STUDIES ON LAVOISIER'S EXPERIMENTAL METHOD

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Lavoisier's famous mass conservation law is clearly mentioned in his Traite elementaire de chimie published in 1789. But, it is not his first statement of the law. When he carried out quantitative experiments, he already used this law in order to check the result and had formulated it in his anterior publications. At first, his law was rather an alternative expression of material conservation. It was useful for evaluating mass of some substance which was not directly measured. When he began to execute quantitative analyses of organic substances, the significance of the law changed. After oxygen was discovered and he realized water is not a simple substance, it was essential for analyzing to decide what were the true composing elements. In effect, by combustion of an organic substance, we obtain mainly water and carbon dioxide. Lavoisier not only compared the mass of substances in reaction and the mass of products, but also compared mass of each element before and after combustion. He determined the composition of ethyl alcohol and sugar by this analytical method with enormous difficulty. That is why he expressed his law in the chapter on "fermentation of sugar into alcohol" in his book. That is his quantitative method of analyses based on his mass conservation law. But soon, he began to lose his strictness in his quantitative analyses : he easily satisfied himself with calculating following his law the mass of a substance he hadn't weighed instead of taking pains to repeat the experiment We think it is because he had no more time to reiterate the same experiment during the agitated torment of the French Revolution.