Rediscovery of the Elements

Element 72- Hafnium- A

James L. Marshall, beta Eta 1 971, andVirginia R. Marshall, Beta Eta 2003,Department of Chemistry, University ofNorth Texas, Denton,TX 76203-5070,jimm@unt.edu

Urbain's Search for Element 72. In a previ-ous HEXAGON" we witnessed the 1914 visitof Georges Urbain (1872-1938) to Oxford,England, to enlist the aid of Henry GwynJeffreys Moseley (1887-1915), who, with hisnew x-ray method2' had been able to deter-

mine the atomic numbers of 38 elementsranging from aluminum (13) to gold (79).2bUrbain wished to study some of his rare earthsamples which he had been investigating fortwo decades." The preparations he broughtfrom his laboratory in Paris had been separat-ed from ytterbium, originally discovered in1878 by Jean-Charles Galissard de Marignac(1817-1894) in Geneva, Switzerland. Urbainhad previously announced the discovery oflutetium' in these ytterbium mixtures, but healso wanted to confirm "celtium," a new ele-ment which he had proposed on the basis ofits different optical spectrum and magneticproperties."

In the matter of a few hours, Moseley wasable to establish that indeed ytterbium andlutetium were present in the mixtures; theirrespective atomic numbers were determined tobe 70 and 71. However, none of the putativeceltium was detected."," Urbain returned toParis disappointed, but determined to continuethe search. With Moseley's previous respectiveidentifications of tantalum and tungsten as 73and 74,2b a vacancy existed at 72 and Urbainassigned this atomic number to his celtium.'

Figure 1. Key sites inrre NIELS BOHR INSTITUTE Copenhagen. The Niels

Bohr Institute is whereGEOLOGICAL MUSEUM hafnium was discovered

-- by Coster and HevesyORSTED'S LABORATOR (Blegdamsvej 17, N55*

YUsUM avn 41.80 E12 34.30). TheOnne Oresund Geological Museum

hi houses the alvite (zircon)samples which were ana-

t naSy-r lyzed to discover hafnium

s E(Voldgade 5-7 - N55. ngens Enghave undb ester 41.24 E12 34.64). At the

* s\ Bymuseum, a commemo-rative hafnium plaque is

! r s4? displayed (Vesterbrogade. mby 59, N55 40.33 E12

33.20). 0rsted's chemicallaboratory (Studiostrxde

6 - N55 40.75 E12 34.24) is where aluminum was discovered.' INot shown:"Telefonhuset,"the discoverysite of electromagnetism by Orsted, Norregade 21 (N55 40.84 E12 34.26), 180 meters north of the chemi-cal laboratory].

After the hiatus of World War I, Urbainresumed his research on rare earths. He per-suaded Alexandre Dauvillier (1892-1979),assistant to Louis-Victor-Pierre-Raymond deBroglie (1892-1987; Nobel Laureate in physics,1929), to reinvestigate his rare earth mixtures.4

In 1919 Dauvillier set up an x-ray laboratory inde Broglie's Parisian mansion, and three yearslater he and Urbain published papers' identi-fying two faint lines as element 72 which"demonstrated the existence of a trace ofceltium." Urbain explained the earlier negativeresults in 1914: Moseley's crude instrumenta-tion "had not been sensitive enough."' Eventhough Urbain was never able to gather anyfurther evidence beyond these "two faint lines,"for years he maintained his claim to the discov-ery of element 72.

The Niels Bohr Institute and Hevesy. NielsBohr (1885-1962; Nobel Laureate in physics,1922) worked with Ernest Rutherford inManchester"- and had adopted Rutherford'smodel of the nuclear atom in his futureresearches. Returning to his home inCopenhagen (Figure 1), Bohr became professorof physics at the University of Copenhagen in1916 and was made director of the newlyfounded Institute of Theoretical Physics twoyears later" (Figure 2). Whereas Urbain hadassumed that the element 72 would be a rareearth, Bohr's work suggested that the undiscov-ered element would belong with the maintransition metals and would lie directly belowzirconium in the Periodic Table. Thus, element72 should be sought not in rare earth mixtures,but instead in zirconium minerals."

