Pauling’s Last Year as a Grad Student

Ava Helen and Linus Pauling, 1924.

Ava Helen and Linus Pauling, 1924.

[Part 3 of 3]

Pauling’s final year of graduate school at the California Institute of Technology, 1924-1925, was quite busy.  During this last phase of his student experience, Pauling’s primary research interests centered on hematite, corundum, and beta-alumina, though a great deal more professional and personal growth can be traced to this time in the budding young scholar’s life.

In his work on corundum and hematite, Pauling was assisted by Sterling B. Hendricks, a Texan who had received his master’s degree from Kansas State in 1924 was now in Pasadena, working on his PhD.  Hendricks became a close associate and personal friend of Pauling’s and, with their mentor Roscoe Dickinson away on a research trip, Pauling became Hendricks’ unofficial adviser. Such was Pauling’s influence that, later in life, Hendricks would come to consider himself to be “Linus’s first student.”

Together, Pauling and Hendricks worked on a theoretical paper that pieced together much of the work that they had completed over the previous year and a half. The paper was published in the Journal of the American Chemical Society (JACS) in March 1926 (nearly a year after Pauling had completed his PhD) and titled “The Prediction of the Relative Stabilities of Isosteric Isomeric Ions and Molecules.”  The paper was a milestone in that it was Pauling’s first paper devoted solely to the subject of the chemical bond.

It was not, however, the first paper that Hendricks and Pauling had co-authored. In 1925 the duo worked together to publish two sets of crystal structures: “The crystal structures of hematite and corundum” (March 1925) and “The crystal structures of sodium and potassium trinitrides and potassium cyanate, and the nature of the trinitride group” (December 1925).  During his last year of grad school, Pauling also collaborated with his friend and former roommate, Paul Emmett, on an X-ray determination of the crystal structure of barite.  Their article, which was published in JACS in April 1925, is another example of Pauling’s work that corrected previous published structures.

Peter Debye, 1926.

Peter Debye, 1926.

On top of the research that he was doing on crystal structures, Pauling also toyed with an idea in which he applied the Debye-Hückel theory, which was used to determine the energy coefficient of ions in dilute solutions. When he learned of this work, A.A. Noyes invited Peter Debye, who was based in Switzerland, to visit Caltech, in part to have him discuss his theory with Pauling. And although Pauling never published his original idea, in July 1925 Debye and Pauling did co-author a different paper, “The Inter-Ionic Attraction Theory of Ionized Solutes.  IV.  The Influence of Variation of Dielectric Constant on the Limiting Law for Small Concentrations.”  Appearing in JACS, the article was a contribution to a larger series published by the journal on the inter-ionic attraction theory of ionized solutes.


Later on in his life, Pauling developed a reputation for staying on top of the latest findings and issuing an informed opinion on a wide range of scientific topics.  This character trait was likely spurred by an experience that he had as a graduate student.

Early on in his graduate career, one of Pauling’s more influential professors, Richard C. Tolman, posed to him a question about diamagnetism. Pauling responded that diamagnetism was just a general property of matter, a lackluster reply that made clear that Pauling had not stayed current with the literature. Tolman kept questioning Pauling for more specific details until Pauling finally answered, “I don’t know.”  For this he was reprimanded by a Caltech post-doc who told him, “You are a graduate student now, and you’re supposed to know everything.” This was advice that Pauling took to heart and that made a big difference throughout his career in science.


The Paulings, 1925.

The Paulings, 1925.

Nearing the end of his graduate school tenure, Pauling read G.L. Clark’s paper on uranyl nitrate hexahydrate and, as he went, he corrected it.  This was a continuation of the critical reading habits that he had first developed at Oregon Agricultural College and had continued to hone by lantern light while working for the Oregon Highway Department the summer prior to his enrollment at Caltech. It was likewise a practice that he would continue throughout his career: closely reading papers and correcting errors, often by letting the author or publisher know what he had found.

By this time, with Roscoe Dickinson away, Pauling had taken up some of his mentor’s responsibilities in the lab and, as with Sterling Hendricks, was serving as an ad hoc advisor to several students.

