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An ion exchange separation of the rare earths from naturally occurring materials with a view to the isolation… Perkins, Harold Jackson 1953

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AN ION EXCHANGE SEPARATION OP THE RARE EARTHS PROM NATURALLY OCCURRING MATERIALS WITH A VIEW TO THE ISOLATION OF ELEMENT NUMBER 61 by HAROLD JACKSON PERKINS A THESIS SUBMITTED IN PARTIAL FULFILMENT OP THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n the Department of Chemistry We accept t h i s thesis as conforming to the standard"required from candidates for the degree of MASTER OP SCIENCE. Members of the Department of THE UNIVERSITY OF BRITISH COLUMBIA October, 1955 i i ABSTRACT The extraction of the Rare Earths from two kilograms of Lindsay Light and Chemical Company's "monazite residues" (hydrated Rare Earth oxides), from two kilograms of Norwegian gadolinite, a nd from five kilograms of Lindsay's "didymium carbonate" (Code Ijll) gave a mixture of Rare Earths which, after purification, fractional crystallisation as the double magnesium nitrates and ion exchange separation, showed some evidence for the existence of naturally occurring element number 61 0 This evidence took the form of unexplained lines i n the arc spectra, anomalous absorption bands, aid an unexplained peak i n the elution curve obtained from the ion exchange work© The evidence presented i s far from conclusive and the suggestion i s made that further research along these lines be carried out 0 i ACKNOWJEDGMENT S The writer wishes to extend his most sincere thanks to Dr. J. Allen Harris, under whose supervision this research was carried outo Dr. Harris unfailing interest, advice, and encouragement were a continued source of inspiration. The xwiter wishes-also to thank Dr e J.G. Hooley for obtaining the Lindsay Didymium Carbonate used in this research and for much helpful advice concerning the radiochemical aspects of the problem. The writer i s indebted to many of the graduate and undergraduate students of the Department of Chemistry of the University of Br i t i s h Columbia for their much-appreciated assistance during the more trying periods of the ion exchange work© Grateful acknowledgment i s hereby made of the invaluable advice offered by Dr. C.G. Woodbridge aid Dr. N. Tomlinson of the Division of Chemistry, Department of Agriculture, Science Service, Summerland, British Columbia, during the preparation of the manuscripto TABLE OF CONTENTS ACKNOWLEDGMENTS ABSTRACT INTRODUCTION A. Historical B. The Project APPAMTUS AND MATERIALS A v Apparatus B« Materials EXPERIMENTS A> Extraction of the Rare Earths I Monaaite Residues II Gadolinite III Lindsay Didymium Carbonate B. Fractional Crystallisation C. Ion Exchange Separation I Theory of Ion Exchange II Preparation of the Column III The ELuting Solution IV Recovery and Analysis of Rare V Procedure ' RESULTS AND DISCUSSION Figure 1 Table I REFERENCES Page i i i 1 6 7 9 10 12 13 l l * 16 18 19 20 20 to follow page 22 to follow Fige 1 26 APPENDIX 29 PLATES I to XI 32 to U2 1 AN ION EXCHANGE SEPARATION OF THE RARE EARTHS FROM NATURALLY OCCURRING MATERIALS WITH A VIEW TO THE ISOLATION OF ELEMENT NUMBER 6l e INTRODUCTION A. Historical* The problem of the existence of naturally occurring element number 61 is one which has been the subject of great controversy since 191U when Moseley's work on X-ray spectra (30,31) proved that an element of atomic number 61 should exist between samarium (element 62) and neo-dymium (element 60) e The history of this problem is complex and will be briefly presented in this section in order that the following in-vestigation may be better understood© At the time of Moseley's work it was generally conceded that the missing element 6 1 , i f it existed at allin nature, would be a typical member of the Rare Earth series. The first announcement of the discovery of this element was made in 1926 by Harris, Hopkins, and Tntema (9,10, lip 12, 13, 1kg 15, 56) working at the University of Illinois* Theseworkersj starting withai extract of monazite sands, a Rare Earth phosphate, fractionally crystallised the Rare Earths as the double magnesium nitrates and as the Rare Earth bromates. They based their claim to the dis-covery of a new element on the following evidence* (1) The presence of lines in the arc spectra of these salts which were c orambn to both the purest available neodymium and samarium and some-what stronger in intermediate fractions containing these elements. There 2 were 130 lines i n the red and infra-red and fiv e lines toward the blue© (2) The presence in the intermediate fractions of absorption bands which became stronger as the characteristic bands of neodymium and sam-arium became weaker© (3) The presence of lines i n the X-ray emission spectrum of the above materials which corresponded closely to the theoretical positions for Lot and 1^ of element 61 • The wave-lengths of these lines deviated from the wave-lengths calculated from Siegbahn's precision values (1*2) by 0«00i|0 A. This deviation was said to have been well within the limits of their experimental error. On the basis of the foregoing evidence, Harris et a l . proposed that the new element be named "illinium" i n honour of the state and the uni-versity, i n which the work was carried out. Within three months of the publication of these results, Rolla and Fernandes at the University of Florence announced (38 , 39 , U0) that they had obtained evidence of the existence of a new element in a small quantity of didymium material which had been fractionally crystallised as the double thallium sulphate. They claimed to have recorded the X-ray ab-sorption spectrum of the K-series and deposited their results i n a sealed packet at the Academy of Lincei i n l°2 l *« They had not published their results previously as they were continuing work along these lines with the hope of obtaining a larger quantity of material* They proposed the name "florentium u for element 61 i n honbur of their university© The Committee on Nomenclature of the International Union of Chemistry decided that the work at I l l i n o i s was both started f i r s t and published 3 fir s t and so element 61 was officially named illiniurao In the same year, J.M. Cork, working with splendid X-ray equipment at the University of Michigan, gave unmistakable evidence (5) of the pre-sence of element 61 in carefully purified heodymium concentrates prepared by James and Fogg at the University of New Hampshireo This evidence took the form of the publication of a l l of the twenty K-series lines of illinium. Further confirmation of the existence of naturally occurring element 61 came from Berlin at the same time when Meyer, Schumacher, and Kotowski obtained (28) the K-series lines of illinium in material which had been fractionated as the double magnesium nitrates and as the bromates* The presence of these lines was confirmed by Dehlinger, Glocker, and Kaupp (7)* Seven years later, Urbain at the Sorbonne in