In Ancient Greece, Leucippus and Democritus believed all matter was made up of tiny pieces they called atoms. In the 18th century, Antoine Lavoisier proved that air and water were not pure substances. He explained an element is a substance which cannot be decomposed and cannot produce anything else than itself. Joseph Blake realized that frozen water and steam were both water, showing that a substance can exist in different states; liquid solid, and gas. In 1792, Jeremias Benjamin Richter mixed acids and bases and noticed that to get the same compound it always takes and identical ratio of raw materials. In the early 19th century, John Dalton demonstrated that all atoms of the same element are identical, but different elements are made up of different atoms, and each atom has a distinctive mass. In 1870, Dmitri Mendeleyev studied the 63 elements and organized them by weight and similar properties, creating a periodically evolving table of the elements. When Paul-Émile Lecoq de Boisbaudran discovered Gallium, it filled a void in Mendeleev's table.