130 MR. H. WILDE ON THE 



it in the Table. The relations which the double atomic 

 weights of In and Yt have to each other, and with their 

 homologues of position Cs, Ba, and A.g, Cd, in Tables 11.^ 

 III.j render it highly probable that the atomic weights of Yt 

 and In in the table are correct. For similar reasons it is 

 probable that the atomic weight of erbium will be found 

 to be 177. It is only very recently that any investigations 

 of the atomic weight of this rare element have been made, 

 from the difficulty attending its isolation from yttrium, 

 with which it is found associated in nature. According 

 to some chemists, the atomic weight of erbium is 11 2*6, 

 which, in relation to 177, is nearly in the ratio of 5 to 8. 

 The more recent researches of M. Cleve on the quanti- 

 valence of this element have, however, raised its atomic 

 weight to 170*55 *, which, considering the wide diflferenee 

 between it and the previous determination, is a near 

 approximation to the number in the Table. The researches 

 of the same chemist have also raised the atomic weight of 

 yttrium from 61 -7, the accepted determination, to 89*5, 

 or three fourths the calculated value. Now the history 

 of chemical science abundantly shows that it is only after 

 long and repeated investigation that the highest quantiva- 

 lence of an element can be ascertained, and the result of 

 M. elevens researches is a further confirmation of the 

 correctness of the atomic weights of yttrium and erbium 

 given in the Table. 



By comparing the electro-positive members of the series 

 Hn with those of H2w, it will be seen that a complete 

 parallelism exists between them ; the light alkaline, and 

 alkaline-earth metals alternating with the heavy members 

 in homologous positions in both series. Odling has 

 already indicated that this is the natural order of the 

 dissimilar members of the zinco-calcic group of elements f, 



* Bull. Societe Ohemique, Paris, tome xxi. p. 344 (1874). 



t Watts, Die. Chem. 1865, vol. iii. p. 963. — "Classification of Metals." 



