Chapter XXIV: 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.
\_____________________________________/ \_______________/
| |
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.
\____________________________________/ \______________/
| |
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.

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 ” ” ” ” ”

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.
\___________________________________/
|
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.
\_______________________________________________________/
|
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.