Aerated Waters is the name applied to the large class of beverages which are rendered sparkling by dissolving in them carbonic acid under pressure. The term does not include champagne or fermented ginger-beer, or any other carbonated beverage in which the carbonic acid gas is produced by the natural process of fermentation. Carbonic acid dissolves readily in water, that liquid absorbing at the ordinary atmospheric pressure and temperature about its own volume of the gas. Under pressure, however, as when the gas is forced into a strong vessel containing the water, it absorbs many times its own volume; and when the pressure is released, the extra amount of carbonic acid escapes, rendering it sparkling or effervescent. The water does not, however, give off all the extra gas at once; hence the well-known experiment of dropping a piece of cork into a tumblerful of lemonade, when immediate effervescence takes place, and carbonic acid is given off. All agitation, or the presence of particles of dust, favours the disengagement of the gas, and so it is that in drawing lemonade from a siphon (see below), the tumbler is filled with froth to an extent not noticed in pouring from a bottle. In this case, the rapidity of discharge through a narrow tube causes immediate liberation of a large volume of the gas, producing the froth referred to. The varying solubility of carbonic acid at different temperatures and pressures explains why siphons or bottles which have been kept in a cold place appear to be deficient in gas, when in reality the gas is only kept in solution by the low temperature of the water.
It would be beyond the scope of this article to describe the various forms of apparatus used in the production on the large scale of aerated water, for in no branch of industry has more ingenuity been expended than in the devising of labour-saving apparatus for aerated water. Essentially, the process consists in the production of Carbonic Acid (q.v.) from whiting or chalk, by the action of sulphuric acid. The refuse, consisting of plaster of Paris, is thrown away, while the gas, after being purified by washing with water, is stored in a copper bell or gasometer. Thence it is pumped along with water into copper or gun-metal vessels lined with pure tin, being made to dissolve in the water either by agitation or by other appliances. When the pressure inside these vessels reaches about 100 lb. per square inch, the water contains about seven times its volume of gas, and is ready to be filled into bottles. The bottling is accomplished with great speed; an expert bottler being able to fill from thirty to fifty dozen of corked bottles per hour; while, when patent (i.e. ball-stoppered) bottles are used, from forty to seventy dozen may be filled. Up till comparatively recent years, only corks were used for closing the bottles; but it is computed that between 200 and 300 forms of patent bottles have been recently introduced, which all depend on the internal pressure of the gas forcing a ball of glass, wood, or other material against a rubber ring placed in the neck, and thus sealing the bottle. The siphon is a glass bottle, fitted with a metal top, and furnished with a lever or handle, which enables a portion of the contents to be drawn off without difficulty. The head should be of the purest tin, to avoid contamination of the aerated water. Formerly there was risk of lead-poisoning by aerated waters, as they readily dissolve lead, but all manufacturers of any repute now make it a point to use no lead-piping whatever in their machinery, pure tin-pipe being alone admissible.
The better known kinds of aerated waters are: (1) Potash and Soda waters, which, when of full medicinal strength, contain fifteen grains of the bicarbonate of potash or soda in each bottle; usually, however, much less is put in, and the amount ranges from one to seven or ten grains; (2) Aerated water, which is frequently sold for soda-water, but is a simple solution of carbonic acid, and contains no admixture; (3) Seltzer water (better Selters water, being named from Selters, in Nassau, where natural mineral water of this composition is obtained), which contains the chlorides of sodium, calcium, and magnesium, along with phosphate and sulphate of sodium; (4) Medicinal waters, containing varying proportions of chemicals, as, for instance, lime, carbonate of iron, citrate of lithia, or bromide of potassium.
The temperance drinks, which include such favourites as lemonade, ginger-beer, ginger-ale, and tonic bitters, are all made by putting the requisite quantity of flavouring syrup into a bottle, and filling up with simple aerated water; and the varying qualities in the market correspond to the variety in the receipts from which they are made.
On the small scale, and for family use, carbonic acid water may be conveniently prepared in the apparatus known as the gazogène or seltzogène. It usually consists of two globes, one above the other, and connected by a tube. Powders of bicarbonate of soda and tartaric acid are then placed in the upper globe, and the apparatus is inclined till water from the lower globe enters by the tube, and fills the upper globe about one-third. The tartaric acid and bicarbonate of soda have no action on each other so long as they are dry; but whenever water is admitted, the tartaric acid combines with the soda and water to form tartrate of soda and water, and at the same time carbonic acid is given off, and descending the tube into the lower globe, dissolves in the water contained therein. Occasionally, bisulphate of potash is used instead of tartaric acid, to save the greater expense of the latter. Aerated fruit-beverages are produced when the water charged with carbonic acid is received in a glass containing about a table-spoonful of any of the fruit-syrups.
A well-known effervescing draught is made from soda-powders, composed of bicarbonate of soda and tartaric acid. Seidlitz-powders contain tartrate of soda and bicarbonate of soda in one paper, and tartaric acid in the other. Many waters naturally aerated have important medicinal properties; these will be discussed under the title of MINERAL WATERS.