John Dalton gave the law of definite proportions.
The law of definite proportion
The law of definite proportions was first put forward by the French chemist Joseph Louis Proust in 1779. The discovery that mass was always conserved in chemical reactions was soon followed by the law of definite proportions, which states that a given chemical compound always contains the same elements in the same proportions by mass.
- The law of constant proportions is often referred to as Proust’s law of definite proportions.
- For example, in a nitrogen dioxide (NO2 ) molecule, the ratio of the number of nitrogen and oxygen atoms is 1:2, but the mass ratio is 14:32 (or 7:16).
- For example, pure water will always contain hydrogen and oxygen in a fixed mass ratio (a gram of water consists of approximately 0.11 grams of hydrogen and 0.88 grams of oxygen, the ratio is 1:8).