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Home , Gustav Rose, Heinrich Rose, Martin Heinrich Klaproth, Niobium, Pelopium, Tantalum

Rediscovery of the Elements and III

James L. Marshall, Beta Eta 1971, and Virginia R. Marshall, Beta Eta 2003, Department of , University of North Texas, Denton, TX 76203-5070, [email protected] Figure 1. Map of . The Apotheke zum weissen Schwan (Apothecary of the White Swan) no longer In the last issue of The HEXAGON 1j we exists; it was across the street from the present Heilige Geist Kirche (Church of the Holy Ghost), which still described how in 1809 stands today, Spandauer Straße 1, N52° 31.26 E13° 24.19. The Apotheke zum Bären (Apothecary of the (1766–1828) proclaimed 2 the two elements Bear) no longer exists; it was next to the present Nikolaikirche (Nicholas church), Probststraße - N52° columbium (known today as niobium), discov- 31.04 E13° 24.46. The Akadamiehaus (Old Berlin Akademie) was at present 28 Dorotheenstraße (original- ered in 1801 by (1765–1847), ly 7 Letzten Straße, then 10 Dorotheenstraße); now a parking garage - N52° 31.14 E13° 23.46. The and tantalum, discovered in 1802 by Anders Humboldt Universität zum Berlin (Berlin University) is located at Unter den Linden 6 - N52° 31.06 E13° Ekeberg (1767–1813), were identical. However, 23.63, with statues of Wilhelm Humboldt, founder of the university (located at “1”) and his brother there was a lingering suspicion among some Alexander Humboldt, the biogeological explorer (located at “2”). chemists that something was not quite right, because the of the source eponymous Rose’s , a low-melting apothecary, and moved on to the Berlin (from Connecticut) and (100°C) of bismuth, , and lead.4a In Academy in 1800, becoming professor of the (from ) were different (5.918 and 7.953, 1771, Martin Heinrich Klaproth (1743–1817), University of Berlin when it was founded by the respectively). This problem was investigated in the discoverer of ,1g joined the pharma- Humboldts in 1810. Klaproth was arguably one detail by of Berlin in the 1840s. cy. That same year Rose died, and Klaproth of the best two analytical chemists of his time, assumed care of the two Rose sons, one of to whom all would send doubtful specimens to The birth of analytical chemistry in whom lived to maturity, Valentin Rose, the be confirmed1g (the other being Louis Nicolas . The origins of modern German younger (1762–1807).4a The apothecary Vauquelin (1763–1829) of Paris1b). chemistry can be traced to two apothecaries in remained in the Rose family for three genera- In 1823, Gustav and Heinrich Rose joined Berlin—the Apotheke zum weissen Schwan tions, passing on to the grandchildren Gustav the University of Berlin.3 Gustav’s specialty was (Apothecary of the White Swan) and the (1798–1873) and Heinrich (1795–1864). ;4b he accompanied Alexander von Apotheke zum Bären (Apothecary of the Bear). The Apotheke zum Bären (Figure 4) was Humboldt (1769–1859)1a during the celebrated Each of these pharmacies is now gone, but their owned (1738–1753) by Andreas Sigismund 1829 geological expedition to Russia. Heinrich’s exact locations can be identified by neighboring Marggraf (1709–1782),1d who isolated zinc from expertise was chemistry4b (Figure 6); he devel- historic churches that still stand (Figure 1). In calamine, identified alum, and differentiated oped qualitative and quantitative analytical the 18th century, workers in these apothecaries and .1d In 1753, Frederick the techniques, including separations and worked closely with the Berlin Akademie der Great (1712-1786) built a state laboratory for systematic tests, and wrote many analytical Wissenschaften (Academy of Science).3 the Akademie (Figure 1), and Marggraf moved treatises. Heinrich and his brother worked The Apotheke zum weissen Schwan was there a year later (Figure 5).2 closely together as Gustav furnished specimens purchased in 1761 by Valentine Rose, the elder Klaproth left the weissen Schwan apothe- for his laboratory work, while in return (1736–1771), (Figures 2, 3), who invented the cary in 1780 to become manager of the Bären Heinrich furnished critical chemical analysis as

