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immediately from each of them, and these are the two
gases of which the water is composed. The oxygen is
always liberated on the one wire, the hydrogen on the
other. The two gases may be collected separately; in
fact, they have been thus collected in these jars. A lighted
taper placed in one jar inflames the gas, which proves it to
be hydrogen; a burning ember of wood placed in the
other jar instantly bursts into vivid combustion, which
proves the gas in the jar to be oxygen. I place upon my
hand a soap-bubble filled with a mixture of both gases in
the exact proportions in which they exist in water. Apply-
ing a taper to the bubble, a loud explosion is heard. The
gases have rushed together with detonation, but without
injury to my hand, and the water from which they were
extracted is the result of the reunion.

I wish you to see with the utmost possible clearness
what has here taken place. First, then, you are to re-
member that to form water the proportions by weight of
oxygen and hydrogen are as eight to one. Eight ounces
of oxygen, for example, unite with one of hydrogen to
form nine ounces of water. But if, instead of comparing
weights, we compare volumes, two volumes of hydrogen
unite with one of oxygen to form water. N ow, these vol-
umes, and not the weights, express the proportions in
which the atoms of hydrogen unite with those of oxygen.
In the act of combination two atoms-of hydrogen combine
with one of oxygen to form what we call the molecule of
water. Every such molecule is a group of three atoms,
two of which are hydrogen and one oxygen.

One consequence of the rushing together of the atoms
is the development of heat. What is this heat? How
are we to figure it before our minds ? I do not despair of
being able to give you a tolerably distinct answer to this
question. Here are two ivory balls suspended from the
same point of support by two short strings. I draw them

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