Joseph Priestley Isolates Many New Gases and Begins a European Craze for Soda Water

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Joseph Priestley Isolates Many New Gases and Begins a European Craze for Soda Water

Overview

Until the late eighteenth century, the accepted theory of chemical reaction was the "phlogiston theory." This theory, whose name was coined by German chemist Georg Stahl (1660-1734) in the early 1700s, stated that a substance "phlogiston," which is Greek for "burned," was liberated when any material underwent combustion or when a metal was oxidized. By the late 1700s chemists, especially Antoine Lavoisier (1743-1794), had applied quantitative measurements and demonstrated that oxidized metals, or metals that had rusted, weighed more than nonoxidized ones, thus proving that phlogiston did not exist. Proponents of the phlogiston theory then countered that phlogiston was a negative quantity. Finally by 1800, after several new gases had been discovered and their role in combustion and oxidation identified, the phlogiston theory was overthrown and modern chemistry was born.

The groundbreaking experiments of one Englishman spurred this scientific revolution. Working alone, this minister and teacher isolated ten new gases and noted their properties. Scientific curiosity led him to dissolve his new gases, or "airs" as he called them, in water. The result with one gas was a carbonated drink, which he called "soda water." He was also among the first to observe and write about the process of photosynthesis and about a plant's respiratory cycle. In addition to his discovery of several gases and their properties, he was also the first to confirm that graphite could conduct electricity. When others could find no use for a New World substance called "India gum," he did, calling it "rubber" because it could rub out or erase pencil marks. In addition to his passion for scientific discovery, he had liberal views of religion and politics, openly criticizing the Church of England and the British government. He was steadfast in his support of both the American and French revolutions. A pioneer in science, religion, education, and politics, Joseph Priestley (1733-1804) was indeed a genius.

Background

Born in Leeds, England, Joseph Priestley was the eldest of six children. His father was a clothier and a member of the Calvinist religion. Young Priestley loved to read and taught himself several languages. His family applauded his choice of the ministry as a career and encouraged him to be a member of the Dissenting congregation, whose members were opposed to the Church of England. In 1752 Priestley entered the Nonconformist Academy and studied literature and natural philosophy.

Priestley entered the ministry by the age of 22; later, as an assistant minister, he established a school that became well known for its high educational standards. By 1761 he had accepted a teaching post at an academy, where a colleague who asked Priestley to assist him in his chemistry classes sparked the young minister's interest in chemistry.

As chair of languages and literature, Priestley's reputation grew. In 1765 he wrote about his philosophy of education in "An Essay on a Course of Liberal Education for Civil and Active Life," and the University of Edinburgh gave him an honorary Doctor of Laws degree. During this same year Priestley met Benjamin Franklin (1706-1790) in London, and the two men became lifelong friends. After Franklin introduced Priestley to electricity, the Englishman's fascination led him to conduct many electrical experiments. At Franklin's behest, Priestley agreed to write a history of electricity. In 1767 he published The History and Present State of Electricity with Original Experiments. Because of his work with electricity, Priestley was elected a fellow of the Royal Society.

Priestley returned to the ministry in 1767, accepting a congregation in Leeds. There he continued to express his liberal religious and political views. He published several articles, one of which condemned the British government for its treatment of the American colonies and another of which criticized the Church of England.

In Leeds the Priestley home was situated near a brewery. Whenever he walked by the brewery, Priestley observed an unusual phenomenon. He noticed that "fixed air" (carbon dioxide) was released in the process of fermentation and that this new "air" would extinguish burning pieces of wood and then drift to the ground. At home Priestley was able to prepare the new gas he observed at the brewery. When he tried to dissolve it in water, the result was a drink with a pleasant, rather tangy taste. Priestley had made carbonated water, or "artificial Pyrmont water" as he called it. Although he was not the first one to make this bubbly water, his methods were the most successful.

