History of an equation: matter is neither created nor destroyed

Portrait of the Lavoisiers, by Jacques-Louis David, (Metropolitan Museum of New York)

We all know the change that the discovery of fire brought about for humanity about 800,000 years ago (it was not even

Homo sapiens

who discovered it, but

Homo erectus

).

For millennia, it was used without knowing how it worked, but this ignorance did not go unnoticed by the heirs of the scientific revolution, who did not hesitate to seek an explanation.

Over time they realized that the key lay in combustion, the chemical process that governs the operation of fire: when an element comes into contact with oxygen, it burns and produces carbon dioxide and water.

It was the first equation to be considered in the field of reactions and it was the beginning of the conversion of alchemy into a rigorous science: chemistry.

A paradigm shift surrounded by circumstances as agitated as fire itself.

X + O₂ → CO₂ + H₂O

Combustion formula

While Lagrange, Euler and Hamilton competed to see who could construct the most abstract and elegant mathematical theory, throughout the 18th century there were several scientists who did not focus on dynamics and calculus, but rather, far from formalities so far removed from the reality and so complex, they toyed with the study of heat and nearly a century anticipated one of the main theories of the nineteenth century: thermodynamics.

At the same time, new substances, chemical elements, were discovered, and laboratories and places of experimentation began to spring up all over the continent.

The scientific method was beginning to replace the magic of alchemy.

European scientists, possessed by the spirit of the Enlightenment, were willing to experiment, but they were not the only ones who wanted to change the

status quo

.

If we talk about Europe and revolutions, we must fix our attention on France.

There, we meet Antoine Laurent Lavoisier, who was born in 1743 into a rich family from which he inherited a great fortune at an early age after the death of his mother.

Since he was an enormously intelligent person and was involved with society, he knew how to use such a fortune.

On the one hand, he drew up a thorough project to improve street lighting, developed mechanisms for the purification of water in Paris, and made reports on unsanitary conditions in prisons, among many other things.

On the other, he took advantage of the inheritance to make different investments and increase the initial fortune he owned.

It was especially profitable the one he carried out in the

ferme générale

(general farm), a semi-feudal institution that in the middle of the Enlightenment collected taxes for the crown (feeding especially on poor peasants).

The main work of the Lavoisiers was to turn chemistry into a science as such, which focused on the careful measurement of all quantities and obtaining knowledge through experimentation

Apart from all this, Lavoisier appears in this book for his great contribution to science, as he is considered the father of chemistry.

His comfortable economic situation allowed him to dedicate himself to research without worries and to build the most advanced chemical laboratory of the moment.

In addition, there was something else in his life that was not usual among the aristocracy of the time: a marriage based on affection and mutual love.

He married Marie-Anne Paulze, a tremendously cultured, intelligent and curious woman.

Their relationship was such that Lavoisier did not hesitate to make her his collaborator.

Paulze had a strong background in the arts (she was a student of Jacques-Louis David) and languages ​​and learned chemistry quickly.

In addition, since Lavoisier only spoke French, her knowledge of English was of vital importance when translating and interpreting the results of her contemporaries, especially as regards the theory of combustion.

• Ptolemy, Lavoisier and scientific plagiarism

Traditionally, Lavoisier has been given full credit for the creative and discovery side, although it is known with certainty that Paulze was responsible for all the illustrations of the experimental devices, as well as being the editor of all the works. and the person responsible for the translation into other languages ​​of his work.

Leaving aside this controversy, we are going to tell about the advances that took place in that laboratory, which would change the history of chemistry forever.

Until now there was no clear boundary between chemistry and alchemy and, despite valuable discoveries made, these were accompanied by obscure spiritist theories.

For example, in 1669 the alchemist Henning Brand discovered phosphorus (the first element found after the Ancient Ages) while trying to distill gold from urine to create the Philosopher's Stone.

The main work of the Lavoisiers was to turn chemistry into a science as such, which focused on the careful measurement of all quantities and on obtaining knowledge through experimentation.

In a display of enlightened and scientific thought, Antoine Laurent would say:

We should not trust anything that is not facts: these are presented to us through nature and cannot deceive us.

We must, in each and every one of the cases, submit our reasoning to the test of experimentation, and never seek the truth except through the natural path of experiment and observation.

One of the great gaps that chemistry had at that time concerned the theory of combustion.

Since ancient Greece, the theory of phlogiston survived (closely linked to Aristotle's four elements).

This theory proposed something quite intuitive: combustible objects (wood, oil, etc.) possessed the element of fire (called phlogiston) and released it when burning.

Despite working from the framework of alchemy and with magical and metaphysical motivations, Georg Ernst Stahl had been able to endow the theory of phlogiston with a solid experimental basis, but there was one question that eluded him: he could not explain why that some elements ignited and vanished (such as wood) and others heated up and gained mass (such as metals).

