Rediscovery of the Elements Soddy and

III~1

Figure 2. This plaque is mounted at 11 University Gardens. The building, now known as the George James L. Marshall, Beta Eta /971, and Service House, presently houses the Humanities Virginia R. Marshall, Beta Eta 2003, Advanced Technology and Information Institute (IIATI!) of the Univcrsity ofGlasgow. Department of Chemistry University of - 9 North Texas, Denton,TX 76203-5070, tion of a known element to another known [email protected] Figure 1. The home of Sir George and Lady Beilby, element; this research was the basis of the the parents of 's wife, Winifred, at future understanding of the alpha particle.' A Dinner Party in , . During 11 University Gardens, Glasgow, Scotland. The In 1904, Soddy became Professor at the a social gathering in 1913 at the home of his in- home is of Victorian architecture and was built in , where he formulated laws, Frederick Soddy (1877-1956) (Figure 1) 1884. Sir George was an industrial chemist who the concept of isotopes. After 10 years at was musing what to call a new concept. For a furnished 50 kilograms of uranyl nitrate to Soddy Glasgow, Soddy moved to the University of decade a plethora of radioelements, each with a for his experiments. This home served as a popular Aberdeen (1914-1919), where he co-discovered unique half-life, had been discovered at various meeting place for politics, science, business, and the element protactinium ("eka-tantalum"). universities throughout Europe and North leisure. In the drawing-room of this home, the World War I had a distressing effect on Soddy; America, and there was no room in the Periodic word ""was coined by Soddy at the the death of Henry Moseley"' elicited the fol- Table to accommodate them. To solve this prob- suggestion of Dr. Margaret Todd. lowing from Soddy,' "When Moseley was killed lem, Soddy was proposing that radioelements at Gallipoli I felt enraged. Sometimes I think with different half-lives but with the same at that university, who was just beginning to that something snapped in my brain.... I felt chemical properties should be confined in one investigate the strange emanation from thori- that governments and politicians, or man in box in the Table. The scholarly Dr. Margaret um.; For the next two years the two colleagues general, was not yet fitted to use science." Todd (1859-1918), an M.D. and novelist friend established the elemental nature of thoron Soddy moved in 1919 to Oxford University, of his wife, Winifred, suggested' such elements (radon-220), developed the understanding of where with a new mission he tried to establish be denoted by the Greek words "same place" radioactive half-lives, and discovered the nat- economic policy based on scientific laws. He ("iso-topos") (Figure 2). Soddy shortly ural transmutation of the elements.' It was retired in 1936, after a frustrating period in his announced his idea of "isotopes" (December 4, actually Soddy the chemist, well versed in the life, with a "sense of failure.... in the field of 1913) in the prestigious journal Nature. history of alchemy, who first understood the economics." He was at Oxford when he accept- significance of transmutation, before Ruther- ed the Nobel Prize in 1921 for his research in The Life of Frederick Soddy. A native of ford the physicist.' radio-elements and isotopy at Glasgow, and for Eastbourne in East Sussex, 85 km south of In 1903, Soddy returned to England and teaching us that could have "identical London, Frederick Soddy was trained at the joined the research group of William Ramsay outsides but different insides."' University of Aberystwyth (Wales) and at (1852-1916; the discoverer of the noble gases) Oxford University, graduating in 1898. After at University College, London, to study the The Discovery of the Radioelements (see three years as researcher at Oxford, Soddy decay by-products of radium. In Ramsay's lab- Figure 3). Radioactivity was discovered by accepted the position of Demonstrator at oratory, Soddy established that helium was Antoine Henri Becquerel when he observed McGill University, Montreal, Canada. After a produced during the decay of radium, thus uranium emitted invisible rays that fogged pho- year he joined the group of Ernest Rutherford furnishing the first evidence of the transmuta- tographic plates wrapped with paper or metal

