This law was put forward by Dalton in 1803. This law is applicable when two elements combine to give more than one chemical compound. The law states that, “When two elements combine to form two or more compounds, the masses of one element which combined with a fixed mass of the other, bear a simple ratio to one another.”

This law can be illustrated by taking an example of the reaction between carbon and oxygen. Carbon(C) reacts with Oxygen (O) to give two compounds, i.e., carbon dioxide (CO2) and Carbon monoxide (CO).

Let us see, if the formation of H2 and H2O2 support the law of multiple proportions. The combining ratios of the two elements in these compounds are, Thus masses of oxygen which combine with 12 g of carbon are in the ratio of 16: 32, or in the ratio of 1:2. The ratio of 1:2 is a simple ratio. Hence, the formation of CO and CO2 verifies the law of multiple proportions. Let us see, if the formation of H2 and H2O2 support the law of multiple proportions. The combining ratios of the two elements in these compounds are,

Thus the masses of oxygen which combine with 1g of hydrogen to form these two compounds are in the ratio of 8:16 or 1:2. The ratio of 1:2 is a simple ratio. Therefore, these results support the law of multiple proportions.