The other gas is called nitrogen; it is a dull gas, with no
life in it, and remains behind when all the oxygen is taken out of the air.
But this part of the air is very useful; it prevents the breathing of men
and animals and the burning of fires and lamps, from going on too fast. If
you had only the life-sustaining part of the air to breathe, you would soon
die; and if the air was all made of that part which burns so well, one
spark falling upon it would be enough to burn up the whole world, for no
one could put the fire out.
These two gases are mixed in nearly the same proportions in all climates
so as to make the beautiful pure air which God has given us to live and
go about in. There is another gas, called carbonic acid, made partly
of oxygen and partly of carbon, or burnt wood, which might be called
"life-destroyer," for it will put out light and make an end of life. It is
one of the most deadly poisons, and forms the "choke-damp" which too often
suffocates the miner; but what we call fresh air contains such a very
small proportion of this dangerous gas that it is harmless. Still we must
remember that every time anyone or any animal breathes, some of the air
by which we live is taken away from that which surrounds us, and some of
this poisonous air is thrown into it. If this is the case, should we not,
by degrees, find the air becoming less and less pure and fit for us to
breathe?
Certainly it would be so, if God had not made a beautiful provision for
keeping the air fresh, which I will try to explain to you.
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