See! I have dipped my pencil into the goblet, and brought up a drop of
water. What force binds together the pencil and the drop? What holds the
drop to other drops? Why is not this ice instead of water? If I shake the
pencil in what direction does the drop fall? If the drop were larger than
the world, which way would the world go? What other force is there in it
which, according to Faraday, is equal to that in a flash of lightning?
Here are, then, five great forces in a drop of water, yet none of them
changes its nature. It is still H₂O.
Let us place this drop of water in the upright tube of an atomizer.
Apply air. See, the drop has broken into thousands of particles. Now,
suppose we could take one of these and place it in a flask. Apply heat,
and we should separate the little particle into thousands of particles
of steam, but each of these, and any lesser division of these, would
still be H₂O. The minutest division of the water _possible_ would be
called a _molecule_, yet it would still be water, and composed of two
parts of hydrogen and one of oxygen. The old ocean itself contains the
same. The Cracow beds of salt are made of chlorine and sodium, and the
minutest dust from one of its crystals would be found to contain the
same elements, and in the same proportion, both by weight and measure.
Molecules, then, combined, make only _masses_ of the same nature. But
molecules are composed of atoms, and whenever atoms of two or more
different substances are combined they always form something different
from either of these. The force that unites them is called chemical
affinity, or sometimes the chemical force. For example, tenacious iron
unites with a gas and forms a brittle, red substance, rust. Chlorine
is a poisonous gas, and sodium will burn on water, both deadly; united
they give us salt; absolutely essential to life. Hydrogen is the best
substance in the world to burn, and oxygen the best supporter of
combustion. When united they form water, which is universally employed
to extinguish fire. Blue vitriol is blue, as the name implies, yet it is
composed of four elements, two of which, H and O, are colorless, copper,
which is red, and sulphur, which is yellow. Sulphur has little or no
odor, and hydrogen has none, but when united they form a gas which has
the odor of spoiled eggs. White sugar is nothing but black charcoal and
water. It will thus be seen that here is a source of _new_ things in
nature. Whatever chemical affinity touches is changed.
And so we have found another force in our drop of water taken from the
goblet, more wonderful than any yet named, a mighty, transforming energy
which has but one worthy rival in the work of creating new things, the
vital principle, and even that must yield at last to this all conquering
power. If our goblet was large, and held a pound of water, (about a
pint,) we should find that to pull the molecules apart, that is, make
it into steam, would require a force which would raise four tons to the
height of one hundred feet. But more wonderful still, to separate the
pound of water into two chemical constituents would require, according to
Prof. Cooke, an energy which would raise 5,314,200 pounds one foot. Our
pint of water would then occupy 1800 times its present volume.
Let us now give a striking and beautiful illustration of chemical
affinity. We will throw into this tumbler a piece of potassium (symbol
K) half as large as a pea. This interesting metal was discovered by Davy
in 1807. Its affinity for O is very great. As soon as it falls upon the
water it abstracts oxygen and forms potassium oxide (potash), while the
hydrogen and a small amount of volatilized K escape and are burned with a
brilliant violet flame, on account of the heat evolved by the energetic
chemical action.
[Illustration: POTASSIUM BURNING BY COMBINING WITH THE OXYGEN OF WATER.]