Paris announced to the French Academy of Science (5U) that illinium had been isolated by Maurice Curie and M» Takvorian of the Radium Institute of Paris* It was with the announcement of this discovery that the fi r s t suggestion that illinium might be radioactive was put forth* Curie, Urbain stated, had noted that the radiation produced by the element consisted of feeble beta particles* Many unsuccessful attempts to repeat the above work led Prandtl of Munich to conclude (33, 3U, 35, 36) that,element 61 did not exist in nature* Prandtl stated that the element-, in question was probably not even a Rare Earth element but a homologue of manganese* His views were supported by von Welsbach (55)« Further controversy was introduced by Herzfinkiel who stated in a review article (16) that the evidence sub-mitted by the Illinois workers was insufficient to warrant their claim to discoverye The next significant development in the history of element 61 did not occur until Law, Pool, Kurbatov, and Quill published a series of papers between 1938 and 19ii3 (19 , 20 , 2 1 , 22) in which -they claimed to have prepared a r t i f i c i a l element 61 in a cyclotron at Ohio State Uni-versity* An isotope of the element was produced as a result of the bomb-ardment of praseodymium with alpha particles.- These results were con-firmed by other workers (Si) as was the formation of a 12©5 hour activity on bombardment of radioactive Nd^^ with deuterons* It was presumed that the latter transformation occurred by beta decay* On the basis of these results, Pool and Quill proposed that the name of the element be changed to "cyclonium,,o More recently, i t was noted during the course of the work on the Manhatten Project in the United States that numerous isotopes of the Rare Earths wer$ being formed in the atomic piles at Oak Ridge, Tennessee^ The identification of these usually radioactive isotopes was materially aided by the work of Marinsky aid Glendenin (26) who adapted ion exchange methods to the separation of trace amounts of the isotopes* First among the radioactive isotopes of element 61 definitely to be identified was a soft-beta-emitting activity with a half-life of 3-7 years and to which was assigned the mass number lU? ( 1 , 2 , 3 , 8 , k3f hh). Similarly, isotopes corresponding to mass numbers of 1U8 and 1U9 have been isolated (32 , 18)* The 1U8 isotope was formed by irradiating 6 1^7 rabh slow neutrons in the Clinton Pile. The half-life was 5«3 days and the act-ivity was composed of a beta particle of approximately 2*5 million elec-tron volts energy and a gamma ray of approximately 0.8 Mev energy. On the basis of this very strong evidence, Marinsky proposed that the name ,,promethium,, be substituted for illinium. The former was formally adopted at the 19!j.° meeting of the International Union of Chemistry (17) • The main argument set forth at the meeting in favour of changing the name of the element was that, according to Mattauch's empirical rule (25) concerning the stability of neighbouring isobars, it is impossible for element 61 to have any stable isotopes. (Mattauch's rule is formulated from examination of the pattern of occurrence of the known stable pu-clides and requires that pairs of neighbouring elements have no stable isobars. In the mass number region lUO to 152 where element 61 might be expected to have a stable isotope, all of the mass numbers are occupied" by stable isotopes of either samarium or neodymium. Hence, no isotope of element 61 can have a. stable nucleus without violating this rule. Radioactive isotopes of element 61 have been definitely assigned mass numbers of lh7} lU8, and lh9» These are all so beta-active with half-lives so short as to preclude their independent existence in nature. I l l 7 The longest lived of these isotopes i f 61 with a half-life of 3.7. years. Other isotopes warranting consideration are those of masses lh3, Ihh, lhS> 1^ 6, 15>0 and 151. Using the Bohr-Wheeler theory, Ballou calculated (k) the beta disintegration energies for each of these and showed that all those except lU5 should be unstable by at least one million electron volts to beta decay or its equivalent. For mass number \hSf the theory indicated essentially no energy difference between neo-dymium lU5 and sixty-one lU5« Consequently, Ballou concludes that i f element 61 exists in nature it is probably the isotope.jof mass number lk$* Experimentally, Libby (23, 2h) found weak beta radiations in neo-dymium. These were soft beta particle s of a bout 11 Kev energy. No harder radiations were found with them and the possibility was suggested that Nd^ 5^ is beta-active, forming element 61 as a disintegration pro-duct. This latter may be a long-lived alpha-emitter. It is noted by Ballou (U) that alpha activity is not unlikely here as samarium and several other members of the Rare Earth group are known to be alpha-activeo The samarium half-life corresponds tol x years. Cuer and Lattes re-ported (6) the observation of a penetrating alpha radiation in samples of neodymium and samarium* These workers believed that this radiation, i f not due to polonium, may be associated with an isotope of element 6lo However, Ballou found (U), after repeated separations of samarium from element 61 tracer, that no appreciable amount of the alpha activity in samarium could be due to an isotope of element 61. It is apparent from the foregoing, that the question of the exist-ence of element 61 in nature has not yet been satisifactorily answered© In an attempt to solve this problem, the following investigation was undertaken. B. The Project The problem resolved itself into two sections** I. The separation of latge amounts of Rare Earth materials into their constituents, and II. Analysis of the material so obtained for traces of any impurity which might be considered as due to the presence of a new elemento It was decided that the most efficient way of dealing with the 7 former would be the fractional crystallisation of a large amount of mater-ial as double magnesium nitrates until rich samarium-neodymium fractions had been built up and then the separation of these fractions on an ion exchange column. Preliminary fractional crystallisations were deemed necessary since a large mixed fraction, relatively free of other Rare Earths, can be built up in a minimum of time using this method© The latter part would be carried out making use of both the emission and ab-sorption spectra of the material so obtained© APPARATUS AND MATERIALS A. APPar&tuso I. Spectrophotometer© The intensities of the Rare Earth absorption bands were measured using a Beckman quartz spectrophotometer, Model DU, Serial Number 321+6© Absorption measurements were made through matched silica cells with opt-. o ical light paths of 10000 cm© For measurements below 3500A. a hydrogen discharge lamp was used, while a tungsten source was used for readings o higher than 3^00 A. The method of analysis followed was that of Moeller and Brantley (29)© It was found necessary to introduce one modification