Bull. Hist. Chem., VOLUME 25, Number 2 (2000) 103
STEFANIE HOROVITZ, ELLEN GLEDITSCH, ADA HITCHINS, AND THE DISCOVERY OF ISOTOPES
M r l n . n r C nh nd G ffr W. n r C nh , S r W lfr d Gr nf l C ll
In th nt f d v r pr , n t nd t f r f 860 (4 . h h t r n l t d th n th "Gr t " nd n r th r r h r h th v th t th f nd t n f h tr d p nd d d th t l d v r r ntr b t d n f ntl p n th n v l f th t ht f h l t th d v r . h f r t d t t n f p l r a nt— nd n th t b l t f th l nt th l x pl h b rv t n d b r d lv . t t d nt, l n rn ll, b t t h r p rv r, h f r t r n th f ç d f tr d t n l h Anth n h, h r v d th b l r z f r th tr th th d v r f r d t v tr n f r d v r ( . In th f r t d d f th 20th nt r , t n ( . h v r p n th d n th l f ttr b t n t th l b b n h r r h r h r d nt f d b n l n d t th t f th p r nt. h d n f nt ff t f h d n th ntr b t n f r x pl , th r d d t th r I, t n nt t , f r f r bl t br thr h th r II, t r d th r , t th r , nd th " l l n " nd tt n r n t n pr r n. At th t , h f th p b l v d t r h r . b n nd n l nt. It M C nd At n n r h r n n n 0 h pr v d d th n xt p n th p zzl th t t pl d t v th h b rd n t r l (2 ( th th t t nt th t (6 : th x pt n f M r C r nd M tn r . r Our experiments tr n l nd t th t r d th r x pl , Ern t th rf rd f r t r r h t nt nt r l n p r bl fr th r b h l pr n— rr t r . W h v r p rt d l h r . n h r r r, n l d n th d v r f th r l f Ex pl f h ll n n p r bl p r ( nd r p th r d t v t ( . In th p p r, th f ll b f r d t v l nt b n t l t v r r p n th ntr b t n f thr n t th rl r dl . th r th n th b r phr r d l n t p : St f n r v tz, Ell n Gl d t h, nd Ad nt h ll n n p r bl , S dd t d th t t h n . But first, it is necessary to r v th r nd th t r t p b ntr d d ( . r th t d th d v r f th x t n f t p p bl . It th j n S dd Gr p pl nt th t pr v d d th n xt t p n th p zzl (8 . In r d Background t v d , l f n p rt l r lt d n t t p h ft t th l ft n th p r d t bl th n p n r nt d nt t t nd t f r t th t, f r th rl n t ht l f f r n t , h l l f b t h t r f h tr , t ht f pr p rt l r lt d n n t p h ft t th r ht th p rt n . r x pl , th v l f th t ht n l bl h n n t ht. St rt n th th f l nt th pr f f th K rl r h C n t f r n nd th r , S dd l
104 Bull. Hist. Chem., VOLUME 25, Number 2 (2000)
lated the expected atomic weights of the lead produced j n n r l z d th t th t [ f pr t from their respective radioactive decay as very differ- ht d t r n t n] r r d h r th t ent from the 207.2 of 'normal' lead (9). To chemists, nl th r lt f r n z d xp rt ld b d l finding samples of lead that had 'abnormal' atomic pt d. S dd p r t d n h ff rt , nl t h v weight would be a confirmation of the existence of iso- h r lt v d pt ll n rt r . topes and proof of the group displacement law. In par- h world's leading expert on the measurement of ticular, lead from the decay of uranium-238 was pre- atomic weights was Theodore William Richards of dicted to have an atomic weight of about 206 while that Harvard (13), but almost as high in estimation were his from the decay of thorium-232 was expected to have an two former students, Gregory Paul Baxter, also of Harvard, and Otto Hönigschmid at the Radium Institut in Vienna (14).
