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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Pauling Becomes a Researcher

Roscoe Dickinson, 1923.

Roscoe Dickinson, 1923.

[Part 2 of 3 in a series investigating Linus Pauling’s life as a graduate student]

As a graduate student at the California Institute of Technology (CIT), Linus Pauling tailored a research program that was focused on the properties of matter, with a particular emphasis placed on molecular structure. This interest and the techniques that he learned would shape Pauling’s scientific thinking for the rest of his life.

Pauling’s focus on the theoretical, and his questioning of why processes move forward as they do or why structures are built as they are, was in keeping with contemporary trends in physical chemistry. Pauling enrolled at Caltech with a strong desire to learn more about the discipline of physical chemistry and his early mentor, Caltech chemistry chair A.A. Noyes, encouraged him to build up his background in x-ray crystallography to further enable this pursuit.

When Pauling began classes in September 1922, he also began his research in x-ray crystallography under the direction of his major professor, Roscoe Gilkey Dickinson.  Not much older than Pauling and a recently minted PhD himself, Dickinson would soon become Pauling’s friend. Within weeks, Pauling began receiving invitations for dinners at the Dickinson house and was soon spending the odd weekend on camping trips with Dickinson and his wife.  After Ava Helen and Linus were married, she too joined in these social gatherings.

Dickinson and Pauling worked closely together for most of Pauling’s first year of grad school, but once Pauling had mastered the techniques necessary to prepare his own research, he mostly moved without Dickinson’s direct supervision. In a 1977 interview, Pauling recalled that Dickinson “was remarkably clear-headed, logical, and thorough” while working in the lab.  And as for the research,

Fortunately the field of x-ray diffraction was in an excellent state in that the procedures were rather complicated but they were thoroughly logical, [and] consisted of a series of logical tests.

The rigor and the logic that were fundamental to the field both pleased Pauling immensely.  And before long, the prodigious young student had moved beyond the expertise of his mentor and had begun to conduct original research that was outside of Dickinson’s own capability. In fact, Pauling’s acumen in the lab and facility as an x-ray crystallographer advanced so rapidly that, by his own recollection

…after about three years…I was making structure determinations of crystals that the technique was not powerful enough to handle, by guessing what the structure was and then testing it.


X-ray apparatus at Linus Pauling's desk, Gates Laboratory, California Institute of Technology. 1925.

X-ray apparatus at Linus Pauling’s desk, Gates Laboratory, California Institute of Technology. 1925.

But in his earlier days, Pauling still needed some help. During November and December of his first year as a graduate student, Pauling prepared approximately twelve crystals and attempted to analyze them using x-rays, but none of the crystals yielded images sufficient enough to make a structure determination.

At this point, Dickinson stepped in and directed Pauling to the mineral molybdenite (MoS2), in the process showing him how to take an adequate sample, mount it, and analyze it using x-ray crystallography. This assistance in hand, Pauling was able to determine the structure of the crystal and Dickinson returned to his own work, confident in his feeling that Pauling was capable of doing the crystallography himself.

Soon after completing the experiment, Pauling was confronted by a very different type of confusion. With a successful structure determination in hand, he assumed that the next step would be to publish the work. So too did he assume that Dickinson would provide him with more direction, but he found that none was offered.  As such, Pauling wrote up his findings and presented them for review to his major professor.

Not long after, A.A. Noyes summoned Pauling to his office and carefully explained to the young graduate student that he had written up a paper with only his name on it and in the process had failed to acknowledge the crucial help that Dickinson had provided. Chagrined, Pauling revised the paper and listed himself as a second author, behind Dickinson. The experience proved to be an important one for Pauling, who was reminded early on of how easy it can be to minimize or discount the role that colleagues can play in one’s own research.


Molybdenite model, side view.

Molybdenite model, side view.

By the end of April 1923, Dickinson and Pauling had submitted their paper on the structure of molybdenite to the Journal of the American Chemical Society (JACS); it was published in June of that same year.  Together they had found the simplest crystal structure of molybdenite – which contains two molecules in a hexagonal unit – based on Laue and spectral photographs, and using the theory of space groups.  Although he published a piece on the manufacture of cement in Oregon while he was in undergrad at Oregon Agricultural College, the molybdenite paper was Pauling’s first true scientific publication.

Later that year, Pauling arrived at another milestone by publishing his first sole-author paper, one in which he described the structure of magnesium stannide (Mg2Sn) as determined, once again, by using x-rays. The paper was a huge accomplishment for another reason as well: the x-ray processes used by Pauling had never been successfully deployed for the study of an intermetallic compound before.  And even though this was his first single author paper, Pauling still made sure to thank Roscoe Dickinson in his conclusion, taking pains to avoid another scholarly faux pas.  He would continue in this practice throughout his graduate career.


