Joseph proust
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Joseph Proust was important during the time around 1794. He found the Law of Definite Proportions after conducting many tests on chemical substance. After doing tests on copper carbonate reactions, he figured out that each pure compound has its own characteristic composition. The ratio of elements never changes even though its mass may have changed. For example: H20 will always be a ratio of 2:1, no matter it is 1 gram or 100 grams. It will also have the same proportion if it is lake water or clear water.