Supplementary article:

"Charles Martin Hall - The Young Man, His Mentor, and His Metal" by Norman C. Craig, J. Chem. Educ. 1986, 63, 557-559
Oberlin College, Oberlin, OH 44074


One hundred years ago aluminum was a semiprecious metal. It was produced commercially on a small scale by Henri Ste. Claire Deville's chemical reduction method, which was the reaction of metallic sodium with anhydrous aluminum chloride. Aluminum sold for $12 per pound; silver was only $15 per pound. When the Washington Monument was completed in 1884, a small, 6-lb pyramid of ornamental aluminum metal was placed at the very top. Intended as the tip of a lightning rod system, this aluminum 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 be found in every clay bank."

In 1880 two men who were interested in aluminum metal had met on the campus of Oberlin College, near Cleveland, Ohio. The older was a world traveler who was 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-one half years was the discovery of a practical electrolytic process for reducing aluminum oxide to aluminum metal. Within three more years the younger man had developed this new process from the laboratory 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.


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 at the University of Göttingen in Germany. There he had become well acquainted with current European science, and, in particular, he had learned about the promise of aluminum. What is more he had met Friedrich Wöhler, who had isolated aluminum in 1827, and he had obtained a sample of aluminum metal. Jewett returned to America to become Wolcott Gibbs' private assistant at Harvard University. Soon he was nominated by the president of Yale to teach at the Imperial University in Tokyo, Japan, where, from 1876 to 1880, he was one of the small group of westerners who initiated the teaching of science at that university. In 1880 at the age of 36 he became the professor of chemistry and mineralogy at Oberlin College.

Charles Martin Hall had learned some chemistry as a serious-minded youth in the town of Oberlin by reading an 1840's textbook found on the shelves of his minister father's study and by doing experiments at home. This was the beginning of a lifelong enthusiasm for doing experimental work in the laboratory. An avid reader in many fields, he also followed closely the popular literature of invention in Scientific American. Young Hall already knew about the romance of aluminum when, as a 16-year-old freshman in the college in the fall of 1880, he went to the chemistry laboratory to obtain some items for his experiments at home. There he met Jewett.


Curricular and Extracurricular Studies

Hall did not take a formal course in chemistry until three years later - the junior year was the customary time for such study in those years - but, under Jewett's guidance and encouragement, he worked on aluminum chemistry in Jewett's laboratory and in his own laboratory at home. He also began investigations 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 course in 1883-84,2 he reportedly heard Jewett lecture on the chemistry of aluminum, display his sample of the metal, and predict the fortune that awaited the person who devised an economical method for winning aluminum from is oxide ore. To a fellow student Hall declared his intention to be that person.

He graduated in June 1885. In his brief commencement oration, entitled "Science and the Imagination", Hall placed the use of imaginative thinking in science above that in poetry. He understood what research required. Eight months later, in the woodshed laboratory attached to his family's home, he obtained his first globules of aluminum metal. He was barely 22 years old.

To accomplish this, Hall had not only to devise the method to isolate aluminum metal but 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 substances of the time.

In preparing some chemicals such as alumina and in other ways, Hall was helped by his older sister Julia Hall, who had studied chemistry and 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.

At the beginning of his investigations, Hall explored chemical reduction methods for obtaining aluminum. He tried, as had others, to adapt to 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 find an inexpensive way to prepare anhydrous aluminum chloride for use in the Deville process. He also treated cryolite (AlF3.3NaF), 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.