Likewise, with Dickinson gone, Pauling began to develop his own techniques to aid in crystal structure determinations. A methodology that was quite different from the formal instruction that he had received, Pauling’s approach used atomic sizes and chemical behaviors to approximate reasonable structures for molecules.  After determining these possible structures, Pauling then used X-ray data to eliminate unlikely possibilities and to isolate the best possible structure for a particular substance.  As it turned out, this approach to scientific inquiry already had a name, the stochastic method, and Pauling ultimately put it to effective use across many different disciplines.


Linus Jr. and Ava Helen, 1925.

Linus Jr. and Ava Helen, 1925.

Pauling’s last year as a grad student also included big changes in his personal life.  After marrying in the summer of 1923, Ava Helen Pauling moved to Pasadena with her husband and kept house while he finished his degree. In the early years of their marriage, these duties also routinely included helping “keep house” in the laboratory, particularly by recording data and taking notes. Pauling’s research notebooks from these years are full of her handwriting, even including one note reminding Linus that she loved him.

In the midst of all his coursework and research, and as Pauling was wrapping up his last Winter term at Caltech, another big change came about when the Paulings’ first child, Linus Jr., was born on March 10, 1925.  By this time, Ava Helen was mostly excused from laboratory duty and focused her energies primarily on raising her children (ultimately there would be four) thus creating an atmosphere at home in which Linus could be as productive as possible.


Graduation day, 1925.

Graduation day, 1925.

Linus Pauling completed his PhD in chemistry in June 1925, tacking on minors in physics and mathematics as well. His dissertation, titled “The Determination with X-rays of the Structure of Crystals,” consisted of a compilation of articles that he had previously published with little more than new pagination connecting them together as a whole.

The summer after graduation, A.A. Noyes helped Pauling to secure a research fellowship that would enable him to stay at CIT and complete a research study on complex fluorides.  Pauling continued in this vein for the next eight months, during which time he began to make plans to leave Caltech to study as a post-doc at Berkeley, where he thought he might pursue a new set of experiments in G.N. Lewis’ lab, using funding from a National Research Fellowship that he had received.

Not wanting to lose Pauling to Berkeley and Lewis, Noyes managed to arrange for Pauling to remain in Pasadena in order to complete additional unfinished work on crystal structures.  Fortunately for Noyes, at the end of 1925, when the Guggenheim Fellowships were announced, Pauling was finally chosen for funding, having at last reached the program’s required minimum age.  At Noyes’s urging, Pauling resigned from his National Research Fellowship once he had received the good news from the Guggenheim Foundation. From there, Linus and Ava Helen took an important trip to Europe and ultimately returned to Caltech, their institutional home for the next thirty-six years.

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Promoting and Reacting to The Nature of the Chemical Bond

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[Celebrating the 75th anniversary of The Nature of the Chemical Bond. Part 5 of 6.]

Once all of the hindrances to getting The Nature of the Chemical Bond printed had finally been overcome, Linus Pauling looked to the next phase – promoting his book.  He started by compiling a list of people to whom he wanted to send the text, a list that included those who had helped him along way,  journals that would review it, previous Baker Lecturers, and chemistry professors who, Pauling thought, would be interested in using it in their courses.  Pauling ultimately came up with a list of sixty-one people, not counting journals.

Cornell University Press chief W. S. Schaefer responded that the press’s policy was to allow for only six free copies, but he could send the book to those on Pauling’s list at a thirty-three percent discount.  Pauling explained that he had drafted the list based on previous experiences with McGraw-Hill, which was much looser in doling out free copies. He had Schaeffer remove sixteen individuals from the list, paid for four copies, and claimed that the remaining individuals would most likely use the book in their courses and so should get a copy as a promotional offer.  Schaefer agreed to this arrangement, charging the bulk of the books to the advertising budget.

Once The Nature of the Chemical Bond was officially released in May 1939, Cornell did its part in getting the word out.  The press sent out an order form addressed to “Students of Chemistry and Molecular Structure” in chemistry departments across the country, alerting them to the opportunity for a ten percent educational discount.  The form summarized the material found in The Nature of the Chemical Bond as including “the structure of molecules and crystals, and the nature of the chemical bond,” and emphasized the book’s grounding in quantum mechanics without relying on “mathematical argument in demonstrating the conclusions reached.”  It went on to describe how

Early chapters discuss the theoretical basis and the nature and properties of isolated bonds between pairs of atoms.  Then complex ions, molecules, and crystals are considered; the extensive illustrative material is drawn about equally from organic and inorganic chemistry.  There are complete chapters on such important subjects as the hydrogen bond, ionic crystals, and metals.

