Law of Multiple Proportions

When carbon is heated in a stream of gas containing oxygen mixed with a nonreactive gas, it is oxidized. When there is little oxygen present in the gas string, the principle product of the oxidation is carbon monoxide. Analysis of the carbon monoxide shows that the mass ratio of oxygen to carbon is 1.33. When oxygen is present in higher concentrations, the principle product of the oxidation of carbon is carbon dioxide. Analysis of carbon dioxide shows that the mass ratio of oxygen to carbon is 2.667. John Dalton first stated the Law of Multiple Proportions: When two elements form two different compounds, the mass ratio of the elements in one compound and the mass ratio of the elements in the other are related by a ratio of small, whole numbers. In our example, the mass ratio of oxygen to carbon in carbon dioxide is two times the mass ratio of oxygen to carbon in carbon monoxide.