68 THE HEXAGON/WINTER 2010 Figure 3 (LEFT). The decay sequences of the natural radioelements (Fajansand 238 U-238 = Klaproth's "uranium" U1 Soddy "Displacement Laws"), patterned after Soddy's original list" and 236 graph."' Atoms decay by emitting an a-particle (moving left two units and U-235 = AcU ("actinourani ") cu down four units) or a /3-particle (moving right one unit). The list of natural 234 UX1 / UX2 (Fajans' "brevium") / U2 radioelements includes some 40 members and organized into three main series: 232 Th-232 = Berzelius' "thorium" T U-238, originally identified as U1 ("radium series,"the black plot), U-235, UY / Hahn's "protactiniu ' originally identified as "actinouranium"("actiniumseries,"the red plot), and 230 ("ionium") Th-232, originally identified as merely "thorium"("thorium series,"the blue 228 MsTh1 / MsTh2 / RdTh plot). The atomic number and mass for each radioelement can be determined Debierne's "actiniu RdAc from the respective abscissa and ordinate. For each radioelement the original 226 Curie's "radium" name is given (in addition to the customary elemental abbreviations, Rd = 224 AcK (Perey's radio, Ms = meso; for example RdAc = radioactinium). (For a more complete "francium" AcX E 222 Rn ("radon") description including half-lives of the radioelements, see reference 11). U- 220 T ("thoron") E An("actinon") 0 218 216 hA 0iPlacedi S.Unier AcA 4 214 RaB / RaC / RaC' SlSOTOPE PLAQ lnivrs 212 ThB / ThC / ThC' CAve c/AcC y 210 RaD / RaE / RaF (Curie's "polonium") ~ University of Glasgow ORD KELVIN'S HOUSE 208 '/ ThD ThD = stable Pb-208 AcD = stable Pb-207 cC" / AcD May Street River Keln 206 RaG RaG = stable Pb 206 [OLD CHEMISTRY B 204 Dumjbarton Road TI Pb Bi Po At Rn Fr Ra Ac Th Pa U 81 82 83 84 85 86 87 88 89 90 91 92 200 m Atomic number MUSEUM STORES

foil.' His discovery prompted the search for Ernest Rutherford attempted to reproduce Figure 4 (ABOVE). Map of Glasgow. Sites of new radioactive elements by Marie Curie, who Crookes' work, but was perplexed by his obser- interest in the University of Glasgow area: canvassed all known elements and determined vation that in his hands purified uranium was Site where Soddy proposed the concept of"isotope," that of these only uranium and thorium exhib- still radioactive. By following Crookes'procedure 11 University Gardens - N55 52.37 W04 17.45. ited activity." After noticing that ores of urani- exactly, Rutherford realized the discrepancy Joseph Black Building (modern chemistry building), um were much more radioactive than expected, was due to Crookes' using the older Becquerel University of Glasgow - N55 52.32 W04 17.57 she launched her classic research with her hus- method of radioactivity detection (fogging of Lord Kelvin's house, University of Glasgow - N55 band, Pierre Curie, to discover polonium and wrapped photograph plates) instead of the 52.28 