The methods used by the author in exploring the nature of the chemical bond include the resonance concept and the techniques of diffraction of electrons by gases and vapors and of X-rays by crystals, the determination of electric and magnetic moments, and various kinds of thermal measurements.

The Press also produced an advertising brochure that expanded upon the information contained in the order form.  In addition to noting the book’s basis in quantum mechanics, the brochure promised an “especial emphasis on the resonance phenomenon, including the new concept of resonance of molecules among alternative electronic structures.”  It also suggested that The Nature of the Chemical Bond was “of unusual importance for chemists and mineralogists,” quoting from a glowing write-up in the August 1939 Scientific Book Club Review, which declared that “the publication of this book is literally epoch making.” The journal also described how Pauling’s final chapter, which he added at the very last minute, dealt “with the future development and application of the concept of resonance” and “will probably prove to have been truly prophetic.”

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By June and July, readers began corresponding with Pauling about the book.  The initial responses, mostly from academics, thanked Pauling for sending a complimentary copy and were generally positive in their evaluation.  Many mentioned how they, or someone in their department, planned to use Pauling’s book in an upcoming course.   Earl C. Gilbert of Oregon State College, for example, told Pauling that the text would “be very successful and fill quite a need” and found Pauling’s account of hydrogen bond properties in particular to be a “convincing treatment” in comparison to Jack Sherman and J. A. A. Ketelaar’s application of quantum mechanics to the carbon-chlorine bond.

Joseph E. Mayer of Columbia University was more effusive in his praise, writing, “It’s the first book that I’ve read through for years!” C. P. Smyth issued a similar response, telling Pauling in mid-October

As evidence of my interest in it I can cite the fact that it is the first scientific book which I can remember reading during the course of a fishing trip, although I have carried many with me in the past.

G.N. Lewis, ca. 1930.

Pauling also received encouragement from a former mentor, Gilbert N. Lewis at Berkeley, who wrote in August,

I have returned from a short vacation for which the only books I took were a half a dozen detective stories and your ‘Chemical Bond’.  I found yours the most exciting of the lot.

Pauling appreciated the responses and was particularly glad that Lewis was happy. He had dedicated the book to Lewis and explained “that I had you in mind continually while it was being written, and I have been hoping that my treatment would prove acceptable to you.”

Along with the praise, Pauling also received constructive advice, which he was eager to incorporate into a second edition.  Joseph Mayer mentioned that the book needed some work regarding its discussion of metals.  Gerold Schwarzenbach of the University of Zurich was also appreciative, but Pauling responded to his note by saying that he “hoped to give proper discussion of” Schwarzenbach’s findings on acid strengths “in a revised edition of my book.” Pauling likewise pressed others for deeper input. He asked Oliver Wulf, who earned his Ph.D. from Caltech in 1926 and would return to Pasadena in 1945, for suggestions on the hydrogen bond spectra, Wulf’s area of interest.

By mid-October, buoyed by all of the responses he was receiving, Pauling began to suspect that he might have a hit on his hands. Curious about sales numbers, he wrote to Schaefer at Cornell University Press for an update and also asked for an interleaved copy which he could use to plan out the next edition.

Glenn T. Seaborg, 1912-1999

Linus Pauling and Glenn Seaborg with three young science students, American Chemical Society Meeting, St. Louis, April 1984.

I hardly noticed that the work was exacting and demanding, because I couldn’t believe that I was being paid to do what I would have chosen as a hobby. It was exciting just to walk into the lab, full of anticipation that that day I might be the first human being ever to see some unimaginable new creation.

–Glenn Seaborg

Advising nine presidents on nuclear policy as the Chairman of the U.S. Atomic Energy Commission, Glenn T. Seaborg, whose centenary we celebrate today, contributed to the discovery and isolation of ten elements, was the author of 500 scientific articles, father of six kids and, most notably, the recipient of the 1951 Nobel Prize in Chemistry. Gaining international fame over the course of his career, Seaborg is best known for discovering the element plutonium in 1941, as well as nine other new transuranic elements.