For example, in the case of phosphorus, the ashes weigh more than the substance before it burns.

Where did this excess mass come from?

This was an impossible question to answer with the phlogiston theory, which understood combustion exclusively as a liberation process.

The scientist realized that the key to everything was in the new element he had discovered, oxygen

In any case, proposing an alternative theory was not so straightforward, and this is where Lavoisier comes into play.

The scientist realized that the key to everything was in the new element he had discovered, oxygen.

No one had been able to explain the existence of fire before because this element was not known and, without it, it is impossible to create fire.

But how did the Lavoisiers come to that conclusion?

Lavoisier set out to burn as many substances as he could in insulated containers, both those that gain mass and those that lose it.

And what did you find?

Well, neither one nor the other is true.

Ironic, right?

In fact, he discovered - and later applied it successfully to all imaginable chemical reactions - that, if we take into account the mass of all the substances that are part of the reaction - including gases, for this reason closed containers were necessary -, the mass total is always preserved.

Their contemporaries made the mistake of not weighing oxygen and, furthermore, they did not take into account the combination of fuel with it, that is why for them bodies gained and lost mass without apparent logic.

However, with this new approach to combustion, Lavoisier not only discovered a new element (something already very remarkable), but also developed the law of conservation of mass, which would mark the definitive leap from alchemy to chemistry as a rigorous science.

In the monumental

Traité élémentaire de chimie

(Elementary Treatise on Chemistry), undoubtedly one of the most influential books in the history of chemistry, Lavoisier described it in its simplest form:

In nature nothing is created, nothing is destroyed, everything is transformed.

Lavoisier worked on all this from 1784, when he made his first explanation of combustion (in which he dismantled the phlogiston theory), until 1789, when the

Elementary Treatise on Chemistry

was published

while the French Revolution was breaking out.

This social earthquake was not traumatic for Lavoisier.

Despite being from a good family and very wealthy, his reformist character and all the effort he had put into improving the nation, especially from a technical point of view, earned him the respect of the revolutionaries, as well as feeling very comfortable with the principles of

Liberté, Égalité, Fraternité

[Liberty, equality, fraternity].

So much so that in 1791 he participated, together with Pierre-Simon Laplace, in the commission of weights and measures that established the metric system as the most suitable.

In addition, he interceded on behalf of his good friend Lagrange (born in Turin) when the Revolution decided to dispossess foreigners of property.

Lavoisier not only discovered a new element (something already very remarkable), but also developed the law of conservation of mass, which would mark the definitive leap from alchemy to chemistry as a rigorous science.

However, the situation changed enormously when the Jacobins came to power in 1793 and the Reign of Terror began.

In November of that same year, the arrest of all the former members of the Ferme générale (the hated fiscal institution), including our protagonist, was ordered.

Marie-Anne busied herself with preparing her husband's defense, emphasizing his innocence and how relevant it was to the Republic.

Among her arguments were some as solid as that she and Lavoisier had created a commission to perfect the gunpowder used by the French army and thereby defend themselves against their enemies when the nations of the Old Regime (Spain and Austria) declared war on the revolution.

All these tests were rejected and the reply of the Jacobin judge Jean-Baptiste Coffinhal became famous: "The Republic does not need scientists."

The author of the law of conservation of mass was executed by guillotine on May 8, 1794.

For Marie-Anne the tragedy was even greater, because among the other twenty-seven former tax collectors who lost their minds along with Lavoisier was also her father.

All the assets of the marriage, including scientific material, were seized and passed into the hands of the State.

However, Paulze fought against the injustice that had been committed and, in 1795, when the Reign of Terror had already ended and Robespierre and Judge Coffinhal had been guillotined, the French State recognized Lavoisier's innocence and returned to Marie-Anne everything confiscated it.

This tireless woman brought together the unpublished scientific work damaged by the requisition and produced the

Mémoires de chimie

(Memoirs of chemistry), another fundamental book in which, for the first time in history, facts such as that water is not a fundamental element, but a composition of hydrogen and oxygen.

In the foreword to the book (deleted in subsequent editions), Marie-Anne Paulze made a bitter criticism of the Revolution and the bloody paths it took.

The French Revolution was both a fascinating and a tragic time.

Stories like Lavoisier's illustrate how good intentions and a desire for change, mixed with haste and fanaticism, led to enormous contradictions and, in many cases, misfortunes.

In contrast, in the field of science, the understanding of a phenomenon as fundamental as fire made us abandon the phlogiston theory and begin to understand that in nature there are chemical elements that react with each other.

And, most importantly, that, in any of these reactions, the mass of all its elements is conserved.

World history in 30 equations

Authors: David Perezagua and Guillermo F. ​​Peñas

Publisher: Main

Pages: 288

Price: € 17.90

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