W04" 17.43. radium in 1898, and her colleague Andr6 "electric method" which utilized an ionization Old Chemistry Building, Main Building, Gilbert Debierne discovered actinium in 1899.4 chamber pioneered by Pierre Curie' Scott Building (now geography), where Soddy The discovery of radioactive elements con- (Rutherford used the Dolezalek electrometer,7 a performed his work on isotopes - N55 52.24 refinement of this method 4'). On the basis of tinued, which became known as the "radioele- W040 17.25. ments." In 1900, William Crookes (1832-1919) his work at Cambridge where he defined a- Museum Stores, site of Soddy's equipment and - the discoverer of thallium-made an aston- and 13-rays, Rutherford realized that pure urani- models, Thurso Street - N55 52.17 W04* 17.84. ishing observation: he found that purified ura- um (and its compounds) was an a-emitter nium nitrate (prepared either by precipitation (whose rays were stopped by paper or foil) and with ammonium carbonate or by extraction that UX1 was a 1-emitter (whose rays passed The thorium and uranium series of with ether) exhibited no radioactivity at all!' through Becquerel's and Crookes' paper wrap- radioelements (see Figure 3). Rutherford and (This puzzling observation was shortly pings). Rutherford designed an ionization Soddy turned to thorium and found it exhibit- explained by Rutherford; vide infra). Instead, chamber in which he could readily distinguish ed similar behavior. Reacting thorium nitrate radioactivity resided in the separated residue, a-rays and 1-rays by alternatively using shields with ammonia (to precipitate thorium hydrox- which Crookes named uranium X, or Ur-X of 0.1 mm aluminum foil (impervious to a-rays) ide) gave a filtrate, which when concentrated (later named UX1). If Crookes had followed up or 5 mm aluminum foil (impervious to P-rays).' gave a very active residue they called thorium- this work, he would have been the discoverer of (The third type of emission, y-emission was X (ThX). Careful study showed ThX in turn the natural transmutation of elements, because recently discovered by Paul Villard in 1900, transmuted into emanation (thoron), which UX1 was actually thorium-234, produced by the could be inferred by its stoppage using by 50 cm itself changed to an entire sequence of new a-decay of uranium-238. of aluminum.) After a period of time, an undis- radioactive products!' After the Christmas hol- turbed sample of purified uranium nitrate pro- idays of 1901, Rutherford and Soddy returned The explanation of UX1 by Rutherford. Now duced a fresh supply of UX1.' Rutherford and to study the original purified sample of thori- active in his research at McGill University Soddy determined the half-life of UX1 to be 22 um, which was found to be replenished with (where he discovered the element radon)' days. the -emitter ThX. Soon Rutherford and his

