The Sceptical Chymist | Urey, deuterium, and the Rosenbergs

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Posted on behalf of Dan O’Leary. It’s much longer than our usual blog entries, but it is more than worth it. Grab a coffee (or other favourite beverage), sit back, and enjoy — Stuart

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This month’s In Your Element essay is entitled ‘The deeds to deuterium’ (subscription req’d). I appreciate Stuart letting me take on the essay, for which he provided such a clever title, and for the opportunity to write this blog post. Many thanks also to Sarah Roh, a Pomona College student who previously fused anime and isotope effects, for the artwork featured in this project.

Now here’s a question: why did the hydrogen isotopes garner names when all others remained numerical? Harold Urey, George Murphy, and Ferdinand Brickwedde published spectroscopic evidence for the mass-2 form of hydrogen in 1932 (ref. 1) and suggested the name deuterium shortly thereafter (ref. 2). They thought a unique name was justified because it would alleviate any formulaic confusion caused by the use of ‘hydrogen two.’ In Cathedrals of Science, Patrick Coffey writes (ref. 3) that Frederick Soddy, who coined the term ‘isotope’ after a suggestion by Margaret Todd, wasn’t even sure that the heavy form of hydrogen met his definition of an isotope. In his view, isotopes had different atomic mass but identical chemical properties. The large mass difference between 1H and 2H gave deuterated substances unique properties relative to their lighter counterparts, thus making their discovery more elemental. Writing in the 1933 pages of Nature (ref. 4), Ernest Rutherford surmised “…the question of a suitable nomenclature is in this case of such general importance to scientific men that it deserves very careful consideration.”

When I started researching the IYE essay, however, I wasn’t much interested in isotopic appellations. I thought that part of the story was old news. At the outset of my research, I was much more intrigued by Harold Urey the person.

While I didn’t know much about him, I had read somewhere that Urey was involved in the Rosenberg espionage case in the 1950s. Chronicling his involvement in that hysteria-induced American tragedy would make for an intriguing essay, I thought, something along the lines of: deuterium & Nobel provide scientist with platform for Cold War political activism. But letters in his archive caused me to change my plan and I instead wrote a piece describing how Urey’s heavy-handed former doctoral advisor played a key role in his decision to name the mass-2 isotope ‘deuterium’. But before we get to that part of the story, indulge me with the activism angle for several more paragraphs.

Urey argued publicly that it made no sense to execute Julius and Ethel Rosenberg, but that was their fate after a brief trial in 1951. The evidence against them and the quality of the atomic secrets they supposedly passed, as known by the public at the time, were disputable. Declassified documents and other information, some made available as recently as 2008, suggests that only Julius was directly involved in delivering classified atomic information to the Soviets. Other conspirators were given prison sentences, but the government’s case against the Rosenbergs came down to a game of chicken in which Ethel could have avoided the electric chair if she testified against her husband. She remained silent, and they were executed within minutes of each other at Sing Sing prison on June 19, 1953.

Urey’s papers (ref. 5) are archived at the University of California at San Diego. An extensive set of documents provide a roadmap of his efforts to galvanize support within the scientific community and speak with the public about the case. The scientist in Urey left an imprint on the record, such as his use of charts to diagram the real and inferred flow of information between the Rosenbergs and Soviet General Consul Anatoli Yakovlev, Klaus Fuchs, Harry Gold, Morton Sobell, and David Greenglass (Ethel Rosenberg’s brother who testified against them at trial and served a 10 year prison term).

Urey even wrote personal appeals to Presidents Truman and Eisenhower to reverse the execution order. When these efforts failed, Urey largely withdrew from the cause and from communists eager to ally themselves with him. Particularly telling is a handwritten draft of a 12 February 1953 telegram (ref. 6) sent to an organizer hoping to use a pre-recorded Urey speech at a Los Angeles rally protesting newly-elected President Eisenhower’s decision not to commute the death sentences: “I believe meeting should be held and do not wish my recording to be used. Case will now be used by communists to embarrass the U.S. (emphasis his) and I do not wish to help them. . (text strikeouts his) Harold C. Urey”

In an unpublished 1970 autobiography (ref. 7), Urey wrote: “I doubted seriously if justice had been done. My own concern was not a matter of communism or capitalism of my country or some other country at all, it was only a question as to whether justice had been done by the courts of the United States. That was my interest entirely. I was not a friend of the Rosenbergs or Sobell.”

Although there is evidence in the archive suggesting Urey regretted his involvement in the Rosenberg case, his spirits were lifted by a letter dated 17 June 1953, which read: “Dear Urey, your intervention in the Rosenberg case has been one my most heartening experiences in the human sphere. With kind greetings and my highest respect, yours, A. Einstein.” Urey responded (ref. 8) on 25 June, saying in part “But your support of my position and your letter have been most heartening to me, for very few scientific people have troubled to consider the case at all.”

