Humphry Davy, Self-Made Chemist

CHEMISTRY CHRONICLES Humphry Davy, Self-Made Chemist This pioneer of electrochemistry and chemical discovery rose from humble beginnings. Richard A. Pizzi he English chemist and inventor near Bristol. Impressed with Davy’s think- 19th century science. Researchers like Davy Sir Humphry Davy was one of the ing, Beddoes arranged to release him from took few precautions with unknown Tfirst professional scientists in the his medical apprenticeship and hired him substances. Ultimately, such risk-taking world. He began his career as a humble as an assistant at the Institution, which was would take a toll on Davy’s health, but of surgeon’s apprentice and ended it as one devoted to the study of the medical value course, rewards came with the risks. of the most famous names in European of various gases. Davy was beginning to establish a repu- chemistry. Beddoes had been experimenting with tation as a scientific star, fast gaining the Humphry Davy was born on Decem- nitrous oxide, or what would come to be respect of his fellow chemists. ber 17, 1778, in the town of Penzance, called “laughing gas”, which was first discov- After his work with nitrous oxide, Davy’s Cornwall, England. His father, Robert, was next and ultimately most important inves- a woodcarver descended from generations tigations were in the field of electrochem- of independent yeoman farmers. Humphry istry. The 18th-century experiments of was the first of Robert and his wife Grace’s Luigi Galvani and Alessandro Volta gener- five children. ated widespread interest in electrochem- Robert Davy died relatively young, at istry. Galvani believed that nerves in animal the age of 48, in 1794. Humphry’s moth- tissues generated electricity. Volta demurred, er operated a millinery shop for a few years, claiming that animal tissues detected rather but the family’s reduced income would not than generated electricity. Volta had exper- allow her or the children a leisurely exis- imented with a “pile” of disks of two differ- tence. In 1795, 16-year-old Humphry went ent metals with damp cardboard layers to work, beginning an apprenticeship with between them. From this “voltaic pile” he Bingham Borlase, an apothecary-surgeon got electricity and attributed the effects in Penzance. At that time, surgeons and to the contact of dissimilar metals. apothecaries were not required to have a In 1800, William Nicholson and university education, but Davy devised his Anthony Carlisle in London repeated Volta’s own program of self-education, reading experiment. They obtained hydrogen everything from theology to physics, botany and oxygen from water and successfully to mathematics. From his earliest years, decomposed the solutions of a variety of Davy expressed broad intellectual interests, Sir Humphry Davy, 1778–1829. common salts. Davy disagreed with Volta which he would pursue throughout his life. that electricity was generated simply by the At the age of 18, Davy began his study ered by Joseph Priestley. Davy continued contact of metals. Instead, he thought that of chemistry by reading Antoine Lavoisi- these inquiries in an attempt to determine a chemical reaction generated the current, er’s classic Elements of Chemistry. Already, the physiological effects of the substance. and that in turn an electric current could he began to imagine a great career in science He prepared impure samples of the gas and stimulate a chemical reaction. for himself. As he indicated in his note- tried breathing it. Within a month, Davy Davy initiated his own experiments and book, Davy aspired to be the Isaac Newton obtained the gas in a pure state and deter- discovered that when he passed electrical of his day. mined its chemical properties and compo- current through some substances, the sition. He inhaled 16 quarts of the gas in substances decomposed. This process was A Gaseous Phase 7 minutes and described its effects in detail. later termed electrolysis. As a result of his In 1798, Davy became friendly with Grego- Davy’s observations of the anesthetic work, Davy determined that the actions ry Watt, son of James Watt. Through effects of nitrous oxide preceded by almost of the voltaic pile and electrolysis were iden- friends of the younger Watt, Davy met 50 years the first use of the gas on patients tical. He ascertained that electrical forces Thomas Beddoes, a physician and by dentists. Davy’s experiments on himself could generate current only when the elec- ENGRAVING: OF MEDICINE LIBRARY NATIONAL researcher at the Pneumatic Institution exemplify the dangers inherent in 18th and trolyte could oxidize one of the metals, and ©2004 AMERICAN CHEMICAL SOCIETY APRIL 2004 TODAY’S CHEMIST AT WORK 49 CHEMISTRY CHRONICLES that the voltage generated was directly relat- the meantime, he had accepted an appoint- rate pure metals by passing current through ed to the