In 1789, the French Chemist, Antoine Lavoisier, discovered the Law of Conservation of Mass. He sought to prove that mass is neither created nor destroyed in chemical reactions. When a pure metal was heated in air it became a calx (now known as an oxide) and increased in mass. To prove that mass was not created Lavoisier designed and conducted experiments to measure both the mass of the metal, calx and the mass of the surrounding air. He found that the amount of mass gained by the metal forming the calx was equal to the moss lost by the surrounding air. This proved his theory correct and established the Law of Conservation of Mass.