1880.] On the Essential Properties, fyc, of Beryllium. 45 



general applicability. Before concluding this memoir, we will just point 

 out that this is not an isolated case of its kind. Eor the element which 

 should take its place between Sb=122 and 1=127, the periodic law 

 requires an atomic weight = 125 ; with regard to its general properties 

 tellurium is quite admissible in this place, but its atomic weight =128 

 is tod high. Although this number was the result of the determina- 

 tions of Berzelius and v. Hauer, this want of accordance with the 

 periodic law induced Willis* to make a new determination, but he 

 only confirmed the former results. Thus neither tellurium nor beryl- 

 lium can be fitted into MendeleefF's system. And further, after 

 Councler'sf discovery of the boroxychloride, BoOCl 3 , boron may 

 be considered as five-atomic, but it certainly cannot be placed among 

 elements of that valence ; and when once the chemistry of the rare 

 earth-metals shall be made clear, where can be placed all these 

 elements, the number of which has already become very great and 

 doubtless will be still augmented ? Already erbium and ytterbium, 

 with the now fixed atomic weights of 166 J and 173,§ for the pure 

 metals (the earths = Er 2 3 and Yb 2 3 ), can scarcely be ranged in 

 Mendeleeif's system in places indicated by their relation to the other 

 earth-metals or by their " atomic analogies." 



In consequence of what has been indicated here, the periodic law in 

 its present condition cannot be said to be quite an adequate expression 

 for our knowledge of the elements ; this theory, however, having 

 given the most striking proofs that the truth in many respects has 

 been found (as for example : the new formulae for the rare earths 

 = R 2 3 instead of RO, and the discovery of gallium and scandium, 

 the existence of which the law has foreseen in the elements eka- 

 aluminium and eka-boron), we may expect that the periodic law may 

 be so modified and developed that it can embrace and explain every 

 fact, stated by experiment. 



* " Liebig's Ann. d. Ch.," ccii, p. 242. 



f " Ber. d. Deutsch. Chem. Gresellsch.," xi, p. 1108. 



% According to Cleve. 



§ According to Nilson. 



