ROGER R. FESTA Northea~tMissouri State University Kirksviiie,MO 63501
Joseph Priestley, Preeminent Amateur Chemist Foll A. Mlller University of Pittsburgh Pittsburgh, PA 15260 Joseph Priestley was one of the greatest chemists of the 18th century. He is best known as the discoverer of oxygen (August 1,1774). but actually Carl Wilhelm Scheele of Swedenhad discovered it independently at least two years earlier. Scheele described his experiments in a book, but his publisher was inexcusably negligent and the hook did not appear until 1777. By then Priestley's account had heen publi~hed,',~ and it is he who generally gets the credit. However, Priestley did much, much more, and even if he were not remembered for oxvgen he would rank as a ereat " chvmist and humanist worthy of honor. He alsu discovered S H t . HCI. i X- 4 .. NO.. NO,.-. 11,s. - . SO.-,..S F l , and CO- more newbasesthan any other person. He was the first to recognize the meat 01-Cog cvcles in nature: that ~ l a n t use s CO2 and pro&ce o2;and;h& animals do the converse. He was the first to realize that blood transports oxygen, and he suggested that the body's use of oxygen is analogous to the calcining of metals. Strangely, though, both he and Scheele believed in the phlogiston theory all their lives, and they never understood the true role of oxygen in combustion. Priestley was a codiscoverer of photosynthesis (with Ingenhousz) and is regarded by many as one of the codiscoverers of nitrogen (with Daniel Rutherford). Priestley is noted for numerous other scientific contributions as well. These discoveries are all the more remarkable because science was only an avocation for Priestley. Professionally he was a clerevman and a teacher. He wrote over 150 books and pamphlets-on an astonishing variety of topics. He was a theologian, a historian, a linguist, and a writer of learned articles on education, oratory, grammar, literary criticism, psychology, political philosophy, perspective, metaphysics, electricity, optics, and chemistry. Today he is remembered mainly as a chemist, but he regarded himself as above all a Christian minister. Priestley was horn on March 24, 1733,3 in Fieldhead, a hamlet near Leeds, England. His father was a weaver and dyer of wool. His mother died when he was six, and he was raised by an aunt who brought him up in the tradition of Calvinist dissent. At that time dissenters were barred by English law from attendance a t the universities and from civil and military appointments. Priestley entered the Nonconformist Academv a t Daventrv in 1752, and after three years there, a t age 22, took the-first of several posts as a pastor. An inherited stutter was an unfortunate handicap in his profession. T o augment his income, he founded and ran a successful day school, and then taught a t Warrington Academy. While there he married Mary Wilkinson, whose father and two brothers were famous iron masters. "This proved to he avery
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Royal Soc Phd Trans 1775, 65. 384- 390 Experrmenfs and Obsewalrons on D~fferenrKmds of
London, 1775, Voi 2 March 13; old style
1963 U.S. stamp honoring Joseph Priestley.
suitable connection, mv wife beina a woman of excellent understanding, much improved by'reading, of great fortitude and strength of mind, and of a temper in the highest degreeaffectionate and generous; feeling strongly for others, and little for herself." They later had a daughter and three sons. Among the publicati&s that earned him a Doctor of Laws degree from the University of Edinburgh in 1764 were "Chart of Biography" and "A New Chart of History", which were very early visual aids. Priestley became involved in science almost accidentally, and through the encouragement of Benjamin Franklin. When the two met in London. Priestlev mentioned that he wmlrl like tt, write a history ut'thc discoveries of rlt:ctricity, l ~ ileeded t rertain l~ooksfor the PurDuse. 1:runklin and some other friends provided them. ~ " r i nhis~ writing, Priestley found that various facts were under dispute, and endeavored to settle them with an electrical machine that he had bought for his teaching. This gradually led him to do many original experiments. Becauseif themhe was made a Fellow of the Royal Society in 1766 a t age 33. His history of electricity was published 1767, and Franklin became his mentor and lifelong friend. The last day of Franklin's 18-year stay in England was spent in Priestley's company. In 1767 Priestley took another ministry in Leeds and moved into a house next door to a brewerv. The accident of its location had a profound influence on i i s scientific studies. He found that the gas above the brew in the fermentation vats provided a convenient supply of "fixed air" (C02), and he carried out many experiments with it. His first puhliVolume 64