To obtain electricity for electrolysis experiments in a small college town in the 1880's one had to construct batteries. Hall and Jewett used the classical Bunsen battery, which consists of a zinc electrode in a 1:10 dilute sulfuric acid solution surrounding a porous ceramic cup that contains a carbon-rod electrode in concentrated nitric acid. (This description of the Bunsen cell can be found in Jewett's "Laboratory Exercises in Inorganic Chemistry".) This cell has an output of about 1.9V and a good current capacity. Nonetheless, assembling enough of these cells to provide adequate 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 experiment of this type Hall attempted electrolysis of aluminum fluoride dissolved in water. Unfortunately, this electrolysis system gave only unwanted hydrogen gas and aluminum hydroxide at the cathode. However, the selection of a fluoride was probably a turning point in his work. Most likely he chose aluminum fluoride because, unlike aluminum chloride, it had not been tried before. Using aluminum fluoride was certainly not a matter of convenience because he had to prepare it from hazardous hydrogen fluoride in special lead vessels in Jewett's laboratory. Nonetheless, aluminum fluoride was easier to make from aluminum oxide than was aluminum chloride. Hall did the first electrolysis experiments in Jewett's laboratory during spare time in his senior year of 1884-85, but after his graduation 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.) To 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 he adapted a second-hand, gasoline-fired stove to heat the interior of a clay-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 1360 oC), aluminum fluoride (s.p. 1291oC), and magnesium fluoride (m.p. 1266 oC). Others - potassium and sodium fluorides - melted in the furnace but did not dissolve useful amounts of aluminum oxide. Hall and Jewett understood that the salts had to be of metals that were more electropositive than aluminum. No doubt they were aware of the earlier work on the electrolysis of aluminum chloride/sodium chloride melts by Deville and Bunsen and on the electrolysis of cryolite by Deville. They were aware of Grätzel's recent success in obtaining magnesium metal by electrolysis of molten magnesium chloride. Certainly they recognized that the fluoride salts had the advantage of not being hygroscopic.

Hall moved on to experiments with synthetic cryolite, the double fluoride of sodium and aluminum. Probably he was aware that mixtures of salts could have lower melting points than the constituent salts. Also Hall had worked with cryolite in some of the chemical reduction experiments. Hall synthesized his cryolite, found that he could melt it (m.p. 1000 oC), and showed that it was a good solvent for aluminum oxide. He did this signal experiment on 9 February 1886 and repeated it the next day.

Six days later, on 16 February, Hall first attempted to prepare aluminum metal by fused-salt electrolysis. He used graphite-rod electrodes, dipping them into a fiery solutions of aluminum oxide in molten cryolite in a clay crucible. Hall let the current pass a while. In his sister Julia's presence he poured the melt out in a frying pan and broke apart the cooled mass. They found only a grayish deposit on the negative electrode - a deposit that did not have the shiny metallic appearance of aluminum. After several repetitions, Hall realized that this deposit was probably elemental silicon originating in the silicates of the clay crucible. Had he not been acquainted with the appearance of metallic aluminum from seeing Jewett's sample, Hall may have been slower to interpret this false result.


Success

Hall then fashioned a small crucible of graphite to serve as a liner for the clay crucible. Also, he lowered the melting point of the electrolyte by adding some aluminum fluoride to the cryolite. The first electrolysis experiment with this new system was performed 23 February 1886. 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 to 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 important discoveries. He did not regard his regular notebook entries as sufficient. Consequently, he mailed two letters to his brother George Hall, who was a minister in Dover, New Hampshire. The second of these letters, mailed on 24 February, described the technical aspects of the discovery in considerable detail. As requested, George Hall kept these letters.


Commercialization

Hall was as adept in overcoming the obstacles to commercialization of his new electrolytic process as he 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 U.S. patent rights by the Frenchman Paul Héroult, who held a French patent dated 23 April 1886 that included a similar electrolytic process using cryolite and aluminum oxide. Remarkably, Héroult was the same age as Hall. Julia Hall and Jewett contributed to the testimony before the patent examiner that established the priority of Hall's discovery in the U.S. on 23 February 1886. The postmarked letters to George Hall were also important evidence. Subsequently, there were two more legal struggles, which were with the Cowles Company, over the Hall patent rights. In the first trial, presided over by Judge William Howard Taft, later President Taft, Hall's interests were upheld. The outcome of the second trial, in which an additional patent on electric-arc furnaces that had been secured by the Cowles company played a role, was finally a "draw" in 1903. (The records of these trials are another detailed source of information about Hall's work.)

A group of investors, organized by Captain Alfred Hunt in the summer of 1888, provided the crucial financial backing and patient support for Hall while he worked at the fledgling Pittsburgh Reduction Company, the predecessor of Alcoa, to bring his process from the laboratory to the commercial scale. Hunt, an MIT graduate and former Army engineer, was experienced in the metals business. By Thanksgiving Day 1888, with the able technical assistance of Arthur Vining Davis, Hall was producing aluminum on a pilot plant scale on Smallman Street in Pittsburgh. Soon after achieving this result, Hall confirmed his earlier belief (expressed to his sister in 1886) that the process could be simplified by using only the resistive heating in the reduction pots to achieve and maintain the molten state. (This feature of the commercial process was claimed as the prior discovery by the Cowles Company in the second lawsuit.) He also found that larger pots worked better than the smaller ones that had caused difficulty in the initial scale-up experiments. The electricity for the process was obtained from new steam-engine-driven Westinghouse dynamos. Indeed, major developments in the manufacture of such dynamos in the preceding decade were a critical technological contribution to the rapid commercialization of the whole field of electro-metallurgy in the last decade of the 19th century. Within two more years Hall and his partners were producing aluminum metal in quantity, producing it faster than markets for its use could be developed.

