Law of Multiple Proportions
The principle that when two elements form more than one compound, the masses of one element combining with a fixed mass of the other are in small whole-number ratios.
Unit
Dimensionless
In depth
Dalton's law was powerful evidence for the atomic theory, because whole-number ratios only make sense if matter comes in indivisible units. It applies to any series of compounds between the same pair of elements and is most striking among the nitrogen and carbon oxides.
Examples in the real world
With 12 g of carbon, CO uses 16 g of oxygen and CO₂ uses 32 g — a ratio of exactly 1:2.