Carl Wilhelm Scheele Biography

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World of Chemistry on Carl Wilhelm Scheele

Scheele's fame has been eclipsed by other chemists who made the same discoveries just a little earlier or who followed through on their experiments more thoroughly. Still, Scheele, who began training at age fourteen to be an apothecary has been recognized by Isaac Asimov as the greatest pharmacist in history.

Scheele was born and raised in the town of Stralsund in Swedish-controlled Pomerania. He eventually moved to Sweden, where he met and befriended many famous scientists, including chemist Johann Gottlieb Gahn (1745-1818) and mineralogist Torbern Olof Bergman (1735-1784). He worked at a series of drugstores, finally establishing his own pharmacy in 1776. Although Scheele could easily have chosen a more secure life as a professor at one of Europe's prominent universities, he preferred to practice pharmacy and to concentrate on his own experiments. He even turned down an opportunity to become the royal druggist to Prussia's Frederick II (1712-1786).

Like many of his contemporaries, Scheele tested many chemicals on himself. In his laboratory he prepared and tasted some of the most poisonous gases known to man, including hydrogen cyanide. Scheele's habit of being his own guinea pig may have contributed to his death. When he died, his symptoms resembled those of mercury poisoning.

Scheele is best remembered for discovering oxygen in 1771 and 1772. He prepared the gas by heating several different oxygen-containing compounds, such as mercuric oxide. Scheele found that many substances require oxygen in order to burn, so he called the oxygen fire air. Like most chemists at that time, Scheele used the phlogiston theory of combustion to describe chemical reactions. According to this theory, which has since been proved wrong, a substance called phlogiston is released from burning materials, and, in order for combustion to take place, air is required to absorb the phlogiston. Although Scheele modified this theory, stating that heat--and not phlogiston--was the necessary ingredient, it was left to French chemist Antoine-Laurent Lavoisier to develop the modern theory of combustion, which states that substances burn by combining chemically with oxygen. (In fact, in corresponding with Lavoisier, Scheele provided him with valuable information about oxygen that enabled the French scientist to complete his theory.)

In studying how oxygen reacts with different compounds, Scheele weighed the gas and found that another gas, which he termed foul air, was also present in the atmosphere. Scheele conducted tests in which all of the oxygen and carbon dioxide in a container of air were consumed, leaving only foul air behind; today we know this gas is nitrogen.

Unfortunately, the publication of Scheele's discoveries was sidetracked by a run of bad luck. He wrote about his experiments in Chemische Abhandlung von der Luft und dem Feuer(Chemical Observation and Experiments on Air and Fire), which he finished in 1775. Publication, however, was first delayed by Scheele's colleague Bergman, who took a long time to write an introduction for the book, and then by printing problems; the book did not appear in print until 1777. Because British chemist Joseph Priestley, who was doing similar experiments with oxygen, was the first to report his findings, most people credit him with discovering the element.

Scheele's pattern of anticipating or independently duplicating others' discoveries is also illustrated by his research on chlorine. In 1774 Scheele produced chlorine by combining hydrochloric acid with a manganese compound. However, he failed to recognize chlorine as an element in its own right, believing instead that it was a compound of oxygen. More than thirty years later, British chemist Sir Humphry Davy isolated chlorine and declared its elemental nature, thus earning the credit for its discovery.

Although Scheele also had a hand in isolating and studying many other elements, he was far more successful in discovering new compounds, especially such organic acids found in plants as tartaric acid. Working with plant juices, Scheele went on to discover citric acid, which he crystallized from lemon juice, and malic acid, which he found in apples. Scheele investigated more than twenty kinds of fruits and berries as well as other vegetable materials, and he obtained oxalic acid from sugar. Turning to the animal kingdom, Scheele studied eggs, blood and glue, and he discovered uric acid which is normally excreted in bodily waste but can cause kidney stones. He also identified lactic acid.

Two additional compounds he studied were named for him: scheelite, a calcium tungstate mineral used in high-speed tools, and copper arsenite, which is called Scheele's green. Scheele also developed new methods for preparing arsenic acid, and he demonstrated that graphite is a form of carbon.

More than fifty years before the development of photography, Scheele discovered the effect of light on silver compounds. Salts of silver modified by the action of light were later used in the first photographic emulsions.