Bohr invited the Hungarian Gyorgy deHevesy (1885-1966), who also had worked inRutherford's laboratory, to join the BohrInstitute in an attempt to isolate element 72.Joining Hevesy was Dirk Coster (1889-1950),who had worked with Karl Manne GeorgSiegbahn (1886-1978), whose sophisticatedinstrumentation had extended Moseley's x-raywork to establish atomic numbers through ura-nium."' Hevesy and Coster procured samplesof zircon (zirconium silicate, ZrSiO4) from theGeological Museum (Figures 3, 4) in

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Figure 2. The Bohr Institute (Niels Bohr Institutet, Kobenhavns Universitet), built in 1920 Jr Niels Bohr,and originally financially sponsored by the Carlsberg brewing company. Niels Bohr studied under ErnestRutherford at Manchester 1912-1916 and then returned to Denmark to work in this building.

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Figure 3. The Geological Museum in Copenhagen houses samples of alvite (hafnium-rich zircon specimens)and cryolite (aluminum minerals) described earlier by the authors."'

Copenhagen" and rapidly established thatindeed element number 72 existed inNorwegian minerals,"' (Figure 5) sometimes tothe extent of 5-10%."b In their paper "On themissing element of atomic number 72," theyproclaimed that they were the first to observethe element, and they named it hafnium (Latinfor Copenhagen)"' (Figures 6, 7). By the use ofpotassium and ammonium tetrafluoro salts

(Figure 8), they were able to concentrate hafni-um and differentiate zirconium and hafnium x-ray lines cleanly.

Hevesy and Coster proceeded with a com-plete chemical and physical characterization ofhafnium. Recognizing that hafnium mighthave unusual electric properties, PhilipsLaboratories of the Netherlands became inter-ested and contracted to own exclusive rights to

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Figure 4. Hafnium-rich specimen of alvite wasused by Coster and Hevesy for their studies.Gemmy crystals of zircon can be pure ZrSiO4, butalvite is a less attractive variety which containstypically 5-10% hafnium (Zr/Hf(SiO4)). Thisspecimen containing 6% hafnium was collected atTangen Mine, Kragero, Norway, the source ofCoster and Hlevesy/'s minerals.

scientific knowledge gained during Coster andHevesy's researches.4 At Philips NatLabs inEindhove'n, Netherlands (Figure 9), ultrapurehafnium was prepared and investigated in elec-tronic devices.'"

Why was hafnium so chemically similar tozirconium? Hevesy in his review" discussedthe almost identical chemistry of zirconiumand hafnium, pointing out that they were"more closely related than any other two ele-ments belonging to different periods [of thePeriodic Table]." He reminded us thatcolumbium [niobium] and tantalum were also"very closely related chemically,"and to a less-er extent other family pairs such as molybde-num and tungsten. (A century earlierWollaston had concluded columbium and tan-talum were the same element, but he was puz-zled over their different densitiesc.

Explanation of this behavior was furnishedby Victor M. Goldschmidt (1888-1947), profes-sor at the Royal Frederick University (becameUniversity of Oslo in 1939)" (he actually sub-mitted a report, a scant 29 days after Coster andHevesy's announcement, that he had alsodetected hafnium in Norwegian mineral sam-ples'2 ). One of Goldschmidt's major contribu-tions was his recognition of the "lanthanidecontraction,"" a gradual decrease in the atomicradii as one progresses through the lanthanides(because of poor shielding by the 4f electrons)with the result that hafnium and zirconiumhave virtually identical ionic radii. Hence, even

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Tangen , Kragero.

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Figure 5. The hingen Mine (N58" 52.29 Lu9'21.24), 1 km west of Kragero, Norway, and 140km southwest of Oslo. The guide to the left isAlf Olav Larsen, who previously had taken theauthors to Lovoya, 25 km northeast, where thoriumwas discovered." Tangen Mine historicallyfurnished feldspar and quartz for the porcelainindustry. Samples of alvite were,discovered hereby the authors (previously reported").

though hafnium is denser than zirconium, itbehaves crystallographically and chemically thesame, even if its electronic and nuclear proper-ties may be different (as an example, hafniumis an efficient neutron-adsorber used innuclear reactors, but zirconium is relativelytransparent).

The Response of the French. In the initialannouncement by Coster and Hevesy"' appear-ing eight months after the x-ray work ofDauvillier and Urbain;, the Bohr Institutescientists did not neglect to mention that theconclusions of Dauvillier's and Urbain were"not justified."