46 THE HEXAGON/FALL 2013 Figure 4. Looking north on Propststrasse with the Nikolaikirche (originally built 1220–1230) on the Figure 2. This water-color painting of the Heilige Geist Kirche was done by Leopold Ludwig Müller in right. The zum Bären pharmacy was at the end of 1804. The church is in the center; to the right is the Apotheke zum weissen Schwan, with a white swan Propststrasse, where a plaque is posted, the site visible above the door on the transom. To the left is the hospital which the church supported; the field to the where Klaproth discovered uranium and zirconi- left is the "Wursthoff" used for raising hogs to furnish food for the hospital. Courtesy, Kupferstichkabineet, um. On the left is the famous shop for "Berliner Staatliche Museum zu Berlin. Bären" (teddy bears).

Gustav devised the “crystal-chemical system,” organizing minerals on the basis of crystalline form and composition.4b

Heinrich takes on the columbite-tantalite problem. Ever since Wollaston “proved” columbium and tantalum were identical,2 Great Britain and the U.S. called the new element “columbium,” but Jöns Jacob Berzelius (1779–1848) campaigned for “tantalum.”1j The name “tantalum,” Berzelius argued, conveyed the important distinction of the element that it resisted solution in , alluding to the legend of Tantalus who, although immersed in water up to his chin, could not quench his thirst.5 (Metal are ordinarily basic, but tantalum could not be dissolved in , even in excess.) Scientists of the European continent dutifully followed the suggestion of the Figure 3. This photograph, taken from the Catholic archives, shows the Heilige Geist Kirche (center) which respected Swedish chemist. looks much the same today. To the right is the apothecary, destroyed in the War. Today the site of the Although columbium and tantalum were apothecary is occupied by high-rise buildings. The date of the photograph is uncertain, but must be after considered to be “the same element,” it was 1906, the construction date of the tower. known that the parent minerals columbite and tantalite, which were isomorphous4c (same mineralogist, enticed Heinrich Rose, the chronicled in Poggendorff’s Annalen (Annalen der ), had different densities. The chemist, to review this question in more detail, Physik und Chemie).6 nagging question persisted, was there actually utilizing the more modern analytical tech- By now, more localities had been discovered more than one element? And if there was, niques that had been developed since the for the source minerals, low-“columbite” could they be separated chemically? Thirty-five beginning of the century. Thus Heinrich and high density “tantalite.” Tantalite could be years after Wollaston’s report, , the embarked on a two-decade research, fully found in Finland and , while columbite

