116 



Mr. H. M. Vernon on the 



distinct elements, and that all that fractionation actually does 

 accomplish is to partially separate these two or three earths, 

 which very much resemble each other in most of their 

 properties, and which are therefore confounded together. 



But, it may be said, even if this be found to be the case, 

 will not the number of distinct earths be so large that it will 

 not be possible to find places for them in the table of elements, 

 arranged according to the Periodic Law, and even then is it 

 possible to explain why such a large number of elements 

 should exist, apparently differing in very little besides their 

 atomic weights and basicity ? 



On examination, I think it will be found that not only is 

 there a place in the table of elements arranged according to 

 the Periodic Law for all of the rare earths at present dis- 

 covered, but for several more besides ; and also that a 

 reasonable explanation can be offered why so many of these 

 elements, so similar in almost every property, should exist. 



The members of these rare earths which have been dis- 

 covered during the last few years are as follows : — 



Lanthanum 



. 138 



Terbium . 



. 124-7 



Cerium 



. 140-2 



Erbium 



. . 166 



Didymium . . 



. 142-3 



Ytterbium 



. 173-7 



Samarium . 



. 150 



Thulium . . 



. 169-5 



Mosandrium 



. 153-6 



Scandium . 



. 44-1 



Holmium . 



. 162 



Yttrium . 



. 89-1 



Several other new elements of this class, besides those 

 mentioned here, have been claimed to have been discovered, 

 but their existence is so exceedingly doubtful that they have 

 not been introduced in this list. Also two or three of those 

 here mentioned have but a very doubtful existence. The 

 numbers attached to these elements are their atomic weights, 

 calculated on the assumption that the earths analysed had a 

 composition expressed by the formula R 2 3 . 



The two constituents neodymium and praseodymium into 

 which Dr. Auer von Welsbach has separated didymium into 

 are not mentioned in this list, as it was thought better to wait 

 for confirmation of this remarkable result by other chemists. 



Let us now take each of these elements separately and see 

 if there is a place for it in the table of elements. 



In this table two series of elements have been introduced 

 between the series commencing with caesium and that com- 

 mencing with gold, as suggested by Brauner (Chem. Soc. 

 Journ. 1882, p. 78). 



