between the Atomic Weights. ae 
. The sub-series affiliate with each other in a most remarkable 
manner. Manganese, for example, not only forms a strong pro- 
toxyd base, but also unites with a larger amount of oxygen, 
forming: ‘both a sesquibase and acids. Its atomic weight places it 
in the first group, and it has therefore been classed there, although 
by its properties it is equally allied to the second. Cobalt and 
nickel certainly resemble much more closely the members of the 
first than of the second sub-series, although their atomic weights 
place them in the secon ith this exception, the subdivision 
of the series which the atomic weights require does not differ 
from that suggested by the properties of the elements. The 
members of this series may of course be still further subdivided 
into groups according to their special properties, as they are in all 
works on chemistry. They are placed together here because the 
atomic weights form but one numerical series. 
The isomorphism of the members of this series will be found 
well established with the limitations .before given. In order to 
establish the isomorphism of cobalt and nickel with iron, the 
isomorphism of one atom of arsenic with two atoms of sulphur 
has been assumed. This is generally admitted; but if it is not, 
no one can doubt in regard to the isomorphism of these three met- 
als, as they constantly replace each other Glucinum, zirconium, 
lanthanum , cerium, and thorium, cannot be shown to be isomorph- 
ous with the other metals by any of their compounds, but their 
oxyds are known to replace the analogous oxyds of the other 
metals. So also is ruthenium known to replace rhodium. There, 
have been doubts a hh in regard to the existence of a mono- 
metric form of zine ; but as we have established its isomorphism 
with the other members of. the series, not only by its own crys- 
talline form, but also by those of its compounds, the fact is of no 
eo to the present question. 
e atomic weights of the members of this series, as deter- 
ined: by observation, very nearly correspond with the theoretical 
humbers, which is the more remarkable, as the limit of error in 
the determination of the atomic weights of the greater number, 
especially of the rarer metals, is quite wide. 
The Three and last Series is composed of hydrogen and the 
metals of the alkalies. The analogies between lithium, sodium and 
potassium, are very close, as is well known, and there can be no 
doubt in regard to the propriety of classing them together. It may 
‘said however, in regard to hydrogen, that it resembles as closely 
Some of the metals of the four series as it does those of the alka- 
lies. Though this cannot be denied, yet the fact that the atomic 
Weight of hydrogen is the nucleus of the series, and the great 
solubility of the alkalies in water, may be urged as reasons oe 
cargg it at the head of the Three Series. 
