205 
erbium is 112’6, which, in relation to 177, is nearly in the 
ratio of 5 to 8. The more recent researches of M. Cleve, 
on the quantivalence of this element have, however, raised 
its atomic weight to 17055* which, considering the wide 
difference between it and the previous determination, is a 
near approximation to the number in the table. The re- 
searches 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 abundant] y 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. 
Cleve's researches is a further confirmation of the correct- 
ness of the atomic weights of yttrium and erbium given in 
the table. 
By comparing the electro-positive members of the series 
H n with those of H2 n, it will be seen that a complete 
parallelism exists between them; the light alkaline, and 
alkaline earth metals alternating with the heavv 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,*^ and similar 
alternations in other natural groups have been recognised 
in the arrangement of elements proposed by Mr. NewlandsJ 
and MendeleefF.|| 
Just as Cu = 62, Ag=108, and x =154, alternate with 
Rb = 85, Cs = 131. and 03 = 177, in the series H n; and Zn = 
64, Cd = 112, and 03 = 160, alternate with Sr = 88, Ba= 136, 
and « = 184; so in the series H3 n, do 03 = 69, Yt = 123, and 
Eb = l77, alternate with 03 = 96, In = 150, and Tl = 204. 
# Bull, Societe Chemique, Paris, tome xxi., 344, 1874. 
f Watts, Die. Chem., 1865, vol. iii., 963 — Classification of Metals. 
t Chem. News, vol. xii., 83 ; vol. xiii., 113. 
|| Die periodische Gesetzmafsigkeit der chemischen elemente — Ann. 
Chem. Pharm. ; Suppl. Band, viii., 133—229, 1872; Phil. Mag. 5th S., 
vol. i., 543, 
