4. _Why do we breathe air?_
Because the air contains _oxygen_, which is necessary to life.
5. _Why is oxygen necessary to life?_
Because it combines with the _carbon_ of the blood, and forms _carbonic
acid gas_.
[Verse: "Be not as the horse, or as the mule, which have
no understanding: whose mouth must be held with the bit and
bridle."--PSALM XXXII.]
6. _Why is this combination necessary?_
Because we are so created that the substances of our bodies are
constantly undergoing change, and this resolving of solid matter into a
gaseous form, is the plan appointed by our Creator to remove the matter
called _carbon_ from our systems.
7. _Why do our bodies feel warm?_
Because, in the union of _oxygen_ and _carbon_, heat is developed.
8. _What is this union of oxygen and carbon called?_
It is called _combustion_, which, in chemistry, means the decomposition
of substances, and the formation of new combinations, accompanied by
heat; and sometimes by light, as well as heat.
9. _What is formed by the union of oxygen and carbon?_
Carbonic acid gas.
10. _What becomes of this carbonic acid gas?_
It is sent out of our bodies by the compressure of the lungs, and
mingles with the air that surrounds us.
11. _Is this carbonic acid gas heavier or lighter than the air?_
Pure carbonic acid gas is the heaviest of all the gases. That which is
sent out of the lungs is not pure, because the whole of the air taken
into the lungs at the previous inspiration has not been deprived of its
_oxygen_, and the nitrogen is returned. Therefore the breath sent out
of the lungs may be said to consist of _air_, with a large proportion
of _carbonic acid gas_.
12. _What is the composition of air in its natural state?_
It consists of _oxygen_, _nitrogen_, and _carbonic acid gas_, in the
proportions of oxygen 20 volumes, nitrogen 79 volumes, and carbonic
acid gas 1 volume. It also contains a slight trace of watery vapour.
13. _What is the state of the air after it has once been breathed?_
It has parted with about one-sixth of its oxygen, and taken up an
equivalent of carbonic acid. And were the same air to be breathed six
times successively, it would have parted with _all_ its oxygen, and
could no longer sustain life.
[Verse: "A prudent man forseeth the evil, and hideth himself; but
the simple pass on, and are punished."--PROVERBS XXVII.]
14. _Is the impure air sent out of the lungs lighter or heavier than
common air?_
At first, being rarefied by warmth, it is _lighter_. But, if
undisturbed, it would become _heavier_ as it cooled, and would descend.
15. _Why is it proper to have beds raised about two feet from the
ground?_
Because at night, the bed-room being closed, the breath of the sleeper
impregnates the air of the room with carbonic acid gas, which,
descending, lies in its greatest density near to the floor.
16. _What are the chief sources of carbonic acid gas?_
The vegetable kingdom (as will be hereafter explained), the combustion
of substances composed chiefly of carbon, the breathing of animals, and
the decomposition of carbonic compounds.
17. _Is breathing a kind of combustion?_
It is. In the breathing of animals, the burning of coals, or of wood,
or candles, &c., similar changes occur. The _oxygen_ of the air
combines with the _carbon_ of the substance said to be burnt, and forms
_carbonic acid gas_, which unfits the air for the purposes of either
breathing or of burning, until it has been renewed by admixture with
the air.
18. _What is carbon?_
It is one of the elementary bodies, and is very abundant throughout
nature. It abounds mostly in vegetable substances, but is also
contained in animal bodies, and in minerals. The form in which it is
most familiar to us is that of _charcoal_, which is carbon almost pure.
19. _What is meant by an elementary body?_
An elementary body is one of those substances in which chemistry is
unable to discover more than one constituent. For instance, the chemist
finds that water is composed of _oxygen_ and _hydrogen_. Water is
therefore a _compound_ body. But _carbon_ consists of _carbon only_,
and therefore it is called a simple, or elementary body.
[Verse: "Where no wood is, there the fire goeth out: so where there
is no tale-bearer, the strife ceaseth."--PROVERBS XXVI.]
20. _Why is it dangerous to burn charcoal in rooms?_
Because, being composed of _carbon_ that is nearly pure, its combustion
gives off a large amount of _carbonic acid gas_.
21. _What is the effect of carbonic acid gas upon the human system?_
It induces drowsiness and stupor, which, if not relieved by
ventilation, would speedily cause death.
22. _What is the reason that people feel drowsy in crowded rooms?_
Because the large amount of carbonic acid gas given off with the
breaths of the people, makes the air poisonous and oppressive.
23. _What other causes of drowsiness are there?_
The candles, gas, or fires that may be burning in the rooms where
people are assembled. Three candles produce as much carbonic acid gas
as one human being; and it is probable that one gas-light produces as
much carbonic acid gas as two persons.
24. _Have people ever been poisoned by their own breaths?_
In the reign of George the Second, the Rajah of Bengal took some
English prisoners in Calcutta, and put 146 of them into a place which
was called the "Black Hole." This place was only 18 feet square by 16
feet high, and ventilation was provided for only by two small grated
windows. _One hundred and twenty-three of the prisoners died in the
night_, and most of the survivors were afterwards carried off by putrid
fevers. Many other instances have occurred, but this one is the most
remarkable.