St f n r v tz
Hönigschmid had the talent and also the opportu- nity, for the major source of radioactive ores at the time was the mine at St. Joachimstal in Austria (15). Much of his work was accomplished with his research student, Stefanie Horovitz. Horovitz was born in Warsaw on April 17, 1887, her family moving to Vienna about 1890 (16). She graduated from the University of Vienna in 1914 with a doctorate in organic chemistry, although she seems to have started as a research worker at the Radium Institute of Vienna with Hönigschmid in late 1913. Hönigschmid was actually affiliated with the Technical University of Prague from 1911 to 1918, but he maintained research facilities in Vienna. Horovitz's initial task was the time-consuming separation of lead from the residues of the radioactive ores after the radium had been extracted. This was fol- lowed by the demanding gravimetric procedures to the Éll n Gl d t h, r d t n ph t , 02. ( . Kr nn n nearest hundred thousandth of a gram. The first report nd A. C. pp by Hönigschmid and Horovitz provided a value of 206.736 for the atomic weight of lead from the St. Joachimstal mine, compared to 207.190 for 'normal' lead atomic weight of about 208. It is the contributions of (17). Such a significant difference from a respected three women scientists to the discovery of lead with 'ab- analytical laboratory was the first definitive evidence normal' atomic weights that will be the focus of this that atomic weights were not necessarily invariant. As study (10). a result of its importance, this paper by Hönigschmid To accomplish this task, researchers needed lead- and Horovitz was chosen by Henry Leicester as one of containing samples from uranium or thorium ores. In the crucial publications in chemistry in the first half of addition, for the results to be accepted among the scien- the twentieth century (18). The two researchers were tific community, the researchers themselves had to have dedicated to their work, as is apparent in a letter from credibility in the field of the determination of atomic Hönigschmid to Lise Meitner (19): weights to high precision. Although Soddy and his col- ... Miss Horovitz and I r d l l . On th laborator, Henry Hyman, and Maurice Curie, nephew b t f l S nd r t ll tt n n th l b r t r of Marie Curie, both reported atomic weights of radio- t 6 l . active-origin lead that were significantly different from Subsequently, Hönigschmid and Horovitz analyzed new that of normal lead (11), neither of these reports was samples from St. Joachimstal as well as samples from sufficiently reliable in the eyes of analytical chemists. two other mines: pitchblende from German East Africa; As Badash has commented (12): and bröggerite from Norway. These results were even Bull. Hist. Chem., VOLUME 25, Number 2 (2000) 105
more convincing, giving values as low as 206.046 (20). firmly fixed ideas concerning the chemical elements A difference of over one mass unit could not be explained and their mutual relations, as well as the nature of by experimental error. There clearly were significant atoms. differences in the atomic weight of lead, depending upon His first report described lead samples with abnormally source. low atomic weights, the lowest value of 206.40 coming from a sample of uraninite from North Carolina (26). Hönigschmid and Horovitz made a second contri- This particular lead sample was noted in the data table bution to the isotope story. Boltwood had claimed the as being provided by Gleditsch. This was Dr. Ellen discovery of another radioactive element, ionium (21). Gleditsch, who at the time was