Rediscovery of the Elements

Moseley and Atomic Numbers

James L. Marshall, Beta Eta 1971, andVirginia R. Marshall, Beta Eta 2003,Department of Chemistry, University ofNorth Texas, Denton, TX 76203-5070,jimm@unt.edu

Introduction. Manchester in northwestEngland was founded as a Roman fort in 79A.D. After the Roman departure it evolved intoa typical Medieval village and after a millenni-um matured into a manufacturing giant. Aninflux of Flemish wool and linen weavers in the14th century, followed by a developing supplyof cotton from India and the American South inthe 1700s, launched a large textile industry dur-

Figure 2. Today the site at 36 George Street inManchester is occupied by Devonshire House,used for University functions. A blue plaque (left,on wall and shown below) reads: "John Dalton(1766-1844), Founder of the scientific AtomicTheory, President of the Manchester Literary andP ilosophical Societi, had hi lal'oratoryl here."

ing the Industrial Revolution which broughtwealth and prosperity to the community. By themid-1800s, Manchester was the second largestcity in England and gained a reputation as acenter of invention and technological progress.In 1781 a prestigious scientific institution wasfounded-the Literary and PhilosophicalSociety (commonly known as the "Lit. andPhil.").' In this society John Dalton(1766-1844),' who arrived in Manchester in1793, formulated his atomic theory at the turnof the century.' At the very same platform'where Dalton proposed his idea of atoms andatomic masses (Figures 1, 2), Ernest Rutherfordone century later first proposed the nuclearatom, a dense positive core surrounded by elec-trons.'

Ernest Rutherford had arrived in 1907 fromMcGill University, Montreal, Canada."' At theUniversity of Manchester (then named theVictoria University of Manchester) he assem-bled a powerful team of gifted individualsincluding an Oxford graduate named HenryGwyn-Jeffreys Moseley (1887-1915), whojoined the group in 1910. During 1913-14Moseley published two papers which estab-lished the physical basis of the atomic numberand resolved several long-standing problems

(continued on page 44)

Figure 1. This was the Literary and Philosophicalbuilding at 36 George Street in Manchester built in1799 which served the scientific community for 140years before being destroyed in a German bombingraid in December 1940. Here the main nieetings ofthe Lit. and Phil. were conducted, including the cen-tury-apart presentations of Dalton's atomic theoryand Rutherfoni's nuclear atom.

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Figure 3. Right: Moseley's X-ray plots ("Moseley's law") establishing thevalidity of atomic number, N, as published in "High Frequency Spectra of theElements, Part II"." This plot is displayed in the Moseley Room of LindemannHall (physics building) of Oxford University. The ordinate is atomic numberN, with elements identified, ranging from aluminum to gold; the abscissa isthe square root of the X-ray frequency. The upper series of the plots are L-lines; the lower are K-lines. The elements included are Al, Si, Cl, K, Ca, Ti, VCr, Mn, Fe, Co, Ni, Cu, Zn, Y, Nb, Mo, Ru, Rh, Pd, Ag, Sn, Sb, La, Ce, Pr, Nd,Sm, Eu, Gd, Ho, Er, Ta, W, Os, Ir, Pt, Au. Expansion at left: Notice the confu-sion of elements 70, 71, 72, misidentified by Moseley as "thulium II,""ytter-bium,"and "lutetium"; these were not corrected until he analyzed Urbain'ssamples (in May 1914; see text) and until hafnium (72) wasdiscovered in Copenhagen (in 1923).

Figure 5. Oxford, England.

ASHMOLEAN MUSEUM OF ART AND ARCHEOLOGY, Beaumont Street-N510 45.31 W01 15.00.

MUSEUM OF THE HISTORY OF SCIENCE, displays of Moseley and others,Broad Street- N510 45.26 W010 15.33.

ROBERT BOYLE, site of original house, High Street, plaque- N510 45.16 W010

15.15.

FRANCIS BACON, site of original home, Old Greyfriars Street, plaque- N510

45.01 W010 15.64.

MUSEUM OF NATURAL HISTORY, several statues and Lewis Carroll exhibit,Parks Road- N510 45.51 W010 15.36.

