His rule of greatest simplicity postulated that if two elements form only one compound, than the compound has the simplest composition: one atom of each element.  
His rule of greatest simplicity postulated that if two elements form only one compound, than the compound has the simplest composition: one atom of each element.  His most famous theory includes Lavoisier's postulate of the conservation of mass and explains Proust's law of definite proportions.  His law states that the total pressure of a mixture of gases is the sum of the partial pressures.  FTP, name this English chemist who proposed the atomic theory of matter.
His rule of greatest simplicity postulated that if two elements form only one compound, than the compound has the simplest composition: one atom of each element.  
John Dalton