working with Bertram Most chemists accepted the existence of this element, it Boltwood at Yale. In the paper, Richards stated that this even being assigned a symbol, Io. However, it was the "most valuable" of atomic weight the samples had and spectro- been supplied by scopic analyses Gleditsch as lead performed by chloride; thus Hönigschmid Gleditsch played an and Horovitz that active role in the showed ionium discovery process to be no more by performing the than an isotope extraction of a pure of thorium, mak- lead salt from the ing thorium only uranium ore. In a the second ele- subsequent paper ment for which (27) Richards re- isotopic behavior ported atomic had been proven weights of 206.12 at that time (22). and 206.08 for lead These were the from uranium ore last publications samples obtained of Horovitz. from Norway. He Many years later, added that these two Horovitz's fate samples "of especial was discussed in Gleditsch, with her assistants Ernst Fyn (left) and Ruth Bakken (right), in the value and signifi- an exchange of Chemistry Laboratory, Oslo, ca 1930 (T. Kronnen and A. C. Pappas) cance (27)" were letters between both obtained from Kasimir Fajans and Elizabeth Róna (23). In the last of Ellen Gleditsch, who had returned, by then, to her na- the correspondence, Fajans commented (24): tive country of Norway. These values were so close to You probably have not received any information from that predicted by Soddy for pure lead produced at the Vienna about the fate of Dr. Stephanie Horovitz. I end of the uranium decay series that the group displace- learned about it from a mutual relative at Warzawa. ment law could no longer be in doubt. Stephanie moved there after World War I and after her parents had died in Vienna to join her married Gleditsch was born on December 29, 1879 in sister. She was not active in chemistry and both were Mandal, in southern Norway (28). After obtaining a liquidated by the Nazis in 1940. pharmacological qualification, she became a research assistant at the University of Kristiania (now Oslo), be- Ellen Gleditsch ing unable to afford to enroll as a university student. From 1907 to 1912, she worked with Marie Curie in Concurrently the master himself, T. W. Richards, had Paris, where she received the qualification of Licenciée launched an investigation into what he called a subject es Sciences. In 1913, Gleditsch received a fellowship of (25): to work with Bertram Boltwood at Yale (29). Although peculiar and extraordinary interest, because it in- he was opposed to women researchers, Gleditsch arrived volves a readjustment and enlargement of many rather before he had a chance to reject her application. Her 106 Bull. Hist. Chem., VOLUME 25, Number 2 (2000)
work on the half-life of radium (30) so impressed her sister, Liv Gleditsch (35). The results showed that, Boltwood that he became a warm friend. While at Yale, unlike lead, the average atomic weight of chlorine was she received an invitation from Richards to visit him at invariant with the mineral source. Gleditsch maintained Harvard, and it was possibly during the meeting that an active life, becoming president of the International she agreed to supply the lead samples that proved most Federation of University Women, and during World War crucial. About this time, she was awarded an honorary II, being an active member of the resistance. She died Doctor of Science degree from Smith College, at the age of 89 on June 5, 1968. Northampton, Massachusetts. Gleditsch was to have a very successful career at Ada Hitchins the University of Oslo, being hired initially as a