FALL 2013/THE HEXAGON 47 Brandenburgische Akademieder Wissenschaften. Figure 6. HeinrichRose, portrait. Courtesy, Berlin- III tantalum chloride (TaCl announced Bodenmais (N49°3.54E13°7.29). In1844, Rose ical mineandmuseumexistatSilberberg 28in ahistor- Bavarian region ofBodenmais—today problem. Through two decadesRosenever resolved the “Unterniobsäure” (lowerniobiumacid). these “Niobsäure” (niobiumacid)and tive mp205and216, bp248and240), andwere physical properties (bothyellow-white, respec- after Pelops, thesonof Tantalus. ered, heasserted, whichhecalled “” elementhadbeendiscov- columbite—another chloride hadbeenproduced from theBavarian was thefactthatniobiumchloride(NbCl chloride was white, infusible, andnotvolatile. yellow, easilyfusibleandvolatile;niobium and gaseouschlorine. Tantalum chloridewas pared by reaction oftheoxideswithcharcoal were thechloridesoftwo elements, pre- tinguished niobiumandtantalum, Rosesaid, after , thedaughterof Tantalus. What dis- lum andanew elementhecalled “niobium,” tantalite was composedoftwo —tanta- composed ofonemetal, whiletheBodenmais ence ofchlorinegas:NbCl minerals were treated withcharcoal inthepres- um—gave andcolumbi- which were present—niobium 48 (but not TaOCl tion statesofthesameelement “pelopium” were actuallydifferent oxida- and “niobium” elements, butthenconcludedthat elements. Firsthetriedtoseparate thethree where Roseattemptedtocharacterize thenew Two years later could befoundinConnecticut Thus followedalongseriesofpublications Rose was misledbecausethe 6f-h 6a three the Finnish/Swedishtantalitewas 3 6b ). Complicating thesituation he reported different chlorideswhenthe 5 ) hadvirtuallyidentical 5 , NbOCl 1j another 6e —he called —he and inthe 3 , and TaCl two 5 ) and elements yellow 6c,d 6a 5 producing “a revolution inmineralogy.” Dr. RolfHaubrichs, UniversityofGeneva. just two, niobiumandtantalum. Portrait, courtesy of elements actuallyexistedinthisgroupofminerals— columbites/tantalites anddeterminedhowmanynew hence, evidently his TaCl ing theformulaofSiO chlorides ofCr, Mo, W,” that Rose, “the discoverer ofthevolatile oxy- nated withNbCl were underscored by theclaim, by otherminer- nearly allofthecompounds heanalyzed. (K rides (NbOCl was hisnotrecognizing thatoneofthesechlo- Rammelsberg covered theisomorphism mineralogy (1845)attheGenevaacademy. Hedis- Paris, Switzerland, attendedtheÉcolepolytechniquein Figure 7. Jean-CharlesMarignac, anativeofGeneva, Brandenburgische Akademieder Wissenschaften. garage. Photograph, courtesy, Berlin- the War; thepresent siteisoccupiedbyaparking during 1844–1861. The buildingwasdestroyedin Rose performedhisniobium/tantalumresearch here saltpeter bythecoloroftheirflametests. Heinrich here, e.g., thedistinctionofpotassiumandsodium Laboratorium.” Klaprothdidsomeofhislatterwork Akademiehaus iscalledthe “Marggrafisches Marggraf wasmadeitsdirector. Onsomemapsthe Sciences establishedalaboratory here in1753and was takenabout1900. The BerlinAcademyof Figure 5. This photograph ofdasAkademiehaus The subtledifferences inthetantalitesystem 2 SnF tures; Undoubtedly allhispreparations were mix- very difficulttoseparate from oneanother. 1e 14 6 and becameprofessorofchemistry(1841) ) andfluorosilicates(K today weknowpure TaCl 7 and Partington 3 ) containedoxygen. Both 5 . A finalflaw inhisresearch 2 for silica(andnotSiO 4c 7 of fluorostannates 5 missed theoxygenin was always contami- 2 SiF 4b have marveled 6 ), thusestablish- 5 is off-white; 4d He studied 3 ) and understanding that someofhis “separations” whelmed by contradictory chemicaldata, not chemists were accustomed. Rosewas over- rare earthsandothermetaloxidestowhich hs “earth acids” These lum andotherimpurities. later showntobemixtures ofniobium/tanta- “discoveries”(1805–1879). All theselatter were Hans RudolphHermannof Moscow and ilmenium(1874), andneptunium(1877)by Wolfgang Franz Kobell ofMunich(1803–1882), (1860), by columbites andtantalites—dianium alogists, ofthree THE HEXAGON/ 14 were unlikethebasic 8,9 additional FALL 2013 elements in Figure 8. This is the old site of the Geneva Academy—the Société de lecture (Grand Rue 11, Geneva, Switzerland, N46° 12.14 E06° 08.70). This academy dates from 1559, founded by Jean Calvin Figure 10. Blomstrand’s laboratory at the University of Lund. Magle Stora Kyrkogata 12A (now History (1509–1564). Marignac resolved the chemistry of Dept.), U. of Lund, Malmöhus, Sweden (N55° 42.17 E13° 11.92). Here he prepared the first pure sample niobium and tantalum in a “dark damp cellar lab” of niobium, a “spiegelnden stahlgrauen metal” (shiny -gray metal).12 A bust of Blomstrand (see inset) in back of this building (no longer exists). stands in the University of Lund, Kemicentrum, at Getingevägen 60 (N55° 42.99 E13° 12.54).