The response was swift. The attack onceltium was an assault on French scienceitself-the words of Charles Adolphe Wurtz(1817-1884) echoed from 56 years earlier: "Lachimie est une science francaise. Elle fut consti-tuee par Lavoisier d'immortelle m moire.""["Chemistry is a French science. It was estab-lished by Lavoisier as an immortal memory."]World War I was still fresh in the minds ofEuropeans, and excessive patriotism coulddominate the national scene. The French pressexcoriated the Copenhagen announcement of

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Figure b. E ntrance to thL Copenhagen Bymuseum ( Village-museum), built in I 787. In the courtyaordl to tlitright is a scale model of Copenhagen in 1530. Insideand history of the city.

hafnium with its opinion: "(a pue le boche"["This reeks of the Hun"].

Urbain and Dauvillier grudgingly admitted"that Coster and Hevesy's work was a "veryimportant result" but denounced the conclu-sions as "regrettable" which "cast discredit" ontheir results. If Coster and Hevesy's elementwas 72, Urbain maintained, then theCopenhagen team was merely lucky to havestumbled on a richer source of the element,'and that in any case the original discoverybelonged with the Parisian research group.'

The British claim to "Oceanium." Hostility tothe Copenhagen group extended across theEnglish Channel-the British press protested,"We do not accept the name which was givento it by the Danes who only pocketed the spoilafter the war."' Not wanting to lose out on theaction, British scientists were exhorted to claimelements from the dwindling list of the undis-covered"before it is too late."" Promptly a dec-laration" was made by Alexander Scott(1853-1947; FRS, Head of Laboratory, BritishMuseum) that he should be given credit for ele-ment 72, having discovered "oceanium" in"black sand from New Zealand."4

Congratulations were extended by theChemical Society for the element which was"identical with that announced by Coster andHevesy;"" but a subsequent careful analysis"indicated nothing but titanium and silicondioxide.{

the museum are exhibits introducing one to the culture

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Figure 7. Plaque in the Bymuseum connemorates"Hafnium/Hf/Element/Number 72/Discovered1922/Copenhagen."The specimen is hafnium oxide.

The Slow Demise of Celtium. In response tothe objections of Urbain and Dauvillier, Costerand Hevesy carefully laid out their case:" boththe optical and x-ray properties of hafnium and"celtium"were not the same; the paramagneticdata which Urbain originally used to argue forceltium was actually due to an ever-increasingconcentration of lutetium in his original crudepreparations." They argued that Urbain's

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Figure 8. The "shoeshine box"full of"Hevesy's Chemical Collection," includes samples of K,'rf KVi i Ft, IHfOCl2, and other compounds prepared by Hevcsy. Hevesy discovered that potassium hexafluorohafnate(K2HJF6) is more soluble than potassium hexafluorozirconate (K2ZrF6). Repeated recrystallizations slowlyled to an enrichment of the hafnium compound in the soluble portion.

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I 're 9. Puir metallic hafnium was first prepared in Anton Eduard van Arkel (1893-1976) and JanHendrik de Boer (1899-1971) at Philips NatLab (Natuurkundig Laboratorium = Physics Laboratory)'" in1925 in the Strijp district of Eindhoven, Netherlands (Kastanjelaan - N510 26.75 E05 27.25). Philips haddrawn up a contract with Coster and Hevesy and was using hafnium in its electronic equipment. In thisbuilding immediately after its construction in 1923, both Lise Meitner and Albert Einstein gave lectures onthe atomic nucleus and quantum mechanics, respectively. Today the area is being renovated into a historicalpark, as Philips NatLab moved in 1968 to its High Tech Campus 4 km south of Eindhoven.'

trivalent rare earths could not contain tetrava-lent hafnium (Hf"). In fact, it was impossiblefor Urbain's rare earth mixtures to contain anyhafnium, even as an accidental impurity,

because Urbain had carefully purified his rareearth mixtures by oxalic acid treatment whichwould have removed any traces of zirconiumand hafnium." The Danish group went further

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and suggested that Welsbach, who had clean-er preparations of lutetium (71), should becredited with the discovery of element 71which should be named "cassiopeium" as hehad suggested.

