Carl Wilhelm Scheele (9 December 1742 – 21 May 1786) was a
German-
Swedish pharmaceutical chemist.
Isaac Asimov called him "hard-luck Scheele" because he made a number of chemical discoveries before others who are generally given the credit. For example, Scheele discovered
oxygen (although
Joseph Priestley published his findings first), and identified
molybdenum,
tungsten,
barium, and
chlorine before
Humphry Davy.
Biography
Scheele was born in
Stralsund, Western
Pomerania,
Germany (at the time under Swedish rule). Instead of becoming a carpenter like his father, Scheele decided to become a pharmacist. His career as a
pharmacist began with his apprenticeship at an apothecary in
Gothenburg when he was only fourteen years old. He retained this position for eight years before becoming an apothecary's clerk in
Malmö. Then Scheele worked as a
pharmacist in
Stockholm, from 1770-1775 in
Uppsala, and later in
Köping.
Scientific career
Existing theories before Scheele
By the time he was a teenager, Scheele had learned the dominant theory of gases in the 1770s, the
phlogiston theory. Phlogiston, classified as "matter of fire", was supposed to be released from any burning material, and when it was exhausted, combustion would stop.. When Scheele discovered
oxygen he called it "fire air" because it supported combustion, but he explained oxygen using phlogistical terms because he did not believe that his discovery disproved the phlogiston theory. Before Scheele made his discovery of oxygen, he studied air.
Air was thought to be an element that made up the environment in which
chemical reactions took place but did not interfere with the reactions. Scheele's investigation of air enabled him to conclude that air was a mixture of "fire air" and "foul air;" in other words, a mixture of two gases. He performed numerous experiments in which he burned substances such as saltpeter (
potassium nitrate),
manganese dioxide, heavy metal nitrates,
silver carbonate and
mercuric oxide. In all of these experiments, he isolated gas with the same properties; his "fire air," which he believed combined with phlogiston to be released during heat-releasing reactions. However, his first publication ,
A Chemical Treatise on Air and Fire, was not released until 1777, at which time both
Joseph Priestley and
Lavoisier had already published their experimental data and conclusions concerning oxygen and the phlogiston theory.
Disproving the theory of phlogiston
Joseph Priestley.
Historians of science no longer question the role of Carl Scheele in the overturning of the
phlogiston theory. It is generally accepted that he was the first to discover oxygen, among a number of prominent scientists (namely his esteemed colleagues
Antoine Lavoisier,
Joseph Black, and
Joseph Priestley). In fact, it was determined that Scheele made the discovery three years prior to Priestley and at least several before Lavoisier. Joseph Priestley relied heavily on Scheele's work, perhaps so much so that he would not have made the discovery of
oxygen on his own. Correspondence between Lavoisier and Scheele indicate that Scheele achieved interesting results without the advanced laboratory equipment that Lavoisier was accustomed to. Through the studies of Lavoisier, Joseph Priestley, Scheele, and others,
chemistry was made a standardized field with consistent procedures. Although Scheele was unable to grasp the significance of his discovery of
oxygen, his work was essential for the invalidation of the long-held theory of phlogiston.
Scheele's study of the gas not yet named oxygen was sparked by a complaint by
Torbern Olof Bergman. Bergman informed Scheele that the saltpeter he purchased from Scheele's employer produced red vapors when it came into contact with acid. Scheele's quick explanation for the vapors led Bergman to suggest that Scheele analyze the properties of
manganese dioxide. It was through his studies with manganese dioxide that Scheele developed his concept of "fire air." He ultimately obtained oxygen by heating
mercuric oxide,
silver carbonate,
magnesium nitrate, and
saltpeter. Scheele wrote about his findings to Lavoisier who was able to grasp the significance of the results.
Pyrolusite or MnO2.
New elements
In addition to his joint recognition for the discovery of oxygen, Scheele is argued to have been the first to discover other chemical elements such as
barium (1774),
manganese (1774),
molybdenum (1778), and
tungsten (1781), as well as several chemical compounds, including
citric acid,
lactic acid,
glycerol,
hydrogen cyanide (also known, in aqueous solution, as prussic acid),
hydrogen fluoride, and
hydrogen sulfide. In addition, he discovered a process similar to
pasteurization, along with a means of mass-producing
phosphorus (1769), leading Sweden to become one of the world's leading producers of
matches.
Chlorine gas.
Statue of Scheele in Köping.
Scheele made one other very important scientific discovery in 1774, arguably more revolutionary than his isolation of
oxygen. He identified
lime,
silica, and
iron, in a specimen of
pyrolusite given to him by his friend,
Johann Gottlieb Gahn, but could not identify an additional component. When he treated the pyrolusite with
hydrochloric acid over a warm sand bath, a yellow-green gas with a strong odor was produced. He found that the gas sank to the bottom of an open bottle and was denser than ordinary air. He also noted that the gas was not soluble in water. It turned corks a yellow color and removed all color from wet, blue litmus paper and some flowers. He called this gas with bleaching abilities, "dephlogisticated muriatic acid" (dephlogisticated hydrochloric acid). Eventually, Sir
Humphry Davy named the gas
chlorine.
See also
