76 Bull. Hist. Chem., VOLUME 28, Number 2 (2003) ERNEST RUTHERFORD, THE “TRUE DISCOVERER” OF RADON James L. Marshall and Virginia R. Marshall, University of North Texas, Denton The proper recognition of the “true (4) Is it possible for a discov- discoverer” of an element is not al- ery to be shared by individu- ways straightforward. The recent als who perform various “por- play Oxygen, for example, skillfully tions” of the work? For ex- demonstrates how claims of ele- ample, element-91 was first ment discoveries may be ambigu- detected by Fajans (8) in 1913 ous (1). To decide who receives the (“brevium”), was later chemi- recognition of discovery, many cally separated and cataloged questions are involved (2-4): correctly in the Periodic Table in 1918 by Soddy and (1) Who gets prior claim, the Cranston (9), and was prepared person who first did the and named as protactinium in work or the person who 1918 by Hahn and Meitner first published? (2) For (10). Some references list example, Scheele recog- these three groups as “co-dis- nized oxygen before coverers” [e.g., Weeks (11)], Priestley, but Priestley while others have limited lists published first (1, 5, 6). [e.g., IUPAC (4)]. (2) What establishes “discov- (5) Is the mere suggestion (ac- ery,” preparation as a com- companied by preliminary pound or preparation in its analysis) that a new material is elemental form? (4) For an element sufficient to attain example, the reactive rare credit for the discovery? earths were “discovered” Figure 1. Friedrich Ernst Dorn (1848-1916), Crawford and Cruikshank per- as their earths; the elemen- Geheimer Regierungs-Rat Professor of formed a crude analysis of tal forms were prepared Friedrichs Universität, Halle (Saale). (Portrait “ponderous spar” (barium car- at the University of Halle; photograph by the decades later (3, 7). bonate) from Strontian and authors). (3) Must an element be “pure” concluded that it must be a before recognition of its discovery is made? “new earth” (12), but the care- (3) Chlorine was “discovered” by Scheele, ful research was done by Charles Hope in even though his preparation must have been Edinburgh (13). IUPAC recognition goes to the air mixed thinly with chlorine (3). latter (4) although various references credit the former (14) or both (15). Bull. Hist. Chem., VOLUME 28, Number 2 (2003) 77 (6) For discoveries since the end of the nineteenth Dorn, “Die von Radioaktiven Substanzen Ausgesandte century, shall an atomic mass determination and Emanation,” published in the insular journal spectral analysis be required before discovery Abhandlungen der Naturforschenden Gesellschaft of an element be accepted? Although these cri- (Halle) (22), could not be procured. We wanted to cor- teria have been unequivocally accepted (4), roborate the popular account that (24): nevertheless for trace elements such as fran- Like all radioactive elements, it [radium] undergoes cium, technetium, or promethium, there may be continuous, spontaneous disintegration into elements exceptions, or at the very least, an understand- of lower atomic weight. M. and Mme. Curie had ing by the scientific world (4) that these experi- noticed that when air comes into contact with radium ments may be delayed until substantial amounts compounds it, too, becomes radioactive. The correct of material can be accumulated. explanation was first given in 1900 by Friedrich Dorn. The discovery of radon presents an interesting case. We traveled to Halle (Saale) and located the journal in In a recent report to the IUPAC (International Union the Deutsche Akademie der Naturforscher Leopoldina, and Pure and Applied Chemistry), it was stated (4): Emil-Abderhalden-Str. 37. The paper began with a ref- Radon was discovered in 1900 by the German chem- erence to Rutherford’s original discovery of the emana- ist Friedrich Ernst Dorn. tion (25) from thorium (22): Similarly, the Handbook of Chemistry and Physics states Rutherford noticed that a sweeping stream of air over (16): thorium or thorium compounds, even after being fil- The element [radon] was discovered in 1900 by tered through cotton, has the property of discharging [Ernst] Dorn, who called it radium emanation. an electroscope. In a second work Rutherford also investigated the ‘secondary activity’ of the ema- Repetitions of the claim in Dorn’s favor can be found nation [the solid material that coats the vessel walls throughout the literature (17), although there are a few that is formed as radon continues along its decay se- isolated suggestions that Ernest quence]. Rutherford said that other Rutherford (18) and even the radioactive substances (such as ura- Curies should at least share the nium) did not exhibit the same prop- credit (19). A difficulty in assign- erties as thorium. I have adopted ing proper credit was recognized the approach of Rutherford and have by Partington (20), who identi- taken a second look at other radioac- tive substances