1885.] Recent Developments of Chemical Science. 15 
more nearly related to each other than to those of the 
even series. 
b. In the elements of the second series the foregoing rule 
is often reversed from carbon to fluorine, and in the 
third series from sodium to silicon inclusively. This 
appears very distinctly on examining Lothar Meyer’s 
“ curve of the elements.” See his “ Moderne Che- 
mische Theorien,” or Pattison Muir’s “ Principles of 
Chemistry,” p. 227). This curve, on reaching carbon, 
instead of falling, rises until it meets sodium, and 
then falls from sodium to silicon, instead of rising. 
This inverted character of the curve accurately illus- 
trates certain properties of the elements which lie 
within the limits above mentioned. 
c. The elements belonging to Mendelejeff’s eighth group 
are peculiar in many respeCts. They form, unques- 
tionably, the conneCting-links between the even series 
on the one hand, and the odd series on the other. 
This faCt is illustrated by Meyer’s curve, which shows 
that they form, step by step, a transit from the even 
to the odd series, or rather from the ascending to the 
descending parts of the curve. The elements of this 
group are found at the lowest points of the curve. 
After having thus laid down the preliminaries upon which 
he takes his stand, Prof. Carnelley proposes the following 
law : — 
1. Elements which belong to uneven series are, as a rule, 
easily obtained in the free or uncombined state, whilst those 
belonging to the even series cannot without difficulty be 
liberated from their combinations. 
The only exceptions to this rule — somewhat numerous, it 
must be confessed — are carbon, nitrogen, oxygen, sodium, 
aluminium, and silicon, the explanation of which is found 
under Mendelejeff’s rule b, and also the elements of group 
VIII. (See c .) 
2. As regards the occurrence of the elements in Nature, 
in a free state, a point naturally connected with their readi- 
ness in being expelled from combination we have then the 
following law : — 
Elements belonging to the even series (with the exception 
of carbon, nitrogen, oxygen, and the eighth group) never 
occur in Nature in a free condition, whilst the elements per- 
taining to the odd series may generally speaking, and even 
frequently, be found in the free condition. Instances of 
