The discovery of the elements. XX. Recently discovered elements

The discovery of the elements. XX. Recently discovered elements. Mary Elvira Weeks. J. Chem. Educ. , 1933, 10 (3), p 161. DOI: 10.1021/ed010p161...
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The DISCOVERY ofthe ELEMENTS. XX. RECENTLY DISCOVERED ELEMENTS* MARY ELVIRA WEEKS The University of Kansas, Lawrence, Kansas

When H . G. J . Moseley discovered the simple relationship which exists between the X-ray spectrum of a n element and its atomic number, there were sezen unjilled spaces i n the periodic table. Elements 43, 61, 72, 75, 85, 87, and 91 were yet to be revealed. Since element 91 i s radioactive, it was discussed i n Part X 1 X . t Early in 1923 Dirk Coster and Georg son Hevesy showed that element 72, or hafnium, as it is now called, i s widely distributed i n nature and that i t had escaped detection because of its close resemblance to zirconium. Elements

43 and 75, masurium and rhenium, were discovered by Walter and Ida Noddack i n 1924, and rhenium i s now a commercial article. Element 61, illinium, was discovered in 1926 by Hopkins, Harris, and Ynterna and independently by Cork, James, and Fogg in the United Stntes and by Rolla and Fernandes in Italy. Traces of elements 85 and 87 have been detected by the magnetooptic method of Alkson and co-workers, who suggest the names alabamine and virginium. Much research into the properties of these elements remains to be done.

+ + + Beyond the violet seek him, .for there i n the dark he hells, Holding the crystal lattice to cast the shadow that tells flow the heart of the atom thickens, ready to burst into flower, Loosina- the bands of Orion with heavenly heat and power. He numbers the charge on the center for each of the elements That we named for gods and demons, colors and tastes andscents. . . . ( 1 ) .

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LTHOUGH MendelCeff's periodic system was a great aid in the search for new elements, there are some anomalies that it does not explain. The atomic weight of argon, for example, is higher than that of potassium, yet argon must precede potassium in the table, for there is no doubt whatever that it is an inert gas like helium and that potassium is an alkali metal like sodium. Tellurium and iodine present a similar discrepancy, and the radioactive isotopes were the cause of much perplexity. A much better basis of classification for the elements was finally found by a young English physicist in the course of his researches on X-rays. Henry Gwyn Jeffreys Moseley was born at Weymouth on November 23, 1887. While he was still a very young child he had the misfortune to lose his father, who was a distinguished zoologist and professor a t Oxford University. Moseley studied at Eton and at Trinity College, Oxford, and received his master's degree in 1910. A year before his graduation he went to Manchester to * Illustrations mllected by F. B. Dains of The University of Kansas. t See J. CHEM.E~uc.,9, 79-90 (Feb., 1933).

discuss with Sir Ernest Rutherford the possibility of undertaking original research in physics (30). After serving the University of Manchester for two years as lecturer and demonstrator in physics, he resigned his position in order to devote all his time to research, and was awarded the John Harling Fellowship. His colleagues soon recognized his superiority as an experimenter, and admired him because of his marvelous technic, broad knowledge of physics, cheerfulness, and friendly cooperation. When the British Association met in Australia in 1914, he entered enthusiastically into the discussion of atomic structure and gave an excellent report of his own researches on the X-ray spectra of the rare earths (32). No scientist of the first rank ever had a shorter career. When Great Britain entered the war he immediately returned to England, entered the military service as a signaling officer, and on June 13, 1915, left for the Dardanelles. On the 10th of August, when he was telephoning an order to his division, a Turkish bullet passed through his head. His will, made while he was in active service, bequeathed all his apparatus and much of his private fortune to the Royal Society. Although Moseley was not quite twenty-eight years old at the time of his death, his researches had so revolutionized the study of atomic structure that his name will endure forever in the annals of science (Z), (36). Before entering the military service he had become intensely interested in Professor Laue's discovery that "the ordered arrangement of the atoms in a crystal would do the same for X-rays that a diffraction grating does for light" (37). When a target, or anticathode, is bombarded with cathode rays, it emits a beam of Xrays which is characteristic of the substance of which

