ay and the lime is left. By this
method of procedure we see the lime, but we do not see the carbonic
acid. If on the other hand you were to powder a little chalk and drop
it into a good deal of strong vinegar, there would be a great bubbling
and fizzing, and finally a clear liquid in which no sign of chalk
would appear. Here you see the carbonic acid in the bubbles; the lime
dissolved in the vinegar vanishes from sight. There are a great many
other ways of showing that chalk is essentially nothing but carbonic
acid and quicklime. Chemists enunciate the result of all the
experiments which prove this, by stating that chalk is almost wholly
composed of "carbonate of lime."

It is desirable for us to start from the knowledge of this fact, tho
it may not seem to help us very far toward what we seek. For carbonate
of lime is a widely spread substance, and is met with under very
various conditions. All sorts of limestones are composed of more or
less pure carbonate of lime. The crust which is often deposited by
waters which have drained through limestone rocks, in the form of what
are called stalagmites and stalactites, is carbonate of lime. Or to
take a more familiar example, the fur on the inside of a tea-kettle is
carbonate of lime; and for anything chemistry tells us to the
contrary, the chalk might be a kind of gigantic fur upon the bottom of
the earth-kettle, which is kept pretty hot below...

But the slice of chalk presents a totally different appearance when
placed under the microscope. The general mass of it is made up of very
minute granules; but imbedded in this matrix are innumerable bodies,
some smaller and some larger, but on a rough average not more than a
hundredth of an inch in diameter, having a well-defined shape and
structure. A cubic inch of some specimens of chalk may contain
hundreds of thousands of these bodies, compacted together with
incalculable millions of granules.

The examination of a transparent slice gives a good notion of the
manner in which the components of the chalk are arranged, and of their
relative proportion. But by rubbing up some chalk with a brush in
water and then pouring off the milky fluid, so as to obtain sediments
of different degrees of fineness, the granules and the minute rounded
bodies may be pretty well separated from one another, and submitted to
microscopic examination, either as opaque or as transparent objects.
By combining the views, obtained in these various method