<h2><SPAN name="CHAPTER_XVIII" id="CHAPTER_XVIII"></SPAN>CHAPTER XVIII</h2>
<h2>OUR RELATIONSHIP TO THE ATOMS</h2>
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<div><span class="pagenum"><SPAN name="Page_178" id="Page_178"></SPAN></span></div>
<h3><i>THE SCRIBE'S NOTE ON CHAPTER EIGHTEEN</i></h3>
<div class="blockquot"><p>We have no doubt that an atom of matter
is a miniature solar system of revolving
electrons.</p>
<p>These electrons, being negative particles of
electricity, would repel each other just as any
two similarly electrified bodies do.</p>
<p>There must therefore be some equivalent of
positive electricity, but whether this exists
in the form of a sphere or in separate particles
we have no definite knowledge.</p>
<p>One atom differs from another in the
number of electrons which go to make up the
atom.</p>
<p>The electron explains how the atoms of
matter are united to one another, how
different compound substances are formed,
and how chemical changes take place.</p>
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<p><span class="pagenum"><SPAN name="Page_179" id="Page_179"></SPAN></span>
I am sorry that this part of my story must
remain incomplete for the present. I am not
free to tell you all I know; you must try and
get behind the scenes on your own account.</p>
<p>One thing I am at liberty to tell you is that
my fellow-electrons who are locked up within
the atoms are not without hope that they
may gain their freedom once more at some
future time. I know this first-hand, for I
have met some fellow-electrons who have
escaped from within an atom, but I shall
delay telling you about these fellows till the
succeeding chapter. My object in mentioning
this fact now is to give you confidence in what
I am about to say regarding the nature of the
atom.</p>
<p>On one occasion I overheard a conversation
between two men who were discussing the
<span class="pagenum"><SPAN name="Page_180" id="Page_180"></SPAN></span>
construction of matter. One remarked that
the atoms were the bricks of the universe,
whereupon the other asked how the little
bricks were cemented together. I wish that
man could have seen a lump of matter as we
see it. He would have been surprised to learn
that the atoms never really touch each other.
They are always surging to and fro, or
<i>vibrating</i>, and it is this motion which constitutes
the <i>temperature</i> of the body which
they compose.</p>
<p>It must be clear, however, that in a solid
body one atom attracts another atom across
the intervening atomic spaces. This is another
duty devolving upon us; what we do, really,
is to upset the electric balance between the
different atoms, and thus produce electrical
attraction.</p>
<p>First of all, perhaps, I should explain that
the different kinds of atoms are simply congregations
of different numbers of electrons.
Of course there is the other part, of which
I am forbidden to speak—the part which man
vaguely describes as <i>positive electricity</i>. However,
you may take it from me that while it is
true that the main difference between an atom
of gold and an atom of iron, or of oxygen, is in
<span class="pagenum"><SPAN name="Page_181" id="Page_181"></SPAN></span>
the number of electrons it contains, there is a
very important difference in the arrangement
of the electrons. You know that they form
rings outside one another, all of which revolve
at enormous speeds. The number of electrons
in the different rings varies according to the
kind of atom.</p>
<p>It is quite correct for man to speak of the
atoms containing certain definite numbers of
electrons, but I should like you to understand
clearly that the exact number of electrons is
not permanently fixed; one or more electrons
can slip off one atom and become attached to
a neighbouring atom which happens to be
capable of accepting it or them. It is the
interchange of these few detachable electrons
that causes one atom to attract another. In
other words, it is the differently charged atoms
which attract each other, just as man crowds
a surplus of electrons on to one object and
finds it attracted bodily towards another object
having a deficiency of electrons.</p>
<p>It is this electrical attraction between the
atoms which enables us to build up the particles,
or <i>molecules</i>, of matter in such a variety
of forms. First of all, we play the most important
part within the atoms. We have
<span class="pagenum"><SPAN name="Page_182" id="Page_182"></SPAN></span>
formed only a limited number of such atoms.
I am not free to tell you exactly how many,
for man has discovered only about eighty of
these different congregations of electrons,
each kind of which he calls an <i>element</i>. The
way in which we have coupled these different
elementary atoms together must appear remarkable
to all thinking men; there seems to
be no end to the possible variety of combinations.</p>
<p>In one case we unite an atom of <i>chlorine</i> to
an atom of <i>sodium</i> and thereby produce a
molecule of common salt. In another case
we unite an atom of <i>oxygen</i> to two atoms of
<i>hydrogen</i>, and the resulting combination is
an invisible molecule of ordinary water.</p>
<p>It has always seemed to me very strange
how some men have difficulty in regard to
these combinations. I have heard a man ask
how two different gases, hydrogen and oxygen,
when united, should form a liquid, and
not a gas. I wish you could see things as
we see them. The atoms are neither gaseous,
liquid, nor solid; they are little worlds of
revolving electrons.</p>
<p>I have spoken of the attraction between
atoms, and again between molecules, in form
<span class="pagenum"><SPAN name="Page_183" id="Page_183"></SPAN></span>ing
a solid body. It will be clear that there
is less of this <i>cohesive force</i> in the case of a
liquid, whereas it is absent entirely in the
case of a gas. In this case the molecules have
become so far separated from one another
that they cease to attract each other, and if
left free they will soon part company, and
spread themselves broadcast over the face of
the earth.</p>
<p>Whether a substance passes into a solid, a
liquid, or a gaseous state, the atoms remain
constant, but their vibratory motion is
altered very considerably. However, I was
about to tell you that we electrons can make
some very interesting combinations of atoms.
Those I have mentioned so far are of a very
simple nature, but we have built up individual
molecules containing hundreds of atoms. We
link about a hundred atoms together and
produce a molecule of what man calls <i>alum</i>,
and we require to unite about a thousand
atoms together to make one molecule of
<i>albumen</i> (the white of an egg).</p>
<p>When man speaks of a chemical change
having taken place in a substance, it is simply
the electrons who have made a friendly
inter<span class="pagenum"><SPAN name="Page_184" id="Page_184"></SPAN></span>change
of detachable electrons, thereby causing
a different assemblage of the same atoms.
During these changes we never alter the
nature of the atom. That little world of revolving
electrons known as an atom of gold,
remains always an atom of gold. But you
must not run away with the idea that the
atoms will never change. Indeed, man has
discovered that the atoms are not eternal, as
I shall explain in the following chapter.</p>
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