<P> In chemistry, the law of definite proportion, sometimes called Proust's law or the law of definite composition, or law of constant composition states that a given chemical compound always contains its component elements in fixed ratio (by mass) and does not depend on its source and method of preparation . For example, oxygen makes up about / of the mass of any sample of pure water, while hydrogen makes up the remaining / of the mass . Along with the law of multiple proportions, the law of definite proportions forms the basis of stoichiometry . </P> <P> The law of constant proportion was given by Joseph Proust in 1779 . This observation was first made by the English theologian and chemist Joseph Priestley, and Antoine Lavoisier, a French nobleman and chemist centered on the process of combustion . </P>

What is an example of the law of definite proportions
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