Conservation of Matter
Year of Discovery: 1789
What Is It? The total amount of matter (mass) always remains the same no
matter what physical or chemical changes take place.
Who Discovered It? Antoine Lavoisier
Why Is This One of the 100 Greatest?
Lavoisier was the first chemist to believe in measurement during and after experiments. All chemists before had focused on observation and description of the reactions during an experiment. By carefully measuring the weight of each substance, Lavoisier
discovered that matter is neither created nor destroyed during a chemical reaction. It may
change from one form to another, but it can always be found, or accounted for. Scientists
still use this principle every day and call it “conservation of matter.”
Lavoisier’s work also established the foundation and methods of modern chemistry.
He did much work with gasses, gave oxygen its name (Joseph Priestley discovered oxygen
but called it “pure air”) , and discovered that oxygen makes up 20 percent of the atmosphere. Lavoisier is considered the father of modern chemistry.
How Was It Discovered?
In the spring of 1781, Frenchman Antoine Lavoisier’s wife, Marie, translated a paper
by English scientist Robert Boyle into French. The paper described an experiment with tin
during which Boyle had noted an unexplained weight change when the tin was heated.
Boyle, like most scientists, was content to assume that the extra weight had been “created”
during his chemical experiment.
Lavoisier scoffed at the notion of mysterious creation or loss of mass (weight) during
reactions. He was convinced that chemists’ traditional experimental approach was inadequate. During experiments chemists carefully observed and described changes in a substance. Lavoisier claimed it was far more important to record what could be measured.
Weight was one property he could always measure.
Lavoisier decided to repeat Boyle’s experiment, carefully measure weight, and discover the source of the added weight. Antoine carried a small sheet of tin to his delicate balancing scales and recorded its weight. Next he placed the tin in a heat-resistant glass flask
and sealed its lid to contain the entire reaction within the flask.
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