Lawrence Brockway, 1907-1979

“Dr. Brockway is the most able, prolific, energetic, and promising young man with whom I have ever been associated.”

– Linus Pauling. Letter to the American Chemical Society, September 27, 1937

Lawrence Olin Brockway, an esteemed physical chemist and one of Linus Pauling’s first graduate students, died forty years ago this month. During his time with Pauling at the California Institute of Technology, and afterwards as a professor at the University of Michigan, Brockway made great scientific strides in the determination of molecular structure using a pioneering technique, gas electron diffraction (GED), which he developed while working as a graduate student and research fellow in Pauling’s laboratory.

Born in Topeka, Kansas on September 23, 1907, Brockway completed his B.S. (1929) and M.S. (1930) in chemistry at the University of Nebraska. From there, he moved on to Caltech where he received his Ph.D. in 1933 and remained as a research fellow until 1937. Brockway left Pasadena to pursue work under a Guggenheim Fellowship. A year later he joined the faculty at the University of Michigan, where he remained for the rest of his prolific career.

During his seven-year stint at Caltech, Brockway spent much of his time working to identify the structure of gas-phase molecules using GED. The ability to determine the molecular structure of gasses by electron diffraction was a brand new field when Brockway arrived in Pauling’s laboratory. Pauling himself had only recently learned of the technique when travelling through Europe and meeting with Herman Mark, an Austrian physicist who had developed an early GED apparatus. Intrigued, Pauling asked Mark’s permission to build a similar instrument at Caltech. Mark expressed no objections to Pauling’s doing so, in part because he had already moved on to new areas of study.

Once returned stateside, Pauling charged Brockway with the complicated task of constructing a local version of Mark’s creation. In later years, Pauling reflected on this piece of Brockway’s legacy, noting that “despite the difficulties involved, he succeeded while still a graduate student,” a triumph that “has been recognized by student and investigators” from all over the world.

A reading of Brockway’s correspondence with Pauling indicates the significant degree to which his years in Pasadena made an impact. While still a research fellow, and before he found out that he had received the Guggenheim – an award that undoubtedly helped raise his profile as an elite chemist – Brockway seemed unsure of his abilities, and even of his own self-worth. In his letters, Brockway expresses a fear of disappointing Pauling after leaving Caltech, and a wariness of being able to follow in Pauling’s footsteps. But Pauling clearly saw Brockway’s true potential and propped him up with multiple notes of support.

Pauling also provided assistance to Brockway in obtaining his faculty position at the University of Michigan. As his time at Caltech neared its end, Brockway was looking for jobs and felt unsure about what direction to take. In what he termed the “Ann Arbor Problem,” Brockway wrestled with the possibility of working at the University of Michigan (which is located in Ann Arbor) versus Ohio State University or the Midgley Foundation. Brockway was initially attracted to Ohio State because of its higher initial salary, but Pauling argued in favor of Michigan as a better fit and offered suggestions on how Brockway might negotiate for more generous compensation.

Pauling also provided a glowing letter of recommendation to the Michigan hiring committee, stating that he did not know “of any man of Dr. Brockway’s age who has made more significant contributions to molecular structure.” Around this same time, Pauling nominated Brockway to serve on the selection committee for the American Chemical Society’s Award in Pure Chemistry, an honor that would be bestowed upon Brockway just a few years later for “his contributions in physical chemistry, particularly in the determination of molecular structure by electron diffraction.”

As one might expect, Brockway’s appreciation for his mentor was clear. In a letter to Pauling letting him know that that he had accepted the Michigan post, Brockway thanked Pauling for giving him his “start in life.” He then continued,

it is difficult and perhaps unnecessary for me to express my feeling, but at least I intend to work good enough that you won’t be ashamed to admit that I was a former student.

To which Pauling replied,

I want to tell you how much I have enjoyed having you in the laboratory during the last seven years. I don’t need to say anything about how profitable your work has been.

