more useful than most histories and readers tend not to exploit it.
Principe's method can be applied by a non-chemist to a limited but real extent. When you meet a cover name in a text, the first question is whether the surrounding passage describes something happening: a colour change, a smell, a residue, a timing, a temperature. Symbolic passages rarely carry that kind of specificity, and technical passages almost always do.
The second question is whether the same name appears elsewhere in the corpus attached to the same behaviours. Consistency across independent texts is evidence of a shared referent, and inconsistency is evidence that the name is doing something else.
The third is what the text tells you about its own intentions. A great many alchemical works state plainly, in their opening pages, that they conceal and how. Readers who take the concealment claims seriously and the recipes symbolically have it exactly backwards.
None of this will let you reproduce Starkey. It will let you tell, reading a text like the Turba, which passages are instructions and which are something else, and that distinction is the one the whole interpretive tradition has been failing to make.
An exercise worth doing once. Take any alchemical passage you have read symbolically and go through it marking every physical detail: what is heated, for how long, what colour it goes, what is left in the vessel. Then read only the marked material. If a coherent procedure emerges, the passage was a recipe. If nothing emerges, you have learned something too. The exercise takes twenty minutes and it permanently changes the way the corpus looks.
Who Should Read It
Read it if you have any serious interest in alchemy, in either direction. It is the single best entry point in print and there is no real competition for the role.
Read it if you have read Jung on alchemy and want to know how much of it came from the sources. That is an uncomfortable exercise and it is the responsible one.
Read it if you are interested in the history of science and have absorbed the tidy story about chemistry emerging by rejecting superstition, which this book dismantles in detail.
Read it alongside the Hermetic background, which supplies the philosophical setting Principe treats only glancingly, and be ready to argue with the last chapter.
Skip it only if what you want from alchemy is confirmation. It will not supply any, and it is honest about that from the first page.
What survives contact with this book, for a reader who came to alchemy through the stone and the stages and the language of inner transformation, is not a debunking. It is a correction of tense. The alchemists were not writing about your inner life. They were writing about matter, carefully, and getting results. That the language they built for it has proved so useful for describing what happens to a person is a fact about the language and about the strange fit between the two domains, and it is more interesting once you stop needing them to have meant it.
The book that put alchemy back in the laboratory without taking it away from anyone.
Affiliate disclosure: Thalira earns a small commission on purchases made through the link above, at no additional cost to you. Our assessment of the final chapter and of the Jung critique is set out above and is independent of the link.
Frequently Asked Questions
What is The Secrets of Alchemy about?
Lawrence Principe's 2013 history of alchemy, arguing that it was a serious material practice with coherent theory and real laboratory results, and that both the occult and the psychological readings of it distort what the alchemists were doing.
Who is Lawrence Principe?
A professor at Johns Hopkins holding doctorates in both organic chemistry and the history of science. He is unusual among historians of alchemy in being able to read the recipes as a chemist and reproduce them in a laboratory.
Did he actually replicate alchemical experiments?
Yes, and it is the most striking feature of the book. He decoded recipes written in deliberately obscure language, ran them, and obtained the described results including the celebrated Philosophical Tree of silver crystals.
What is his view of Jung on alchemy?
Critical. He argues Jung read the alchemical texts through a psychological framework brought from outside, relied on a narrow and unrepresentative sample, and mistook technical procedure for symbolic projection.
Was alchemy the same thing as chemistry?
Principe argues the two were not separate fields in the seventeenth century. Chymistry covered both, the split was made retrospectively in the eighteenth century, and figures like Boyle and Newton worked across what we now treat as a boundary.
Why did alchemists write so obscurely?
For trade protection and for control of who could reproduce the work. Principe shows that Decknamen, cover names, follow decodable conventions rather than being mystical evasion, and that the recipes work once decoded.
Does he deny alchemy had a spiritual dimension?
No, and this is often misreported. He accepts that religious and philosophical concerns ran through the tradition. His argument is that these coexisted with real laboratory work rather than replacing it.
Is transmutation possible?
Not by chemical means, since chemical processes do not alter atomic nuclei. Principe's point is that given a theory of matter in which metals differ by proportion of shared principles, transmutation was a reasonable expectation rather than a fantasy.
Is the book readable for a general audience?
Yes. The prose is clear, the technical passages are explained, and no chemistry background is required. It is scholarly in standard without being difficult to follow.
What was Newton's involvement?
Extensive. Newton left roughly a million words of alchemical manuscript, worked at it for decades, and Principe places this within the ordinary intellectual life of the period rather than treating it as an embarrassing aberration.
What does the book leave out?
The living reception of alchemy from the nineteenth century onward gets one chapter and is treated dismissively. Readers interested in how alchemical language functions in modern spiritual practice will find little sympathy here.
Should someone reading Jung read this too?
Yes, particularly then. It provides the historical control on what the texts said in their own context, which makes it possible to assess how much of Jung's reading came from the sources.
Read the recipe as a recipe first
The discipline this book teaches is worth more than its conclusions. Before you decide what a difficult text means, find out what it says. Principe took images that had been read as symbols for four hundred years, worked out what substances they named, and grew the thing in a flask. Whatever you make of alchemy afterwards, that order of operations is the right one, and most readers of most esoteric material never attempt the first step because the second is more immediately rewarding.
Sources & References
- Principe, Lawrence M. (2013). The Secrets of Alchemy. University of Chicago Press.
- Principe, L. M. The Aspiring Adept: Robert Boyle and His Alchemical Quest.
- Newman, W. R. and Principe, L. M. On the terminology of chymistry.
- Starkey, George. Laboratory notebooks and the Philalethes corpus.
- Newton, Isaac. Alchemical manuscripts, the Chymistry of Isaac Newton project.
- Jung, C. G. Psychology and Alchemy, the position under critique.