COMPOUNDS OF CARBON AND OXYGEN.
While compounds of carbon and _hydrogen_ are very numerous, those
already known being numbered by hundreds, the affinities of _oxygen_
and carbon give rise to a strikingly different result.
When combined with oxygen alone, carbon forms but two compounds. These
are expressed by the following names and formulas:
Carbon monoxide, CO.
Carbon dioxide, CO₂.
Carbon Monoxide (CO).
This gas is most familiarly known as that one which often plays upon
the surface of a hard coal fire and burns there with a dark blue,
feebly luminous, flame. Most of the phenomena of its production and
final burning may be presented as follows: When an ordinary coal
fire, burning in a stove, is amply supplied with air at the bottom,
the oxygen of the air burns the lower portions of carbon into carbon
dioxide. Next, this carbon dioxide is carried up, by the draft, between
any masses of fresh coal that may be upon the top of the fire. This
fresh coal has itself affinity for oxygen under the circumstances just
described as prevailing. As a result, each molecule of carbon dioxide
from the lower portion of the fire yields one of its atoms of oxygen to
an atom of carbon in the upper part.
The chemical change is represented by the following equation:
=CO₂= + =C= = =2CO.=
One molecule of One atom of Two molecules of
Carbon dioxide, Carbon, Carbon monoxide,
44 12 56
parts by weight. parts by weight. parts by weight.
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56 56
As a result, therefore, carbon monoxide is formed and escapes as a
colorless gas from the top of the fuel; there, if the upper door of the
stove admits a sufficient amount of air, the carbon monoxide combines
with the oxygen of this air, and burns with the blue flame already
referred to, and so produces carbon dioxide again.
This chemical change is represented by the following equation:
=2CO= + =O₂= = =2CO₂=
Two molecules of One molecule of Two molecules of
Carbon monoxide, Oxygen, Carbon dioxide,
56 32 88
parts by weight. parts by weight. parts by weight.
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88 88
The carbon monoxide is a very poisonous gas, far more injurious to
health than carbon dioxide.
Carbon Dioxide (CO₂).
This substance and its manner of production have been referred to more
than once in preceding chapters. A more extended notice of it, however,
is appropriate to this place.
It has already been stated that carbon dioxide exists ready-formed in
nature—notably in the atmospheric air. Its principal natural source
in the atmosphere is the combustion of fuel; for almost all fuel is
carbonaceous. Thus coal, wood, oil, illuminating gases, are all highly
carbonaceous substances, and one of the principal products of their
combustion is the gas now under consideration.
[Illustration: FIG. 90.—Machinery for filling bottles with artificial
mineral waters.]
As has already been described, the respiration of animals is closely
connected with a real combustion in the living being. It is true
that this sort of combustion is not attended by the evolution of
light; it is productive of heat, nevertheless, and the heat afforded
by respiration is an important factor in the sustenance of animal
existence. For this heat not only enables the living being to
endure the chilling effects of the winter’s cold; it also keeps the
temperature of the internal organs up to that point which is necessary
for the proper performance of certain animal functions—of which
digestion is a most important example. Now by this combustion carbon
dioxide is generated just as truly as would be the case if the flesh
of the living animal were consumed in a glowing fire. The product of
respiratory combustion is the same carbon dioxide as that recognized
in well-established burnings. The quantities of carbon dioxide evolved
by man and certain of the domestic animals, in each hour of their
existence, have been calculated. They are approximately stated in the
following table:
A man exhales 4 gallons carbon dioxide per hour.
A dog ” 4½ ” ” ” ” ”
A horse ” 50 ” ” ” ” ”
An ox ” 70 ” ” ” ” ”
[Illustration: FIG. 89.—Production of carbon dioxide by combustion of a
diamond in oxygen gas.]
And M. Boussingault has calculated that the approximate amount
of carbon dioxide produced in the city of Paris during a single
twenty-four hours is as follows:
Amount produced by living animals, 55,000,000 cubic feet.
Amount produced by burning of various
kinds of fuel, 27,000,000 cubic feet.
——————————
Total CO₂ produced in twenty-four hours, 82,000,000 cubic feet.
