AERATED WATERS.
The invention of soda-water, in the state in which it is now known, as an effervescing beverage impregnated with three or four times its volume of carbonic acid gas, is of very modern date. There are, indeed, to be found in most of the old works on chemistry descriptions of Nooth's apparatus for impregnating liquids with carbonic acid; but all that was attempted to be done by that apparatus was to produce an impregnation of the water with little more than the quantity of gas it will naturally absorb under the pressure of the atmosphere. It was not until about the year 1815 that mechanical pressure was applied to force a larger quantity of gas into combination with water, to imitate the briskly effervescing medicinal waters of Germany.
Mr. Schweppe and Mr. Paul were the first who introduced the manufacture of artificial effervescing waters into England, and soda-water was then considered, as tea was on its first introduction, entirely medicinal. Indeed, the quantity of soda which was at that time usually dissolved in the water gave it a disagreeable taste; but when the manufacturers diminished the quantity of alkali, and increased the volume of gas forced into the water, they produced a pleasant beverage, which soon became in request for its refreshing, wholesome qualities.
The apparatus for the manufacture of soda-water, as it is usually made on a large scale, consists of a strong vessel, furnished with a safety valve, in which the water is impregnated with gas. This vessel, containing about nine gallons, is made of thick wood, well seasoned and nicely fitted, and bound round with strong iron hoops, the heads of the cask being well secured by means of iron bolts and screw nuts. It is requisite that the receiver should be capable of bearing a pressure of at least six atmospheres, which is equal to 90 lbs. to the square inch.
The carbonic acid gas is generated from chalk or whiting and diluted sulphuric acid. The materials are mixed together in a small closed wooden or leaden vessel, provided with an agitator, that can be worked by a handle fixed to a projecting axis at the top. The gas, as generated, enters by a bent tube into a gas-holder, the opening of the tube being under water. By this means the gas is freed from the fumes of sulphuric acid vapour, and from the fine particles of chalk that become mingled with it during its sudden liberation. The gas sometimes undergoes a further purification, by passing through a gas washer, before it is forced into the water.
A small force-pump, worked by a crank, with the assistance of a fly-wheel, draws the carbonic acid from the gas-holder, and forces it into the water. The combination of the gas and water is facilitated by an agitator, the axle of which projects through a stuffing box, and it is worked either by hand, or is turned by means of a small cog-wheel, that works into the teeth of a larger one fixed to the crank axle, so as to produce rapid rotation.
It is found requisite, in the first place, to expel the atmospheric air in the receiver; for which purpose the safety valve is left open for a short time after the gas is being forced in, otherwise it would retard the impregnation of the water by the gas. When the gas and water are well incorporated, the liquid will contain as many volumes of gas as there are atmospheres of pressure in the air-space above it in a state ready to effervesce, and one other volume, with water absorbs under the pressure of the atmosphere. Thus, when there are three atmospheres of gas under pressure, each bottle of soda-water contains four bottles full of gas, which are absorbed without perceptibly increasing its bulk. The perfect impregnation of the water with gas, however, requires time. The water will, indeed, become brisk almost as soon as two or three atmospheres of gas have been forced in, but it will not acquire the flavour of good soda-water until the gas and water have been allowed at least half an hour to digest; and it is improved by remaining in contact for several hours.
The temperature has considerable influence in the process of impregnation, for in hot weather the gas will not combine so readily, nor will the water absorb an equal volume of gas. In summer time, therefore, soda-water should be made before the heat of the day, and ice should be added to the water.
When the receiver is fully charged, and the operation of bottling begins, every bottle-full that is drawn off diminishes the pressure on the water that remains; and if no means were taken to add more gas, the soda-water would gradually become weaker and weaker as each bottle was drawn off. It is usual, in the best arranged apparatus, to have two tubes connected with the force-pump, one of which feeds it with water, the other with gas, by which contrivance water and gas, in their proper proportions, are continually forced into the receiver, which may thus be always kept nearly full.