TOWNSEND HALL (Electrical Building), Physics Department, laboratory ofMoseley, Parks Road- N51T 45.56 W01 15.39.

LINDEMANN HALL, Physics Department, Moseley Room with originalapparatus and memorabilia, Parks Road- N51 45.59 W010 15.41.

Figure 4. Manchester, England landmarks, including those not only for Rutherford and Moseley, but also Dalton and Roscoe (discussed inprevious HEXAGON articles'):

OWENS COLLEGE (now a barrister's office building), whereRoscoe first prepared metallic vanadium, N53 28.72 W02 15.12.

OWENS COLLEGE OW " LIT. a PHI TOWN HALL, marble statues of Dalton and Joule, Ford Maddox', Brown's famous mural paintings portraying the history of

oo/ MUSEUM OF SCENCEo Manchester, including one of Dalton collecting marsh gas; AlbertAND INDUSTR F Square-N530 28.77 W020 14.66.

6 RR STATION LIT. & PHIL. (Literary and Philosophical Society), destroyed inv WWII raid (December 1940); now Devonshire House, 36 George

cnin a Street, blue plaque- N53 28.76 W02 14.38.

MANCHESTER METROPOLITAN UNIVERSITY, site of DaltonUNIVE RSIT\ ctsn bronze statue, Chester Street- N53 28.32 W02 14.44.

UNIVERSITY OF MANCHESTER: [OLD] COUPLAND 1BUILDING (now called Rutherford Building), site of Rutherford'sand Moseley's pioneering studies, Coupland Street- N53 27.96

- . W020 14.08.

400 m - UNIVERSITY OF MANCHESTER: COURTYARD, University ofRUTHERFORD BLDG Manchester, WWI tribute to Moseley- N53 27.93 W02 14.05.

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concerning the Periodic Table. With Moseley'sdiscoveries one could now establish the correctordering of elements and predict specificallywhich ones were yet to be discovered.

Henry Moseley came from a distinguishedscientific family. His paternal grandfather hadbeen a famous mathematician and physicist atKing's College, and his maternal grandfathertrained as a barrister but later pursued his loveof conchology (mollusks). His father (who diedin 1891) was a professor of biology at OxfordUniversity; he was part of the scientific staff ofthe H. M. S. Challenger oceanographic expedi-tion of 1872-1876. The young Henry (who wasknown as "Harry" by his friends) attended the

famous Eton College and then Trinity Collegeat Oxford where in 1910 he received his M.A.degree.-

A natural experimenter, Harry wanted to dooriginal research. Impressed with the superiorphysics program at Manchester, he joinedRutherford's group after graduating fromOxford. Moseley was assigned a problem inradioactivity, but he was intrigued by the newphenomenon of X-rays (discovered by WilhelmRintgen in 1895).' In July of 1912 it was dis-covered by William Lawrence Bragg(1890-1971) that X-rays generated a diffractionpattern when passed through a crystal:Moseley traveled to Leeds to the laboratory ofWilliam Henry Bragg (1862-1942) to learn theart of X-ray analysis (father William Henry andson William Lawrence received the Nobel Prizein 1915 for X-ray spectroscopy). Back inManchester, Henry Moseley and CharlesGalton Darwin (1887-1962; a grandson of thefamous Charles Robert Darwin 1809-1882) ini-tiated an X-ray investigation of metals, wherethey investigated the behavior of reflected X-rays from crystal surfaces.-

Meanwhile, Moseley had independently for-mulated a new research idea. In 1906 CharlesGlover Barkla (1877-1944) had discovered thata metal target when bombarded by electronswould emit homogenous X-rays characteristicof the metal; he had observed two series andnamed them K-lines ("hard" radiation) and L-lines ("soft" radiation)" (these are now knownto arise from electrons falling to vacancies inthe lowest two atomic electronic levels, logical-ly named the K and L shells). Moseley decidedhe would explore the possibility of relating thefrequency of these emitted X-rays to a physicalproperty of the element. These physical para-meters-which we know were discussed dur-ing a conversation of Moseley, Darwin, Bohr,and Hevesy in June 1913 at Manchester" -might include some function of A (atomicmass) or of Z (nuclear charge). These parame-ters of A and Z had been developed on thebasis of the famous alpha particle scatteringexperiments at Manchester of Rutherford and

Figure 6. The Rutheriford Building in Manchester This was the original plnsics building opened in 1960.known at first as the Schuster Building and then as the Coupland I Building. Here Rutherford assembledhis distinguished team of nuclear pioneers. A plaque on the building reads: "Ernest Rutherford... led thislaboratory 1907-1919-Herein discovered the nuclear atom, split the atom, and initiated the field ofclear physics."

