Antoine Lavoisier

Antoine Lavoisier

Lived 1743 – 1794.

Antoine Lavoisier revolutionized chemistry. He named the elements carbon, hydrogen and oxygen; discovered oxygen’s role in combustion and respiration; established that water is a compound of hydrogen and oxygen; discovered that sulfur is an element, and helped continue the transformation of chemistry from a qualitative science into a quantitative one.

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Beginnings

Antoine-Laurent Lavoisier was born into a privileged family on August 26, 1743 in France’s capital city, Paris.

His father was Jean-Antoine Lavoisier, a lawyer in the Paris Parliament.

His mother was Émilie Punctis, whose family wealth had come from a butchery business. She died when Antoine was five years old, leaving him a large amount of money.

Between the ages of 11 and 18, Antoine was educated at Collège des Quatre-Nations, a college of the University of Paris. He studied general subjects there, including the sciences in his final two years.

Although he was very attracted to the sciences, he enrolled in the college’s law school at 18, aiming to pursue the same career as his father. (His father had encouraged him to believe that science was merely a hobby, not a serious profession.)

After two years studying law, he was awarded a bachelor’s degree. A year later, in 1764, he obtained a license to practice as a lawyer, but decided against this.

Antoine Lavoisier’s Science

While studying for his law degree Lavoisier had maintained his interest in science, attending science lectures in addition to law lectures.

In 1764, the year he obtained his license to practice law, he also published his first scientific paper. In the same year he read a paper to the elite French Academy of Sciences. He was elected to the French Academy of Sciences in 1769, aged just 26.

Forms of Carbon

In 1772 Lavoisier and other chemists bought a diamond and placed it in a closed glass jar. They used a remarkable giant magnifying glass to focus the sun’s rays on the diamond. The diamond burned and disappeared.

Lavoisier's Lens

Lavoisier’s remarkable combustion apparatus

Lavoisier noted the overall weight of the jar was unchanged, even though all of the diamond had disappeared. This observation would later be part of the evidence convincing him that his law of mass conservation was correct.

Whether diamond or charcoal were burned by the giant lens, the same gas was produced – we now call it carbon dioxide. Lavoisier realized that diamond and charcoal are different forms of the same element.

He gave this element the name carbon.

Oxygen and Combustion

In 1772 people did not understand the process of burning. They had inconsistent, confused theories, chief of which was the theory of phlogiston, an undetectable substance which sometimes had negative mass!

We now know that combustion happens when substances react with oxygen at high temperatures. In 1772, however, when Lavoisier began working in this field, oxygen’s discovery by Joseph Priestley still lay two years in the future.

Lavoisier’s work enjoyed a great advantage over many other scientists – his great passion for accurate measurements – quantitative rather than qualitative science.

In 1772 Lavoisier discovered that when phosphorus or sulfur are burned in air the products are acidic. The products also weigh more than the original phosphorus or sulfur, suggesting the elements combine with something in the air to produce acids. But what?

In 1774 Joseph Priestley visited Paris. He told Lavoisier about the gas produced when he decomposed the compound we now called mercury oxide. This gas supported combustion much more powerfully than normal air. Priestley believed the gas was a particularly pure version of air. He started calling it dephlogisticated air, believing its unusual properties were caused by the absence of phlogiston.

Lavoisier did not believe it was dephlogisticated anything, because he did not believe in phlogiston.

In 1779 Lavoisier coined the name oxygen for the element released by mercury oxide. He found oxygen made up 20 percent of air and was vital for combustion and respiration. He also concluded that when phosphorus or sulfur are burned in air, the products are formed by the reaction of these elements with oxygen.

Antoine Lavoisier“Sulfur, when burning, absorbs oxygen gas; the resulting acid is considerably heavier than the sulfur burned; its weight is equal to the sum of weights of the sulfur burned and the oxygen absorbed.”

Antoine Lavoisier
Elementary Treatise on Chemistry
 

Sulfur is an element

In 1777 Lavoisier correctly identified sulfur as an element. He had carried out extensive experiments involving this substance and observed that it could not be broken down into any simpler substances.

The Conservation of Mass

In 1778 Lavoisier found that when mercury oxide is heated its weight decreases. The oxygen gas it releases has exactly the same weight as the weight lost by the mercury oxide.

While this may seem obvious to us today, it was less so in those days (hence the general support for the phlogiston theory). After carrying out work with a number of different substances, and recalling earlier work such as his work in 1772 with carbon, Lavoisier announced a new fundamental law of nature: the law of conservation of mass:

  • matter is conserved in chemical reactions

or stated in another way:

  • the total mass of a chemical reaction’s products is identical to the total mass of the starting materials

It is often said that Lavoisier was the first scientist to state the principle of mass conservation. This is not strictly incorrect. In 1630 Jean Rey had formulated a similar law; in 1755 Joseph Black had assumed the law was true in his work discovering magnesium; and in 1760 Mikhail Lomonosov had published a statement of the law.

The law of mass conservation only became firmly established after Lavoisier independently discovered it.

Antoine Lavoisier“In performing experiments, it is necessary… that they be simplified as much as possible, and that every circumstance that could complicate the results should be completely removed.”

Antoine Lavoisier
Elementary Treatise on Chemistry
 

Combustion and respiration

Lavoisier suspected that combustion and respiration are chemically the same. He demonstrated this with the help of Pierre-Simon Laplace. The pair measured the amount of carbon dioxide and heat given off by a guinea pig as it breathed. They compared this to the amount of heat produced when they burned carbon to produce the same amount of carbon dioxide as had been exhaled by the guinea pig.

