Law of Definite Proportions - Wikipedia - Joseph Proust  ## Metadata - Author: **Joseph Proust** - Full Title: Law of Definite Proportions - Wikipedia - Category: #articles - URL: https://en.wikipedia.org/wiki/Law_of_definite_proportions ## Highlights - In chemistry, the law of definite proportions, sometimes called Proust's law, 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 8/9 of the mass of any sample of pure water, while hydrogen makes up the remaining 1/9 of the mass: the mass of two elements in a compound are always in the same ratio. Along with the law of multiple proportions, the law of definite proportions forms the basis of stoichiometry.[1]