Gay Lussac formulated his law of combining volumes following experiments exploding together given volumes of Hydrogen and Oxygen and discovering that water comprised two volumes of hydrogen to one volume of oxygen. His law states that when gases react they do so in volumes bearing a simple ratio to one another and to the volumes of their gaseous products provided that temperature and pressure remain constant. Dalton refused to accept the new law as it appeared to contradict his theory of the atom. The difference between the atom and molecule was not clearly understood until the work of Avogadro in 1811.