Richard Tolman, 1931.

Richard Tolman, 1931.

“The crystal structure of magnesium stannide,” was one of eight articles that Pauling published during his grad school years – he completed an impressive total of six structures before receiving his doctorate. Having authored these articles, Pauling found himself on the forefront of a shift in physical chemistry: as crystallography advanced, it was becoming increasingly clear that the properties of specific compounds were based on their structures, which could now be described with mounting confidence. Indeed, several of Pauling’s articles included reevaluations of existing structures, with revised explanations as to why the structures in question had not complied with the new data that Pauling collected.

One such article was “The Entropy of Supercooled Liquids at the Absolute Zero,” which Pauling wrote with CIT faculty member Richard C. Tolman.  In their paper, the two authors corrected an earlier claim made by Ermon D. Eastman, a professor of physical chemistry at Berkeley, who had stated that complicated crystals (those with large unit cells) have greater entropy at absolute zero than do simple crystals. Using statistical mechanical techniques, Pauling and Tolman were able to show that, at absolute zero, the entropy of all perfect crystals, even those with large unit cells, also has to be zero.


Detail from 'Atombau und Spektrallinien' containing x-ray diffraction images.

Detail from ‘Atombau und Spektrallinien’ containing x-ray diffraction images.

Pauling had become familiar with Tolman through a different means. During his third term at Caltech, Spring of 1923, Pauling took Tolman’s course in advanced thermodynamics, an experience that boosted his subsequent interest in quantum theory. It was also during this period that he read Arnold Sommerfeld’s Atombau und Spektrallinien (Atomic Structure and Spectral Lines) and began to be exposed to cutting edge research in quantum theory through the numerous physics and chemistry research colloquia hosted by Caltech.

Sommerfeld would become a lasting influence on Pauling’s life and Pauling would eventually study with him in Germany while there on a Guggenheim Fellowship in 1926-27. But well before then, in 1923, Sommerfeld visited CIT to talk about his work with the new quantum theory. As an aid to his lectures, Sommerfeld used crystal models that he brought from Germany, which he hoped would help him to better explain this complicated work. Afterward, Pauling felt emboldened enough to to show Sommerfeld some of the models that he himself had made in the course of his own research; models that turned out to be much better than those constructed by Sommerfeld.

Pauling in Graduate School

Pauling in Pasadena, 1922.

Pauling in Pasadena, 1922.

[Part 1 of 3]

“My ambition to become a factor in the advancement of human knowledge can be realized only if I prepare myself properly for my work.”

-Linus Pauling, letter to A.A. Noyes, January 26, 1922

By all measures a successful chemical engineering undergraduate at Oregon Agricultural College, and wanting very much to continue his education and earn his PhD in chemistry, Linus Pauling wrote to several graduate programs across the country, inquiring in particular about fellowships. Though he had proven himself to be prodigious talent as a student and, already, as a teacher, Pauling’s location in Corvallis didn’t carry a great deal of cache with the country’s elite institutions. And given his family’s shaky financial health, some measure of institutional funding was going to be required if he were to advance in the academy.

Pauling heard back from Harvard first, but was disappointed by their offer, which was for a half-time instructorship. Harvard also suggested that it would take him an estimated five years to complete his degree.  A more promising option was the University of California, Berkeley, an institution that would continue to tempt Pauling in the years to come. But as soon as he received a favorable reply from the California Institute of Technology (CIT), he rescinded all other pending applications, including Berkeley. Pauling had a good feeling about Caltech, and indeed his choice would pay significant dividends for the next four decades.


noyes-sherril-1

Once frustrated with chemistry at Oregon Agricultural College because he found it too easy, in graduate school Pauling was both presented with more challenging questions and received more considered guidance from some of the best scientists of the day.  One such man was Arthur Amos Noyes, the chair of Caltech’s chemistry department who also served as Pauling’s contact throughout his application process.

In their correspondence, Noyes encouraged Pauling to develop his coursework independently during his final quarters at OAC. Doing so would enable the bright but undertrained Pauling to enter CIT with the strongest background the he could muster in physical chemistry.  Noyes’ suggestions included building up a solid understanding of both French and German, and also working through a more rigorous physical chemistry text than the one that Pauling was currently using in his class.

This more appropriate text, An Advanced Course in Chemical Principles, was co-authored by Noyes himself, along with a Caltech colleague, Miles S. Sherrill.  Noyes implored Pauling to move through the book, methodically solving all of its example problems, the end goal being to provide Pauling with a better understanding of the field, and to prepare him to pursue both advanced coursework at CIT as well as his own unique research agenda.

