June 17, 1922] 



NA TURE 



781 



Identification of a Missing Element. 



IN two recent communications to the Paris 

 Academy of Sciences [Comptes rendus, May 22), 

 by M. A. Dauvillier and Prof. G. Urbain respectively, 

 very definite conclusions have been reached as to the 

 identity of celtium with the missing element of number 

 72 on the Moseley classification. This discovery is 

 of special interest to British workers, since Moseley's 

 last work dealt with this particular problem. Prof. 

 Urbain adds a statement on the unpublished work 

 of Moseley on the X-ray spectra of his preparations 

 of the rare earths. In his paper M. Dauvillier an- 

 nounces the discovery of certain lines in the L X-ray 

 spectrum of celtium which show that its atomic number 

 is 72. An improved De Broglie photographic spectro- 

 meter was used, and the oxides of lutecium and 

 \ tterbium in a preparation of Urbain's were attached 

 to the anti-cathode. The tube was run at a potential 

 of 40 k.v., and nearly complete L-spectra of lutecium 

 and ytterbium were obtained. In addition three 

 lines of thulium were found and two feeble lines which 

 were identified as the aj_and (5^ radiations of celtium. 

 These lines (ai= 1-5618 A ; /32= 1-3194 A) fall in the 

 correct places for the element of atomic number- 72, 

 between the corresponding lines of lutecium and 

 ytterbium. The fiy and y^ lines of celtium which 

 might have been expected are coincident with the 

 ^'2 and 73 lines of lutecium. Reasons are given why 

 these lines of celtium cannot be due to any impurities, 

 such as other rare earths. 



The following is a translation of Prof. Urbain's 

 paper in the Comptes rendus : 



The Atomic Numbers of Ytterbium, 

 Lutecium, and Celtium. 

 "The results of M. Dauvillier's examination of my 

 preparations containing celtium have a theoretical 

 importance obvious to all who have followed recent 

 scientific developments with regard to the chemical 

 elements and their atomic structure. 



" It is now unquestionable that the element of 

 atomic number 72 is actually celtium. The atomic 

 weight of celtium must therefore lie between 175 

 (lutecium) and 181-5 (tantalum). Characterised by 

 two sets of spectral lines (arc and X-ray) and by the 

 order of magnitude of its atomic weight, celtium 

 has conclusively won its place among the chemical 

 elements. 



"Thus the problem of the constituent elements 

 of Marignac's ' ytterbium ' has been solved. The 

 method of X-ray analj^sis is the most significant, and 

 probably the crucial, test of a chemical element, 

 and this method has confirmed the work I have 

 done over a period of more than ten years on ' ytter- 

 bium,' using more difficult and probably less conclu- 

 sive methods. Though I only succeeded in obtaining 

 a partial separation, this was sufficient to permit the 

 high-frequency spectra method to assign its atomic 

 number to each of the constituents I discovered, 

 namely, (neo-) ytterbium 70, lutecium 71, celtium 72. 



" Now that these results are clear, I wish to outline 

 a part of the history of these elements that has not 

 yet become known to the scientific public. When I 

 originally announced the discovery of celtium, 

 Moseley's law of the atomic numbers was still un- 

 known. After this law had been found it seemed 

 evident that it should be possible to define the three 

 elements of the ytterbium group by their X-ray 

 spectra. Moseley himself put forward the hypothesis 

 that celtium and the element with atomic number 

 72 were one and the same. On the other hand, 

 Moseley, relying on the evidence of Auer von Welsbach, 

 in his first lists of the elements had included two 

 thuliums, while my experiments only permitted the 

 existence of one. 



" In order to settle this question, in June 1914 

 Ramsay and I visited Prof. Townsend's laboratory 

 at Oxford, where Moseley was working. Our inten- 

 tion was to examine the different products of my 

 separation of ytterbium by this young investigator's 

 method, then unique. 



" We found one thulium of atomic number 69, one 

 ytterbium of atomic number 70, and one lutecium 

 of atomic number 71. The spectra which Moseley 

 obtained included only a few lines, and we could 

 not, find any corresponding to the element of atomic 

 number 72. The first of these results was announced 

 several years ago, but as the result of the researches 

 of others. No claim of priority was possible, since 

 Moseley himself was responsible for the publication 

 of these results, and for this purpose had kept the 

 necessary documents. But the war broke out before 

 he had time to write his paper. He was among the 

 first to enlist, and by great misfortune was killed at 

 the Dardanelles. 



" Sir Ernest Rutherford, who prepared the obituary 

 notice of his pupil, wrote to me about these last 

 researches of Moseley's, at which I had assisted. In 

 the absence of precise data I thought I must forgo 

 the publication of results that would rest on my 

 memory alone. 



" M. Dauvillier's discoveries complete the early 

 results obtained at Oxford. They show that the 

 negative result given by Moseley's method in the 

 case of celtium was due only to the insensitiveness 

 of the method, since the preparation examined by 

 M. Dauvillier is the same as that used in Moseley's 

 own X-ray tube." 



Now that the missing element of number 72 has 

 been identified, there remain only three vacant places 

 of ordinal numbers — 43, 61, 75 — between hydrogen and 

 bismuth in the Moseley classification of the elements. 

 With the rapidly increasing perfection of technique of 

 X-ray spectra and the use of powerful installations, it 

 is to be anticipated that the missing elements should 

 soon be identified if they exist in the earth. The law of 

 the X-ray spectra, as found by Moseley, is an infallible 

 guide in fixing the number of an element, even if 

 present in only small proportion in the material under 

 examination. E. Rutherford. 



Recent Excavations at Stonehenge.^ 



By Col. William Hawley, F.S.A. 



''T^HE arrangement of the stones at Stonehenge 



-*- includes on the outside a circle of sarsen stones, 



which were originally thirty in number and were capped 



» Address to members of the Portsmouth Literary and Philosophical 

 icty on the occasion of a visit to Stonehenge on May 6, 1922. 



NO. 2746, VOL. 109] 



with lintels, forming a continuous ring round the top. 

 Inside this circle is another of smaller stones, originally 

 forty-three in number, but without lintels and of a 

 different rock from those of the outer circle. 



Within the second circle of small stones were five 



