According to Duckworth, that obtained this information in an old book of chemistry of Klaproth, 13th century Chinese already knew the composition of water and, in a certain way, the nature of the atmosphere. They knew that the air had more than a constituent and that the element, now called oxygen, tended to bond with many metals, sulfur and carbon, but not with gold. According to them, the oxygen could be prepared by heating up saltpeter (potassium nitrate) and certain minerals like pyrolusite (manganese dioxide). Be sides, they also recognized that the oxygen was one of the constituents of water.