WINTER 2010/THE HEXAGON 69 from chemically similar barium (solved by the Curies during their discovery of radium") had been"merely formidable," the problem of sepa- dk4 rating elements of a certain grouping appeared to be practically impossible, suggesting group- ings of virtually indistinguishable chemical behavior.

The Fajans and Soddy Displacement Laws. Meanwhile, the roadmap (Figure 3) by which these radioelements were being trans- formed into one another was becoming understood. One could trace the zig-zag route of an as it followed its predestined path from its progenitor to stable lead by alterna- tively shedding a- and -particles. In early 1913, two defining articles appeared almost simultaneously by Fajans and Soddy," which stated that all a-decays resulted in movement two units to the left and all p- decays in movement one unit to the right (the I igur' At the Unmversity of Glasgow, o. Soddy so-called Fajans and Soddy "Displacement performed his work in the southeast corner of the Figm 5. This plaque dcdicatcd to Soddy is Laws"). Whereas Fajans' approach was more 1 Main Building. His laboratory now houses the theoretical, Soddy's conclusions were based mounted in the Joseph Black Building, the main Geography Department. When he abandoned this on extensive chemical analysis, with a heavy chemistry building of the University of Glasgow. working space, it had to be thoroughly scrubbed dependence upon final analysis of his student and reconstructed because of the intense radioac- Alexander Fleck (1889-1968) at Glasgow who tivity; even the doorknobs had to be replaced. colleague Soddy had carefully outlined a had proven the chemical identicalness of a Nearby is the historic home of William Thomson sequence of transmutations:' number of 13-emitters." (Lord Kelvin, 1824-1907, named after the river Th (half-life =10yr) -+ ThX (4 days) + In his 1913 articles,"' Fajans organized the that flows nearby). Emanation (54 sec) -+ThA (11 hr) -+ radioelements in the , lumping ThB (1 hr) similar elements in a "pleiad,"''2 a name con- Did other radioactive elements exhibit a cas- inating from uranium). These three series noting a tight cluster of chemical properties, cade of radioelements? Rutherford and Soddy included three different emanations of inert alluding to the Pleiades, the well known star turned to radium and found the following gases (radon, thoron, and actinon; all isotopes cluster in the constellation Taurus. Fajans then sequence:2 of radon), as well as later intermediate mem- boldly proposed that there should be an ele- bers named ionium (Th-230), mesothoriuml Ra (1500 yr) -+ Emanation (4 days) -- ment "UX2" just to the right of Crookes'UX1 - and -2 (Ra-228 and Ac-228), radiothorium (Th- RaA (3 min) -+.- RaB (28 min) -+ and several months later he and his student RaC (21 min) -- RaD (40 yr) + 228), eka-tantalum (Pa-231), etc., and all end- Oswald Helmuth Gohring (1889-?) electroplat- RaE (6 days) -- RaF (143 days) ing with inert lead.' Because the quantities ed out the element whose electrochemical involved were generally unweighable traces, More researchers join the hunt. The research the major way to characterize and identify these of Rutherford and Soddy sparked the hunt and elements was by means of their half-lives. discovery of more radioelements by many sci- It was unclear just how to organize this mot- entists during the first decade of the 20th cen- ley collection, whose half-lives and random tury (Figure 3). These researchers included behavior of a- or 13-emission exhibited no Herbert Newby McCoy (1870-1945; University apparent pattern. A major additional problem of Chicago), Alexander Smith Russell was the impossibility of fitting these new"ele- (1888-1972; Oxford University), Bertram ments" into the Periodic Table - the situation Borden Boltwood (1870-1927; Yale University), was bad enough with the rare earths, a dozen Otto Hahn and Lise Meiter (1879-1968 and unusual elements that seemed to form an inde- 1878-1968, respectively; Kaiser Willhelm pendent series (Bohr's atom with the f-subshell Institute, Dahlem-Berlin), Kasimir Fajans was yet to be formulated). So how could one (1887-1975; Karlsruhe University), and accommodate three times that many rogue Frederick Soddy (and colleagues) now at the radioelements? University of Glasgow (Figures 4-7).' 'The list figure 7. Dr Jot' Conall/, our host at the of radioelements ballooned during the first two The clue of chemical similarity. The key to University of Glasgow, looks upon one of Soddy's decades of the 20th century, reaching a total of organization of the radioelements was found machines in the Historic Museum ("Museum almost 40 members, perplexing the scientific through wet laboratory chemistry. As chemists Stores"). This is the "Statis machine,"which has a world with a"radium series" (RaA through RaG, worked their analytical separations, they column with a series of chambers connected by originating from uranium), a "thorium series" noticed that there was difficulty in separating differently sized orifices; as water flows through (ThA through ThD, originating from thorium), some of the members of the radioelements. the column, one can visualize the steady-state dis- and an actinium series (AcA through AcD, orig- Whereas the challenge of separating radium tribution of elements in a radioactive ore sample.

