oct 18, 1771 - Antoine de Lavoisier (late 1700's)
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Antoine de Lavoisier was a very intelligent chemist. He defined the word "element" as a pure substance that cannot be broken down into a lesser or smaller substance. He also discovered and identified 23 different elements. He found those elements by using precise measurements and observations. IN his experiments he realized that there must be mixtures of substances and he figured that air must be a mixture of oxygen and another substance. He believed this because oxygen burns but if the air was made up of only oxygen then when there was a fire then the fire would take a very long time to put out and it would spread rapidly. So air had to be made of two different substances, one that will burn and one that will not. His theory was correct.
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