AMERICAN CHEMICAL SOCIETYDivision of the History of Chemistry andThe Office of Public Outreach

PRODUCTION OFALUMINUM METAL BYELECTROCHEMISTRYOBERLIN, OHIOSEPTEMBER 17, 1997

A NATIONAL HISTORICCHEMICAL LANDMARK

On the Cover: (Clockwise) C. M. Hall,1885; Hall reading American ChemicalJournal, about 1905; F.F. Jewett, Hall’smentor; Hall family home and woodshed.Background: Letter from Hall to hisbrother February 24, 1886.

Background (this page): Diagram fromC.M. Hall’s patent.

Acknowledgments:The American Chemical Society gratefully acknowledges the assistance

of those who helped prepare this booklet, including: Norman C. Craig, Robertand Eleanor Biggs Professor of Natural Science, Oberlin College; Lewis V.McCarty, retired Research Associate, Inorganic Chemistry, General Electric,Nela Park, Cleveland, Ohio; Roland M. Baumann, Archivist, Oberlin College;and Peter J. T. Morris, Science Museum, London, the National HistoricChemical Landmarks Program Advisory Committee liaison.

This booklet was produced by the ACS Office of Public Outreach.Layout: Dahlman Middour Design. Copyediting: Elizabeth A. Mitchell, ACS.Photographs courtesy of Oberlin College and the Aluminum Company ofAmerica.

Copyright © 1997 American Chemical Society

This booklet commemorates the designation of

the production of aluminum metal by electro-

chemistry as a National Historic Chemical

Landmark. The designation was conferred by

the American Chemical Society, a nonprofit scientific and

educational organization of more than 152,000 chemists and

chemical engineers.

A plaque marking the designation was presented to

Oberlin College on September 17, 1997. The inscription

reads: “On February 23, 1886, in his woodshed laboratory at

the family home on East College Street, Charles Martin Hall

succeeded in producing aluminum metal by passing an elec-

tric current through a solution of aluminum oxide in molten

cryolite. Aluminum was a semiprecious metal before Hall’s

discovery of this economical method to release it from its ore.

His invention, which made this light, lustrous, and nonrust-

ing metal readily available, was the basis of the aluminum

industry in North America.”

Sketch of the woodshed laboratory by Julia Severance,made while Hall was alive.

CHARLES MARTIN HALLSOLVES THE ALUMINUM CHALLENGE

From Semiprecious toAbundant

Before 1886, aluminum was a semi-precious metal comparable in price to silver.Although the element had been discovered in1825 and had been investigated by manyEuropean scientists, the only way to preparethe metal was by the complex and difficultprocess that culminated in reacting metallicsodium with aluminum chloride. When theWashington Monument was completed in 1884, a6-lb pyramid of this costly aluminum was placed asan ornament at the very top. It also served as thetip of the lightning rod system, a practical applica-tion of the high electrical conductivity and corro-sion resistance of this remarkable metal. However,economical methods were needed to wrest alu-minum from its abundant minerals, which HenriSainte-Claire Deville, the great French chemist,observed “could be found in every clay bank.”

Two men with a common interest in alu-minum metal met on the campus of Oberlin Collegenear Cleveland, Ohio, in 1880. Frank Jewett was aworld traveler and as well educated in chemical sci-ence as any American academic of his day. CharlesHall was a local youth, self-educated in science, whohoped to become a successful inventor and entrepre-neur. Their association over the next five-and-one-half years led to the discovery of a practical processfor making aluminum from its ore by an electric cur-rent. Within three more years, Hall was producingpure aluminum metal on an industrial scale.Aluminum, the curiosity, became a widely usedmaterial, and the younger man achieved his goal ofa financially successful career in technology andindustry.

Professor and StudentFrank Fanning Jewett received his undergradu-

ate education and did some graduate work in chem-istry and mineralogy at Yale University. From 1873to 1875, he continued his chemistry studies at theUniversity of Göttingen in Germany. There he

became well acquainted with cur-rent European science andbecame interested in thepromise of aluminum. He metProfessor Friedrich Wöhler,who had isolated aluminum asa metal in 1827 followingH. C. Oersted’s lead in 1825.Before Jewett returned toAmerica in 1875 to become

Oliver Wolcott Gibbs’s privateassistant at Harvard University, heobtained a sample of aluminummetal. In 1876, he was nomi-nated by the president of Yale toteach science at the Imperial

University in Tokyo, where he was one of a smallgroup of Westerners. In 1880 at the age of36, Jewett became the professor ofchemistry and mineralogy at OberlinCollege.

