You will be astonished when I tell you what this curious play of carbon
amounts to. A candle will burn some four, five, six, or seven hours. What,
then, must be the daily amount of carbon going up into the air in the way
of carbonic acid! What a quantity of carbon must go from each of us in
respiration! What a wonderful change of carbon must take place under these
circumstances of combustion or respiration! A man in twenty-four hours
converts as much as seven ounces of carbon into carbonic acid; a milch cow
will convert seventy ounces, and a horse seventy-nine ounces, solely by
the act of respiration. That is, the horse in twenty-four hours burns
seventy-nine ounces of charcoal, or carbon, in his organs of respiration,
to supply his natural warmth in that time. All the warm-blooded animals
get their warmth in this way, by the conversion of carbon, not in a free
state, but in a state of combination. And what an extraordinary notion
this gives us of the alterations going on in our atmosphere. As much as
5,000,000 pounds, or 548 tons, of carbonic acid is formed by respiration
in London alone in twenty-four hours. And where does all this go? Up into
the air. If the carbon had been like the lead which I shewed you, or the
iron which, in burning, produces a solid substance, what would happen?
Combustion could not go on. As charcoal burns, it becomes a vapour and
passes off into the atmosphere, which is the great vehicle, the great
carrier for conveying it away to other places. Then, what becomes of it?
Wonderful is it to find that the change produced by respiration, which
seems so injurious to us (for we cannot breathe air twice over), is the
very life and support of plants and vegetables that grow upon the surface
of the earth. It is the same also under the surface, in the great bodies
of water; for fishes and other animals respire upon the same principle,
though not exactly by contact with the open air.
Such fish as I have here [pointing to a globe of gold-fish] respire by the
oxygen which is dissolved from the air by the water, and form carbonic
acid; and they all move about to produce the one great work of making the
animal and vegetable kingdoms subservient to each other. And all the
plants growing upon the surface of the earth, like that which I have
brought here to serve as an illustration, absorb carbon. These leaves are
taking up their carbon from the atmosphere, to which we have given it in
the form of carbonic acid, and they are growing and prospering. Give them
a pure air like ours, and they could not live in it; give them carbon with
other matters, and they live and rejoice. This piece of wood gets all its
carbon, as the trees and plants get theirs, from the atmosphere, which, as
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