In short
The law of constant proportions says that a pure chemical compound always contains the same elements in the same proportion by mass, however it was made or wherever it came from.
Joseph Proust stated it. Water from a river, from rain or from burning hydrogen always has hydrogen and oxygen in the mass ratio . The law is also called the law of definite proportions or the law of constant composition. It does not apply to mixtures, whose parts can be mixed in any ratio.
Water contains of hydrogen for every of oxygen. In of any sample of water there are of hydrogen and of oxygen. In there are and .
Also searched as: law of constant proportion, law of constant composition, law of definite proportions.
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