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argon and potassium and between iodine and tellurium disappear. Moseley's work not only shed much light on the periodic system and the relationships between known elements and the radioactive isotopes, but it was also a great stimulus in the search for the few elements remaining undiscovered (47). One of the first chemists to utilize the new method was Professor Georges Urbain of Pans, who took his rare earth preparations to Oxford for examination. Moseley showed him the characteristic lines of erbium, thulium, ytterbium, and lutecium, and confirmed in a few days the conclusions which Professor Urbain had made after twenty years of patient research. The latter was greatly surprised to find that a scientific contribution of such fundamental importance had been made by one so young, and immediately began to teach Moseley's method of X-ray analysis. "His law," said he, "substituted for the rather romantic classification of Mendele&, a precision entirely scientific" (36).

HENRYGwuw JEFFREYS MOSELEY, 1887-1915 English physicist who studied the X-ray spectra of more than fifty elements and discovered the relation existing between the atomic number of an element and the frequency of the X-rays which it emits when bombarded by cathode rays. At the age of twenty-seven years he was killed while in active service at the Dardanelles.

the target is made. With the help of Mr. C. G. Darwin, a grandson of the famous biologist, Moseley mapped the high-frequency spectrum of an X-ray tube provided with a platinum anticathode (37). In the hope of finding some relationship between the frequency of the rays and the atomic number, or ordinal number of the element in the periodic table, he then carried out an elaborate investigation in which many different elements served as anticathodes. Upon examining these rays by diffracting them through a crystal, he found the following simple and beautiful relationship: When all the known elements are numbered in the order of their positions in the periodic system, the square root of the frequency of the X-rays emitted is directly proportional to the atomic number. Thus Moseley's series is almost the same as Mende16eff's series of increasing atomic weights. When, however, the elements are arranged, not according to their atomic weights, but according to their atomic numbers (Moseley numbers), the discrepancies between

HAFNIUM (ELEMENT 72) Moseley stated that, within the limits of his researches, which covered all the elements between aluminum (number 13) and gold (number 79), there were spaces for three missing onesnumbers 43, 61, and 75 and that, since their X-ray spectra can he accurately predicted, it ought to be rather easy to find them. I t was then believed that the celtium whose arc spectrum Professor Urbain had described in 1911 was element 72 (3), (36), (56). However, when Moseley and Urbain examined the rare earth residues supposed to contain the new element, they found only about ten limes, all of which could he attributed to lutecium and ytterbium. In 1922, after a long period of interruption because of military duties, Professor Urbain resumed his search for element 72 in the same rare-earth residues which he and Moseley had examined before the war. At his suggestion M. A. Dauvillier used de Broglie's improved method of X-ray analysis and observed two faint lines which almost coincided with those predicted for element 72 (33), (54). After titanium was discovered in 1791 by the Reverend William Gregor in Cornwall, its atomic weight was determined by such able chemists as Rose, Mosander, and Dumas, hut the results showed such great discrepancies that Mendeleeff predicted that another element would he found in titanium ores (4). It was in zirconium ores, however, that large quantities of element 72 were finally revealed (34), (38), (42). On the basis of his quantum theory of atomic strncture, Niels Bohr believed that, since Urhain's celtium had been obtained from the rare earths, it could not he element 72, for the latter must be quadrivalent rather than trivalent and must belong to the zirconium family. He showed that the chemical properties of an atom are determined by the number and arrangement of the electrons within it and especially by the number and arrangement of the outermost ones, the