reactivity of the electrolyte with ment at the Royal Institution in London. molten compounds. In 1807, he separat- the metal. Davy also discovered that metals Thus, he was recognized as one of the lead- ed potassium from molten potash and sodi- were not necessary, as he made a pile ing lights of British science. um from common salt. When observing with zinc and charcoal. The Royal Institution provided Davy potassium particles in water, Davy famous- Davy proposed that electrical forces with significantly more resources than he ly exclaimed that they “skimmed about hold the elements of a chemical compound had at the Pneumatic Institution. He was excitedly with a hissing sound and soon together. In June 1801, he presented a given a bigger voltaic battery with which burned with a lovely lavender light.” He paper to the Royal Society explaining his to perform his experiments. With better presented the results of this experiment work. Two years later, at age 24, he was working conditions, Davy’s innovative in his Bakerian Lecture of 1807. elected a Fellow of the Royal Society. In research continued. He was able to sepa- Chemical Discovery Using electrolysis, Davy in 1808 isolated calcium, barium, strontium, and magne- sium. He used a mercury cathode and was the first to create an alloy with mercury. Davy, however, was not the first to inves- tigate the “alkaline earths”. He was preceded by two Swedish scientists: Carl Wilhelm Scheele, who had distinguished baryta from lime in 1774, and J. J. Berzelius, who had prepared a calcium alloy by elec- trolyzing lime in mercury. Davy was the first, however, to isolate the pure metals, though many historians think that Berzelius would eventually have made similar discov- eries. Davy also developed the method of separating potassium from sodium, and he used potassium to prepare boron. Another important aspect of Davy’s career was his research on chlorine. As was the case with the “alkaline earths”, Scheele had anticipated his work in the 18th century. When Scheele exposed muriatic acid to manganese dioxide, a green gas result- ed. Scheele did not regard the gas as an element but as “dephlogisticated marine acid.” He believed that phlogiston was practically synonymous with hydrogen. Lavoisier, on the other hand, had assumed that the green gas was an oxide of an unknown “radical”. Davy was suspicious of Lavoisier’s theory and performed experiments to confirm the presence of oxygen. Davy first combined the green gas, “oxymuriatic acid” as the British called it, with ammonia, but he found only muriatic acid and nitrogen. He then exposed it to heated carbon in an attempt to remove the oxygen as carbon dioxide. None of his experiments yielded any oxygen or compounds known to contain oxygen, and Davy ultimately concluded that the gas was an element. He named it “chlorine” from the Greek word chloros, which means yellow-green. Additional experiments in 1810 revealed that muriatic acid was a compound of hydrogen and chlorine, and contained 50 TODAY’S CHEMIST AT WORK APRIL 2004 www.tcawonline.org no oxygen. Davy’s research on chlorine led greater fame throughout Europe. In 1818 and on May 29 of that year, Davy died of to a rejection of Lavoisier’s theory that he was named a baronet, and in 1820 he a heart attack in Geneva, leaving a scien- oxygen was an essential constituent of acids. was appointed President of the Royal Soci- tific legacy that few have been able to match. The year 1810 was also an important ety, an office he held for seven years. As one in British science for a less obvious successful as he was, however, in the mid- Further Reading reason. It was the first year a young Michael 1820s Davy’s health began to deteriorate. Knight, D. Humphry Davy: Science & Power; Cambridge Faraday began attending Davy’s lectures at He became seriously ill in 1827 and moved University Press: Cambridge, U.K., 1998. Humphry Davy; www.chemheritage.org/Educational the Royal Institution. In 1813, Davy hired to Rome in 1828. Much of his ill health Services/chemach/eei/hd.html. Faraday as an assistant, the first step in a was later attributed to the inhalation of professional and personal relationship that toxic gases over the course of a long career. Richard A. Pizzi is a freelance writer with an M.A. in lasted many years. In the winter of 1829 he had a stroke, history from the University of Florida. ◆ Davy was knighted by King George III in 1812; that same year, he married Jane Apreece, a wealthy widow from a promi- nent family. Now financially comfortable, Davy ceased lecturing at the Royal Institu- tion, but he was granted the title Honorary Professor of Chemistry and continued to use the Institution’s laboratory for his research. He also served as Secretary of the Royal Society and undertook two lecture tours of Ireland.

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