HOW SODA WATER IS MADE. Certain firms make pure carbon dioxid (commercially known as carbonic acid gas) and compress it in iron tanks. These iron tanks of carbon dioxid (CO2) are shipped to soda-water fountains and soda-bottling works. Here the compressed carbon dioxid is dissolved in water under pressure,–this is called “charging” the water. When the charged water comes out of the faucet in the soda fountains, or out of the spout of a seltzer siphon, or out of a bottle of soda pop, the carbon dioxid that was
dissolved in the water under pressure bubbles up and escapes,–the soda water effervesces.Sometimes there is compressed carbon dioxid down in the ground.
This dissolves in the underground water,and when the water bubbles up from the ground and the pressure is released, the carbon dioxid foams out of
the water; it effervesces like the charged water at a soda fountain.
But the most useful and best-known effervescence is the kind you got when you stirred the baking soda in thelemonade. Baking soda is made of the same elements as caustic soda (NaOH), with carbon dioxid (CO2)
combined with them.
The formula for baking soda could be written NaOHCO2, but usually chemists put all of the O’s together at the end and write it NaHCO3. Whenever baking soda is mixed with any kind of acid, the caustic soda part (NaOH) is used up in neutralizing the acid. This leaves the carbon dioxid (CO2) part free,
so that it bubbles off and we have effervescence. Baking soda mixed with an acid always effervesces. That is why sour milk muffins and pancakes are light as well as not sour. The effervescing carbon dioxid makes
bubbles all through the batter, while the caustic soda (NaOH) in the baking soda neutralizes the acid of the
EFFERVESCENCE GENERALLY DUE TO THE FREEING OF CARBON DIOXID
Since baking soda is
so much used in the home for neutralizing acids, people sometimes get the idea that whenever there is
neutralization there is effervescence. Of course this is not true. Whenever you neutralize an acid with baking
soda or washing soda, the carbon dioxid in the soda bubbles up and you have effervescence. But if you
neutralize an acid with ammonia, lye, or plain caustic soda, there is not a bit of effervescence. Ammonia, lye,
and plain caustic soda have no carbon dioxid in them to bubble out.
Baking powder is merely a mixture of baking soda and dry acid (cream of tartar or phosphates in the better
baking powders, alum in the cheap ones). These dry acids cannot act on the soda until they go into solution.
As long as the baking powder remains dry in the can, there is no effervescence. But when the baking powder
is stirred into the moist biscuit dough or cake batter, the baking powder dissolves; so the acid in it can act on
the baking soda and set free the carbon dioxid.
In most cases it is the freeing of carbon dioxid that constitutes effervescence, but the freeing of any gas from
liquid is effervescence. When you made hydrogen by pouring hydrochloric acid (HCl) on zinc shavings, the
acid effervesced,–the hydrogen gas was set free and it bubbled up.
Stirring or shaking helps effervescence, just as it does crystallization. As the little bubbles form, the stirring or
shaking brings them together and lets them join to form big bubbles that pass quickly up through the liquid