so-called "valence electrons." Since there is usually an appreciable difference in the outer electrons of two adjacent elements in the periodic system, there is also, as a rule, a marked difference in chemical properties. In the rare-earth group, however, and in the triads of the iron and platinum families, the only structural differences are in the deeper shells of the atoms, and therefore these elements are more difficult to separate. According to Bohr's theory these deep-seated differences in the rare earths lie in the interval between lanthanum (element 57) and lutecium (element 71). Element 72 should, however, according to his theory, be quite different from lutecium in the constitution of its outer group of electrons, and should therefore exhibit properties entirely different from those of the rare-earth elements (54), but closely resembling those of zirconium. Bohr therefore advised Dr. Hevesy to search for this element in zirconium ores (5), (28). It was in January, 1923, that Dirk Coster and Georg von Hevesy in Copenhagen brought their search for the new member of the zirconium family to a successful conclusion. Its discovery in zirconium ores was made possible by Moseley's method of X-ray analysis, and it was Costa's previous work in the same field that enabled him to recognize the new element (2). Although they named it hafniumC for the city of Copenhagen, neither of these investigators is Danish. Professor Coster lives in the Netherlands and Professor von Hevesy is a Hungarian. The former is a professor of physics and meteorology at the Royal University of Groningen and director of the physical laboratory. The Dutch, French, English, German, and American journals contain many of his papers on such subjects as X-ray spectra, theory of atomic structure, Stokes's law in the L-series of X-rays, and the rotational oscillation of a cylinder in aviscous liquid. Professor von Professor of physical chemistry a t the University of Freiburg. Hungarian chemist who, with Dr. Dirk Caster of the University of Graningen, discovered t h e elemcnt hafnium in iirmnium ores and mddr a thorough study of i t s propcrtics. Author of mAnv naoers on chemical analysis by X-rays;kdbactivity, the rare earths, and electrolytic conduction.

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* Both sides of the controversy regarding the name of element 72arepresented in the English jaurnals, N a t u r e a n d Chemistry end Industry (28), (54).

Hevesy was born in Budapest in 1885 and was educated in the universities of Budapest, Berlin, and Freiburg. His r e s e a r c h e s have brought him i n t o close contact with such famous scientists as Haber at Karlsmhe, Rutherford at Manchester, and DonnanatLiverpool, and the X-ray investigation with Dr. Coster which resulted in the discovery of hafnium was carried out while both were connected Professor of physics and meteorwith Bohr's Institute ology a t the Royal University of of Theoretical Phys- Groningen. Co-discovererwith Georg von Hevesv of the element hafnium. ics at Copenhagen. Author of-many papers on X-rays Since 1926 Professor and atomic structure. von Hevesy has been professor of physical chemistry a t the University of Freiburg. In 1930 he served as the George Fisher Baker Non-Resident Lecturer in Chemistry at Cornell University. His researches have been in the fields of physical chemistry, electrochemistry, radioactivity, and the separation of isotopes. Hafnium had lain hidden for untold centuries, not because of its rarity but because of its close similarity to zirconium (54), and when Professor von Hevesy examined some historic museum specimens of zirconium compounds which had been prepared by Julius Thomsen, Rammelsherg, Nordenskjold, Marignac, and other experts on the chemistry of zirconium, he found that they contained from one to five per cent. of the new element (26), (55). The latter is far more abundant than silver or gold. Since the earlier chemists were unable to prepare zirconium compounds free from hafnium, the discovery of the new element necessitated a revision of the atomic weight of zirconium (71, (28). Professor von Hevesy and Thal Jantzen separated hafnia from zirconia by repeated recrystallization of the double ammonium or potassium fluorides (26), (38). Metallic hafnium has been isolated and found to have the same crystalline structure as zirconium. A. E. van Arkel and J. H. de Boer prepared it by passing the vapor of the tetraiodide over a heated tungsten iilament (26), (53). MASURIUM AND RHENIUM (ELEMENTS 43 AND