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Ernest Marsden (1889-1979), the original basisfor Rutherford's nuclear atom."' The scatteringexperiments suggested"' that, at least for thelowest elements of the Periodic Table, Z = A/2.

An amateur Dutch scientist, Anton van denBroek (1870-1926), had proposed that an ele-ment's position in the Periodic Table might

Figure 7. The Roll ofHonor and the WorldWar I Memorial in thecourtyard of WhitworthHall. In the center isinscribed: "To the mem-bers of the University ofManchester and of theOfficers Training Corpswho laid down their livesin the Great War of1914-1919. In gratefuland enduring remem-brance. He has broughthis etenity witha little hour and is notdead."Moseley was amember of the RoyalEngineers.Inset at bottom: 'Moseley's entn/.

reflect this "intra-atomic charge" of Z." Broekproposed definite values for Z (he preferred thenotation M, for "Mendeleev's number") forselected elements through uranium," calculat-ed by the use of formulas he contrived whileemploying assumed (but incorrect) pre-Bohrelectronic configurations. Broek actually put

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I mare . lownsend I Iall, where Moseley performed his research in Oxford. This building presentli lies100 i north of the Museum of Natural History which includes specimens of a dodo, a flamingo, and othercreatures which inspired the creatures in Lewis Carroll's (Charles Lutwidge Dodgson 1832-1898) Alice inWonderland. Townsend Hall was originally known as the Electrical Science Building, built in 1910, just intime for Moseley to continue his X-ray studies in 1913. It is, unfortunately, not known which laboratoryinside the building he used. Next door (north) is Lindemann Hall (not shown) with the Moseley LectureHall with a small display on Moseley (see Figure 3). This photograph was taken in 2001; in 2007 a plaquewas mounted by the door (see next figure).

forward correct values through 50, but then fellinto error for the heavier elements, e.g., W = 78,Au = 83, U = 96 (instead of correct 74, 79, 92,respectively). But before Moseley's work, noone knew how to get at an independent mea-sure of this intra-atomic charge.

Moseley's goal was specific: "My work wasundertaken for the express purpose of testingBroek's hypothesis..."" Moseley had gained areputation of perhaps being the only one toequal Rutherford's hard work, drive, andresults; and by the fall of 1913 he had obtainedthe K-line spectra of the series calcium (20)through zinc (30) (excepting the scarce elementscandium, 21). Accurate measurements werepossible because of the preparatory collabora-tive work with Darwin. The calcium-zinc seriesincluded the perplexing pair nickel and cobalt:nickel had a lower atomic mass, but its chemi-cal behavior more closely resembled the higherfamily including palladium and platinum.Moseley's results were dramatic and simple,which he described in an article entitled "TheHigh Frequency Spectra of the Elements.""Hefound that the frequency v of K-alpha (thestrongest line) was accurately described by theequation v/v,) = 3/4 (N-1)2, where vo was theRydberg frequency (previously developed inspectroscopic studies) and N was a numbertermed "the atomic number" by Moseley (andperhaps jointly with Rutherford)." The 3/4coefficient was recognized by Moseley as the

1/1' - 1/22 term already observed in Rydbergexpressions, and the"1"in the (N - 1) term wasrapidly identified as the shielding effect of innerelectrons." Moseley pointed out that his workclearly established that indeed nickel had ahigher atomic number than cobalt. The confi-dent Moseley unequivocally stated: "We havehere a proof that there is in the atom a funda-mental quantity, which increases by regularsteps as we pass from one element to thenext. The quantity can only be the charge onthe central positive nucleus, of the existenceof which we already have definite proof.""Moseley went on to predict: "It [the correla-tion of X-ray spectra with N] may even lead tothe discovery of missing elements, as it will bepossible to predict the position of their char-acteristic lines....

