Proust gave the Law of constant proportions in 1779.
Law of constant proportion
The law of definite proportions was first put forward by the French chemist Joseph Louis Proust in 1779. The law of constant proportions states that chemical compounds are made up of elements present in a fixed ratio by mass. This implies that any pure sample of a compound, no matter the source, will always consist of the same elements that are present in the same ratio by mass.
- This ratio does not depend on the source of the chemical compound or the method through which it was prepared.
- The ratio of the number of atoms of each element is provided below the mass ratio. For example, in a nitrogen dioxide (NO2 ) molecule, the number of nitrogen and oxygen atoms is 1:2, but the mass ratio is 14:32 (or 7:16).