acs n e w s (1742-86), who also discovered chlorine. Scheele isolated oxygen by several meth ods, including heating various oxides and nitrates, at least a year before Priestley's discovery. He suggested that air consist ed of two components: "foul air" which did not support combustion, and "fire air" which did. However, whereas Priestley publicly announced his discovery in 1774, Scheele's book that described his discov eries did not appear until 1777. Over a period of several years, Priestley carried out a se ries of experiments on his "air." He showed that water is formed by exploding a mixture of hydro gen and oxygen. He also showed that plants give off oxygen and that animals require the gas for respiration. Soon after his discovery of this new "air," Priestley breathed the gas himself and wrote that he felt peculiarly light and easy for some time afterwards. "Who can tell but that in time, this pure air may be come a fashionable article in luxu ry," he wrote. "Hitherto only two mice and myself have had the priv ilege of breathing it" He suggested that the gas his historic breakthroughs here in En might prove useful as a medicine, and gland, he exchanged ideas with great might be used in the manufacture of men of science from other countries, in powerful explosives and in blast furnac cluding America's Benjamin Franklin, es for smelting iron. Priestley did not, however, identify the and France's Antoine Lavoisier," he said. "He came to our country and be new gas or "air" as oxygen. The prevail came one of the most important influ ing theory of combustion at that time was ences on American chemistry." the phlogiston theory, according to Wasserman explained that the found which combustible substances contained ing of ACS emerged out of a meeting at two components: phlogiston and calx. On Priestley's home in Northumberland in burning a substance, the phlogiston was 1874 to celebrate the centennial of Priest released, leaving the calx, or ash. "He christened the eminently respiley's discovery of oxygen. ACS, formed two years later, dedicated Priestley House as a historic chemical landmark in 1994. "Priestley denied that he had extraor dinary talents, though we would disagree with his attractive modesty and see his fe cundity in isolating gases as indicating chemical genius and the prepared mind that responds to happy accidents," David M. Knight, professor of the history and philosophy of science at Durham Univer sity, England, remarked at the Bowood House ceremony. Priestley shares the credit for discov ering oxygen with Swedish pharmacist and chemist Carl Wilhelm Scheele
A CANDLE BURNING BRIGHTLY
Historic chemical landmark commemorates Joseph Priestley's discovery of oxygen Michael Freemantle C&EN London ι ut what surprised me more than I can well express, was that a ' candle burned in this air with a remarkably vigorous flame," observed Joseph Priestley following his discovery that a gas, or "air" as he called it, was readily expelled on heating "red calx" of mercury [mercury(II) oxide]. Priestley, who was born in Yorkshire, England, discovered the gas in 1774 in a small laboratory at Bowood House, Calne, England, where he was employed by the Earl of Shelburne, the owner of the house and a future prime minister of Britain. Priestley's discovery of oxygen was designated as an International Historic Chemical Landmark jointly by the American Chemical Society and its Brit ish counterpart, the Royal Society of Chemistry (RSC), at a ceremony in the chapel at Bowood House last month. During the ceremony, Ed Wasserman and Anthony Ledwith, immediate past-presidents of ACS and RSC, respec tively, presented a commemorative plaque to the present Earl of Shelburne. The inscription on the plaque reads as follows: "Joseph Priestley (1733-1804)— Unitarian minister, teacher, author, and natural philosopher—was the Earl of Shelburne's librarian and tutor to his sons. In this room, then a working labora tory, Priestley pursued his investigations of gases. On 1 August 1774 he discovered oxygen. Twenty years later he emigrated to America where he continued his re search at his home and laboratory in Northumberland, Pennsylvania." Priestley discovered not only oxygen but also numerous other gases: nitro gen, three nitrogen oxides (N20, NO, and N02), ammonia, carbon monoxide, sulfur dioxide, and silicon tetrafluoride. In Wasserman's remarks at the cere mony, he suggested that Priestley's work is a perfect example of the international na ture of scientific research and discovery. 'While doing the research that led to
Β
34
SEPTEMBER 11,2000 C&EN
Mldda (left), Boulton (center), and Djerassl (right) read excerpts from "Oxygen" by Djerassl and Hoffmann.
