Charles Martin Hall-The Young Man, His Mentor, and His Metal Norman C. Craig Oberlin College, Oberlin, OH 44074 One hundred years ago aluminum was a semiprecious metal. I t was vroduced commerciallv on a small scale by Henri Ste. ciaire Deville's chemical reduction method, which was the reaction of metallic sodium with anhydrous aluminum chloride. Aluminum sold for $12 per pound; silver was onlv $15 per pound. When the Washington Monument was completed in-1884, a smnll, 6-lh pyramid of ornamental aluminum metal was placed at the very top. Inwnded as the tip of a lightning rod Bystem, this aluminm cap was a practical application of the high electrical conductivity as well as the ~-~~ corrosion resistance of this remarkable new metal. Meanwhile, many investigators, mostly in Europe, sought economical methods to wrest aluminum from its abundant ore, which, as Deville had remarked, "could he found in everv clav hank." 1n-1880 two men who were interested in aluminum metal had met on the campus of Oherlin College, near Cleveland, Ohio. The older was; world traveler whobas as well educated in chemical science as any young American academic of his day. The younger was a local youth who was self-educated in science and intent on becoming a successful inventor. The outcome of their association over the next five-and-onehalf years was the discovery of a practical electrolytic process for reducine aluminum oxide to aluminum metal. Withthe younger man had developed this new in three more mocess from the lahoratorv scale to a practical industrial scale. As a consequence, aluminum metal was swiftly transformed from a curiosity into a widely useful material, and the younger man was launched on a successful career in technology and industry. ~
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Professor and Student Frank Fanning Jewett had received his undergraduate education and some graduate education in chemistry and mineralogy at Yale University. For two more years, 1873 to 1875, he had studied chemistry a t the University of Gottingen in Germanv. There he had become well acauainted with current European science, and, in particular, he had learned about the promise of aluminum. What is more he had met Friedrich Wahler, who had isolated aluminum in 1827, and he had obtained a sample of aluminum metal. Jewett returned to America to hecome Wolcott Gihhs' private assistant a t Harvard University. Soon he was nominated by the president of Yale to teach a t the Imperial University in Tokyo, Japan, where, from 1876 to 1880, he was one of the small e r o k of Westerners who initiated the teachine of science at that university. l n 1880 a t the age of 36 he became the nrofessor of chemistrv and mineraloev a t Oherlin Colleee. Charles Martin HHII had learnersome chemistry a s a serious-minded youth in the town of Oherlin by reading an 1840's textbook found on the shelves of his minster father's study and by doing experiments a t home. This was the beginning of a lifelong enthusiasm for doing experimental work in the lahoratorv. An avid reader in manv fields, he also followed closely the popular literature of in;ention in Scientific American. Young Hall already knew about the romance oi aluminum when, as a 16-year-old freshman in the college in the fall of 1880, he went to the chemistry lahoratory to
obtain some items for his experiments a t home. There he met Jewett.
Curricular and Extracurrlcular Studles Hall did not take a formal course in chemistry until three vears later-the iunior vear was the customarv time for such study in those years-Lkt, under Jewett's &dance and encouragement, he worked on aluminum chemistry in Jewett's lahoratory and in his own lahoratory a t home. He also began investieations in two other notable areas of invention: one was tungsten metal for filaments in electric light bulbs, and the other was fuel cells, in which he hoped to use hydrogen gas or illuminating gas to produce electrical energy directly. (Some of Hall's ideas were not so good. In the late 1890's, perhaps encouraged by the then current discoveries of natural radioactivity, he thought he had found evidence of the transmutation of iron into platinum metals.) When Hall finally took the chemistry c o k e in 1883-84,' he reportedly heard Jewett lecture on the chemistrv of aluminum, disvlav his sample of the metal, and predict the fortune t h a t awaited the person who devised an economical method for winning aluminum from its oxide ore. T o a fellow student Hall declared his intention to he that person. He graduated in June 1885: In his brief commencement oration. entitled "Science and the Imagination", Hall placed the usd of imaginative thinking in science above that in poetry. H e understood what research required. Eight months later, in the woodshed lahoratory attached to his family's home, he obtained his first globules of aluminum metal. He was harelv 22 vears old. I not only to devise the methT o accomplish this, H ~ Ihad od to isolate aluminum metal hut also to fabricate most of his apparatus and prepare many of his chemicals. For example, he probably prepared pure aluminum oxide from alum and washing soda, which were common household suhstances of the time. In preparing some chemicals such as alumina and in other wav*. Hull was helped by his older sister Julia Hall, who had studied chemistryand who followed his experiments closely. Through most of his life Hall maintained a lively correspondence with his sister. She saved these letters and some of his notebooks. Together these materials helped provide an exceptional record of the day-to-day life of an inventor.
