[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.
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.
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.
“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.
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.
Filed under: Facets of Linus Pauling, Nature of the Chemical Bond Tagged: | A.A. Noyes, Arnold Sommerfeld, California Institute of Technology, graduate school, Linus Pauling, Richard Tolman, Roscoe Dickinson, x-ray crystallography