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cation on "airs" described means for impregnating water with C01. He discovered the oleasant taste of the solution and reco-mmended the refreshing hrvernge 10 his friends. (He would pruhably hr astounded 111 the magnitude of today's cnrlwnntt.(i drink industry.~This was the first of manv st~~~liesin"~)~~eumaticcl~emis~rs"and led to theaward of thr Royal society's gold Copley ~ e d ainl 1773. From 1770 on, Priestley's experimental work dealt almost exclusively with "pneumatic chemistry", which became the most exciting branch of chemistry in the second half of the 18th century. His concentration on this subject began relatively late in his career (at age 37) and continued for the rest of his life. Before Priestley, no one had examined the nature of the "airs" that might he released from various substances. This was the task that he undertook. He used a variety of techniques to produce gases, including heating materials, mixing them, calcining, using- vegetative growth, and oassine an electrical discharg&hrough vapors. ' "When I began these experiments," he wrote, "I knew very little of chemikry . . .this circumstance was no disadvantage to me; as in this situation I was led to devise an apparatus, and processes of my own, adopted to my peculiar views. Whereas, if I had been previously accustomed to the usual chemical processes, I should not have so easily thought of any other; and without new modes of operation I should hardly have discovered anything new." For his early experiments, Priestley adapted household utensils such as laundry tubs, dishes and howls, beer and wine glasses, and clay tobacco pipes. Later he developed his own amaratus. The oneumatic trough for collectina eases was airlady known, but Priestley improved it by adding an underwater shelf on which the collecting vessel could rest. Henry Cavendish had been the first to use mercury in place of water in the trough, but Priestley exploited i t to great advantage. I t was the use of mercury that enabled him to isolate several gases that react with or dissolve readily in water, most notably HCI, NO2, SiF4, NHs, and S02. His friend Josiah Wedgwood, the famous potter, supplied him with ceramic tubes, dishes, mortars, and crucibles. The London firm of William Parker and Sons provided glassware, including the burning lenses that he frequently used to heat substances within the receivers of his pneumatic trough. Graduallv Priestlev" acauired . a laboratorv that was wellstocked withsophisticated equipment and a aide range of chemicals. Much of it was paid for by admiring patrons. The lahoratory which he later huilt in Birmingham was one of the best equipped in the world. After its destruction by a mob, he prepared an inventory to support his claim against the government, which gave the value of the contents at over 600bounds. The more costly items included five telescopes, four microscopes, five burning glasses, five electrical machines, nine furnaces, three eudiometers, two air pumps, one theodolite, and a large number of thermometers. There were also 600-700 substances and 80 pounds of mercury! Initially the tests that Priestley used to characterize an " , 3, alr were simple. What was its appearance? Its taste? Did it turn limewater turbid? Did it burn or support comhustion? How long would a mouse live in a container filled with it? Gradually the tests became more sophisticated. He noted flame size and color, and the color of sparks through the gas. He developed a method of eudiometry using NO. (The eudiometer is a graduated glass tube for the measurement of gas volumes.) NO reacts rapidly with 0 2 to form NO2, which then dissolves in the water in which the lower end of the eudiometer is immersed. The decrease in gas volume is a measure of the amount of 0 2 that was present. From 1772 t o 1779 Priestley was in the service of Lord Shelhurne. Officially he was librarian and adviser to the household tutor. hut in fact he was a resident intellectual. This post gave him more time for his scientific experiments, and it was during this ~ e r i o dthat he discovered oxvaen. On August 1, 1774, ke usid a 12-in.-diameter lens t h a t h e had 746
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just obtained to focus sunlight onto mercuric oxide in a oneumatic trough and produced "dephlogisticated air" (oxigen). He had expect& the product t o be the same as the CO?he had obtained by heating impure redlead. (Red lead is had impurity.) l ' b . ' ~ ,hut , h i s s a m p l e ~ p p a r t ~ n t l \ ~ ~mrhonate .'Hut what surprisrd me more than I can well express. was. that a candle burned in this air with a remarkable vigorous flame.. ." At first Priestley confused the new gas with N20,which he had isolated earlier. That fall he toured Europe with Lord Shelhurue-Priestlev's onlv " t r i.~to the continent. In Paris he met Lavoisier and told him of his puzzling experiments with the new gas. Lavoisier confirmed the results and went on to develop an understanding of the role of oxygen in comhustion and thus initiate the era of modern chemistrv. Ry hlarch I775 Priestley realized that the gas was ðing new. He found that it would keep a mouse ali\,e more than-four times as long as an equal volume of ordinary air. His eudiometer test showed that the new gas was about five times as pure as common air. Since i t was much more deficient in -phlogiston, it could absorb more phlogiston so that mice lived longer and candles burned more brightly in it. Hence he named it "dephlogisticated air". "The feeling of it to my lungs was not sensibly different from that of common air; but I fancied that my breast felt peculiarly light and easy for some time afterwards. Who can tell hut that, in time, this pure air may he a fashionable article of luxury. Hitherto only two mice and myself have had the privilege of breathing it." Priestlev left Lord Shelburne's service in 1780 and moved to Himiniham. The parting was