75) Two new elements of the manganese group, numbers 43 (ekamanganese) and 75 (dwimanganese), were discovered in June, 1924, by theiGermau chemists, Dr. Walter Noddack and Dr. Ida Tacke of the Physico-

technical Testing Officein Berlin and Dr.OttoBergofthe Werner-Siemens Laboratory. T h e discovery was not accidental, but the result of a long search in platinum ores a n d i n t h e mineral columbite (15). Platinumores contain t h e elements 24 to 29, 44 to 47, and 76 to 79 (chromium to copper, ruthenium to silver, and osmium J. I h ~ n n v s ~ + to gold), whereas Professor of physical chemistry at columbite contains Charles University, Prague. Author of an uIntroductio,, to Radioactivity.22 numbers 39 to 42 With E. Voto&k he edits the Collection and 71 to 74 (ytof Czechoslovak Communicatrium to molybdetions, a monthly journal published in ~~~~h and ~ ~ g l ito~ make h the numandluteciumto contributions of Czechoslovakian and tungsten). Hence Russian chemists to those it was hoped that who do not read the Slavonic languages. one or both of these sources might yield the missing elements, 43 and 75. Upon studying the relative frequencies of known elements in the earth's crust. Noddack. Tacke, and Berg found that those of oddatomic number are less common than those of even number, and from the known frequency of occurrence of platinum ores and of columbite they obtained an approximate idea of the extent to which they would have to carry their processes of extraction. Moreover, since elements 43 and 75 belong to the manganese group, many of their physical and chemical properties could be predicted. Both these so-called ekamanganeses were finally separated from columbite, and were named masnrium and rhenium in memory of two districts which Germany lost in the World War (Z), (39). The difficult concentration processes were carried out by Dr. Noddack and Dr. Tacke alone, but Berg assisted in making the observations with the X-ray spectroscope (40). Before the discovery of masnrium and rhenium, manEanese had no companions in sub-group VIIa of the periodic system. On September 5, 1925, Fraulein Tacke lectured on the new elements before the Verein deutscher Chemiker in Nuremberg (9). After thanking her for the address, the president mentioned that this was an historic occasion, for i t was the first time that a woman had ever spoken before the Verein. He also expressed the hope that other "Chemikerinnen" might soon follow her example. Fraulein Tacke and Dr. Noddack have since been united in mamage and have continued their joint researches. In recognition of their discoveries they have been awarded the Liebig Medal. In 1925 F. H. Loring and J. G. F. Druce in England

and V. Dolejkk and J. Heyrovskf in Czechoslovakia independently discovered that commercial manganese salts and even the so-called "pure" preparations contain small amounts of element 75 as an impurity (57), (58), (59). While searching for an element of atomic number 93, the English chemists removed manganese and other heavy metals by precipitation as the sulfides, and evaporated the filtrate to dryness. An X-ray analysis of the residue revealed the lines of element 75. Dr. J. Heyrovskf, professor of physical chemistry a t the Charles University of Prague, and Dr. Dolejsek of the Prague Academy of Sciences detected element 75 in manganese salts by a different method. They examined some manganese solutions with their dropping mercury cathode, plotted the current intensity as ordinates against the applied electromotive force as abscissas, and noticed a peculiar "hump" in the curve. Since this was located in the region between - 1.00 and - 1.19 volt from the potential of the calomel electrode, the impurity was a t first thought to be zinc. After showing that zinc, nickel, cobalt, and iron were absent, Heyrovskf and Dolejkk suspected the presence of the undiscovered ekamanganeses, elements 43 and 75. The saw-like character of the curve indicated that the impurity did not alloy with mercury. Using their dropping mercury cathode in conjunction with an instrument called a golarogragh, they obtained automatically a permanent record of the electrolytic reaction.

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WILL~AM FREDERICK M I I G G T R S Physicist at the U. S. Bureau of Standards since 1914. Chief of the spectroscopy section. Author of many papers on optics, astrophysics, photography, measurement of wave-length standards, and description and analysis of spectra. The instrument in the foreground is a concave grating spectograph, used for photographing the emission spectrum of rhenium.