ly lamented, “Ein solches Verhalten ist aber ein elements until the middle of the 20th century. so eigenthümliches, dass wir im ganzen Later, liquid-liquid extraction using, e.g., Gebiete der Chemie kein analoges kennen.”6e , would preferentially (“Such behavior is so unusual that in the whole extract the tantalum compounds from a hydro- realm of chemistry I know of no analog.”) fluoric or solution.11 Marignac suffered from ill health, owing to A Swiss chemist resolves the problem. In his hours of labor in the cramped damp labora- 1866, Jean-Charles Galissard Marignac tory of l’Académie de Genève. He moved with (1817–1894), (Figure 7) a professor of chemistry the Academy (now the University of Geneva) to at l’Académie de Genève,4d (Figure 8) separated its new site in 1872 (Uni-Bastion, Rue de and characterized the double salts of Candolle, 5 - N46° 11.93 E06° 08.65). In 1878, 10b niobium and tantalum. These salts, K2NbF7 he retired and continued research in his own and K2TaF 7, established the oxides of niobium home laboratory (Figure 9) for the rest of his life. and tantalum as Nb2O5 and Ta2O5 (and not NbO2 and TaO2, as presumed by Rose). The work of Blomstrand. Christian Marignac’s determination of the pentavalency Wilhelm Blomstrand (1826–1897) (Figure 10) of of niobium and tantalum, and of accurate Lund University contributed to the final solu- atomic weights of each (1866), was delivered tion by studying the chlorides,12 identifying the just in time for proper placement in the first oxychloride of niobium (NbOCl3) which had Periodic Tables of Dimitri Mendeleev and been proposed by Marignac.10a Thus the riddle Figure 9. Marignac retired in 1878 and established 1f Lothar Meyer (1869). of Rose’s three chlorides of NbCl5, TaCl5, and a laboratory (“third floor”) in his Geneva home at Marignac’s separation procedure involved NbOCl5 was solved. Henry Enfield Roscoe Rue Jean-Sénebier, 16 (N46° 11.84 E06° 08.88). the initial treatment of a niobium oxide/tanta- (1833–1915), an expert himself in the complex Here he discovered (1880, separated lum oxide mixture with hydrofluoric chemistry of (he was the first to pre- from didymia) and ytterbium (1878, from erbia). acid/, which produced a pare metallic vanadium,1i) lauded the final suc-

mixture of potassium fluorotantalate K2TaF 7 cess: “It is to Marignac and Blomstrand that we were merely chemical transformations between 10a,b and potassium oxyfluoroniobate K2NbOF7. owe a deliverance from this state of uncertain- chlorides and oxychlorides. Rose had experi- The tantalum salt precipitated out, while the ty and contradiction that surrounded the met- enced the first example of two elements of a niobate salt remained in solution. (Further als existing in such minerals as columbite and chemical group which, because of the lan- treatment of K2NbOF5 with HF could produce tantalite. They have independently proved that thanide contraction,1h were of similar size and K2NbF7.) This separation method was used as only two metals in reality exist—niobium and exhibited the same chemical behavior. He final- the basis of industrial production of the two tantalum, and that all the other supposed met-

FALL 2013/THE HEXAGON 49 Figure 11 (left). Pure tantalum was prepared by Bolton (see inset) for use as filaments in incandescent bulbs at Siemens A.G. (then Siemens-Halske Company), Helmholtzstrasse 2- 9, Berlin, Germany. Today the original building is used for business offices and workshops of various trades (N52° 31.28 E13° 19.42).