available locally at our fied an erroneous citation by Institute. Hevesy (21). In Hevesy’s paper an incorrect reference was given Dorn’s paper continued with an elabo- to Dorn's original paper (22) rate pastiche covering uranium, tho- where radium was observed to rium, radium (in the form of crude ra- produce an emanation; this incor- dioactive barium), and polonium rect reference was copied into all (crude radioactive bismuth). Dorn subsequent works of reference repeated Rutherford’s procedure, us- until Partington corrected the er- ing an electrometer to detect activity, ror 44 years later (20). In the and found that indeed uranium and meantime, Dorn’s paper appar- polonium did not display the emana- ently was not widely read and its tion phenomenon of thorium, but that exact contents were lost in time. radium did. Dorn further explored the ‘secondary activity,’ just as Rutherford In our current Rediscovery Figure 2. Ernest Rutherford (1871- had. In his study, Dorn examined prin- of the Elements project (23), we 1937), Macdonald Professor of McGill cipally the influence of moisture and have frequently uncovered sur- University, Montreal, Canada, heat on activity. He could not find any collaborated with his colleague Frederick prising information when inves- obvious correlations, except that mois- tigating original sites; and we Soddy to develop their “transformation theory” which led to the Nobel Prize for ture and heat appeared to accentuate were eager to explore the story Rutherford in 1908. (Portrait at the Dept. the activity. He concluded (22): of radon. However, we were frus- of Physics, McGill University; I have not found a simple universally trated that the original article of photograph by the authors). valid relation between the activity and 78 Bull. Hist. Chem., VOLUME 28, Number 2 (2003) the moisture content. ecules of air (32).” Ru- . It appears to me that therford vigorously at- there is a strong depen- tacked the problem, dence between [both] considering explana- the emanation and the tions that included not secondary activity upon only phosphorescence, the amount of moisture. but also deposition of Dorn made no speculation gaseous ions, deposi- regarding the nature of the tion of radioactive par- emanation, except that the ticles, and stray dust phenomenon apparently (31). Eventually he and concerned ‘a physico- his colleague Frederick chemical process.’ Soddy were able to Dorn had stumbled show that not only did onto the isotope of radon the emanation pass un- (Rn-222) (26) that was the scathed through a Figure 3. Physikalisches Institut Building of Friedrichs physical barrier such as easiest to investigate, with Universität. Ernst Dorn conducted his “radium emanation” cotton or water, but its “long” half-life of 3.823 studies on the steps of the basement of this building. days (27). The isotope that (Photograph by the authors). also through chemical emanated from thorium barriers such as P2O5, (Rn-220) (26) observed by Rutherford, with its half-life sulfuric acid, lead chromate, heated magnesium, and of 54.5 seconds (27), was more difficult to study. [Ac- even “platinum heated to incipient fusion (33);” that it tinium was observed by Debierne to have an analogous obeyed Boyle’s Law, could be condensed out, and thus emanation (28), but this isotope, Rn-219 had an even behaved just like a gas (34). By 1903 they could claim shorter half-life of 3.92 second] (27). Although the na- that the emanation must be matter in the gaseous state ture of the emanation was not contemplated by Dorn, it (35). By the next year Mme. Curie herself had been certainly was by Rutherford and the Curies. By 1903 persuaded by Rutherford’s contention that the radioac- Mme. Curie stated, in the first edition of her thesis (29): tive emanation was a gas present in such minute quanti- ties that it could not be detected by ordinary spectro- Mr. Rutherford suggests that radioactive bodies gen- scopic or chemical means (32). erate an emanation or gaseous material which car- ries the radioactivity. In the opinion of M. Curie and As early as 1902 Rutherford and Soddy believed myself, the generation that they were dealing of a gas by radium is a with a new element (36): supposition which is not so far justified. We It will be noticed that the consider the emanation only gases capable of as radioactive energy passing in unchanged stored up in the gas in amount through all the a form hitherto un- reagents employed are known (30). the recently-discovered members of the argon In a private note to Ru- family. therford, Mme. Curie suggested the phenom- [Ramsay and Rutherford enon might be a form of had discovered argon, and phosphorescence (31). Ramsay had discovered This “radioactive en- the inert gases neon, kryp- ergy” was baffling; ton, and xenon during the vague descriptions were previous decade] (37). All offered, for example, this research was done on that they were “centers Figure 4.