If the temperature at which a liquid has been impregnated with carbonic acid gas increases, or the pressure at which it was done diminishes, a corresponding amount of gas will escape.
Beverages impregnated at too high a pressure have absolutely no advantage. As high as the pressure may be, as soon as the beverage is poured into a glass, the greatest part of the carbonic acid gas disappears and only about 1 1/2 volumes gas remains, which answers a pressure of about 20 pounds; and this pressure is soon reduced still more in a few moments.
The effect of a high pressure is a great effervescence, and when mixed with syrup a foaming, which makes the beverage appear, in the eyes of the consumer, much more favorable. Water, charged with carbonic acid gas and containing much air is even more effervescent than airless water, as the atmospheric air escapes much quicker from water than carbonic acid gas. When the pressure in a bottle gets diminished by opening, the atmospheric air escapes violently and also with it part of the carbonic acid, before the consumer can manage to swallow the liquid. The greater the violence with which the liquid is forced out of the bottle, the greater is the loss of gas; but such a drink ceases sooner to sparkle. The removal of atmospheric air from carbonated beverages should, therefore, deserve a great deal of attention by all manufacturers, as the process refines and improves the drink and gives it that refreshing and acidulous taste necessary and required of a carbonated beverage, besides preserving it by the absence of air, which is so frequently the source of trouble and destruction to saccharine beverages.
Water impregnated with pure carbonic acid gas will sparkle less violently in an open glass for 10 to 15 minutes, preserving its refreshing and prickling taste, while a beverage containing much air soon becomes flat. At the usual temperature and usual pressure of air water will absorb but its own volume of carbonic acid gas, therefore it would be insufficient to only expose water to the gas for our service. To impregnate water with a greater amount of gas it is necessary to use pressure and the aid of mechanical apparatus to cause and promote the absorption.
The cooler the water is used for impregnating with carbonic acid gas the more gas it will absorb and the longer it will retain it; the warmer the water is the more difficult it will be or the less it will absorb, and the more pressure is necessary to impregnate a certain quantity of gas with the water the quicker the gas will disappear when the drink gets poured into a glass or the bottle is opened. If a fluid impregnated with carbonic acid gas is exposed to the air an exchange of gases takes place, and soon nothing but atmospheric air remains. The same takes place with cylinders or fountains charged with carbonic acid gas. They are never tight enough to prevent the interchange of atmospheric air, and at last nothing but water without carbonic acid gas will be left, when standing too long after they have been charged.