Law of definite proportions

The law of definite proportions, also known as the law of constant composition, is a chemical law that says that a chemical compound will always have the same elemental composition, that is that it will always contain the same chemical elements in the same proportions. It has been variously called Proust's law, Richter's law and Wenzel's law, as the priority of discovery is somewhat confused, but it was Proust who stated it most clearly and defended it against its critics (notably Berthollet). It was extended by Dalton in 1803 in his law of multiple proportions, and the two are often defined in modern discussions.