Without the atomic hypothesis the law of the additivity of masses and the law of definite proportions
remain entirely independent of one another.
In 1789 Antoine Lavoisier formulated the law of conservation of mass, and in 1799 Joseph-Louis Proust stated the law of definite proportions
, allowing chemists to distinguish between mixtures and compounds.
He went on to make a similar case for a number of other compounds and maintained that there was a general law of definite proportions
, often called Proust's law.