Seaborg describes the search for Plutonium, “element 94.”

Alongside Edwin McMillan, Seaborg received the Nobel Prize in Chemistry for discoveries in the structure and function of the transuranium elements. In addition, Seaborg and his colleagues can be credited for the identification of more than 100 isotopes of elements throughout the periodic table. At the time that he was publishing it, Seaborg’s work required a major realignment of the periodic table of the elements, which was naturally controversial among his contemporaries, but Seaborg was willing to take a risk and it paid off. On hearing the news that he had received the Nobel Prize in Chemistry, Seaborg was quoted as saying,

One November morning as I drove to work, the radio cackled with news of my reward for taking this chance – the 1951 Nobel Prize in chemistry shared with colleague Ed McMillan. At 39, I was one of the youngest winners ever of the world’s most prestigious award.


Education is the best investment we can make in the future, and like any investment, it costs money. We can’t continue to pretend that it doesn’t. We must invest money for buildings, money for supplies, money to improve the curriculum, and money to pay teachers a salary that will attract our brightest people to the profession.

-Glenn Seaborg

Glenn Theodore Seaborg was born in Michigan on April 19, 1912. Ten years later, his family moved to California in search of opportunity. Seaborg graduated as class valedictorian from David Starr Jordan High School and continued his studies at UCLA. Attending graduate school at the University of California-Berkeley, Seaborg blossomed as a scientist, noting

By day I ran experiments on acids and bases as the personal assistant of cigar-chewing Gilbert N. Lewis, the world’s pre-eminent physical chemist. And by night I spent my free time exploring the mysteries of the atom.

Receiving his Ph.D. in chemistry in 1937, Seaborg continued on as laboratory assistant to G. N. Lewis, who was himself an important mentor to Linus Pauling. In 1939 he was hired as an instructor of chemistry at Berkeley, later becoming Professor of Chemistry.


Most of my scientific work has been basic research. There were no immediate uses for my discoveries – but today the radioisotopes are the workhorses of nuclear medicine, an isotope of plutonium is a major energy source in the space program, and the element americium is critical to the smoke detectors in every house in the country. The cost of neglecting basic research will be a continued decline in America’s technological innovation and competitiveness.

-Glenn Seaborg

In 1958, seven years after his receipt of the Nobel Chemistry Prize,  Seaborg was named Chancellor of the University of California-Berkeley.  Over the course of his short chancellorship, the university saw an increase in enrollment as well as in student activism – a harbinger of things to come in Berkeley.

Three years later, in 1961, he was appointed by President John F. Kennedy to the Atomic Energy Commission. During this time, Seaborg pushed for commercial nuclear energy and peaceful applications of nuclear science. He believed his most significant achievement while at the AEC to be the growth of the civilian nuclear power program.

While Pauling’s feelings on these issues were mixed, and his relationship with the AEC often combative, it is clear that on other matters of nuclear policy, he and Seaborg shared common ground.  In a 1986 typescript, Pauling recalled

At a recent national meeting of the American Chemical Society, held in St. Louis, Glen Seaborg and I participated in a press conference, with many reporters and television crews present.  Seaborg, who had been Chairman of the Atomic Energy Commission, accompanied the United States negotiators when the partial bomb test treaty was made [in 1963].  The Soviet Union was eager to make a comprehensive bomb test treaty, but the administration in Washington, Seaborg said, had instructed the U.S. team not to agree to a comprehensive test ban, which would hamper seriously the program of continually developing new nuclear weapons.

Indeed, throughout his career, Seaborg corresponded with Linus Pauling on a number of issues, including the investigation of uranium hexafluoride and mutual congratulations shared on the occasion of one another’s Nobel Prizes. In May 1969, when Pauling was made an Honorary Member of the American Institute of Chemists, Seaborg wrote, “Your accomplishments had already qualified you for such an honor and your work during the intervening years of our friendship has added much to this early distinction.”

On April 13, 1981, Seaborg visited Oregon State University as part of a lecture series on “Technology and Change.”  While in Corvallis, he led a seminar titled “The Transuranium Elements,” as well as public talk titled, “Our Energy Problem.” One of the transuranium elements that Seaborg discussed in his seminar, element 106, was named “seaborgium” in August 1997, making it the first element to be named for a living person.