The text itself was not merely descriptive, but also guided students through the problems that it presented by giving them the information necessary to solve them. This approach was unlike that taken by other popular texts at the time, which focused instead on leading students more directly to a solution. Noyes believed that his and Sherrill’s approach would help students to internalize what they were learning and assist them in understanding the processes required to arrive at the correct answer.

noyes-sherril-2

Noyes’ specific suggestion was that Pauling work through the text in conjunction with the OAC physical chemistry class in which he was currently enrolled, beginning at a point in the book that matched where he was at in class.  Instead, Pauling opted to commence with an independent study of the text during the summer after he graduated from OAC and before he enrolled at CIT.  Doing so, he believed, would allow him to work through the problems systematically and would also help to occupy his time while he was working in the field, assisting with road construction and pavement testing for the Oregon Highway Department. Before he reached the Caltech campus during the third week of September 1922, Pauling had worked through the entirety of book, solving many of its problems by lantern light in his tent.

And just as he would continue to do for the rest of his life, Pauling questioned the accuracy of certain answers posed by the authors of the book.  Upon finally arriving in Pasadena that fall, a first order of business for Pauling was to compare his notes with those of Paul Emmett, his childhood friend and OAC classmate who had likewise entered a course of graduate study in chemistry at CIT.


sci1.001.38-lauephotos-900w

While Pauling was still at OAC, Noyes passed along a few more ideas that might help in preparing for the rigors of Caltech. In addition to his own physical chemistry book, Noyes also suggested that Pauling read X-Rays and Crystal Structure, authored by Sir William Henry Bragg and his son William Lawrence Bragg, and likewise advised that Pauling take a mineralogy class at OAC that would cover the fundamentals of x-ray crystallography.

It is interesting to note that, while reading X-Rays and Crystal Structure (once again, put off until the summer of 1922), Pauling wrote to Emmett and told him that he was not learning much from it. The Braggs, of course, eventually became chief scientific competitors of Pauling’s, and the techniques that they described in their book proved fundamental to many of Pauling’s own early discoveries.


A.A. Noyes, ca. 1920s.

A.A. Noyes, ca. 1920s.

As he tried to help Pauling secure funding for the coming school year, Noyes found himself questioning whether or not Pauling had the experience necessary to receive a teaching fellowship. Wanting to insure his study at CIT, Noyes encouraged Pauling to send further information that might help with finding a grant to cover tuition or even a graduate assistantship, which would promise a “somewhat larger payment.” Noyes assured Pauling that he assumed Pauling would eventually be qualified for a teaching fellowship the next year.

In applying to graduate programs, Pauling expressed full confidence in his capacity to succeed as a student in physical chemistry, due to his strong grasp of mathematics, his previous experience teaching quantitative analysis and his work as a teaching assistant in general chemistry.  But he also believed that the environment at Caltech was top-notch and would provide him with the training that he needed to carry out research, even though he had no prior experience in this area.

Noyes ultimately was able to offer Pauling a prized graduate assistantship, confident in his interest in pursuing pure science and a career in university teaching. Pauling would foster a close relationship with Noyes over the years, and it was Noyes who worked hardest to keep Pauling at Caltech after he had completed his PhD, warding off the advances of G.N. Lewis at Berkeley in particular.


Paul Emmett with his mother, ca. 1920s.

Paul Emmett with his mother, ca. 1920s.

Pauling moved in with Paul Emmett and Paul’s mother in September 1922, and stayed with them for his first school year in Pasadena. During this time, Emmett and Pauling shared the same bed, sleeping in shifts. Pauling’s habits were such that he would stay up late studying while Emmett slept, and around 3:00 AM Emmett would get up to go to the lab, at which time Pauling then went to sleep. During this first year in California, Pauling also took Richard Chace Tolman’s class, Introduction to Mathematical Physics, which helped cement Pauling’s desire to become a theoretical physical chemist.

During his sparse free time, Pauling wrote letter after letter to his girlfriend, Ava Helen Miller, who remained in Corvallis to continue work on her Home Economics degree at OAC. Having expressed a desire to marry at least twice before Linus left for California, only to be rebuffed by their families, the two decided in their letters that they would absolutely be wed once Pauling had finished his first year of classes and just prior to his resumption of more construction work during the summer. Their plan came to fruition in Salem, Oregon on June 17, 1923, and Ava Helen moved to Pasadena that fall to accompany her new husband during his second year as a graduate student.