450 



NA TURE 



\_'l/airk lo, 1887 



samarium, especially Of. On dilution wiLh lime, the phosphor- 

 escent line of Qy vanishes before that of Ge. 



U5. — An earth phosphorescing with a citron colotired light, 

 and showing in the spectroscope a citron line having a wave- 

 length of 574. GS is one of the least basic of all the bodies 

 associated in yttritmn, occurring almost at one extremity of the 

 fractionation. It is not very diflicidt to separate chemically G5 

 from all the other accompanying bodies except the one which I 

 have called Ga (giving the deep blue line). Not only caa 08 

 be ol>tained free from the other four constituents of yttiium, 

 but the body called by M. de Marignac Vo is a proof that the 

 other four components of yttrium can be obtained quite free from 

 G5. Lime intensifies the phosphorescence of G5, and deadens 

 that of 0/3, while strontium has the opposite action. The 

 behaviour of GS in the phosphoroscope, when mixed with lime, 

 strontia, or baryta, also affords a striking evidence of individual- 

 ity, lime enhancing the residual glow, while strontia or baryta 

 altogether suppress it. 



Ge. — An earth phosphorescing with a yellow colour, and, in 

 the spectroscope, showing a sharp yellow line having a wave- 

 length of 597. It is seen in the samarium spectrum as a sharp 

 yellow line superposed on a hazy double band. As I have 

 already pointed out, Ge fractionates out high up among the most 

 basic earths, and generally accompanies lanthanum. In the phos- 

 phorescent sp;ctrum of lanthanum the line Ge is seen quite free 

 from the lines of other bodies. 



Gf. — .\n earth phosphorescing with a red light, showing in 

 the spectroscope a red line of wave-length 619. This body is 

 always more plentiful in yttrium obtained from samarskite and 

 cerite than from gadolinite, hielmite, and euxenite, and is almost 

 .ibsent in yttrium from xenotime. Gf is of about intermediate 

 basicity. Working with samirskile yttria, Gt,' becomes most 



brilliant after the line of G») has completely disa])peared. Further 

 fraction.ation causes the line of Gf to fade out, and the citron and 

 blue lines are then left. 



The phosphorescence of Gf is developed to a different extent 

 according to the metal svith which the yttria is mixed. The 

 order (beginning with the substance having the greatest action) 

 is zirconium, tin, aluminium, bismuth, glucinum. 



Gij. — An earth phosphorescing with a deep red light, and 

 showing in the spectroscope a red line having a wave-length of 

 647. Like its fellow red constituent, G?) occurs most plentifully 

 in samarskite yttrium, and scarcely at all in yttrium from hielmite, 

 euxenite, and cerite. It is the first of the strictly yttrium con- 

 stituents to separate out, on fractionation, at the most basic 

 extremity, leaving Ga, G/3, G5, and Gf. In almost all samples 

 of yttria, except when very highly purified, (;•>) is seen very 

 brilliantly, and by its side can be detected the faint red band of 

 samarium. In the phosphoro-scope the line of Gr; is the last to 

 appear when yttria alone is being observed ; strontia and baryta 

 enhance the residual glow of Gr;, strontia in moderate quantities 

 bringing it out before that of G^, while baryta brings it out 

 after G;3. 



S5. — An earth giving in the spectroscope when phosphoresc- 

 ing a very sharp orange line of wave-length 609. I have already 

 (Roy. Soc. Proc. vol. xl. 1886, p. 504) discussed the claims of 

 this earth to be considered a separate entity. It is not present 

 in the rare earths from gadolinite, xenotime, monazite, hielmite, 

 euxenite, and arrhenrte ; it is present in small quantity in cerite, 

 and somewhat more plentifully in samarskite. In samai-skite 

 yttrium it concentrates at a definite part of the fractionation. Its 

 sharp orange line is not strong enough to be seen in the phos- 

 phoroscope. A little calcium entirely suppresses the orange line, 

 while samarium or yttrium seems to intensify it. 



Fig. 5. 



In addition to the above earths, it is not improbable thai the 

 sharp green line ( — 325 ] mentioned under the heading 



" Yttrium " may be caused by still another earth. 



The brilliant and characteristic spark spectra yielded when 

 certain elements are volatilised and rendered incandescent by the 

 spark from a powerful induction coil are relied on by chemists 

 as an indisputable proof of the identity of such elements. Bear- 

 ing this in mind I have endeavoured to ascertain how these 

 yttrium constituents would behave in respect to the spark 

 spectrum. Do the definite system of lines in the old yttrium 

 spark spectrum belong to one constituent only, or are the 

 yttrium lines broken up and distributed among the different 

 bodies I have designated as Go, G/3, &c. ? Also do the other 

 constituents possess special spark spectra of their own ? Very 

 careful and long-continued experiments have shown me that 

 neither of these hypothetical cases occur. 



The spark spectrum given by old yttrium is shown in the 

 dra\\ing (Fig. 5). It is chiefly characterised by two very strong 

 groups of lines in the red and orange. I now take the earth 

 GS. This occurs near one end of the fractioning, and not only 

 diffes from the parent yttrium in its phosphorescent spectrum, 

 but by virtue of the process adopted for its isolation it must 

 likewise differ in its chemical properties. On examining its 

 spark spectrum I see absolutely no difference between this 

 spectrum and the one given by old yttrium. 



I now pass to the other end of the fractionation of yttrium, 

 where occurs a concentration of a body giving a totally different 

 phosphorescent spectrum from the one at the first end. And it 

 also differs chemically from old yttrium, and in a more marked 

 manner from its brother, GS, at the other extremity of the frac- 

 tionation. Here again its spark spectrum is perfectly identical 

 both with old yttrium and with GS, and however closely I 



examine these three spectra in my laboratory, the whole system 

 of lines is still identical. 



Respecting the theoretical considerations involved in these 

 results, I see two possible explanations of the facts brought 

 forward. According to one hypothesis, research has somewhat 

 enlarged the field lying between the indications given by ordinary 

 coarse chemistry and the searching scrutiny of the prism. Our 

 notions of a chemical element have expanded. Hitherto, the 

 molecule has been regarded as an aggregate of two or more 

 atoms, and no account has been taken of the architectural design 

 on which these atoms have been joined. We may consider that 

 the structure of a chemical element is more complicated than 

 has hitherto been supix)sed. Between the molecides we are 

 accustomed to deal with in chemical reactions and the ultimate 

 atoms, come smaller molecules or aggregates of physical atoms ; 

 these sub-molecules differ one from the other, according to the 

 position they occupied in the yttrium edifice. 



An alternative theory commends itself to chemists, to the 

 effect that the various bodies discussed above are new chemical 

 elements differing from yttrium and samarium in basic powers 

 and several other chemical and physical properties, but not 

 sufficiently to enable us to eft'tct any but a slight separation. 

 One of these bodies, GS, gives the phosphorescent citron line, 

 and also the brilliant electric spectrum. The other seven do 

 not give electric spectra which can be recognised in the presence 

 of a small quantity of GS, whilst the electric spectrum of GS is 

 so sensitive that it shines out in undiminished brilliancy even 

 when the quantity present is extremely minute. In the process 

 of fractionation, Ga, G/3, GS, &c. , are spread out and more or 

 less separated from one another, yet the separation is imperfect 

 at the best, and at any part there is enough GS to reveal its 

 presence by the sensitive electric spark test. The arguments in 

 favour of each theory are strong and pretty evenly balanced. 



