LECTURE XV.] HISTORY OF CHEMISTRY. 313 



The atomic weight of indium was assumed to be 113, or 

 one and a half times as great as previously, and this number 

 was very soon confirmed by the determination of the specific 

 heat of the metal by Bunsen 84 and by Mendelejeff. 85 The 

 atomic weight of uranium was doubled a proceeding which 

 was found by the excellent and detailed investigations of 

 Zimmermann 8 * 5 to be in complete agreement with the facts. 

 Finally, it may be pointed out that Mendelejeff adopted 125 

 as the atomic weight of tellurium, in opposition to the previous 

 determinations which had furnished the number 128. This 

 was also apparently confirmed by the redetermi nation of the 

 atomic weight in a specially purified sample, 87 but Brauner's 

 most recent experiments gave essentially different results. 



But Mendelejeff's predictions respecting new elements have 

 been followed by results which are simply marvellous. In 

 order to render possible the arrangement into groups and series, 

 and to attain approximately equal differences in successive 

 members, blanks had to be left, which, according to Mendelejeff, 

 would be filled up by existing, but at that time unknown, 

 elements. He was able to foretell the atomic weights and 

 other properties of these elements from their position in the 

 system, with the aid of the properties observed in the groups 

 and series, which, like a system of co-ordinates, could be called 

 in to assist. Three such blanks occurred in the first five series, 

 and these he indicated as representing the positions of eka-boron 

 (at. wt. 44), eka-aluminium (at. wt. 68), and eka-silicon (at. wt. 

 72). Since that time, these three elements have been dis- 

 covered, and they have been found to possess, approximately, 

 the properties predicted by Mendelejeff. They are: scandium, 

 discovered by Nilson, 88 with atomic weight 44.1 ; gallium, dis- 

 covered by Lecoq de Boisbaudran, 89 with atomic weight 70; and 

 germanium, discovered by Winkler, 90 with atomic weight 72. 



But these are not the only results which render this theory 



84 Pgg- Ann - I 4 I > I' 85 Bull, de 1'Acad. Imp. de St. Petersbourg. 

 16, 45. 86 Annalen. 213, 285 ; 216, I. 87 Brauner, Berichte. 16, 



3055 ; compare p. 346. 88 Uerichte. 12, 550, 554 ; 13, 1439. 8<J Comptes 

 Rendus. 8l, 493. iioo ; 86, 475, etc. 90 J. pr. Chem. [2], 34, 177. 