in the method, namely, the solution of the Rare Earth chlorides in 1©5N hydrochloric acid instead of distilled water as recommended by these authors. The Rare Earth chlorides were found to hydrolyse very readily in water unless the acid concentration was maintained at 1.5N© The cell containing the sol-vent blank was filled with 1©5N hydrochloric acid. 8 II Spectrographs* 1» For photographs of the Rare Earth absorption spectra, a Hilger Model D-72 constant deviation wave-length spectrometer was used. The serial numbers are as follows© Spectrometer D773Q1 Camera D72302 27200 , 29211 The l i g h t source was a tungsten arc ("Fointolite"),. Reference lines were obtained by means of a direct current iron arc. The spectra were recorded on Eastman Kodak Panchromatic plates Type M, negative size 3 j " x 1*J»© These plates were found to be of extremely high contrast when processed as described below* 2. For photographs of the Rare Earth emission spectra, a Hilger Model E medium quartz spectrograph was used. The manufacturer1 s descrip-tion of the instrument i s : Size EU98 Serial Number EU98.306 1*9683 The source of excitation was provided by either direct current copper or "graphite arcs. The graphite rods were obtained from Central Scien-t i f i c Company and were of their highest purity. The copper rods were supplied by Johnson, Matthey, and Mallory, England. Their analysis (laboratory control number 2035) showed the presence of minute amounts of silver, nickel, calcium, magnesium, manganese, iron, and lead as impuri-tiese The negative size for the medium quartz spectrograph was either 2" x 10" or kn x 10" • Eastman Kodak spectroscopic plates, Types II F-2, II F-3, and 103 a-0 were used to record the spectra. ' 9 A l l measurements using this instrument were made under the following standarized conditions. (a) Direct current arc operating at 110 volts and 7 amperes, with an arc gap of 3 mm0 (b) S l i t height U mm» (c) S l i t width 0o02 mm. (d) Exposure time 20 secondso (e) Developer - Kodak D-19 forfour minutes* (f) Short Stop - Kodak SB-1 for 30 seconds© (g) Fixer - Kodak acid fixer F-5 for l£ minutes. B. Materialse A l l chemical s used i n this investigation were of analytical reagent grade quality unless otherwise statedo It may be noted that technical grade oxalic acid was used for pre-cipitating the Rare Earth oxalates. Spectroscopic analysis.showed that no elements capable of interfering with either the separations or the analyses were present. The Rare Earth materials used in this investigation were obtained from three sources. The f i r s t was Lindsay Light and Chemical Company, Chicago, I l l i n o i s , hydrated: oxides. This material consists of hydrated oxides of the Cerium group earths from which most of the cerium and thorium has been commercially extracted. These oxides had their origin i n Indian monazite and were-part of the same material from which Harris et aL. f i r s t isolated i l l i n i u m 0 10 The second was Norwegian gadolinite, a ferrous beryllium yttrium s i l i c a t e corresponding roughly to the formula 2BeOoFeO.Y203.2Si02. The third was c ommercial "didymium carbonate", Code I4II, supplied by Lindsay Light and Chemical Companyo Spectrophotometry analysis showed this to consist mainly of praseodymium, neodymium, aid samarium, together with small amounts of the other Rare Earths© The methods used to extract each of the above materials willbe dis— cussed i n thenext section. EXPERIMENTAL A. Extraction of the Rare Earths. I Monaaite residues (Lindsay hydrated oxides) These were treated i n porcelain evaporating dishes with four l i t r e s of technical hydrochloric acid per kHgram of sample. The mixture was digested for two and one-half hours at 73>-80°C. and allowed to cool over-night. The supernatant solution was removed and a further four l i t r e s of acid added per kilogram of residue. The residue was then extracted at the same temperature for two hours. This process was repeated twice more to ensure complete extraction of the Rare Earths. Two kilograms of material were treated in this manner. After four hydrochloric acid ex-tracjsdons, the residue was washed with hot water containing a small anount of hydrochloric acid and the washings were combined with the f i l t r a t e s from the acid treatments. The extract was dark red-brown i n colour. The residue was examined for completeness of extraction by photographing i t s emission spectrum© The results showed that only one or two percent of Rare Earths were s t i l l contained i n the residue* H L The combined f i l t r a t e s from the acid treatments wereevaporated on the steam bath to about one-half the original volume, pa r t i a l l y neutral-ised with 50% sodium hydroxidesolution, and the pH adjusted to 6 with 6N sodium hydroxide* The colour of the solution changed from amber to yellow. During the ini t i a l stages of the precipitation, the pH was not allowed to f &1 below 6 . If the pH was allowed to become too high, heavy red hydroxides were precipitated. To the slightly acid solution, 250 ml* of saturated oxalic acid were added* Solid oxalic acid was then added in excess* The mixture was digested om a hot plate for one hour, and the heavy white Rare Earth oxalates were f i l t e r e d off* It should be noted here that the Rare Earth oxalates, although relatively insoluble i n dilute mineral acids, would not precipitate from 3N hydrochloric acid. If the pH was allowed to f a l l below 6 , the yield of Rare Earths was very poor* It was for this reason that the sodium hydroxide neutralisation was necessaryo The oxalates, after digestion, were f i l t e r e d through Whatman No* 5 f i l t e r piper with suction, washed with 2% oxalic acid solution, and dried overnight at 111°C« They were almost pure white in colour* The dried oxalates were then ignited i n an electric muffle furnace at a temperature of °00°Cfor four hours. The oxides were chocolate brown i n colour and, from two kilograms of hydrated oxides originally extracted, U32 grams were obtained. Subsequent analysis of the original material for total Rare Earth content showed that the extraction was 9$% efficient i n f a i r agreement with the results obtained by analysis of the residue* These oxides were purified by solution i n dilute hydrochloric acid, 12 by r e - p r e c i p i t a t i o n with oxalic acid, and by r e - i g n i t i o n . The p u r i f i e d oxides showed a decided radioactivity,, Spectrographs analysis showed that the oxides consisted p r i n c i p a l l y of Cerium group earths together with a samll amount of the Yttrium group elements. The Yttrium group earths were separated from the Cerium group earths using the double si3phate p r e c i p i t a t i o n method of Schoeller and Powell (I4I)© This separation was necessary t o s i m p l i f y the ion exchange work which i s described later© Since element 61, i f present, w i l l appear i n the middle of the Cerium group, i t i s reasonable t o assume that i t w i l l behave i n a si m i l a r