The next step in Moseley's research was toproduce the X-ray spectra of the higher ele-ments. But Moseley performed no more workat Manchester. In November of 1913, after writ-ing his seminal paper,'" Moseley returned toOxford. It is apparent that he was homesick for"The City of Dreaming Spires" with its morescholarly atmosphere, and he wished to becloser to his widowed mother" and the oppor-tunities of the countryside where he had spentmany pleasant years pursuing bird-nest collect-ing and other hobbies.' A letter to his motherfrom Manchester gives an insight to his feel-ings: "Today the fog is so thick, that I shall

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iFigure 9. Royal Society of Chemistrn (RSC)plaque mounted at entrance of Townsend Hall.The Clarendon Laboratory of physics encompassesTownsend and Lindemann Halls. Courtesy, JimWilliamson, Emeritus, Atmospheric, Oceanicand Planetary Physics, University of Oxford.

probably get lost on my way to the College; ittastes acrid and tickles the throat... . Mondaythe fog was thinner but more yellow. Sunday itpoured all day...." Also, he was apparentlyuneasy in the less formal industrial culture andmixed student body of Manchester, perhaps"feeling himself above students, even equalwith Rutherford, whose tea-time conversationof slang, banter, and wisecracks he judged moresuitable to a caricature of a colonial rather thana professor of physics."" Whatever the reasons,the motivation to return to Oxford was strong,because he departed Manchester immediatelyupon finishing his work, even though noappointment awaited him in Oxford.

Once settled in Oxford, Moseley was givenaccess to a laboratory in the Electrical ScienceBuilding (physics building), and by privatemeans he assembled equipment to continue hisresearch (his X-ray tube had been broken and anew one needed to be constructed). By April of1914, he had gathered data from additionallower elements using K-lines as well as higherelements using L-lines. The equation for the L-alpha lines was v/vo = 5/36 (N-7.4)', where 5/36was recognized as the Rydberg expression 1/22-1/32 and 7.4 was an electron shielding factor. Inall he was able to establish unambiguously Zvalues for 38 elements in a range from alu-minum (13) to gold (79) (Figure 3) which hepresented in his second paper,"High FrequencySpectra of the Elements, Part II."" Again, hisplot clarified the situation of "odd pairs"-lighter potassium had a higher atomic numberthan argon, and lighter iodine had a higheratomic number than tellurium (the iodine-tel-

lurium problem had existed since 1871, whenMendeleev reversed tellurium and iodine inaccordance with their chemical properties; heresolved the difficulty by assuming the atomicmass determined for tellurium was incorrect!).Furthermore, Moseley's plot removed confu-sion with the lighter rare earths 57-68 (but not69-71; see caption to Figure 3). And lastly, hisatomic numbers unequivocally identified thelocation of the true gaps where elements wereyet to be discovered. Moseley did not analyzeelements beyond gold (79) but two years laterthe Swedish physicist Karl Manne GeorgSiegbahn (1886-1978; Nobel Laureate 1924)determined"' that uranium lay at the high endof the natural elements with atomic number 92,establishing the prediction that future elementswould be discovered with N =43, 61, 75, 85, and87 (Tc, Pm, Re, At, and Fr, respectively).

Georges Urbain (1872-1938), a rare-earthchemist in Paris and one of the co-discoverersof lutetium, heard of Moseley's remarkabletechnique and visited him in May of 1914. Oneof Urbain's goals was to verify his tentative dis-covery of a new rare earth "celtium." He was"flabbergasted""' that his samples were ana-lyzed in one session- the samples which hadtotally occupied his attention with his laboriouscrystallization schemes for many years.Moseley's X-ray analysis removed confusionregarding the heavier rare earths (see Figure3)- but no trace of c.eltium was found, andgaps remained at 61 (promethium) and 72(hafnium). Urbain returned to France disap-pointed but amazed at the power of Moselev'stechnique.