Charles Martin Hall firstlearned chemistry as a serious-minded youth in the town ofOberlin by reading an 1840stextbook he found on the shelvesof his minister father’s study. Healso carried on experiments athome, the beginning of a lifelongenthusiasm for experimental work.An avid reader in many fields, heeagerly followed the popular inventionliterature in Scientific American. Hallwas already intrigued by the romanceof aluminum when, as a 16-year-oldfreshman at Oberlin College in the fall of 1880, hewent to the chemistry laboratory to obtain someitems for his home laboratory. There he metProfessor Jewett.

1

Frank Jewett at about 40years of age when Hallmade his discovery.

C. M. Hall at graduationfrom Oberlin College, 1885.

Hall took his first formal course in chemistry asa junior in college. Earlier, with Jewett’s guid-ance and encouragement, he had worked on

aluminum chemistry and other projects in Jewett’s lab-oratory and in his own laboratory at home. He heardJewett lecture on the chemistry of aluminum, displayhis sample of the metal, and predict the fortune thatawaited the person who devised an economicalmethod for winning aluminum from its oxide ore. To afellow student, Hall declared that he intended to bethat person.

After many unsuccessful experiments withchemical methods of reducing aluminum ores to themetal, Jewett and Hall turned to electric current toprovide the powerful reducing conditions that wereneeded. To obtain electricity in a college town inthe 1880s, one had to assemble batteries. Hall andJewett used Bunsen–Grove cells, which consist of alarge zinc metal electrode in a sulfuric acid solutionthat surrounds a porous ceramic cup containing acarbon rod immersed in concentrated nitric acid.Assembling enough of these cells to provide suffi-cient electrical energy for aluminum production was

a large undertaking. The eventual laboratory processused about 1 lb of zinc electrodes, hand cast by Hall,to obtain 1 oz of aluminum.

Hall did the first experiments with electricityin Jewett’s laboratory during his senior year of1884–85. He prepared aluminum fluoride from haz-ardous hydrofluoric acid in special lead vessels, and

he passed a currentthrough aluminumfluoride dissolved inwater. Unfortunately,this system producedonly unwanted hydro-gen gas and aluminumhydroxide at the nega-tive electrode.

After graduation,Hall continued thework in the woodshedbehind his family’shouse. He experi-mented with moltenfluoride salts as water-free solvents. He knewthat the fluoride saltshad the advantage overpreviously studied chlo-ride salts of not absorb-

ing water from the air. Hall was aware of RichardGrätzel’s success in obtaining magnesium metal byusing an electric current in a magnesium chloridemelt as reported in the Scientific American in 1885.

To work with molten fluoride salts, he neededa furnace capable of producing and sustaining highertemperatures than the coal-fired furnace of his ear-lier experiments. For this purpose, Hall adapted asecond-hand, gasoline-fired stove to heat the inte-rior of a clay-lined iron tube. Despite the highertemperature of this furnace, he was unable to meltcalcium, aluminum, or magnesium fluorides.Potassium and sodium fluorides melted but did notdissolve useful amounts of aluminum oxide.

Hall moved on to experiment with cryolite(sodium aluminum fluoride) as a solvent. He madecryolite, found that it would melt in his furnace, andshowed that it would dissolve more than 25% byweight of aluminum oxide. The melting point ofcryolite is 1000 ˚C, an exceptionally high tempera-ture for electrochemistry. He did this crucial experi-ment early in February 1886 and repeated it thenext day for his sister Julia to witness.

Six days later, Hall first attempted to preparealuminum metal by passing an electric current

2

THE CHALLENGE

Julia B. Hall in 1881.Julia helped her brother bypreparing chemicals such asaluminum oxide. She had studiedchemistry and followed hisexperiments closely. Throughmost of his life, Hall maintaineda lively correspondence with hissister and other family members.Julia saved many of these lettersand some of his notebooks,which provide an exceptionalrecord of the day-to-day life ofan inventor.

Hall family home with attached woodshed.

through a solution of aluminum oxidein molten cryolite. He immersedgraphite rod electrodes into the fierysolution in a clay crucible and let thecurrent run for a while. In Julia’s pres-ence, he poured the melt into a fryingpan and broke apart the cooled massbut found no aluminum. There wasonly a grayish deposit on the negativeelectrode, a deposit that did not havethe shiny metallic appearance of aluminum. Afterrepeating this process several times, Hall realizedthat this deposit was probably silicon from silicatesdissolved out of the clay crucible. If he had not beenacquainted with the appearance of metallic alu-minum from seeing Jewett’s sample, Hall might havebeen slower to interpret this false result.