After dipping strips of zinc into concentrated solutions of manganese salts, they scraped off a deposit containing zinc, lead, cadmium, nickel, and cobalt. After complete removal of these heavy metals by precipitation as the sulfides, they found no evidence of element 43, but did find the X-ray lines of number 75, for which they advocated the retention of the name dwimanganese which MendeEeff had used (44). When Dr. Druce took his dwimanganese preparation to the Charles University in Prague for polarographic examination, the Czechoslovakian chemists confirmed his conclusions. Although masurium has never been purified, the production of rhenium has increased a t such a surprising rate that the price* has fallen from $10,000 per gram in 1928 to $3 per gram in 1930 (43). Dr. William F. Meggers of the United States Bureau of Standards has made a thorough study of its arc spectrum. ILLIN~UM (ELEMENT 61) All the rare-earth elements except one were found before the introduction of X-ray spectroscopy. In the estimation of Professor von Hevesy,

. .. t o have discovered and isolated nearly all of the rare earths without further guidance, in spite of their great similarity and the great rarity of some of these, is one of the most brilliant accomplishments that experimental chemistry has ever produced (38). As early as 1902, however, Professor Bohuslav

* According to Science Service the price of rhenium in August, 1932, was about $1600 per pound.

Director of the chemistry department a t the University of New Hampshire. Author of many papers an the rare earths. Independent discoverer of luteciurn and illinium. He was born in England and studied under Sir William Ramsay.

.I. I 1 c ~ r o u i i : i . ( - ~ i l h u , i n r . C h i r n .

Comniunicolions

Bonusmv BRAUNER, 1855Professor of chemistry at the Bohemian University of Prague. He has made brilliant contributions to analytical chemistry, the determination of atomic weights, and the chemistry of the rare earths. In 1902 he predicted the existence of element 61, now known as illinium.

Brauner of the Bohemian University of Prague, a friend of Mendelkeff, predicted the existence of an element between neodymium and samarium (11). It was noticed that there is a sudden change in certain properties of the rare-earth elements a t this point: the double magnesium rare-earth nitrates differ, for example, by nearly equal increments except in the case of neodymium and samarium, whereas these two elements can be sharply separated by fractional crystallization. This method of fractionation of the double magnesium nitrates was introduced by the late Professor Charles James of the University of New Hampshire (41), who worked for years in an attempt to reveal the missing rare-earth element, the existence of which seemed all the more probable after Moseley had disclosed the vacant place for element 61. In 1926, while Professor J. M. Cork was using the excellent X-ray apparatus a t the University of Michigan to examine some rare-earth material that had been carefully purified by Professor James and H. C. Fogg in

B . SMITHHOPKINS,P R a s ~ s s o nOa CHEMISTRYAT THE UNIVERSITY OF ILLINOIS

Discoverer of illinium (element 61). His researches on the rare earths and atomic weights and his recent investigation of the magneto-optic method of chemical analysis are well known.

New Hampshire, Professor B. Smith Hopkins and his colleagues a t the University of Illinois announced the discovery of t h e elusive element ( 1 8 ~(221, (41). Since monazite sand contains neodymium (element 60) and samarium (element 62), Professor H o p k i n s thought t h a t i t might reasonably be expected to containelement 61also. The Lindsay Light Company and the Welsbach M a n t l e Company presented him withsome rareearth residues from monazite, from which the thorium and part of the cerium had been removed for t h e m a n u f a c t u r e of I n the lower center is the kenetron. On a shelf above it is the vacuum chamber for the X-rav amaratus. The metal X-rav tube itseif &iects fmm the front of th; vacuum chamber toward the observer's right. At the right-hand of the picture is the liquid air trap which serves to keep mercury out of the vacuum chamber.

Welsbach gas mantles, and from which he prepared some very pure neodymi& &d samarium saltsto send tothe United States Bureau of Standards. Spectroscopic examination revealed a number of new lines which were common to both samples (18), (20). Professor Hopkins and Dr. Hams recrystallized the bromates rather than the double magnesium nitrates. Since the double magnesium nitrates have solubilities which increase with atomic number, fractionation by this method senarates the elements in the order of their atomic numbers and brings element 61 between neodymLABORATORY FOR RARE-EARTH FRACTIONATION AT THE UNIVERSITY OP ILLINOIS* ium and samarium, which are relaThe four large earthenware utensils in the left foreground are stone filters. On the When the bradesk in front of these are four 90-liter evaporating dishes with stirring devices and tiyely abundant' reagent bottles in position. These evaporating dishes are mounted on wash-tubs mates are recrystallized, however, which serve as a steam-bath. The reaeents are added from the lame bottles hv compressed air. These are used in the e&ly stages of the rare-earti work when the volume of material used is large. On the desk toward the right are flasks containing rare-earth fractions just as they are used in the process of fractional crystallization.