Figure 12 (right). The Swanson quarry in the Haddam area in Connecticiut was a

III commercial source of lithium in the early 20th century. Recently it has been filled in and must look much as it did centuries ago (except for the transmission lines) when columbite was first collected by Native Americans or colonists.1j It was closed to collectors in 2010.

als, pelopium, decinium, and ilmenium, are Thomas Thomson originally favored “columbi- In 1949, at the 15th meeting of the IUPAC either simple mixtures of niobium and tanta- um,”1j accepted the choice of the Continental (International Union of Pure and Applied lum in varying proportions, or such a mixture scientists. Chemistry) in Amsterdam, it was declared that containing, in addition, some other metals, However, in the the name “niobium (and not columbium) is accepted”18 such as , , or .”8 “columbium” was preferred. In 1877, J. (Note 2). Dutifully complying, American text- The conclusions of Marignac and Lawrence Smith, the second (1877) president of books and Periodic Tables adopted the new Blomstrand were supported by vapor pressure the American Chemical Society and 21st (1874) name, although the use of “columbium” per- studies of his French colleagues13 H. Saint- president of the American Association of sisted for decades. In 1960, the international Claire Deville of the École Normale1d and L. Advancement of Science,16 and himself a spe- committees reaffirmed “the name niobium for Troost of the Sorbonne1d in Paris.13 cialist in mineralogy, made the case for element 41 in spite of the fact that many in the “columbium”:17 “It is the common practice of all United States, particularly outside of chemical Pure metals. The purification schemes of American chemists and mineralogists to speak circles, still retain the name columbium.”19 Even Marignac allowed the preparation of pure sam- of the metal which is called Niobium by English today one occasionally sees “columbium,” ples of metallic niobium and tantalum. and continental chemists, as Columbium. This notably in engineering or trade journals. Blomstrand prepared the first pure sample of is eminently just, since the metal was discov- niobium by treating the niobium chloride in a ered and well defined, and named columbium, What was the actual composition of the stream of in red heat12 (Figure 10). forty-five years before the name niobium was original columbite and tantalite? The table Producing a tractable, pure sample of tantalum given to it. . . . Subsequent examination . . . con- on page 51 demonstrates that columbite/tanta-

was more difficult, owing to its very high melt- vinced Rose . . . that the two metallic acids lite (Fe,Mn)(Nb,Ta)2O6 can have wide ranges of ing point (3017 vs. 2477C); early attempts obtained from the Bodenmais columbite were Fe-Mn and Nb-Ta (Note 3). By luck the original resulted only in brittle, crude material. Werner really the original columbic acid of Hatchett, sample of Hatchett still exists and has been von Bolton (1868–1912) of Siemens AG (then discovered in 1801, and the tantalic acid discov- analyzed by the London Museum of Natural Siemens-Halske) in 1903 prepared the first ered by Ekeberg in 1802. Instead, however, of History.20 Also included in the table are data pure tantalum suitable for making filaments for calling the first mentioned acid niobic acid, its from Connecticut specimens of columbite col- incandescent light bulbs, by treating potassium original name should have been left to it . . . In lected by the authors. The original specimen of fluorotantalate with potassium in an electric arc addition to the above, . . . [columbite has] been tantalite from Skogsböle, Finland (the source of vacuum oven15 (Figure 11). discovered in greater quantities and in larger Ekeberg’s tantalite1j) is not available for analy- crystals in the United States than in other sis, and the site is depleted of tantalite. “Columbium” or “Niobium”? Now that it known localities . . . [including] where the spec- Nevertheless, a chemical analysis was per- was clear that Hatchett’s “columbium” was the imen was obtained that was sent to Hatchett . . formed 70 years after Ekeberg’s discovery by same as Rose’s “niobium,” the question . .”17 (Note 1). Rammelsberg on a Skogsböle specimen.7 remained, which name should be used for the For more than seventy years, Periodic Tables The Ti, Sn, W impurities can serve as iso- element? The European chemists, captivated published in the United States continued to morphic substituents4c in naturally occurring with the large amount of work performed by utilize “columbium.” Despite a latter attempt by minerals for Nb/Ta21 and were noted by the Rose, preferred his choice of “niobium.” Even Roscoe to adopt the American usage of early analytical chemists. Hatchett missed the the British, whose Sir and “columbium,”9 the European choice prevailed. presence of in his original analysis