docent The search for the higher atomic weight value of lead and, by the time she retired, becoming a professor of derived from thorium-232 decay was pursued by chemistry. She spent most of her nonteaching time in ön h d Paris. For ex- ( 6 nd b ample, during Soddy. Soddy, in World War I, Curie the report of his pleaded with definitive result Gleditsch to return of 207.74, noted to Paris to super- the contribution vise the radium ex- of his research traction facilities. student, Ada This journey in- Hitchins, for the volved a danger- separation and ous voyage across analysis work the U-boat ridden (37). The sample North Sea; and used by Ernest Rutherford, Hönigschmid was a friend of provided by Gleditsch, ar- Soddy (37); thus ranged for a secu- both teams prob- rity clearance for ably relied on her stopover in Hitchins' extrac- England on the tions. Born in De- way. Her teaching von, England (38) demands at Oslo in 1891, Hitchins were very heavy, graduated with a leaving little time B.Sc. from th for research. She C n r n d t v t , Oxf rd, 2, Gl d t h rr nd d b Irèn University of did manage some, l t C r (l ft nd r tz n th nd M r r t r (r ht . Glasgow in 1913. however, particu- ( . Kr nn n nd A. C. pp She commenced larly during her many sojourns in Paris (31). Following research with Soddy during her last undergraduate r Richards' work, she reported on the atomic weight of and when Soddy moved to the University of Aberdeen lead in another mineral sample from Norway, this one in 1915, Hitchins accompanied him, obtaining a posi- giving a value of 206.17 (32). Then she commenced tion as Carnegie Research Scholar. It was during this work on a study of the atomic weight of chlorine. Irène period that Hitchins performed the extraction and ana- Curie had claimed to find a salt sample in which the lytical work on the lead samples from thorium ores. In atomic weight of chlorine was above the normal value addition, Hitchins took over the research on protactinium (33). Gleditsch and coworker B. Samdahl showed that of Soddy's other student, John Cranston, when the lat- the value resulted from a contamination with bromide ter was drafted for World War I (39). ion (34). Nevertheless, Gleditsch pursued a more thor- ough study of possible variations in the atomic weight In 1916 Hitchins herself was drafted to work in the of chlorine, some of the research being performed with Admiralty Steel Analysis laboratories (40). She rejoined
Bull. Hist. Chem., VOLUME 25, Number 2 (2000) 107
S dd n 2 , b h h t h h d v d t Oxf rd 5. See, for example: A. Romer, "The Transformation Un v r t . p t b l r z n Ch tr , S dd Theory of Radioactivity," r , 1958, 49, 3-12. h d r t d ff lt n ttr t n r d t t d nt t 6. H. N. McCoy and W. H. Ross, "The Specific Radioac- r th h (4 th t h n pl d r l r l tivity of Thorium and the Variation of the Activity with Chemical Treatment and with Time," n S dd r r h pr r . In t ll pp nt d t h . A . Ch . S ., 1907, 2 , 1709-1718. n l t nt, h pr t d t pr v t r r h 7. It is from the placement of different species in the same t nt n 22. S dd n t d (42 : box in the periodic table that t p — 'same place' ... she has also charge of my radioactive materials — derives. The origin of the name is described by ... and has worked up considerable quantities of ra- Alexander Fleck: "Up to 1913 we used the phrase 'ra- dioactive residues and other materials for general . dio elements chemically non-separable' and at that time t h n f n ll l ft S dd pl n 2 , v n the word isotope was suggested in a drawing-room dis- cussion with Dr. Margaret Todd in the home of Soddy's t K