70 THE HEXAGON/WINTER 2010 Figure 8. This is the man building of the University of Karlsruhe, 12 Kaisserstrascse; the original building of Universitat Fridericiana Figur 9. Otto H ahn Building ( Thielallee 63 - N52 26.85 E13 17.11), of th prsnt Inn Lniursitat of 0 (N49 00.56 E08 24.72), where Lothar Meyer Dahlem, Germany, previously the Kaiser Wilhelm Institute, where Otto Hahn and Lise Meitner discovered refined his Periodic Table. Behind lay the Chemical protactinium-231." As has been done with so many buildings in Berlin, this edifice was extensively dam- Institute (Kollegium) where Kasimir Fajans dis- aged in World War II but was reconstructed to closely replicate the original architecture. The building is covered "brevium""" (Pa-234m), the first isotope of now used for biochemical studies. Much important history has occurred here, including the discovery of element-91 in 1913 (now Kollegiengebdude der nuclear fission (announced by the plaque attached to the turret, seen here to the right). On the second 6tage 0 Ehrenhof Englerstrasse 11 - N49 00.61 E08 (third floor) is the Lise Meitner Horsaal (lecture hall). 24.72). Nearby is the Stdndehaus, where in 1860 the internationalChemical Congress was held, was resolved: different radioelements could be "smoothed over the rough edges of isotopes"' which inspired the conception of Dimitri simply lumped into preexisting boxes. The term when his method of X-ray spectroscopy was Mendeleev's and Lothar Meyer's Periodic Tables.4 " Soddy coined-isotope-was fully intended to expanded by Karl Manne Siegbahn (1886-1978, convey the meaning that two species resided at Nobel Laureate in physics in 1924) to include potential placed it in this vacant space (Figure the identical location in the Periodic Table, even the atomic number of uranium. Siegbahn 8)." This element could be detected because of if they had different atomic masses and half- showed that even though uranium was com- its high activity, with a short half-life of 1.17 lives. Soddy was proposing an astonishing con- posed of several isotopes (Note 3), nevertheless minutes, even though ponderable quantities cept: A specific element, which historically was the element appeared to exhibit a clearly could not be collected. Because"it was the only once considered not fully characterized without defined atomic number." The method of mass element in the 5th group of the last row,"he felt a specific atomic mass, now could be variable in spectrometry, developed by Francis William justified in giving it a name, "brevium"" (now its mass! Aston (1877-1945, Nobel Laureate in chemistry known to be protactinium-234m) (Note 1). in 1922), soon allowed the direct observation of Fajans in his studies was using an electro- Corroboration of the predicted different isotopes and he wrote the definitive article on plating technique whereby he could plate out masses for isotopes. It remained to prove that the isotopes of uranium, lead, and other traces of specific radioelements and could char- chemically identical elements did in fact have radioactive elements." Even Fajans, who had acterize each by determining its half-life. By different masses. According to both Fajans and long viewed each radioelement as a "new ele- contrast, Soddy was using wet laboratory pro- Soddy, lead (Pb) from different decay ment," by 1923 had abandoned his concept of cedures and was impressed with the apparent sequences should have different atomic mass- the scattered pleiads and had accepted the view impossibility of chemical separation of various es. Fajans took the initiative and sent his stu- that isotopes should be tightly boxed in indi- radioelements. Soddy considered the elements dent Max Ernest Lembert (1891-1925) to the vidual cubicles of the Periodic Table." of a grouping not "a scattered pleiade," but as laboratory of Theodore William Richards chemically identical. While Fajans had grouped (1868-1928) at Harvard University, the recog- Epilogue-the construction of the nucleus. the radioelements loosely in a table,2 ' Soddy nized expert in atomic mass determinations. What was the genesis of the different isotopes drew a precise two-axis graph." Soddy under- Richards and Lembert repeated the atomic of an element? The prevalent view during the stood the implications of chemical indistin- mass determination for ordinary lead and first quarter of the twentieth century was that guishability-for example, ionium (Th-230, the reproduced the published value of 207.15. Lead the nucleus was composed of protons and a precursor to radium in the uranium sequence) from uranium samples from around the world lesser number of electrons that partially neu- was identical to native thorium (Th-232) (Note gave a value ranging from 206.40-206.82," a tralized the positive charge, but it was not 2), even to the point of identical spectra," value soon confirmed in three more laborato- known where these electrons resided. Fajans despite their different half-lives (7.54x 104 and ries. There was no doubt about it-lead from thought all electronic processes (either chemi- 1.40x 10'" years, respectively). If one believed radioactive sources was lighter than ordinary cal redox or nuclear decay) must occur in the Soddy, then the disconcerting problem of stuff- lead, and there proved to be no spectroscopic same region of the atom, since the particles ing too many elements into the Periodic Table differences. Later, the method of Moseley"' (continued on page 74)

WINTER 2010/THE HEXAGON 71 AXI

t . vdKzo . I 47 / 1i a * s

01 1 2 1 '6,36.Ann Fr 107 1 11 1 8 1 11 23 9 12 3 32 65 Crstn. Gi _g" -9 7 s 7 79 82 93 a 2 62s 3 s , $9 6 67. Katherini Sti 6 6.3 3 e e se 9 70--6.pncrRc 9 11 12 1 14 1S 9 17 1 19 2 21 a 4 " 4 2 - 69. ebecaAd 22 -276 Robert Duf,.

