25. _What is oxygen?_
Oxygen is one of the most widely diffused of the elementary substances.
It is a gaseous body.
[Verse: "Stand in awe and sin not: commune with your own heart upon
your bed and be still"--PSALM IV.]
26. _Why do persons who are walking, or riding upon horseback feel
warmer than when they are sitting still?_
Because as they breathe more rapidly, the combustion of the _carbon_
in the blood is increased by the _oxygen_ inhaled, and greater heat is
developed.
27. _Why does the fire burn more brightly when blown by a bellows?_
Because it receives, with every current of air, a fresh supply of
_oxygen_, which unites with the _carbon_ and _hydrogen_ of the coals,
causing more rapid combustion and increased heat.
28. _Why does not the oxygen of the air sometimes take fire?_
Because oxygen, _by itself_, is incombustible. The wick of a candle,
which retains the slightest spark, being immersed in oxygen, will
instantly burst into a brilliant flame; and even a piece of iron wire
made red-hot, and dipped in oxygen, will burn rapidly and brilliantly.
Oxygen, though non-combustible of itself, is the most powerful
_supporter of combustion_.
29. _Why do we know that oxygen will not burn of itself?_
Because when we immerse a burning substance into a jar of oxygen, it
immediately burns with intense brilliancy; but directly it is withdrawn
from the oxygen, the intensity of the flame diminishes, and the oxygen
which remains is _unaffected_.
30. _Why do we know that oxygen is necessary to our existence?_
Because animals placed in any kind of gas, or in any combination of
gases, where oxygen _does not exist_, die in a very short time.
31. _Where is oxygen found?_
It is found in the air, mixed with _nitrogen_; in water combined with
_hydrogen_; in the tissues of vegetables and animals; in our blood; and
in various compounds called, from the presence of oxygen, _oxides_.
32. _Why is the oxygen of the air mixed so largely with nitrogen?_
Because _oxygen_ in any greater proportion than that in which it is
found in the atmosphere, would be too exciting to the animal system.
Animals placed in _pure oxygen_ die in great agony from fever and
excitement, amounting to madness.
[Verse: "As vinegar is to the teeth, and as smoke to the eyes, so is
the sluggard to him that sent him."--PROVERBS X.]
33. _What is nitrogen?_
Nitrogen is an elementary body in the form of gas.
34. _Where is nitrogen found?_
It is chiefly found in the air, of which it constitutes 79 out of 100
volumes. It may be mixed with oxygen in various proportions; but in the
atmosphere it is uniformly diffused. It is found in most animal matter,
_except fat and bone_. It is not a constituent of the _vegetable
acids_, but it is found in most of the _vegetable alkalies_.
35. _What are acids?_
Acids are a numerous class of chemical bodies. They are generally sour.
Usually (though there are exceptions) they have a great affinity for
water, and are easily soluble therein; they unite readily with most
_alkalies_, and with the various _oxides_. All acids are compounds of
two or more substances. Acids are found in all the kingdoms of nature.
36. _What are alkalies?_
Alkalies are a numerous class of substances that have a great affinity
for, and readily combine with, _acids_, forming _salts_. They exercise
peculiar influence upon vegetable colours, turning blues green, and
yellows reddish brown. But they will restore the colours of vegetable
blues which have been reddened by _acids_; and, on the other hand,
the _acids_ restore vegetable colours that have been altered by the
_alkalies_. Alkalies are found in all the kingdoms of nature.
37. _Could animals live in nitrogen?_
No; they would immediately die. But a mixture of _oxygen_ and
_nitrogen_, in equal volumes, constitutes _nitrous oxide_, which gives
a pleasurable excitement to those who inhale it, causing them to be
merry, almost to insanity; it has, therefore, been called _laughing
gas_.
38. _Why does nitrous oxide produce this effect?_
Because it introduces into the body more _oxygen_ than can be consumed.
It, therefore, deranges the nervous system, and being a powerful
stimulant, gives an unnatural activity to the nervous centres and the
brain.
[Verse: "Lord, make me know mine end, and the measure of my days,
that I may know how frail I am."--PSALM XXXIX.]
39. _In what proportions are the atmospheric gases found in the blood?_
The mean quantity of the gases contained in the human blood has been
found to be equal to 1-10th of its whole volume. In _venous_ blood, the
average quantity of _carbonic acid_ is about 1-18th, that of _oxygen_
about 1-85th, and that of _nitrogen_ about 1-100th of the volume of
the blood. In _arterial_ blood their quantities have been found to be
_carbonic acid_ about 1-14th, _oxygen_ about 1-38th, and _nitrogen_
about 1-72nd.
40. _Then is nitrogen taken into the blood from the air?_
Such a supposition is highly improbable. It is probably derived
from _nitrogenised food_, just as _carbonic acid_ is derived from
_carbonised food_.
41. _What is venous blood?_
Venous blood is that which is returning through the _veins_ of the body
from the organs to which it has been circulated.
42. _What is arterial blood?_
Arterial blood is that which is flowing from the heart through the
_arteries_ to nourish the parts where those arteries are distributed.
43. _What is the difference between venous and arterial blood?_
Venous blood contains _more_ carbonic acid, and _less_ oxygen and
nitrogen than arterial blood.
44. _Will nitrogen burn?_
It will not burn, nor will it support combustion.
45. _What is the difference between "burning" and "supporting
combustion?"_
Oxygen gas will not burn of itself, but it aids the decomposition
by fire of bodies that are combustible. It is therefore called a
_supporter of combustion_. But hydrogen gas, _though it burns of
itself_ will extinguish a flame immersed in it. It is therefore said
to be a body which will _burn_, but _will not support combustion_.
[Verse: "As coals are to burning coals, and wood to fire; so is a
contentious man to kindle strife."--PROVERBS XXVI.]
46. _What becomes of the nitrogen that is inhaled with the air?_
It is thrown off with the breath, mixed with _carbonic acid gas_, and
flies away to be renewed by a fresh supply of oxygen.
47. _Where does nitrogen find a fresh supply of oxygen?_
In the atmosphere. Nitrogen is said to possess a remarkable tendency to
_mix_ with oxygen, without having a positive chemical _affinity_ for
it. That is to say, neither the _oxygen_ nor the _nitrogen_ undergoes
any change by the union, except that of _admixture_. The oxygen and
the nitrogen still possess their own peculiar properties. Oxygen and
nitrogen are found in nearly the same proportions in all climates, and
at all altitudes.
48. _In combustion does any other result take place besides the union
of oxygen and carbon forming carbonic acid gas?_
Yes. Usually _hydrogen_ is present, which in burning unites with
_oxygen_, and forms _water_.