When two pure substances react to form a compound, they do so in a definite proportion by mass. For example, when water is formed from the reaction between hydrogen and oxygen, the 'definite proportion' is 1 g of H for every 8 g of O.
LAW OF DEFINITE PROPORTIONS
Meaning of LAW OF DEFINITE PROPORTIONS in English
General chemistry English glossary. Английский глоссарий общей химии. 2012