nnot be prevented
from uniting under ordinary conditions. Contrariwise, under ordinary
conditions the substances of high molecular weights--the "noble
metals"--are indifferent to other substances; and such compounds as they
do form under conditions specially adjusted, are easily destroyed. Thus
as, among the bodies we know to be compound, increasing molecular weight
is associated with the appearance of certain characters, and as, among
the bodies we class as simple, increasing molecular weight is
associated with the appearance of similar characters, the composite
nature of the elements is in another way pointed to.

There has to be added one further class of phenomena, congruous with
those above named, which here specially concerns us. Looking generally
at chemical unions, we see that the heat evolved usually decreases as
the degree of composition, and consequent massiveness, of the molecules,
increases. In the first place, we have the fact that during the
formation of simple compounds the heat evolved is much greater than that
which is evolved during the formation of complex compounds: the
elements, when uniting with one another, usually give out much heat;
while, when the compounds they form are recompounded, but little heat is
given out; and, as shown by the experiments of Prof. Andrews, the heat
given out during the union of acids and bases is habitually smaller
where the molecular weight of the base is greater. Then, in the second
place, we see that among the elements themselves, the unions of those
having low molecular weights result in far more heat than do the unions
of those having high molecular weights. If we proceed on the supposition
that the so-called elements are compounds, and if this law, if not
universal, holds of undecomposable substances as of decomposable, then
there are two implications. The one is that those compoundings and
recompoundings by which the elements were formed, must have been
accompanied by degrees of heat exceeding any degrees of heat known to
us. The other is that among these compoundings and recompoundings
themselves, those by which the small-moleculed elements were formed
produced more intense heat than those by which the large-moleculed
elements were formed: the elements formed by the final recompoundings
being necessarily later in origin, and at the same time less stable,
than the earlier-formed ones.

NOTE II. May we from these propositions, and especially from the last,
dr