An example of the law of multiple proportions is carbon monoxide and carbon dioxide. Carbon combines with oxygen in different proportions to form two different oxides. The ratio of the fixed weights of carbon that combines with oxygen in both oxides is a simple whole number.
Another example is the formation of water and hydrogen peroxide, or H2O and H2O2 respectively. The weight of hydrogen that combines with oxygen to form these two compounds bears a simple ratio. The law of multiple proportions is also observed in the formation of two oxides of nitrogen, namely NO and NO2. The law of multiple proportions was formulated by John Dalton in 1804. It is regarded as a very important law in chemistry as it determines the way elements combine to form compounds.