1 2 3a 4 2s 2s

n 41 a .. i AX 5

AlLJ- r 16L .Aua1Ni- e I,

- i

r Tom

-%*~~

Photo by John Becker

50th Biennial cu 72 THE HEXAGON/WINTER 2010 50 (Rediscovery continued from page 71) Figure 10. Marischal College in Aberdeen, Scotland, where (electrons) were identical. However, a logical argument of Soddy in 1913 underscored the -p- if Soddy independently discovered "eka-tantalum" clear difference between orbiting electrons and (protactinium-231) in 1917 nuclear electrons.' Soddy compared the oxida- (Broad Street, N57 08.93 tion of tetravalent uranous to give hexavalent W020 05.81). Although some uranyl (U' + U") with the radioactive preliminary work on decay of UX1, which loses two electrons to form eka-tantalum had been done U2 (Th-234 -- U-234). If electron loss (oxida- in Glasgow, his finished tion) and beta loss (radioactive decay) were objective was not completed identical processes, then UX1 and U2 should be until he moved here in 1917. chemically identical-but instead they could be cleanly separated. Clearly there was some- thing special about "nuclear electrons." Piccard (1882-1962) of high-altitude (balloon 11. J. L. Marshall and V. R. Marshall, The answer to the riddle of the nuclear elec- flights) and deep sea (bathyscape) fame. In Rediscovery of the Elements, [DVD], 2010, trons was solved by James Chadwick 1917, he proposed" an element actinouranium, ISBN 978-0-615-30793-0,"Historical (1891-1974, Nobel Laureate in physics in 1935), incorrectly suggesting a mass of 239; the correct Sketch of Discoveries," 101-113. who discovered" the neutron in 1932. This neu- mass of 235 was established by the mass spec- 12. K. Fajans, Phys. Zeitschrift, 1913, tral particle was not simply a combination of a 14, (a) tral work of Aston," and Rutherford immedi- proton and an electron, but an entirely new 131-136; (b)136-142. ately realized'' that protactinium (discovered by particle that could eject an electron (to become 13. F. Soddy, Chem News, 1913, 107, 97-99. Hahn and Soddy independently) would have a a proton) in special cases defined by a low pro- 14. A. Fleck, J. Chem. Soc., 1913, 103, 381-399. mass of 231 (promptly verified in Hahn's labo- ton/neutron ratio. With Bohr's description of ratory). Piccard's concept of a naturally occur- 15. K. Fajans and O. H. G6hring, Phys. electronic structure," a complete picture ring isotope of uranium giving rise to the actini- Zeitschrift, 1913, 14, 877-84. emerged of the atom and its behavior in the um series was acknowledged by Soddy in his 16. K. Fajans, Ber d'utsch. chem. Gcs., 1913, 46, radioelement decay sequences. With this Nobel address.; 3486-3497. understanding, the story of radiochemistry with 17. T. W. Richards and M. Lembert, J. Amer. its "suicidal success"' was completed, paving Chem. Soc., 1914, 36, 1329-1344. the way for the next chapter- "Nuclear References. 18. K. Fajans, Radioaktivitat und die neueste Chemistry" and the birth of the artificial ele- 1. Personal communication, Professor Alan Entwicklung der Lehre von den chemischen ments. This shall be the topic of a future article Cooper, Department of Chemistry, Elementen, 1920, Friedr.Vieweg in The HEXAGON "Rediscovery" series. 