Urbain should have been suspicious fromthe very beginning: the faintness of the twolines did not portend an element which exhib-ited an intense optical spectrum and measur-able magnetic properties which he had report-ed as being characteristic of celtium.b However,he was bitterly disappointed that years ofpainstaking work might be preempted by ayounger group of theoretical physicists, and hiszeal to prevent "Teutonic priority claims"19'overwhelmed his judgment. With no new evi-dence supporting celtium, he resorted to "dis-tortions of historical facts."4 He called upon theexpertise of Moseley,21 affirming that the now-deceased scientist "himself set forward thehypothesis that celtium is identified with ele-ment number 72."'" In fact, Moseley had orig-inally accepted celtium only upon the word ofUrbain; and after his rare earth x-ray analysis,Moseley declared"' that clearly Urbain's"lutetium" was merely crude ytterbium conta-minated with lutetium, and his "celtium" wassimply more highly purified lutetium (this pro-nouncement was later shown to be correct)."Next, Dauvillier claimed he and Urbain hadactually anticipated hafnium being a tetravalenthomologue to zirconium 2-when all along theFrench scientists had been searching in thetrivalent rare earths.4 Finally, Urbain contendedthat even though he may have been mistakenabout the optical and magnetic spectral data,nevertheless his claim was validated by his x-ray spectrum of celtium, which was the same asCoster and Hevesy's. 3 Careful inspection ofDauvillier's spectrum" shows this was embar-rassing nonsense (Figure 10).

Hevesy and Coster fully characterized hafni-um by 1925, including its atomic weight.Nevertheless, that year the Committee onChemical Elements, which was chaired byUrbain (Note 1), omitted element 72 in its"International Table of Atomic Weights of theChemical Elements"!" Bohr was frustrated:"[Urbain pays] no regard to the important sci-entific discussion of the properties of the ele-ment 72, but tries only to claim a priority forannouncing a detection of such an element."4

Rutherford quietly told him not to fret, thatthey"need pay no attention to such irrespon-sible utterances."4 Fortunately, during thispost-war period of "national prejudices andprofessional jealousy,"4 cooler heads eventual-ly prevailed, notably Ernest Rutherford, NielsBohr, Marie Curie, and Charles James, whoseprofessionalism reined in extrascientific pro-paganda. Finally, in 1927 the Committee offi-cially recognized "hafnium," which finally

Tm Ct Ct Lu Ybi t 12 a i a I

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tiFigure 10. This is the x-ray spectrum of Dauvillier, the only spectral evidence for the existence of"celtium."2 'In reality, the source sample is merely a crude mixture of lutetium and ytterbium. The lines attributed toceltium are identified by"Ct," the chemical symbol for the putative "celtium." However, the overall arrange-ment and the position of the lines do not correspond with the six hafnium lines ' observed by Coster andHevesy, and crucially an even stronger line" is missing; hence, the "Ct"lines cannot be due to element 72.The impartial Swede and x-ray expert Manne Siegbahn, who directly inspected the original spectrum dur-ing a visit to Paris in 1922, opined that the two "Ct"lines were probably imaginary'-in fact, Dauvillierstated that in the published spectrum the lines of celtium had been "strengthened to permit the accompany-ing illustration to be made."" If indeed they are real, the lines are probably due to elemental impurities,some of whose known lines fall at the observed locations.

gained its rightful place with the chemical ele-ments as element 72,'16 and celtium passedinto obscurity (Note 2).

The Belated Recognition of the Co-discover-ers of Lutetium. In the early 1900s three scien-tists were working to separate out the suspect-ed companion in Marignac's ytterbium-notonly Georges Urbain in France, but also CarlAuer von Welsbach (1858-1929) in Austria andCharles James (1880-1928) of the University ofNew Hampshire (AXI, Mu, '11). The first toreport evidence of this element was Welsbach''(30 March 1905), obtaining convincing spectraldata by 1906.2b, Nevertheless, the InternationalCommittee on Atomic Weights stated that, in1909, Urbain had"clear priority" '-because henamed it' one month before the more cautiousand meticulous Welsbach ("cassiopeium" 21)-

even though the Committee admitted thatUrbain's atomic weight values were inferior toWelsbach's values." The course of theCommittee proceedings is puzzling until it isremembered that the four-man committeeincluded Urbain (Note 1). Countries of EasternEurope, recognizing the injustice of theCommittee's action, used the name "cas-siopeium" for years. (In their travels the authorsthemselves have seen several archived PeriodicTables with"Cp"under element 72).