So the IYE essay was almost about the deuterium-enabled Urey and his frustrating quest for justice in the Rosenberg case. But the essay could have been about other heavy topics, such as H-bombs and their deuterated fusion cores, prepared by a post-war team led by Ferdinand Brickwedde. Of these devices, Urey — himself a key player in the Manhattan Project — wrote (ref. 7): “I once thought deuterium would be as useful as to be produced in small amounts to be used for trace techniques in chemistry, and turns out to be an important part in the hydrogen bomb. I am sorry that that it is part of such a destructive instrument as that, and I would be awfully glad if it were not.”

I was taking a break from Rosenberg-related material at the UCSD library when I reached for a folder containing letters between Urey and Brickwedde, his collaborator and supplier of hydrogen enriched in the heavy isotope. This correspondence, dated May and June of 1933, surprised me. It revealed that Urey and Brickwedde were all over the place in terms of what to name the ‘the hydrogen.’ Early candidates, beyond ‘iso-hydrogen’, were property-based: Pycnydrogen or pycnogen [pycnos = thick or dense (Greek)], barydrogen, barogen, or barhydrogen [baro/bary/bar = weight, heavy (Greek)]. Urey was favoring pycnogen in the first of these letters (ref. 9).

Brickwedde then suggested a numbers-based system inspired by a colleague: diplogen or diplohydrogen for the heavy form while hydrogen would become haplogen or haplohydrogen [diplous = double (Greek), haplous = single (Greek)]. He anticipated that Urey wouldn’t like those names and wrote “I know you won’t like them when you first hear them but after a few days they don’t sound so bad.”

Urey vs. Lewis. Credit: Seo (Sarah) Roh

Where was the name deuterium in these exchanges? Well, if Urey has been considered the naming protagonist then it is only fitting this drama has a deuteragonist. The character of secondary importance was none other than Urey’s doctoral advisor, G.N. Lewis. He was also working on the isotope and had lobbied Urey to name the isotope dygen. Then he changed his mind and suggested the name deuton for the mass-2 nucleus. This suggestion, coupled with Brickwedde’s numerical proposition, seems to have inspired Urey to consider the name deutium and then, after consulting Greek experts at Columbia University, deuterium. These names worked nicely, because they could be bookended by names like protium or proterium and tritium or triterium. Urey and his crew ultimately decided to go with protium, deuterium, and tritium and published these in the Journal of Chemical Physics on 1 July 1933 (ref. 2).

One of my favorite quotes from the exchange is Urey’s prediction (ref. 9) to Brickwedde on 6 June 1933: “As to tritium, it will probably never be needed, for we have proven here that it does not exist to more than one part in five billion of protium, and therefore, I believe it does not exist at all.”

A year or so later, tritium’s existence was discovered in Ernest Rutherford’s deuterated collision experiments. As noted earlier, the Right Honourable Lord Rutherford — who named the proton — also had strong nomenclature opinions and published his preferences in Nature on 23 December 1933: diplon for the nucleus and diplogen for heavy hydrogen (ref. 4). Urey’s names persisted, although it took some time for the matter to settle down. News of the disagreement went as viral as one could imagine in the 1930s, with Time magazine even reporting on the controversy (ref. 10).

A very detailed account of the interactions between Lewis, Urey, and Rutherford was written by physicist Roger Stuewer in 1986 (ref. 11). In addition to the diplon/diplogen possibility, Rutherford had also considered deuteron/deuterogen and dion/diogen as names for the nucleus and the heavy isotope and was discussing names with Lewis before he did with Urey. Stuewer also chronicles a part of the story that was new to me, that Urey apparently lost his temper at a meeting of the American Physical Society on 19 June 1933, where he introduced his soon-to-be published names and received a negative response.

Missing from accounts such as Steuwer’s is what was happening within the Urey camp. It is now clear that it was Lewis who suggested a name based upon the Greek deuteros, and Urey grudgingly says as much in a letter to Brickwedde. Of course, you’ll need to read the IYE essay to see his exact language. The letters in the UCSD archive left me with the impression that some historical accounts need correcting. Coffey’s Cathedrals, for example, accurately portrays Lewis as trying to influence Urey but is incorrect in asserting that Urey “had already decided the isotope’s name.” Then again, Coffey studied correspondence from the Lewis archive at UC Berkeley, and these letters reflect only what Urey wanted Lewis to hear. The Urey–Brickwedde exchange puts the matter in a new light. One can imagine Urey maintaining a poker face in communications with his overstepping former advisor. Stuewer’s article affirms this view by reproducing tracts from the Urey–Lewis correspondence, and in these Urey comes across both polite and blunt.

