When two or more elements together formed a compound The ratio by mass of the elements that are.The element is always constant, regardless of the compound preparation by any method.
When elements from two or more together as a compound. Mass ratio of the elements are the elements that are constant, whether the compounds are prepared in any way whatsoever.
When the elements from two kinds of up together as compounds. Mass ratio of elements is the element that is constant no matter prepared compound that with any method.