In a "masterpiece of historical detectivework,"4 Hansen and Werner studied the opticalspectra of hafnium and lutetium salts andproved that Urbain's original crude lutetium"'upon further purification (putatively givingenriched celtium), only produced purelutetium.'' Hence, Urbain claimed evidence for"celtium" by using his concentrated sample oflutetium, when pure lutetium had already beenprepared by Welsbach and James. It is not sur-prising that members of the scientific commu-nity were disturbed that Urbain claimed discov-ery3 of both elements 71 and 72 whenWelsbach's earlier evidence for cassiopeium3

was stronger than Urbain's "Note prfliminaire"for lutetium 3'-let alone for the illusoryceltium. Meanwhile, the cautious CharlesJames had delayed publication of his researchto prepare perhaps the purest samples availableof lutetia (Lu2O3).' Today the injustice of thelutetium episode has been moderated by a gen-eral recognition that credit for its discovery isshared among the three scientists-Urbain,Welsbach, and James.''

We confirm the neutrality of science... Sciencehas no native country, or rather: the country ofscience includes the whole ofhumanity.. .2 -LouisPasteur, 1884. 0

Acknowledgements.The authors extend their gratitude to Felicity

Pors and Finn Aaserud of the Niels BohrInstitute for serving as gracious hosts and alsofor providing much useful information from theInstitute archives about Bohr, Hevesy, Coster,and Orsted. Also in Copenhagen Ole Petersenprovided samples and information about zircon(type alvite) and cryolite (aluminum). InNorway Alf Olaf Larsen, leading mineralogistof Norway, kindly guided us to the TangenMine, Kragero, Norway, the source of the hafni-um-rich alvite for Coster and Hevesy's studies.Finally, special and warm gratitude is extendedto Dr. Gerry Dobson, Beta Eta '70 (GMA 1980;Kuebler Award winner 1990) and RegentsProfessor Emeritus of UNT, who over the pastdecade has reviewed extensively the"Rediscovery" articles and who has alwaysmade many insightful suggestions.

Notes.Note 1. Urbain was appointed to the

International Committee on Atomic Weights in1907 upon the death of Henri Moissan(1852-1907; Nobel Laureate in chemistry,1906). Moissan had been appointed in 1903 tofill out the three-man committee elected fromthe USA, England, and Germany two years ear-lier (Moissan was the only Frenchman toreceive a vote out of a slate of 12). It is easy tounderstand how the ardent Urbain wished torectify what he considered to be undue Germaninfluence on international chemical committeesat the turn of the century. After World War I, theCommittee on Atomic Weights was reorga-nized (1921) and renamed the Committee onChemical Elements, presided over by Urbain."

Note 2. Upon Urbain's death in 1938,authors of his obituary" lauded the late-Renaissance man by extolling his skills as apainter, sculptor, and scientist, but unfortunate-ly they elected to promote la gloire while com-posing a parody of chemical history:"[Urbain]recognized the presence of still another ele-ment, celtium, not of the rare earth family. Thiselement was thought by Moseley to be themissing element number 72 . .. [Dauvillier'sexamination] indicated the presence of elementnumber 72... The element was isolated in larg-er concentrations by Hevesy and Coster in1922. .. [T]he International Committee onAtomic Weights has accepted two names,celtium and hafnium, and two symbols Ct andHf." Even today the fable persists in FrenchWikipedia, where Urbain is given credit as "thediscoverer of celtium later called hafnium"[http://frwikipedia.orgwikiGeorgesUrbain].

THE HEXAGON/FALL 201140

References.1. James L. and V. R Marshall, The Hexagon of

Alpha Chi Sigma, (a) 2001, 92(4), 70-73; (b)2002, 93(1), 9-11; (c) 2004, 95(2), 24-28; (d)2006, 97(2), 24-29; (e) 2010, 101(2), 22-26;(f) 2010, 101(3), 42-47.