manner to the other l i g h t earths when undergoing a double sulphate separation* Further to f a c i l i t a t e the subsequent ion exchange work, the cerium was removed from the Rare Earths as follows© The oxides of the cerium group elements were dissolved i n d i l u t e hydrochloric acid and made just a l k a l i n e with d i l u t e aimioniae Three percent hydrogen peroxide was then added and the yellow eerie hydroxide f i l t e r e d off© This procedure was repeated u n t i l the precipitate showed no yellow colour© I I '.. Gadolinifre© The extraction of the Rare Earths from gadolinite proved to be a more complex task than that from monazite© One complicating factor was the fact that the ore was radioactive and, as a consequence, great care had to be exercised i n handling it© Two kilograms of gadolinite were treated with concentrated hydrochloric acid i n the same manner as for the monazite residues© Again, four extractions with acid were made© The 13 amber-coloured f i l t r a t e was pa r t i a l l y neutralised with $0% sodium hydroxide and while the solution was s t i l l very strongly acid, a voluminous brown-black gritty precipitate was thrown down. The mixture was neutralised and made strongly alkaline with caustic soda and the precipitate f i l t e r e d off with suction through Whatman No© 50 f i l t e r paper. The f i l t r a t e was colourless ai d spectrographs analysis indicated that the only metal s present were beryllium and aluminum. The precipitate was dissolved i n 6N hydrochloric acid and the solution" diluted with water to about twenty times i t s original volume. Addition of saturated oxalic acid, followed by a very large excess of solid oxalic acid gave a voluminous pink pre-cipitate of Rare Earth oxalates. The oxalates were washed, dried at 110°C. overnight, and ignited i n the muffle furnace at °00°C. for four hours© The purified Rare Earth oxides were then subjected to a double sulphate separation as outlined i n the preceding section, followed by removal of cerium. At this pointy the anount of cerium-free, Cerium group oxides was very small since most of the oxides consisted of members of the Yttrium group, and cerium comprised the greater part of the lighter earths which were present. The f i n a l product from this treatment was combined with the cerium-free, Cerium group Rare Earths obtained from the monazite extraction© III Lindsay Didymium Carbonate (Code Ull)«> Lindsay Light and ChemicaL Company's Didymium Carbonate was particu*» l a r l y useful to these studies in that spectrophotometric analysis i n d i -cated that i t contained praseodymium, neodymium, lanthanum, samarium, and only small amounts of gadolinium and other members of the Yttrium groupo lit The total Rare Earth content was 60.8#» The extraction of the Rare Earths from this material was a relatively simple matter. Five kilograms of didymium carbonate were dissolved in sufficient UN hydrochloric acid to give a clear, faintly acid solution* The solution of the material was accompanied by the evolution of a large volume of carbon dioxide* Upon dilution with water to five times the original volume, and addition of the excess oxalic acid, a heavy, pink, crystalline precipitate of Rare Earth oxalates separated from the solution* Digestion for one hour on a hot plate gave a readily filterable mixture* The oxalates were dried and ignited to oxides in the muffle furnace* The oxides were purified in the usual manner© Bo Fractional Crystallisation of the Rare Earth  Double Magnesium Nitrates* The final products from the sections above were combined and i n t i -mately mixed together* The Rare Earth double magnesium nitrates were pre-pared by dissolving 6 7 6 gm* of this mixture in dilute nitric acid and ad-ding 1 2 3 gm. of anhydrous, chemically pure, magnesium oxide. Dilute nitric acid was added until a clear solution was obtained on heating* These quantites were used assuming the ration 3Mg0.2R203*2ljH20 aid assuming an average atomic weight for the Rare Earths of ll£« The method of fractional crystalisation used was as follows* The nitric acid solution was evaporated over a hot plate until a few crystals formed aid, on cooling, the mixture consisted mostly of crystals with only a small anount of mother liquor* The mother liquor was decanted into an-other large evaporating dish, and the crystal dissolved in water con-taining a small anount of nitric acid* The process of evaporation 15 aad decaa tation was repeated three times, the mother liquor being added to the same large evaporating dish each time* The combined mother liquors were designated as Fraction 2, and the crystals were designated Fraction 1» Fraction 3 was b u i l t up by processing Fraction 2 in a similar manner to Fraction 1 except that after pouring the supernatant from Fraction 2 into a dish which was to contain Fraction 3, the crystals from Fraction 2L were dissolved in mother liquor from Fraction 1» In this manner, fractions were bu i l t up, each mother liquor being poured into the next dish before the crystals were dissolved i n mother liquor from the preceding fraction 0 A new fraction was started after six such pourings had been made, with the exception of the f i r s t three fractions which were started after only three pourings-in order to f a c i l i t a t e handling* When a fraction becaue too small for convenient handling, normally after fifteen pourings, i t was removed from the series and set aside for analysis* In this manner, the le ss soluble salts were c oncentrated to-wards the beginning, and the more soluble salts towards the end, of the series* As the fractional crystal l i s a t i o n proceeded, decided differences i n colour were noted from fraction to fraction* Further, as the lighter elements were concentrated at the beginning of the series, the crystals showed an increasing tendency to hydrclyse and the acidity had to be maintained at a high level* In some cases, particularly the lanthanum-r i c h fractions, i t was necessary to resort to the use of 30% hydrogen peroxide to ensure solution of the crystalse Three such series of double magnesium nitrates were bu i l t up and IS designated respectively Series P, P-A, and P-B© The progress of each of the three series was f oilowed by making use of the absorption spectra of the saturated solutions© When the separation had proceeded to the stage where some fractions containing 90% pure or better neodymium and some containing samarium of the same purity had been obtained in each of the three series, fractionation was discontinued© Several hundred pourings were made in aLl© The fractions intermediate between the relatively pure neodymium aid samarium fractions were combined and converted to the chlorides i n pre-paration for the separation of the mixture on the ion exchange column© The emission and absorption spectra of a l l other fractions were photographed for comparison purposes© C» Ion exchaige separation of the Rare Earth chlorides© I. Theory of ion exchange© The fundamental principle