On 18 May 1933: “As to the name deuton for the hydrogen two nucleus, it is a very suggestive one. My own personal reaction to it, however, is that it is unnecessary [to provide a name for something not a fundamental particle].” And later in the same letter, Urey wrote (ref. 11): “If the California group will not give us a little time and be a little patient, they will force us into publishing a name for this isotope which may not be satisfactory for some reason or another. I would suggest, therefore that the California group use the name hydrogen two provisionally and allow the discoverers of this element to name it when they see fit.”

It’s interesting that the Urey archive at UCSD, as extensive as it is, does not catalogue any Urey–Lewis or Urey–Rutherford correspondence. In their absence, the record is defined by the drafts sent or received by Lewis and Rutherford (ref. 11). Steuwer’s excerpts project Urey as diplomatic once he’s made up his mind to publish his names. After writing a measured letter outlining protium/deuterium/tritium to Lewis on 29 May 1933 he closes with a request to hear Lewis’ opinion of them before publication. Lewis, who by Steuwer’s account had started the naming rush in the first place, answered by saying he felt Urey’s names were “very good” although he would “slightly prefer ‘protium’ and ‘deutium,’ or even ‘protum’ and ‘deutum’… .” But he also realized that he had caused a ruckus and closed with “kindest regards, and apologies for the deuton’… .”To a 20 June Rutherford letter outlining the diplon/diplogen, deuteron/deuterogen , and dion/diogen possibilities, Urey responded on 6 July outlining the names he was publishing and apologized for not reaching out to scientists in Europe regarding the names, citing the rush caused by the Berkeley people. He added that it was “interesting that so many people have thought of very much the same names.”

But there is another snippet (ref. 11) from that 6 July letter that is perhaps most revealing about how Urey felt about the entire nomenclature quagmire. “Protium” and “deuterium,” Urey wrote to Rutherford, were “as good a compromise as we could get.”

In his autobiography written some forty years later, Urey wrote (ref. 7) of Lewis’ presence in the hunt for deuterium: “I have always felt badly about Professor Lewis’ attitude in this matter. I have tried in the years since then, whenever my former students make an important discovery, to help them as much as possible rather than to try to take the subject matter away from them.” In a 1972 children’s book about Urey (ref. 12), written from the autobiography, these sentiments were rephrased as “Urey felt a little hurt at this. In future years, whenever one of his students made an important discovery, he tried to help the student as much as possible, rather than take the subject away from them.”

Urey’s philosophy of support for his students — forged in the early deuterium years — is probably best exemplified by one of his other significant works, the single-authored Science paper by then-graduate student Stanley Miller, whose Miller–Urey experiment opened the field of prebiotic chemistry. Urey has been quoted (ref. 13) as saying “There are a lot of people around who are smarter than me. But I pick only the most important problems.” Indeed, these contributions included a method to determine geological temperatures, the development of the field of cosmochemistry, and providing a leading role in lunar science and exploration. Any one of these accomplishments would have made a scientist’s career. Readers who want to learn more about Harold C. Urey, a remarkable chemist, are encouraged to read his biographical memoir at the US National Academy of Sciences.

DAN O’LEARY is in the Chemistry Department at Pomona College in Claremont, California 91711, USA.


1. Urey, H. C., Brickwedde, F. G. & Murphy, G. M. Phys. Rev. 39, 164–165 (1932). [LINK]
2. Urey, H. C., Murphy, G. M. & Brickwedde, F. G. J. Chem. Phys. 1, 512–513 (1933). [LINK]
3. Coffey, P. Cathedrals of Science: the Personalities and Rivalries That Made Modern Chemistry. Oxford University Press, 2008.
4. Rutherford, Rt Hon. Lord Nature 132, 955–956 (1933). [LINK]
5. Harold Clayton Urey Papers, Mandeville Special Collections Library, University of California, San Diego. An online catalog of the collection can be found here.
6. Rosenberg file, Harold Clayton Urey Papers, Mandeville Special Collections Library, University of California, San Diego.
7. Unpublished autobiography dated 1970, Harold Clayton Urey Papers, Mandeville Special Collections Library, University of California, San Diego.
8. Urey–Einstein correspondence, by date, Harold Clayton Urey Papers, Mandeville Special Collections Library, University of California, San Diego.
9. Urey–Brickwedde correspondence, by date, Harold Clayton Urey Papers, Mandeville Special Collections Library, University of California, San Diego.
10. Science: Deuterium v. Diplogen
11. Stuewer, R. H. Am. J. Phys. 54, 206–218 (1986). [LINK]
12. Silverstein, A., & Silverstein, V. Great Men of Science: Harold Urey, the Man Who Explored From Earth to Moon. John Day Company, 1971.
13. Harold Urey, Scientist, Dies at 87; War foe’s work led to H-bomb

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