2. H. G. J. Moseley, Phil. Mag., (a) 1913, 26,1025-1034; (b) 1914, 27, 703-713.

3. G. Urbain, Compt. rend., (a) 1907, 145,759-762; (b) 1911, 152, 141-143; (c) 1922,174, 1349-1351; (d) 1923, 176, 469-470.Urbain originally announced "lutecium,"whose spelling was changed to"lutetium"in 1949.

4. H. Kragh, Centaurus XXIII, 1980, 23,215-301.

5 A. Dauvillier, Compt. rend., 1922, 174,1347-1348.

6. Archival notes of Niels Bohr Institute,courtesy Felicity Pors; J. L. Heilbron,Historical Studies in the Theory of AtomicStructure, 1981, Arno Press, (with T. S.Kuhn),"The Genesis of the Bohr Atom,"149-228.

7 H. Kragh and P. Robertson, J. Chem. Ed.,1979, 56(7), 456-459.

8 (a). D. Coster and G. von Hevesy, 1923,Nature, 111, 79; (b) 182; (c) 252; (d).462-263.

9. G. Hevesy, Chem. Rev., 1925, 2(1), 1-41.

10. K. Boersma, Inventing Structures forIndustrial Research. A History of the PhilipsNat. Lab. 1914-1946, 2002, AksantPublishers, Amsterdam; M. J. de Vries, 80Years of Research at the Philips NatuurkundigLaboratorium, 1914-1994, 2005, PallasPublications, Amsterdam.

11. G. B. Kauffman, The Chemical Educator,

1997, 2(5), 1-26.12 V. M. Goldschmidt and L. Thomassen,

Norsk geol. Tidsskr. 1923, 7, 61-68.13. A. Rocke, Nationalizing Science. Adolphe

Wurtz and the Battle for French Chemistry,2001, MIT Press, 333.

14. G. Urbain and A. Dauvillier, Nature, 1923,111, 218.

15. ,Chem. & Ind., 1923, 42, 113-114.

16. A. Scott, J. Chem. Soc. Trans., 1923, 123,311-312.

17. ' Chem. News, 1923, 126, 81.18. Nature,1923, 111,195.19. J. L. Heilbron, H. G. J. Moseley. The Life and

Letters of an English Physicist, 1887-1915,1974, University of California Press, (a)133; (b) 236-237.

20. G. Urbain, Chem. & Ind., 1923, 42, 764-768.21. H. M. Hansen and S. Werner, Nature, 1923,

111, (a) 322; (b) 461.22. A. Dauvillier, Chem. & Ind., 1923, 42,

1182-1183.23. G. Urbain, Chem. Rev., 1924, 1,143-185.

24. G. P. Baxter, J. Amer. Chem. Soc. (a) 1924,46(3), 523-533; (b) 1927, 49(3), 583-590.

25. C. Auer v. Welsbach, (a) "Die SpaltbarkeitdesYtterbiums,"Akademie derWissenschaften in Wien, 30 March 1905,Sitzung der mathematisch-naturwissen-schaftlichen Masse; (b) AkademischenAnzieger, Jahrgang 1905, Nr. X; (c)"Uberdie elemente derYttergruppe" erster Teil,Sitzungsberichte der kaiser. Akademie derWissenschaften in Wien, Bd. CXV, Abt. IIb,Juli 1906; (d) Monatshefte fur Chemie, 1908,

29(2), 181-225 (read before the ViennaAcademy Dec. 19, 1907).

26. F. W. Clarke, W. Ostwald, T. E. Thorpe, andG. Urbain, J. Amer. Chem. Soc., 1909, 31(1),1-6. [received November 9, 1908].

27. G. R. Dobson, The Hexagon of Alpha ChiSigma, 1981, 72, 23-27. J. L. Marshall andG. R. Dobson, "Charles James, pioneer inrare earths," 223rd National AmericanChemical Society Meeting, April 9, 2002,paper HIST025.

28. R.Vallery-Radot, La vie de Pasteur, 1900,

Paris, 570.29. N. E. Holden, Chemistry International, 2004,

26(1),4-7.30. C. Champetier and C. H. Boatner, J. Chem.

Ed., 1940, 17(3), 103-109.31. A. E. van Arkel and J. H. de Boer, Z. Anorg.

Allgem. Chem., 1925, 148, 345-350.

Look for moreinformationon the AlphaChi Sigmawebsite, inJanuary 2012.

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