| Noun | 1. | law of multiple proportions - (chemistry) law stating that when two elements can combine to form more than one compound the amounts of one of them that combines with a fixed amount of the other will exhibit a simple multiple relation law of nature, law - a generalization that describes recurring facts or events in nature; "the laws of thermodynamics" chemical science, chemistry - the science of matter; the branch of the natural sciences dealing with the composition of substances and their properties and reactions |