on which an ion exchange separation i s based i s the adsorption of the ions to be separated on a column of ion exchange resin followed by elution with a suitable reagent© The resins used for this adsorption are ionic solids i n which one of the ionic species i s a highly cross-linked, polymeric, high-molecular-weight non-diffusible ion whose multivalent charge i s balanced by relatively small diffusible ions of the opposite charge© When a solution containing certain cations i s brought into contact with the resin, the cations of the solution are exchanged for the cations which were originally held by the resin© In most cases, the resin gives up hydrogen ions and adsorbs the cations from the solution i n question© Once a cation has been adsorbed by the resin 17 there are only two ways in which i t cai be freed. It can be replaced with another cation whose a f f i n i t y for the resin i s greater than that of the originally adsorbed ion, or another ion can be introduced whose concen-tration i n the solution phase i s greater than that of the originally ad-sorbed ion© One of the most effective means of reducing the concentration of an ion i s to introduce a complexing agent. If the pH i s suitably ad-justed, competition i s set up for the cations to be separated between the complex and the active centres of the resin. In the case of Rare Earth separations, the complexing agent used i s a c i t r i c acid-ammonium citrate buffer. Briefly, what happens when the elutjbng solution i s passed through the c olumn i s as f ollowse When the buffer solution, at a pH which w i l l barely support the formation of a complex ion, i s introduced into the column, ammonium ions in the solution exchange withtthe Rare Earth ions adsorbed on the top fex* centimetres of the resin bed. This exchange causes the pH to be altered and, as a con-sequence, the Rare Earth citrate complex breaks down and the Rare Earth ions are re-adsorbed a l i t t l e farther down the column. When sufficient Rare Earth ions have been re-adsorbed to bring the pH back to i t s original value (that i s , a pH at which the complex i s stable), then these begin once again to be desorbed. Hence, as the eluting solution i s passed through the column, the Rare Earth ions are being continuously adsorbed and desorbed as they travel down the column. Since the equilibrium con-stats for the Rare Earth citrate complexes vary slightly among the d i f -ferent members of the group, their rates of travel down the column d i f f e r sufficiently so as to lead to their separation into bandse The most efficient column length i s , of course, that length at which 18 the baids are just completely developed. At shorter lengths* separation willnot be complete, while at longer lengths no further separation can be attained (1+5, 1+6, 1+7, 1+8, 1+9, 50, 51, 52, 53). The repated cycles i n the column effectively replace the thousands of operations required by the older methods for separating the Rare Earths. The efficiency of the separation i s dependent on many factors such as column length, column diameter, resin particle size, pH of the eluting solution, concentration of the eluting solution, flow rate, the weight of material to be separated, and the temperature at which the separation i s carried out* The preceding description of the theory of ion exchange i s purely qualitative for, i n the words of Spedding (1+8) "*.sThe exact mechanism by which this (separation) occurs i s very complex*.*. We have spectrophoto-metric evidence... that there are at least four c i t r a t e complexes involved. ..» II. Preparation of the ion exchange column* The ion exchange resin selected for this investigation was Dowex 50, a synthetic cation exchange resin with a cross-linked (9%) aromatic hy-drocarbon chain (divinylbenzene) containing nuclear sulphonic acid groups as the only active group*- It i s a strongly acidic resin with a rapid rate of exchange combined with a high capacity of about 5*0 milliequivalents per gram* The column, constructed of Pyrex glass tubing of 6*0 cm* internal diameter was closed at the bottom with a plug of glass wool* The glass wool was supported on a metal disk sealed to the glass tube* A small glass tube passed through the metal disk* A piece of rubber tubing attached to 19 the small tube and a screw clamp served as an effective means of adjusting the flow ratea This arrangement was found to give very steady flow rates© The eluting solution was stored i n 18 l i t r e carboys which were f i t t e d with a constant head device to ensure a constant flow rate regardless of the- height of the l i q u i d i n the bottles The Dowex 50, which was screened to uniform mesh size 20, was slurried into the column with water u n t i l the bed height was 78 cm. In order to ensure uniformity of particle distribution and to inhibit channelling, the column was backwashed with water th i r t y times© The resin was c onverted to the hydrogen cycle by passing 36 l i t r e s of h% hydrochloric acid through the column at a very slow flow rates, The excess acid was then removed from the column by passing through d i s t i l l e d water u n t i l the eluate gave no test for chloride ions with silver nitrate© A\bout 92 l i t r e s of water were used in 31, III. The eluting solution. The eluant, designated as 0ol% c i t r i c acid contained originally 1.10 gm0 of c i t r i c acid monohydrate per l i t r e and 1.0 gm. of phenol per litre© The solution was adjusted to a pH of 6©00-.02 with concentrated ammonium hydroxide. The phenol was added to prevent the growth of mould i n the co-lumn (US) but i n spite of this precaution a small amount of an unidentified mould was observed to be growing at the top of the resin bed after about six weeks of continuous operation. This growth did not appear to have any effect on the separation or on the behaviour of the column as a whole a l -though a longer period of operation might have resulted i n the plugging 20 of the bed by the mycelia© IV. Recovery and Analysis of the Rare Earths© The RareEarths were recovered from the eluate as oxalates and i g -nited to the exides for weighing*, The oxalates were precipitated by ad-ding excess solid oxalic acid to the eluate and digesting on a hot plate for one-half hour. The oxides were obtained by igniting the dried Rare Earth oxalates i n a muffle furnace at 900°C. The various fractions were aialysed on the Model E and on the Model D72 Hilger spectrographs* Ab-sorpotion measurements were invariably taken i n a 1©5N hydrochloric acid solution of the respective chloride. V. Procedure© Sixtythre'e- grams of the mixed Rare Earth chlorides, obtained as described previously, were dissolved i n k l i t r e s of 1©!?N hydrochloric acid aid were poured slowly into the top of the column© The reason for using a slow flow rate and a dilute Rare Earth solution was to ensure the adsorption of the Rare Earth elements on the top few centimetres of the resin bed© D i s t i l l e d water wasthen passed through the column until