amicable, and Shrlhurne pro\.idvd nn nnnuirv 01 130 pounds for the. rest of Pricstley's iife in accordance k i t h the terms of employment. In ~ i r mingham Priestley served as a minister and also constructed a fine laboratory to continue his experiments. Unfortunately his scientific productivity declined during his 10 years there. He became a member of the Lunar Society, so named hecause i t meetings were held on the Monday nearest the full moon. The members, sometimes called "Lunatics", included Josiah Wedgwood, James Watt, Matthew Boulton (a manufacturer), William Small (former tutor to Thomas Jefferson at the College of William and Mary), and Erasmus Darwin (biologist and grandfather to Charles Darwin). Benjamin Franklin was a frequent guest. The Society offered useful opportunities for contact and exchange of ideas between scientists and industrialists. Throughout his ministry Priestley held a number of unpopular Giews. He was against the monarchy, favored separation of church and state, and supported the American and French Revolutions. These hroueht " much criticism. On Julv 14, 1791, the second anniversary of Bastille Day, a dinner in Birmingham to commemorate the French Revolution incited a three-day riot. Although Priestley had not attended the affair, the mob turned on him as a principal advocate and hurned his home, laboratory, and church. He and his family escaoed with difficultv and lived in London for the next three years. Hecsusefeelingsagainsr him wrrr still strong, he lrft England in 1:9.1. lie had heen made an honorary citizen of ~ r a n c ehut , he chose to go to America instead. ~ e i he e was offered the chair in chemistry a t the University of Pennsylvania, hut he declined it in favor of living in Northumberland, Pennsylvania, on the hanks of the Susquebanna River north of Harrisburg. His sons had already settled there and were attempting to establish a colony for British emigres fleeing political repression. There Priestley huilt a home and lahoratory where he spent the last 10 years of his life. I t is now an official Pennsvlvania and U.S. Historical Site. He continued his beloved experiments and discovered C d at Northumherland. He gave some sermons in Philadelohia in 17YBthar led tothe fo;ndin#of the first permanent i'niriirian church in the IInittvi Statrs. l ~ uhc t declined an invitation to he its minister. He corresponded with Presidents John
Adams and Thomas Jefferson. Priestley died on February 6, and to Thomas cboper. After finishing he said, " T h a t i s right. I have done now," and within an hour he was dead. He is buried at Northumberland. He was survived by two sons in the United States and by a married daughter in England. One of his grandsons, Henry Hobson Richardson, became a distinguished American architect. Priestlev's scholarlv contributions were astonishine in quantity and scope. In science, which was only an avocation, he wrote 12 hooks and about 50 Daners. . . For over a decade, from about 1775 to 1785, he dominated science in Britain until Lavoisier's new ideas in chemistry took precedence. There were also about 50 works on theology, 13 on history and education, and 18 on oolitical and social suhiects. In religion he played a key role in the development o f ~ n i t a r i anism. His ideas on the reform of education led ultimately to the basic English "grammar school" curriculum. A minor but interesting contribution was his introduction of the word
(a) Encyclopedia Brittanica. 1966. Article on Pencil. (b) Oesper, The Human Side of Scientists;University of Cincinnati: Cincinnati. OH 1975; p 159. R.
"rubber". Prior to then the substance had gone by the awkward name "caoutchouc". In 1770 he wrote to a friend that a piece of caoutchouc makes a good "rubber" to erase pencil marks.' Humphry Davy wrote of Priestley, "Chemistry owes to him some of her most important instruments of research, and many of her most useful combinations; and no single person ever discovered so many new and curious suhstances." Suggested Readings s a , m d , R. E. Joseph Priestley in Dictionary of S e i a n W Biography; Gillispie, C. C., F.d.:Scribnor's: New Ysrk. 1975. ,Second Centennial nfChemistry Celebration."BroehuredistributedattheThird Biennial Conference on Chemical Education Northumberland, PA. August 1, 1971. (Copies may he available from the Department of Chemistry Pennsylvania State University or from 'he Division "1 Education. American Chemical Saciety.1. Rhees. D.J."Juseph Prierfley, Enlightened Chemist" I . Center forthe HistoryofChemirtry, University of Pennsylvania. E. F. Smith Hall D-6, 215 South 34th Street. Philadelphia.PA 19104. Brochurepropared foranexhibiteelebratingthe250th birtbdayof Priestley, 1983. Enryclnpedio Rriftanico, 1966. Article: Joseph Priestley. Weeks. M. E.: Loicestor, H. M. Dircov~ryo/ the Elements. 7th ed.: Chemical Education Publishing: Es~ton.PA. 1968, pp 216223. ~ s i m o v I. , ~ s i m o u bBiographical Enryrlop~dioof Scisnea and Technology, 2nd ed.; Doubleday: New York, 1982. Articles on PriesUey. Schoelo, and Lavoider. Partington, J. R.A Short HirturyalChemiatry.3rd ed.: Maemillan: London, 1957:pp 110121. Partington, J. R. A Hiltor? 0fChemistry; Macmillsn: NeuYork. 1962;Vol. 3, pp 237-301. J. Chem. Educ. 1927,4, 145-199. Several papers devatod mainly to Prietley's home and activities in Northurnherland.
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