SuccessFrom a large graphite rod, Hall made a

graphite crucible to line the clay crucible. He alsolowered the melting point of the cryolite solution byadding aluminum fluoride. The first experimentwith this new system was performed on February 23,1886. The electric current ran for several hours, andonce again he cooled the melt and broke it open inthe presence of his three sisters and father. This timethey found several small silvery globules, which hetested with hydrochloric acid. He took them toJewett, who confirmed that they were aluminum.

On July 9, 1886, Hall applied for a patent.Meanwhile, Paul L.T. Héroult was granted a Frenchpatent on April 23, 1886, for a comparable processbased on cryolite and aluminum oxide; he had alsoapplied for a U.S. patent in May. This meant thatHall had to prove that he had made aluminum bythe new method before the date of the Frenchpatent to obtain patent protection in the UnitedStates. Evidence from his family and Jewett, includ-ing two postmarked letters to his brother, George,helped to establish the priority of Hall’s discovery inthe United States in a ruling made by the PatentExaminer. Hall’s patent rights were also upheld intwo subsequent legal struggles with the CowlesElectric Smelting Co. of Cleveland, Ohio, whichmade copper–aluminum alloy.

SimultaneousDiscoveries

How could it be that PaulHéroult in Paris, France, andCharles Hall in Oberlin, Ohio,made nearly simultaneous, yetindependent discoveries of thesame process of refining alu-minum? Many factors seem to

have contributed. Finding an economical process forrefining aluminum was widely recognized as a primetarget for inventors. Electrochemistry had begun tomature as an applied science. Large electricity-gen-erating dynamos were being developed commer-cially. Interest had been aroused in the chemistry offluorine-containing substances. Although Hall wasworking in a small U.S. college town, he had accessto the latest in scientific thought with Jewett as hismentor. Proximity to Cleveland and its emergingtechnical industries, such as Standard Oil for gaso-line, Brush Electric for large graphite rods, andGrasselli for chemicals, was also a contributing factor.

Hall, likeHéroult, was aresourcefulexperimentalist,who not onlydevised amethod of mak-ing aluminummetal, but mademost of hisapparatus andprepared manyof his chemicals.Like Héroult, Hall had a burning desire to be a suc-cessful inventor and industrialist. In recognition ofthe contribution these two young men made to thedevelopment of this electrochemical process onboth sides of the Atlantic, it is now called theHall–Héroult process.

3

Diagram from patent No. 400,664.

Letter from C. M.Hall to his brotherGeorge written theday after thediscovery.

Paul L. T. Héroult, whodiscovered the sameelectrochemical process forrefining aluminum metal inFrance. He was born the sameyear and died the same year asCharles Hall (1863–1914).

4

COMMERCIALIZATION

In the summer of 1888, a group of investors orga-nized by Captain Alfred Hunt, an MIT graduateinvolved in the metallurgical business in

Pittsburgh, provided sustained support for Hall. Heworked at the fledgling Pittsburgh ReductionCompany, the predecessor of Alcoa, to bring hisprocess from laboratory to commercial scale. ByThanksgiving day 1888, with the able assistance ofArthur Vining Davis, Hall was producing aluminumin a pilot plant on Smallman Street in Pittsburgh.

The process was soon simplified by using internalheating caused by electrical resistance in the reac-tion pots to achieve and maintain the molten state.Steam-driven Westinghouse dynamos provided theelectricity. Further cost improvements resulted laterfrom the use of hydroelectricity.

The Pittsburgh Reduction Company becamethe Aluminum Company of America (Alcoa) in1907, just before the patent rights ran out. At firstaluminum was a solution in search of a problem, but

gradually many uses were found for it, ranging fromaircraft and other modes of transportation to powerlines for long-distance transmission of electricity,construction, food storage, and decoration. Theready availability of this light, lustrous, and nonrust-ing metal has changed our lives.

RecognitionIn 1911 Hall became the fifth recipient of the

Perkin Medal, which was awarded for “valuablework in applied chemistry” by the Society ofChemical Industry (American Section) with thesupport of the Electrochemical Society and theAmerican Chemical Society. Paul Héroult attendedthe award ceremony in New York and made a grace-ful contribution to the speeches. Hall respondedwith equal warmth.