50 THE HEXAGON/FALL 2013 (he lumped it together with iron). Berzelius The problems generated by the References. used Hatchett’s oversight as an argument contraction with were even more 1. J. L. and V. R. Marshall, The HEXAGON of attesting Ekeberg’s superior analysis, thus bol- severe. The element lay hidden in Alpha Chi Sigma, (a) 2003, 94(4), 60-62, 65; stering his case that “tantalum” was a better minerals until 1923, when it was detected by 5 1h (b) 2004, 95(2), 24-28; (c) 2005, 96(1), 8-13; name for Hatchett’s original discovery. X-ray analysis. It is astonishing that the ana- (d) 2006, 97(2), 24-29; (e) 2007, 98(1), 3-9; The abundance of niobium in the earth’s lytical chemists 60–80 years earlier progressed (f) 2007, 98(2), 23-29; 2008, 99(2), 20-24; (h) crust is 10 times that of tantalum (20 ppm vs 2 as far as they did. 2011, 102(3), 36-41; (i) 2012, 103(2), 20-24; 21 ppm). Hence, the low Nb/Ta ratio of Finnish (j) 2013, 104(2), 20-25. tantalite is quite remarkable. This geological Notes. 21 2. W. H. Wollaston, Phil. Trans., 1809, 99, concentration of tantalum has been explained Note 1. Rose referred to the mineral from both 246-252. by the partitioning of complexes under 6c New England and Bodenmais as “columbite.” 3. H.-H. Müller, “Das Laboratorium special acid-alkaline conditions of the crystal- After analyzing a portion of half a pound of Dorotheenstraße 10,” Berlinische lizing medium. These were the very conditions New England columbite from Benjamin Monatsschrift, 1999, 5 (Mai), 86-89. found serendipitously by Marignac to be an Silliman (1779–1864; the first ever to deliver a 4. J. R. Partington, A History of Chemistry, 1961, efficient separation method in his laboratory! chemistry lecture at Yale College), Rose con- Vol. III, Macmillan, London, (a) 3, 659; (b) 4, 6c cluded North American and Bodenmais 185-190; (c) 4, 207-212; (d) 4, 875; (e) 4, 899. The legacy of Heinrich Rose and Charles columbite were the same, "both containing Marignac. In spite of the fact that Rose was the 5. T. Thomson, Annals of Philosophy, 1814, 4, niobium and pelopium," differing only slightly 467-469. master of analytical separations in the mid- in their specific gravity. Rose was familiar with 14 6. H. Rose, Annalen der Physik und Chemie, (a) 1800s, the niobium/tantalum system in his Hatchett’s work and his naming his element 14 1844, 63, 317-341; (b) 1846, 69, 115-141; (c) hands defied purification. An excellent review 6a “columbium.” In a paper one year before his 1847, 70, 572-574; (d) 1848, 73, 313-326; (e) of Rose’s “lengthy and exhaustive publications” death,6h Rose admitted, by implication, that research, and “how he was diverted from the 1853, 90, 456-471; (f) 1856, 99; 65, 481, 575; Hatchett’s “columbium” was the same as (g) 1861, 112, 468-485; (h) 1863, 118, right way and fell unconsciously into error” is 6h “Unterniobsäure” (which he considered to be 339-356. given by Karl Friedrich Rammelsberg the lower oxide, actually NbOCl3). (1813–1899), professor of mineralogy and 7. C. Rammelsberg, J. Chem. Soc., 1872, 10, chemistry, University of Berlin7 (Rammelsberg Note 2. In the same meeting “wolfram” was 189-204. was a student of Rose, and succeeded him at adopted as the official name for element 74. 8. H. E. Roscoe, Chem. News, 1878, 37, 25. the University of Berlin4e). Rammelsberg appre- However, the British announced that “.. . the 9. H. E. Roscoe and C. Schorlemmer, A Treatise ciated the difficulty of his task and commented, name ‘tungsten’ will not be replaced by ‘wol- on Chemistry, 5th ed., 1913, Vol. II, “The discovery of a new element, niobium, was fram’ [in British scientific literature]”18 This is Macmillan, 944-962. a splendid result of this great, laborious, and . . the reason for the present use of the German 10. C. Marignac, (a) Comptes rendus, 1865, 60, . . difficult investigtion, and history will forever “W” and “Wolfram” for the original Swedish 234-237; (b) Ann. chim. phys., 1866, 4e ser. 8, attribute to it an honourable place in science. “tungsten.”1c 5-75. And although the celebrated founder of 11. A. Agulyanski, The Chemistry of Tantalum Note 3. Mineralogists recognize four mineral Analytical Chemistry [Ausführliches Handbuch and Niobium Fluoride Compounds, 2004, names encompassing the Fe/Mn/Nb/Ta system: der analytischen Chemie] failed to discover the Elsevier, 5. ferrocolumbite, manganocolumbite, ferrotanta- right path, nevertheless young chemists, in 12. C. W. Blomstrand, J. prak. chem., 1866, 97, lite, and manganotantalite.22 studying that long series of memoirs on tanta- 37-50; translated from Oefversigt af Akad. lum and niobium, published in Poggendorff’s Förh., 1864, 21, 541. Annalen, will also understand by what circum- Next Rediscovery: 13. H. S.-C. Deville and L. Troost, Compt. stances the guide was diverted from the right the two missing elements of the rendus, 1865, 60, 1221-1226. way and fell unconsciously into error.”7 manganese family are found! 14. A. J. Berry, From Classical to Modern Readers of The HEXAGON may recall simi- Chemistry: Some Historical Sketches, 1954, 1h lar difficulties in the discovery of hafnium. Cambridge Press, 133-134. 15. W. von Bolton, Z. für Elektrochem., 1905, 11, 45–51. 16. J. P. Phillips, J. Chem. Ed., 1965, 42(7), SELECTED ANALYSES OF COLUMBITE/TANTALITE 390-391.