Their results allowed Lavoisier to conclude that respiration is a form of combustion. The heat produced by mammals during respiration keeps their bodies above room temperature.

Lavoisier Respiration

Lavoisier measures the oxygen in air exhaled from a man’s lungs. Lavoisier’s wife Marie-Anne makes notes. A skilled artist, she also created the engraving from which this image was taken.

Water is not an element

In 1783 Lavoisier coined the name ‘hydrogen’ for the gas which Henry Cavendish had recognized as a new element in 1766; Cavendish had called the gas inflammable air.

Working again with Pierre-Simon Laplace, Lavoisier burned hydrogen with oxygen and found that water was produced, establishing that water is not an element, but is actually a compound made from the elements hydrogen and oxygen. This result astonished many people, because at that time ‘everyone knew’ that water was itself one of the ‘indivisible’ elements.

Hydrogen means water former in Greek.

Antoine Lavoisier“It required 85 parts by weight of oxygen and 15 parts of hydrogen to compose 100 parts of water.”

Antoine Lavoisier
Elementary Treatise on Chemistry
 

There is no such thing as phlostigon!

Lavoisier’s work with oxygen and his demonstration of mass conservation had made it absolutely clear to him that phlostigon was fictitious. In 1783 his paper Reflections on Phlogiston marked the beginning of the end for phlogiston and a triumph for Lavoisier’s oxygen theory and quantitative chemistry.

Lavoisier’s list of elements

In 1789 Lavoisier published his groundbreaking Elementary Treatise on Chemistry.

Aristotle’s elements of earth, water, air, fire and quintessence had been abandoned by medieval alchemists, and Lavoisier now abandoned their tria prima of sulfur, mercury and salt.

Elementary Treatise on Chemistry detailed his oxygen theory of chemistry (banishing phlostigon), made clear the difference between a compound and an element, and contained a list of chemical elements. The list included oxygen, nitrogen, hydrogen, sulfur, phosphorus, carbon, antimony, cobalt, copper, gold, iron, manganese, molybdenum, nickel, platinum, silver, tin, tungsten, and zinc.

Curiously, and consistent with chemistry’s infancy, Lavoisier included light as one of the chemical elements.

He also included a substance called caloric, which was later shown, like phlogiston, to be fictitious. In fact, so much of Elementary Treatise on Chemistry involves caloric in explanations that it slightly spoils the work. Again though, we must remember that chemistry was still in its infancy, and Lavoisier was largely responsible for pulling it up on to firmer ground.

Antoine Lavoisier“Experiments upon vegetation give reason to believe that light combines with certain parts of vegetables, and that the green of their leaves, and the various colors of flowers, is chiefly owing to this combination.”

Antoine Lavoisier
Elementary Treatise on Chemistry
 

The Metric System

Starting in 1791, Lavoisier served on the committee of the French Academy of Sciences which developed the metric system of measurement. Other members of the committee including the well-known mathematicians Pierre-Simon Laplace and Adrien-Marie Legendre.

Some Personal Details and The End

In addition to his scientific research, Lavoisier was industrious in other fields. At the age of 26 he bought into a company which gathered tax for the French government. Having done this, he tried to reform tax law to help poorer taxpayers. He also served on the government’s gunpowder commission, improving the quality of French gunpowder considerably.

Lavoisier married Marie-Anne Pierrette Paulze in 1771. He was 28 and she was just 13. In marrying Marie-Anne so young, he was acting at the request of her father, who was a senior member of the tax company Lavoisier had bought into. The Count d’Amerval, who was about 40, had made a proposal of marriage to Marie-Anne and her father had been threatened with dismissal from the tax company if she did not say yes. Lavoisier stepped in and married her to provide Marie-Anne and her father with a suitable excuse for her not marrying The Count.

lavoisier-and-marie-anne

Antoine Lavoisier and his wife Marie-Anne, painted by Jacques-Louis David in c. 1788.

Marie-Anne was a skilled artist and well-educated. She helped Lavoisier considerably with his work, translating scientific papers from English into French – adding her own notes and scientific criticisms of papers, helping with laboratory work, making accurate drawings of laboratory apparatus for Lavoisier’s scientific publications, and keeping accurate written records of Lavoisier’s experiments.

During the French Revolution, which began in 1789, wealthy people and anyone who had worked for the government were under threat. In 1793 the revolutionaries put an end to the French Academy of Sciences and other academic societies.

In 1794 Lavoisier was branded a traitor because of his involvement with taxation. He was also unpopular with revolutionaries because he had supported foreign scientists, whom the revolutionaries wished to strip of their assets.

Lavoisier was sentenced to death by the revolutionaries. Trumped-up charges against him included stealing money from France’s Treasury and giving it to France’s enemies.

Antoine Lavoisier died by the guillotine at the age of 50 on May 8, 1794 in Paris. Marie-Anne’s father and 26 other people were executed on the same occasion.

At the end of 1795, in a U-turn, the French government found Lavoisier innocent of all charges. By then, of course, it was too late: he was just another innocent victim of the revolution’s Reign of Terror.

Lavoisier’s wife and his tremendous contributions to chemistry survived. Ironically his wife, Marie-Anne, later married Benjamin Thompson, who played a key role in establishing that caloric, like phlogiston, was merely a figment of people’s imaginations.

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Further Reading
Antoine-Laurent Lavoisier
Elements of Chemistry
Dover Publications Inc, 1965

Robert D. Whitaker
An Historical Note on the Conservation of Mass
J. Chem. Educ., 1975, 52 (10), p 658

Arthur Donovan
Antoine Lavoisier: Science, Administration and Revolution
Cambridge University Press, 1996