pirical
knowledge--solely upon the fact that the thing had been done before
over and over, always with the same result. Why the silver forsook the
nitrogen atom and grappled the atom of oxygen no one knows. Nor can any
one as yet explain just why it is that the new compound is an insoluble,
colored, opaque substance, whereas the antecedent ones were soluble,
colorless, and transparent. More than that, no one can explain with
certainty just what is meant by the familiar word soluble itself. That
is to say, no one knows just what happens when one drops a lump of salt
or sugar into a bowl of water. We may believe with Professor Ostwald
and his followers that the molecules of sugar merely glide everywhere
between the molecules of water, without chemical action; or, on the
other hand, dismissing this mechanical explanation, we may say with
Mendeleef that the process of solution is the most active of chemical
phenomena, involving that incessant interplay of atoms known as
dissociation. But these two explanations are mutually exclusive, and
nobody can say positively which one, if either, is right. Nor is either
theory at best more than a half explanation, for the why of the strange
mechanical or chemical activities postulated is quite ignored. How is
it, for example, that the molecules of water are able to loosen the
intermolecular bonds of the sugar particles, enabling them to scamper
apart?

But, for that matter, what is the nature of these intermolecular bonds
in any case? And why, at the same temperature, are some substances held
together with such enormous rigidity, others so loosely? Why does not
a lump of iron dissolve as readily as the lump of sugar in our bowl
of water? Guesses may be made to-day at these riddles, to be sure, but
anything like tenable solutions will only be possible when we know much
more than at present of the nature of intermolecular forces and of the
mechanism of molecular structures. As to this last, studies are
under way that are full of promise. For the past ten or fifteen years
Professor Van 't Hoof of Amsterdam (now of Berlin), with a company of
followers, has made the space relations of atoms a special study, with
the result that so-called stereo-chemistry has attained a firm position.
A truly amazing insight has been gained into the space relations of the
molecules of carbon compounds in particular, and other compounds are
under investigation. But these results, wonderful though they seem
w