;
$*&
rable air he had isolated as 'dephlogisticated air' because it would absorb more phlogiston than ordinary air, and thus allow combustion to go on longer," Knight explained. In October 1774, Priestley visited Paris as part of Shelburne's entourage and met Lavoisier. "Priestley put Lavoisier onto the track which led to his 'chemical revolution' of 1789, contemporary with the political one," Knight pointed out. "Priestley never accepted the 'oxygen' theory. The French, on the other hand, interpreted oxygen as the key to modern chemistry." Lavoisier, who was aware of both Scheele's and Priestley's isolation of the new gas, repeated Priestley's experiment with mercury (II) oxide and subsequently found that the gas combined with metals and other substances. Because the compounds that were produced were often ac-
ids, Lavoisier named the gas "oxygen," which derives from two Greek words meaning "acid maker." The French chemist built on Priestley's and Scheele's discoveries and used his own work to develop a general theory of combustion, oxidation, and the composition of air, which replaced the phlogiston theory. The oxygen theory became firmly established in 1789 with the publication of Lavoisier's "Elementary Treatise on Chemistry." The publication, which marked the foundation of modern chemistry, coincided with the start of the violent French Revolution (178999). Lavoisier was executed by guillotine in 1794.
at a meeting at the Royal Swedish Academy of Sciences, Stockholm. The meeting isfictionaland Svanholm is not a real person but a character in the play "Oxygen," by Stanford University chemistry professor Carl Djerassi and Roald Hoffmann, chemistry professor at Cornell University and winner of the 1981 Nobel Prize in Chemistry. Djerassi and Hoffmann were awarded the Priestley Medal, ACS's highest award, in 1992 and 1990, respectively. Excerpts | from the play were read by Djerassi and professional actors Justine Midda and Nicholas Boulton at the Bowood House ceremony. "Both Hoffmann and I picked [oxygen for the play] because that really started the chemical revolution in the latter part of the 18th century," Djerassi told C&EN. "The play will almost certainly be performed during the ACS meeting in San Diego between April 1 and 5,2001." The play's action takes place alternately in 1777 and in 2001, the centenary of thefirstNobel Prize awards, when the Nobel Foundation decides to inauguParticipants gather for the landmark ceremony at Bowood House (above); Ledwith (left) and Wasserman rate a "Retro-Nobel" Award for great discoveries that preceded (right) present plaque to Earl ofShelbume. the establishment of the Nobel in Birmingham. His house, library, Prizes. The key question is: Who should manuscripts, letters, notes, and labora- be honored for the discovery of oxygen: tory were destroyed. Priestley and his Lavoisier, Priestley, or Scheele? In ficfamily escaped to London. On April 8, tional encounters in Stockholm, the play 1794, Priestley and his wife, Mary, fled brings together the three protagonists to the U.S. and eventually moved to and their wives in 1777. And in a meeting Northumberland, where two of their in 2001, members of the Nobel Committee argue about the conflicting claims of sons had already settled. "Seventeen ninety-four was a bad year the three men. for chemists," Knight said. "Lavoisier was "In the case of Priestley, the selfbeheaded and Priestley decided to leave taught chemist just happened to be a England, where he was cold-shouldered minister," Svanholm says in one scene. as a sympathizer with French anarchy, "He published 50 works on theology, 13 for exile in the land of the free." on education, 18 on political, social, and Priestley continued to work on the metaphysical subjects... and 50 papers isolation and characterization of gases and no less than 12 books on science!" In another scene involving Priestley in his laboratory in Northumberland. Though Priestley's major claim to fame and his wife, a narrator comments on the is his discovery of oxygen in England, irony of Priestley's life. "Priestley—a he discovered carbon monoxide in chemical conservative... just think of his 1799. He observed that the gas burned undying defense of phlogiston—was with a blue flame and named it "heavy such a political and religious revolutioninflammable air" to distinguish it from ary that a mob burned his house in Birmingham," the narrator says. "light inflammable air," or hydrogen. "Priestley lived at the right time in According to Djerassi and Hoffmann, the right country: England . . . the 18th- the ethical issues around priority and century hothouse of pneumatic chemis- discovery at the heart of this play are as try," remarked Ulf Svanholm, a member timely today as they were in 1777—as of the Nobel Committee for Chemistry, are the ironies of revolutions.^ Priestley was not only a scientist and a teacher, he was also a theologian with convictions that differed radically from the established Church of England. He was not popular in the country because of his antiroyalist views and his sympathy with the French and American revolutions. In 1791, two years after the start of the French Revolution, mobs attacked the homes and meeting places of antiroyalists, including Priestley's home
SEPTEMBER 11,2000 C&EN
35
