239 years ago today, on May 21, 1786 (April 24, 1786 lunar calendar), the Swedish chemist Carl Wilhelm Scheler died. Born in southern Sweden on December 19, 1742, Carl Wilhelm Scheler was a rather famous scientist from the mid-18th century to the late 18th century. Scheler became interested in chemistry early on, and he repeated experiments in some famous chemistry books of the time. He conducted a large number of experimental studies and discovered many new substances in his experimental research. On February 4, 1775, Scheler was elected to the Swedish Academy of Sciences. Scheler worked in pharmacies in Gothenburg, Malmö, Uppsala, Stockholm, and other places in his early years. Most of the time, he worked in pharmacies in the small town of Cherpin, and a large number of experimental studies were also carried out in Cherpin. Scheler was often in poverty, and a lot of experimental work was carried out in cold laboratories with rudimentary equipment. He also often worked at night, which greatly damaged his health. He developed asthma and died prematurely on May 21, 1786, at the age of 44. Scheler's life was short, but he achieved considerable results. First, he discovered dozens of new elements and compounds such as oxygen, chlorine, fluorine, ammonia, chloride, hydrofluoric acid, tungsten acid, molybdic acid, etc. He discovered more than 30 new substances in his lifetime. This was unique at the time. Among Scheler's discoveries, the most outstanding contributions were the discovery of oxygen and chlorine. The discovery of chlorine has been introduced in textbooks. The discovery of oxygen was made in 1773 by Scheler through the thermal decomposition of salts such as potassium nitrate, magnesium nitrate, silver carbonate, mercury carbonate, and mercury oxide, and the co-heating of pyrolusite and concentrated sulfuric acid. The properties of oxygen were studied. Scheler collected his research results in the book "On the Chemistry of Air and Fire", but due to publisher delays, the book was not published until 1777. After the British chemist Priestley prepared and studied oxygen in 1774, he published his paper soon. Therefore, the history of chemistry believes that Scheler and Priestley independently discovered oxygen, and they were both discoverers of oxygen. Many of Scheler's experimental research results were not published during his lifetime. In 1892, on the occasion of the 150th anniversary of his birth, chemical historians detailed his diary and letters during his lifetime, but they were not officially published. It was not until 1942, when the 200th anniversary of Scheler's birth was commemorated, that all his experimental records were reorganized and officially published, with a total of eight volumes.