Just before his death on February 25, 1999, the ultimate result of a stroke, Seaborg’s lifetime of achievement was honored by the American Chemical Society, who named him one of the “Top 75 Distinguished Contributors to the Chemical Enterprise.”  Seaborg was among the top four vote-getters for this decoration, joining Robert B. Woodward, Wallace Carothers and, in first place, Linus Pauling, at the top of the list.

Developing the Theory of Resonance

Linus Pauling, 1930.

[Part 1 of 2]

“I think my work on the chemical bond probably has been most important in changing the activities of chemists all over the world – changing their ways of thinking and affecting the progress of the science.”

Linus Pauling, 1977.

In early 1932, Linus Pauling spent several months visiting the University of California, Berkeley and the Massachusetts Institute of Technology to present two different lecture series on the theory of resonance and its implications for molecular structure and function. This topic, a product of Pauling’s adventures in Europe as a Guggenheim fellow, would profoundly impact the ways in which twentieth-century chemists ultimately understood the chemical bond and predicted molecular structures.

Throughout his long career, Pauling sought to improve his understanding of molecular structure in order to better predict chemical function. As Pauling saw it, molecular structure dictates function and should thus be considered accordingly.  As he wrote in 1946

…I am confident that, as our knowledge of the structure not only of simple molecules but also of proteins and other complex constituents of organisms increases, we shall in time achieve an insight into physiological phenomena which will serve as an effective guide in biological and medical research, and will contribute to the solution of such great practical problems as those presented by cancer and cardiovascular disease.

Indeed, much of Pauling’s work sought to develop the tools necessary to enable chemists to bridge the gap between structure and function.  Pauling spoke somewhat literally of this quest in 1936, in a speech where he compared the tools of the chemist to those of an architect.

The structural chemist of the past and present has been an architect working with materials of whose nature he is largely ignorant – an architect who does not know what an I beam is, but only that it can be used in his construction, and who must proceed to design structure after structure, to find ultimately that certain designs lead to satisfactory results – to a building with rooms adapted to the use of certain visitors, to bridges strong enough to hold their load, and so on. The structural chemist of the future will be able to plan his structures and forecast their properties in the same definite way that the architect and engineer plan the macroscopic, even gargantuan, structures of modern civilization.

In the years just prior to, and at the start of, Pauling’s career, great strides had been made in  molecular structure determinations.

G.N. Lewis, ca. 1930s.

In 1916, for example, Gilbert Newton Lewis developed a theory of molecular diagrams based on valence electrons, now referred to as Lewis-dot structures. The subsequent application of spectroscopic methods to molecular chemistry allowed for more direct quantitative studies of atomic and molecular structure. Later, advancements in quantum mechanics increased chemists’ and physicists’ understanding of the detailed interactions that occur between nuclei and electrons that ultimately determine atomic and molecular structure.  Meanwhile, various valence bond theories had been developed but were not applicable to all matter uniformly.

While these and other contributions were significant, many questions still remained as not all quantitative data aligned with current theories. To provide an explanation for the many apparent holes in understanding, Pauling developed his theory of resonance – an idea which became the central concept of Pauling’s valence theory.

Resonance, or electron exchange, is a property integral to the formation and maintenance of chemical bonds, as it accounts for the formation of hybrid structures that cannot be explained by the classical models of molecular structure alone.

Pauling used his theory of resonance to explain why many molecules can be drawn in various forms according to Lewis’s scheme even though no single structure could be differentiated as the “correct” structure based on energy theories and quantum mechanics.

According to Pauling’s theory, these structures could not be differentiated quantitatively because the electrons exchanged between atoms caused the molecule to resonate between multiple structures. Thus the structure of a molecule is not made up of one single structure, but in some cases, such as in carbon monoxide (CO), the true nature of the molecule resonates between multiple structures. Pauling therein predicted that the CO molecule fluctuates rapidly between multiple conformations thus creating a more stable structure, known as a “resonance hybrid.”

By Pauling’s way of thinking, the theory of resonance explained many of the obvious inconsistencies in the understanding of specific molecules at that time, and he argued that the theory should be applied when predicting new molecular structures and functions.  In our next post, we’ll talk more about the impact of the theory of resonance by examining its application to the study of the enigmatic structure of benzene.