n th h r f l . h r h r d G v father-in-law, Sir George Beilby. Dr. Todd was an rn nt A r nd Ch t n th M n n nd G Édinburgh trained medical doctor and was a writer of l l p rt nt f th C l n l G v rn nt nt l some distinction under the name of Graham Travers. The h r t r d n 46 nd r t rn d t En l nd. At readiness and etymological accuracy with which she p nt, l t n l f , h rr d f r r, hn produced isotopes is a standing testimony to her practi- St ph n . Sh d d n r t l n n r 4, 2. cal knowledge of the Greek tongue." A. Fleck, "Frederick Soddy," r. M . ll . S ., 1957, Commentary , 208. 8. L. Badash, "The Suicidal Success of Radiochemistry," r. . t. S ., 1979, 2, 245-256. S nt f r r h n th rl d d f th 20th n 9. 'Natural' lead has an isotopic composition of Pb-204 t r nl r rd d l pr rv , x pt ( . % , Pb-206 (23.6%), Pb-207 (22.6%), and Pb-208 f r th t f M r C r . r , thr n nt t (52.3%). h v b n d nt f d h pl d n f nt r l n th 10. A more general survey has been given by G. B. d v r f th x t n f t p , n f th t Kauffman, "The Atomic Weight of Lead of Radioactive r l nt f f nd n f th p r d. In n r h n Origin," . Ch . Ed ., 1982, , 3-8 and 119-123. n nt t r l r l nf n d t pp rt r l 11. F. Soddy and H. Hyman, "The Atomic Weight of Lead (4 , t p rt nt t rr t th h t r l r rd nd from Ceylon Thorite," . Ch . S ., 1914, 0 , 1402- n l d th ntr b t n f r v tz, Gl d t h, 1408; M. Curie, "Sur les &arts de poids atomiques obtenus avec le plomb provenant de divers minéraux," nd t h n . C. . bd. Sé n A d. S ., S r. C, 1914, 8, 1676- 1679. 12. Ref. 8, p 251. 13. G. S. Forbes, "Investigations of Atomic Weights by REFERENCES AND NOTES Theodore William Richards," . Ch . Ed ., 1932, , 453-458; and H. Gay, "The Chemical Philosophy of 1. N. Wade, "Discovery of Pulsars: A Graduate's Story," Theodore W. Richards," A b x, 1997, 44, 19-38. S n , 1975, 8 , 358-364. 14. E. Zintl, "Otto Hönigschmid zum 60. Geburtstag," 2. It is noteworthy to recall that Marie Curie was a lecturer . An r . All . Ch ., 8, 2 6, 3-11; R. É. Oesper, "Otto at the teaching college at Sèvres, her ability to do re- Hönigschmid," . Ch . Ed ., 1941, 562; and L. search being primarily a result of her egalitarian mar- 8, Birckenbach, "Otto Hönigschmid 1878-1945: In Memo- riage to Pierre. She emerged from Pierre's shadow only riam," Ch . , ., 1949, 82, 9-65. following Pierre's untimely death, when she was judged 15. F. A. Paneth, "St. Joachimstal and the History of the to be his only suitable heir at the Sorbonne. See, for Chemical Elements," in H. Dingle and G. R. Martin, example: R. Pflaum, Gr nd Ob n: M d C r Éd., Ch tr nd nd: A S l t n fr th Wr t nd r W rld, Doubleday, New York, 1991 and S. n f th t r f r .A. n th, Interscience, New Quinn, M r C r : A f , Simon & Schuster, New York, 1964, 20-28. York, 1995. 16. M. F. Rayner-Canham and G. W. Rayner-Canham, "Ste- 3. M. F. Rayner-Canham and G. W. Rayner-Canham, fanie Horovitz: A Crucial Role in the Discovery of Iso- rr t r n r l r S nt t, McGill- topes," in M. F. Rayner-Canham and G. W. Rayner- Queen's University Press, Montreal, 1992. Canham, Ed., A v t n t th r S n : n r 4. C. de Milt, "The Congress at Karlsruhe," J. Ch . Ed ., W n f d t v t , Chemical Heritage Foundation, 1951, 28, 421-425; and A. J. Ihde, "The Karlsruhe Con- Philadelphia, PA, and McGill-Queen's University Press, gress: A Centennial Retrospect," . Ch . Ed ., 1961, Montreal, 1997, 192-195. 8, 83-86. 108 Bull. Hist. Chem., VOLUME 25, Number 2 (2000)
