"Lavoisier's quantitative examination of the change... proved that the total mass of the reacting substances mercury and air, remained unchanged. ...the masses of the two elements which combine are always in the ratio of one of oxygen to 12.5 of mercury. When the compound mercuric oxide is strongly heated, it is changed into the elements mercury and oxygen; the sum of the masses of the two elements obtained is exactly equal to the mass of the compound changed; the masses of the mercuric oxide, mercury, and oxygen, are always in the ratio of 13.5 to 12.5 to 1."