One of the problems with the whole idea of
a single Scientific Revolution is that some
disciplines decided not to join any revolution.
And others just took a long time to get there.
In the case of chemistry—the study of what
stuff is—a real scientific revolution, like
in the Thomas Kuhn sense, didn’t really
get going until the 1770s.
Until then, mainstream chemistry in Europe
was based on phlogiston theory, which may
be difficult to wrap your head around because
it is the opposite of how we understand chemical
To shake loose that particular scientific
status quo, it took the power of the Enlightenment,
and one of its most emblematic natural philosophers,
[Intro Music Plays]
If the 1600s was the century of science in
Europe, centered on London, then the 1700s
was the century of philosophy, centered on
This new philosophy largely consisted of a
movement called the Enlightenment—dated
by some from 1715, when France’s powerful
“Sun King,” Louis the Fourteenth, died,
to 1789, when the French Revolution started.
The Enlightenment was a shift in ideas about
knowledge, away from traditional sources of
authority, like the Church, and toward the
kind of scientific rationality described by
This aspect of the Enlightenment is summed
up by the catchphrase sapere aude, or “dare
This suggested that knowing is something you
should do—a moral good.
This was an “Age of Reason.”
The Enlightenment was also about social values,
such as individual liberty, the progress of
civilization, and religious tolerance, including
the separation of church and state.
The Enlightenment at times even fed into anti-religious,
specifically anti-Catholic, feelings, setting
the stage for a later perceived break between
science and religion.
The term “Enlightenment” was coined by
German writer Johann Wolfgang von Goethe,
and it was used by Voltaire, and later by
Thinkers like them—called les philosophes,
or “the philosophers”—met in scientific
societies, literary salons, and coffeehouses.
The philosophes saw it as their job to discover
the laws of nature—the natural law that
helped guide human behavior.
They dreamed of a “republic of letters,”
a world ruled by rational thought and guided
by reasoned debate.
So, yes, if you remember episode two: the
philosophes were kinda like the Presocratics.
The ideas of the Enlightenment undermined
the authority of kings and churches and helped
set the intellectual stage for the soon-to-come
revolutions in the United States, France,
But the Enlightenment was also about increasingly
centralized state power and colonization of
non-Europeans, which we talked about two episodes
Statistics, for example, was developed at
this time to serve the interests of nation-states
and early corporations.
So we can also call this the Age of Empire…
Perhaps no object better represents the Enlightenment
than the ambitious book named the Encyclopédie.
Edited by Jean d’Alembert and Denis Diderot
from 1751 to 1777, the twenty-two volume Encyclopédie
attempted to organize literally all of the
knowledge available to humanity.
The Encyclopédie physically demonstrated
three big ideas: First, knowledge is cumulative.
Humans add new knowledge to our collective
pool all the time.
Second, knowledge is recordable.
We can transmit knowledge through things like
And third, knowledge is political.
Diderot, like Bacon, believed that knowledge
should be used to alleviate human misery.
Diderot hoped to “change the general way
of thinking” by popularizing recent achievements
in science and technology and combating superstition.
He wanted to use knowledge to help people
He also thought that all traditional beliefs
should be reexamined “without sparing anyone’s
But strict censorship by the state made any
explicitly anti-religious articles impossible,
so Diderot had to cleverly slip in critiques
of the church.
For example, in the cross-reference for the
entry on the Eucharist: “see cannibalism.”
Now, the Encyclopédie systemized knowledge
in a neat way, but it was largely qualitative,
describing things according to values—for
example, what a good ship looks like.
But Enlightenment thinkers increasingly dreamed
of quantification, or describing things in
numbers—like units of length, mass, heat,
and so on.
But for quantification to work, you have to
have an agreement about how to measure things.
In other words, you have to have standards.
The meter, for example, was defined by a commission
of scientists in France in the 1790s as one
ten-millionth of the earth’s meridian through
The commission included Pierre-Simon Laplace,
who wrote the five-volume
Celestial Mechanics, starting
This greatly expanded Newton’s work on classical
mechanics, opening up a range of topics to
the problem-solving power of calculus.
Celestial Mechanics became a sort of Principia – volume two.
And in order to actually measure the meter,
the commission sent out two guys, Pierre Méchain
and Jean-Baptiste Delambre, to make measurements.
…I’m not good at French.
This was a time of widespread war in Europe.
Méchain and Delambre struggled against skirmishes,
yellow fever, and imprisonment—but they
got the job done.
And along with standards, measurement required
new instruments, like the barometer and electrometer,
as well as new ways of interpreting data,
AKA statistics, which were also pioneered
By the end of the eighteenth century, physics
was already well on its way to rationalization,
quantification, and even standard measurement.
But what about chemistry?
In the late 1700s, natural philosophers believed
that chemical reactions occurred thanks to
an ether—a colorless, odorless, “self-repulsive,”
extremely fine, and therefore hard-to-measure
According to phlogiston theory, this ether
was released during combustion.
For example, a burning candle was thought
to release phlogiston.
If you covered that candle with a jar, the
flame would go out, because the air would
become saturated with phlogiston and couldn’t
absorb any more.
This is exactly the opposite of how we now
understand it: that the flame goes out because
it’s used up all of the oxygen, which is
necessary for a chemical reaction.
Likewise, it was thought at the time that,
when plants grew, they absorbed phlogiston
from the air.
When their wood was burned, it released phlogiston
back into the air.
Or when we ate them, our bodies released phlogiston
through respiration and body heat.