. O. ön h d nd St. r v tz, "S r l p d t 2. E. Gl d t h, . lt n, nd O. W. r , " t r n d pl b d l p hbl nd ," C. R. Hebd. Séances Acad. t n d p d t d l n t p d pl b Sci., Ser. C, 4, 158, 6 8 nd O. ön h d d l l v t d A t A d r, rvè " J. Chim. Phys., nd St. r v tz, "Üb r d At ht d 2 , 22, 2 26 . Ur nbl , " Monats. Chem., 4, 35, 60. . I. C r , "S r l p d t d hl r d n l 8. . M. t r, Ed., Source Book in Chemistry 1900- n r x," C. R. Hebd. Séances Acad. Sci., Ser C, 2 , 1950, rv rd Un v r t r , C br d , MA, 68, 172, 02 8. 82 84. 4. É. Gl d t h nd . S d hl, "S r l p d t d . Ott ön h d t M tn r, n 2 , 4, hl r d n n n r l n n, l p t t d l ," C. M tn r C ll t n, Ch r h ll C ll , C br d Un R. Hebd. Séances Acad. Sci., Ser. C, 22, 174, 46 8. v r t . . E. Gl d t h, "S r l p d t d hl r ," J. Chim. 20. O. ön h d nd St. r v tz, "Üb r d Phys., 24, 21, 4 6 460 nd É. Gl d t h nd . At ht d Ur nbl II," Monats. Chem., , Gl d t h, "C ntr b t n l t d d t p . S r l 36, 80. p d t d hl r d n l l d p t 2 . . . lt d, "On I n , d A t v El d l ," J. Chim. Phys., 2 , 24, 2 8 244. nt," Am. J. Sci., 08, 25, 6 8 . 6. O. ön h d, "Üb r d h r bl ," . 22. O. ön h d nd St. r v tz, " r K nntn d Electrochem., , 23, 6 6 . At ht d l n ," Monats. Chem., 6, , . . S dd , " h At W ht f h r d," 0 4 ibid., " v n d At ht d Nature, 6 , 98, 46 . It t pr b bl th t h r . An l d h r br d ," Monats. t h n d d t f th t l b n h r S dd h d Chem., 6, 37, 4 . S d n n: . d h, h v t h n l d nd h br l d h lf n n Radioactivity in America: Growth and Decay of a Sci- v r t p l t . S : K. . , " r d r S dd : h ence, hn p n Un v r t r , lt r , Ab rd n Int rl d ," Ab rd n Univ. Rev., , 48, 2 M , , 20 . 48. 2 . M. . n r C nh nd G. W. n r C nh , 8. M. . n r C nh nd G. W. n r C nh , "Ad "El z b th ón : h l n W n," n f. 6, t h n : r h A t nt t r d r S dd ," n f. pp 20 2 6. 6, pp 2 . 24. K r j n t Él z b th ón , A t , 6 , . . S dd nd . A. Cr n t n, " h r nt f A t n ," ntl t r l br r , Un v r t f M h n, Ann Proc. R. Soc., rt A, 8, 94, 8 40 . h p p r n t : Arb r, MI. "... th xp r nt r nt n d f r t b M 2 . . W. h rd , " h r bl f d t v d," Ad t h n ... r v l bl t n h ntr b Science, , 59, . t d v r t r ll t th d f n t n f th n l 26. . W. h rd nd M. E. b rt, " h At W ht n th t t h b n p bl t rr v t." f d f d t v Or n," J. Am. Chem. Soc., 4, 40. M. . n r C nh nd G. W. n r C nh , " rít 36, 2 44. h W n Ch t nd th r t W rld W r," Bull. 2 . . W. h rd nd C. W d rth, " rth r St d f Hist. Chem., , 23, 20 2 . th At W ht f d f d t v Or n," J. 4 . A. . Cr h n , "S dd t Oxf rd," Br. J. Hist. Sci., Am. Chem. Soc., 6, 38, 26 2622. h rd l , 12, 2 288. n l d d th " ndn " f Gl d t h n ppl n 42. . S dd , nd t d r f r n f r A. . . t h n , Ox th l d pl f r d n t d t r n t n n th p n f rd Un v r t Ar h v . n p r r ph f: W. h rd nd C. W d rth, 4 . M. . n r C nh nd G. W. n r C nh , " n t f d d fr r r n Cl v t ," "W n ld f Ch tr : 00 20," .1. Chem. J. Am. Chem. Soc., 6, 38, 6 8 660. Educ., 6, , 6 8 nd M. . n r C nh nd 28. A M. W. K b n nd G. . Grz r , "Ell n Gl d t h: G.W. n r C nh , "W n n Ch tr : rt r f r nd n t," n f. 6, pp . p t n d r n th rl nt th C nt r ," J. Chem. 2 . Gl d t h h d pr b bl d v l p d d r t r th Educ., 6, 73, 20 20 . lt d b f h r rl r t d n th r t f r n nd r d n r n h h lt d r r h xt n v l t d. S : E. Gl d t h, "S r l r pp rt ntr l r n t l r d d n l n r x ABOUT THE AUTHORS t f ," Le Radium, , 8, 2 6 2 . 0. E. Gl d t h, " h f f d ," Am. J. Sci., 6, Marelene F. Rayner-Canham is a Laboratory Instructor 41,112-24. in Physics at Sir Wilfred Grenfell College, Memorial . On v t t r n 20, h n d th t f University, Corner Brook, Newfoundland, Canada A2H p rv n f th C r r r h r p h l M r 6P9, while Geoffrey W. Rayner-Canham is Professor of C r t r n S th A r . Chemistry at the same institution.