Martha Markham, age 11, of Charleston, West Virginia, for her question:
What is the fizzy stuff in carbonated water?
Our ancestors drank fizzy water made from nature's own recipes. They found it in mineral springs and some varieties were said to cure various ailments. Nature's fizzy recipes were copied and improved and nowadays we drink up oceans of bubbly, man made soda pop every year.
The fizzy bubbles in a bottle of carbonated water are imprisoned balls of gas. As a rule, the gas is carbon dioxide the waste gas we breathe out from our lungs. You can create fizzy bubbles by adding a pinch of powdery white bicarbonate of soda to a glass of water. This soda water lends its name to our carbonated soda water but the two liquids are not the same. Actually there is no soda in our soda pops. They are carbonated with gassy bubbles of carbon dioxide.
This waste gas is harmful only when it replaces all the oxygen in the lungs. At everyday temperatures it is a gas, one and a half times heavier than ordinary air. When chilled to minus 78 degrees Centigrade, carbon dioxide becomes a watery liquid. With still more chilling, it becomes the colder than cold solid we call dry ice. Carbon dioxide molecules are large and heavy and the gas can be squeezed and compressed. Extra pressure makes it cool faster into its liquid or solid forms.
As a rule, the liquid carbon dioxide used in carbonated water is chilled under pressure. If the pressure is 70 times heavier than the weight of the atmosphere, no outside refrigeration is needed to change the gas into a watery liquid. This chilly liquid is hard to handle, for if it reaches the air it boils up and becomes gas again. It is sealed in strong steel tanks until needed.
The next ingredient for the pop is water, pure water. Every faint odor and flavor will be very noticeable in the finished drink. Sugary sweeteners;.. juices and other flavorings must be measured strictly and added with care. The liquid carbon dioxide mixes with the drink and loses itself. But if the mixture is allowed to stand in the air, it begins to change itself into tiny bubbles of gaseous carbon dioxide. The fizzy bubbles rise to the top of the drink and escape.
We want, of course, to keep the fizz in the pop until we are ready to drink it. Pressure, remember, helped to change the gaseous carbon dioxide into a liquid. And pressure can be used~to keep it dissolved and hidden in the carbonated water. The mixture is kept under pressure by the cap on the top of the bottle. When the cap is removed, the bubbles of gas come fizzing up and add a refreshing tingle to the soda pop.
There is very little carbon dioxide in the air, but there is lots of it combined with certain rocky minerals in the ground. The gaseous and the mineral forms dissolve readily in water. Underground water often contains large amounts of carbon dioxide dissolved under pressure. When such a spring comes to the surface, the gas escapes in bubbles. Then we have a natural spring of fizzy carbonated water.