the eluate gave no test for chloride ions with silver nitrate© The eluting solution was passed through the column at a constant linear flow rate of 0.60 cm© per minute. Fractions of £00 were col-lected with the aid of an automatic fraction cutter© The time for col-lecting one fraction at this flow rate was one-half hour® The breakthrough volume (that i s , the volume of eluant which must be passed through the column before Rare Earths can be detected i n the eluate) 21 was calculated by means of Spedding's formula (52 )s Vw= A ** b Tifcere, = breakthrough volume in l i t r e s , A = exchange capacity of the resin bed i n milliequivalents, b = milliequivalents of Rare Earth adsorbed on the resin bed, and -Cjjjj-f- _ milliequivalents of ammonium ion per l i t r e of eluant© The calculated breakthrough volume was 2°2 litres© The observed breakthrough came at 296 l i t r e s . This close agreement with the theoreti-cal indicates that the column was operating at a high efficiency, for examination of the preceding formula reveals that the calculation assumes 100$ conversion of the resin to the anmonium cycle. This conversion can only be attained i f the effects of channelling are almost non-existent© The pH of the eluate was checked constantly throughout the run i n order to determine the point at which a new Rare Earth would appearo The pH at breakthrough was 3©50 and at the end of the run was 5©80. The absorption spectrum of every f i f t h fraction was both photographed and observed visually, the lat t e r with the aid of the telescope attachment for the constant deviation wave-length spectrometer. The emission spectrum of every second fraction was photographed using the medium quartz spectro-graph. The fractions which occurred in the overlap portions of the elution curve were analysed spectrophotometrically i n order to determine the shape of the leading and t r a i l i n g edges of the bands. RESULTS AND DISCUSSION The separation of the Rare Earth mixture with the ion exchange column 22 was very efficient, the bands being sharply defined with steep leading and t r a i l i n g edges© Examination of the elution curve (Fig© 1) and of the accompanying Table (Table I) shows that the bands in no case overlapped by more than six l i t r e s of eluate, that i s to say, the mixed fractions did not exceed twelve in number for any two adjacent Rare Earth elements© The total recovery of Rare Earths was 39 gm« as oxides© This re-presents a recovery-efficiency of 93%* Of the amount recovered, approxi-mately three grams of the oxides were heavy earths (gadolinium, europium), twelve grams were spectroscopically pure samarium, fifteen grams were spectroscopically pure neodymium, and six grams were spectroscopically pure praseodymium© The remaining three grams of material were made up of mixed fractions from the overlapping portions of the elution curve© The term "spectroscopically pure" as used here implies a purity greater than 99*9999%» The pure oxides showed colours characteristic of each element© The neodymium oxide was pale l i l a c blue, the samarium oxide was pale yellow, and the praseodymium oxide was dark brown, almost black© Since the equilibrium constants for the Rare Earth citrate complexes are such that the heavier ions move down the ion exchange faster than the lighter ones, the order of appearance of the elements in the eluate should bes (1) Heavy Earths (as gadolinium, europium) (2) Samarium (3) Element 61 (?) (k) Neodymium (5) Praseodymium (6) Lighter Earths (as cerium, lanthanum)8 0> QL E I IO O CM tr o 6 z o o 2801— 240 200 — 160 — 120 — Sm Nd 1 310 325 340 355 370 385 VOLUME OF E L U A T E — litres Pr 4Q0 415 4 30 FIG I — THE ELUTI0N OF 63gm- OF A MIXTURE OF RARE EARTH CHLORIDES FROM A 6 0 cm DIAMETER BED OF 20 M E SH DOWEX 50, 78 cm- LONG, USING 011% CITRATE BUFFER A T A pH OF 6 0 0 AND A LINEAR FLOW RATE OF 0-6cm/min D O T T E D LINES DETERMINED SPE CTROPHOTOMETRICALLY TABLE I The weights of the various fractions obtained from the ion exchange column* The fractions were weighed as the oxides after recovery from 500 ml* portions of eluate as the oxalates* The data in this table was used in plotting the elution curve (Fig* 1)« Fraction Weight Number mg® Fraction Weight Number mg* Fraction Weight Number mgs 1 2 3 1+ 5 6 7 8 9 10 11 12 13 l l * 15 16 17 18 19 20 21 22: 23 21* 25 26 27 28 29 30 31 32 33 31* 35 36 37 e * 75 76 2*1 3.0 5.2 6*3 10,1 12*0 15*3 18*1 15«0 13.9 10*3 7*1* 6*5 12.1 20*1* 21**5 28aO 39*1 1*1**6 1*8.3 51** 7 60*3 70.8 80.1* 86*0 92*1 100*1+ 110.8 117*1 121**3 126*5 127*7 130*1* 132*1 132*0 132*1* 131*9 130*1 125*3 7 7 79 80 81 "82 83 81* 85 86 87 88 89 90 91 92 93 91* 95 96 97 98 ©a 161* 165 166 167 168 169 170 171 172 173 171* *** 239 21*0 21*1 21*2 21*3 122*9 120*0 117*8 111*1 96*6 86*1 79*1* 83*1 81**0 80.1 79*1* 81**2 93*5 96*1 97*1* 99*1 100*1* 100*5 161*0 102*1* 101*9 102*0 101*1* 99*0 96*3 89*9 82*2 78.7 78.0 77*9 ?8*2 78.0 77*8 **•*-75*1 72*5 71*0 67*3 61**1 2l*U 21*5 21*6 21*7 21*8 21*9 250 251 252 253 251* 255 256 257 258 259 260 261 262 263 261* 265 266 267 268 269 270 60*5 58*1* 53*9 50*1 1*8*1 1*1**8 1*0.2 38*1* 33*9 31*3 26*1 21*0 18*5 11**5 10*0 9*0 5o9 1* 1* 3, 2, 2, 1 I 1 trace n i l 23 Examination of the spectrographic plates showed that such was indeed the cases The f i r s t smallpeak i n the elution curve was attributed to gado-linium and europium. (Under the conditions used in this ion exchange separation, these two elements are separated only poorly and give but one peak). The three large bands which follow were found to be due to samarium, neodymium, and praseodymium respectively. The absence of "humping" of these bands indicates that the column was not overloaded. The absence of any peaks beyond that for praseodymium indicates that the original material adsorbed on the column was free of cerium and lanthanum* The elution curve shows an anomalous small peak.,occurring between the neodymium and samarium bands* Three fractions of a li g h t brown coloured oxide were obtained in this region, the tot a l weight being 82 rag* Spectre-graphic analysis of this material showed the presence of five f a i r l y strong emission lines which corresponded to wave-lengths of 3306, 332°, 331+2, o 3378, and 3379 A* These lines were present in the entire region of mixed samarium-neodymium oxides but not at a l l in the spectroscopically pure samples of these two elements and were considerably stronger i n the three fractions mentioned previously than i n any other sample analysed. Careful examination of a l l the possible lines i n these wave-length regions indi -cated that, when relative intensities were considered, the lines could not be explained by the presence of any element which could conceivably have been present* These five lines agree closely with those assumed by Harris et a l . to be due to illinium* Conversely, none of these lines appear i n the published emission spectrum for a r t i f i c i a l l y prepared promethium (27). The absorption spectrum of the material i n