Law of multiple proportions
In chemistry, the law of multiple proportions states that in compounds which contain two particular chemical elements, the amount of Element A per measure of Element B will differ across these compounds by ratios of small whole numbers. For instance, the ratio of the hydrogen content in methane (CH4) and ethane (C2H6) per measure of carbon is 4:3.
Source: Wikipedia — Law of multiple proportions (CC BY-SA 4.0)