d d 17. J. L.Smith, J. Amer. Sci., 1877, 13, 359-369; Nb2O5 Ta 2O5 FeO MnO TiO2 SnO2 WO3 Y2O3 Ann. de chim., 1877, 12, 253-264. Hatchett’s specimena 54.2 25.7 15.0 3.5 0.6 - 0.2 - 18. J. Chem. Soc., 1950, 3699-3705. Hadam sampleb 60.2 16.6 16.8 4.3 0.8 1.3 - - 19. J. Amer. Chem. Soc., 1960, 82(21), 5523-5544. 20. (a) Personal communication, C. T. Williams, Hadam (Swanson)b 56.0 25.8 8.2 9.3 - - - 0.7e 2001, Museum of Natural History, London. Skogböle Quarryc 10.9 70.4 10.9 3.3 0.3 3.5 - - (b) analyses by the authors. aMicroprobe, ref 20a. bEDX, ref 20b. Swanson quarry in Connecticut is a famous mineral collection site 21. R. L. Parker and M. Fleischer, Geochemistry of Niobium and Tantalum, 1968, Geological (Figure 12). cRef 7. dExtreme ranges of Nb/Ta include 0% of Ta () to 91% (certain Finland e Survey Professional Paper 612, 1-43. specimens, ref 9). Probably an yttrotantalite impurity, YTaO4. 22. Dana’s New Mineralogy, 8th Ed., John Wiley & Sons, N.Y. 1997.

FALL 2013/THE HEXAGON 51