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*Thelaboratoryphotographsanddescriptions were graciously contributed by Dr. B. Smith Hapkins

neodymium goes into the more soluble fractions, and ment 61, prefers to call i t porentium (13), (14), (19). the order of crystallization is: europium (which has the His method consisted in separating some didymium least soluble bromate), samarium, gadolinium, element material from Brazilian monazite and fractionating 61, terbium, and neodymium @I), (23). Although neo- i t as the double thallium sulfates. When Miss Rita dymium and samarium obscure the presence of other Brunetti of Arcetri, a professor a t the Institute of Inelements, terbium and gadolinium do not have this organic and Physical Chemistry a t the University of troublesome property. Florence, examined the X-ray absorption spectra of Professor Hopkins was assisted in these researches the K series, she concluded that a new element must by Dr. J. Allen Harris and Dr. Yntema. The frac- be present. Professor Rolla's results were deposited tionations were made a t Urbana, while Dr. Yntema, as a sealed package with the Reale Accademia dei Lincei a Fellow of the National Research in Tune. 1924. The contents were Council, made the X-ray examinanot published, however, until Notion in the Sloane Laboratory of vember, 1926 (19), (29). The work Physics a t Yale (25). After five of these Italian scientists is of a high years of searching, an inspiring thing order of excellence. happened. Just as in TschaikowVIRGINIUM (ELEMENT 87) sky's "1812 Overture" the strains of the French hymn fade away in the Speculations have long been made triumphant swelling oi the Russian as to the probable nature of element anthem, so in Professor Hopkins' 87, the unknown alkali metal, and spectra the neodymium lines faded element 85, the unknown halogen, out and the new lines (5816 A. U. and many carefully planned searches and 5123 A. U.) of the absorption for them have failed. Since both spectrum became stronger; moreof these unfilled spaces lay in the over, the lines of the X-ray spectrum radioactive region of the periodic were found to coincide with those system, and since no inactive isopredicted from Moseley's rnle. Thus topes of elements having atomic element number 61, illinium, the weights greater than 83 had ever last of the rare earths, took its place been found, Professor von Hevesy in the periodic table (lo), (18), thought that elements 85 and 87 ought to be radioactive, and that (20, (24). B. Smith Hopkins was born a t they might possibly be formed by Owosso, Michigan, on September 1, disintegration of radon, mesotho1873, and was educated a t Albion rium 2, or polonium, or their isotopes College, Columbia University, and (elements 86, 89, or 84). From the The Johns Hopkins University. He rule deduced by Soddy, Fajans, Director of the Institute of Inorganic has taught a t Nebraska Wesleyan Fleck, and Russell, he reasoned that Chemistry. Independent discoverer of University, a t Carroll College in element 87 might be an alpha-ray element 61. Author of uauers on the rare earths in the atmoipheres of the Wisconsin, and, since 1912, a t the product of element 89 or a betastars and on ionization potentials with University of Illinois, and thouray product of element 86 and that relation to the periodic system of the elements. sands of students remember his element 85 might be formed by kindly encouragement, his masal~ha-disinteaationof the unknown sumed modesty; and his generous fairness in judg- element 87 or by beta-disintegration of a polonium ing the contributions of other investigators of the isotope (60). rare earths. He has published a number of books, C. F. Graham believes, however, that, "since the including two on the rarer elements (12), and is the radioactive degeneration series does not pass through first American to fill one of the vacant places in the the element [87], there is no reason to expect that it periodic table. Professor Boltwood's ionium, although will be radioactive to any greater degree than the it has specific radioactive properties, is chemically in- other alkali elements" (61). separable from thorium. While Druce and Loring were searching for element Since the rare-earth preparations of Professor James 93, they observed a faint but clear X-ray line between exhibited the lines of illinium when examined with the the theoretical Lal and L a lines of element 87 (63). X-ray spectroscope, he is to be regarded as an indeBetween 1927 and 1930 Dr. Fred Allison of the pendent discoverer of the element. His early attempts physics department of the Alabama Polytechnic Instito reveal this ekaneodymium and his other contribu- tute perfected the magneto-optic method of chemical tions to the chemistry of the rare earths have been ably analysis. When a transparent aqueous solution of discussed by B. Smith Hopkins (41) and by H. A. the chemical compound to be examined is placed in Iddles (52). the path of a monochromatic beam of polarized light Professor Luigi Rolla of the Royal University of and subjected to the simultaneous action of a magnetii: Florence, who is also an independent discoverer of ele- field, there is a time lag of about a billionth of a second