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This paper was presented on March 3, 1986 as an invited address at the Light Metals Sessions of The Metallurgical Society of the AlME (American Instituteof Mining, Metallurgical and PetroleumEngineers). This paper and a companion paper on Paul Heroult, presented by Christian Bickert, marked the centennial of the discovery of the HallHerouit process for refining aluminum. Reprinted with the permission from Hall-Heroult Centennial First Century of Aluminum Process Technology, Volume 1 of Light Metals, 1986, pp 96-101, The Metallurgical Society, 420 Commonwealth Drive, Warrendale. PA 15086. ' He was not in college in 1882-83. Hespent the year selling books door-todoor and experimenting.
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At the beginning of his investigations, Hall explored chemical reduction methods for obtaining aluminum. He tried. as had others. to a d a ~to t aluminum oxide the graphite-based reduction methods that were used for obtaining iron and other metals of intermediate chemical activity. In a second initiative, he attempted to findan inexpensive way t o prepare anhydrous aluminum chloride for use in the Deville process. He also treated cryolite (AIFr3NaF), a naturally occurring substance, with sodium metal but obtained disappointing results. Electrolysis Experiments Finally, Jewett and Hall recognized that electrolysis could provide the potent reduction conditions that were needed. Perhaps pertinent to this decision was the accessioning in 1883 by the college library of the book "The Theory and Practice of Electro-deposition" by George Gore (Houlston and Wright, London, 1859). Whatever the particular sources, we may presume that Hall had access to much scientific literature from Jewett's personal library and from the college's library. T o obtain electricitv for electrolvsis exneriments in a small college town in the 1880's one had to construct batteries. Hall and Jewett used the classical Bunsen hattew, which consists of a zinc electrode in a 1:10 dilute sulf&ic acid solution surrounding a porous ceramic cup that contains a carbon-rod electrode in concentrated nitric acid. (This description of the Bunsen cell can he found in Jewett's "Lahoratory Exercises in Inorganic Chemistry".) This cell has an output of about 1.9 V and agood current capacity. Nonetheless. assembline"~ enough of these cells to nrovide adeauate electrical energy for aluminum production was a large undertaking. About one pound of zinc metal would have been consumed in securing one ounce of aluminum. In his first exneriment of this tvne Hall a t t e m ~ t e delectrolysis of a l u m k n fluoride d i s s h e d in water:~nfortunately, this electrolysis system gave only unwanted hydrogen gas and aluminum hydroxide a t the cathode. However, the selection of a fluoride was probahly a turning point in his work. Most likely he chose aluminum fluoride because, unlike aluminum chloride, it had not been tried before. Using aluminum lluor~dewascertainly not a matter of convenience because hr had to prepare it from ha~arduushydrogen tluuride in special lead vessels in Jewett's laboratory. Nonetheleis, aluminun~fluoride was easier to make from aluminum oxide than was aluminum chloride. Hall did the first elertrolysis experiments in Jewett's laboratory during spare time in his senior w a r of 1dd.l-85. hut after hisrraduation in June 1885 he continued work full-time in his woodshed laboratory. Experimentation with fused salts as solvents was Hall's next, important step. As his sister reports, it is possible that he came to this crucial idea while playing classical sonatas on the family's "ancient' piano. (Throughout his adult life Hall, who was an accomplished pianist, played the piano in order to renew his spirits.) T o work with fused salts of fluorides he had to build a furnace capable of producing and sustaining higher temperatures than the coal-fired, bellows-driven furnace of his earlier experiments. For this purpose be adapted a second-hand, gasoline-fired stove t o heatthe interior of a clav-lined iron tube. Despite the higher temperature of this furnace, he was unable to melt some of the fluoride salts he tried. Such was the case with calcium fluoride (melting point 136OoC),aluminum fluoride (s.p. 1291°C), and magnesium fluoride (m.p. 1266°C). Others-potassium and sodium fluorides-melted in the furnace but did not dissolve useful amounts of aluminum oxide. Hall and Jewett understood that to be of metals that were more electrouosi.