44 SIR WILLIAM CROOKES ON SCANDIUM. 



Added April 30th, 1908. 



Scandium is remarkable inasmuch as its existence was foretold by MENDELEEFF,* 

 and called by him ekaboron, eight years before its actual discovery by NILSON. To-day 

 I may be permitted to indulge still further in speculations on the genesis and 

 degradation of the chemical elements speculations which a few years ago might have 

 Iteen derided even by a learned Society. But the undoubted fact of the production 

 of helium from radium, the probability that chemical elements of high atomic weight 

 are slowly breaking up into bodies of lower atomic weight, and the suspicion that 

 some well-known chemical elements of low atomic weight are degradation products, 

 embolden me to speculate on the past history and genesis of scandium. 



In 1898 I brought before the Eoyal Society a scheme of the arrangement in Space 

 of the chemical elements in which scandium was seen to fall in place between boron 

 and yttrium. I hesitated to introduce ytterbium into the scheme, as its atomic 

 weight was not known with sufficient accuracy to enable it to be properly placed. 

 To-day it is seen to fill a gap below yttrium, and the group is: Boron, scandium, 

 yttrium, ytterbium. These four elements have a close relationship, thus : 



B atomic weight . .... I TO x 1(5 == 176'0 



Se 44-1 . x 4 == .176-4 



Y 89-0 x 2 = 178-0 



Yb m-0 x 1 = 173-0 



In reference to this table it must be remarked that the atomic weight of scandium 

 certainlv is not known with absolute accuracy, the '1 being little more than a guess. 

 Yttrium, moreover, is now seen to be very liable to contain scandium ; when 

 CLEVE determined its atomic weight it was impossible, without further refined 

 spectroscopic examination not available at that date to detect in it the trace of 

 scandium sufficient to lower the atomic weight by one unit. Ytterbium certainly is 

 too low, for URBAIN recently has announced the discovery in it of an element of a 

 lower atomic weight ; this being removed might raise the atomic weight of ytterbium 

 a few units. With these reasonable corrections the last column will not be far from 

 the same whole number, 17G. 



The frequent occurrence of the triad ytterbium, yttrium, and scandium in a very 

 limited group of rare minerals may be explained by assuming the instability of 

 ytterbium, the atom of highest weight, and letting it split into two atoms, when 

 yttrium would be produced. Assume the same action to take place with yttrium, its 

 splitting up again into two atoms would produce scandium ; and scandium (" eka-boron, 



* D. I. MENDELEEFF, " A Natural System of the Elements, and its Application to the Indication of the 

 Properties of Undiscovered Elements," ' Russ. Chem. Soc. Journ.,' 1871, iii., pp. 25-56. 