Meanwhile, Héroult in France was preoccupied with the commercial development of that part of his patent which was concerned with an electric-arc aluminum-alloy process, one similar to that employed by the Cowles Company. He was not involved in making any pure aluminum in a commercial scale until the end of 1889. According to J. W. Richards the author of "Aluminum", Third Edition, 1896, "it appears that Héroult was not aware of the possibilities of his process until Hall's process showed the way."


Recognition

Among scientists, engineers, and industrialists Hall soon gained wide recognition. He was elected to membership in AIME (now, American Institute of Mining, Metallurgical, and Petroleum Engineers) in 1890. He was a charter member and vice president of the American Electrochemical Society upon its founding in 1902. He was also a member of the American Philosophical Society and of the Franklin Institute. In 1911 Hall became the fifth recipient of the Perkin Medal, which was awarded for "valuable work in applied chemistry" by the combined action of the Electrochemical Society, the American Chemical Society, and the Society of Chemical Industry (Great Britain). Paul Héroult attended the award ceremony in New York and made a graceful contribution to the speeches. Hall responded with equal warmth.

How could it be that Paul Héroult in France and Charles Hall in the U.S. made nearly simultaneous, yet independent discoveries of the same process for refining aluminum? Such simultaneity in scientific discovery is not infrequent when "the time is right." In this case, many factors seem to have contributed to the time being right. Finding an economical process for refining aluminum was widely recognized as a prime target for invention. Electrochemistry had begun to mature as a science. Large electricity-generating dynamos had recently come into commercial production. Interest had been aroused in the chemistry of fluorine-containing substances. Perhaps more surprising to a distant scientific observer is that one of the successful inventors was working in Paris while the other was located in a small U.S. college town. Yet, this account has shown that Hall had access to the latest in scientific thought through Jewett. Hall, like Héroult, was a resourceful experimentalist with a burning desire to be a successful inventor and businessman.


The Person

A number of Charles Martin Hall's personal qualities have emerged in the description of the discovery and commercialization of the electrolytic process for refining aluminum. However, we shall conclude this account with a few more remarks about Hall the person. Throughout his life colleagues found him to be serious-minded and exceptionally hard-working. According to his brother, "The sports and games in which youth of his day delighted had no place in this thoughts." So God-fearing was Hall that in writing letters he referred to the devil as the d-l. Until he was 39 years old he lived frugally in boarding houses, although his skill as a player of classical music led him to furnish these rooms with rented pianos. As he prospered in the aluminum industry and had increasing opportunities to travel, he satisfied his interest in concert music and opera by attending performances in the great halls of the United States and Europe. And, he developed a collector's eye for fine oriental rugs and porcelains.

Hall had intended to marry his college sweetheart, Josephine Cody. Though engaged for a while, she grew tired of waiting for Hall to make his fortune and broke the engagement. Disappointed, Hall found solace in his strong ties to his family and in his continuing interest in Oberlin College for which he served a s trustee from 1905 until his death. In characterizing this latter interest, his brother commented, "the College was to him wife and children and all, his life." Upon his death in 1914 at the age of 51, Hall left most of his material possessions and about one-third of his Alcoa stock and other investments to Oberlin College. Another significant part of his bequest went to Berea College in Kentucky. Much of the rest went to other educational enterprises at home and abroad.


Notes

1. This paper was presented on March 3, 1986 as an invited address at the Light Metals Sessions of The Metallurgical Society of the AIME (American Institute of Mining, Metallurgical and Petroleum Engineers). This paper and a companion paper on Paul Héroult, presented by Christian Bickert, marked the centennial of the discovery of the Hall-Héroult process for refining aluminum. Reprinted with the permission from Hall-Héroult Centennial First Century of Aluminum Process Technology, Volume 1 of Light Metals, 1986, pp 96­101, The Metallurgical Society, 420 Commonwealth Drive, Warrendale, PA 15086.


2. Hall was not in college in 1882­1883. He spent the year selling books door-to-door and experimenting.