~ the salts had ~~-~~~ t i w than aluminum. S u d ~ , u t )they t were aware of the earlier work on the electrolvsis uf aluminum chloride/sodium chluride melts by ~ e v i l Gand Bunsen and on the electrolysis of u
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cryolite bv Deville. They were aware of Gritzel's recent success in obtaining magnesiummetal by electrolysis of molten magnesium chloride. Certainly they recognized that the fluoride salts had the advantage i f not beine hverosco~ic. "" Hall moved on to experhe& with synthetic cryolitk, the double fluoride of sodium and aluminum. Probablv be was aware that mixtures oisalts could have lower melting points rhiln thr consrirueur salts. AISUHall had worked with crvolite in some of the chemical reduction experiments. Hall synthesized his cryolite, found that he could melt it h p . 100O0C),and showed that it was a good solvent for aluminum oxide. He did this signalexperiment o n 9 February 1886 and repeated i t the nextday. Six days later, on 16 February, Hall first attempted to orenare . aluminum metal bv fused-salt electrolvsis. He used graphite-rod electrodes, dipping them intoa iierysolurion of aluminum oxide in molten crvolitr in arlav crucihle Hall let the current pass a while. 1; his sister Jilia's presence he noured the melt out in a frvine t . . Dan . and broke a ~ a r the cooled mass They f m n d only a greyish deposit on the negative electrode- a d e ~ o s i that t did not have the shinv rnetallic appearance of al&inum. After several repetitions, Hall realized that this deposit was probably elemental silicon originating in the silicates of the clay crucihle. Had be not been acquainted with the appearance of metallic aluminum from seeing Jewett's sample, Hall may have been slower to interpret this false result.
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Success Hall then fashioned a small crucible of graphite to serve as a liner for the clav crucible. Also. he lowered the meltina point of theelecrroiytr ~ ~ y a d d i n g s ~ m e a l u m i nfluoridet; um the crvolite. The first electrulvsis experiment with this new system was performed 23 fehruary8886. The electric current ran for several hours. Once again in his sister's presence, he cooled the melt and broke it open. This time they found several small silvery globules which he tested with hydrochloric acid. Immediately he took these t o Jewett, who confirmed that they were aluminum. Because of his familiarity with the literature of invention, Hall was aware of the need to record definitively the date and the essentials of imuortant discoveries. He did not regard his regular notebook entries as sufficient. ConsequentIv. he mailed two letters to his brother George Hall, who was minister in Dover, New Hampshire. hes second of these letters, mailed on 24 February, described the technical asp e c k o f the discovery in considerable detail. As requested, George Hall kept these letters.
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Hall was as adept in overcoming the obstacles to commercialization of his new electrolytic process as be was in discovering it. He survived the defection of his original Boston backers and an awkward, year-long association with the Cowles Electric Smelting and Aluminum Company of Cleveland. He also withstood a challenge to his application for US.patent rights by the Frenchman Paul HBroult, who held a French patent dated 23 April1886 that included a similar electroly