0 University of Glasgow; who furnished a & Sohn, Braunschweig. manuscript of a B.B.C. radio program, Notes. "Science Survey"where Soddy was 19. F. W. Aston, Nature, 1929, 123. Note 1. "Brevium" was Pa-234m. interviewed, broadcast 10:30 p.m. 14 June, 20. F. Fajans, Radioactivity and the latest "Protactinium" (Pa-231) was discovered and 1951 (also described in less detail in ref 8). developments in the study of the chemical elements, 1923, Metheun & Co., London, xii. isolated in weighable quantities four years later, 2. F. Soddy, Nature, 1913, 92, 399-400. 2 independently by Hahn and Meitner 1 in Berlin 3. M. Howorth, The Life Story of Frederick 21. F. Soddy, Nature, 1913, 92, 399-400. (Figure 9) and Soddy and Cranston" in Soddy, 1958, New World Publications, 22. J. Chadwick, James, Nature, 1932, 129, Aberdeen (Figure 10), and named because it London. 312; Proc.Roy. Soc., 1932, 136 (Ser A), was the precursor to actinium (Pa-231-* Ac- 4. J. L. Marshall and V. R. Marshall, 692-708. 227). Fajans also predicted a pleiad just to the The HEXAGON of Alpha Chi Sigma, (a) 23. J. L. Heilbron, Historical Studies in the right of the emanation pleiad (radon)''-veri- 2006, 97(4), 50-55; (b) 2010, 101(1), 6-11; Theory of Atomic Structure, 1981, "The fied when francium with a half-life of 21.8 (c) 2010, 101(2), 22-26; (d) 2010, 101(3), Genesis of the Bohr Atom,"Arno Press, minutes was discovered in 1939 by Marguerite 42-47. 147-228. Catherine Perey (1909-1975).'' Fajans had a 5. F. Soddy,"The origins of the conception of 24. 0. Hahn and L. Meitner, Phys. Zeitschrift, celebrated career but never received the Nobel isotopes," Nobel lecture, Dec. 12, 1922. 1918, 19, 208-218. Prize, perhaps in part owing to political ene- 25. F. Soddy and J. A. Cranston, Proc. Roy. Soc. mies he made in the science world by his brash 6. W. Crookes, Proc. Roy. Soc. (Ser. A), 1900, (London), 1918, 94, 384-404. behavior.' 66, 409. 7. E. Rutherford, Radioactive Transformations, 26. M. Perey, Comptes rendu., 1939, 208, 97-99. Note 2. Ironically, it was later found that iso- 1906, 27. L. S. Bartell, Bull. Hist. Chem., 2010, 35(1), topes can have different chemical and physical University Press, Cambridge. 62-63. properties, particularly where a small atomic 8. F. Soddy and J. A. Cranston, Isotopy. mass can be a significant difference in the zero- Lectures by Soddy and Cranston, 1954, 28. H. C. Urey, Ferdinand G. Brickwedde, and point energy; deuterium was discovered by [lectures delivered 1953-19541, New World G. M. Murphy, Phys. Rev., 1932, 39, Urey in 1931 by distillation of liquid hydrogen' Publications, Westminster. 164-165. and pure heavy water was prepared in 1933 by 9. L. Badash, Brit. J. His. Sci., 1979, 12, 29. G. N. Lewis and R. T. MacDonald, R. T., G. N. Lewis using electrolysis.2 ' 245-256. J. Chem. Phys., 1933, 1, 341-344. Note 3. The possibility of more than one iso- 10. F. Soddy, The chemistry of the radio-elements, 30. A. Piccard, Arch. sci. phys. nat., 1917, 44, tope of uranium giving rise to additional decay (a) Part 1, 1911, and (b) Part II, 1914, 161-164. sequences was first proposed by Auguste Longsmans, Green & Co., NewYork. 31. E. Rutherford, Nature, 1929, 123, 313-314.

74 THE HEXAGON/WINTER 2010