As the years progressed and Brockway found his footing, the relationship between the two men changed accordingly. No longer quite so timid, Brockway began to write to Pauling as a peer and, eventually, as a co-author. In addition to collaborating on ten published papers, Pauling and Brockway took the time to verify one another’s work, recommend graduate students (among those supervised by Brockway was Jerome Karle, the 1985 Nobel Chemistry laureate) and weigh in on the value of proposed projects.

But their relationship was also, at times, light. When Ernest B. Rutherford, a prominent chemist, died in 1937, Pauling and Brockway wrote to each other opining on who would succeed Rutherford as the head of the Cavendish Laboratory at the University of Cambridge (both thought E.O. Lawrence would get the position, which went to Lawrence Bragg instead). Brockway, who was then in England on his Guggenheim Fellowship, also commented to Pauling that his new space at Oxford University had so many chemistry relics that he should “take off” his shoes “before entering.” In response, Pauling suggested that he think of his situation as an “implied compliment.” In later years, the two bragged to one another about the number of grandchildren they had.

When Brockway passed away in November 1979 from pancreatic cancer, his death seemed to rattle Pauling. Upon learning the news, Pauling wrote to Brockway’s widow, Hazel, and offered a supreme compliment: “He was the most satisfying of my many graduate students – that is, the one in whose work I took the greatest satisfaction.”

Reflecting on their long relationship, Pauling continued,

I remember with much pleasure the time when he took me, as his guest, to see the [1932] Olympic Games in Los Angeles. I also, of course, remember with still greater pleasure the many years of close collaborations with him, when he came as an eager graduate student and continued as a post-doctoral fellow with me.

The Crystal Structure of Sulvanite

Sulvanite model, side view.

Sulvanite, Cu3VS4 (copper = light grey, vanadium = dark grey, sulfur = yellow)

A cubic crystal system with perfect cleavage.  Each vanadium atom is surrounded by four sulfur atoms at the corners of a regular tetrahedron.  Each sulfur atom is surrounded by three copper atoms at three corners of a nearly regular tetrahedron, and a vanadium atom – in the negative position – at the fourth corner of this tetrahedron.

Sulvanite is a rare copper sulfide generally found in hydrothermal copper deposits containing vanadium as a primary sulfide. Its structure was conclusively determined by Linus Pauling and Ralph Hultgren in 1933, but was first examined by J. Orcel and then by W. F. de Jong in 1928. De Jong, using a mineral sample from Burra in Australia, prepared powder X-ray photographs for his determination. Pauling and Hultgren noticed potential discrepancies in de Jong’s final analysis of the crystal structure and decided to examine the mineral themselves using Laue and oscillation photographs.

Previously, Pauling had utilized Laue and spectral photography for crystal determinations. Laue photography involves the analysis of patterns collected by passing X-rays through a crystal to determine the positions of atoms in the unit cell. Spectral photography incorporates the use of two crystals – one whose structure is known for reference, and the other (unknown) crystal whose structure is being determined. The two crystals are rotated in front of an X-ray beam in a manner such that the reflections from the interaction fall onto a photographic plate. The distances between like planes and the type of repeating unit can then be determined.

Laue photographs taken by Linus Pauling, October 1922.

For their examination of sulvanite, Pauling and Hultgren decided to use oscillation photography, of which Pauling had become aware while on a trip to Europe in 1930. During his stay in Ludwigshafen, the scientist Hermann Mark shared with Pauling this method of electron diffraction, and showed him the apparatus that was used to carry out the technique. Upon his return to Pasadena, Pauling had a new graduate student, Lawrence Brockway, construct the electron-diffraction apparatus that was eventually used to help determine the crystal structure of sulvanite.

Herman Mark.

(Image courtesy of the S. N. Bose Project)

Oscillation photography is a type of X-ray diffraction. It is similar in a way to spectral photography, but instead of using a reference crystal, a single crystal is made and oscillated through a small angle on an axis perpendicular to a beam of monochromatic X-rays or particles.