There are certain other natural sources of carbon dioxide that are
worthy of passing mention. Thus in many parts of the world the gas
is continually evolved not only from active volcanoes but also from
extinct ones. Again, another interesting source—though not in the
aggregate a very important one—is found in natural mineral springs. In
these the water often comes to the surface highly charged with carbon
dioxide, and the gas, escaping into the air, imparts to the water its
well-known bubbling appearance.
Experiments with Carbon Dioxide.
For chemical purposes carbon dioxide is commonly produced by the action
of an acid upon some one of the salts known as carbonates. Accordingly
chlorohydric acid and calcic carbonate (that is, common marble) when
brought together produce carbon dioxide. This fact may be readily
shown by the performance of a simple but interesting experiment. The
operation may also serve for the display of some of the principal
properties of the gas.
The experiment in question may be conducted advantageously somewhat
as follows: Provide two convenient glass jars—such as candy jars or
preserve jars; also a short candle, a piece of copper wire, a bottle
of chlorohydric acid and some fragments of white marble. Now attach
the candle to the wire and after lighting the former let it down into
the jars, still burning. The combustion continues because the jars are
full of air and contain ample quantities of oxygen. Next withdraw the
candle and extinguish it for a moment. Now place in the bottom of the
larger jar some chlorohydric acid and into it gently drop some of the
fragments of marble. Effervescence immediately commences. A careful
examination of effervescence shows that in this, as in other cases, the
process consists in the evolution of a gas from a liquid. In the case
in question a colorless gas is plainly evolved, and this gas is carbon
dioxide.
The chemical change is represented by the following equation:
=CaCO₃= + =2HCl=
One molecule of Two molecules of
Calcic carbonate, Chlorohydric acid,
100 73
parts by weight. parts by weight.
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173
= =CO₂= + =CaCl₂= + =H₂O=
One molecule of One molecule of One molecule of
Carbon dioxide, Calcic chloride, Water,
44 111 18
parts by weight. parts by weight. parts by weight.
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173
After allowing the effervescence to continue for five or ten minutes,
relight the candle and again lower it into the jar now containing
carbon dioxide. If a sufficient quantity of the gas is present,
the light will be promptly extinguished when the wick passes below
the surface of the gas. The experiment displays at this stage the
additional fact that the carbon dioxide is heavy, and in filling the
jar it does so from the bottom upward. Now relight the candle and
immerse it in the second jar; this is proved to contain air by the fact
that the candle continues to burn. While it is still quietly burning
there, pour gently upon it the carbon dioxide accumulated in the other
jar. If the amount of this gas is large enough, it will fill the jar
containing the lighted candle and so will readily extinguish the latter.
These experiments demonstrate simply and clearly, certain of the most
important properties of carbon dioxide. Its action in extinguishing
flame is to quench it, very much as water would. When the candle dips
beneath the surface of the carbon dioxide, the flame expires simply
from lack of that oxygen of the air which ordinarily supports the
combustion. And this leads very naturally to the additional statement
that, in similar fashion, living beings are drowned if immersed in
carbon dioxide. For just as water prevents the access of air to the
lungs, and then drowning ensues, so when the animal is beneath the
surface of carbon dioxide he dies from the similar deprivation of air.
Effervescing Beverages.
A large quantity of carbon dioxide taken into the _lungs_ is promptly
fatal to animal life, and even a small increase of that gas, in the
atmospheric air breathed, also produces a marked lowering of the
vitality. It is an interesting fact however that when this gas is taken
into the _stomach_, especially in its solution in water, it has a
wholesome and stimulating effect.
When carbon dioxide is dissolved in water it seems to produce a
true acid, though an unstable one. In accordance with the present
nomenclature, this acid is called carbonic acid and is represented by
the formula H₂CO₃. This substance is present as the main constituent,
or as a subordinate one, in certain natural mineral waters, and
in many simple effervescent beverages. Thus plain soda-water is
merely a solution of carbon dioxide in water. Such solutions are now
manufactured on a large scale, and by mechanical appliances are filled
into siphonlike bottles in such a way that small quantities of the
liquid may be withdrawn without loss of the principal stock of gas.