between the instant of application of the force and the appearance of one or more minima of light intensity which are characteristic of the given compound. Dr. Allison interprets this phenomenon as a differential time lag in the appearance of the Faraday effect (the rotation of the plane of polarization caused by the passage of a beam of light through a magnetic field) (481, (661, (68). These characteristic minima are produced even when other substances are present in the solution, and do not disappear until the concentration is decreased to about 1 part of the compound to 10" parts of water. By examining a series of solutions of the chlorides, nitrates, sulfates, and hydroxides of many elements varying in equivalent weight from hydrogen (1.008) to thallium (204.39), Dr. Allison and Edgar J. Murphy found that the differential time lag is an inverse function of the chemical equivalent of the cation; in other words, that the minima appeared a t points along their arbitrary wire path scale in the order of the equivalentweights of the metallic elements of the compounds studied (48). In the fall of 1929 Allison and Mumhv examined some specimens of lepidolite, a lithium ore, and pollucite, a mineral containing cesium, and consistently found minima a t points on their scale corresponding to the undiscovered alkali metal, ekacesium. The chloride, nitrate, sulfate, and hydroxide all yielded characteristic minima a t the proper points (17). Dr. Allison has therefore proposed that element 87 be called virginium in honor of his native state (49). In October, 1931, Professor Jacob Papish and Eugene Wainer of the chemistry department of Cornell University obtained spectroscopic evidence of the existence of this element. In searching for it they believed that it must bear some resemblance to cesium and radium, that its primary spectral lines must lie in the infra-red (27), (35), and therefore be difficult to observe when the ekacesium is present in low concentrations, and that, since the electroscope had not already revealed it, i t could not be appreciably radioactive. These assumptions led them to search for the missing element in a specimen of samarskite which was rich in uranium and its disintegration products, and which also contained rubidium and cesium. By repeated recrystallization of the aluminum alums prepared from this material, they obtained a fraction which exhibited five of the X-ray spectrographic lines predicted from Moseley's rule. These lines were produced, as might be expected, by the fractions containing the least soluble alums (27). Since the Cornell chemists were unable to verify the magneto-optic observations of Professor Allison and his colleagues, they believed that the light intensity minima attributed to element 87 had been caused by some complex ion, such as SnC13+or ReCl+, which would have about the same equivalent weight as that predicted for ekacesium. The Alabama chemists found, however, that the minima caused by these complex tin or rhenium ions can be made to disapA