Urbain's analyses were the last laboratorywork Moseley performed. During the summerof 1914 he traveled to Canada, the U.S., and toAustralia, where he attended the annual meet-ing of the British Association. When World WarI broke out in August, Moseley returned toEngland and was determined to enlist, despitethe fact that he could have served as a non-combatant.' He was commissioned in the RoyalEngineers and was shipped to the Dardanellesin June 1915. At the tragic Battle of Gallipoli inTurkey, he was killed August 10, 1915.

Rediscovering Moseley. The two cities whichcan (and do!) claim credit for Moseley's discov-eries, Manchester and Oxford, have their mapspresented in Figures 4 and 5. In the map forManchester are also included locations relatingto John Dalton and Henry Enfield Roscoe(1813-1915) (respectively discussed in previousHEXAGON articles2. The site of Rutherford'slaboratory (Figure 6) was originally the physicsbuilding Coupland I, now called the RutherfordBuilding, located at the present University ofManchester. The Rutherford Building is nowused by the Department of Psychology, but

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Figure 10. X-tube used by Aosely in Oxtbrd, constructed tho nuc the one he used at M1anu ester hadben broken (on exhibit in the Lindemann Hall Moselei Room).

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Figure 11. 1 his is the classic plhotograph of Aloseley in 1910, in the Balliol--Trinity laboratories during hisearlier stay at Oxford, before he went to Manchester. Moseley was a brilliant experimenter and customarilydesigned and prepared his own equipment. He once wrote to his mother while at Manchester: "Remakingthe apparatus took a long time, as the laboratory assistant spent his time mending Rutherford's motorcar,and I had to make everything myself",

present plans include developing an exhibit onRutherford there. At the main Courtyard at theUniversity of Manchester is the World War Imemorial which includes the name of Moseley(Figure 7). At Oxford Moseley performed hisresearch at the Townsend Hall (physics build-ing) (Figure 8). A tribute was erected to him andposted on this building in 2007 (Figure 9). Anexhibit at the adjoining Lindemann Hall(physics building) Moseley Room, as well ascollections at the Ashmolean Science Museum

in Oxford, include a large portion of Moseley'sequipment and apparatus he used in his stud-ies (Figures 3, 10).

Moseley's Legacy. It is difficult to overestimatethe importance of Moseley's work (Figure 11).In two papers he interlaced physics and chem-istry, and put Rutherford's atom on a firm foot-ing acceptable to all scientists. In a personalinterview in 1962, Niels Bohr explained: "Yousee actually the Rutherford work [the nuclear

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atom] was not taken seriously.... There was nomention of it in any place. The great changecame from Moseley." When Urbain had visitedMoseley in May of 1914, Moseley was aston-ished to find that Urbain did not care to under-stand the origin of the X-ray K- and L-lines.Urbain had not the slightest curiosity of whyMoseley's law worked. Moseley marveled,"Where we try to find models or analogies, they[Continental scientists] are quite content withlaws." But soon it became apparent that thewell-known British need for "the robust formand vivid colouring of a physical illustration"-was perfect for the times-and it was Moseley'sdiscoveries that persuaded the Continental sci-entists that the "childish British" atomic mod-els' were in fact real.

Moseley performed his famous work on hislaw of atomic numbers during a period of abouteight months. There is little doubt that if he hadlived, he would have become a Nobel laureatebefore the other members of Rutherford'steam-Soddy, Hahn, Bohr, Hevesy." WithMoseley's passing, both sides of the Great Warmourned. Asimov remarked, "In view of whathe might have accomplished (he was only 27when he died), his death might well have beenthe most costly single death of the war tomankind generally." Moseley's death prompt-ed Rutherford and others to convince the pub-lic and the British Ministry of Defence that sci-entists should be preserved in wartime sincethey are an asset not only to the public at largebut to the military.