The process of bottling requires great manual dexterity. The neck of the bottle is pressed by a lever against a collar of leather fixed to a flange on the tap, so that, when the soda-water rushes in, no air nor gas can escape. The pressure inside the bottle therefore quickly becomes equal to that of the receiver, and the water ceases to flow through the tap, until some of the air is allowed to escape. When the bottle is nearly full, the operator quickly withdraws it with one hand, and having a cork ready in the other, he puts it in before the water can rush out. The cork is then forced in further by pressure, and fastened down by wires or strings.
A bottling apparatus has been invented for facilitating the process; but a man accustomed to bottle by hand can do it more quickly, and with as little waste of gas and water as with a machine. Much depends, however, upon the state of the soda-water in the receiver; for if the gas be well digested, and the temperature low, it rushes into the bottle with much less force, though the water may contain a greater quantity of gas, than when it is newly made, and apparently more brisk. The bottles very frequently burst during the operation with great violence, and unless they are enclosed in a guard, the men are liable to be severely injured. Glass bottles have now generally supplanted those made of earthenware, which were formerly used; and though the glass bottles are much stronger than the earthenware ones, the bursting of them, when it does occur, is far more dangerous.
The process of forcing gas into the water by mechanical pressure, in the manner described, requires great labour, for the pump has to be worked against a pressure exceeding fifty pounds on the square inch. With a view to remove that inconvenience, and to avoid the use of costly machinery, so that private individuals might manufacture soda-water, the author contrived a modification of Nooth's apparatus, for which he obtained a patent in 1831. By that means, the gas is generated in a closed vessel, and forces itself into the water by its own elasticity. Any amount of pressure can thus be obtained by chemical action alone. The accompanying woodcut represents a section of the apparatus in its improved form. The vessel, A, is made of very strong stone ware, inside which is the gas generator b. A few inches from the bottom of the generator is the partition, a, perforated with holes, and near the top there is inserted the small tube, c, which conveys the gas down to a perforated expansion of the tube, d, through the apertures of which the gas issues into the water contained in A. Another tube, e, reaches near the bottom, and is connected with a stop-cock for the purpose of drawing off the aerated liquid. In charging the apparatus, the interior, A, is nearly filled with water, or other liquid, through the opening, f, which is then closed by cork, which is kept in its place by a screw nut. A few ounces of carbonate of soda, mixed with water, are then poured into the generator through the opening at g. The mixture flows through the apertures in the partition, and occupies the lower part of the generator. A proportionate quantity (about three-fourths of the weight of the soda) of tartaric acid in crystals is then introduced through g, which lodge on the top of the partition without touching the soda. The opening being then closed by a screw-nut, the apparatus, which is mounted on pivots, with an appropriate stand, is swung backwards and forwards like a pendulum. The effect of this agitation is to force a portion of the water saturated with carbonate of soda through the apertures at a, where it comes in contact with the tartaric acid, and instantly generates carbonic acid gas. The gas, having no other escape than through the tube, c, is forced into the vessel A, and becomes mingled with the water by the same act of vibration that brings the soda and tartaric acid together. The continuance of the vibratory action for a short time generates sufficient gas to aerate the water or other liquid contained in the vessel, A. When the aeration is completed, the soda-water may be drawn off, as required, through the stop-cock. The apparatus is made of two sizes, to hold one and two gallons.
The tartaric acid and soda in the generator do not mingle with the water, and the tartrate of soda, resulting from the combination, is emptied after the soda-water is drawn off, before renewing the charge.
A French modification of this apparatus, in glass vessels protected by cane netting, called a "gasogene," has recently been introduced, and is extensively used. The materials for generating the carbonic acid gas are put into the smaller vessels, and kept separate until the apparatus is inverted, and then gas is rapidly generated, and forces itself through the water.
The powders that are sold for making soda-water, by mixing them together, consist of carbonate of soda and tartaric acid. When brought together in solution, a violent effervescence ensues, but the gas is not combined with the water in the same manner as when it is forced in and allowed to remain for some time with the liquid to be aerated. There is the further disadvantage attending such powders, that the tartrate of soda, formed by the tartaric acid and the carbonate of soda, employed to generate the gas, is drunk with the water.