these mixed fractions showed, in dilute hydrochloric acid, an intensification of the bands at 2h o 5816 and 5123 A* to element 61 by the I l l i n o i s workers was made by Prandtl (33) who stated that a concentration effect might be involved and hence that the evidence dealing with these bands was meaningless* However, Q u i l l , Selwood, and Hopkins (37) extensively studied the effect of the concen-tration of both the acid (in the case of hydrochloric aid n i t r i c acids) and of the Rare Earth on the absorption bands for neodymium, samarium, and erbium and found that the effects of t he shifting and broadening of the bands i n no case interfered i n the region where the two strong bands of i l l i n i u m x*ere said to appear* Sufficient material was not available for an X-ray emission spectro-gram of the three samples to be taken since a large amount of the material was lost i n the process of preparing the emisaon spectrograms* It may be pointed out here that emisaon spectroscopy w i l l detect at least one part pet million in the case of the stronger lines of an element and absorption spectroscopy w i l l detect the stronger bands of a Rare Earth i n dilutions of one part i n one hundred thousand without d i f f i c u l t y * X-ray spectroscopy, on the other hand, would require a concentration of at least one part per thousand i n order that the emission lines of an element could be observed. Ths three fractions suspected of containing element 61 were examined for radioactivity by the Department of Physics of the University of British Columbia. The results of these tests were somewhat inconclusive i n that the background count was 16 counts per minute, while the count from the sample was 20 counts per minute. This increase i n background i s just a l i t t l e more than natural fluctuation and so l i t t l e weight can be given to this evidence* The Geiger tube used was not capable of couniiig alpha particles and a counter of sufficient sensitivity to detect weak alpha 25 radiation was not available* The small anount of radiation observed could have been due to hard betas and/or soft gammas* The spectro-scopics!, l y pure neodymium samples gave a count of the same order of magni-tude and so i t i s assumed that the radioactivity i n the mixed samples was due to the neodymium in them* The spectroscopics! l y pure samarium gave no count with the instrument used* More conclusive evidence in this regard might prove to be significant for, i f the neodymium were emitting hard betas, the decay product would, of course, be element 61* Time was not sufficient to allow such a study to be undertaken* It i s apparent from the foregoing discussion that, while no con-clusive evidence for the existence of naturally occurring element 61 has been obtained, the evidence which has been submitted i s such that further study of the problem of the existence of t h i s element i n nature i s most certainly warranted* .26 REFERENCES 1. BALLOU, N.E. March. P r o j . Rep. cc-680 : May, 1943. 2. BALLOU, N.E. i b i d , cc-3418 : Feb., 1946. 3. BALLOU, N.E. P l u t . P r o j . Rec. 9B : 7.54.1. 1946. 4. BALLOU, N.E. Phys. Rev. 73 : 630. 1948.. 5. CORK, J.M., JAMES, C. and FOGG, H.C. Proc. Natl.-Acad. S c i . 12 : 696. 1926. 6. CUER and LATTES. Nature, 158 : 197. 1946. 7. DEHLINGER, GLOCKER and KAUPP. Naturwiss. 14 : 772. 1926. 8. GOLDSCHMIDT, B.L. and MORGAN, F. Canadian P r o j . Rep. MC-11. August, 1943. 9. HARRIS, J.A. J . Am. Chem. Soc. 48 : 1585. 1926. 10. HARRIS, J.A. w i t h YNTEMA, L.F. and HOPKINS, B.S. i b i d . 48 : 1594. 1926. 11. HARRIS, J.A. w i t h YNTEMA, L.F. and HOPKINS, B.S. Nature, 117 : 792. 1926. 12. HARRIS, J.A. w i t h YNTEMA, L.F. and HOPKINS, B.S. S c i e n c e , 63 : .575. 1926. 13. HARRIS, J.A. w i t h YNTEMA, L.F. and HOPKINS, B.S. News Ed. Ind. Eng. Chem. page 5, March 20, 1926. 14. HARRIS, J.A. w i t h YNTEMA, L.F. and HOPKINS, B.S. Nature, 119, .637. 1927. 15. HARRIS, J.A. w i t h YNTEMA, L.F. and HOPKINS, B.S. Z. anorg. allgem. Chem. 157 : 371. 1927. 16. HERZFINKIEL• Compt. Rend. 184 : 968. 1927. 17. INT. UNION OF CHEM. XV Conf., Amsterdam. J u l y , 1949. . . Reported.in Chem. and Eng. News. 27 : 2996. 1949. 18. LANTZ, P.M. et a l . Phys. Rev. 72 : 85. 1947. 19. LAW, H.B., POOL, M.L., KURBATOV, J.D. and QUILL, L.L. Phys. Rev..53 : 4 3 6 . 1938. 27 20. LAW, H.B., POOL, M.L., KURBATOV, J.D. and QUILL, L.L. i b i d . 59 : 936. 1941. 21. LAW, H.B., POOL, M.L., KURBATOV, J.D., and QUILL, L.L. i b i d . 61 : 166. 1942. 22. LAW, H.B., POOL, M.L., KURBATOV, J.D. and QUILL, L.L. i b i d . 63 : 463. 1943. 23. LIBBY, W.P. i b i d . 45 : 845. 1938. 24. LIBBY, W.P. i b i d . 46 : 196. 1934. 25. MATTAUCH, J. Z. Physik. 91 : 361. 1934. 26. MARINSKY,"J.A., GLENDENIN, L.E. and CORYELL, CD. J. Am. Chem. Soc. 69 : 2781. 1947. 27. MEGGERS, W.P., SCRIBNER, B.P. and BOZMAN, W.R. J . Res. Natl. Bur. Stds. 46 : No.2, 85. Feb., 1951. RP 2179. 28. MEYER, R.J., SCHUMACHER, G. and KOTOWSKI, A. Naturwiss. 14 : 771. 1926. 29. MOELLER, T. and BRANTLEY, J.C. Anal. Chem. 22 : 433. 1950. 30. MOSELEY, H.J.G. P h i l . Mag. 26 : 1024. 1913. 31. MOSELEY, H.J.G. i b i d . 27 : 703. 1914. 32. PARKER, G.W., INGHRAM, M.G., HESS, D.C., J r . and HAYDEN, R.J. Phys. Rev. 71 : 743. 1947. 33. PRANDTL, W. Z. Angew. Chem. 39 : 897. 1926. 34. PRANDTL, W. Z. anorg. allgem. Chem. 136 : 283. 1924. 35. PRANDTL, W. Ber. 60B : 621. 1927. 36. PRANDTL, W. and GRIMM, L. Z.. Angew. Chem. 39 : 1333. 1926. 37. QUILL, L.L. and SELWOOD, P.W. with HOPKINS, B.S. J. Am. Chem. Soc. 50 : 2929. 1928. 38. ROLLA, L. and FERNANDES, L. Gazz. chim. I t a l . 56 : 435. 1926. 39. ROLLA, L. and FERNANDES, L. i b i d . 56 : 862. 1926. 40. ROLLA, L. and FERNANDES, L. Z. anorg. allgem. Chem. 160 : 190. 1927. •2B: 41. SCHOELLER, W.R. and POWELL, A.R. i n "The analysis of minerals and ores of the rare elements". 2nd ed. Charles G r i f f i n and Co., LONDON, W.C.2. 1940. 42. SIEGBAHN, M. "The spectroscopy of X-rays". Oxford University Press. 1925. 43. SEILER, J.A. and WINSBERG, L. Man. Pr o j . Rep. cc-2310 : 227. Jan. 1945. 44. SEILER, J.A. and WINSBERG, L. Plut . P r o j . Rec. 9B : 7.54.2. 1946. 45. SPEDDING, F.H., VOIGT, A.P., GLADROW, E.M. and SLEIGHT, N.R. J. Am. Chem. Soc. 69 : 2777. 1947. 46. SPEDDING, P.H., VOIGT, A.P., GLADROW, E.M., SLEIGHT, N.R., POWELL, J.E., WRIGHT, J.M., BUTLER; T.A. and PIGARD, P. J. Am. Chem. Soc. 69 : 2786. 1947. 47. SPEDDING, P.H., PULMER, E.I., BUTLER, T.A., GLADROW, E.M., GOBUSH, M., PORTEffi, P.E., POWELL, J.E. and WRIGHT, J.M. J. Am. Chem. Soc. 69 : 2812. 1947. 48. SPEDDING, P.H. Disc. Par. Soc. No. 7. 214. 1949. 49. SPEDDING, P.H.., PULMER, E.I., BUTLER, T.A. and POWELL, J.E. J. Am. Chem. Soc. 72 : 2349. 1950. 50. SPEDDING, F.H., PULMER, E.I., POWELL, J.E. and BUTLER, T.A. i b i d . 72 : 2354. 1950. 51. SPEDDING, P.H., PULMER, E.I., POWELL, J.E., BUTLER, T.A. and YAFFE, I.S. I b i d . 73 : 4840. 1951. 52. SPEDDING, P.H., and POWELL, J.E. i b i d . 74 : 856. 1952. 53. SPEDDING, P.H., and POWELL, J.E. i b i d . 74 : 857. 1952. 