The discovery of a new sulvanite cache in Utah provided the opportunity for Pauling and Hultgren to carry out their examination. A sample was lent to them and they used it to conduct an extensive evaluation of sulvanite’s atomic arrangement. The two initially hypothesized that the structure would be a superstructure of sphalerite. Instead, they found that each copper atom of sulvanite is surrounded by four sulfur atoms at the corners of a nearly regular tetrahedron, and that four atoms of sulfur form a regular tetrahedron around each atom of vanadium.

Pauling and Hultgren were also very interested to find that each sulfur atom in sulvanite is surrounded by three copper atoms which form three corners of a regular tetrahedron.  The fourth corner however, is not formed by copper but by a single vanadium atom found in the negative position – that is, the vanadium atom rests in a “pocket” created by the three sulfur atoms. This particular relationship was unusual in comparison to similar sulfur-containing covalent crystal structures that had been determined with certainty at that time, and the new discovery was a pleasant surprise for both of the researchers.

In the mid-1960s, Pauling briefly revisited the structure of sulvanite in his Research Notebooks 24 and 25.  Much more on Pauling’s breakthroughs as a structural chemist is available on Linus Pauling and the Nature of the Chemical Bond:  A Documentary History.

The Crystal Structure of Chalcopyrite

Chalcopyrite model, top view.

Chalcopyrite, CuFeS2 (copper = dark silver, iron = orange, sulfur = yellow)

A tetragonal crystal system constructed from sulfur atoms surrounded by two copper atoms and two iron atoms each at the corners of a nearly regular tetrahedron. Each metal atom is surrounded by four sulfur atoms.

In the early 1930s, Pauling was finishing his work with silicate structure determinations, and began to analyze the crystal structures of sulfide minerals. Pauling opened his study of sulfides with a reinvestigation of chalcopyrite, the structure of which had already been published by C. Lalor Burdick and James H. Ellis in 1917.

C. Lalor Burdick received his M.S. degree from the Massachusetts Institute of Technology in 1914 and his Ph.D. from the University of Basel in 1915. He learned how to use an X-ray ionization spectrometer in the Braggs’ London laboratory, and built one at MIT before moving to Pasadena in 1916. James H. Ellis, a research professor of physical chemistry at Caltech, worked with Burdick and his new spectrometer to carry out the initial chalcopyrite investigation.

Chalcopyrite model, side view.

Chalcopyrite, or copper iron sulfide, looks very similar to and is easily confused with Pyrite (iron sulfide). Chalcopyrite is also just one of the many minerals to have been labeled “fool’s gold,” because of its shiny bright golden color. (In comparison, real gold is more malleable and is buttery yellow in color.) The major use for chalcopyrite is as an ore for copper, though the yield of copper from chalcopyrite compared to that of other copper-yielding ores is relatively low.

Pauling and Brockway’s primary reason for studying chalcopyrite was their mutual interest in inter-atomic distances. The duo was also very critical of the initial investigation of the substance – both the method and the results – by Burdick and Ellis. After an examination of their own oscillation and Laue photographs, Pauling and Brockway concluded that the structure of chalcopyrite is twice as large as was theorized by the Burdick and Ellis examination, and that the distribution of copper and iron atoms is completely different than what was initially reported.

Lawrence Brockway, 1937.

Pauling first began working with Brockway in 1930, when he instructed the new graduate student to construct an electron-diffraction apparatus. Pauling had learned about the electron-diffraction technique from Herman Mark in Ludwigshafen during his trip to Europe in the spring and summer of the same year. Pauling was extremely interested in the possibilities of the technique, and acquired permission from Mark to build and operate the device in Pasadena. After helping Pauling build the electron-diffraction apparatus and publish the analysis of the crystal structure of chalcopyrite, Brockway later went on to set up his own laboratory in Michigan.

Pauling references his and Brockway’s work on chalcopyrite in his Research Notebook 8.  Those interested in the larger story of Pauling’s achievements in structural chemistry are referred to the website Linus Pauling and the Nature of the Chemical Bond: A Documentary History.