Upon Hall’s death in late 1914, his holdings inAlcoa stock amounted to a sizeable fortune, most ofwhich he bequeathed to educational institutions inthis country and abroad.

Hall reading the American Chemical Journal on theporch of the new family home, which Hall had built.

Sketch of the pot room at the original aluminum production facility onSmallman Street in Pittsburgh.

Christian Bickert. “Paul Héroult — The Man Behind TheInvention.” In Hall-Héroult Centennial, edited by Warren S.Peterson and Ronald E. Miller, 102–5, Warrendale, Pa.: TheMetallurgical Society, Inc., 1986.

Charles C. Carr. Alcoa an American Enterprise. NewYork:Rinehart & Company, 1952.

Norman C. Craig. “Charles Martin Hall—The Young Man,His Mentor and His Metal.” Journal of Chemical Education,63 (1986): 557–59.

Junius D. Edwards. The Immortal Woodshed. New York:Dodd Mead & Co., 1955.

Margaret B. W. Graham and Bettye H. Pruitt. R&D forIndustry: A Century of Technical Innovation at Alcoa.Cambridge:Cambridge University Press, 1990.

Harry N. Holmes. “The Story of Aluminum.” Journal ofChemical Education 7 (1930): 233–44.

Charles M. Hall v. Paul L. [T.] Héroult. Interference. Processfor Reducing Aluminum by Electrolysis. U.S. Patent Office,October 24, 1887.

Seabury C. Mastick. “Chemical Patents II.” Journal ofIndustrial and Engineering Chemistry 7 (1915): 874–82.

George D. Smith. From Monopoly to Competition: TheTransformation of Alcoa, 1888–1986. Cambridge: CambridgeUniversity Press, 1988.

Privately Published Materials in the Oberlin CollegeArchives

George E. Hall, ed. Charles Martin Hall, 1863–1914[addresses at the Memorial Service, Oberlin, Ohio, January22, 1915], N.p., n.d.

Frances Gulick Jewett. Frank Fanning Jewett, the BelovedTeacher, 1844–1926, N.p., n.d.

FOR FURTHER READING

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NATIONAL HISTORICCHEMICAL LANDMARK

PRODUCTION OFALUMINUM METAL BYELECTROCHEMISTRY

Oberl in, Ohio1886

On February 23, 1886, in his woodshed laboratoryat the family home on East College Street, CharlesMartin Hall succeeded in producing aluminum metalby passing an electric current through a solutionof aluminum oxide in molten cryolite. Aluminumwas a semiprecious metal before Hall ’s discoveryof this economical method to release it from itsore. His invention, which made this l ight, lustrous,and nonrusting metal readily avai lable, was thebasis of the aluminum industry in North America.

American Chemical Society September 17, 1997

The American Chemical SocietyPaul S. Anderson, PresidentPaul H. L. Walter, President–ElectJoan E. Shields, Board ChairmanJohn K Crum, Executive DirectorDenise Graveline, Director of Communications

ACS Division of the History of ChemistryHarold Goldwhite, ChairVera V. Mainz, Secretary–Treasurer

ACS Cleveland SectionJames D. Burrington, Section ChairDavid W. Ball, Chair–ElectKatherine M. Juhasz, SecretaryEvelyn Nevel, TreasurerCharles K. Beck, Chair, Archives Committee

Oberlin CollegeNancy S. Dye, PresidentClayton R. Koppes, Dean, College of Arts and

SciencesRobert Q. Thompson, Chair, Department of

ChemistryNorman C. Craig, Robert and Eleanor Biggs

Professor of Natural Science

ACS Advisory Committee onNational Historic Chemical LandmarksChair: Ned D. Heindel, Lehigh UniversityJames J. Bohning, American Chemical SocietyJon B. Eklund, National Museum of

American HistoryYasu Furukawa, Tokyo Denki UniversityLeon Gortler, Brooklyn CollegePaul R. Jones, University of MichiganJames W. Long, University of OregonPeter J. T. Morris, Science Museum, LondonMary Virginia Orna, Chemical Heritage

FoundationStanley I. Proctor, Jr., Proctor Consulting ServicesJeffrey L. Sturchio, Merck & Co., Inc.Frankie K. Wood-Black, Phillips PetroleumAnn C. Higgins, ACS Staff Liaison

American Chemical Society1155 Sixteenth Street, N.W.

Washington, DC 20036