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At the heart of alchemy was the quest to turn ordinary metals into gold. Despite the hopelessness of that goal, alchemists still made a lot of discoveries that formed the foundation of modern chemistry and medicine.

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For hundreds of years, alchemy has captured our imaginations, taking center stage in games, novels, and films. It became popular in the Middle Ages, but has existed in one form or another for thousands of years.

And at the heart of it was the quest to create the philosopher’s stone: a waxy, red material that alchemists believed could turn ordinary metals into gold. Unfortunately for them, of course, there is no such thing as the philosopher’s stone. And this is impossible, unless they’re radioactive or in a nuclear reaction, atoms are stuck forever as the same element.

But while on that hopeless quest, alchemists spent a lot of time studying the properties of various chemicals and how they interacted. So, although we often talk about alchemy in the same way we might describe magic, it actually formed the foundation of modern chemistry and medicine, and it led to some huge discoveries. Before Mendeleev put together his draft of the periodic table in 1869, alchemists worked mostly off Aristotle’s understanding of the elements, back from around 300 BCE.

Aristotle had proposed that all matter was divided into four elements: water, earth, fire, and air. But through their experimentation, alchemists discovered some of the official chemical elements we know today. One of those was phosphorus, a critical ingredient in modern matches, fertilizers, and explosives.

Phosphorus was discovered by the German alchemist Hennig Brand in 1669, after a long, smelly day of searching for the philosopher’s stone. Smelly, because Brand’s experiment used...human urine. He’d spent about two weeks boiling more than four and a half tons of it.

Now, it isn’t clear why he was doing this, but alchemists were often experimenting with various chemicals, trying to create new compounds. So, like, maybe that was a normal Tuesday for him. Either way, when it was done, Brand was left with a tar-like substance, which he heated again with sand and charcoal.

He kept the mixture at the highest temperature he could sustain. And, after many hours, a white vapor formed and then condensed into thick drops that glowed brightly for hours. Brand named the substance phosphorus, from the Latin for “light-bearing”.

He believed that phosphorus’s unique properties would help him come closer to unlocking the secrets of the philosopher’s stone. I mean, it wouldn’t. But he did figure out some pretty significant chemistry.

See, urine contains both the chemical phosphate and a bunch of organic molecules. When it’s heated, the oxygen atoms in the phosphate react with carbon from the organic material and the charcoal, and they form carbon monoxide gas. The carbon monoxide escapes, and then you’re just left with elemental phosphorus — first as a vapor, then ultimately as a solid once it drops below 44 degrees Celsius.

Was Brand lucky that he didn’t kill himself with the carbon monoxide that he produced? Absolutely! But weirdly enough, this is basically the same process used to produce phosphorus today, although instead of pee, we use phosphate ore from the ground.

So against all odds, Brand was really onto something. And at first, he tried to keep his discovery a secret. However—and this probably wasn’t a great plan if he was trying to keep a secret—he sold the recipe for phosphorus to a fellow German alchemist.

That guy let slip to yet another alchemist, named Robert Boyle, that phosphorus, quote, “belonged to the body of man”. That led Boyle to make some educated guesses and he began to also experiment with urine, discovering the secret of phosphorus for himself. And at that point, the secret was out for good.

Boyle not only published the recipe for phosphorus; he also used it to create an early prototype of phosphorus-tipped matches. Next, alchemy is also responsible for the discovery of three super important chemicals, called the mineral acids: nitric acid, sulfuric acid, and hydrochloric acid. All of these are frequent players in common chemical reactions, and can be found everywhere from high school chemistry labs to leading research institutions and factories.

And all three were discovered by alchemists again, as part of their hunt for the philosopher's stone. This time, these acids interested alchemists because of their unique properties. For one, when mixed with other substances, they helped transform one compound into another.

Not, like, lead into gold, but stuff like turning baking soda into table salt. That seems like a pretty significant transformation, so maybe lead to gold is possible! Also, when concentrated and combined with each other, the mineral acids could create incredibly corrosive compounds, such as aqua regia, which can dissolve metal.

Since their main goal was to convert lead into gold, any chemical that interacted with metal like this was something alchemists were super fascinated by. Now, some of these reactions were pretty simple, so it’s not that surprising that somebody stumbled upon them. Like, to make hydrochloric acid, alchemists just heated table salt in a crucible.

That broke the salt into compounds including chlorine gas. And that reacted with water in the air to make hydrochloric acid. But other processes seemed a little more complicated or at least, a little more random.

Like, take nitric acid. Alchemists called this aqua fortis, or “strong water,” because of its corrosive properties. It isn’t clear who first discovered it, but we know its history begins in the works of.

Persian alchemists in the 800s, and then, later, in the works of the German saint. Albert the Great in the 13th century. And thankfully, they did not make it using urine.

Instead, it was prepared by heating saltpeter with the seemingly-random combination of alum and copper sulfate pentahydrate. When these compounds are heated together, their chemical bonds break apart, and new bonds are formed. This ultimately gets you nitrogen dioxide and water, which then combine to form nitric acid.