The first Lord of the Admiralty, Lord Sandwich, and his colleagues believed that this new water was more healthful than ordinary drinking water and might even prevent scurvy at sea. Officials were impressed by Priestley's experiments before the College of Physicians, and two Royal Naval battleships were subsequently equipped with the necessary machinery to make Priestley's soda water. He was asked to accompany Captain James Cook (1728-1779) to the South Seas, but Priestley's extreme religious views made this unacceptable to the Royal Navy. In 1772 Joseph Priestley published his famous booklet that described how to make his soda water. Entitled "Directions for Impregnating Water with Fixed Air," the booklet cost one schilling.

Priestley's scientific work began to earn him international recognition. He was elected to the French Academy of Sciences in 1772, and he received the Copley Medal in 1773 from the Royal Society of London for his articles about fixed air and water solutions and for his experiments on gases.

Priestley then became the tutor to the son of the Earl of Shelburne, a position that allowed him more free time for his experiments and writing. He started a 14-year project, writing a 6-volume work, Experiments and Observations of Different Kinds of Air, and also continued his experiments. On August 1, 1774, Priestley conducted one experiment that led to a scientific breakthrough. Using a magnifying glass to heat mercuric oxide, he collected a colorless gas above the mercury and noticed that this gas would vigorously support a burning candle. He did further tests that showed that this new gas, compared to ordinary air, could double the lifespan of mice.

Priestley had, of course, discovered oxygen. (Swedish chemist Karl Scheele [1742-1786] had discovered oxygen a year earlier, but Priestley published his findings first and is therefore credited with the discovery.) As his new "air" sustained combustion, Priestley postulated that it was low in phlogiston; he therefore called it "dephlogisticated air."

When he traveled to the European Continent in October 1774, Priestley met with Antoine Lavoisier, the brilliant French chemist who immediately realized the importance and significance of Priestley's discovery. Lavoisier conducted his own tests and identified the new gas as an element vital to combustion and respiration. In 1789 he gave it the name "oxygine," later "oxygen," which is Greek for "acid former" because he mistakenly thought that all acids contained this gas.

Joseph Priestley maintained his belief in phlogiston, however, and continued his experiments. He discovered several new "airs": ammonia, sulfur dioxide, silicon, nitrogen, and carbon monoxide. He observed photosynthesis when he experimented with plants. He saw that if his containers were left in sunlight, a green matter grew inside the container, and that this green matter emitted the same "air" that had been produced in his mercuric oxide experiments. In another experiment, he made water by combining oxygen and hydrogen gases with a spark of electricity.

In 1779 Priestley returned to the ministry with a parish in Birmingham. By then, his vigorous support of the American and French independence movements and his treatise, History of the Corruptions of Christianity, antagonized both political and religious factions and made him many enemies. On July 14, 1791, the second anniversary of the storming of the Bastille, an angry mob in Birmingham attacked Priestley's home, which, along with his laboratory and library, was burned to the ground.

Priestley and his family left Birmingham to live in London. Three years later, he and his wife emigrated from England to join their three sons in America. They chose to live in Northumberland, Pennsylvania, where he continued to publish religious and political articles and work on his scientific experiments. Among his friends and acquaintances in America were George Washington, John Adams, and Thomas Jefferson, the latter two sharing Priestley's liberal religious and political views. Joseph Priestley died on February 6, 1804, in Pennsylvania, still clinging to the phlogiston theory.

Impact

After Priestley met with Antoine Lavoisier in 1774, the French chemist continued laboratory testing of the gas he had named "oxygen." Lavoisier's experiments not only conclusively disproved the phlogiston theory but also showed that oxygen formed 20% of air and that the element was a component of combustion. Lavoisier then defined the nature of an element as a substance that cannot be broken down further by any chemical means; he proposed naming elements with the nomenclature still used today.

Lavoisier, whose contributions to chemistry are legion, was inspired by the findings of Joseph Priestley. The English theologian has rightly been called one of the most important men in the history of science. Although Priestley's scientific background was minimal, his inquisitive mind and innovative experiments launched the field of modern chemistry. Scientists have forgiven Joseph Priestley for his stubborn belief in the existence of phlogiston and acknowledge his contribution to the foundation of chemistry. The American Chemical Society honored this remarkable man and his outstanding accomplishments by naming its highest award the Priestley Medal.

ELLEN ELGHOBASHI