Carl Wilhelm Scheele- Scientist killed by his own experiments

3 years ago by in Featured, Scientists, Scientists
Statue of Scheele in Köping.

Statue of Scheele in Köping.

Carl Wilhelm Scheele (9 December 1742 – 21 May 1786) was a Swedish Pomeranian 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, hydrogen, and chlorinebefore Humphry Davy, among others.

Scheele was born in Stralsund, in western Pomerania, which was at the time under the control of Sweden. Scheele’s father Joachim Christian Scheele, was a merchant of a respected German family. At fourteen, he was sent as an apprentice pharmacist in Gothenburg with Martin Andreas Bauch. He retained this position for eight years before becoming an apothecary’s clerk in Malmö. Then Scheele worked as a pharmacist inStockholm, from 1770-1775 in Uppsala, and later in Köping.

Scheele preferred speaking German his whole life, and German was commonly spoken among Swedish pharmacists.

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 in materials to be released during heat-releasing reactions. However, his first publication, Chemische Abhandlung von der Luft und dem Feuer, was delivered to the printer Swederus in 1775, but not published until 1777, at which time both Joseph Priestley and Lavoisier had already published their experimental data and conclusions concerning oxygen and the phlogiston theory. The first English edition, Chemical Observation and Experiments on Air and Fire was published in 1780, with an introduction “Chemical Treatise on Air and Fire”

THE THEORY OF PHLOGISTON

Historians of science no longer question the role of Carl Scheele in the overturning of the phlogiston theory, although Scheele himself never discarded the 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 prompted by a complaint by Torbern Olof Bergman a professor at Upsala University who would eventually become Scheele’s friend. Bergman informed Scheele that the saltpeter he had purchased from Scheele’s employer, after long heating, produced red vapors (now known to be nitrogen dioxide) when it came into contact with acetic acid. Scheele’s quick explanation was that a the saltpeter had absorbed phlogiston with the heat (had been reduced to nitrite, in modern terms) and gave off a new phlogisticated gas as an active principle when combined with an acid (even a weak acid).

Bergman next suggested that Scheele analyze the properties of manganese dioxide. It was through his studies of manganese dioxide that Scheele developed his concept of “fire air” (his name for oxygen). He ultimately obtained oxygen by heating mercuric oxide, silver carbonate, magnesium nitrate, and other nitrate salts. Scheele wrote about his findings to Lavoisier who was able to see the significance of the results.

Although Scheele would always believe in some form of the phlogiston theory, his work reduced phlogiston to an unusually simple form, complicated only by the fact that chemists of Scheele’s day still believed that light and heat were elements and were to be found in combination with them. Thus, Scheele assumed that hydrogen was composed of phlogiston (a reducing principle lost when objects were burned) plus heat. Scheele speculated that his fire air or oxygen (which he found the active part of air, estimating it to compose one quarter of air) combined with the phlogiston in objects to produce either light or heat (light an heat were presumed to be composed of differing proportions of phlogiston and oxygen).

When other chemists later showed water is produced when buring hydrogen and that rusting of metals added weight to them and that passing water over hot iron gave hydrogen, Scheele modified his theory to suggest that oxygen was the salt (or “saline principle” of water), and that when added to iron, water was reproduced, which added weight to the iron as rust.

Pyrolusite or MnO2.

Pyrolusite or MnO2.

NEW ELEMENTS AND COMPOUNDS

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.

Chlorine gas.

Scheele made one other very important scientific discovery in 1774, arguably more revolutionary than his isolation of oxygen. He identifiedlime, silica, and iron in a specimen of pyrolusite (impure manganese dioxide) given to him by his friend, Johann Gottlieb Gahn, but could not identify an additional component (this was the manganese, which Scheele recognized was present as a new element, but could not isolate). 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, or oxidized hydrochloric acid). Eventually, Sir Humphry Davy named the gas chlorine.

Chlorine’s bleaching properties were eventually turned into an industry by Berzelius, and became the foundation of a second industry of disinfection and deodorzation of putrified tissue and wounds (including wounds in living humans) in the hands of Labarraque, by 1824.

DEATH 

While Scheele’s experiments generated substances which have long since been found to be hazardous, the compounds and elements he used to start his experiments were dangerous to begin with, especially heavy metals. Scheele had a bad habit of sniffing and tasting any new substances he discovered. Cumulative exposure to arsenic, mercury, lead, their compounds, and perhaps hydrofluoric acid which he had discovered, and other substances took their toll on Scheele, who died on 21 May 1786 at his home in Köping. He married the widow Pohl two days before he died, so that he could pass on his possessions and his pharmacy to her.

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