Wednesday, 21 May 2014
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 chlorine before Humphry Davy, among others. Scheele discovered organic acids tartaric, oxalic, uric, lactic, and citric, as well as hydrofluoric, hydrocyanic, and arsenic acids. He preferred speaking German his whole life, and German was commonly spoken among Swedish pharmacists.
Scheele was born in Stralsund, in western Pomerania, which was at the time part of Sweden. Scheele's father Joachim (or Johann) Christian Scheele, was a grain dealer and brewer from a respected German family. His mother was Margaretha Eleanore Warnekros. Friends of his parents taught him the art of reading prescriptions and the meaning of chemical and pharmaceutical signs. Then in 1757, at age fourteen, Carl was sent to Gothenburg as an apprentice pharmacist with another family friend and apothecary, Martin Andreas Bauch. He retained this position for eight years. During this time he ran experiments late into the night and read the works of Nicolas Lemery, Caspar Neumann, Johann von Löwenstern-Kunckel and Georg Ernst Stahl (the champion of the phlogiston theory). Much of his later theoretical speculations were based upon Stahl.
Scheele arrived in Stockholm some time between 1767 and 1769 and worked as a pharmacist. During this period he discovered tartaric acid, and with his friend Retzius, studied the relation of quicklime to calcium carbonate. In the fall of 1770 he became director of the laboratory of the great pharmacy of Locke, at Uppsala. The laboratory supplied chemicals to professor of chemistry Torbern Bergman, and a friendship developed after Scheele analyzed a reaction which Bergman and his assistant Johan Gottlieb Gahn could not resolve. The reaction was between melted saltpetre and acetic acid, producing a red vapor. Further study of this reaction later led to Scheele's discovery of oxygen.
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".
In 1775 he was elected as a member of the Royal Swedish Academy of Sciences and also managed a pharmacy for a short time in Köping, and between the end of 1776 and the beginning of 1777, established his own business there. On October 29, 1777, he took his seat for the first and only time at a meeting of the Academy of Sciences, and on November 11 he passed the examination as apothecary before the Royal Medical College, with highest honors. After his return to Köping he devoted himself, outside of his business, to scientific researches resulting in a long series of important papers.
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 asbarium (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(1777). 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.
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 (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.
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 at the early age of 43, on 21 May 1786, at his home in Köping. Doctors said that he died of mercury poisoning .