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pear by suitable chemical treatment, leaving the characteristic minima of element 87 undisturbed (50). Dr. Allison's results have been confirmed by Professor J. L. McGhee and Miss Margaret Lawrenz of Emory University, Georgia (51). According to Science Senice, another carefully planned search for the missing alkali metal resulted in a serious accident. As a result of the explosion of his apparatus, Professor Gustave A. Aartovaara* of the Helsingfors Technical University suffered severe injury to his eyes (65). ALABAMINE (ELEMENT 85) Since element 85, ekaiodine, must lie between polonium and radon, Dr. Allison and Dr. Murphy, with the assistance of Professor Edna R. Bishop and Miss Anna L. Sommer, worked up one hundred pounds of the radioactive mineral, monazite sand. In May, 1931, they announced the discovery of this element, which has since been named alabamine. When they digested the monazite sand with aqua regia, extracted it with water a few times, and examined it with their magneto-optic apparatus, they found minima indicating that alabamine was present in the solution in the form of peralabamic acid, HAbOa. After fuming off the aqua regia with sulfuric acid and reducing the solution with sulfur dioxide, they found minima corresponding to hydroalabamic acid, HAb. They also prepared a concentrate which they believe contains 2.5 X gram of alabamine in the form of lithium alabamide (16), (50). Dr. B. Smith Hopkins and Dr. Gordon Hughes have recently investigated the magneto-optic method of chemical analysis, and have found it to be a thousand times more sensitive than analysis by arc spectra. Since the eyes are not easily trained to read the minima of light intensity, these investigators are trying to perfect a photoelectric method of reading them which will make the method dependable (62). Dr. Allison has also succeeded in making a photoelectric cell circuit sensitive enough to replace the eye, and is trying to make the magneto-optic apparatus a convenient and reliable laboratory tool (64), (68). When the existence of elements 85 and 87 has been thoroughly verified, all the gaps in the periodic table will be filled. A large amount of careful research must still be done, however, before the chemical and physical properties of these elusive elements are made manifest. Although all attempts to demonstrate the existence of an element having an atomic weight greater than that of uranium have thus far been unsuccessful, many chemists regard the recently discovered neutron as an element of atomic number zero. CONCLUSION

If the reader has been led through closer acquaintance with the discoverers of the chemical elements to a deeper appreciation of their glorious achievements, * Professor Aartovaara has recently reported the presence of element 87 in Finnish feldspars (67).

the foregoing articles have not been written in vain. The author gratefully acknowledges the valuahle assistance of Dr. F. B. Dains, who has been untiring in his search for suitable illustrations, and of Mr. Oren Bingham, who bas made most of the photographic reproductions. The generous cooperation of the library staff at The University of Kansas, the Edgar Fahs Smith Memorial Library, the AustroAmerican Institute of Education, Science Sem.ce, and the JOURNAL OF CHEMICAL EDUCATION is deeply appreciated. The publication of a number of valuable illustratious was made possible through the courtesy of the Aluminum Co. of America, the Bausch and Lomb Optical Co., the Central Scientific Co., Cornell University, the Fansteel Products Co., the Fisher Scientific Co., Gauthier-Villars et Cie., Harvard University, The Johns Hopkins University, Macmillan and Co., Masson et Cie., the McGraw-Hill Book Co., the Arthur Nemayer Buchdruckerei und Verlag, the Scientific American, the Scientific Monthly, and the University of New Hampshire. The author wishes to thank Mr. M. K. Elias and Miss Mary Larson for the Russian and Swedish translations. The kind cooperation of the following persons who assisted in the search for illustrations and other historical material is also acknowledged with pleasure: Dr. Fred Allison, Miss Eva Armstrong, Dr. William H. Barnes, Dr. Otto Brunck, Dr. Fritz Chemnitius, Dr. F. G. Coming, Dr. Dirk Coster, Dr. Tenney L. Davis, Dr. A. S. Eve, Dr. P. V. Faragher, Dr. A. Fleck, Dr. Neil E. Gordon, Dr. J. Heyrovskjs Dr. B. Smith Hopkins, Dr. L. W. McCay, Dr. Julius Meyer, Dr. L. C. Newell, Dr. R. E. Oesper, Mr. R. B. Pilcher, Professor Luigi Rolla, Dr. A. S. Russell, Dr. H. G. Soderbaum, Dr. Max Speter, Dr. W. T. Taggart, Dr. L. G. Toraude, and Dr. M. W. Travers. LITERATURE CITED

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r.

~

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.. (22)

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