In this system, “phlogisticated air” or
“fixed air” was what we would now call
Joseph Black isolated fixed air in 1756.
“Dephlogisticated air,” on the other hand,
This system worked pretty well to explain
chemical reactions qualitatively—why they
seemed to appear a certain way—but no one
could quantify phlogiston.
And minor anomalies in phlogiston theory kept
For example, mercury gained weight during
combustion, even though, by releasing phlogiston,
it should have lost weight.
The person who changed chemistry from a qualitative
discipline to a quantitative one was Antoine-Laurent
A good example of an Enlightenment natural
philosopher, Lavoisier was born to a noble
family in Paris in 1743.
He studied law but was obsessed with geology
Lavoisier also worked on the metric system.
Lavoisier first presented research on chemistry,
in a paper about gypsum, to the French
Academy of Sciences in 1764.
In 1768, the Academy made Lavoisier a provisional
Two decades later, he would become the founder
of the “new chemistry,” revolutionizing
the entire discipline.
ThoughtBubble, show us what this means:
Lavoisier knew phlogiston theory well.
But he began his chemical research with
the hypothesis that, during combustion, something
is taken out of air rather than put into it.
That hypothesis turned out to be correct,
and that something turned out to be oxygen.
Lavoisier’s tested his hypothesis by accounting
for inputs and outputs in chemical reactions—a
perfect example of the eighteenth-century
quantification of science.
And Lavoisier also discovered that the mass
of matter remains the same even when it changes
form or shape.
Which is very important!
Working carefully over years, he generated
the first modern list of elements.
He named oxygen in 1778, hydrogen in 1783,
and silicon—merely a prediction at that
In fact, Lavoisier and his allies developed
a whole new nomenclature for chemistry, in
“Inflammable air” became hydrogen.
“Sugar of Saturn” became lead acetate.
“Vitriol of Venus”—which had also been
called blue vitriol, bluestone, and Roman
vitriol—became copper sulfate.
Yeah, the new naming system was less fun than
the old one.
But it was more rational:
the terms better described the underlying
stuff they pointed to.
“Copper sulfate” meant a compound of sulfur
Lavoisier published the textbook Elementary
Treatise of Chemistry in 1789, which taught
only the new chemistry.
In the introduction to his book, Lavoisier
also separated heat and chemical composition.
So water is water whether it’s heated up
to steam or cooled down to ice.
He understood that heating something up doesn’t
always change what it is, fundamentally.
To explain these state changes, Lavoisier
made up a new ether, which he called the
Caloric could penetrate a block of ice, melting
it into water by pushing the ice particles apart.
Thanks Thought Bubble.
Spoiler: caloric is not thought to be a real
(Many people wish calories weren’t real,
but, here we are.)
Led by the prominent English chemist Joseph
Priestley, these old-timers kept modifying
phlogiston theory so that it could rationally
account for chemical reactions without falling
apart, due to the whole phlogiston-in versus
Well into the 1780s, many chemists still
believed in phlogiston—which no one had
actually seen or measured—simply because
it was familiar.
What changed their minds?
Well, Lavoisier and his allies published results
that favored their system.
But more importantly, the students who learned
from them could only speak the language
of the new chemistry.
The phlogiston believers were increasingly
Thus in a couple of decades, phlogiston moved
from the center of chemistry into exile.
With the new chemistry, Lavoisier brought
the discipline into the system of rational,
experimental science dreamed up by methodologists
such as Bacon and fleshed out by Newton.
Outside of chemistry, Lavoisier was a noble
with a powerful state job: he worked at the
hated tax collection agency of the French
kingdom, known for being both secretive and
He profited from his job there, helping fund
his chemical research.
But the French Revolution broke out in 1789,
and being an aristocratic tax collector was
not a good look.
Lavoisier was tried for defrauding the people
And the judge denied the appeal to save his
life, despite his immense contributions to
knowledge, declaring that: “The Republic
needs neither scientists nor chemists; the
course of justice can not be delayed.”
Lavoisier died by guillotine in 1794.
His friend, mathematician Joseph-Louis Lagrange,
said of Lavoisier’s death: “It took them
only an instant to cut off his head, but France
may not produce another such head in a century.”
Now, how was Lavoisier so successful at setting
up the new chemistry as a paradigm?
Well, he had a lot of support!
Marie-Anne Pierrette Paulze, AKA “Madame
Lavoisier,” was born into a noble family
in south-central France in 1858.
And she contributed significantly to Antoine’s
She translated his texts into English, and
after Antoine’s death, she published his
complete papers, securing his legacy in the
Madame Lavoisier eventually remarried another scientist, Count
Rumford, a physicist who had a role in shaping
But she insisted on keeping Lavoisier’s
name to show her allegiance to the man she
Also, Madame Rumford is way less cool.
After the Lavoisiers, a new generation of
thinkers continued to develop their ideas,
in France and beyond.
Notably, John Dalton observed that the ratio
of elements in reactions were often made up
of small numbers, meaning that chemical elements
are in fact discrete particles, not fluids.
He called these particles chemical atoms—true
And Joseph Fourier published the Analytical
Theory of Heat in 1822, using calculus to
describe how heat flows.
Fourier also discovered the greenhouse effect,
or the capture of the sun’s radiation in
the earth’s atmosphere.
Next time—we’ll classify plants’ sexy
parts, disintegrate a willow tree, and debate
whether whole species can … go extinct.
Join us for biology before Darwin!
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