But beyond this, Moseley's death representsso much more. Mustafa Kemal Atatirk(1881-1938), Turkish leader at the Battle ofGallipoli and founder and first president (1923)of the Republic of Turkey," lamented the futilityof war-his words are inscribed on the AnzacCove Memorial (N40 14.32 E26 16.62), over-looking the main staging area in the GallipoliCampaign:" "Those heroes that shed theirblood and lost their lives.... You are now lyingin the soil of a friendly country. Therefore rest inpeace. There is no difference between theJohnnies and the Mehmets to us where they lieside by side here in this country of ours.... You,the mothers, who sent their sons from far awaycountries wipe away your tears. Your sons arenow lying in our bosom and are in peace. Afterhaving lost their lives on this land they havebecome our sons as well." Atatrk's evocativewords truly apply to Henry Moseley. Of the ca.130,000 Allied and Turkish personnel who per-ished in this campaign April 25, 1915-January9, 1916-an attempt of the Allies to control theDardanelles straits leading to Istanbul(Constantinople)2'"-virtually all are buried onthe Gallipoli peninsula, and a major portion ofthese lie in unidentified graves, including, as faras anyone knows, Moseley. Henry Moseley's

name is memorialized by the inscription on theHelles Memorial (N40 02.81 E26 10.68) at thesouthernmost tip of the Gallipoli Peninsula, 23km south of the Anzac Cove Memorial'

ReferenCes.1. R. H. Kargon, Science in Victorian Manchester,

1977, Johns Hopkins University Press,Baltimore, Maryland, 2-10.

2. J. L. Marshall and V. R. Marshall,The HEXAGON of Alpha Chi Sigma, (a)2006, 97(4), 50-55; (b) 2007, 98(2), 23-29;(c) 2008, 99(3), 42-46; (d) 2010, 101(2),22-26.

3. John Dalton, A New System of ChemicalPhilosopln, 18o8, Manchester.

4. Personal communication, Allan Jefferies,Administrator, Lit. & Phil. Soc.,Manchester.

5. E. Rutherford, Proc. Man. Lit. Phil. Soc.,1911, 55, xviii-xx.

6. J. L. Heilbron, Historical Studies in theTheory of Atomic Structure, 1981, ArnoPress, (a)"The Work of H. G. J. Moseley,"229-364; (b) "The Scattering of a and RParticles and Rutherford's Atom,"84-145.

7. J. L. Heilbron, H. G. J. Moseley. The Life andLetters of an English Physicist, 1887-1915,1974, University of California Press.

8. W. L. Bragg, Proc. Cambridge. Phil. Soc.,1913, 17, 43-57; Nature, 1912, 90, 410.

9. C. G. Barkla, Phil. Mag., 1906, 11, 812-828.

10. J. L. Heilbron, Ernest Rutherford and theExplosion of Atoms, 2003, OxfordUniversity Press.

11. A. van den Broek, Nature, 1911, 87, 78;1913, 92, 372-373; 1913, 92, 476-478.

12. H. Moseley, Nature, 1913, 92, 554 [receivedJan. 5, 1914].,

13. H. G. J. Moseley, Phil. Mag., 1913, 26,1025-1034.

14. E. Rutherford, Nature, 1913, 92, 423.

15. H. G. J. Moseley, Phil. Mag., 1914, 27,703-713.

16. M. Siegbahn and E. Friman, Phil. Mag.,1916, 31, 403-406.

17. I. Asimov, Asimov's Biographical Encyclopediaof Science and Technolog,1964, Doubleday& Company, 512-513.

18. A. Mango, Atatiirk, 2000, Overlook Press,Woodstock, N.Y.

19. B. States, Return to Gallipoli, 2006,Cambridge Univ. Press, Cambridge UK.

20. E. W. Bush, Gallipoli, 1975, St. Martin'sPress, N.Y.

21. Records of the Commonwealth War GravesCommission, http://www.czogc.org/.

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/01111 Iand Ji1 Am -a ll

RediscoveringThe Periodic Table,One Element at a ine

Shortly after getting married 12 year'sago, Jim Marshall, a chemistry professorat the University of North Texas, took hisnew bride Jenny, a now-retired middleschool computer teacher, on the honey-moon of a lifetime. Together, they set outin search of the birthplace of each of the114 elements on the periodic table.They've finally completed their journeyand compiled a comprehensiveinteractive DVD called"Rediscoveryof the Elements."

"Rediscovery of theElements" featured onPRI's "Here and Now"

There is a wonderful segment of PRI's"Here and Now" that ran on September8, 2010, featuring an interview with Jimand Jenny Marshall, creators and authorsof the popular "Rediscovery of theElements" series. http://www.hereandnow.org/2010/09/rundown-98-2/

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