Experiments with Carbonic Acid Gas
In a [previous chapter], when describing how to make a miniature cannon, it was explained that the “gunpowder” with which the “shell” was fired is in reality carbonic acid gas.
It may not be amiss to show how to generate it, in order that you may discover for yourselves some of its properties.
There are several ways of obtaining carbonic acid gas, but most of these are of a complicated nature. The following, however, is an extremely simple method.
Take a 6-oz. or 8-oz. flask, and fit it with a cork with a hole, in which may be fitted a piece of glass tubing.
This tubing should be bent twice at right angles, as shown in [Fig. 15], and the longer end should be allowed to dip into a large glass.
Fig. 15.—A carbonic acid gas experiment.
Into the flask pour a little lemonade, soda water or ginger ale, and after replacing the cork or tube, heat the flask by means of a gas-burner or spirit lamp.
You will notice that bubbles of gas are given off, and, as this gas is considerably heavier than air, it will, after being forced up the tube, displace the air in the glass, and gradually fill it. To test whether the glass is full, hold a match in the top. If the match is extinguished, the glass which is full may be removed. In this way several glasses can be filled, care being taken to cover each with a glass plate or cardboard disc to prevent diffusion.
From this experiment you will have discovered the three main properties of this gas (commonly known as carbon dioxide)—that it is colorless, is considerably heavier than air, and will not support combustion. Its high density affords another interesting experiment, which consists of pouring the gas from one glass to another ([Fig. 16]).
Fig. 16.—Pouring carbon dioxide from one glass to another.
Take two glasses, one full of air and the other containing the carbonic acid gas, and into each plunge a lighted match. The match of course will burn in the glass containing air, whilst it will be immediately extinguished when it comes in contact with the carbon dioxide. You have thus clearly shown which glass contains air and which contains the gas. Now take the glass containing the gas and pour its contents into the other glass, in exactly the same way as you would pour in water. Again test with a lighted match and you will find that the gas has passed from one glass to another, thus proving that it is much heavier than air.
Next take two glasses, one containing air and the other carbonic acid gas, and, by means of a clay pipe, blow a soap bubble into each, carefully watching the different manners in which they behave. That dropped into the glass containing air will sink to the bottom, where, coming in contact with the glass, it will burst. The other bubble, however, as soon as it reaches the gas in the glass, rebounds owing to the high density of the carbon dioxide, but after a time, when it has settled down, it will float motionless on the surface ([Fig. 17]).
Fig. 17.—Soap bubbles in A (air), and B, carbon dioxide.
Before you finish experimenting you should know how to detect the presence of carbon dioxide. Take a little lime water, which may be obtained from any druggist, and pour it into a glass containing carbon dioxide. Shake the glass, and carefully observe the change which takes place. The lime water, which was previously colorless, has assumed a certain milkiness, and if allowed to stand the white powder causing this milkiness will settle at the bottom of the glass. This powder proves to be calcium carbonate, or chalk, which is always formed when lime water comes in contact with carbon dioxide, so that you have here a means of detecting the presence of carbon dioxide. Breathe into a little lime water and you will learn, from the milky appearance it at once assumes, that the air we exhale contains a certain quantity of this interesting gas.