Today, we’ve figured out how to make this more efficiently using ammonia, but this early alchemy work really set the stage for that. So even though it’s not clear exactly how alchemists came up with these ideas, we are grateful they did. Today, nitric acid arguably plays an even bigger role in our world than it did back then, since we use it for the production of fertilizers, plastics, dyes, and also in explosives.

Similarly, the discovery of sulfuric acid also goes quite a ways back. It’s often credited to either the Persian alchemist Muhammad ibn Zakariya al-Razi in the late 800s, or to the Islamic writer Jabir ibn Hayyan in the 1200s. Like many of these stories, it’s not clear what they were ultimately up to besides the whole “make the philosopher’s stone” bit.

But in the al-Razi story, he somehow found himself roasting iron sulfate with copper sulfate pentahydrate. When these compounds are heated together, water and sulfur trioxide evaporate from the mixture, reacting in the air to form sulfuric acid, which can be collected as it condenses. Although back then, it was called “oil of vitriol.” I assume because it was mean!

Sulfuric acid produced by this process was functional but weak it was often mixed with water and other impurities. So again, this isn’t how we make it today. But sulfuric acid is still widely-used, of course.

In particular, it’s a key ingredient in the production of phosphoric acid, a major component of fertilizers and detergents. It’s also used in the iron and steel industry to remove rust from metal before it’s sold, and it has roles in papermaking, petroleum refining, and water purification. And because sulfuric acid is great for dissolving organic material, it’s often used in drain cleaners.

So the next time you’re unclogging your bathroom sink, thank an alchemist, as you pour it down and you say “OIL OF VITRIOL!” From the basic elements to acids, alchemists set the stage for a great deal of modern chemistry. But to be fair, that’s not what every alchemist was interested in. Some were interested more in biology and medicine.

And their work was no less groundbreaking. One such man was a Swiss alchemist who wrote under the pseudonym Paracelsus. He believed that the principles of alchemy could be applied to the organs of the body.

Basically, he thought that the primary purpose of the body’s organs was to separate the pure from the impure. This was a broader definition of alchemy than most of his peers might have used. And Paracelsus wasn’t so much interested in finding the philosopher’s stone as he was in just understanding the world and the rules that governed it.

Which was very modern of him. One of his most controversial ideas was that our quote, “inner alchemist” worked to separate poison from non-poison. And while that definitely isn’t right, in exploring the idea,.

Paracelsus came to a conclusion that still applies today: whether something is poisonous is a question of dosage. At the time, he was researching the therapeutic properties of several compounds that his contemporaries thought were too poisonous to be used in medicine. But he argued that at low doses, poisonous substances could have important medicinal benefits.

Conversely, large amounts of anything, even water and oxygen, could be poisonous. And he was totally right. And people even today struggle with this idea, that it’s okay to have small amounts of things that would otherwise be poisonous.

This was a dramatically new way of thinking about poison, and it led to a new science: toxicology. Paracelsus was also responsible for bringing chemistry into medical treatments, by using synthetic chemical compounds to create new drugs, rather than relying only on herbal remedies. Still, despite all these contributions, alchemy had a lot of problems as a science.

At the time, alchemists were looked at with suspicion, particularly by the Church, who worried that alchemists were heretics or practitioners of witchcraft. So, to avoid trouble, many kept their findings secret. Maybe just to avoid people asking, “why did you need so much urine!?” When they did write notes, they wrote them in code so that no one else would be able to make sense of them.

Including, you know, modern-day historians trying to piece together the history of science. Many were also suspicious of their peers and reluctant to share their results with each other. This secrecy meant that new compounds weren’t given standardized names and were possibly discovered multiple times by different alchemists.

And because there was no good peer-review process, alchemists could claim just about anything they wanted. The only people who could prove them wrong were other alchemists, and because alchemists didn’t share their methods, it often took forever for claims to be disproven. Also, there was no established scientific method, so many alchemists’ investigations were nothing like the experiments of scientists today, which are based around testing a hypothesis.

That said, alchemists weren’t just illusionists or liars, either. Many of them were serious about understanding nature. And while some might only have been in it to discover eternal life or the ability to create gold, others had the same goals as modern scientists: to understand the rules that governed the world around them.

Still, as modern scientific thought developed and more rigorous standards became commonplace, alchemy eventually faded away and the chemistry that we know today emerged. But alchemy remains an important part of the field’s history, and a reminder that science doesn’t always need to get it right on the first try to be important and useful. Through testing and experimentation, we can sort out our missteps and distill them down into something closer to the truth.

We’ll probably never know everything about the universe, but if we consistently test ourselves and the world around us, we can start to uncover big pieces of it. The result might not be as shiny as gold, but it’ll be a whole lot more valuable. If you liked this episode, you can thank our patrons on Patreon!

We could not make this show without them, so to all our patrons thank you for giving us the ability to dive deep into science and history and make more content like this. If you want to learn more about becoming a patron and supporting free science education on the internet, you can go to [♩OUTRO].