54. URBAIN, G. Proc. French Acad. S c i . 1933, 55. von WELSBACH, C.A. Chem.-Ztg. 50 : 990. 1926. 56. YNTEMA, L.F. J. Am. Chem. Soc. 46 ...37. 1926. / 57. wv, C.S. and SEGRE, E. Phys. Rev. 61: 203. 1942. 29 APPENDIX It has been impossible to reproduce, i n this thesis, a l l of the spectrographs plates which were taken i n the course of the outlined worko On the following pages, eleven plates are presented which have been chosen in such a mainer as to i l l u s t r a t e the various phases of the work. In order not to destroy the continuity of the thesis, reference to these plates has been deliberately omitted from the text. It should be noted that only certain of the more significant lines on each plate have been identified here. Standard procedure was f oilowed in identifying any lines with a particular element, namely, the positive identification of at least three of the stronger persistent lines of such an element. As a consequence, although only one l i n e may be attributed to a given element in the following plates, at least three other lines have been positively associated with the arc spectrum of the element. A brief description of each of the plates follows. Plate I : Illustrates the separation obtained in the fractionaly crystal-l i s a t i o n of the Series P double magnesium nitrates after 15 pourings of Fraction 1 and after 12 pourings of Fraction 5» The third exposure i s of the carbon arc alone. The lanthanum lines in Fraction 1 are much stronger than those in Fraction 5, while the praseodymium lines in the l a t t e r fraction are stronger than those i n the former. Plate II s Technical grade oxalic acid, analytical reagent grade oxalic acid, the purified oxalates of the Rare Earths obtained from Norwegian gadolinite e 30 plate III : The same as Plate II, covering a different wave-length region. Plate I? : The Rare Earth chlorides loaded on the ion exchange column, carbon arc blaik, technical oxalic acid. The f i r s t exposure shows the presence of the five lines originally ascribed to i l l i n i u m . Plate V : The three fractions collected at the peak of the anomalous hump in the ion exchange elution curve. The five unidentified lines be-come stronger from l e f t to righto The l i n e at 3306 JL. i s par t i a l l y db~ o scured i n exposures 2 and 3 by the sodium doublet 3302 and 3303 A. Ex-posure 1 i s of the carbon arc alone. Plate VI s Fraction 1 of the Series P double magnesium nitrates after three pourings, followed by two exposures of the carbon arc alone. Exposure 3 i s longer than 2 i n an attempt to develop more lines due to impurities in the graphite. Plate VII s Varying exposures of an iron arc for purposes of calibrating the wave-length scale. Plate VIII : The same as Plate VII, covering a different wave-length region 9 Plate LX t Absorption spectra of the indicated fractions from the ion exchange column. Fraction 235 i s spectroscopically pure praseodymium, while Fraction 210 i s praseodymium which contains some neodymiume The neodymium bands do not show up well since they were of such low intensity as to preclude satigf actory printing. 31 Plate X and Plate XI s Absorption spectra of various fractions from the ion exchange columno Fractions 31* 36, and 1|1 are spectroscopic ally pure samarium, while the earlier fractions contain varying amounts of gadolinium and europiums PLATES Plate I - Emission spectra of f r a c t i o n s from Series P double magnesium n i t r a t e s taken on H i l g e r Model E.498 medium quartz spectrograph using graphite electrodes. Exposure 1 - Fraction 1 a f t e r 15 pourings, Exposure 2 - Fraction 5 a f t e r 12 pourings, Exposure } - Carbon arc alone. CD GO a. OJ co CO M Plate II - Emission spectra taken on Hilger Model E . 4 9 & medium quartz spectrograph using graphite electrodes. £\ Exposure 1 - P u r i f i e d Rare Earth oxalates obtained from ^ [Norwegian g a d o l i n i t e , Exposure 2 - A.R. oxalic acid, Exposure 3 - Technical grade ox a l i c a c i d . CM r H 2,2 23 24 I I I I I I f I I I I I I I I I I I I I I I I I I I | | | 22 ' 23 / • 24 I I I I I I I I I I I I I I I I I I I I I I I I I I I I i II 2 i 2 , 23 124 v I I I I I I I I I i I I I I I I I I I jI I I I I I I I - -* <x> Plate I I I - The same as Plate I I , covering a 0 d i f f e r e n t wave-length region. I I I I 25 26 27 26 29 I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I M I I 25 26 27 2.8 I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I r,I I 25 I I I I I I 1 it * 26 I I I I I I M i l l 11 "« I I I I l l l l l I I I I I PLATE TSL 35 ? ? 3 306 T 3 3 78 Y 3379 The above f i v e l i n e s are the ones o r i g i n -a l l y a t t r i b u -ted to i l l i n -ium by Harris et a l . (9) VAJ CD K H X I o *d tr o i-3P co <!> £ 1 C ocm i tr CD CD H ct CD 3 H* O 1—1 03 1 o o rq 05 M 1 ct K N £ N S 3 H3 H-cm 5 tr co cn «• ro 'c? co P CD p. t?: W o o CD X P ct 3 O O CD O CO X CO (ft *d p C K >1 <D H 4 B) P O CD ^  ^ C t O ct tr y ro tr P P a 1 O CO ct tr H - P a o M o ?r • P O (ft CD Of H-(ft o a 4 o t» CD p t* co >d P tr tc <-i M H- H-O O c t p P CD (ft (1) CI CD M CD (D ""J O P- I—1 0 CD g m o n o » 3 e t c CD ct O H X tr a CD CD K O CO • CO H' • -F~ £ O vO •i 3 Oft ro Plate Y - Emission spectra taken on Hilger Model E.498 medium quartz spectrograph using graphite electrodes. Exposures 2,3,4 - The three f r a c t i o n s collected at the peak of the anomalous hump i n the ion exchange e l u t i o n curve (Fig. 1), Exposure 1 - Carbon arc alone. Plate V i - Emission spectra taken on Hilger Model E .498 medium quartz spectrograph using graphite electrodes. Exposure 1 - Fraction 1 of the Series P double magnesium ni t r a t e s a f t e r three pourings, Exposures 2,3 - Carbon arc alone. i i ummJ 1 i n m o t o . . ON C— to t o -4" U U fU OH Plate VII - Varying exposures of a d i r e c t current iron arc. Taken on Hilger Model E.49&* medium quart spectrograph. I I I I 21 22 I I I I I I I I I I I 23 I I 24 Ii I I I 2 i ' I I I I I I I I 22 I I I I I I I 23 24 I I I I I I I I I I I I I I I 21 22 23 l I I I I I I I I 34 I I I I I I 21 l I I I I 22 I I I I 23 I I I I I I ,4 I I I I I I I I I I I \£> CM • . CM CV CD 0) ON Plate VIII - The same as Plate VII, covering a di f f e r e n t wave-length region. o -co ON • • • to to rH O vO •oo to CV CM CM <D <D o fe fe fe P L A T E I X F R A C T I O N N U M B E R 235 2 30 2 25 2 2d 2 15 210 Plate I I - Absorption spectra of various fra c t i o n s from ion exchange column. Taken on Hilger Model l)n2 constant deviation wave-length spectrometer. Iron arc reference l i n e s . z m o CD Plate X - Absorption spectra of various f r a c t i o n s from ion exchange column. Taken on Hilger Model D72 constant deviation wave-length spectrometer. Iron arc reference l i n e s . to>t>-ON-00 3 o v O o -4" cc UJ CO s 3 Plate XI - Absorption spectra of various f r a c t i o n s from ion exchange column. Taken on Hi l g e r Model D72 constant deviation wave-length spectrometer. Iron arc reference l i n e s . i i > 

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